The Microstructural Evolution of a Cold Rolled AlSi9Mg Aluminum Alloy after Semi-Solid Isothermal Treatment Process

The key factor in semi-solid metal forming process is the preparation of semi-solid billet with fine and spherical microstructure. The recrystallization and partial melting (RAP) process consists of cold deformation and semi-solid isothermal treatment (SSIT) is a promising method, because that many alloys are always supplied in the deformed state. In this work, a cold rolled AlSi9Mg aluminum alloy was used directly to fabricate semi-solid billets. During the RAP process, samples cut from the cold rolled AlSi9Mg aluminum alloy were treated with different isothermal holding temperatures and times, and the effects of isothermal treatment parameters on the microstructures of AlSi9Mg alloy semi-solid billets were investigated. The results show that, with increasing the isothemal holding temperature and time, the average grain size of solid grains is gradually increased, the spheroidization degrees of solid grains are sharply increased and then follows by a slight improvement. The high-quality semi-solid billets can be prepared with SSIT process at 570 °C for 5~10 min.