Al-4%Mg-0.3%Cu alloy castings were solution heat treated at temperature of 530°C between solidus temperature and final solidification temperature, quenched into water at 25°C and artifically aged at 200°C. These casting have yield stress, ultimate tensile strength and elongation which are superior to those of AC7A (Al-5%Mg alloy). These phenomena are notable in the slowly solidified castings. The improvements of mechanical properties are brought about by the easy dissolution of Al-Cu-Mg compounds in the solution treatment, by the precipitation hardening due to the second phase particles and by the good castability of this alloy.
