Extrusion: Second Edition Copyright © 2006 ASM International® M. Bauser, G. Sauer, K. Siegert, editors, p 195-321 All rights reserved. DOI:10.1361/exse2006p195 www.asminternational.org CHAPTER 5 The Production of Extruded Semifinished Products from Metallic Materials* THE HOT-WORKING PROCESS extrusion ered to be the most important of the hot-working is, in contrast to other compressive deformation processes. processes used to produce semifinished prod- ucts, a deformation process with pure compres- sive forces in all three force directions. These favorable deformation conditions do not exist in other production processes for semifinished products. Even in rolling, which is the most im- Extrusion of Materials with portant compressive working process for pro- ducing semifinished products, tensile forces oc- Working Temperatures cur in the acceleration zone of the roll gap as between 0 and 300 ЊC well as in the cross rolling process used to pierce blanks in the rolling of steel tubes. These Gu¨nther Sauer* tensile forces cause problems in the rolled prod- uct if the deformation conditions are not opti- mized. The benefits of this three-dimensional compression in terms of deformation technol- 5.1 Extrusion of Semifinished ogy, which have already been discussed in this Products in Tin Alloys book, can be clearly seen in Fig. 5.1 based on experimental results for face-centred cubic (fcc) Tin is a silver-white, very soft metal with a aluminum and zinc with its hexagonal lattice stable tetragonal lattice in the temperature range structure. 20 to 161 ЊC. The pure metal has a density of The extensive variations in the extrusion pro- 7.28 g/cm3 and a melting point of 232 ЊC. cess enable a wide spectrum of materials to be The material can be easily worked with its extruded. After rolling, extrusion can be consid- recrystallization temperature below room tem- *Extrusion of Materials with Working Temperatures between 0 and 300 ЊC, Gu¨nther Sauer Extrusion of Semifinished Products in Magnesium Alloys, Gu¨nther Sauer Extrusion of Semifinished Products in Aluminum Alloys, Rudolf Akeret Materials, Gu¨nther Scharf Extrusion of Semifinished Products in Copper Alloys, Martin Bauser Extrusion of Semifinished Products in Titanium Alloys, Martin Bauser Extrusion of Semifinished Products in Ziroconium Alloys, Martin Bauser Extrusion of Iron-Alloy Semifinished Products, Martin Bauser Extrusion of Semifinished Products in Nickel Alloys (Including Superalloys), Martin Bauser Extrusion of Semifinished Products in Exotic Alloys, Martin Bauser Extrusion of Powder Metals, Martin Bauser Extrusion of Semifinished Products from Metallic Composite Materials, Klaus Mu¨ller 196 / Extrusion, Second Edition perature. Consequently, the softest condition de- surface and the container inner wall because of velops rapidly in tin materials after cold work- these good bearing properties. Tin-base extruded ing. Work hardening by cold working is not alloys, therefore, tend to flow largely according possible. to flow pattern A (Fig. 3.11) in direct extrusion. Tin is very stable at room temperature and is The flow stress kf that has to be overcome for not poisonous. Unlike lead, it can therefore be the deformation of very soft pure tin is signifi- used in contact with food. The metal is used as cantly higher than that of pure lead, as can be the base material for soft solder, anode materials clearly seen in Fig. 5.2. It is, however, extremely as well as bearing materials and for tin plating low at 20 to 32 N/mm2 for logarithmic strains steel sheet (tin plate). ug up to 0.7 [Sac 34]. Therefore, a specific press Soft solders are the main application for tin. pressure of maximum 400 N/mm2 is sufficient Lead, silver, antimony, and copper are used as for the direct extrusion of tin alloys when the alloying elements. Special soft solders also con- low friction between the billet and the container tain cadmium and zinc. Aluminum is used as an liner surface is taken into account. alloying component for soft solders used to join Tin-base alloys for the production of soft sol- aluminum alloys. Bearing metals based on tin ders are generally extruded transversely at billet contain antimony, copper, and lead as the alloy- temperatures of 50 to 60 ЊC and a container tem- ing elements as well as additions of cadmium, perature of approximately 100 ЊC. It is often suf- arsenic, and nickel. ficient to heat the front third of the billet to this The production of semifinished products in tin temperature so that, on one hand, the billet up- alloys by extrusion is limited today to the pro- sets from the front to the back to prevent air duction of feedstock for the manufacture of soft entrapment and, on the other hand, the optimal and special soft solders on transverse extrusion welding conditions for the resultant transverse presses and to the direct extrusion of feedstock weld in the extruded product are obtained. This for the manufacture of anodes with solid and transverse weld in soft solders has to be capable hollow cross-sectional geometries for electro- of withstanding the drawing loads during the re- chemical plating. Tin is also used for the pro- duction in diameter of the extruded wires on duction of rolled strip, as the feedstock for the multispindle drawing machines. manufacture of high-capacity electrical con- Semifinished products in tin materials includ- densers, as well as for roll cladding of lead-base ing bar, wire, tubes, and sections are produced strips for organ pipes, wine bottle caps, and on direct extrusion presses. For productivity rea- Christmas ornaments (tinsel). sons, higher extrusion speeds are desired in this In general, tin-base materials have good bear- process than those used in the transverse extru- ing properties and are consequently used as the sion of soft solders, which are typically 4 m/min. base material for bearing metals. Very little fric- It is therefore advantageous to heat the billets to tion occurs in direct extrusion between the billet 100 to 150 ЊC. Again, it is beneficial to have a temperature profile with the temperature de- creasing toward the back of the billet. In auto- matic fully integrated extrusion plants complete Fig. 5.1 Improving the workability of aluminum and zinc with a hydraulically produced increasing mean compressive stress p measured by the increase in the reduction Fig. 5.2 Flow stress kf as a function of the logarithmic strain in area at fracture u in tensile tests at room temperature of pure lead and pure tin (Source: Rathjen) Chapter 5: The Production of Extruded Semifinished Products from Metallic Materials / 197 with melting furnaces and mold casting ma- Simple two-column horizontal oil-hydraulic chines, as shown in Fig. 5.3, the cast billets re- extrusion presses are used. Figure 5.3 shows a tain the heat from the casting process to assist typical two-column extrusion press for tin and the deformation process. Care has to be taken to tin alloys with a maximum press load of ensure that the heat from the casting process, 5000 kN. when combined with the deformation heat, does not result in excessive temperatures at high ex- trusion speeds in the deformation zone of the extrusion tooling. The solidus of the lead-tin eu- 5.2 Extrusion of Semifinished tectic at 183 ЊC has to be taken into account in Products in Lead Materials the tin alloys containing lead. If melting occurs in the solid tin matrix, transverse cracks will def- Lead is a soft metal, matte blue in appearance initely be produced in the extruded products. with a fcc lattice structure. The pure metal has Controlled cooling of the extrusion tooling im- a very high density of 11.34 g/cm3 and a melting proves the situation. In addition, the billet sur- point of 327 ЊC. Lead alloys can also be easily face is sometimes brushed with a lubricant to worked. Work hardening after cold working at improve the product surface. room temperature, for example, from 40 to 120 Tin alloys will weld during the extrusion pro- N/mm2 disappears within a few minutes because cess under suitable deformation conditions in- the recrystallization temperature of the base ma- cluding the extrusion load and temperature. terial is about 0 ЊC. Cold working of lead-base They can, therefore, be used with porthole and alloys can be approximately compared in its ef- bridge dies as well as for billet-on-billet extru- fect to hot working of other metals. Work hard- sion with feeder chamber dies. These extrusion ening by cold working is not possible. tools are, in principle, similar to those used in Pure lead is very soft and ductile. Soft lead aluminum extrusion. Their design is simpler in has a very low flow stress kf as shown in Fig. detail and the dies are nitrided. 5.2. It is, therefore, not possible to draw pure Fig. 5.3 Modern integrated fully automatic 5000 kN extrusion plant for the production of bar, wire, tube, and sections in lead and tin alloys complete with casting oven, triple billet casting plant, hot-billet shear, and oil hydraulic long-stroke extrusion press (Source: Collin) 198 / Extrusion, Second Edition lead to wire. However, lead alloys have higher the production of soft solders. Lead forms a eu- flow stresses. Additions of antimony and tin pro- tectic with 38.1% tin at 183 ЊC. These soft sol- duce solid-solution hardening of the lead, in- ders can be used to solder steel and copper al- creasing both the base strength and the work- loys. Organ pipes are produced from lead-tin hardening capability. This raises the alloy strips with similar tin contents. Tin con- recrystallization temperature. The loads needed tents from 45 to 75 wt% are used depending on in deformation processes also increase.