Microstructure evolution of semi-solid 7075 Al alloy slurry during temperature homogenization treatment

Semi-solid 7075 Al slurry was prepared by inverted cone-shaped pouring channel process (ICSPC) and temperature homogenization (TH) treatment was combined to make the slurry uniform and have a controllable solid fraction suitable for the follow-up rheocasting. The influence of cooling rate on the microstructure evolution of primary α(Al) during TH treatment was investigated. The results show that as the cooling rate of the slurry after being prepared reduces, the growth of primary α(Al) in the slurry tends to be nearly spherical and the uniformity of the organization is also enhanced. This may be due to the fact that lower cooling rate plays an important role in achieving the uniformity of temperature and composition in the remaining liquid, which is crucial to the formation of the spherical and homogeneous microstructure. However, a too low cooling rate will lead to a significant increase in grain growth time, which makes too coarse grains and more particles coalesce, so a certain abnormal growth of grain appears and the shape factor decreases slightly.