Cast Al Alloys

Low melting temperature, insolubility to gases except H₂ and good surface finish are characteristics of these alloys. Important drawback of cast aluminium alloys is their shrinkage after solidification and hence careful mould design is called for. Mechanical properties are inferior to wrought alloys except in creep. Alloys can be sand cast gravity die cast, and cold chamber pressure die cast. Si, Cu, Mg and Sn increase fluidity when casting thin sections. Mechanical properties of cast Al alloys is improved by adding Cu which induces age hardening to impart hardness and stability upto 250^oC. Alloys used for die casting are: 380 (Al, Si, 3.5 Cu) and 413 (Al, 11.5 Si). Alloys preferred for permanent mould casting are: 332 (Al, 9 Si, 3 Cu, 1 Mg) and 319 (Al, 6 SI, 4 Cu). Y-alloy containing 4% Cu and 2% Ni retain strength at high temperatures. It is used for piston and cylinders of IC engines.