Effects of process parameters on the microstructure and hardness of semi-Solid AlSi9Mg aluminum alloy prepared by RAP Process

This paper investigated the microstructure and hardness of the cold rolled AlSi9Mg aluminum alloy after the heating at different maintained (semi-solid) temperatures with different duration times. The effects of process parameters on the microstructural evolution and hardness of semi-solid alloy were investigated. Results showed that the increase in the maintained temperature enlarged both the average grain size and the shape factor. The average grain size also increased when the duration time increased. The shape factor increased first and then decreased with the increase in the duration time at the maintained temperature of 560 and 565°C. However, the shape factor kept improved with increasing the duration time at the maintained temperature of 570°C. The coarsening of solid grains in the microstructure resulted from the coalescence and Ostwald ripening mechanisms. The latter one played a more significant role when the maintained temperature or the duration time increased. The hardness of semi-solid AlSi9Mg alloy decreased with the increase in the duration time or the temperature. The parameters in the Hall-Petch and the Lifshitz-Slyozov-Wagner relationships for the semi-solid alloy were identified. The coarsening rate of solid grain at 560, 565 and 570°C were 85.47, 1177.93 and 1357.2μm3/s, respectively.