铸态AZ31-xGd镁合金在半固态等温热处理中显微组织和富Gd相的演变

Microstructure and Gd-rich phase evolution of as-cast AZ31-xGd magnesium alloys during semi-solid isothermal heat treatment

本文深入研究了铸态AZ31-xGd(x=0,1.5 wt%,2.0 wt%,2.5 wt%)镁合金在半固态等温热处理中显微组织和富Gd相的演变。结果表明,添加Gd的AZ31镁合金中的层状(Mg,Al)3Gd相在半固态等温热处理过程中转变为颗粒状Al2Gd相,导致形成更多的球状α-Mg晶粒。当Gd含量为2.0%(质量分数)时,半固态球状晶粒的尺寸达到最小值。晶粒细化的主要机理在于树枝晶的重熔以及少量充当孕育剂的Al2Gd相的辅助作用。同时,固液界面处富集的Al2Gd颗粒可以显著阻碍α-Mg晶粒的粗化长大。与铸态AZ31镁合金(280 MPa)和半固态AZ31镁合金(209 MPa)相比,经过等温热处理的半固态AZ31-2.0Gd镁合金具有适中的压缩变形抗力(230 MPa),实现了变形阻力的降低。

The microstructure and Gd-rich phase evolution of as-cast AZ31-xGd(x=0,1.5 wt.%,2.0 wt.%and 2.5 wt.%)magnesium alloys during semi-solid isothermal heat treatment were investigated deeply in the present work.Results showed that the lamellar(Mg,Al)3Gd phases transformed into the particle-like Al2Gd phases in AZ31 magnesium alloys with Gd addition during semi-solid isothermal heat treatment,leading to yielding more sphericalα-Mg grains.When Gd content is 2.0 wt.%,the size of semi-solid spherical grains reaches the minimum.The main mechanism of grain refinement lies in the remelting of dendritic branches as well as the auxiliary effect of a small number of Al2Gd particles as grain refining inoculants.Meanwhile,Al2Gd particles enriched at the solid-liquid interfaces can remarkably retard the growth rate ofα-Mg grains.A reduction of deformation resistance has been successfully achieved in AZ31-2.0Gd magnesium alloy after semi-solid isothermal heat treatment,which shows a moderate compressive deformation resistance(230 MPa),comparing to the as-cast AZ31 magnesium alloy(280 MPa)and semi-solid AZ31 magnesium alloy(209 MPa).