This aluminum piece serves as the chassis supension support for a snowmobile. The one-piece casting replaced multiple stamped and riveted pieces.
To improve properties and enhance
strength and ductility, aluminum castings often are thermally processed by a series of heating and cooling cycles called heat treatment. T is thermal processing involves three basic operations: solution, quench and age. Combinations of these three heat treatments are called tempers (Table 1). T e benefi ts of heat treatment include:
• Homogenization of alloying elements—this is desirable to distribute elements evenly throughout the matrix, so properties in the casting will be uniform;
• Stress relief—residual stresses are created during cooling from elevated cast- ing and solution tempera- tures; heating the casting to an intermediate tem- perature can relieve these residual stresses;
• Improved dimensional stability and machin- ability—changes in the microstructure can cause castings to grow over
2013 CASTING SOURCE DIRECTORY
This electric valve housing was cast in C355 aluminum via semi-permanent mold casting.
time; to maintain tight dimensional tolerances during and after machin- ing, castings should be heat treated to form stable precipitate phases;
• Mechanical property improvement— the greatest use of heat treatment is to enhance mechanical and corro-
sion properties through spheroidizing constituent phase particles and by precipitation hardening. Rarely are all of the desired
properties optimized in a single casting. More often, heat treat- ment is a compromise, maximizing some properties at the expense of others. For example, tensile and yield strengths can be increased, but this results in lower elonga- tion. Contrarily, higher elonga- tions result in lower tensile and yield strengths.
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METAL CASTING DESIGN & PURCHASING 31
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