Development of Filler Metals and Procedures for Vacuum Brazing of Aluminum Several brazing filler metal compositions have been developed which offer significant improvements over existing compositions. They braze in vacuum at temperatures lower than normal flow temperatures and have equal or better flowability

BY W. J. WERNER, G. M. SLAUGHTER AND F. B. GURTNER

Introduction ry cleanliness levels under production vantages. As a single entity, it was This report documents work per­ conditions. The maximum allowable immediately more desirable from a formed toward the development of lag between cleaning and brazing was cleaning, assembling and material found to be 12 hours. handling standpoint. Metallurgically, new brazing filler metals for vacuum- 2 fluxless brazing (1 X 10~6 torr) C. S. Beuyukian developed tech­ the 4045 brazing filler metal with its certain aluminum alloys of interest to niques for vacuum or inert gas fluxless lower silicon content allowed greater the Army. The base metals under brazing of aluminum cold plates for latitude in processing parameters than consideration were alloys 6061, 2219, use in Apollo command modules. In did alloy No. 718. 7075 and 2024. Brazing filler metal this work, brazing filler metal No. 718 Finally, the workers at Aeronca, and No. 23 brazing sheet were evalu­ Inc. completed a study on inert gas flow temperatures needed for these 3 alloys encompass the temperature ated. Alloy No. 718 is nominally 88% brazing of aluminum in early 1967. range 900 to 1200F. Specifically, the aluminum, 12% silicon; No. 23 braz­ Their work was concerned with de­ contract called for the development of ing sheet is comprised of 6951 base velopment of high strength brazed alloys with flow temperatures of 950, alloy clad on one side with 4045 aluminum honeycomb structures 1000, and 1050F. Finally, corrosion brazing filler metal—nominally 90% which would withstand a range of compatibility of the brazing filler met­ aluminum, 10% silicon. Base metals cryogenic (—423F) through elevated al with certain chemical agents was 6061 and 5052 were considered for (600F) temperatures. All of the base necessary and to this end a survey of the main body of the assembly. metals involved in the study, X7005, potentially compatible elements com­ In general, better results were ob­ X7106, and 7039, began to melt with­ piled by the contractor was utilized. tained using vacuum. The techniques in the range of 1080 to 1120F. As a result, a 1050F maximum flow tem­ We began the investigation with a developed are unique in that stringent flatness requirements placed on the perature for the brazing filler metal survey of the literature. Unfortunate­ was needed. ly, there is very little published work assembly by design required that braz­ on fluxless-vacuum and/or inert gas ing operations be performed in heated Three commercial brazing alloys brazing of aluminum. M. M. platen presses at moderate pressures. were evaluated in combination with Schwartz1 et al showed the feasibility The use of pressure during brazing the aforementioned base metals— of vacuum fluxless brazing production undoubtedly influenced oxide penetra­ 716, 718, and 719. Number 716 con­ quantities of aluminum alloy 6061 tion and/or displacement during the tains nominally 86% aluminum, 10% containers of helium leaktight quality brazing operation. Production brazing silicon, and 4% copper; 718 contains by closely controlling process parame­ was carried out in the temperature nominally 88% aluminum, 12% sili­ ters using a commercial brazing filler range 1055 to 1095F using brazing con; and 719 contains nominally 76% metal. Brazing alloy No. 718 (nomi­ times of at least 10 minutes. aluminum, 10% silicon, 10% zinc and nally 88% aluminum, 12% silicon) Under these conditions, aluminum 4% copper. It was found that the was used. This alloy is widely used alloy 6061 was preferred over 5052 aluminum-silicon brazing alloys per­ commercially for both dip and fur­ because alloy 5052 exhibited a greater formed best as claddings. nace brazing and is available in both susceptibility to intergranular penetra­ The researchers developed several wire and foil form. As might be ex­ tion by silicon. Use of alloy 5052 new brazing filler metals during the pected, the success of the endeavor would therefore have required more course of their investigation. Two in was largely due to the use of laborato- rigid time-temperature control during particular showed promise. Both al­ the brazing cycle. In addition, silicon loys had a base composition of 68% diffusion resulted in embrittlement of aluminum, 7% silicon, 15% germani­ MESSRS. WERNER and SLAUGHTER are 5052. um; their compositions were modified with the U.S. Atomic Energy Commission. Tenn. which is operated by Union Carbide No. 23 brazing sheet was chosen with 10% zinc, and 10% silver, re­ Corp. MR. GURTNER is with the Dept. for production over the combination spectively. Both alloys brazed at ot the Army, Technical Support Directo­ rate. Industrial Operations Div., Edge- of brazing alloy Nos. 718 and 6061 1020F. These new alloys looked espe­ wood Arsenal, Md. for both metallurgical and process ad­ cially good in combination with

64-s ] FEBRUARY 1972 Table 1—Nominal Compositions, Li mits and Melting Ra nges of Alloys Under Con sideration Approximate . - Composition weight pe -, melting Alloy designation Si Fe Cu Mn Mg Cr Zn Ti range, °F 6061 (limiting) 0.40-0.8 0.7 0.15-0.40 0.15 0.8 -1.2 0.04-0.35 0.25 0.15 1080-1200 6061 (nominal) 0.6 — 0.27 — 1.0 0.20 — — 1080-1200 22191 (limiting) 0.20 0.30 5.8 -6.8 0.20-0.40 0.02 — 0.10 0.20-0.10 1010-1190 22192 (nominal) — — 6.3 0.30 — — — 0.06 1010-1190 7075 (limiting) 0.40 0.50 1.2 -2.0 0.30 2.1 -2.9 0.18-0.35 5.1 -6.1 0.20 890-1180 7075 (nominal) — — 1.6 — 2.5 0.30 5.6 — 890-1180 2024 (limiting) 0.50 0.50 3.8 -4.9 0.30-0.9 1.2 -1.8 0.10 0.25 — 935-1180 2024 (nominal) — — 4.4 0.6 1.5 — — — 935-1180

1 Vanadium 0.05-0.15, zirconium 0.10-0.25 "- Vanadium 0.10, zirconium 0.18

X7106. Alloy 719 remained the num­ industrially; and alloys with magnesium eter. Our measurements show that it ber one choice for brazing X7005. contents greater than 2.5% are con­ takes 25 minutes for the sample to sidered unbrazeable. This is due to the reach brazing temperature after the Materials fact that state-of-the-art fluxes do not furnace is pushed onto the muffle. The Table 1 shows the nominal com­ remove the tenacious oxides formed variation in temperature setting was positions and compositional limits of on these alloys. found to be ±5F. It is believed that the base metals under consideration in the inherently poor heat transfer char­ the program, along with their melting Equipment and Experimental acteristics of a vacuum are responsible ranges. Joining of alloys 6061 and Procedure for the 15-minute delay between con­ 2219 is accomplished industrially by The vacuum furnace apparatus for troller indication of the attainment of dip or furnace brazing techniques both flow temperature and wettability de­ brazing temperature and the actual at­ of which employ liberal amounts of terminations is shown in Fig. 1. The tainment of brazing temperature since flux. In addition, alloy 6061 has also system is capable of maintaining a the sensing couple for the controller been brazed without flux using vacu­ vacuum of 1 X 10~r> torr at brazing is outside of the vacuum. um and/or inert atmospheres.1* 2 As temperature. The picture shows the The majority of our brazing filler a result, good cleaning and handling furnace rolled back off the muffle. In metal wettability and flowability de­ procedures are not a problem with a typical brazing cycle the specimen is terminations were done using V2 by these two alloys. In fact, cleaning placed into the cold muffle. After V2 by V16 in. 6061 aluminum base procedures are available in the Metals pump-down, the heated furnace is metal pads. Those tests that were run and Ceramics Division for both of rolled onto the muffle, and the work on the other base metals of interest these alloys since they are routinely very rapidly comes to temperature. were performed on this same standard hot roll-bonded into dispersion type After holding for the proper brazing pad size. Both the pads and the exper­ fuel plates using standard picture time, the furnace is rolled off the imental brazing filler metals were frame techniques. muffle. Simultaneous with the former cleaned prior to undergoing a thermal Alloys 7075 and 2024, on the other operation, helium can be admitted to cycle for determination of melting hand, are not considered brazeable facilitate rapid cooling or quenching temperature and wettability. using established commercial tech­ of the test assembly. Diffusion effects Attention to cleanliness is of prime niques and commercial brazing filler can probably be limited by both of importance to the fluxless brazing alloys. In the first place, both alloys these operations. process. Aluminum oxide forms on have melting points below the flow A typical time-temperature re­ "clean" aluminum surfaces immedi­ temperatures of the commercial braz­ sponse curve for the furnace is shown ately at room temperature. This oxide ing filler metals (Table 1). Secondly, in Fig. 2; the temperature measure­ is one of the most stable known. Its both alloys contain appreciable ments indicated are those of an actual melting point is approximately 3700F, amounts of magnesium (2.5 and sample. Chromel-P versus alumel and it is not reduced by heat and/or 1.5%, respectively). Normally, alloys thermocouples were attached to a normal chemical cleaners. In commer­ with magnesium contents greater than specimen and temperature measure­ cial furnace and dip brazing processes 2.0% are considered difficult to braze ments were made using a potentiom- where liberal amounts of flux are em-

«*(&••- • ["TIME REQUIRED TO REACH 600 1 BR AZING T EMPERA1 URE m 500 •'••"•:.• ';•..: 77\ '" 77 • ti'*~*i

300 570 -FURNAC E A 1 ROLLEC ONTO \ 399 i 1 -CONTROLLER INDICATES MUFFLE <.«•«•- ~- THAT BRAZING 1 100 I 1 212 BEEN r EACHED 1 ; 1 1/ t 0—"" H5 1i0 15 20 25 30 35 40 45 50 TIME (mini

Fig. 1—Apparatus for determining flow temperatures and Fig. 2—Typical time-temperature response curve for brazing wettability of experimental brazing filler metals furnace

WELDING RESEARCH SUPPLEMENT | 65-s ployed, care is taken to reduce the Table 2--List of Potentially Compatible Elements for Brazing Filler oxide thickness to a "workable" mini­ Metal Alloy Formulation Supplied by Edgewood Arsenal mum before flux is applied. Ele­ Potential, Melting Boiling Specific Solid The consensus on the mechanism of ment volts point, °F point, °F gravity solubility %/°F* flux action is as follows: First, as the Al -1.706 1220.4 4442 2.6989 assembly is brought to brazing tem­ Am 1562 — 11.7 perature the oxide film microfissures Sb +0.212 1166.9 2516 6.691 0.1%/1232.6 due to the differences in coefficients of Ba -2.90 1317 2980 3.5 thermal expansion between the oxide Be 2460/2640 5378 1.848 0.05%/1166 and base metal. Flux readily enters B 3690 — 2.34 0.00190/1190.86 these microfissures and undermines Ca -2.76 1540 2908.6 1.55 2.8770/1108.8 Ce -2.335 1495 6278 8.23/6.67 the oxide to some extent. If the oxide Cr -0.41 3407 4829 7.18-2 0.61%/1166 is workably thin, it breaks up during Cu +0.158 1981.4 4703 8.96 4.10%/932 the undermining process. This contin­ Dy 2565 4226 8.526 ues until the flux is consumed or the Er 2727 4766 9.051 metal surface is cleared of oxide. Ge 1719 5125 5.323 In fluxless brazing, we must assume Au +1.42 1945.4 5380 19.32 that, as in commercial operations, a Hf 4032 9750 13.29 1.22%/1223.6 workably thin oxide film is microfis- In -0.49 313.1 3632 7.31 13%/1173.2 Ir 4449 9570 22.42 sured during heat-up to the brazing Fe +0.777 2799 5432 7.874 0.052%/1211 temperature. Undermining of the ox­ 1688 6276.2 5.98/5.186 0.0370/1121 ide in the fluxless process must be due Li -3.045 357 2426 0.534 5.2%/ to the action of the brazing filler Mg -2.375 1202 2025 1.728 11.5%/752 metal. It is noteworthy that diffusion Mn -1.029 2273 3900 7.21/7.44 1.35%/1158.8 (over short distances) may play an Mo 4730 10,040 10.22 important role in the fluxless brazing Nd -2.246 1866 5756 6.80/7.004 process. Rate of heating to brazing Ni -0.23 2647 4950 8.902 0.040%/1157 temperature is also a factor of major Nb +0.344(?) 4474 8901 8.57 Os 4900 9950 22.57 importance since oxidation of alumi­ Pd 2826 7200 12.02 0.1%/1139 num takes place in the best vacuums Pt 3217 8185 21.45 and/or inert atmospheres. In addition, Pr 1686 5468 6.6/6.7 faster heating rates may affect the Re 5755 10,650 21.02 degree of oxide microfissuring. In any Rh 3571 8130 12.41 0.1%/1215.5 event, there is a multiplicity of factors Ru 4530 4900 12.41 0.1%/1218.2 to consider which probably will affect Sm 1962 2966 7.5/7.4 the vacuum brazing of aluminum. Ag +0.7966 1760.9 4010 10.50 Eutectic 28% Ta 5425 9800 16.6 Both 6061 and 2219, as well as all Te +0.593 842 1813.6 6.24 the experimental brazing filler metals, Th 3182 6332 11.66 0.1%/1173.2 were cleaned by immersion into a 20 Ti -2.0 3035 5900 4.54 1-1.5%/1220 vol%HN08—2 vol %HF—water solu­ V -0.255 3450 6150 6.11 0.6%/1224.5 tion at room temperature. The clean­ Yb 1515 2786 6.977 ing step was followed immediately by Y 2723 5800 4.45 0.1%/1191.2 a cold water rinse which, in turn, was Zr 3366 6470 6.35 0.28%/1220 followed by flushing with acetone. Al­ loys 2024 and 7075 did not respond to * Percent at temp (°F). the aforementioned chemical cleaning COMPOSITION («>%) process to our satisfaction. Both alloys did, however, respond to a low- temperature perchloric acid electropol- ishing treatment. £ 11Z0° In our very first experiments we noted that test results were influenced " BOO ... —— -- . 5 tst S by the time span between cleaning and / ! , 400 brazing. As a result, we held the time between cleaning and brazing to a In maximum of 1 hour which, although possibly somewhat difficult for pro­ duction work, was felt to be optimum for experimental brazing filler metal evaluation. Brazing Alloy Development Experimental brazing filler metal compositions were formulated using binary phase diagram information to estimate the behavior of ternary al­ loys. A list of potentially compatible elements compiled by the contractor Fig. 3—Ternary plot of the Al-Si-ln system with attached was used as a guide (Table 2) but it binary phase diagrams for estimating compositions of poten­ was not utilized absolutely since this tial interest to program would have seriously limited the choice

66-s i FEBRUARY 1972 COMPOSITION (wl ? 20 40 60 BO S

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Fig. 4—Ternary plot of the Al-Si-Ge system with attached Fig. 5—Ternary plot of the Al-Si-Y system with attached binary phase diagram for estimating compositions of poten­ binary phase diagrams for estimating compositions of poten­ tial interest to program tial interest to program of elements for alloying additions. This Each experimental heat was melted sive reaction with the base metal. report covers the results obtained in several times in an effort to achieve a Aluminum brazing results are highly three promising ternary systems. reasonable degree of homogeneity. sensitive to small changes in brazing Our method of estimating ternary time and temperature due to the fact compositions of potential interest Aluminum-Silicon-Indium System that the melting points of the brazing using binary phase diagrams is shown Nine different compositions were in Figs. 3, 4 and 5. The numbers on the formulated and tested for flow tem­ ternary plots designate experimental perature and flowability-wettability in brazing filler metal compositions that this system. The location of these were actually formulated, manufac­ experimental brazing filler metals on tured and tested. The heavily shaded the ternary layout is shown in Fig. 3. areas on the layouts indicate those Table 3 gives the flow temperatures of compositions which show promise the alloys along with their specific from the standpoints of flow tempera­ compositions. All of the formulated ture and wettability. The areas of alloys melted at a reasonable tempera­ lighter shading (Figs. 3 and 4) indicate ture and flowed well on the 6061 base WATER-COOLED compositions which our preliminary meterial. The alloys with the lowest investigations indicated may also be of melting ranges (5, 6, 8, and 9) are in interest. a rectangular array on one corner of These three series of alloys are the box which encompasses the Al-Si- ternary modifications of the alumi­ In compositions. As a result, we feel it num-silicon system which is the basis is necessary to extend the investigation of present commercial brazing filler in this particular system to the lightly metals. Our germanium and indium shaded area in the ternary layout to additions were based on a potential determine if the optimum alloy has for melting point depression, as evi­ been formulated. denced by the aluminum-germanium The pad tests for determining flow Fig. 6—Schematic of apparatus used for and aluminum-indium phase dia­ temperatures and flowability-wettabili­ casting experimental brazing filler metals grams. Yttrium additions were based ty of the experimental alloys were on thermochemical information as examined metallographically so that well as on melting point depression. a metallurgical evaluation could be The free energy of formation of yttri­ made. Figure 7 shows a macro of Table 3—Flow Temperatures and um oxide (Y203) is of the same order the pad test made on alloy No. 8. As Compositions of the Al-Si-ln Alloys of magnitude as that for aluminum you can see, excellent wetting and Flow oxide. It was felt that there was a flow of the alloy was obtained. Figure Alloy Composition, wt. % temp, possibility that this property might 8 shows the base metal braze metal number Al Si In °F enhance the wettability and flowability interface of the same specimen at of these alloys over the basic alumi­ 1 88 10 2 1095 250X. No excessive reaction is evi­ 2 80 18 2 1095 num-silicon binary. dent. 3 75 23 2 1095 The alloys were formulated using Figure 9 shows a macro of the pad 4 83 7 10 1095 arc melting techniques in conjunction test made with alloy No. 6. In this 5 75 15 10 1085 with a water cooled copper hearth. particular case, the test was carried 6 70 20 10 1085 The apparatus used for casting but­ out at 1085F and the photo clearly 7 80 2 18 1095 tons for wettability and flow tempera­ shows that the brazing temperature 8 72 10 18 1075 9 65 17 18 1085 ture evaluation is shown in Fig. 6. time relationship produced an exces­

WELDING RESEARCH SUPPLEMENT | 67-s Fig. 7—Macro of pad test with Al-Si-ln Alloy No. 8 vacuum brazed for 7 minutes at 1075F

Fig. 8—Micro of interface between 6061 base metal and No. 8 Al-Si-ln alloy. Mag: 250X

Fig. 9— Macro of pad test on Al-Si-ln alloy No. 6 vacuum brazed for 7 minutes at 1085F. Note excessive filler metal- Table 4—Flow Temperatures and base metal reaction Compositions of the Al-Si-Ge Alloys Flow Alloy Composition, wt. % temp, number Al Si Ge °F 1 55 5 40 1020 2 55 10 35 1060 3 55 15 30 1060 4 55 20 25 1065 5 45 5 50 1020 6 45 10 45 1060 7 45 15 40 1065 8 45 20 35 1095 9 35 5 60 1020 10 35 10 55 1065 11 35 15 50 1075 12 35 20 45 1075

Fig. 10—T-joint brazed with Al-Si-ln alloy No. 6 at 1085F for 5 minutes

filler metals are quite close to the experimental brazing filler metals on pad tests made at different tempera­ melting points of the base metals. The the ternary layout is shown in Fig. 4. tures (in vacuum) with the filler met­ same alloy was subsequently used to Table 4 gives the flow temperatures of al No. 9. Using successively lower test braze the T-joint shown in Fig. 10 these alloys along with their composi­ temperatures, we established that the using a slightly shorter brazing cycle tions. All of the formulated alloys flow temperature of this alloy was with obviously much improved results. melted at reasonable temperatures 1020F. Note the excellent flowability Our experience indicates that even and flowed on the 6061 base metal and wettability of this experimental further improvement is possible. (heavily shaded area on the plot). composition at all temperatures Initial attempts to fabricate this al­ Generally speaking, the flow tempera­ tested. We subsequently used this loy by hot swaging have met with tures of these alloys increased with same alloy to make the T-joint shown limited success. It may be necessary to increasing silicon content. All of the in Fig. 12, in which the brazing filler break down the cast structure by ex­ alloys containing 5% Si (1, 5, and 9) metal is preplaced at one end of the trusion before hot swaging to wire. exhibited flow temperatures of 1020F. joint and flow proceeds along the Increasing the silicon content to 20% capillary. The base metal for the T- Aluminum-Silicon-Germanium System raised the flow temperature to as high joint was 6061 and the braze was Twelve different compositions were as 1095F. The lightly shaded area of performed by holding for 2.5 minutes formulated and tested for flow tem­ the layout shows those compositions at 1020F. Good filleting is evident. perature and flowability-wettability in which may be of further interest. Figure 13 shows a macro of the this system. The location of these Figure 11 shows a series of typical 1020F pad test performed on alloy

68-s i FEBRUARY 1972 No. 5. The 1020F brazing tempera­ quite brittle and are not amenable to obtained. Alloy No. 18 (70 Al- 25 Si- ture, 7 minute brazing time combina­ fabrication into wire or sheet by con­ 5Y) exhibited the lowest flow temper­ tion appears to be slightly excessive ventional techniques. ature. However, as was the case for for this alloy since reaction completely some compositions in the other series through the pad has taken place. Nev­ Aluminum-Silicon-Yttrium System investigated, base metal-filler metal in­ ertheless, the wetting and flow ex­ Twenty different compositions were teraction occurred rapidly and exces­ hibited is quite good. It should be formulated and tested for flow tem­ sive penetration was a problem. Thus, noted that this brazing temperature is perature and flowability-wettability in careful control of the time- lower than that used for commercial this system. The location of these temperature thermal cycle (or further state-of-the-art brazing filler metals experimental brazing filler metals on alloying with additional melting point and, as such, is a significant advance­ the ternary layout is shown in Fig. 5. depressants) is necessary. ment in aluminum brazing technol­ The lightly shaded area shows the The alloys in the Al-Si-Y system ogy. location of the most promising com­ were much more fabricable than any Figure 14 shows a high magnifica­ positions. Table 5 gives the flow tem­ of the other experimental brazing tion view of the interface between peratures of the alloys that melted filler metals investigated. They were base metal and braze metal for this below the melting point of the 6061 readily reduced to V16-in. wire, as particular pad test. Both photos sug­ base metal and the compositions of all shown in Fig. 17. gest that this composition is very near the alloys tested. the Al-Si-Ge eutectic composition. The higher flow temperatures of Summary and Conclusion Figures 15 and 16 show the pad these alloys rather limit their use per During the course of this program, test results for one of the higher melt­ se as ternary alloys. However, one we have developed several brazing ing Al-Si-Ge alloys, No. 8. This was must remember that additions of mi­ filler metal compositions that appear the highest melting of this series of nor quantities of elements such as Cu, to exhibit significant improvements alloys. This filler metal also has excel­ Sn and Zn could result in considerable over existing commercial composi­ lent flow and wetting characteristics flow point reduction. tions. They braze in vacuum at tem­ and is typical of the higher melting Of the seven experimental composi­ peratures lower than the flow temper­ alloys. The degree of reaction with the tions in this ternary system which did atures of commercial brazing alloys base metal is satisfactory. melt below 1150F, excellent wetting and have equal or better flowability. All of the Al-Si-Ge alloys were and flow on 6061 base metal was

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Fig. 11—Wetting tests on Al-Si-Ge No. 9 made at successively higher temperatures proceeding from the left. (1) 1020F, (2) 1065F, (3) 1075F, (4) 1095F. Excellent wetting is evident over the 75F range of temperature shown

Fig. 14—Micro of interface between 6061 base metal and No. 5 Al-Si-Ge alloy. Mag: 250X

Fig. 12—T-joint of Al-Si-Ge alloy No. 9 and 6061 base metal. Fig. 13—Macro of pad test on Al-Si-Ge alloy No. 5 vacuum Brazing was performed at 1020F for 2.5 minutes. Excellent brazed for 7 minutes at 1022F. An excessive reaction occurred flow is evident at one spot

WELDING RESEARCH SUPPLEMENT | 69-s /

Fig. 15—Macro of pad test on Al-Si-Ge alloy No. 8 vacuum brazed for 7 minutes at 1095F Fig. 17—Photo of 1/16-in. wire produced by swaging of Al-Si-Y alloy No. 18 from a casting.

particularly promising and exhibited Table 5--Flow Temperatu res and flow temperatures of 1020 to 1095F. Compositions of th5 Al-S -Y Alloys Of particular interest in this system Flow are the 55Al-5Si-40Ge, 45Al-5Si- Alloy Compos ition, wt. % temp, 50Ge, and 35Al-5Si-60Ge alloys, all number Al Si Y °F of which flowed at 1020F; these flow 1 85 5 10 — temperatures are approximately 50F £ * 2 80 5 15 — below those of commercial alloys. 3 75 5 20 — lt should be emphasized at this 4 70 5 25 — point that we feel that the full poten­ * i. 5 65 5 30 — tial of these alloys is yet to be real­ 6 85 10 5 1120 ized. That is, further work is necessary 7 80 10 10 — to show that the optimum composi­ 8 75 10 15 f — •: 7 9 70 10 20 tions in these systems have been — found. Secondly, further minor addi­ 10 65 10 25 — 11 80 15 5 1140 tions of other elements such as Cu, Zn 12 75 15 10 1110 and Sn should be investigated since 13 70 15 15 — they may result in further flow tem­ 14 65 15 20 — perature reductions and/or wettabili- 15 75 20 5 1130 ty-flowability improvements. Also, op­ 16 70 20 10 1140 timum time-temperature relationships 17 65 20 15 1140 for vacuum brazing with these alloys 18 70 25 5 1095 must be established. Fig. 16—Micro of interface between 6061 19 65 25 10 — 20 65 30 base metal and No. 8 Al-Si-Ge alloy. 5 — References Mag: 250X 1. Schwartz, M. M., Gurtner, F. B., and Shutt, P. K., Jr., "Vacuum (or Fluxless) flowed on aluminum alloy 6061 in Brazing-Gas Quenching of 6061 Aluminum Our lowest flow temperature—1020F vacuum without the use of flux. The Alloy," WELDING JOURNAL, Vol. 46, No. 5, —is about 50F lower than the gener­ Al-Si-ln alloys exhibited flow temper­ May 1967, pp. 423-431. 2 Beuyukian, C. S., "Fluxless Brazing of ally accepted flow temperature of the atures in the range 1075 to 1095F and Apollo Cold Plates—Development Produc­ 88A1-12 Si commercial alloy. the Al-Si-Y alloys exhibited flow tem­ tion", WELDING JOURNAL, Vol. 47, No. 9, Sept. 1968, pp. 710-719. We specifically studied alloys in peratures in the range 1095 to 1140F. 3 "Fluxless Brazing Makes Headway", three ternary systems and they all Alloys in the Al-Si-Ge system were Iron Age 200, Vol. 67, No. 8, Aug. 10, 1967.

"Unified Theory of Cumulative Damage in Metal Fatigue" By Julien Dubuc, Bui Quoc Thang, Andre Bazergui and Andre Biron A review is made of the different cumulative damage theories available in the literature. A new approach ("unified theory") is suggested which can be applied WRC to stress-controlled or strain-controlled conditions, and which considers the order of application of different stress or strain levels. Comparison is made with a large Bulletin number of test results using several different levels. The theory is also applied to No. 162 some cases of random loading. It is found that the proposed theory yields an improved agreement with experi­ June 1971 mental results, especially for cases where there is a large difference between levels. The price of WRC Bulletin 162 is $1.50 per copy. Orders for ten or more copies should be sent to the Welding Research Council, 345 E. 47th St., New York, 10017. Single copy orders should be sent to AWS, 2501 N.W. 7th St. Miami, Fla. 33125.

70-s | FEBRUARY 1972