Influence of process conditions on microstructures and mechanical properties of T5-treated 357 aluminum alloys

Abstract

The effect of casting processing and natural aging on microstructures and mechanical properties of T5-treated Al–7wt.%Si–0.5 wt.%Mg–0.01 wt.%Sr (ASTM 357) alloys has been investigated. An artificial aging gives fine precipitation microstructures, and the thixo-cast processing provides much finer distributions of eutectic Si phases and Al8Si6Mg3Fe phases than the gravity-cast and die-cast processing, leading to higher level of strength-ductility balance in the thixo-cast alloys than that of T6-treated Al–Si based cast alloys. Although the prolonged natural aging significantly changes the subsequent artificial age-hardening behaviors and precipitation microstructures, it is interesting to note that the cast alloys could keep their good strengths even after the T5-treatment including the long-term natural aging. This finding will open up the development of strong and ductile cast Al–7wt.%Si–Mg based alloys which can broaden the application of aluminum alloys in automotive industry.