|Title：||Effect of La addition on semi-solid microstructure evolution of Mg-7Zn magnesium alloy|
|Author：||Zhan-yu Zhang, *Xiao-feng Huang, Fan Yang, Sheng Zhang, and Jiao-li Fu|
|Address：||State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China|
|Key words：||magnesium alloy; La element; semi-solid microstructure evolution; coarsening rate constant|
Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment. The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated. Meanwhile, the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied. Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure. During the semi-solid thermal transformation, the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time. The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605 °C for 30 min is the optimal. The average size of solid particles, shape factor, and solid fraction are 42 μm, 1.45 and 61.8%, respectively. At the same time, a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg 7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.