Abstract
Al–Si eutectic alloys have excellent castability and sufficient strength when combined with other alloying elements. Especially, Al–Si alloy containing Mg, used for high-quality die-casting, is well-known as a high strength alloy created by appropriate heat treatment and consequential precipitation hardening of Mg2Si intermediate phase. To understand the age hardening behavior of Al–10 mass%Si–0.5 mass%Mg and Al–10mass%Si–0.8mass%Mg alloys in detail, microstructure observation and hardness measurement were performed. These alloys quenched in iced water, naturally aged at room temperature and artificially aged at 423–523 K, showed conspicuous age hardening behavior. The age hardening curve from the theoretical hardness by the composite rule almost agreed completely with the age hardening curve from the measurement. Consequently, it's thought that the age hardening of these alloys is composed with the change of hardness in alpha Al and the eutectic phases of Al+Si.
