Mg-6Zn-1Cu-0.5Ce镁合金的非枝晶组织演变及机理

Non-dendritic microstructure evolution process and mechanism of Mg-6Zn-1Cu-0.5Ce magnesium alloy

半固态金属坯料部分重熔是半固态金属触变成形工艺的重要技术环节,采用等温热处理法对Mg-6Zn-1Cu-0.5Ce镁合金在部分重熔过程中的非枝晶组织演变过程和机理进行研究。结果表明:在半固态重熔初始阶段,Mg-6Zn-1Cu-0.5Ce合金沿晶界分布的共晶相逐渐向α-Mg基体中扩散溶解,达到共晶熔化温度后,剩余部分开始熔化。随着保温时间的进一步延长,为了降低系统的界面能,颗粒将发生合并长大。其中,非枝晶颗粒的分离是由液相沿亚晶界浸渗和根部重熔两种机制起主导作用。Mg-6Zn-1Cu-0.5Ce合金的最佳等温热处理工艺为保温温度600℃和保温时间25 min,采用该工艺处理后所得非枝晶颗粒平均尺寸为57μm,形状因子为1.16,固相率为68%。

Partial remelting is the important part of semi-solid metal(SSM)ingots forming technology.The non-dendritic microstructure evolution process and mechanism of Mg-6Zn-1Cu-0.5Ce magnesium alloy during partial remelting were investigated by isothermal heat-treatment.The results indicate that the eutectic phases of Mg-6Zn-1Cu-0.5Ce alloy initial microstructure distribute on grain boundary,which gradually dissolves intoα-Mg matrix due to the diffusion of the solute,and the remainder is melted when the temperature up to eutectic melted during the initial stage of partial remelting.With the heat preservation time further extending,the semi-solid particles will combine and grow up to reduce the surface energy of the system.Furthermore,the appearance of subboundary and root remelting are the predominant separation mechanisms of particles during partial remelting.The best parameters of isothermal heat treatment are 600℃in holding temperature and 25 min in holding time,obtaining the semi-solid microstructure with the average partial size of 57μm,the roundness of 1.16 and the solid fraction of 68%.