Effect of cross-sectional reduction ratio on microstructure evolution of semi-solid 7075 aluminum alloy prepared by RFSIMA process

Semisolid billets of 7075 aluminum alloy were fabricated by radial forging strain induced melting activation (RFSIMA) process. Effect of the cross-sectional reduction ratio on microstructure of fabricated 7075 aluminum alloys was analyzed. The results indicate that the average grain size of α-Al decreased from 109μm to 65μm as the cross-sectional reduction ratio increased from 0% to 73% during the 20-minute isothermal treatment at 620°C.The spheroidization trend of the grains became more pronounced; During the semisolid isothermal treatment, the segregation of Cu at grain boundaries increased slowly with the increase in the cross-sectional reduction ratio. Zn and Mg exhibited uniform distribution without significant segregation at low cross-sectional reduction ratios (43% and below). When the cross-sectional reduction ratio reached 62%, slight segregation of Zn and Mg was observed at the grain boundaries. At a cross-sectional reduction ratio of 73%, the segregation of Zn and Mg at the grain boundaries reached a level similar to that of Cu. The optimal cross-sectional reduction ratio for the RFSIMA process was found to be 62%; the microstructural evolution mechanism of the semi-solid 7075 aluminum alloy prepared by the RFSIMA method was investigated.