Recrystallization and Coarsening Kinetics of 7075 Al Alloy during Conventional and New Modified SIMA Processes

In this research, recrystallization behavior and coarsening kinetics of 7075 alloy were investigated during conventional and newly modified SIMA processes. The conventional SIMA process consisted of applying 10-55% uniaxial compression strain at ambient temperature and subsequent semi-solid treatment at various temperatures and times. A new modified SIMA process was developed by introducing repetitive upsetting-extrusion (RUE) for the first time for semi-solid processing of 7075 Al alloy. Specimens of 7075 alloy were subjected to different RUE cycles at 250 °C, and then the semi-solid treatment was carried out. Microstructural studies revealed that the recrystallization rate is accelerated, the average grain size is reduced considerably and the sphericity of solid grains is improved by the newly modified SIMA process. Lifshitz-Slyozov-Wagner (LSW) theory was used to describe the coarsening process of the semi-solid slurries. Coarsening rate of the solid grains in the newly modified SIMA process was slower than the conventional SIMA process.