等温处理对Mg-7Zn-x La镁合金半固态组织的影响

Effect of Isothermal Treatment on Microstructure of Mg-7Zn-xLa Alloys

采用等温热处理法制备Mg-7Zn-xLa(x=0,0.1,0.3,0.5,wt.%)合金的半固态坯料。探索La元素及其含量对Mg-7Zn-xLa合金半固态组织的影响,分析La元素对固相颗粒粗化常数值的影响。结果表明:在相同的等温热处理工艺下,随La元素含量的增加,固相颗粒的平均尺寸和形状因子先减小后增加。当合金中La元素含量为0.3 wt.%时,对半固态组织的优化效果最佳。同时,添加La元素可以有效降低固相颗粒的粗化常数值,抑制固相颗粒的粗化。此外,通过分析二次凝固组织发现:随初生固相颗粒的部分熔化,液相中的Mg含量增加,导致次生α_(2)-Mg的数量和晶粒尺寸均明显增加。

Semi-solid billets of Mg-7Zn-xLa(x=0,0.1,0.3,0.5,wt.%)alloys were prepared by semi-solid isothermal heat treatment.The effects of the La element on the semi-solid microstructure of Mg-7Zn-xLa alloys were investigated.The influence of La element on the coarsening rate constants of solid particles was analyzed.The results show that at the same isothermal heat treatment process,the average size and shape factor of solid particles decrease firstly and then increase with the increase of La content.The optimum effect was achieved when the addition amount of La was 0.3wt.%.Meanwhile,the addition of La element could effectively decrease the coarsening rate of solid particles and restrict the growth of solid particles.It was also found that the amount and particle size ofα_(2)-Mg formed by secondary solidification increased obviously when the liquid phase increased with the partial melting of the primary solid particles.