The semisolid microstructural evolution of a severely deformed A356 aluminum alloy

A cast A356 aluminum alloy was successfully processed through applying a new severe plastic deformation method, accumulative back extrusion (ABE), at the temperature of 300 °C. In consequence, a severely deformed microstructure consisting of round and fine Si particles has been obtained. Microstructural evolution of the ABE-processed material soaked for various times at different isothermal temperatures in semisolid state was investigated. It has been shown that the proposed semisolid thermomechanical route would lead to a fine semisolid microstructure, where the spheroidal α-Al globules are surrounded by continuous liquid film. The results indicate that the ABE processing followed by 10 min holding at 580 °C and/or 6 min at 590 °C has led to the best thixotropic characteristics, i.e., the high shape factors and low globule sizes. The thixotropic structure characteristics have been also properly discussed in terms of globularization and coarsening mechanisms as well as the kinetics of microstructural evolutions. The almost linear semisolid coarsening behavior of the processed material indicates the outstanding role of Ostwald ripening mechanism in the growth of globules.