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ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials Copyright © 1990 ASM International® ASM Handbook Committee, p 123-151 All rights reserved. DOI: 10.1361/asmhba0001061 www.asminternational.org

Aluminum Products

Revised by A. Kearney, Avery Kearney & Company Elwin L. Rooy, Aluminum Company of America

ALUMINUM ALLOYS are wrought alloys. Aluminum casting alloys cast aluminum alloys are grouped according the most versatile of all common foundry must contain, in addition to strengthening to composition limits registered with the alloys and generally have the highest cast- elements, sufficient amounts of eutectic- Aluminum Association (see Table 3 in the ability ratings. As casting materials, alumi- elements (usually ) in order article " and Temper Designation Sys- num alloys have the following favorable to have adequate fluidity to feed the shrink- tems for Aluminum and Aluminum Al- characteristics: age that occurs in all but the simplest cast- loys"). Comprehensive listings are also • Good fluidity for filling thin sections ings. maintained by general procurement specifi- The phase behavior of aluminum-silicon • Low relative to those re- cations issued through government agencies compositions (Fig. 1) provides a simple quired for many other (federal, military, and so on) and by techni- • Rapid heat transfer from the molten alu- eutectic-forming system, which makes pos- cal societies such as the American Society sible the commercial viability of most high- minum to the mold, providing shorter for Testing and Materials and the Society of casting cycles volume aluminum casting. Silicon contents, Automotive Engineers (see Table 1 for ex- • is the only gas with apprecia- ranging from about 4% to the eutectic level amples). In addition, aluminum casting al- ble solubility in aluminum and its alloys, of about 12% (Fig. 1), reduce scrap losses, loys are sometimes grouped according to permit production of much more intricate and hydrogen solubility in aluminum can their quality level or intended end-use ap- be readily controlled by processing meth- with greater variations in section plication (see the section "Selection of thickness, and with higher ods Casting Alloys"). Of these various meth- • Many aluminum alloys are relatively free surface and internal quality. These benefits ods, the grouping of aluminum casting al- derive from the effects of silicon in increas- from hot-short cracking and tearing ten- loys in terms of chemical compositions is dencies ing fluidity, reducing cracking, and improv- discussed below. • Chemical stability ing feeding to minimize shrinkage porosity. The Aluminum Association designation The required amounts of eutectic formers • Good as-cast with lustrous system attempts alloy family recognition by surfaces and little or no blemishes depend in part on the casting process. Al- the following scheme: loys for casting generally are lower in Aluminum alloy castings are routinely eutectics than those for casting in • lxx.x: Controlled unalloyed compositions • 2xx.x: Aluminum alloys containing cop- produced by pressure-, permanent-mold, molds because sand molds can tolerate a per as the major alloying element green- and dry-sand, investment, and plas- degree of hot shortness that would to ter casting. Aluminum alloys are also readi- extensive cracking in nonyielding metal • 3xx.x: Aluminum-silicon alloys also con- taining and/or ly cast with , low-pressure, centrif- molds. Resistance to cracking during cast- ugal, and -related processes such as ing is favored by a small range of solidifica- • 4xx.x: Binary aluminum-silicon alloys • 5xx.x: Aluminum alloys containing mag- lost foam. Total shipments of aluminum tion temperature, which drops from about nesium as the major alloying element foundry products (all types of castings ex- 78 °C (140 °F) at 1% Si to zero at about 12% • 6xx.x: Currently unused clusive of ) in the United States for Si. Good feeding characteristics to mini- • 7xx.x: Aluminum alloys containing 1988 were about 10 6 Mg (10 6 tons), of which mize shrinkage porosity are benefited by a as the major alloying element, usually about 68% was accounted for by die cast- profile of volume fraction solidified versus also containing additions of either cop- ings (see the shipment statistics in the arti- temperature that is weighted toward the low- per, magnesium, , , cle "Introduction to Aluminum and Alumi- er portion of the temperature range--that is, or combinations of these elements num Alloys" in this Volume). toward increased eutectic concentration. • 8xx.x: Aluminum alloys containing as In the binary aluminum-silicon system, the major alloying element Alloy Systems under the nonequilibrium conditions of casting, the volume fraction of eutectic in- • 9xx.x: Currently unused Aluminum casting alloys are based on the creases linearly from about 0 to 1 as silicon Designations in the form xxx.l and xxx.2 same alloy systems as those of wrought content increases from 1 to 12%. include the composition of specific alloys in aluminum alloys, are strengthened by the remelt ingot form suitable for foundry use. same mechanisms (with the exception of Alloy Groupings and Designations Designations in the form xxx.O in all cases strain ), and are similarly classi- Although the systems used to identify and define composition limits applicable to cast- fied into non-heat-treatable and heat-treat- group aluminum casting alloys are not inter- ings. Further variations in specified compo- able types. The major difference is that the nationally standardized, each nation (and in sitions are denoted by prefix letters used casting alloys used in the greatest volumes many cases individual firms) has developed primarily to define differences in impurity contain alloying additions of silicon far in its own alloy nomenclature. In the United limits. Accordingly, one of the most com- excess of that found (or used) in most States and , for example, mon gravity cast alloys, 356, has variations 124 / Specific Metals and Alloys

3000

2600 jf

2200 ~-'"/ 99.95% AI ~ solutionLiquid / L +si 100% Si 1ooo /

1400 --L +(AO-- /

1000 . "(,4/) (.41) + Si , \'7 600

~ \~ 200 /'/ " ' " " "'~.. 40 50 60 70 80 90 100 ~ ~ ~'~ ~"

% Silicon ~ Si . • - %~" =

8% Si 12% Si 20% Si 50% Si

Aluminum-silicon phase diagram and cast microstructures of pure components and of alloys of various compositions. Alloys with less than 12% Si are referred Fig, 1 to as hypoeutectic, those with close to 12% Si as eutectic, and those with over 12% Si as hypereutectic.

A356, B356, and C356; each of these alloys remelted for making castings, and zinc When available, a second phase will aid the has identical major alloy contents but has contents tend to increase and magnesium required feeding of shrinkage areas and will decreasing specification limits applicable to content tends to decrease. help compensate for solidification stresses. impurities, especially iron content. General Composition Groupings. Al- When these alloys, and other single-phase Composition limits of casting alloys reg- though the nomenclature and designations alloys, are cast using permanent mold or istered with the Aluminum Association are for various casting alloys are standardized other rigid mold casting methods, special given in Table 3 in the article "Alloy and in North America, many important alloys techniques are required to relieve solidifica- Temper Designation Systems for Aluminum have been developed for engineered casting tion stresses. Careful techniques are also usu- and Aluminum Alloys." production worldwide. For the most part, ally needed to promote the progress of the In designations of the lxx.x type, the each nation (and in many cases the individ- metal solidification from the remote areas of second and third digits indicate minimum ual firm) has developed its own alloy no- the casting to the hotter and more aluminum content (99.00% or greater); menclature. Excellent references are avail- casting areas, to the risers, and then to the these digits are the same as the two to the able that correlate, cross reference, or feeders. When these necessary and more right of the decimal point in the minimum otherwise define significant compositions in exacting casting techniques are used, the aluminum percentage expressed to the near- international use (Ref 1, 2). aluminum-copper alloys can and have been est 0.01%. The fourth digit in lxx.x desig- Although a large number of aluminum successfully used to produce high-strength nations, which is to the right of the decimal alloys has been developed for casting, there and high- castings. More exacting point, indicates product form: 0 denotes are six basic types: casting techniques are also helpful and re- castings (such as electric motor rotors), and quired when casting other single-phase alumi- • Aluminum-copper 1 denotes ingot. num casting alloys or alloy systems. • Aluminum-copper-silicon In 2xx.x through 8xx.x designations for In terms of alloy additions, manganese in • Aluminum-silicon aluminum alloys, the second and third digits small amounts may be added, mainly to • Aluminum-magnesium have no numerical significance but only combine with the iron and silicon and re- • Aluminum-zinc-magnesium identify the various alloys in the group. The duce the embrittling effect of essentially • Aluminum-tin digit to the right of the decimal point indi- insoluble phases. However, these alloys cates product form: 0 denotes castings, 1 Aluminum-copper alloys that contain 4 to demonstrate poor castability and require denotes standard ingot, and 2 denotes ingot 5% Cu, with the usual impurities iron and more carefully designed gating and more having composition ranges narrower than silicon and sometimes with small amounts extensive risering if sound castings are to be but within those of standard ingot. Alloy of magnesium, are heat treatable and can obtained. Such alloys are used mainly in sand modifications, as previously mentioned, are reach quite high strengths and ductilities, es- casting; when they are cast in metal molds, identified by a capital letter preceding the pecially if prepared from ingot containing less silicon must be added to increase fluidity and numerical designation. than 0.15% Fe. The aluminum-copper alloys curtail hot shortness, and this addition of Alloying-element and impurity limits for are single-phase alloys. Unlike the silicon silicon substantially reduces ductility. ingot are the same as those for castings of alloys, there is no highly fluid second phase AI-Cu alloys with somewhat higher cop- the same alloy except that, when the ingot is available at the late stages of solidification. per contents (7 to 8%), formerly the most Aluminum Foundry Products / 125

Table 1 Cross-referencechart of frequently used specifications for aluminum alloy sand If high strength and are needed, and permanent mold (PM) castings magnesium additions make these alloys heat treatable. Alloys with silicon contents ] QQ-A-6OIE Federal QQ-A-S96d I [ B26 BI08 AMS or Arllm°Yer dessgnation I ASTM(a) --] as low as 2% have been used for casting, but • " (sand) (PM) (sand) (PM) SAE(b) MIL-21180c silicon content usually is between 5 and 208.0 108 ...... 108 "'" CS43A CS43A 13%. Strength and ductility of these alloys, 213.0 C113 ...... • • " 113 CS74A CS74A 33 "-" 222•0 122 ...... 122 122 CGIOOA CG100A 34 ... especially those with higher silicon, can be 242.0 142 ...... 142 142 CN42A CN42A 39 4222 substantially improved by modification of 295.0 195 ...... 195 "'" C4A 38 4231 the A1-Si eutectic. Modification of hypoeu- 296.0 B295.0 ...... " " • B 195 • • - 380 tectic alloys (<12% Si) is particularly ad- 308.0 AI08 ...... • " • AI08 - • • 319.0 319, AUcast ...... 319 319 SC64D SC64D 326 vantageous in sand castings and can be 328.0 Red X-8 ...... Red X-8 - • - SC82A 327 effectively achieved through the addition of 332.0 F332.0 ...... F132 ••. SC 103A 332 a controlled amount of sodium or strontium, 333.0 333 ...... -- 333 ... which refines the eutectic phase. Calcium 336.0 A332.0 ...... •.. A132 -.- SN122A 321 354.0 354 ...... - ...... "'" C354(c) and additions are also used. 355.0 355 ...... 355 355 SC51A SC51A 322 4210 Pseudomodification, in which the fineness C355.0 C355 ...... -- C355 ..- SC51B 355 C355(c) of the eutectic but not the structure is 356.0 356 ...... 356 356 SG70A SG70A 323 (d) affected, may be achieved by control of A356.0 A356 ...... A356 •.- SG70B 336 A356(c) solidification rates. 357.0 357 ...... --- 357 ... • " 4241 A357.0 A357 ...... • ...... • " A357(c) In hypereutectic AI-Si alloys, refinement 359.0 359 ...... • ...... -" 359(c) of the proeutectic silicon phase by phospho- B443.0 43 ...... 43 43 S5A S5A rus additions is essential for casting and 512.0(e) B514.0 ...... B214 ... GS42A GS42A 513.0 A514.0 ...... -.. A214 ... GZ42A product performance• 514.0 214 ...... 214 ... G4A 320 ... Aluminum-magnesium casting alloys are 520.0 220 ...... 220 ... G10A 324 4240 essentially single-phase binary alloys with 535.0 Almag35 ...... Almag35 "•" GM70B GM70B "•" 4238 moderate-to-high strength and toughness 705.0 603, Ternalloy 5 ..... Ternalloy 5 Ternalloy 5 ZG32A ZG32A 311 •.. 707.0 607, Ternalloy 7 ..... Ternalloy 7 Ternalloy 7 ZG42A ZG42A 312 ... properties. High resistance, espe- 710.0 A712.0 ...... A612 ... ZG61B 313 ..• cially to seawater and marine atmospheres, 712.0 D712.0 ...... 40E • - • ZG61A 310 -•- is the primary advantage of castings made 713.0 613, Tenzfloy ...... Tenzaloy • • • ZC81A 315 ... of A1-Mg alloys• Best corrosion resistance 771.0 Precedent 71A ...... Precedent 71A ...... 850.0 750 ...... 750 750 ... requires low impurity content (both solid 851.0 A850.0 ...... A750 A750 ... and gaseous), and thus alloys must be pre- 852.0 B850.0 ...... B750 B750 ... pared from high-quality metals and handled (a) Former designations. ASTM adopted the Aluminum Association designation system in 1974. (b) Former designations used in SAE with great care in the foundry• These alloys specifications J452 and/or J453. In 1990, SAE J452 adopted the ANSI/Aluminum Association numbering system for alloys. SAE J453-1986 has also superceded SAE J452. (c) Designation in MIL-21180c. (d) Alloy 356.0 is specified in AMS 4217, 4260, 4261, 4284, are suitable for welded assemblies and are 4285, and 4286. (e) Alloy 512.0 is no longer active; it is included for reference purposes only. often used in architectural and other deco- rative or building needs• Aluminum-magne- sium alloys also have good machinability commonly used aluminum casting alloys, niques to avoid problems with hot-short and an attractive appearance when anod- have steadily been replaced by AI-Cu-Si alloys• ized. In comparison to the aluminum-silicon alloys and today are used to a very limited A1-Cu-Si alloys with more than 3 to 4% alloys, all the aluminum-magnesium alloys extent• The best attribute of higher-copper Cu are heat treatable, but usually heat treat- require more care in gating and greater A1-Cu alloys is their insensitivity to impuri- ment is used only with those alloys that also temperature gradients to produce sound ties. However, these alloys display very contain magnesium, which enhances their castings• This often means more chilling low strength and only fair castability. response to heat treatment. High-silicon and larger risers• Also, careful melting and Also in limited use are AI-Cu alloys that alloys (>10% Si) have low thermal expan- pouring practices are needed to compensate contain 9 to 11% Cu, whose high-tempera- sion, an advantage in some high-tempera- for the greater oxidizing tendency of these ture strength and wear resistance are attrac- ture operations• When silicon content ex- alloys when molten• This care is also need- tive for use in aircraft cylinder heads and in ceeds 12 to 13% (silicon contents as high as ed because many of the applications of automotive (diesel) pistons and cylinder 22% are typical), primary silicon crystals these alloys require and/or fine blocks• are present, and if properly distributed, , where defects caused by Very good high-temperature strength is impart excellent wear resistance. Automo- oxide inclusions are particularly undesir- an attribute of alloys containing copper, tive blocks and pistons are major able. The relatively poor castability of AI- , and magnesium, sometimes with uses of these hypereutectic alloys. Mg alloys and the tendency of the magne- iron in place of part of the nickel• Aluminum-silicon alloys that do not con- sium to oxidize increase handling Aluminum-Copper-Silicon Alloys• The tain copper additions are used when good difficulties, and therefore, cost. most widely used aluminum casting alloys castability and good corrosion resistance Aluminum-zinc-magnesium alloys natu- are those that contain silicon and copper• are needed. Metallograpbic structures of rally age, achieving full strength by 20 to 30 The amounts of both additions vary widely, the pure components and of several inter- days at room temperature after casting• so that the copper predominates in some mediate compositions are shown in Fig. 1. This strengthening process can be acceler- alloys and the silicon in others. In these The intermediate compositions are mixtures ated by artificial aging• The high-tempera- alloys, the copper contributes to strength, of aluminum containing about 1% Si in solid ture solution heat treatment and drastic and the silicon improves castability and solution as the continuous phase, with par- required by other alloys (A1-Cu reduces hot shortness; thus, the higher- ticles of essentially pure silicon• Alloys with and A1-Si-Mg alloys, for example) are not silicon alloys normally are used for more less than 12% Si are referred to as hypoeu- necessary for optimum properties in most complex castings and for permanent mold tectic, those with close to 12% Si as eutec- A1-Zn-Mg alloy castings• However, micro- and processes, which often re- tic, and those with over 12% Si as hypereu- segregation of Mg-Zn phases can occur in quire the use of more exacting casting tech- tectic. these alloys, which reverses the accepted 126 / Specific Metals and Alloys

rule that faster solidification results in high- requires small interdendritic spacing, and cessfully demonstrated to date have been er as-cast properties. When it is found in an small spacing is obtained only with casting sand, permanent mold, low-pressure per- AI-Zn-Mg alloy casting that the strength of methods in which cooling is rapid. manent mold, high-pressure die casting, and the thin or highly chilled sections are lower From a foundry standpoint, the alumi- , both shell and plaster. than the thick or slowly cooled sections, the num-tin alloy system is unique. In the mold, Additional information on castable alumi- weaker sections can be strengthened to the the solidification starts at about 650 °C (1200 num-base MMC materials is given in the required level by solution heat treatment °F), and the tin constituents of the alloy are section "Discontinuous Aluminum MMC" and quenching, followed by natural or arti- liquid until 229 °C (444 °F). This extremely in the article "Metal-Matrix Composites" ficial () aging. large solidification range presents unique in this Volume. These alloys have moderate to good problems. Rapid solidification rates are rec- tensile properties in the as-cast condition. ommended to avoid excessive macrosegre- Selection of Casting Alloys With , good dimensional stability gation. in use is developed. The eutectic melting Some 850.0 T5 castings are cold worked The major factors that influence alloy points of alloys of this group are high, an by reducing the axial dimension 4% (T101 selection for casting applications include advantage in castings that are to be assem- temper). This provides a substantial in- casting process to be used, casting , bled by . The alloys have good crease in the compressive yield strength. required properties, and economic (and machinability (and resistance to general Aluminum- casting alloys may of- availability) considerations. These five fac- corrosion, despite some susceptibility to fer the same benefits as their wrought coun- tors consist of the following characteristics stress corrosion). They are not generally terparts but have not been developed or of an alloy: recommended for service at elevated tem- commercialized as have the wrought alumi- • Casting process considerations: fluidity, peratures. The tensile properties of these num-lithium alloys. (See the article "Alumi- resistance to hot tearing, solidification alloys develop at room temperatures dur- num-Lithium Alloys" in this Volume.) The range ing the first few weeks after casting due to wrought and cast aluminum-lithium alloys • Casting design considerations: solidifica- . This process con- consist of aluminum-copper alloys with lith- tion range, resistance to hot tearing, flu- tinues thereafter at a progressively slower ium additions to reduce weight and improve idity, die (die casting) rate. Heat treatments of the T6 and T7 strength. • Mechanical-property requirements: type may be applied to the 707.0, 771.0, The behavior of both cast and wrought strength and ductility, heat treatability, and 772.0 alloys. AI-Li alloys differs from conventional alu- hardness Castability of AI-Zn-Mg alloys is poor, minum alloys in terms of fracture mecha- • Service requirements: pressure tightness and careful control of solidification condi- nisms and temperature effects on mechani- characteristics, corrosion resistance, sur- tions is required to produce sound, defect- cal properties. Unlike conventional face treatments, dimensional stability, free castings. Moderate to steep tempera- aluminum alloys, the toughness of AI-Li thermal stability ture gradients are required to assure alloys does not increase with increasing • Economics: machinability, , adequate feeding to prevent shrinkage de- aging temperature beyond the point of over- ingot and melting costs, heat treatment fects. Hot tear cracking where resistance to aging (that is, the point required for peak contraction during solidification and cooling strength). The benefits of reduced Several of these characteristics for vari- is resisted. However, good foundry tech- and improved modulus of elasticity are the ous alloys are listed in Tables 2 and 3. Table niques and control have enabled well-qual- main incentives in the development of AI-Li 2 gives the solidification range and thermal ified sand to produce relatively alloys. properties, while Table 3 ranks various al- intricate castings. Permanent mold castings, Aluminum--Matrix Composite loys in terms of castability, corrosion resis- except for relatively simple designs, can be (MMC) for Casting. Although aluminum- tance, machinability, and weldability. Note difficult. composites offer exceptional spe- that the rankings in Table 3 can vary with Aluminum-tin alloys that contain about cific stiffness (elastic modulus-to-weight ra- the casting process. Each casting process 6% Sn (and small amounts of copper and tio), the initial development (prior to 1986) may also require specific metal characteris- nickel for strengthening) are used for cast of aluminum-base MMC materials required tics. For example, die and permanent mold bearings because of the excellent lubricity energy- or labor-intensive methods, such as casting generally require alloys with good imparted by tin. These tin-containing alloys , thermal spray, diffusion fluidity and resistance to hot tearing, where- were developed for applications (in bonding, and high-pressure squeeze cast- as these properties are less critical in sand, which load-carrying capacity, fatigue ing. None of the composites produced from plaster, and investment casting, where strength, and resistance to corrosion by these methods could be remelted and shape molds and cores offer less resistance to internal-combustion lubricating oil are im- cast, and each proved to be prohibitively shrinkage. portant criteria). Bearings of aluminum-tin expensive for most applications, even in the Also note that Table 2 groups aluminum alloys are superior overall to bearings made aerospace/defense sector. casting alloys into the following nine cate- using most other materials. An ingot-metallurgical method for pro- gories: Aluminum-tin casting Alloys 850.0, ducing a castable aluminum-base MMC ma- 851.0, and 852.0 can be cast in sand or terial with the name of Duralcan was • Rotor alloys permanent molds. However, 850.0 (6.3Sn- introduced in 1986. The product consists, in • Commercial alloys ICu-lNi) and 852.0 (6.3Sn-2Cu-l.2Ni- foundry ingot form, of foundry alloys to • Premium casting alloys 0.8Mg) usually are cast in permanent molds. which 10, 15, or 20 vol% of particulate • Piston and elevated-temperature alloys Major applications are for connecting rods silicon carbide (SIC) had been added. The • Standard, general-purpose alloys and crankcase bearings for diesel . most attractive feature of this ingot-metal- • Die castings Sand cast bearings, such as large mill lurgical product is its low cost, especially at • Magnesium alloys (see the earlier section bearings, usually are made of Alloy 851.0 industrial production levels, and its ability "General Composition Groupings" in (6.3Sn-2.5Si- ICu-0.5Ni). to be remelted without an impairment of this article) Bearing performance of A1-Sn alloys is properties. The AI-SiC composite foundry • Aluminum-zinc-magnesium alloys (see the strongly affected by casting method. Fine ingot can be remelted and shape cast easily section "General Composition Group- interdendritic distribution of tin, which is using standard aluminum foundry practices ings") necessary for optimum bearing properties, and equipment. The casting methods suc- • Bearing alloys Aluminum Foundry Products / 127

Table 2 Typical physical properties of aluminum casting alloys Coefficient of , per *C x 10-6 Electrical Thermal (per °F × 10-6) Temper and Specific Density(b) Approximatemelting range conductivity, conductivity at 25 °C 20-100 *C 20-300 *C Alloy product form(a) gravity(b) kg/m3 Ib/in.3 °C *F %IACS (77 *F), eai/em.s.*C (68-212 OF) (68-570 OF)

Aluminum rotor alloys (pure aluminum) Pure aluminum 99.996% AI .... 0 °F 2.71 2713 0.098 660.2-660.2 1220.4-1220.4 64.94 0.57 23.86 (13.25) 25.45 (14.14) EC Alloy 99.45% AI, similar to 150.0 alloy ...... 0 °F 2.70 2713 0.098 657--643 1215-1190 57 0.53 23.5 (13) 25.6 (14.2) Commercial Duralumin alloys (AI-Cu) 222.0 ...... F(P) 2.95 2962 0.107 520-625 970-1160 34 0.32 22.1 (12.3 23.6 03.1) O(S) 2.95 2962 0.107 520-625 970-1160 41 0.38 T61(S) 2.95 2962 0.107 520--625 970-1160 33 0.31 22.1 (12.3 23.6 (13.1) 224.0 ...... T62(S) 2.81 2824 0.102 550-645 1020-1190 30 0.28 238.0 ...... F(P) 2.95 1938 0.107 510--600 950-1110 25 0.25 21.4 (11.9 22.9 (12.7) 240.0 ...... F(S) 2.78 2768 0.100 515-605 960-1120 23 0.23 22.1 (12.3 24.3 (13.5) 242.0 ...... O(S) 2.81 2823 0.102 530-635 990-1180 44 0.40 T77(S) 2.81 2823 0.102 525-635 980-1180 38 0.36 22.1 (12.3 23.6 (13.1) T571(P) 2.81 2823 0.102 525-635 980-1180 34 0.32 22.5 (12.5 24.5 (13.6) T61(P) 2.81 2823 0.102 525-635 980-1180 33 0.32 22.5 (12.5 24.5 (13.6) Premium casting alloys (high strength and toughness alloys) 201.0 ...... T6(S) 2.80 2796 0.101 570-650 1000-1200 27-32 0.29 19.3 (10.7) 24.7 (13.7) T7(P) 2.80 2796 0.101 570~50 1000-1200 32-34 0.29 19.3 (10.7) 24.7 (13.7) 206.0 ...... T4(S) 2.8 2796 0.101 570-650 1000-1200 30 0.29 19.3 (10.7) 24.7 (13.7) 204.0 ...... T4(S) 2.8 2800 0.101 570--650 1060-1200 29 0.29 19.3 (10.7) • • • 204.0 ...... T6(S)(P) 2.8 2800 0.101 570~50 1060-1200 34 0.29 19.3 (10.7) " - " 224.0 ...... T62(S) 2.81 2824 0.102 550-645 1020-1190 30 0.28 295.0 ...... T4(S) 2.81 2823 0.102 520-645 970-1190 35 0.33 22.9 (12.7) 24.8 (13.8) T62(S) 2.81 2823 0.102 520-645 970-1190 35 0.34 22.9 (12.7) 24.8 (13.8) 296.0 ...... T4(P) 2.80 2796 0,101 520-630 970-1170 33 0.32 22.0 (12.2) 23.9 (13.3) T6(P) 2.80 2796 0.101 520-630 970-1170 33 0.32 22.0 (12.2) 23.9 (13.3) T62(S) 2.80 2796 0.101 520--630 970-1170 33 0.32 C355.0 ...... T61(S) 2.71 2713 0,098 550-620 1020-1150 39 0.35 22.3 (12.4) 24.7 (13.7) A356.0 ...... T6(S) 2.69 2713 0.098 560-610 1040-1130 40 0.36 21.4 (I 1.9) 23.4 (13.0) A357.0 ...... T6(S) 2.69 2713 0,098 555-610 1030-1130 40 0.38 21.4 (11.9) 23.6 (13.1) Piston and elevated-temperature alloys 332.0 ...... T5(P) 2.76 2768 0.10O 520-580 970-1080 26 0.25 20.7 (ll.5) 22.3 (12.4) 360.0 ...... F(D) 2.68 2685 0,097 570-590 1060-1090 37 0.35 20.9 (11.6) 22.9 (12.7) A360.0 ...... F(D) 2.68 2685 0.097 570-590 1060-1090 37 0.35 21.1 (ll.7) 22.9 (12.7) 364.0 ...... F(D) 2.63 2630 0.095 560--600 1040-1110 30 0.29 20.9 (11.6) 22.9 (12.7) 380.0 ...... F(D) 2.76 2740 0.099 520-590 970-1090 27 0.26 21.2 (11.8) 22.5 (12.5) A380.0 ...... F(D) 2.76 2740 0.099 520-590 970-1090 27 0.26 21.1 (11.7) 22.7 (12.6) 384.0 ...... F(D) 2.70 2713 0,098 480-580 900-1080 23 0.23 20.3 (11.3) 22.1 02.3) 390.0 ...... F(D) 2.73 2740 0.099 510-650 950-1200 25 0.32 18.5 (10.3) •. ' T5(D) 2.73 2740 0.099 510--650 950-1200 24 0.32 18.0 (10.0) • • • Standard general-purpose alloys 208.0 ...... F(S) 2.79 2796 0,101 520-630 970-1170 31 0.29 22.0 (12.2) 23.9 (13.3) 308.0 ...... F(P) 2.79 2796 0.101 520-615 970-1140 37 0.34 21.4 (11.9) 22.9 (12.7) 319.0 ...... F(S) 2.79 2796 0.101 520---605 970-1120 27 0.27 21.6 (12.0) 24.1 (13.4) F(P) 2.79 2796 0.101 520---605 970-1120 28 0.28 21.6 (12.0) 24.1 (13.4) 324.0 ...... F(P) 2.67 2658 0.096 545-605 1010-1120 34 0.37 21.4 (11.9) 23.2 (12.9) 238.0 ...... F(P) 2.95 2962 0.107 510-600 950-1110 25 0.25 21.4 (11.9) 22.9 (12.7) 240.0 ...... F(S) 2.78 2768 0.100 515-605 960-1120 23 0.23 22.1 (12.3) 24.3 (13.5) 242.0 ...... O(S) 2.81 2823 0.102 530-635 990-1180 44 0.40 T77(S) 2.81 2823 0.102 525-635 980-1180 38 0:36 22.1 (12.3) 23.6 (13.1) T571(P) 2.81 2823 0,102 525-635 980-1180 34 0.32 22.5 (12.5) 24.5 (13.6) T61(P) 2.81 2823 0,102 525-635 980-1180 33 0.32 22.5 (12.5) 24.5 (13.6) 295.0 ...... T4(S) 2.81 2823 0.102 520--645 970-1190 35 0.33 22.9 (12.7) 24.8 (13.8) T62(S) 2.81 2823 0.102 520--645 970-1190 35 0.34 22.9 (12.7) 24.8 (13.8) 296.0 ...... T4(P) 2.80 2796 0.101 520-630 970-1170 33 0.32 22.0 (12.2) 23.9 (13.3) T6(P) 2.80 2796 0.101 520-630 970-1170 33 0.32 22.0 (12.2) 23.9 (13.3) T62(S) 2.80 2796 0.101 520-630 970-1170 33 0.32 308.0 ...... F(P) 2.79 2796 0.101 520--615 970-1140 37 0.34 21.4 (11.9) 22.9 (12.7) 319.0 ...... F(S) 2.79 2796 0.101 520-605 970-1120 27 0.27 21.6 (12.0) 24.1 (13.4) F(P) 2.79 2796 0.101 520-605 970-1120 28 0.28 21.6 (12.0) 24.1 (13.4) 324.0 ...... F(P) 2.67 2658 0.096 545--605 1010-1120 34 0.37 21.4 (11.9) 23.2 (12.9) 333.0 ...... F(P) 2.77 2768 0.100 520-585 970-1090 26 0.25 20.7 (ll.5) 22.7 (12.6) T5(P) 2.77 2768 0.100 520-585 970-1090 29 0.29 20.7 (11.5) 22.7 (12.6) T6(P) 2.77 2768 0.100 520-585 970-1090 29 0.28 20.7 (11.5) 22.7 (12.6) T7(P) 2.77 2768 0.100 520-585 970-1090 35 0.34 20.7 (11.5) 22.7 (12.6) 336.0 ...... T551(P) 2.72 2713 0.098 540-570 1000-1060 29 0.28 18.9 (10.5) 20.9 (11.6) 354.0 ...... F(P) 2.71 2713 0.098 540--600 1000-1110 32 0.30 20.9 (11.6) 22.9 (12.7) (continued) (a) S, sand cast; P, permanent mold; D, die cast. (b) The specific gravity and weight data in this table assume solid (void-free) metal. Because some porosity cannot be avoided in commercial castings, their specific gravity or weight is slightly less than the theoretical value. 128 / Specific Metals and Alloys

Table 2 (continued) Coefficient of thermal expansion, per °C × 10-6 Electrical Thermal (per °F × 10 -6) Temper and Specific Density(b) Approximate melting range conductivity, conductivity at 25 *C 20-100 °C 20--300 *C Alloy product form(a) gravity(b) kg/m3 Ib/in. 3 °C OF %IACS (77 OF), cal/cm.s-°C (68-212 *lO (68-570 OF)

Standard general-purposealloys (continued) 355.0 ...... T51(S) 2.71 2713 0.098 550-620 1020-1150 43 0.40 22.3 (12.4) 24.7 03.7) T6(S) 2.71 2713 0.098 550-620 1020-1150 36 0.34 22.3 (12.4) 24.7 03.7) T61(S) 2.71 2713 0.098 550-620 1020-1150 37 0.35 22.3 (12.4) 24.7 (13.7) T7(S) 2.71 2713 0.098 550-620 1020-1150 42 0.39 22.3 (12.4) 24.7 03.7) T6(P) 2.71 2713 0.098 550-620 1020-1150 39 0.36 22.3 (12.4) 24.7 (13.7) 356.0 ...... T51(S) 2.68 2685 0.097 560-615 1040-1140 43 0.40 21.4 01.9) 23.4 (13.0) T6(S) 2.68 2685 0.097 560-615 1040-1140 39 0.36 21.4 (11.9) 23.4 (13.0) T7(S) 2.68 2685 0.097 560-615 1040-1140 40 0.37 21.4 (11.9) 23.4 (13.0) T6(P) 2.68 2685 0.097 560-615 1040-1140 41 0.37 21.4 (11.9) 23.4 (13.0) A356.0 ...... T6(S) 2.69 2713 0.098 560-610 1040-1130 40 0.36 21.4 (ll.9) 23.4 (13.0) 357.0 ...... T6(S) 2.68 2713 0.098 560-615 1040-1140 39 0.36 21.4 (11.9) 23.4 (13.0) A357.0 ...... T6(S) 2.69 2713 0.098 555-610 1030-1130 40 0.38 21.4 (11.9) 23.6 (13.1) 358.0 ...... T6(S) 2.68 2658 0.096 560-600 1040-1110 39 0.36 21.4 (il.9) 23.4 (13.0) 359.0 ...... T6(S) 2.67 2685 0.097 565--600 1050-1110 35 0.33 20.9 (il.6) 22.9 (12.7) 392.0 ...... F(P) 2.64 2630 0.095 550-670 1020-1240 22 0.22 18.5 (10.3) 20.2 (ll.2) 443.0 ...... F(S) 2.69 2685 0.097 575-630 1070-1170 37 0.35 22.1 (12.3) 24.1 (13.4) O(S) 2.69 2685 0.097 575-630 1070-1170 42 0.39 ...... F(D) 2.69 2685 0.097 575-630 1070-1170 37 0.34 ...... F(P) 2.68 2685 0.097 575--630 1070-1170 41 0.38 21.8 (12.1) 23.8 (13.2) Die casting alloys 360.0 ...... F(D) 2.68 2685 0.097 570-590 1060-1090 37 0.35 20.9 (ll.6) 22.9 (12.7) A360.0 ...... F(D) 2.68 2685 0.097 570-590 1060-1090 37 0.35 21.1 (ll.7) 22.9 (12.7) 364.0 ...... F(D) 2.63 2630 0.095 560-600 1040-1110 30 0.29 20.9 (ll.6) 22.9 (12.7) 380.0 ...... F(D) 2.76 2740 0.099 520-590 970-1090 27 0.26 21.2 (11.8) 22.5 (12.5) A380.0 ...... F(D) 2.76 2740 0.099 520-590 970-1090 27 0.26 21.1 (!1.7) 22.7 (12.6) 384.0 ...... F(D) 2.70 2713 0.098 480-580 900-1080 23 0.23 20.3 (11.3) 22.1 02.3) 390.0 ...... F(D) 2.73 2740 0.099 510--650 950-1200 25 0.32 18.5 (10.3) --" T5(D) 2.73 2740 0.099 510-650 950-1200 24 0.32 18.0 (10.0) '-" 413.0 ...... F(D) 2.66 2657 0.096 575-585 1070-1090 39 0.37 20.5 (ll.4) 22.5 (12.5) A413.0 ...... F(D) 2.66 2657 0.096 575-585 1070-1090 39 0.37 ...... 443.0 ...... F(S) 2.69 2685 0.097 575-630 1070-1170 37 0.35 22.1 (12.3) 24.1 (13.4) O(S) 2.69 2685 0.097 575-630 1070-1170 42 0.39 ...... F(D) 2.69 2685 0.097 575-630 1070-1170 37 0.34 ...... 518.0 ...... F(D) 2.53 2519 0.091 540--620 1000-1150 24 0.24 24.1 (13.4) 26.1 (14.5) A535.0 ...... F(D) 2.54 2547 0.092 550-620 1020-1150 23 0.24 24.1 (13.4) 26.1 (14.5) Aluminum-magnesium alloys 511.0 ...... F(S) 2.66 2657 0.096 590--640 1090-1180 36 0.34 23.6 (13.1) 25.7 (14.3) 512.0 ...... F(S) 2.65 2657 0.096 590-630 1090-1170 38 0.35 22.9 (12.7) 24.8 (13.8) 513.0 ...... F(P) 2.68 2685 0.097 580--640 1080-1180 34 0.32 23.9 (13.3) 25.9 (14.4) 514.0 ...... F(S) 2.65 2657 0.096 600--640 1110-1180 35 0.33 23.9 (13.3) 25.9 (14.4) 518.0 ...... F(D) 2.53 2519 0.091 540-620 1000-1150 24 0.24 24.1 (13.4) 26.1 (14.5) 520.0 ...... T4(S) 2.57 2574 0.093 450-600 840-1110 21 0.21 25.2 (14.0) 27.0 (15.0) 535.0 ...... F(S) 2.62 2519 0.091 550-630 1020-1170 23 0.24 23.6 (13.1) 26.5 (14.7) A535.0 ...... F(D) 2.54 2547 0.092 550-620 1020-1150 23 0.24 24.1 (13.4) 26.1 (14.5) B535.0 ...... F(S) 2.62 2630 0.095 550-630 1020-1170 24 0.23 24.5 (13.6) 26.5 (14.7) Aluminum-zinc alloys(AI-Zn-Mgand AI-Zn) 705.0 ...... F(S) 2.76 2768 0.100 600--640 1110-1180 25 0.25 23.6 (13.1) 25.7 (14.3) 707.0 ...... F(S) 2.77 2768 0.100 585-630 1090-1170 25 0.25 23.8 (13.2) 25.9 (14.4) 710.0 ...... F(S) 2.81 2823 0.102 600-650 1110-1200 35 0.33 24.1 (13.4) 26.3 (14.6) 711.0 ...... F(P) 2.84 2851 0.103 600-645 1110-1190 40 0.38 23.6 (13.1) 25.6 (14.2) 712.0 ...... F(S) 2.82 2823 0.102 600-640 1110-1180 40 0.38 23.6 (13.1) 25.6 (14.2) BeaHngailoys (aluminum-fin) 713.0 ...... F(S) 2.84 2879 0.104 595--630 1100-1170 37 0.37 23.9 (13.3) 25.9 (14.4) 850.0 ...... T5(S) 2.87 2851 0.103 225-650 440-1200 47 0.44 ...... 851.0 ...... T5(S) 2.83 2823 0.102 230-630 450-1170 43 0.40 22.7 (12.6) - - " 852.0 ...... T5(S) 2.88 2879 0.104 210-635 410-1180 45 0.42 23.2 (12.9) " - " (a) S, sand cast; P, permanent mold; D, die cast. (b) The specific gravity and weight data in this table assume solid (void-free) metal. Because some porosity cannot be avoided in commercial castings, their specific gravity or weight is slightly less than the theoretical value.

This grouping of alloys is useful in the controlled pure-alloy conditions 100.0, each alloy grade are: selection of alloys because many foundries 150.0, and 170.0 (99.0, 99.5, and 99.7% AI, Minimum conductivity, Typical conductivity, are dedicated to a particular type of casting respectively). Impurities in these alloys Alloy %IACS %IACS alloy. Each group, with the exception of the are controlled to minimize variations in magnesium and the AI-Zn-Mg alloy groups, electrical performance based on conduc- 100.1 ...... 54 56 150.1 ...... 57 59 is discussed below. tivity and to minimize the occurrence of 170.1 ...... 59 60 Rotor Castings. Most cast aluminum mo- microshrinkage and cracks during casting. IACS, International Copper Annealed Standard tor rotors are produced in the carefully Minimum and typical conductivities for Aluminum Foundry Products / 129

Table 3 Ratings of castability, corrosion resistance, machinability, and weldability for aluminum casting alloys 1, best; 5, worst. Individual alloys may have different ratings for other casting processes. Resistance Resistance to hot Pressure Shrinkage Corrosion Machin. Weld- to hot Pressure Shrinkage Corrosion Machin- Weld- Alloy cracMng(a) tightness Fluidity(b) tendency(c) resistance(d) abinty(e) ability(f) Alloy cracking(a) tightness Fluidity(bJ tendency(e) resistance(d) ability(e) ability(f)

Sand casting alloys alloys

201.0 ...... 4 3 3 4 4 238.0 ...... 2 3 2 2 4 2 3 208.0 ...... 2 2 2 2 4 240.0 ...... 4 4 3 4 4 3 4 213,0 ...... 3 3 2 3 4 296.0 ...... 4 3 4 3 4 3 4 222.0 ...... 4 4 3 4 4 308.0 ...... 2 2 2 2 4 3 3 240.0 ...... 4 4 3 4 4 319.0 ...... 2 2 2 2 3 3 2 242.0 ...... 4 3 4 4 4 332.0 ...... 1 2 1 2 3 4 2 A242.0 ...... 4 4 3 4 4 333.0 ...... 1 1 2 2 3 3 3 295.0 ...... 4 4 4 3 3 336.0 ...... 1 2 2 3 3 4 2 319.0 ...... 2 2 2 2 3 354.0. .. 1 1 1 1 3 3 2 354.0 ...... 1 1 1 1 3 355.0 ...... 1 1 1 2 3 3 2 355.0 ...... 1 1 1 1 3 C355.0 ...... 1 1 1 2 3 3 2 A356.0 ..... 1 1 1 1 2 356.0 ...... 1 1 1 1 2 3 2 357.0 ...... 1 1 1 1 2 A356.0 ...... 1 1 1 1 2 3 2 359.0 ...... 1 1 1 1 2 357.0 ...... 1 1 1 I 2 3 2 A390.0 ..... 3 3 3 3 2 A357.0 ...... 1 1 1 1 2 3 2 A443.0 .... I 1 1 1 2 359.0 ...... 1 1 1 1 2 3 1 444.0 ...... I 1 1 1 2 A390.0 ...... 2 2 2 3 2 4 2 511.0 ...... 4 5 4 5 443.0 ...... 1 1 2 1 2 1 512.0 ...... 3 4 4 4 A444.0 ...... 1 1 1 1 2 1 514.0 ...... 4 5 4 5 512,0 ...... 3 4 4 4 1 4 520.0 ...... 2 5 4 5 513.0 ...... 4 5 4 4 1 5 535.0 ...... 4 5 4 5 711,0 ...... 5 4 5 4 3 3 A535.0 ...... 4 5 4 4 771.0 ...... 4 4 3 3 2 " " B535.0 ...... 4 5 4 4 772.0 ...... 4 4 3 3 2 " ' • 705.0 ...... 5 4 4 4 850.0 ...... 4 4 4 4 3 4 707.0 ...... 5 4 4 4 851.0 ...... 4 4 4 4 3 4 710.0 ...... 5 3 4 4 852.0 ...... 4 4 4 4 3 4 711.0 ...... 5 4 5 4 Die casting alloys 712.0 ...... 4 4 3 3 713.0 ...... 4 4 3 4 3 360,0.,...... 1 1 2 2 3 4 771.0 ...... 4 4 3 3 • • " A360.0 ...... 1 1 2 2 3 4 772.0 ...... 4 4 3 3 • • • 364.0.,...... 2 2 1 3 4 3 850.0 ...... 4 4 4 4 4 380.0•...... 2 1 2 5 3 4 851.0 ...... 4 4 4 4 4 A380.0 ...... 2 2 2 4 3 4 852.0 ...... 4 4 4 4 4 384.0...... 2 2 1 3 3 4 390.0...... 2 2 2 2 4 2 Permanent mold casting alloys 413.0.., ..... 1 2 1 2 4 4 201.0 ...... 4 3 3 4 4 1 2 C443,0 ...... 2 3 3 2 5 4 213.0 ...... 3 3 2 3 4 2 2 515.0...... 4 5 5 1 2 4 222.0 ...... 4 4 3 4 4 1 3 518.0.,...... 5 5 5 1 1 4

(a) Ability of alloy to withstand stresses from contraction while cooling through hot short or brittle temperature range, (b) Ability of liquid alloy to flow readily in mold and to fill thin sections. (c) Decrease in volume accompanying freezing of alloy and a measure of amount of compensating feed metal required in form of risers. (d) Based on resistance of alloy in standard . (e) Composite rating based on ease of , chip characteristics, quality of finish, and life, (f) Based on ability of material to be fusion welded with filler rod of same alloy

Rotor alloy 100.0 contains a significantly larg- by composition. Table 4 lists the effects of precipitates with these elements before er amount of iron and other impurities, and the various elements in and out of solution casting. In addition the iron and silicon this generally improves castability. With on the resistivity of aluminum. Simple cal- contents are subject to control with the higher iron content crack resistance is im- culation using these values accurately pre- objective of promoting the alpha AI-Fe-Si proved, and a lower tendency toward shrink- dicts total resistivity and its reciprocal con- phase intermetallics least harmful to cast- age formation will be observed. This alloy is ductivity for any composition. A more ability. Ignoring these important relation- recommended when the maximum dimension general and easy-to-use formula for conduc- results in variable electrical perfor- of the part is greater than 125 mm (5 in.). For tivity that offers sufficient accuracy for mance, and of at least equal importance, the same reasons, Alloy 150.0 is preferred most purposes is: variable casting results. over 170.0 in casting performance. Commercial Duralumin Alloys. These al- For motor rotors requiring high resistivity Conductivity, %IACS = 63.50 - 6.9x - 83y loys were first produced and were named by (for example, motors with high starting where 63.5% is the conductivity of very Durener Metallwerke Aktien Gesellschaft torque) the more highly alloyed die casting pure aluminum in %IACS, x = iron + in the early 1900s. They were the first compositions are commonly used. The most silicon (in wt%), and y = + vana- heat-treatable aluminum alloys. popular are Alloys 443.2 and A380.2. By dium + manganese + chromium (in wt%). The Duralumin alloys have been used choosing alloys such as these, conductivi- References to specific composition limits extensively as cast and wrought products ties from 25 to 35% IACS can be obtained; and techniques for rotor al- where high strength and toughness are re- in fact, highly experimental alloys with even loys show the use of composition controls quired. Being essentially a single-phase al- higher resistivities have been developed for that reflect electrical considerations. The loy, improved ductility at higher strengths is motor rotor applications. peritectic elements are limited because their inherent as compared to the two-phase sili- Although gross casting defects may ad- presence is harmful to electrical conductiv- con alloys. However, this difference also versely affect electrical performance, the ity. The prealloyed produced to these makes these alloys more difficult to cast. conductivity of alloys employed in rotor specifications control conductivity by mak- After World War I, the European alumi- manufacture is more exclusively controlled ing boron additions, which form complex num casting community developed AU5GT 130 / Specific Metals and Alloys

Table 4 Effect of elements in and out of is extensively used in the United States for 242-T571 (142-T571) is also used in some solid solution on the resistivity of premium casting procurement. Mechanical heavy-duty pistons because of its higher aluminum properties of premium aluminum castings thermal conductivity and superior proper- Average increase(a) are given in the section "Properties of Alu- ties at elevated temperatures. Maximum in resistivity minum Casting Alloys" in this article. solubility per wt%, microhm-cm Other applications of aluminum alloys for Element in AI, % In solution Out of solution(b) Alloys considered premium by definition elevated-temperature use include air-cooled and specification are A201.0, A206.0, cylinder heads for airplanes and motorcy- Chromium ...... 0.77 4.00 0.18 Copper ...... 5.65 0.344 0.030 224.0, 249.0, 354.0, A356.0 (D356.0), cles. The 10% Cu Alloy 222.0-T61 was used Iron ...... 0.052 2.56 0.058 A357.0 (D357.0), and 358.0. All alloys em- extensively for this purpose prior to the Lithium ...... 4.0 3.31 0.68 ployed in premium casting 1940s but has been replaced by the 242.0 Magnesium ...... 14.9 0.54(c) 0.22(c) work are characterized by optimum concen- and 243.0 compositions because of their Manganese ...... 1.82 2.94 0.34 Nickel ...... 0.05 0.81 0.061 trations of hardening elements and restric- better properties at elevated temperatures. Silicon ...... 1.65 1.02 0.088 tively controlled impurities. Although any For use at moderate elevated tempera- Titanium ...... 1.0 2.88 0.12 alloy can be produced in cast form with tures (up to 175 °C, or 350 °F), Alloys 355 ...... 0.5 3.58 0.28 properties and soundness conforming to a and C355 have been extensively used. Zinc ...... 82.8 0.094(d) 0.023(d) ...... 0.28 1.74 0.044 general description of premium values rela- These applications include aircraft motor tive to corresponding commercial limits, and housings. Alloy A201.0 and the (a) Add above increase to the base resistivity for high-purity aluminum, 2.65 microhm-cm at 20 *C (68 °F) or 2.71 microhm-cm only those alloys demonstrating yield A206.0 type alloys have also been used in at 25 °C (77 °F). (b) Limited to about twice the concentration given for the maximum solid solubility, except as noted. (c) strength, tensile strength, and especially this temperature range when the combina- Limited to approximately 10%. (d) Limited to approximately 20% elongation in a premium range belong in this tion of high strength at room temperatures grouping. They fall into two categories: and elevated temperatures is required. high-strength aluminum-silicon composi- Standard General-Purpose Aluminum (204 type) and similar AI-Cu-Mg alloys. In tions, and those alloys of the 2xx series, Casting Alloys. Alloys with silicon as the the United States, alloys 195 and B195 of which by restricting impurity element con- major alloying constituent are by far the the AI-Cu-Si composition were popularized. centrations provide outstanding ductility, most important commercial casting alloys, Between World Wars I and II, and in both toughness, and tensile properties with nota- primarily because of their superior casting communities, these alloys served well in the bly poorer castability. characteristics. Binary aluminum-silicon al- special situations in which strength and In all premium casting alloys, impurities loys (443.0, 444.0, 413.0, and A413.0) offer toughness were required. This came at the are strictly limited for the purposes of im- further advantages of high resistance to expense of the extra production costs re- proving ductility. In aluminum-silicon al- corrosion, good weldability, and low specif- quired because of the poorer castability. loys, this translates to control iron at or ic gravity. Although castings of these alloys Since World War II, the higher-purity below 0.01% Fe with measurable advantag- are somewhat difficult to machine, larger aluminum available from the smelters has es to the range of 0.03 to 0.05%, the practi- quantities are machined successfully with enabled the foundryman to make substan- cal limit of commercial capability. sintered carbide and flood application tial improvements in the mechanical prop- Beryllium is present in A357 and 158 of lubricant. Application areas are: erties of highly castable AI-Si, AI-Si-Cu, alloys, not to inhibit oxidation (although and AI-Si-Mg alloys. As a result, the use of that is a corollary benefit), but to alter the • Alloy 443 (Si at 7%) is used with all the Duralumin alloys has dramatically de- form of the insoluble phase to a more nod- casting processes for parts where high creased. ular form less detrimental to ductility. strength is less important than good duc- The more recently developed A1-Cu-Mg The development of hot isostatic pressing tility, resistance to corrosion, and pres- alloys and applications include many that is pertinent to the broad range of premium sure tightness emphasize the unusual strength and tough- castings but is especially relevant for the • Permanent mold Alloys 444 and A444 (Si ness achievable with impurity controls. more diffficult-to-cast aluminum-copper se- at 7%) have especially high ductility and New developments in foundry equipment ties. are used where impact resistance is a and control techniques also have helped Piston and Other Elevated-Temperature primary consideration (for example, high- some foundries to solve the castability Alloys. The universal acceptance of alumi- way -rail support castings) problems. num pistons by all gasoline engine manufac- • Alloys 413.0 and A413.0 (Si at 12%) are Premium-quality castings provide higher turers in the United States can be attributed close to the eutectic composition, and as levels of quality and reliability than are to their light weight and high thermal con- a result, have very high fluidity. They are found in conventionally produced parts. ductivity. The effect of the lower inertia of useful in die casting and where cast-in These castings may display optimum prop- the aluminum pistons on the bearing loading lettering or other high-definition casting erties in one or more of the following char- permits higher engine speeds and reduced surfaces are required acteristics: mechanical properties (deter- counterweighting. In the silicon-copper alloys (213.0, 308.0, mined by test coupons machined from Aluminum automotive pistons generally 319.0, and 333.0), the silicon provides good representative parts), soundness (deter- are permanent mold castings. This design casting characteristics, and the copper im- mined radiographically), dimensional accu- usually is superior in economy and design parts moderately high strength and im- racy, and finish. However, castings of this flexibility. The alloy most commonly used proved machinability with reduced ductility classification are notable primarily for the for passenger car pistons, 332.0-T5, has a and lower resistance to corrosion. The sili- mechanical property attainment that re- good combination of foundry, mechanical, con range is 3 to 10.5%, and the copper flects extreme soundness, fine dendrite-arm and physical characteristics, including low content is 2 to 4.5%. These and similar spacing, and well-refined grain structure. thermal expansion. Heat treatment im- general-purpose alloys are used mainly in These technical objectives require the use proves hardness for improved machinability the F temper. The T5 temper can be added of chemical compositions competent to dis- and eliminates any permanent changes in to some of these alloys to improve hardness play the premium engineering properties. dimensions from residual growth due to and machinability. Alloys considered to be premium engi- aging at operating temperatures. Alloy 356.0 (7 Si, 0.3 Mg) has excellent neered compositions appear in separately Piston alloys for heavy-duty engines in- casting characteristics and resistance to negotiated specifications or in those such as clude the low-expansion alloys 336.0-T551 corrosion. This justifies its use in large military specification MIL-A-21180, which (A132-T551) and 332.0-T5 (F132-T5). Alloy quantities for sand and permanent mold Aluminum Foundry Products/131

castings. Several heat treatments are used Table 5 Characteristics of aluminum die cussed in the section "Aluminum-Tin Al- and provide the various combinations of casting alloys loys" in this article. Aluminum-tin bearing tensile and physical properties that make it See Table 3 for other characteristics. alloys are also discussed in the article "Tin

attractive for many applications. This in- Resistance to Die filling and Tin Alloys" in this Volume. cludes many parts in both the auto and Alloy die soldering(a) capadty Effects of Alloying aerospace industries. The companion alloy 360.0 ...... 2 of 356.0 with lower iron content affords A360.0 ...... 2 Antimony. At concentration levels equal higher tensile properties in the premium- 380.0 ...... 1 to or greater than 0.05%, antimony refines quality sand and permanent mold castings. A380.0 ...... 1 eutectic aluminum-silicon phase to lamellar 383.0 ...... 2 Even higher tensile properties are obtained 384.0 ...... 2 form in hypoeutectic compositions. The ef- using this premium casting process using 413.0 ...... I fectiveness of antimony in altering the eu- 357.0, A357.0, 358.0, and 359.0 alloys. The A413.0 ...... 1 tectic structure depends on an absence of high properties of these alloys, attained by C443.0 ...... 4 phosphorus and on an adequately rapid rate T6-type heat treatments, are of special in- 518.0 ...... 5 of solidification. Antimony also reacts with terest to aerospace and military applica- (a) Rankings from ASTM B 85. Relative rating of die casting alloys from 1 to 5; 1 is the highest or best possible rating. A rating either sodium or strontium to form coarse tions. of 5 in one or more categories does not rule an alloy out of intermetallics with adverse effects on cast- commercial use if other attributes are favorable; however, ratings The 355.0 type alloys, or AI-Si-Mg-Cu of 5 may present manufacturing difficulties. ability and eutectic structure. alloys, offer greater response to the heat Antimony is classified as a heavy metal treatment because of the copper addition. with potential toxicity and hygiene implica- This gives the higher strengths with some tions, especially as associated with the pos- sacrifice in ductility and resistance to cor- 380.0 family of alloys provides a good com- sibility of stibine gas formation and the rosion. Representative sand and permanent bination of cost, strength, and corrosion effects of human exposure to other antimo- mold alloys include 355.0 (5 Si, 1.3 Cu, 0.4 resistance, together with the high fluidity ny compounds. In cases of direct exposure, Mg, 0.4 Mn) and 328.0 (8 Si, 1.5 Cu, 0.4 Mg, and freedom from hot shortness that are OSHA Safety and Health Standards 2206 0.4 Mn). Some applications include cylinder required for ease of casting. Where better specifies the following 8-h weighted average blocks for internal combustion engines, corrosion resistance is required, alloys low- exposure limits for antimony and other se- engine compressor cases, and accessory er in copper, such as 360.0 and 413.0, must lected metals: housings. be used. Rankings of these alloys in terms • Antimony, 0.5 mg/m 3 Alloy C355.0 with low iron is a higher- of die soldering and die filling capacity are • Chromium, 0.5 mg/m 3 tensile version of 355, for heat-treated, pre- given in Table 5. The hypereutectic alumi- • Copper, 0.1 mg/m 3 mium-quality, sand, and permanent mold num-silicon alloy 390.0 type has found • Lead, 0.2 mg/m 3 castings. Some of the applications include many useful applications in recent years. In • Manganese, 1.0 mg/m 3 tank engine cooling fans, high-speed rotat- heavy-wear uses, the increased hardness • Nickel, 1.0 mg/m 3 ing parts such as impellers. When the pre- has given it a substantial advantage over • , 0.01 mg/m 3 mium-strength casting processes are used, normal 380.0 alloys (without any significant • Zinc, 5.0 mg/m 3 even higher tensile properties can be ob- problems related to castability). Hypereu- • Beryllium, 2.0 ixg/m 3 tained with heat-treated Alloy 354.0 (9 Si, tectic aluminum-silicon alloys are growing • Cadmium, 0.2 mg/m 3 1.8 Cu, 0.5 Mg). This is also of interest in in importance as their valuable characteris- aerospace applications. tics and excellent die casting properties are As an additive for aluminum alloys, there is The 390.0 (17 Si, 4.5 Cu, 0.5 Mg) type exploited in automotive and other applica- no indication of danger of antimony in alu- alloys have enjoyed much growth in recent tions. minum alloys, particularly at the 0.08 to years. These alloys have high wear resis- Magnesium content is usually controlled 0.15% levels of antimony in alloys that have tance and a low thermal expansion coeffi- at low levels to minimize oxidation and the been produced for years. cient but somewhat poorer casting and generation of oxides in the casting process. Beryllium additions of as low as a few parts characteristics than the other Nevertheless, alloys containing appreciable per million may be effective in reducing oxi- alloys in this group. B390.0 is a low-iron magnesium concentrations are routinely dation losses and associated inclusions in version of 390.0 that can be used to advan- produced. Alloy 518.0, for example, is oc- magnesium-containing compositions. Studies tage for sand and permanent mold casting. casionally specified when the highest corro- have shown that proportionally increased be- Some uses and applications include auto sion resistance is required. This alloy, how- ryllium concentrations are required for oxida- engine cylinder blocks, pistons, and so ever, has low fluidity and some tendency to tion suppression as magnesium content in- forth. hot shortness. It is difficult to cast, which is creases. Die Casting Alloys. In terms of product reflected in higher costs per casting. At higher concentrations (>0.04%), be- tonnage, the use of aluminum alloys for die Iron content of 0.7% or greater is pre- ryllium affects the form and composition of casting is almost twice as large as the usage ferred in most die casting operations to iron-containing intermetallics, markedly im- of aluminum alloys in all other casting meth- maximize elevated-temperature strength, to proving strength and ductility. In addition ods combined. In addition, alloys of alumi- facilitate ejection, and to minimize - to changing beneficially the morphology of num are used in die castings more exten- ing to the die face. Iron content is usually 1 the insoluble phase, beryllium changes its sively than for any other base metal. --- 0.3%. Improved ductility through re- composition, rejecting magnesium from the Aluminum die castings usually are not heat duced iron content has been an incentive AI-Fe-Si complex and thus permitting its treated, but occasionally are given dimen- resulting in widespread efforts to develop a full use for hardening purposes. sional and metallurgical stabilization treat- tolerance for iron as low as approximately Beryllium-containing compounds are, ments (variations of aging and annealing 0.25%. These efforts focus on process re- however, numbered among the known car- processes). finements and improved die lubrication. cinogens that require specific precautions in Compositions. The highly castable AI-Si Additions of zinc are sometimes used to the melting, molten metal handling, family of alloys is the most important group enhance the fluidity of 380.0, and at times, handling and disposition, and of of alloys for die casting. Of these, alloy other die casting alloys. alloys. Standards define the maximum be- 380.0 and its modifications constitute about Aluminum-base bearing alloys are primar- ryllium in welding rod and weld base metal 85% of aluminum die cast production. The ily alloyed with tin. These alloys are dis- as 0.008 and 0.010%, respectively. 132 / Specific Metals and Alloys

Bismuth improves the machinability of form a myriad of insoluble phases in alumi- formation in hypereutectic AI-Si alloys. At cast aluminum alloys at concentrations num alloy melts, the most common of which parts per million concentrations, phospho- greater than 0.1%. are FeAl3, FeMnAlr, and etAlFeSi. These rus coarsens the eutectic structure in hy- Boron combines with other metals to essentially insoluble phases are responsible poeutectic AI~Si alloys. Phosphorus dimin- form borides, such as A12 and TiB 2. Titani- for improvements in strength, especially at ishes the effectiveness of the common um boride forms stable nucleation sites for elevated temperature. As the fraction of eutectic modifiers sodium and strontium. interaction with active grain-refining phases insoluble phase increases with increased Silicon. The outstanding effect of silicon such as TiA13 in molten aluminum. iron content, casting considerations such as in aluminum alloys is the improvement of Metallic borides reduce tool life in ma- flowability and feeding characteristics are casting characteristics. Additions of silicon chining operations, and in coarse particle adversely affected. Iron participates in the to pure aluminum dramatically improve flu- form they consist of objectionable inclu- formation of sludging phases with manga- idity, hot tear resistance, and feeding char- sions with detrimental effects on mechani- nese, chromium, and other elements. acteristics. The most prominently used cal properties and ductility. At high boron lead is commonly used in aluminum cast- compositions in all casting processes are concentrations, borides contribute to fur- ing alloys at greater than 0.1% for improved those of the aluminum-silicon family. Com- nace sludging, particle agglomeration, and machinability. mercial alloys span the hypoeutectic and increased risk of casting inclusions. How- Magnesium is the basis for strength and hypereutectic ranges up to about 25% Si. ever, boron treatment of aluminum-contain- hardness development in heat-treated AI-Si In general, an optimum range of silicon ing peritectic elements is practiced to im- alloys and is commonly used in more com- content can be assigned to casting pro- prove purity and electrical conductivity in plex A1-Si alloys containing copper, nickel, cesses. For slow cooling-rate processes rotor casting. High rotor alloy grades may and other elements for the same purpose. (such as plaster, investment, and sand), the specify boron to exceed titanium and vana- The hardening-phase MgESi displays a use- range is 5 to 7%, for permanent mold 7 to dium contents to ensure either the complex- ful solubility limit corresponding to approx- 9%, and for die casting 8 to 12%. The bases ing or precipitation of these elements for imately 0.70% Mg, beyond which either no for these recommendations are the relation- improved electrical performance (see the further strengthening occurs or matrix soft- between cooling rate and fluidity and section "Rotor Castings" in this article). ening takes place. Common premium- the effect of percentage of eutectic on feed- Cadmium in concentrations exceeding strength compositions in the AI-Si family ing. Silicon additions are also accompanied 0.1% improves machinability. Precautions employ magnesium in the range of 0.40 to by a reduction in specific gravity and coef- that acknowledge volatilization at 767 °C 0.070% (see the section "Premium-Quality ficient of thermal expansion. (1413 °F) are essential. Castings" in this article). Silver is used in only a limited range of Calcium is a weak aluminum-silicon eu- Binary AI-Mg alloys are widely used in aluminum-copper premium-strength alloys tectic modifier. It increases hydrogen solu- applications requiring a bright surface finish at concentrations of 0.5 to 1.0%. Silver bility and is often responsible for casting and corrosion resistance, as well as attrac- contributes to precipitation hardening and porosity at trace concentration levels. Cal- tive combinations of strength and ductility. stress-corrosion resistance. cium concentrations greater than approxi- Common compositions range from 4 to 10% Sodium modifies the aluminum-silicon eu- mately 0.005% also adversely affect ductil- Mg, and compositions containing more than tectic. Its presence is embrittling in alumi- ity in aluminum-magnesium alloys. 7% Mg are heat treatable. Instability and num-magnesium alloys. Sodium interacts Chromium additions are commonly made room-temperature aging characteristics at with phosphorus to reduce its effectiveness in low concentrations to room-temperature higher magnesium concentrations encour- in modifying the eutectic and that of phos- aging and thermally unstable compositions age heat treatment. phorus in the refinement of the primary in which germination and grain growth are Manganese is normally considered an im- silicon phase. known to occur. Chromium typically forms purity in casting compositions and is con- Strontium is used to modify the alumi- the compound CrA17, which displays ex- trolled to low levels in most gravity cast num-silicon eutectic. Effective modification tremely limited solid-state solubility and is compositions. Manganese is an important can be achieved at very low addition levels, therefore useful in suppressing grain growth alloying element in wrought compositions but a range of recovered strontium of 0.008 to tendencies. Sludge that contains iron, man- through which secondary foundry composi- 0.04% is commonly used. Higher addition ganese, and chromium is sometimes en- tions may contain higher manganese levels. levels are associated with casting porosity, countered in die casting compositions, but it In the absence of work hardening, manga- especially in processes or in thick-section is rarely encountered in gravity casting al- nese offers no significant benefits in cast parts in which solidification occurs more loys. Chromium improves corrosion resis- aluminum alloys. Some evidence exists, slowly. Degassing efficiency may also be ad- tance in certain alloys and increases quench however, that a high-volume fraction of versely affected at higher strontium levels. sensitivity at higher concentrations. MnAI6 in alloys containing more than 0.5% Tin is effective in improving antifriction Copper. The first and most widely used Mn may beneficially influence internal cast- characteristics and is therefore useful in aluminum alloys were those containing 4 to ing soundness. Manganese can also be em- bearing applications. Casting alloys may 10% Cu. Copper substantially improves ployed to alter response in chemical finish- contain up to 25% Sn. Additions can also be strength and hardness in the as-cast and ing and . made to improve machinability. Tin may heat-treated conditions. Alloys containing 4 . Compositions containing mercu- influence precipitation-hardening response to 6% Cu respond most strongly to thermal ry were developed as sacrificial anode mate- in some alloy systems. treatment. Copper generally reduces resis- rials for cathodic protection systems, espe- Titanium is extensively used to refine the tance to general corrosion, and in specific cially in marine environments. The use of grain structure of aluminum casting alloys, compositions and material conditions, these optimally electronegative alloys, which often in combination with smaller amounts of stress-corrosion susceptibility. Additions of did not passivate in seawater, was severely boron. Titanium in excess of the stoichiom- copper also reduce hot tear resistance and restricted for environmental reasons. etry of TiB 2 is necessary for effective grain decrease castability. Nickel is usually employed with copper to refinement. Titanium is often employed at Iron improves hot tear resistance and enhance elevated-temperature properties. It concentrations greater than those required for decreases the tendency for die sticking or also reduces the coefficient of thermal ex- grain refinement to reduce cracking tenden- soldering in die casting. Increases in iron pansion. cies in hot-short compositions. content are, however, accompanied by sub- Phosphorus. In AlP3 form, phosphorus Zinc. No significant technical benefits are stantially decreased ductility. Iron reacts to nucleates and refines primary silicon-phase obtained by the addition of zinc to aluminum. Aluminum Foundry Products / 133

(a) Sand cast 443.0-F (b) Permanent mold cast B443.0-F (c) Die cast C443.0-F

Typical tensile properties Typical tensile properties Typical tensile properties Tensile Yield Elonga- Tensile Yield Elonga- Tensile Yield Elonga- strength strength tion, strength strength tion, strength strength tion, MPa ksi MPa ksi % MPa ksi MPa ksi % MPa ksi MPa ksi % 130 19 55 8 8 160 23 60 9 10 230 33 110 16 9

Aluminum, 5% Si alloy microstructures resulting from different solidification rates characteristic of different casting processes. Dendrite cell size and constituent Fig. 2 particle size decrease with increasing cooling rate, from sand cast to permanent mold cast to die cast. Etchant, 0.5% hydrofluoric acid. 500x

Accompanied by the addition of copper and/ ing grain size and interdendritic spacing, verse effects on properties. Thus, small or magnesium, however, zinc results in at- minimizing time for growth of microconstit- interdendritic spacing is necessary for high tractive heat-treatable or naturally aging com- uents calls for rapid cooling. Thus, it is casting quality. Figure 3, for example, illus- positions. A number of such compositions are evident that high cooling rate is of para- trates the improvement in mechanical prop- in common use. Zinc is also commonly found mount importance in obtaining good casting erties achievable by the change in dendrite in secondary gravity and die casting compo- quality. formation controlled by solidification rate. sitions. In these secondary alloys, tolerance Microstructural features such as the size Although several factors affect spacing to for up to 3% zinc allows the use of lower and distribution of primary and intermetal- some extent, the only efficient way of en- grade scrap aluminum to make these alloys lic phases are considerably more complex suring fine spacing is use of rapid cooling. and thus lowers cost. to control by . However, chemis- In premium engineered castings and in try control (particularly control of impurity many other casting applications, careful at- Structure Control element concentrations), control of element tention is given to obtaining solidification ratios based on the stoichiometry of inter- rates corresponding to optimum mechanical The microstructural features that most metallic phases, and control of solidification property development. Solidification rate strongly affect mechanical properties are: conditions to ensure uniform size and dis- affects more than dendrite cell size, but • Grain size and shape tribution of intermetallics are all useful. The dendrite cell size measurements are becom- • Dendrite-arm spacing use of modifiers and refiners to influence ing increasingly important. • Size and distribution of second-phase eutectic and hypereutectic structures in alu- Grain Refinement. A fine, equiaxed grain particles and inclusions minum-silicon alloys is also an example of structure is normally desired in aluminum the manner in which microstructures and castings, because castings with fine, equi- Some of these microstructural features, macrostructures can be optimized in found- axed grains offer the best combination of such as grain size and dendrite-arm spacing, ry operations. strength and ductility. The type and size of are primarily controlled by cooling and so- Dendrite-Arm Spacing. In all commercial grains formed are determined by alloy com- lidification rates. Figure 2, for example, processes, solidification takes place position, solidification rate, and the addition shows the variation in microstructures and through the formation of dendrites in the of master alloys (grain refiners) containing mechanical properties resulting from the liquid solution. The cells contained within intermetallic phase particles, which provide different solidification rates associated with the dendrite structure correspond to the sites for heterogeneous grain nucleation. different casting processes. dimensions separating the arms of primary Grain size is refined by increasing the Like grain size and interdendritic spac- dendrites and are controlled for a given solidification rate but is also dependent on ing, the finer the dispersion of inclusions composition primarily by solidification rate. the presence of grain-refining elements and second-phase particles, the better the Another factor that may affect interden- (principally titanium and boron) in the alloy. properties of the casting. Fine dispersion dritic spacing is the presence of second- To some extent, size and shape of grains requires small particles; large masses of phase particles and oxide or gas inclusions. can be controlled by addition of grain refin- oxides or intermetallic compounds produce During freezing, inclusions and second- ers, but use of low pouring temperatures excessive brittleness. Controlling size and phase particles can segregate to the spaces and high cooling rates are the preferred shape of microconstituents can be done to between dendrite arms and thus increase methods. some extent by controlling composition, but the spacing. All aluminum alloys can be made to so- is accomplished more efficiently by mini- The farther apart the dendrite arms are, lidify with a fully equiaxed, fine grain struc- mizing the period of time during which the coarser the distribution of microconstit- ture through the use of suitable grain-refin- microconstituents can grow. Like minimiz- uents and the more pronounced their ad- ing additions. The most widely used grain 134 / Specific Metals and Alloys

Dendrite cell size, in. x 10 4 tensile properties and appreciably improved 5 10 15 20 25 30 35 40 45 ductility when compared to similar but un- 303 • 44 modified structures. Figure 5 illustrates the desirable effects on mechanical properties that can be achieved by modification. Im- 276 A 40 proved performance in casting is character- ~'~ Ultimate tensile strength ized by improved flow and feeding as well as by superior resistance to elevated-tem- perature cracking. 248' 36 Refinement of Hypereutectic Aluminum- Silicon Alloys. The elimination of large, coarse primary silicon crystals that are 221 32 harmful in the casting and machining of Yield -- hypereutectic silicon alloy compositions is a ~J o function of primary silicon refinement. Phosphorus added to molten alloys contain- 193 28 ing more than the eutectic concentration of silicon, made in the form of metallic phos- 16: phorus or phosphorus-containing com- pounds such as phosphor-copper and phos- phorus pentachloride, has a marked effect on the distribution and form of the primary silicon phase. Investigations have shown

c- that retained trace concentrations as low as © 0.0015 through 0.03% P are effective in achieving the refined structure. Disagree- c 0 ments on recommended phosphorus ranges k~ and addition rates have been caused by the 4 extreme difficulty of accurately sampling and analyzing for phosphorus. More recent ( ~'-"------__A O developments employing vacuum stage 0 ~ spectrographic or quantometric analysis 13 25 38 51 64 76 89 102 114 now provide rapid and accurate phosphorus Dendrite cell size, ,um measurements. Following melt treatment by phosphorus- Fig. 3 Tensile properties versus dendrite cell size for four heats of aluminum alloy A356-T62 plaster cast plates containing compounds, refinement can be expected to be less transient than the effects of conventional modifiers on hypoeutectic refiners are master alloys of titanium, or of certain elements such as calcium, sodium, modification. Furthermore, the solidifica- titanium and boron, in aluminum. Alumi- strontium, and antimony. It is also under- tion of phosphorus-treated melts, cooling to num-titanium refiners generally contain stood that increased solidification is useful room temperature, reheating, remelting, from 3 to 10% Ti. The same range of titani- in achieving modified structures. and resampling in repetitive tests have um concentrations is used in AI-Ti-B refin- In general, the greatest benefits are shown that refinement is not lost; however, ers with boron contents from 0.2 to 1% and achieved in alloys containing from 5% Si to primary silicon particle size increases grad- titanium-to-boron ratios ranging from about the eutectic concentration. The addition of ually, responding to a loss in phosphorus 5 to 50. Although grain refiners of these modifying elements (such as calcium, sodi- concentration. Common degassing methods types can be considered conventional hard- um, strontium, and antimony) to these hy- accelerate phosphorus loss, especially eners or master alloys, they differ from poeutectic aluminum-silicon alloys results when chlorine or freon is used. In fact, brief master alloys added to the melt for alloying in a finer lamellar or fibrous eutectic net- inert gas fluxing is frequently employed to purposes alone. To be effective, grain refin- work (Fig. 4). Although there is no agree- reactive aluminum phosphide nuclei, pre- ers must introduce controlled, predictable, ment on the mechanisms involved, the most sumably by resuspension. and operative quantities of aluminides (and popular explanations suggest that modifying Practices that are recommended for melt borides) in the correct form, size, and dis- additions suppress the growth of silicon refinement are as follows: tribution for grain nucleation. Wrought re- crystals within the eutectic, providing a • Melting and holding temperature should finer in rod form, developed for the contin- finer distribution of lamellae relative to the be held to a minimum uous treatment of aluminum in primary growth of the eutectic. It has also been well • The alloy should be thoroughly chlorine operations, is available in sheared lengths established that phosphorus interferes with or freon fluxed before refining to remove for foundry use. The same grain-refining the modification mechanism. Phosphorus phosphorus-scavenging impurities such compositions are furnished in waffle form. reacts with sodium and probably with stron- as calcium and sodium In addition to grain-refining master alloys, tium and calcium to form phosphides that • Brief fluxing after the addition of phos- Salts (usually in compacted form) that react nullify the intended modification additions. phorus is recommended to remove the with molten aluminum to form combina- It is therefore desirable to use low-phospho- hydrogen introduced during the addition tions of TiA13 and TiB2 are also available. rus metal when modification is a process and to distribute the aluminum phosphide Modification of hypoeutectic aluminum- objective and to make larger modifier addi- nuclei uniformly in the melt silicon alloys involves the improvement of tions to compensate for phosphorus-related properties by inducing structural modifica- losses. Hydrogen Porosity. In general, two types tion of the normally occurring eutectic. Effects of Modification. Typically, modi- of porosity may occur in cast aluminum: gas Modification is achieved by the addition of fied structures display somewhat higher porosity and shrinkage porosity. Gas poros- Aluminum Foundry Products 1 135

Grain size, in. 0 0.016 0.032 0.048 0.064 t 8 [ I I I I I I 7 • Sodium modified alloy_ • Unmodified alloy <,4 6 I I I E .o 5 T -r 4 ~

2 1

:E 314 j::" =-

.~ 294 -L ~ ~ "~ a~ 284 a~ 274 __

- 2641I "-- ""'L- ,-,.-i~,---~... 38 E .E 2541 =

9o ca 89 [E l .---.....,.. [ 2:88 ~ 'I,1" "E,,zl~."' 1;i<4" %( A ~"¢~;..o;. E 87 E 86 85 0 0.2 0.6 1.0 1.4 1.8 Grain size, mm

I:|o Mechanical properties of as-cast A356 alloy "'t~" 5 tensile specimens as a function of modifica- tion and grain size • ; -Z

..... ° 2.0[ r ~ r .. [ 98.8% AI, Al-l.7Si, AI-6Si, Al-12Si 1 /~--992%AI .8 j- .... AI-4.6Cu - 99.99% AI 1.6

14 ....

1.2 / / -~ 10 / o o_ 0.8 I:;e Varying degrees of aluminum-silicon eutectic modification ranging from unmodified (A) to well 4 t "'b" modified (F). These are as-cast structures before any solution heat treatment• 0.6 /

ity, which generally is fairly spherical in solved hydrogen contents are low, and void 0.4 /" shape, results either from precipitation of formation is characteristically subcritical. 0.2 -- P hydrogen during solidification (because the Finely distributed hydrogen porosity may J solubility of this gas is much higher in the not always be undesirable. Hydrogen pre- molten metal than in the solid metal) or 0 , cipitation may alter the form and distribu- 0.1 02 0.3 04 0.5 06 07 from occlusion of gas bubbles during the tion of shrinkage porosity in poorly fed Hydrogen, % high-velocity injection of molten metal in parts or part sections. Shrinkage is general- die casting. ly more harmful to casting properties. In Porosity as a function of hydrogen content in Two types or forms of hydrogen porosity isolated cases, hydrogen may actually be Fig, 6 sand-cast aluminum and aluminum alloy bars may occur in cast aluminum when the pre- intentionally introduced and controlled in cipitation of molecular hydrogen during the specific concentrations compatible with the It is often assumed that hydrogen may cooling and solidification of molten alumi- application requirements of the casting in be desirable or tolerable in pressure-tight num results in the formation of primary order to promote superficial soundness. applications. The assumption is that hy- and/or secondary voids. Of greater impor- Nevertheless, hydrogen porosity adversely drogen porosity is always present in the tance is interdendritic porosity, which is affects mechanical properties in a manner cast structure as integrally enclosed encountered when hydrogen contents are that varies with the alloy. Figure 6 shows the rounded voids. In fact, hydrogen porosity sufficiently high that hydrogen rejected at relationship between actual hydrogen content may occur as rounded or elongated voids the solidification front results in solution and observed porosity. Figure 7 defines the and in the presence of shrinkage may de- pressures above atmospheric. Secondary effect of porosity on the ultimate tensile crease rather than increase resistance to (micron-size) porosity occurs when dis- strength of selected compositions. pressure leakage. 136 / Specific Metals and Alloys

450 I I I I 66 • Increase strength and/or produce the me- very often is dictated by costs. As a general AI-4.5Cu chanical properties associated with a par- rule, the cheaper the tooling (patterns, ~ AI-11Mg ticular material condition n ~ ~ AI-5Si molds, and auxiliary equipment), the great- • Stabilize mechanical and physical proper- er the cost of producing each piece. There- ~s ~3 375 ties fore, number of pieces is a major factor in .c .c • Ensure dimensional stability as a function the choice of a casting method. If only a few of time under service conditions pieces are to be made, the method involving • Relieve residual stresses induced by cast- the least expensive tooling should be used, _.~ 300 44 ing, quenching, machining, welding, or even if the cost of casting each piece is very c other operations high. For very large production runs, on the 0) other hand, where cost of tooling is shared E To achieve these objectives, parts can be by a large number of castings, use of elab- ~ 225 33 annealed, solution heat treated, quenched, orate tooling usually decreases cost per precipitation hardened, overaged, or treat- piece and thus is justified. In mass produc- ed with combinations of these practices. In tion of small parts, for example, costs often some simple shapes (for example, bear- 150 ~ 22 are minimized by use of elaborate tooling 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 ings), thermal treatment can also include that allows several castings to be poured Porosity, % deformation in the form of cold simultaneously. Die castings are typical of work. Typical heat treatments for various this category. Ultimate tensile strength versus hydrogen aluminum casting alloys are given in Table Fig. 7 porosity for sand-cast bars of three aluminum Quality factors are also important in the alloys. The difference in tensile strength among the 6. selection of a casting process. When applied three alloys may be a function of heat treatment. The to castings, the term quality refers to both AI-11Mg alloy is typically used in the T4 temper (high toughness and ductility), while the other alloys are Casting Processes degree of soundness (freedom from porosi- typically in the T6 condition (highest strength with ty, cracking, and surface imperfections) and acceptable ductility). Aluminum is one of the few metals that levels of mechanical properties (strength can be cast by all of the processes used in and ductility). From the discussions in the casting metals. These processes, in decreas- section "Control of Structure," it is evident Shrinkage Porosity. The other source of ing order of amount of aluminum cast, are: that high cooling rate is of paramount im- porosity is the liquid-to-solid shrinkage that die casting, permanent mold casting, sand portance in obtaining good casting quality. frequently takes the form of interdendritically casting (green sand and dry sand), plaster The tabulation below presents characteris- distributed voids. These voids may be en- casting, and investment casting. Aluminum tic ranges of cooling rate for the various larged by hydrogen, and because larger den- also is continuous cast. Each of these pro- casting processes. drites result from slower solidification, the cesses, and the castings produced by them, size of such porosity also increases as solidi- are discussed below. Other processes such Cooling Dendrite-arm Casting processes rate, °C/s spacing, nun fication rate decreases. It is not possible to as lost foam, squeeze casting, and hot iso- establish inherent ratings with respect to an- static pressing are also mentioned. Plaster, dry sand ...... 0.05-0.2 0.I-I ticipated porosity because castings made by There are many factors that affect selec- Green sand, shell ...... 0.1-0.5 0.05--0.5 tion of a casting process for producing a Permanent mold ...... 0.3-I 0.03-0.07 any process can vary substantially in Die ...... 50-500 0.00~-0.015 soundness---from nearly completely sound to specific aluminum alloy part. Some of the Continuous ...... 0.5-2 0.03-0.07 very unsound----depending on casting size and important factors in sand, permanent mold, design as well as on foundry techniques. and die casting are discussed in Table 7. However, it should be kept in mind that in Heat Treatment. The metallurgy of alumi- The most important factors for all casting die casting, although cooling rates are very num and its alloys fortunately offers a wide processes are: high, air tends to be trapped in the casting, range of opportunities for employing ther- • Feasibility and cost factors which gives rise to appreciable amounts of mal treatment practices to obtain desirable • Quality factors porosity at the center. Extensive research combinations of mechanical and physical has been conducted to find ways of reduc- properties. Through alloying and temper In terms of feasibility, many aluminum alloy ing such porosity; however, it is difficult if selection, it is possible to achieve an im- castings can be produced by any of the not impossible to eliminate completely, and pressive array of features that are largely available methods. For a considerable num- die castings often are lower in strength than responsible for the current use of aluminum ber of castings, however, dimensions or low-pressure or gravity-fed permanent mold alloy castings in virtually every field of design features automatically determine the castings, which are more sound in spite of application. Although the term heat treat- best casting method. Because metal molds slower cooling. ment is often used to describe the proce- weigh from 10 to 100 times as much as the Die Casting. Alloys of aluminum are used dures required to achieve maximum strength castings they are used in producing, most in die casting more extensively than alloys in any suitable composition through the se- very large cast products are made as sand of any other base metal. In the United quence of solution heat treatment, quenching, castings rather than as die or permanent States alone, about 2.5 billion dollars worth and precipitation hardening, in its broadest mold castings. Small Castings usually are of aluminum alloy die castings is produced meaning heat treatment comprises all thermal made with metal molds to ensure dimen- each year. The die casting process con- practices intended to modify the metallurgical sional accuracy. Some parts can be pro- sumes almost twice as much tonnage of structure of products in such a way that duced much more easily if cast in two or aluminum alloys as all other casting pro- physical and mechanical characteristics are more separate sections and bolted or weld- cesses combined. controllably altered to meet specific engineer- ed together. Complex parts with many un- Die casting is especially suited to pro- ing criteria. In all cases, one or more of the dercuts can be made easily by sand, plaster, duction of large quantities of relatively following objectives form the basis for temper or investment casting, but may be practical- small parts. Aluminum die castings weigh- selection: ly impossible to cast in metal molds even if ing up to about 5 kg (10 lb) are common, sand cores are used. but castings weighing as much as 50 kg • Increase hardness for improved machin- When two or more casting methods are (100 lb) are produced when the high tooling ability feasible for a given part, the method used and casting-machine costs are justified. Aluminum Foundry Products / 137

Table 6 Typical heat treatments for aluminum alloy sand and permanent mold castings ] Solution heat treatment(b) ] ] Aging treatment Type of [-- Temperatm~(e) --I [ Temperature(c) I Alloy Temper casting(a) °C °F Time, h *C *F Time, h

201.0(d) ...... T4 S or P ...... 490-500(e) 910-930(e) 2 ...... +525-530 +980-990 14-20 Minimum of 5 days at room temperature T6 S ...... 510-515(e) 950-960(e) 2 ...... +525-530 +980-990 14-20 155 310 20 T7 S ...... 510-515(e) 950-960(e) 2 ...... + 525-530 + 980-990 14-20 190 370 5 T43(f) - • • ...... 525 980 20 24 h at room temperature + 1/2 to 1 h at 160 °C T71 ...... 490-500(e) 910-930(e) 2 ...... +525-530 +980-990 14--20 200 390 4 204.0(d) ...... T4 S or P ...... 530 985 12 Minimum of 5 days at room temperature T4 S or P ...... 520 970 10 ...... T6(g) S or P ...... 530 985 12 (g) (g) • • • 206.0(d) ...... T4 S or P ...... 490-500(e) 910-930(e) 2 ...... +525-530 +980-990 14-20 Minimum of 5 days at room temperature T6 S or P ...... 490-500(e) 910-930(e) 2 ...... +525-530 +980-990 14-20 155 310 12-24 T7 S or P ...... 490-500(e) 910-930(e) 2 ...... +525-530 +980-990 14-20 200 390 4 T72 S or P ...... 490-500(e) 910-930(e) 2 ...... + 525-530 + 980-990 14-20 243-248 470-480 208.0 ...... T55 S ...... 155 310 16 222.0 O(h) S ...... • ...... 315 600 3 T61 S ...... 510 950 12 155 310 11 T551 P ...... • ...... 170 340 16--22 T65 .-...... 510 950 4-12 170 340 7-9 242.0 ...... O(i) S ...... 345 650 3 T571 S ...... • ...... 205 400 8 P ...... - ...... 165-170 330-340 22-26 T77 S ...... 515 960 50) 330-355 625-675 2 (minimum) T61 S or P ...... 515 960 4-120) 205-230 400-450 3-5 295.0 ...... T4 S ...... 515 960 12 ...... T6 S ...... 515 960 12 155 310 3-6 T62 S ...... 515 960 12 155 310 12-24 T7 S ...... 515 960 12 260 500 4-6 296.0 ...... T4 P ...... 510 950 8 ...... T6 P ...... 510 950 8 155 310 1-8 T7 P ...... 510 950 8 260 500 4-6 319.0 ...... T5 S ...... - ...... 205 400 8 T6 S ...... 505 940 12 155 310 2-5 P ...... 505 940 4-12 155 310 2-5 328.0 ...... 1"6 S ...... 515 960 12 155 310 2-5 332.0 ...... T5 P ...... • ...... 205 400 7-9 333.0 ...... T5 P ...... • ...... 205 400 7-9 T6 P ...... 505 950 6-12 155 310 2-5 T7 P ...... 505 940 6-12 260 500 4-6 336.0 ...... T551 P ...... • ...... 205 400 7-9 T65 P ...... 515 960 8 205 400 7-9 354.0 ...... --- (k) ...... 525-535 980-995 10-12 (h) (h) (1) 355.0 ...... T51 S or P ...... • ...... 225 440 7-9 T6 S ...... 525 980 12 155 310 3-5 P ...... 525 980 4-12 155 310 2-5 T62 P ...... 525 980 4-12 170 340 14-18 T7 S ...... 525 980 12 225 440 3-5 P ...... 525 980 4-12 225 440 3-9 T71 S ...... 525 980 12 245 475 4-6 P ...... 525 980 4-12 245 475 3-6 C355.0 ...... T6 S ...... 525 980 12 155 310 3-5 T61 P ...... 525 980 6-12 Room temperature 8 (minimum) 155 310 10-12 356.0 ...... T51 S or P ...... • ...... 225 440 7-9 T6 S ...... 540 1000 12 155 310 3-5 P ...... 540 1000 4-12 155 310 2-5 T7 S ...... 540 1000 12 205 400 3-5 P ...... 540 1000 4-12 225 440 7-9 TT1 S ...... 540 1000 10-12 245 475 3 P ...... 540 1000 4-12 245 475 3-6 A356.0 ...... T6 S ...... 540 1000 12 155 310 3-5 T61 P ...... 540 1000 6-12 Room temperature 8 (minimum) 155 310 6-12

(continued) (a) S, sand; P, permanent mold. (b) Unless otherwise indicated, solution treating is followed by quenching in water at 65-100 °C (150-212 °F). (c) Except where ranges are given, listed temperatures are -+6 °C or + 10 °F. (d) Casting wall thickness, solidification rate, and grain refinement affect the solution heat-treatment cycle in alloys 201.0, 204.0, and 206.0, and care must he taken in approaching the final solution temperature. Too rapid an approach can result in the occurrence of incipient melting. (e) For castings with thick or other slowly solidified sections, a pre-solution heat treatment ranging from about 490 to 515 °C (910 to 960 °F) may be needed to avoid too rapid a temperature rise to the solution temperature and the melting of CuAI 2. (f) Temper T43 for 201.0 was developed for improved impact resistance with some decrease in other mechanical properties. Typical Charpy value is 20J (15 ft • lb). (g) The French precipitation treatment technology for the heat treatment of 204.0 alloy requires 12 h at temperature. The aging temperatures of 140, 160, or 180 °C (285,320, or 355 °F) are selected to meet the required combination of properties. (h) Stress relieve for dimensional stability as follows: hold 5 h at 413 + 14 °C (775 + 25 °F); furnace cool to 345 °C (650 °F) over a period of 2 h or more; furnace cool to 230 °C (450 °F) over a period of not more than IA h; furnace cool to 120 °C (250 °F) over a period of approximately 2 h; cool to room temperature in still air outside the furnace. (i) No quench required; cool in still air outside furnace. (j) Air-blast quench from solution-treating temperature. (k) Casting process varies (sand, permanent mold, or composite) depending on desired mechanical properties. (1) Solution heat treat as indicated, then artificially age by heating uniformly at the temperature and for the time necessary to develop the desired mechanical properties. (m) Quench in water at 65-100 °C (150-212 °F) for 10-20 s only. (n) Cool to room temperature in still air outside the furnace. 138 / Specific Metals and Alloys

Table 6 (continued)

Solution heat treatment(b) I [ Aging treatment I Type of Temperature(c) I i Temperature(c) ] Alloy Temper casting(a) *C *F Time, h °C *F Time, h

357.0 ...... T6 P ...... 540 1000 8 175 350 6 T61 S ...... 540 1000 10-12 155 310 10-12 A357.0 ...... (k) ...... 540 1000 8-12 (h) (h) (h) 359.0 ...... ''' (k) ...... 540 1000 10-14 (h) (h) (h) A444.0 ...... T4 P ...... 540 1000 8-12 520.0 ...... T4 S ...... 430 810 18(m) 535.0 ...... T5(h) S ...... 400 750 705.0 ...... T5 S ...... " " Room temperature 21 days 100 210 8 P ...... • . Room temperature 21 days 100 210 10 707.0 ...... T5 S ...... • . 155 310 3-5 P ...... • . Room temperature, or 21 days I00 210 8 T7 S ...... 530 990 8-16 175 350 4-10 P ...... 530 990 4--8 175 350 4-10 710.0 ...... T5 S ...... • ..... Room temperature 21 days 711.0 ...... TI P ...... Room temperature 21 days 712.0 ...... T5 S ...... Room temperature, or 21 days 155 315 6-8 713.0 ...... T5 SoFP ...... • • Room temperature, or 21 days 120 250 16 771.0 ...... T53(h) S ...... 415(n) 775(n) 5(n) 180(n) 360(n) 4(n) T5 S ...... 180(n) 355(n) 3-5(n) T51 S ...... 205 405 6 T52 S ...... (h) (h) (h) T6 S ...... 590(n) 1090(n) 6(n) 130 265 3 T71 S ...... 590(i) 1090(0 6(i) 140 285 15 850.0 ...... T5 S or P ...... 220 430 7-9 851.0 ...... T5 S or P ...... • ..... 220 430 7-9 T6 P ...... 480 900 6 220 430 4 852.0 ...... T5 S or P ...... 220 430 7-9

(a) S, sand; P, permanent mold. (b) Unless otherwise indicated, solution treating is followed by quenching in water at 65-100 °C ( 150-212 °F). (c) Except where ranges are given, listed temperatures are +6 °C or + 10 °F. (d) Casting wall thickness, solidification rate, and grain refinement affect the solution heat-treatment cycle in alloys 201.0, 204.0, and 206.1), and care must be taken in approaching the final solution temperature. Too rapid an approach can result in the occurrence of incipient melting. (e) For castings with thick or other slowly solidified sections, a pre-solution heat treatment ranging from about 490 to 515 °C (910 to 96t) °F) may be needed to avoid too rapid a temperature rise to the solution temperature and the melting of CuAI 2. (f) Temper T43 for 201.0 was developed for improved impact resistance with some decrease in other mechanical properties. Typical Charpy value is 20J (15 fl . Ib). (g) The French precipitation treatment technology for the heat treatment of 204.0 alloy requires 12 h at temperature. The aging temperatures of 140, 160, or 180 °C (285,320, or 355 °F) are selected to meet the required combination of properties. (h) Stress relieve for dimensional stability as follows: hold 5 h at 413 -+ 14 °C (775 ± 25 °F); furnace cool to 345 °C (650 °F) over a period of 2 h or more; furnace cool to 230 °C (450 °F) over a period of not more than iA h; furnace cool to 120 °C (250 °F) over a period of approximately 2 h; cool to room temperature in still air outside the furnace. (i) No quench required; cool in still air outside furnace. (i) Air-blast quench from solution-treating temperature• (k} Casting process varies (sand, permanent mold, or composite) depending on desired mechanical properties. (I) Solution heat treat as indicated, then artificially age by heating uniformly at the temperature and for the time necessary to develop the desired mechanical properties. (m) Quench in water at 65-100 °C (150-212 °F) for 10-20 s only. in) Cool to room temperature in still air outside the furnace.

Typical applications of die cast aluminum are restricted to simple shapes that permit range also is helpful. The use of vacuum alloys include: straight-line removal. for cavity venting is practiced in some die Die castings are made by injection of casting foundries for production of parts Alloy 380.0 ...... Lawnmower housings, gear molten metal into metal molds under sub- for some special applications. In the "pure cases, cylinder heads for air-cooled engines stantial pressure. Rapid injection (due to the free" process, the die cavity is purged Alloy A380.0 ...... Streetlamp housings, high pressure) and rapid solidification under with before injection. The en- typewriter frames, dental high pressure (due to the use of bare metal trapped oxygen reacts with the molten equipment molds) combine to produce a dense, fine- aluminum to form oxide particles rather Alloy 360.0 ...... Frying skillets, cover plates, instrument cases, grain surface structure, which results in than gas pores. parts requiring corrosion excellent wear and fatigue properties. Air Approximately 85% of aluminum alloy resistance entrapment and shrinkage, however, may die castings are produced in aluminum-sili- Alloy 413.0 ...... Outboard motor parts such result in porosity, and machine cuts should con-copper alloys (alloy 380.0 and its sev- as pistons, connecting rods, and housings be limited to 1.0 mm (0.040 in.) to avoid eral modifications). This family of alloys Alloy 518.0 ...... Escalator parts, conveyor exposing it. Mold coatings are not practical provides a good combination of cost, components, aircraft and in die casting, which is done at pressures of strength, and corrosion resistance, together marine hardware and 2 MPa (300 psi) or higher, because the with the high fluidity and freedom from hot fittings violence of the rapid injection of molten shortness that are required for ease of cast- metal would remove the coating (produc- ing. Where better corrosion resistance is With die casting, it is possible to maintain tion of thin-section die castings may involve required, alloys lower in copper, such as close tolerances and produce good surface cavity fill times as brief as 20 ms). 360.0 and 413.0, must be used. finishes; aluminum alloys can be die cast to Aluminum alloy die castings usually are Alloy 518.0 is occasionally specified basic linear tolerances of -+4 mm/m (-+4 not heat treated but occasionally are given when highest corrosion resistance is re- mils/in.) and commonly have finishes as fine dimensional and metallurgical stabilization quired. This alloy, however, has low fluid- as 1.3 ixm (50 i~in.). Die castings are best treatments. ity and some tendency to hot shortness. It is designed with uniform wall thickness; min- Die castings are not easily welded or difficult to cast, which is reflected in higher imum practical wall thickness for aluminum heat treated because of entrapped gases. cost per casting. alloy die castings is dependent on casting Special techniques and care in production The physical and mechanical properties size. Small parts are cast as thin as 1.0 mm are required for pressure-tight parts. The of the most commonly used aluminum die (0.040 in.). Cores, which are made of metal, selection of an alloy with a narrow freezing casting alloys are given in the section Aluminum Foundry Products / 139

Table 7 Factors affecting selection of casting process for aluminum alloys the metal molds at pressures of 170 kPa (25 [ Casting process psi) or less. Gating systems are used to Factor Permanent mold casting Die casting introduce this metal into the mold inlet at Cost of equipment ...... Lowest cost if only a Less than die casting Highest the bottom of the mold so as to aid smooth few items required and nonturbulent flow of the molten metal Casting rate ...... Lowest rate 11 kg/h (25 Ib/h) 4.5 kg/h (10 lb/h) into the casting cavity. Filling of the mold common; higher common; 45 kg/h (100 and control of solidification are aided by rates possible lb/h) possible Size of casting ...... Largest of any casting Limited by size of Limited by size of application of mold coating to method machine machine selected areas of the die cavity, which slows External and internal shape ..... Best suited for Simple sand cores can Cores must be able to down cooling in those areas. Thinner walls complex shapes be used, but more be pulled because can be cast by low-pressure casting than by where coring difficult to insert they are metal; required than in sand castings undercuts can be regular permanent mold casting. Low-pres- formed only by sure casting also has the economic advan- collapsing cores or tage in that it can be highly automated. loose pieces Some common aluminum permanent Minimum wall thickness ...... 3.0-5.0 mm 3.0-5.0 mm 1.0-2.5 mm (0.125-0.200 in.) (0.125-0.200 in.) (0.100-0.040 in.); mold casting alloys, and typical products required; 4.0 mm required; 3.5 mm depends on casting cast from them, are presented below. (0.150 in.) normal (0.140 in.) normal size Type of cores ...... Complex baked sand Reuseable cores can be cores; must be Alloy 366.0 ...... Automotive pistons cores can be used made of steel, or simple and straight so Alloys 355.0, C355.0, nonreuseable baked they can be pulled A357.0 ...... Timing , impellers, cores can be used compressors, and aircraft Tolerance obtainable ...... Poorest; best linear Best linear tolerance is Best linear tolerance is and missile components tolerance is 300 10 mm/m (10 mils/in.) 4 mm/m (4 mils/in.) requiring high strength mm/m (300 mils/in.) Alloys 356.0, A356.0 ..... parts, aircraft Surface finish ...... 6.5-12.5 p.m (250-500 4.0-10 ixm (150~00 1.5 ~m (50 pan.); best wheels, pump parts, pLin.) pan.) finish of the three marine hardware, valve casting processes bodies Gas porosity ...... Lowest porosity Best pressure tightness; Porosity may be Alloy B443.0 ...... Carburetor bodies, waffle possible with good low porosity possible present technique with good technique Alloy 513.0 ...... Ornamental hardware and Cooling rate ...... 0.1-0.5 °C/s 0.3-1.0 °C/s 50-500 °C/s architectural fittings (0.2-0.9 °F/s) (0.5-1,8 °F/s) (90-900 °F/s) Grain size ...... Coarse Fine Very fine on surface Strength ...... Lowest Excellent Highest, usually used in the as-cast condition Other aluminum alloys commonly used for Fatigue properties ...... Good Good Excellent permanent mold castings include 296.0, Wear resistance ...... Good Good Excellent 319.0, and 333.0. Overall quality ...... Depends on foundry Highest quality Tolerance and Sand casting, which in a general sense technique repeatability very involves the forming of a casting mold with good Remarks ...... Very versatile as to • • • Excellent for fast sand, includes conventional sand casting size, shape, internal production rates and evaporative pattern (lost-foam) casting. configurations This section focuses on conventional sand casting, which uses bonded sand molds. Evaporative pattern casting, which uses un- "Properties of Aluminum Casting Alloys" used, the process usually is referred to as bonded sand molds, is discussed in the next in this article. Other characteristics of alu- semipermanent mold casting.) section. minum die casting alloys are presented in Permanent mold castings are gravity-fed In conventional sand casting, the mold is Tables 3 and 5. Final selection of an alumi- and pouring rate is relatively low, but the formed around a pattern by ramming sand, num alloy for a specific application can best metal mold produces rapid solidification. mixed with the proper bonding agent, onto be established by consultation with die cast- Permanent mold castings exhibit excellent the pattern. Then the pattern is removed, ing suppliers. mechanical properties. Castings are gener- leaving a cavity in the shape of the casting Permanent mold (gravity die) casting, like ally sound, provided that the alloys used to be made. If the casting is to have internal die casting, is suited to high-volume produc- exhibit good fluidity and resistance to hot cavities or undercuts, sand cores are used tion. Permanent mold castings typically are tearing. to make them. Molten metal is poured into larger than die castings. Maximum weight Mechanical properties of permanent mold the mold, and after it has solidified the mold of permanent mold castings usually is about castings can be further improved by heat is broken to remove the casting. In making 10 kg (25 lb), but much larger castings treatment. If maximum properties are re- molds and cores, various agents can be used sometimes are made when costs of tooling quired, the heat treatment consists of a for bonding the sand. The agent most often and casting equipment are justified by the solution treatment at high temperature fol- used is a mixture of and water. (Sand quality required for the casting. lowed by a quench (usually in hot water) bonded with clay and water is called green Surface finish of permanent mold cast- and then natural or artificial aging. For sand.) Sand bonded with oils or , ings depends on whether or not a mold small castings in which the cooling rate in which is very strong after baking, is used wash is used; generally, finishes range the mold is very rapid or for less critical mostly for cores. Water (sodium sili- from 3.8 to 10 txm (150 to 400 Ixin.). Basic parts, the solution treatment and quench cate) hardened with CO2 is used extensively linear tolerances of about ---10 mm/m may be eliminated and the fast cooling in as a bonding agent for both molds and (-+0.10 in./in.), and minimum wall thick- the mold relied on to retain in solution the cores. nesses of about 3.6 mm (0.140 in.), are compounds that will produce age harden- The main advantages of sand casting are typical. Tooling costs are high, but lower ing. versatility (a wide variety of alloys, shapes, than those for die casting. Because sand In low-pressure casting (also called low- and sizes can be sand cast) and low cost of cores can be used, internal cavities can be pressure die casting or pressure permanent minimum equipment when a small number fairly complex. (When sand cores are mold casting), molten metal is injected into of castings is to be made. Among its disad- 140 / Specific Metals and Alloys

vantages are low dimensional accuracy and the process was limited to one-of-a-kind costs are higher, and size and complexity of poor surface finish; basic linear tolerances rough castings because the foam material castings that can be produced are limited. of -+30 mm/m (-+0.030 in./in.) and surface was coarse and hand fabricated and because Plaster Casting. In this method, either a finishes of 7 to 13 wm, or 250 to 500 v~in., as the packed green sand mold would not permeable (aerated) or impermeable plaster well as low strength as a result of slow allow the gases from the decomposing foam is used for the mold. The plaster in slurry cooling, are typical for aluminum sand cast- pattern to escape rapidly from the mold (the form is poured around a pattern, the pattern ings. Use of dry bonded with resins or trapped gases usually resulted in porous is removed and the plaster mold is baked water glass results in better surface finishes castings). Later, in 1964, T.R. Smith was before the casting is poured. The high insu- and dimensional accuracy, but with a cor- granted a patent (3,157,924) for the utiliza- lating value of the plaster allows castings responding decrease in cooling rate. tion of loose; unbonded sand as a casting with thin walls to be poured. Minimum wall Casting quality is determined to a large medium. With this important breakthrough, thickness of aluminum plaster castings typ- extent by foundry technique. Proper metal- the EPC became an emerging subject of ically is 1.5 mm (0.060 in.). Plaster molds handling and gating practice is necessary for investigation in automotive company re- have high reproducibility, permitting cast- obtaining sound castings. Complex castings search facilities. Use of the process has ings to be made with fine details and close with varying wall thickness will be sound only been increasing rapidly and many casting tolerances; basic linear tolerances of ---5 if proper techniques are used. A minimum facilities are now dedicated to the EPC mm/m (---0.005 in./in.) are typical for alumi- wall thickness of 4 mm (0.15 in.) normally is process. num castings. Surface finish of plaster cast- required for aluminum sand castings. The major difference between sand cast- ings also is very good; aluminum castings Typical products made from some com- ings and castings made by the EPC process attain finishes of 1.3 to 3.2 ixm (50 to 125 mon aluminum sand casting alloys include: is in subsequent machining and cleaning win.). For castings of certain complex operations. The castings in the EPC process shapes, such as some precision impellers Alloy C355.0 ...... Air-compressorfittings, are consistently poured at closer tolerances and electronic parts, mold patterns made of crankcases, gear housings with less stock for grinding and finishing. rubber are used because their flexibility Alloy A356.0 ...... Automobiletransmission cases, oil pans, and Dimensional variability associated with makes them easier to withdraw from the rear-axle housings setting, mating of cope, and drag are molds than rigid patterns. Alloy 357.0...... Pump bodies, cylinder eliminated. Mechanical properties and casting quality blocks for water-cooled The use of untreated, unbonded sand depend on alloy composition and foundry engines Alloy 443.0...... Pipe fittings, cooking makes the sand system economical and technique. Slow cooling due to the highly utensils, ornamental easy to manage. Casting cleaning is also insulating nature of plaster molds tends to fittings, marine fittings greatly reduced and (except for removal of magnify solidification-related problems, Alloy 520.0...... Aircraft fittings, truck and the wash coating) is sometimes eliminated and thus solidification must be controlled bus frame components, levers, brackets because of the absence of flash, sand, and carefully to obtain good mechanical proper- Alloy 713.0...... General-purpose casting . ties. alloy for applications that Casting yield can be considerably in- Plaster casting is sometimes used to make require strength without creased by pouring into a three-dimensional prototype parts before proceeding to make heat treatment or that involve brazing with the castings gated to a center tooling for production die casting of the . An EPC casting facility also has the part. ability to produce a variety of castings in a Cost of basic equipment for plaster cast- Other aluminum alloys commonly used for continuous and timely manner. Foundries ing is low; however, because plaster mold- sand castings include 319.0, 355.0, 356.0, with EPC can pour diverse metals with very ing is slower than sand molding, cost of 514.0, and 535.0. few changeover problems, and this adds to operation is high. Aluminum alloys com- Evaporative (lost-foam) pattern casting the versatility of the foundry. monly used for plaster casting are 295.0, (EPC) is a sand casting process that uses an Further benefits of the EPC process re- 355.0, C355.0, 356.0, and A356.0. unbonded sand mold with an expendable sult from the freedom in part design offered Investment casting of aluminum most polystyrene pattern placed inside of the by the process. Assembled patterns can be commonly employs plaster molds and ex- mold. This process is somewhat similar to used to make castings that cannot be pro- pendable patterns of or other fusible investment casting in that an expendable duced by any other high-production pro- materials. A plaster slurry is "invested" material can be used to form relatively cess. Part-development costs can be re- around patterns for several castings, and intricate patterns in a surrounding mold duced because of the ability to prototype the patterns are melted out as the plaster is material. Unlike investment casting, how- with the foam. Product and process devel- baked. ever, evaporative pattern casting (EPC) in- opment can be kept in-house. Investment casting produces precision volves a polystyrene foam pattern that va- The major concern in the EPC process is parts; aluminum castings can have walls as potizes during the pouring of molten metal shrinkage of the foam pattern. The major thin as 0.40 to 0.75 mm (0.015 to 0.030 in.), into a surrounding mold of unbonded sand. difference between traditional methods of basic linear tolerances as narrow as -+5 With investment casting, a wax or plastic foundry tooling and evaporative pattern mm/m (-+5 mils/in.) and surface finishes of pattern is encased in a ceramic mold and tooling is the continual heating and cooling 1.5 to 2.3 p.m (60 to 90 p.in.). Some internal removed by heat prior to the filling of the of the tool and the subsequent stresses and porosity usually is present, and it is rec- mold with molten metal. geometrical considerations that this condi- ommended that machining be limited to The EPC process (also known as lost tion implies. avoid exposing it. However, investment foam or evaporative foam casting) originat- Shell Mold Casting. In shell mold casting, molding is often used to produce large ed in 1958 when H.F. Shroyer was granted the molten metal is poured into a shell of quantities of intricately shaped parts re- a patent (2,830,343) for a cavityless casting resin-bonded sand only 10 to 20 mm (0.4 to quiring no further machining so internal method using a polystyrene foam pattern 0.8 in.) thick--much thinner than the mas- porosity seldom is a problem. Because of embedded in traditional green sand. A poly- sive molds commonly used in sand found- porosity and slow solidification, mechani- styrene foam pattern left in the sand mold is ties. Shell mold castings surpass ordinary cal properties are low. decomposed by the molten metal, thus re- sand castings in surface finish and dimen- Investment castings usually are small, placing the foam pattern and duplicating all sional accuracy and cool at slightly higher and thus gating techniques are limited. of the features of the pattern. Early use of rates; however, equipment and production Christmas-tree gating systems often are em- Aluminum Foundry Products/141

Table 8 Effect of squeeze casting on tensile properties into the gates, and thus castings have prop- Tensile strength Yield strength Elongation, erties that closely match those of wrought Alloy Process IVIPa ksl MPa ksi % products. Limitations on shape and size are severe, and cost of castings is very high. 356-1"6 aluminum ...... Squeeze casting 309 44.8 265 38.5 3 Permanent mold 262 38.0 186 27.0 5 Wheels, wheel hubs, and papermaking or Sand casting 172 25.0 138 20.0 2 rolls are examples of aluminum parts 535 aluminum (quenched) ...... Squeeze casting 312 45.2 152 22.1 34.2 produced by centrifugal casting. Aluminum Permanent mold 194 28.2 128 18.6 7 alloys suitable for permanent mold, sand, or 6061-T6 aluminum ...... Squeeze casting 292 42.3 268 38.8 10 262 38.0 241 35.0 10 plaster casting can be cast centrifugally. A356 T4 aluminum ...... Squeeze casting 265 38.4 179 25.9 20 . Long shapes of sim- A206 T4 aluminum ...... Squeeze casting 390 56.5 236 34.2 24 ple cross section (such as round, , CDA 377 forging ...... Squeeze casting 379 55.0 193 28.0 32.0 and hexagonal rods) can be produced by 379 55.0 145 21.0 48.0 CDA 624 aluminum ...... Squeeze casting 783 113.5 365 53.0 13.5 continuous casting, which is done in a Forging 703 102.0 345 50.0 15.0 short, bottomless, water-cooled metal CDA 925 leaded tin bronze ...... Squeeze casting 382 55.4 245 35.6 19.2 mold. The casting is continuously with- Sand casting 306 44.4 182 26.4 16.5 drawn from the bottom of the mold; be- Type 357 (annealed) ...... Squeeze casting 614 89.0 303 44.0 46 Sand casting 400 58.0 241 35.0 20 cause the mold is water cooled, cooling rate Extrusion 621 90.0 241 35.0 50 is very high. As a result of continuous Type 321 (heat treated) ...... Squeeze casting 1063 154.2 889 129.0 15 feeding, castings generally are free of poros- Forging 1077 156.2 783 113.6 7 ity. In most instances, however, the same product can be made by extrusion at ap- proximately the same cost and with better properties, and thus use of continuous cast- ing is limited. The largest application of continuous casting is production of ingot for rolling, extrusion, or forging. Composite-Mold Casting. Many of the molding methods described above can be combined to obtain greater flexibility in casting. Thus, dry sand cores often are used in green sand molds, and metal chills can be used in sand molds to accelerate local cool- ing. Semipermanent molds, which comprise metal molds and sand cores, take advantage of the better properties obtainable with met- al molds and the greater flexibility in shape of internal cavities that results from use of cores that can be extracted piecemeal. Hot isostatic pressing of aluminum cast- ings reduces porosity and can thus decrease the scatter in mechanical properties. The method also makes possible the salvaging of castings that have been scrapped for rea- sons of internal porosity, thereby achieving (al (bl improved foundry recovery. This advantage Comparison of aluminum alloy 357 (AI-7Si-0.SMg). (a) A dendritic microstructure from conventional is of more significant importance in the Fig. 8 casting. (b) A nondendritic microstructure formed during rheocasting or tbixocasting. Both 200× manufacture of castings subject to radio- graphic inspection when required levels of ployed to produce many parts per mold. baked sand, plaster, , or soundness are not achieved in the casting Investment casting is especially suited to molds and cores are used for centrifugal cast- process. The development of hot isostatic production of jewelry and parts for preci- ing of aluminum. Metal dies or molds provide pressing is pertinent to the broad range of sion instruments. Recent strong interest by rapid chilling, resulting in a level of soundness premium castings, but is especially relevant the aerospace industry in the investment and mechanical properties comparable or su- for the more diffficult-to-cast aluminum-cop- casting process has resulted in limited use perior to that of gravity-poured permanent per series. of improved technology to produce premi- mold castings. Baked sand and plaster molds Hybrid Permanent Mold Processes. Al- um quality castings. The "near-net-shape" are commonly used for centrifuge casting though die casting, centrifugal casting, and requirements of aerospace parts are often because multiple mold cavities can be ar- gravity die casting constitute, on a volume attainable using the investment casting ranged readily around a central pouring basis, the major permanent mold processes, techniques. Combining this accurate dimen- sprue. Graphite has two major advantages as there are also some hybrid processes that sional control with the high and carefully a mold material: its high heat conductivity use permanent molds. This includes controlled mechanical properties can, at provides rapid chilling of the cast metal, and squeeze casting and semisolid metal pro- times, justify casting costs and prices nor- its low specific gravity, compared to ferrous cessing. mally not considered practical. mold materials, reduces the power required Squeeze casting, also known as liquid- Aluminum alloys commonly used for in- to attain the desired speeds. metal forging, is a process by which molten vestment castings are 208.0, 295.0, 308.0, Centrifugal casting has the advantage metal solidifies under pressure within 355.0, 356.0, 443.0, 514.0, 535.0, and 712.0. over other casting processes in that, if closed dies positioned between the plates of Centrifugal Casting. Centrifuging is anoth- molds are properly designed, inclusions a hydraulic press. The applied pressure and er method of forcing metal into a mold. Steel, such as gases or oxides tend to be forced the instant contact of the molten metal with 142 / Specific Metals and Alloys

Continuous 1.05 alloy feed g ~ Magnesium "~ 1.00 ~ - Zinc I I o-O ~ "c~opper E 0.95 OH H//J ]//IO Induction Aluminum oxide E~ ~- / OOHO~O ~ao~O~ Liquid HO "//O heating JT: (.3o 0.90 Nickel ~, "6 __o 0.85 O O g= 0.80 o o o o Cooling 0.75 I Finished 0 4 8 12 16 20 casting Alloyingelement, % Effects of alloying elements on the thermal Fig. 10 expansion of aluminum. Fraction is based on a value of 1.00 for 99.996 AI. Source: L.A. Willey, / on,inuoo.", l Alcoa eoca.,er

•.:.-', :'~':'~'i" / Mold microstructural refinement and integrity of squeeze-cast products are desirable for many critical applications. ,..,,- • :~,;,: U///////////////////~ Semisolid-Metal Processing. Semisolid metalworking, also known as semisolid v//////J ...:..: Slurry in forming, is a hybrid manufacturing method it: ,:': shot chamber Slurry injected that incorporates elements of both casting ~//// into die and forging. It involves a two-step process Ingot sectioned Rheocast into "charges" ingot for the near-net shape forming of metal parts using a semisolid raw material that Semisolid-metal processing with a rheocaster. Commercial semisolid-metal processing is based on incorporates a unique nondendritic micro- Fig. 9 thixocasting. structure (Fig. 8). The basic process of semisolid-metal pro- Table 9 Tensile properties and hardness of typical semisolid forged aluminum parts cessing is shown schematically in Fig. 9. Ultimate Tensile The (and first step) to the process tensile strength yield strength Hardness, involves vigorous agitation of the melt dur- Aluminum alloy Temper MPa ksi MPa ksl Elongation, ,% HB ing earlier stages of solidification so as to 206 ...... T7 386 56.0 317 46.0 6.0 103 break up the solid dendrites into small 2017 ...... T4 386 56.0 276 40.0 8.8 89 spherulites. There are two general ap- 2219 ...... T8 352 51.0 310 45.0 5.0 89 proaches to this process: rheocasting and 6061 ...... T6 330 47.8 290 42.1 8.2 104 6262 ...... T6 365 52.9 330 47.9 10.0 82 thixocasting. Rheocasting is a term coined 7075 ...... T6 496 72.0 421 61.0 7.0 135 by the researchers at the Massachusetts 356 ...... T5 234 34.0 172 25.0 11.0 89 Institute of Technology (MIT) who initially 356 ...... T6 296 43.0 193 28.0 12.0 90 discovered the techniques of semisolid-met- 357 ...... T5 296 43.0 207 30.0 11.0 90 357 ...... T6 358 52.0 290 42.0 10.0 100 al processing during research on hot tearing undertaken at MIT in the early 1970s. Seek- ing to understand the magnitude of the Table 10 Comparison of semisolid forging and permanent mold casting for the forces involved in deforming and fragment- production of aluminum automobile wheels ing dendritic growth structures, MIT re- See Example 1, searchers constructed a high-temperature viscometer. They poured molten lead-tin I Characteristic alloys into the annular space created by two Weight Finished Production UIt/mate direct from part rate per die tensile Yield concentric cylinders and measured the forc- die or mold weight or mold, Aluminum Heat strength strength Elongation, es transmitted through the freezing alloy Process kg Ib kg Ib pieces per h alloy treatment MPa ksi MPa ksi ,% when the outer cylinder was rotated. During Semisolid forging ...... 7.5 16.5 6.1 13.5 90 357 T5 290 42 214 31 10 the course of these experiments, it was Permanent mold casting ...11.1 24.5 8.6 19.0 12 356 T6 221 32 152 22 8 discovered that when the outer cylinder was continuously rotated, the semisolid alloy ex- hibited remarkably low strength even the die surface produces a rapid heat trans- compositions. Applications of squeeze-cast at relatively high fractions solidified. This fer condition that yields a pore-free fine- aluminum alloys include pistons for en- unique property was attributed to a novel grain casting with excellent mechanical gines, disk brakes, automotive wheels, nondendritic (that is, spheroidal) micro- properties (Table 8). The squeeze casting truck hubs, barrel heads, and hubbed flang- structure. process is easily automated to produce es. Squeeze casting is simple and economi- As these ideas unfolded, research into the near-net to net-shape high-quality compo- cal, efficient in its use of raw material, and nature of semisolid alloys progressed, and it nents. has excellent potential for automated oper- became apparent that bars could be cast Squeeze casting has been successfully ation at high rates of production. The pro- from semisolid fluids possessing the rheo- applied to a variety of ferrous and nonfer- cess generates the highest mechanical prop- cast nondendritic microstructure. The final rous alloys in traditionally cast and wrought erties attainable in a cast product. The freezing of these bars captures this micro- Aluminum Foundry Products / 143

Table 11 Typical (and minimum) tensile properties of aluminum casting alloys 0.2% offset 0.2% offset Ultimate tensile yield Elongation(a) Ultimate tensile yield Elongation(a) strength(a) strength(a) in 50 mm strength(a) strength(a) in 50 mm Alloy Temper MPa ksi MPa ksi (2 in.), % Alloy Temper MPa ksi MPa ksi (2 in.), %

Rotor alloys (pure aluminum) Sand casting alloys (continued) 100.1 ingot ...... • • • 70 10 40 6 20 T6 278 40 278 40 <1.0 150.1 ingot ...... • - - 70 10 40 6 20 T7 250 36 250 36

Table 11 (continued) 0.2% offset 0.2% offset yield Elongation(a) yield Elongation(a) Ultimate tensile strength(a) strength(a) in 50 mm Ultimate tensile strength(a) strength(a) in 50 mm Alloy Temper MPa ksi MPa ksi (2 in.), % Alloy Temper MPa ksi MPa ksi (2 in.), %

Permanent mold casting alloys (continued) Permanent mold casting alloys (continued) (214) (31) (. • .) (. - .) (1.5) 443.0 ...... F 160 23 62 9 10.0 324.0 ...... F 207 30 110 16 4.0 B443.0 ...... F 160 23 62 9 10 '1"5 248 36 179 26 3.0 444.0 ...... T4 193 28 83 12 25 "I"62 310 45 269 39 3.0 A444.0 ...... F 165 24 76 11 13.0 332.0 ...... T5 248 36 193 28 1.0 "1"4 160 23 70 10 21 333.0 ...... F 234 34 131 19 2.0 513.0 ...... F 186 27 110 16 7.0 T5 234 34 172 25 1.0 050) (22) (..-) (--.) (2.5) T6 290 42 207 30 1.5 705.0 ...... T5 240 35 103 15 22 T7 255 37 193 28 2.0 707.0 ...... T5 (290, min) (42, rain) (4, rain) (215) (31) (. • -) (- - .) (- • -) 711.0 ...... F 248 36 130 19 8 336.0 ...... T551 248 36 193 28 0.5 713.0 ...... T5 275 40 185 27 6 T65 324 47 296 43 0.5 850.0 ...... T5 160 23 76 11 12.0 354.0 ...... T6 380 55 283 41 6 (124) (18) (''') (''') (8) T62 393 57 317 46 3 Tl01 160 23 76 l 1 12 355.0 ...... T51 (185, min) (27, min) ...... 851.0 ...... T5 138 20 76 I 1 5.0 T6 290 42 185 27 4 852.0 ...... T5 221 32 159 23 5.0 (255) (37) (- • -) (- - .) (!.5) (185) (27) (..-) (-..) (3) T62 310 45 275 40 1.5 (290) (42) (. - .) (. • .) (. • .) T71 (235, min) (34, min) ...... Die casting alloys 356.0 ...... F 179 26 124 18 5.0 360.0 ...... F 324 47 172 25 3.0 T51 186 27 138 20 2.0 A360.0 ...... F 317 46 165 24 5.0 T6 262 38 186 27 5.0 364.0 ...... F 296 43 159 23 7.5 (207) (30) (138) (20) (3) 380.0 ...... F 330 48 165 24 3.0 T7 221 32 165 24 6.0 A380.0 ...... F 324 47 160 23 4.0 A356.0 ...... T61 283 41 207 30 10.0 383.0 ...... F 310 45 150 22 3.5 (255) (37) (" • -) (" - ') (5) 384.0 ...... F 325 47 172 25 1.0 357.0 ...... F 193 28 103 15 6.0 A384.0 ...... F 330 48 165 24 2.5 T51 200 29 145 21 4.0 390.0 ...... F 279 40.5 241 35 1.0 T6 360 52 295 43 5.0 T5 296 43 265 38.5 1.0 (310) (45) (- • -) (- - ") (3) A390.0 ...... F 283 41 240 35 1.0 A357.0 ...... T61 359 52 290 42 5.0 B390.0 ...... F 317 46 248 36 - • - 358.0 ...... T6 345 50 290 42 6 392.0 ...... F 290 42 262 38 <0.5 T62 365 53 317 46 3.5 413.0 ...... F 296 43 145 21 2.5 359.0 ...... T61 325 47 255 37 7 A413.0 ...... F 241 35 110 16 3.5 T62 345 50 290 42 5 443.0 ...... F 228 33 110 16 9.0 A390.0 ...... F 200 29 200 29 < 1.0 C443.0 ...... F 228 33 95 14 9 T5 200 29 200 29 < 1.0 513.0 ...... F 276 40 152 22 10.0 T6 310 45 310 45 <1.0 515.0 ...... F 283 41 ...... 10.0 T7 262 38 262 38 < 1.0 518.0 ...... F 310 45 186 27 8.0 (a) Minimumvalues are shown in parenthesis and are listed below their typical values.

structure. The bars then represented a raw To date, none has shown economic viabil- die castings and stampings. Applications material that could be heated at a later time ity. include automobile wheels, master brake or a remote location to the semisolid tem- There have been several attempts in the cylinders, antilock brake valves, disk brake perature range to reclaim the special theo- United States and abroad to commercialize , power steering pump housings, logical characteristics. This process, using rheocasting, but none of these ventures is power steering pinion valve housings, en- semisolid alloys heated from specially cast known to have been commercially success- gine pistons, compressor housings, steering bars, was termed thixocasting (Ref 3). This ful (Ref 4, 8). On the other hand, semisolid column mechanical components, airbag distinguished it from rheocasting, which has forging, which exploits the manufacturing containment housings, power brake propor- come to be known as the process used for advantages of thixotropic semisolid alloy tioning valves, electrical connectors, and producing semisolid structures and/or form- bars, began commercial production in 1981 various covers and housings that require ing parts from slurry without an intermedi- and is now a rapidly expanding commercial leak-tight integrity. Table 9 lists mechanical ate freezing step. process. The production of raw material has properties of selected aluminum alloys used A number of alternative approaches to been brought to full commercial realization, in these components. the production of the semisolid raw mate- and the use of semisolid forged parts is There are several potential advantages of rial have been developed. Although sever- broadening in the aerospace, automotive, semisolid alloys. First, and particularly sig- al of these techniques build upon the me- military, and industrial sectors. nificant for higher-melting alloys, semisolid chanical agitation approach (Ref 4, 5), The advantages of semisolid forging have metalworking afforded lower operating tem- others utilize a passive stirring technique enabled it to compete effectively with a peratures and reduced metal heat content for stimulating turbulent flow through variety of conventional processes in a num- (reduced enthalpy of fusion). Second, the cooling channels (Ref 6, 7). At least one ber of different applications. Semisolid viscous flow behavior could provide for a approach uses isothermal holding to in- forged parts have replaced conventional more laminar cavity fill than could generally duce particle coarsening. Most of these , permanent mold and investment be achieved with liquid alloys. This could alternatives appear to be confined to the castings, impact , machined ex- lead to reduced gas entrainment. Third, laboratory, although one or two have been trusion profiles, parts produced on solidification shrinkage would be reduced in demonstrated at a pilot production level. machines, and in unusual circumstances, direct proportion to the fraction solidified Aluminum Foundry Products / 145

088 ~1~ Germanium,I zinc, silver, iron, manganese,copper faces and details that reflect the die surfac- / es. Therefore, the designer has a selection Silicon of surface conditions to enhance the style O O / n and can obtain exact replication of the fine o o 0 detail designed in the die.

Properties of Aluminum Casting Alloys Although the physical and mechanical properties of aluminum casting alloys are well documented, the data given in this Z section should only be used for alloy com- parison and not for design purposes. Prop- 0.64 erties for design must be obtained from '••" pertinent specifications or design standards ~/~----~----~,~ .... ~ Calcium or by negotiation with the producer. Addi- Magnesium ~~.~ tional information on properties is also 0.56 available in the "Selected References" list- ed at the end of this article and in the next Antimony article "Properties of Cast Aluminum Al- Lithium loys" in this Volume. O Lead 0.48 Physical Properties Table 2 gives typical values for some of ~ ",O-,~ the important physical properties of various aluminum casting alloys, which are grouped 0.40 into the nine alloy categories mentioned 0 2 4 6 8 10 12 earlier in the section "Selection of Casting Alloying element, % Alloys." The effects of alloying elements on electrical conductivity and thermal expan- Fig. 11 Effect of various elements on surface tension of 99.99% AI in argon at 700 to 740 °C (1290 to 1365 °F) sion is shown in Table 4 and Fig. 10, respec- tively. Other important physical properties related to castability are fluidity and shrink- within the semisolid metalworking alloy, (magnetohydrodynamic casting) billet with age. which should reduce both shrinkage poros- an engineered metallurgical structure, Factors Affecting Fluidity. Fluidity de- ity and the tendency toward hot tearing. In closely controlled chemistry, and consistent pends on two major factors: the intrinsic addition, the viscous nature of semisolid casting variables, supplying an extremely fluid properties of the molten metal, and alloys provides a natural environment for consistent raw material with complete casting conditions. The properties usually the incorporation of third-phase particles in traceability. The wheel-forming process is thought to influence fluidity are viscosity, the preparation of particulate-reinforced computer controlled and automated with surface tension, the character of the surface metal-matrix composites. The semisolid precise control of the heating and forging oxide film, inclusion content, and manner in state also allows greater use of process variables, making the entire pro- which the particular alloy solidifies. in material handling. cess adaptable to statistical process control. Casting conditions that influence fluidity Example 1 : Comparison of Semisolid Forg- Structure and Properties. The semisolid include part configuration; physical mea- ing and Permanent Mold Casting in the forged wheel is fine grained, dense struc- sures of the fluid dynamics of the system Production of Aluminum Automobile tured, and formed to close tolerances in such as liquidstatic pressure drops, casting Wheels. Aluminum automobile wheels have precision tooling in which the temperature head, and velocities; mold material; mold been produced by permanent mold casting is controlled to provide consistent forging surface characteristics; heat ; rate of (gravity and low pressure), squeeze casting, conditions. This provides consistency in pouring; and degree of superheat. and fabrications of castings or stampings part dimensions and metallurgical proper- Viscosity. The measured viscosities of welded to rolled rims. Semisolid forging is a ties. Forging in the semisolid state avoids molten aluminum alloys are quite low and more recent process. Table 10 compares the the entrapment of air or mold gas, and the fall within a relatively narrow range. Kine- characteristics of aluminum automobile high fraction of solid material, together with matic viscosity (viscosity/specific gravity) wheels produced by semisolid forging and the high pressure after forming, reduces the is less than that of water. It is evident on permanent mold casting. In addition to an microporosity due to liquid/solid shrinkage. this basis that viscosity is not strongly in- economic advantage, semisolid forging of- Unlike conventional forgings, the wheel fluential in determining casting behavior fers other advantages that are discussed properties are isotropic, reflecting the non- and therefore is an unlikely source of vari- below. dendritic structure of the high-performance ability in casting results. Lighter Weight. The ability to form thin- aluminum alloy 357 used in the billet. Surface Tension and Oxide Film. A high ner sections without heavy ribs to aid in Design Versatility. The ability to form surface tension has the effect of increasing filling the cavity allows a wheel to be semi- thin sections (roughly one-quarter to one- the pressure required for liquid metal flow. solid formed nearer to net size with light half the thickness of casting) permits not A number of elements influence surface ribs on the brake side. This results in a only a reduction in the weight of the wheel, tension, primarily through their effects on finished wheel that is up to 30% lighter than but also allows the designer to style the the surface tension of the oxide. Figure 11 a cast wheel of the same style. wheel with thinner ribs/spokes and finer illustrates the effect of selected elements on Consistent Quality. The forging process detail. Forming in the semisolid state under surface tension. In aluminum alloys, the employs a high-quality, specially prepared very high final pressure provides part sur- true effect of surface tension is overpow- 146 / Specific Metals and Alloys

Table 12 Typical values of hardness, shear strength, fatigue strength, and compressive yield strength of various aluminum casting alloys Compressive Compressive Shear Fatigue(a) Hardness, yield strength Shear Fatigue(a) Hardness, yield strength Alloy Temper MPa ksi MPa ksi HB(b) MPa ksi Alloy Temper MPa ksi MPa ksi HB(b) MPa ksi

Sand eastlngs Permanent moid (continued)

204.0 ..... T4 110 16 77 11 90 296.0 .... T4 206.0 ..... T4 ...... 95 296.0 .... T6 220 32 70 10 90 179 26 A206.0 .... T4 255 37 100 296.0 .... T62 A206.0 .... T71 ...... 110 296.0 .... T7 206.0 ..... T6 ...... 100 213.0 .... F 85 ...... 208.0 ..... F 117 17 76 I l 55 103 15 308.0 .... F 152 22 89 13 70 117 17 295.0 ..... T4 179 26 48 7 6O 319.0 .... F 186 27 83 12 85 138 20 T6 207 30 50 7.5 75 172 25 T6 220 32 83 12 95 193 28 T62 227 33 55 8 9O 333.0 ..... F 186 27 96 14 90 131 19 T7 ...... • "" T5 186 27 83 12 100 172 25 208.0 ..... F 117 17 76 l 1 55 103 15 T6 228 33 103 15 105 207 30 T55 ...... • • • T7 193 28 83 12 90 193 28 319.0 ..... F 152 22 70 10 7O 131 19 354.0 ..... T6 262 38 117 17 100 289 42 T5 165 24 76 11 8O • "" T62 276 40 117 17 110 324 47 T6 200 29 76 I l 80 172 25 355.0 ... T51 90 • • • • • • 355.0 ..... F ...... 7O • '" T6 234 34 70 10 90 186 27 T51 152 22 55 8 65 165 24 T62 248 36 70 10 105 276 40 T6 193 28 62 9 8O 179 26 TTI T61 248 36 70 10 100 255 37 356.0 ... F T7 193 28 70 10 85 248 36 T51 T71 241 35 70 l0 75 248 36 T6 207 30 90 13 80 186 27 T77 179 26 70 l0 80 200 29 T7 172 25 76 11 70 165 24 C355.0 .... T6 193 28 70 l0 9O • "" A356.0 .... T61 193 28 90 13 90 220 32 356.0 ..... F ...... -'- 357.0 ..... T6 241 35 90 13 100 303 44 T51 138 20 55 8 6O 145 21 A357.0 .... T61 241 35 103 15 100 296 43 T6 179 26 59 8.5 7O 172 25 358.0 ..... T6 296 43 ...... 105 289 42 T7 165 24 62 9 75 214 31 T62 317 46 ...... • .. 317 46 T71 138 20 59 8.5 6O • '' 359.0 ..... T61 220 32 103 15 90 262 38 357.0 ..... F ...... • - • T62 234 34 103 15 100 303 44 T51 ...... • • • A390.0 .... F, T5 110 ...... T6 164 24 62 9 9O 214 31 T6 ...... 117 17 145 413 60

T7 ...... 6O " • • T7 ...... 103 15 120 352 51 A357.0 .... T6 ...... 85 -'' 393.0 .... F A390.0 .... F, Fs ...... 70 10 100 • .- B443.0... F 110 16 55 8 45 62 9 T6 ...... 90 13 140 ... 444.0 .... T4 50 77 11 T7 ...... 115 • "- 513 ...... F 152 22 70 10 50 96 14 443.0 ..... F 96 14 55 8 4O 62 9 705.0 .... T5 152 22 ..... 55 124 18 511.0 ..... F 117 17 55 8 5O 9O 13 707.0 .... T5 512.0 ..... F ...... 5O 96 14 707.0 .... T 514.0 ..... F 138 20 48 7 5O 83 12 711.0 ..... F 193 28 76 11 70 138 20 75 172 25 535.0 ..... F 193 28 70 10 7O 165 24 713.0 ..... T5 179 26 62 9 ... 850.0 ..... T5 103 15 62 9 45 76 11 B535.0 .... F 207 30 62 9 65 96 14 62 9 45 76 11 520.0 ..... T4 234 34 55 8 75 186 27 851.0 ..... T5 852.0 ..... T5 145 21 76 11 70 158 23 705.0 ..... F, T5 ...... 850.0 ..... TI01 103 15 62 9 45 145 21 707.0 ..... F, T5 ......

F, T7 ...... • • • Die casting alloys 710.0 ..... F, T5 179 26 55 8 75 172 25 360.0 ..... F 207 30 131 19 "" 712.0 ..... F, T5 179 26 62 9 75 518 75 A36O.0 .... F 200 29 124 18 "" 713.0 ..... F, T5 179 26 63 9 74 364.0 ..... F 200 29 124 18 '' 771.0 ..... F ...... 380.0 ..... F 214 31 145 21 "" T2 ...... A380.0 .... F 207 30 138 20 "" T5 ...... 383.0 ..... F T6 ...... A384.0 .... F 200 29 138 20 '" 772.0 ..... F ...... • - 390.0 ..... F ...... 76 11 "" T6 ...... • - 392.0 ..... F 850.0 ..... T5 96 14 55 8 45 76 11 A39O.0 .... F 851.0 ..... T5 96 14 45 ... B39O.0 .... F ... 392.0 ..... F 852.0 ..... T5 124 18 70 10 65 A413.0 .... F 172 25 130 19 '" Permanent mold A413.0 .... F 159 23 130 19 "" C443.0 .... F 130 19 110 16 "" 90 204.0 ..... T4 ...... 513.0 ..... F 179 26 124 18 '" 206.0 ..... T4 ...... ''' 515.0 ..... F 186 27 130 19 "" 206.0 ..... T6 255 37 110 "'" 518.0 ..... F 200 29 138 20 " A206.0 .... T71 255 37 207 30 I10 (a) Strength for 5 x l0s cycles with R.R. Moore rotating beam test. (b) 10 mm (6.4 in.) ball with 500 kgf (1100 lbf) load

ered by the influence of surface oxide film Solidification. It has been shown that Shrinkage. For most metals, the transfor- characteristics. The oxide film on pure alu- fluidity is inversely proportional to freez- mation from the liquid to the solid state is minum, for example, triples apparent sur- ing range (that is, fluidity is highest for accompanied by a decrease in volume. In face tension• pure metals and eutectics, and lowest for aluminum alloys, volumetric solidification Inclusions in the form of suspended insol- solid-solution alloys). The manner in shrinkage can range from 3.5 to 8.5%. The uble nonmetallic particles dramatically re- which solidification occurs may also influ- tendency for formation of shrinkage poros- duce the fluidity of molten aluminum. ence fluidity. ity is related to both the liquid/solid volume Aluminum Foundry Products / 147

Table 13 Typical mechanical properties of premium-quality aluminum alloy castings and elevated-temperature aluminum casting alloys Ultimate Tensile Elongation in Compressive Hardness, tensile strength yield strength 50 mm yield strength Shear strength Fatigue strength(b) Alloy and temper HB(a) MPa ksi MPa ksi (2 in.), % MPa ksi MPa ksl MPa hsi

Premium-quality castings(c)

A201.0-T7 ...... • • 495 72 448 65 6 97 14 A206.0-T7 ...... '• 445 65 405 59 6 90 13 224•0-T7 ...... • - 420 61 330 48 4 86 12.5 249.0-T7 ...... • - 470 68 407 59 6 75 11 354.0-T6 ...... • • 380 55 283 41 6 135(d) 19.5(d) C355.0-T6 ...... '• 317 46 235 34 6 97 14 A356.0-T6 ...... • " 283 41 207 30 10 90 13 A357.0-T6 ...... • ' 360 52 290 42 8 90 13 Piston and elevated-temperature sand cast alloys 222.0-T2 ...... 80 185 27 138 20 1 ...... 222.0-T6 ...... 115 283 41 275 40 <0.5 ...... 242.0-T21 ...... 70 185 27 125 18 1 ...... 145 21 55 8 242.0-T571 ...... 85 220 32 207 30 0.5 ...... 180 26 75 I1 242.0-T77 ...... 75 207 30 160 23 2 165 24 165 24 72 10.5 A242.0-T75 ...... 215 31 ...... 243.0 ...... 95 207 30 160 23 2 200 29 70 10 70 10 328.0-F ...... --- 220 32 130 19 2.5 ...... 328.0-T6 ...... 85 290 42 185 27 4.0 180 26 193 28 ... Piston and elevated-temperature alloys (permanent mold castings) 222.0-T55 ...... 115 255 37 240 35 ... 295 43 207 30 59 8.5 222.0-T65 ...... 242.0-T571 ...... 105 275 40 235 34 1 ...... 207 30 72 10.5 242.0-T61 ...... 110 325 47 290 42 0.5 ...... 240 35 65 9.5 332•0-T551 ...... 105 248 36 193 28 0.5 193 28 193 28 90 13 332.0-T5 ...... 105 248 36 193 28 1 200 29 193 28 90 13 336.0-T65 ...... 125 325 47 295 43 0.5 193 28 248 36 .. 336.0-T551 ...... 105 248 36 193 28 0.5 193 28 193 28 .. (a) 10 mm (0.4 in.) b~l with 500 kgf (1100 lbf) load. (b) Rotating beam test at 5 × 10s cycles. (c) Typical values of premium-quality casting are the same regardless of class or the area from which the specimen is cut; see Table 14 for minimum values. (d) Fatigue strength for 106 cycles

fraction and the solidification temperature suits• By references to general process erties, whether of separately cast test bars range of the alloy• Riser requirements rela- specifications, these documents also invoke or of full-size castings, are dependent on tive to the casting weight can be expected to standards and limits for many additional two main factors: increase with increasing solidification tem- supplier obligations, such as specific prac- • Alloy composition and heat treatment perature range. Requirements for the estab- tices and controls in melt preparation, heat • Solidification pattern and casting sound- lishment of more severe thermal gradients, treatment, radiographic and liquid pene- ness such as by the use of chills or antichills, also trant inspection, and test procedures and increase. interpretation. Tables 11 and 14 include Some specifications for sand, permanent minimum tensile properties of various cast- mold, plaster, and investment castings have Mechanical Properties ing alloys, defined the correlation between test results Typical mechanical properties of various Mechanical Test Methods. Typical and from specimens cut from the casting and aluminum casting alloys are given in Tables minimum mechanical-property values com- separately cast specimens. A frequent error l l, 12, and 13. These typical values should monly reported for castings of particular is the assumption that test values deter- be used only for assessing the suitability of aluminum alloys are determined using sep- mined from these sources should agree. an alloy for a particular application, and not arately cast test bars that are 1/2 in. diameter Rather, the properties of separately cast for design purposes. Design-stress values (for sand and permanent mold castings) or specimens should be expected to be superi- are significantly below typical properties as 1/4 in. diameter (for die castings). As such, or to those of specimens machined from the discussed in the section on "Mechanical these values represent properties of sound casting. In the absence of more specific Test Methods" later in this article. Actual castings, 13 or 6 mm (1/2 or 1/4 in.) in section guidelines, one rule of thumb defines the design strength depends on several factors, thickness, made using normal casting prac- average tensile and yield strengths of ma- including: tice; they do not represent properties in all chined specimens as not less than 75% of sections and locations of full-size produc- the minimum requirements for separately • Section size tion castings. Typical and minimum proper- cast specimens, and elongation as not less • Expected degree of porosity ties of test bars, however, are useful in than 25% of the minimum requirement. • Presence of sharp corners determining relative strengths of the various These relations may be useful in establish- • Probability of cyclic loading in service alloy/temper combinations. Minimum ing the commercial acceptability of parts in Minimum mechanical property limits are properties--those values listed in applicable dispute. usually defined by the terms of general specifications--apply, except where other- Test Specimens. Accurate determination procurement specifications, such as those wise noted, only to separate cast test bars. of mechanical properties of aluminum alloy developed by government agencies and These values, unlike minimum values based castings (or of castings of any other metal) technical societies. These documents often on bars cut from production castings, are requires proper selection of test specimens. specify testing frequency, tensile bar type not usable as design limits for production For most wrought products, a small piece of and design, lot definitions, testing proce- castings. However, they can be useful in the material often is considered typical of dures, and the limits applicable to test re- quality assurance. Actual mechanical prop- the rest, and mechanical properties deter- 148 / Specific Metals and Alloys

Table 14 Minimum tensile properties of premium-quality aluminum alloy castings In hypoeutectic A1-Si alloys, the coarse These mechanical property values are attainable in favorable casting configurations and must be negotiated silicon eutectic has been refined and dis- with the foundry for the particular configuration desired. persed by modification. The modified Ultimate tensile 0.2% offset yield structure increases both ductility and me- strength (mitt), strength (min) Elongation in 50 mm chanical strength. Modification is accom- Alloy Class MPa ksi MPa ksi (2 in.), % plished by addition of small amounts (0.02%) of sodium or strontium. Making Specimens cut fromde~gnatedcasfing areas those additions often introduces gas into A201.0-T7(a)...... Class 1 414 60 345 50 5 the melt. Their use, therefore, must be Class 2 414 60 345 50 3 224.0-T7 ...... Class 1 345 50 255 37 3 weighed against applicable radiographic Class 2 379 55 255 37 5 specifications. In the hypereutectic alumi- 249.0-T7 ...... Class 1 345 50 276 40 2 num-silicon alloys (silicon greater than Class 2 379 55 310 45 3 11.7%), refinement of primary silicon in Class 3 414 60 345 50 5 354.0-T6(a) ...... Class 1 324 47 248 36 3 sand and permanent mold castings is ac- Class 2 345 50 290 42 2 complished by adding 0.05% P. (Phospho- C355.0-T6(a) ...... Class 1 283 41 214 31 3 rus modification is required in only those Class 2 303 44 228 33 3 die castings that have thick walls.) In these Class 3 345 50 276 40 2 A356.0-T6(a) ...... Class 1 262 38 193 28 5 alloys, the phosphorus addition provides Class 2 276 40 207 30 3 moderate improvements in strength and Class 3 310 45 234 34 3 machinability. A357.0-T6(a)...... Class 1 310 45 241 35 3 Where heat treatment is required, choice Class 2 345 50 276 40 5 224.0 ...... Class 1 345 50 255 37 3 of temper affects properties. Class 2 379 55 255 37 5 variables such as solution time and temper- Specimens cutfromany area ature, temperature of quenching medium, and quench delay also can alter properties. A201.0-T7(a)...... Class 10 386 56 331 48 3 Class 11 379 55 331 48 1.5 Casting variables also contribute to me- 224.0-T7 ...... Class 10 310 45 241 35 2 chanical-property variations. The differ- Class ll 345 50 255 37 3 ences between typical test-bar properties 249.0-T7 ...... Class l0 379 55 310 45 3 and mechanical properties of full-size cast- Class 11 345 50 276 40 2 354.0-T6(a) ...... Class 10 324 47 248 36 3 ings result from differences in soundness Class I l 296 43 228 33 2 and solidification characteristics. Casting 355.0-T6(a) ...... Class l0 283 41 214 31 3 soundness depends on the amount of poros- Class II 255 37 207 30 1 ity or other imperfections present in the Class 12 241 35 193 28 l A356.0-T6(a)...... Class l0 262 38 193 28 5 casting. The presence of dross, shrinkage Class 11 228 33 186 27 3 porosity, and gas porosity will all decrease Class 12 221 32 152 22 2 properties. Dross inclusions and gas poros- A357.0-T6(a)...... Class l0 262 38 193 28 5 ity are minimized by proper melting and Class II 283 41 214 31 3 224.0 ...... Class l0 310 45 241 35 2 pouring techniques. Class 11 345 50 255 37 3 Properties of production castings vary (a) Values from specification MIL-A-21180 depending on two aspects of the solidifica- tion characteristics in each section of the casting--solidification rate and location and form of shrinkage. Shrinkage results when mined from that small piece also are consid- be designed carefully to ensure that test supply of molten metal is not adequate ered typical. Properties of castings, howev- bars and castings have equivalent micro- throughout solidification. Shrinkage may be er, vary substantially from one area of a structure and integrity. Also, if there are apparent as sponge shrinkage, centerline given casting to another, and may vary from substantial differences between test-bar di- shrinkage, shrinkage porosity, or a large casting to casting in a given heat. ameter and wall thickness in critical areas of shrinkage cavity. Shrinkage, however, can If castings are small, one from each batch the casting, use of integrally cast test panels be controlled by proper use of directional can be sacrificed and cut into test bars. If equal in thickness to those critical areas, solidification. castings are too large to be economically instead of standard test bars, should be Directional solidification in a casting sec- sacrificed, test bars can be molded as an considered. tion is accomplished by starting solidifica- integral part of each casting, or can be cast ASTM E8 defines the test bars suitable tion at a selected point and allowing it to in a separate mold. for evaluation of aluminum castings. The progress toward a riser. If solidification also Usually, test bars are cast in a separate use of test bars cut from die castings is not starts at a second point (such as a thinner mold. When this is done, care must be taken recommended; simulated service (proof) region), then shrinkage between these two to ensure that the metal poured into the testing is considered more appropriate. points results, as illustrated in Fig. 12. In test-bar mold is representative of the metal Chemical Composition and Heat Treat- designing a gating system for a casting, each in the castings that the test bars are sup- ment. Mechanical properties of castings de- section is examined in an attempt to estab- posed to represent. In addition, differences pend not only on choice of alloy but also lish directional solidification by proper use in pouring temperature and cooling rate, depend somewhat on other considerations of chills, risers, and insulating materials. which can make the properties of separately linked with the alloy. Variations in chemical Casting design also is very important in cast test bars different from those of pro- composition, even within specified limits, can ensuring that the necessary thermal gradi- duction castings, must be avoided. have measurable effects. Metallurgical con- ents are established. For highly stressed castings, integrally siderations such as coring, phase segregation, When the solidification characteristics of cast test bars are preferable to separately and modification also can alter properties. the entire casting are examined, solidifica- cast bars. When integrally cast bars are Modification is commonly used for those alu- tion may be faster in some areas of the selected, however, gating and risering must minum alloys with 5% or more silicon. casting than in others; for example, the rate Aluminum Foundry Products / 149

Riser Riser more sound castings; design is very impor- tant in ensuring the proper solidification pattern. Because of high solidification rates, the properties of die and permanent mold castings are relatively insensitive to casting variables. Due to relatively long solidification times, properties of sand and plaster castings are very sensitive to variations in casting tech- Shrinkage nique; chills, risers, and gates significantly affect properties. Plaster molds, with their insulating properties, keep solidification Chill rate low and consequently produce castings with relatively low properties. (a) (b) The fatigue strength of castings is normal- Fig. 12 Effect of gating system on formation of shrinkage cavities. Solidification starts at the chill and ly lower than that of wrought materials progresses toward the riser. In (a), molten metal can easily feed from the riser into the entire length when the specimens are smooth. However, of the casting. In (b), the narrow portion of the casting can freeze shut before solidification of the left portion of the casting is completed, and thus the riser can no longer feed that portion and a shrinkage cavity develops. because castings are less notch sensitive than wrought products, castings may be beneficial in applications with multidirec- will be faster at a chilled area than at a riser thus is subject to high chill rates. This tional loading and/or notch susceptibility. area. The solidification rate of a casting results in rapid solidification and a fine Table 12 gives typical fatigue-strength limits section can be determined using a metallo- metallographic structure at the surface. The of various casting alloys. graphic technique that measures dendrite- fast chill rate and rapid rejection, however, Premium (high-strength, high-toughness) arm spacing. High solidification rates pro- usually result in centerline shrinkage. It has castings combine a number of conventional duce relatively small dendrite-arm spacing. generally been impractical to achieve direc- casting procedures in a selective manner to As explained in the section "Structure tional solidification in die castings to over- provide premium strength, soundness, di- Control" in this article, casting processes come this centerline shrinkage. In perma- mensional tolerances, surface finish, or a all are characterized by solidification mode. nent mold casting chill rate also is high, but combination of these characteristics. As a In die casting, metal is rapidly injected and slower pouring allows longer feed times and result, premium engineered castings typi- cally have somewhat higher fatigue resis- Yield strength, ksi Yield strength, ksi tance than conventional castings. Table 13 gives fatigue limits on various premium 0 10 20 30 40 50 60 70 80 O 10 20 30 40 50 60 70 80 zo :::::::::::::::::::::::::: castings. Figure 13 compares premium cast- I ings and wrought plate in terms of notch- yield ratio and propagation energy values. The production of premium-quality cast- ings is an example of understanding and using the solidification process to good ad- 1 • 6 vantage. In production of premium-quality castings, composite molds combining sever- Band f ~ al mold materials are used to take advantage of the special properties of each casting iiiii iiii i!ii!i il process. High mechanical properties in des- :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ignated areas are obtained by use of special 0 1.2 ~i Band for : ~ :*:*:::*:*:~::~: chills. Plaster sections and risers may be used to extend the feeding range of the aluminum 1 casting. alloy plate Premium-quality castings are made to the Z "r°uh ii;;iii tight radiographic and mechanical specifica- 0.8 tions required for aerospace and other crit- ical applications. Basic linear tolerances of 6 iiiiiiiiii iii ±15 mm/m (± 15 mils/in.) are possible with aluminum alloy castings, depending on mold material, equipment, and available 0.4 fixtures, and minimum wall thickness of 3.8 8 N mm (0.150 in.) is typical. Aluminum alloys commonly poured as premium-quality cast- ings include C355.0, A356.0, and A357. 7 Table 14 gives mechanical property limits O normally applied to premium engineered O 50 100150200250300350400450500550 0 50 100150200250300350400450500550 castings. It must be emphasized that the Yield strength, MPa Yield strength, MPa negotiation of limits for specific parts is usual practice, with higher as well as lower (a) (b) specific limits based on part design needs Fig. 13 Comparison of (a) notch yield ratio and (b) unit propagation energy versus yield strength for various and foundry capabilities. Properties of the aluminum alloy premium-quality castings and wrought aluminum alloy plate. I, XA201.0-T7; 2, premium casting alloys at elevated temper- 249.0-T7; 3, 224.0-T7; 4, C355.0-T6; 5, 354.0-T6; 6, A356.0-T6; 7, 356.0-T6; 8, A357.0-T6 atures are shown in Fig. 14, 15, and 16. 150 / Specific Metals and Alloys

Temperature, °F Temperature exposure (104h), °F 100-h temperature exposure, °F 100 200 300 400 500 100 200 300 400 500 300 400 500 600 550 I I 80 550 I I I 80 345 2, ~1 ' 50 a_ 1, XA201.0-T7 280 '-'~,~.xx'~x 2, 249.0-T7 40 500 1, XA201.0-T7 -- 500 1, XA201.0-T7 -- - 70 3,224.0-T7 -~ 1 2,249.0-T7 2, 249.0-T7 70 • 3,224.0-T7 ~_ 210 "'..."•,, %,~ 0355.0-T6 30 ~- ~. 450 ~. 450 1 . 3, 224.0-T7 ~ 4, 0355.0-T6 4, C355.0-T6 140 4 "'.." .-,.~ 20 - 60 2., ~ 60 400 .E 400 d= ,,, - ..... --3 - \ \ 70 - 10 & 350 \ 09 03 - 50 ~ 35O \ 50 0 E 150 205 260 315 300 "~ 300 100-h temperature exposure, °C - 40 .E "'".. 40 o) 250 -~ 250 100-h stress rupture of premium-quality alu- \ . "5" 1 6 minum alloy castings for elevated-tempera- 200 - 30 4" \f ~- 200 • ,, ture service o) 150 E 20 Eo 150 . k 20 rr8 and 8xx.O series), the cutting tools are often ~. lOO nq° 100 ground or fitted with chip breakers• The 10 "- ...... 10 50 main problem in machining aluminum is the 50 tendency to form long continuous chips. 0 0 0 0 Coarse grain and large silicon constituent 550 I 80 size in a casting can detract from the ma- 550 I I 80 1 chinability because they accelerate tool 500 1 ~ - 70 t~ 500 wear. In the same manner alloys containing o. LN~ 70 450 high contents ofFe, Mn, Cr, B, or Ti tend to "~. 450 form very hard second phases and may also --\ -6o ~ 3 ...... ~, , - 60 400 400 cause excessive tool wear. ~".. ~ Alloys that contain small amounts of the 350 50 ~ -~ 3so o..° --..% 5O a~ low-melting-point metals like Sn, Pb, and Bi 300 4" k--_ o may exhibit free-machining characteristics. .t= •• \ x - 40 40 E Weldability. The weldability ratings given " E 250 •; ,, x . ,~ ~ 250 % in Table 2 are based on the ability to be fusion "~ " -30 =m m welded with of the same alloy• = 200 ~ 30 ; " ~: ~ 200 This relates to the salvage problem of surface 150 ', ; ~ and dimensional defects and surface irregu- - 20 ~ E 150 % o) 20 larities. The inert gas-shielded E processes are normally used in preference to otO0 o """.. 10 o salt fluxes or flux-coated filler rods. The 50 rr 10 ...... 50 welding techniques used on castings are sim- ilar to those used on wrought products. How- 0 0 0 0 0 50 I00 150 200 250 300 0 50 100 150 200 250 300 ever, special consideration must be made for Temperature, °C Temperature exposure (104h), °C the thicker as-cast surface aluminum oxide film and the gas porosity content of the cast- Elevated-temperature tensile strengths of I:|,r, 14 Room-temperature tensile strengths of var- ings. During welding this gas expands and "'~" various premium casting alloys suggested Fig. 15 iousaluminum alloy premium-quality cast- for elevated-temperature service. Duration of temper- ings after 10 O00-h temperature exposure "bubbles" up through the weld pool, causing ature exposure was 10 000 h. defects in the weld. From this one must recognize that the quality of the weld is close- lower corrosion resistance, whereas silicon ly related to the casting quality or soundness Other Engineering Characteristics and magnesium enhance corrosion resis- in the area of the weld. The modulus of elasticity of cast aluminum tance. The most widely used test for corro- The large amount of oxides and porosity alloys varies somewhat with alloy contents, sion resistance is the standard salt spray test. usually found in commercial die castings but 71 GPa (10.3 × 106 psi) is an appropriate Relative rankings are given in Table 3. makes welding of these castings impractical average value for most design considerations. Machinability. Aluminum-exhibits better in most cases• Recent quality-enhancing die Poisson's Ratio. The ratio of transverse machinability than most metals and alloys. casting techniques have, in a few cases, contraction to the longitudinal elongation of Its high thermal conductivity fosters long overcome this limitation. a strain specimen is about 0.33 for alumi- tool life by quickly diffusing heat away from Welding of castings to extrusions or other num casting alloys. the cutting tool. The typically low cutting wrought aluminum products is often done. Corrosion Resistance. Aluminum and alu- forces permit the use of almost limitless This part-assembly technique has been useful minum alloys have a highly protective, tightly machining speeds. In most cases the surface in many applications. Here the techniques adherent, invisible oxide film on its surface. quality is exceptional. The casting alloys normally used for welding wrought products Because of this film there is an inherent containing silicon (3xx.0 and 4xx.O series) apply, keeping in mind the effects of casting ability to resist corrosion. When this film is are less of a problem with regard to large discontinuities on the weld quality• broken in most environments, it begins to chips because the cast structure is less reform immediately, the protective cover is homogeneous than wrought products. The REFERENCES restored, and deterioration by corrosion is grain-boundary segregation and second- resisted. Resistance to corrosion is greatly phase silicon constituent aid chip breakage. Woldman's Engineering Alloys, 6th ed., dependent on alloy content and its effect on To overcome problems with long chips of R.C. Gibbons, Ed., American Society the oxide film. For example, copper additions the single-phase alloys (2xx.0, 5xx.O, 7xx.O, for Metals, 1979 Aluminum Foundry Products / 151

2. Handbook of International Alloy Com- 7. G.B. Brook, Mater. Des., Vol 3, Oct 1987 positions and Designations, Metals and 1982, p 558-565 • M. Holt and K. Bogardus, The "Hot" Information Center, Batelle 8. U. Feurer and H. Zoller, Effect of Li- Aluminum Alloys, Prod. Eng., Aug Memorial Institute, 1976 censed Consection on the Structure of 1965 3. R.G. Riek, A. Vrachnos, K.P. Young, D.C. Cast Aluminum Ingots, pre- • F. Mollard, Understanding Fluidity, Pa- and R. Mehrabian, Trans. AFS, Vol 83 sented at the 105th AIME Conference per 33, Trans. AFS, 1987 4. J. Collot, Gircast--A New Stir-Casting (Las Vegas), The Metallurgical Society, • E. Rooy, Improved Casting Properties Process Applied to Cu-Sn and Zn-A1 Inc., 1976 and Integrity With Hot Isostatic Process- Alloys, Castability and Mechanical ing, Mod. Cast., Dec 1983 • G. Scott, D. Granger, and B. Cheney, Properties, in Proceedings of Interna- SELECTED REFERENCES tional Symposium on Zinc-Aluminum Al- Fracture Toughness and Tensile Proper- loy, Canadian Institute of and • G. Bouse and M. Behrendt, Metallurgi- ties of Directionally Solidified Alumi- Metallurgy, 1986, p 249 cal and Mechanical Property Character- num Foundry Alloys, Trans. AFS, 1987, 5. A.C. Arruda and M. Prates, Solidifica- ization of Premium Quality Vacuum In- p 69 tion Technology in the Foundry and Cast vestment Cast 200 and 300 Series • J. Tirpak, "Elevated Temperature Prop- House, The Metals Society, 1983 Aluminum Alloys, Adv. Cast. Technol., erties of Cast Aluminum Alloys A201-T7 6. R.L. Antona and R. Moschini, Metall. Nov 1986 and A357-T6," AFWAL-TR-85-4114, Air Sci. Technol., Vol 4 (No. 2), Aug 1986, p • Directionally Solidified Aluminum Force Wright Aeronautical Laboratories, 49-59 Foundry Alloys, Paper 69, Trans. AFS, 1985