applications where strength and hard- ness at high temperatures are required. Typical applications include heavy-duty pistons; motorcycle, diesel and aircraft pistons; aircraft generator housings; and air-cooled cylinder heads. Alloys 319, A319, B319 and 320—
Alloys 319 and A319 exhibit good castability, weldability, pressure tight- ness and moderate strength and are stable, meaning their casting and me- chanical properties are not affected by fluctuations in the impurity content. Alloys B319 and 320 show higher strength and hardness than 319 and A319 and are generally used with the permanent mold casting process. Characteristics other than strength and hardness are similar to those of 319 and A319. Typical applications for sand castings
of these alloys include internal com- bustion and diesel engine crankcases, gasoline and oil tanks and oil pans. Per- manent mold cast components include water-cooled cylinder heads, rear axle housings and engine parts. Alloy 356—Alloy 356 has excel-
lent casting characteristics and has largely replaced alloy 295. Permanent mold castings of this alloy are used for machine tool parts, aircraft wheels
Table 1. Common Aluminum Heat Treatment Tempers
Temper Thermal Processing T4
T6 T61 T7 T71 T5
Solution treat and age naturally to a substantially stable condition. Natural aging may continue slowly, particularly at elevated service temperatures, so structural stability may not be satisfactory.
Solution treat and age artificially. In castings, T6 commonly describes optimum strength and ductility.
Solution treat, quench and age artificially for maximum hardness and strength. This variant of T6 yields additional strength and stability but at reduced ductility.
Solution treat, quench and artificially overage or stabilize. This temper improves ductility, thermal stability and resistance to stress corrosion cracking.
Solution treat, quench and artificially overage to a substantially stable condition. This temper further increases thermal stability and resistance to stress corrosion cracking and reduces strength.
Age only. Stress relief or stabilization treatment. Cool from casting temperature and artificially age or stabilize (without prior solution treatment). Frequently, the as-cast condition provides acceptable mechanical properties but is accompanied by micro- structural instability or undesirable residual stresses. Perhaps the possibility of in-service growth is the only constraint against using a casting in the as-cast state. In each case, the T5 temper is appropriate.
Annealing Castings that have low strength requirements but require high dimensional stability are annealed. Annealing also substantially reduces residual stress, a need in die castings. Annealing is a severe stabilization treatment and an elevated temperature variant of the T5 temper. Softening occurs because annealing depletes the matrix of solutes, and the precipitates formed are too large to provide hardening.
and hand wheels, pump parts, tank car fittings, marine hardware, valve bodies and bridge railing parts, as well as for aileron control sectors, rudder control supports, fuselage fittings and fuel tank elbows for airplanes and mis- siles. Automotive applications include
miscellaneous castings for trucks and trailers, spring brackets, cylinder heads, engine blocks, passenger car wheels and transmission cases. Uses for sand castings of 356 include flywheel housings, automotive transmis- sion cases, oil pans, rear axle housings,
28 METAL CASTING DESIGN & PURCHASING
2014 CASTING SOURCE DIRECTORY
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