Microstructural coarsening of 6061 aluminum alloy semi-solid billets prepared via recrystallization and partial melting

In this study, the Recrystallization and partial melting (RAP) process was performed to prepare 6061 aluminum alloy semi-solid billets. The microstructural evolution and coarsening of the materials were investigated. During the RAP process, the 6061 aluminum alloy plate supplied in cold rolled state was heated to the semi-solid range. The results showed that both the average grain size and shape factor of solid grains increased along with the isothermal holding time and temperature. The coarsening of solid grains could be attributed to the coalescence and Ostwald ripening mechanisms, with the latter playing an increasingly important role as the isothermal holding time and temperature increased. At isothermal holding temperatures of 620, 625, 630 and 635 °C, the coarsening rate constants reached 333.1, 833.8, 1034.7 and 1271.9 μm/s3, respectively. Moreover, the coarsening rate constant gradually increased along with isothermal holding temperature.