Effects of Heat Treatment on the Microstructure and Mechanical Properties of Ductile AlSi9MgMn Die Castings

Conventional solution heat treatment is normally considered detrimental to high-pressure die-cast (HPDC) products. High-temperature solution treatment leads to expansion of pores of gas entrapped during the casting process inside the HPDC products causing surface blistering. Surface blisters act as crack initiators making the material less usable. To avoid surface blistering and improve the mechanical properties, a low-temperature solution heat treatment is suggested in this work. A heat treatment consisting of a low-temperature solution treatment and subsequent ageing is expected to give better properties in the HPDC AlSi9MgMn alloys owing to spheroidization of Si particles and subsequent age hardening. The heat-treated material had higher yield strength compared to the as-cast material, stored for 1 year (naturally aged), due to the precipitation of Mg2Si particles. However, it is observed that the as-cast and stored material work-hardened better as compared to the heat-treated material.