Effects of holding temperature and time on semi-solid isothermal heat-treated microstructure of ZA84 magnesium alloy
(1. College of Materials Science and Engineering, Chongqing Institute of Technology, Chongqing 400050, China;2. College of Materials Science and Engineering, Chongqing University, Chongqing 400030, China)
Abstract: The feasibility of fabricating ZA84 magnesium alloy with non-dendritic microstructure by a semi-solid isothermal heat treatment process and the effects of holding temperature and time on the semi-solid isothermal heat-treated microstructure of the alloy were investigated. The results indicate that it is possible to produce ZA84 alloy with non-dendritic microstructure by suitable semi-solid isothermal heat treatment. After being treated at 560−575 ℃ for 120 min, ZA84 magnesium alloy can obtain a non-dendritic microstructure with 14.2%−25.6% liquid fraction and an average size of 56−65 μm of the unmelted primary solid particles. With the increasing holding time from 30 to 120 min or holding temperature from 560 to 575 ℃, the average size of unmelted primary solid particles decreases and globular tendency becomes more obvious. Under the experimental condition, the microstructural evolution of ZA84 alloy during semi-solid isothermal treatment is mainly composed of three stages of initial coarsening, structural separation and spheroidization. The subsequent coarsening of spheroidal grains is not observed.
Key words: ZA84 magnesium alloy; semi-solid state; isothermal heat treatment