微量钪、锆对Al-Zn-Mg合金铸态组织演变的影响

Influence of minor Sc and Zr on as-cast microstructure evolution of Al-Zn-Mg alloy

对复合添加了稀土元素Sc、Zr的Al-Zn-Mg合金采用光学显微镜(OM)、电子探针(EPMA)、差热分析(DSC)等分析和测试方法,探究不同含量的Sc、Zr添加量对Al-Zn-Mg合金铸态组织演变的影响。结果表明,稀土元素Sc、Zr的复合添加对铸态晶粒产生了细化效果,铸态合金元素大多数偏聚在晶界或者晶内,随着Sc、Zr的含量增加,元素分布趋于均匀,第二相数目开始减少,晶粒大小也逐渐减少。470℃×24 h均匀化退火之后,枝晶组织得到消除,大部分非平衡T相也溶入基体,只有少量难溶的Fe、Si杂质相残留在晶界上,同时合金中重新析出小尺寸的MgZn_2相。随着Sc、Zr含量的增加,第二相的回溶和晶粒细化效果得到了提高。

The as-cast microstructure evolution of Al-Zn-Mg alloy with different content of Sc and Zr adding was investigated by means ofoptical microscopy ( OM) , electron probe micro-analyzer ( EPMA) and differential scanning calorimetry ( DSC ) analysis. The results showthat refinement effect on grain of the as-cast alloys is caused by the Sc and Zr addition and the element aggregation of the as-cast alloysoccurred in grain boundary or inside the grain. With the increase of the contents of Sc and Zr, the distribution of elements becomes uniform,the number of secondary phase begins to decrease and the size of grain becomes smaller. After homogenization treatment at 470 °C for 24 h,dendritic microstmcture is eliminated and most of nonequilibrium T phase is dissolved into matrix, there is only a little insoluble Fe and Siimpurity phase remained on the grain boundary and undersized MgZn2 re-precipitated from the alloys. With the increase of the contents of Scand Zr, the dissolving of secondary phase and the refinement effect on grain can be improved.