Sr对过共晶Mg-Si合金微观组织的影响

Effects of Strontium on Microstructures of Hypereutectic Mg-Si Alloy

利用Mg-25%Sr中间合金对过共晶Mg-Si合金进行变质处理,研究碱土元素Sr对Mg2Si初晶的变质效果(主要包括形态和尺寸),并讨论其变质机理。研究结果表明:碱土元素Sr对过共晶Mg-Si合金中的Mg2Si初晶可有效变质。初生Mg2Si的尺寸明显降低(平均尺寸由50μm左右降低为20μm左右),其形态由粗大树枝状晶、非规则外形颗粒变化为外形相对规则颗粒。共晶Mg2Si由明显的汉字状变化为呈细短的棒状。其变质机理主要有两点:一是Sr的富集颗粒作为异质形核点诱导更多的初生Mg2Si生长;二是Sr富集于共晶Mg2Si相生长表面,抑制其优先生长晶向的生长。

The hypereutectic Mg-4%Si alloy was modified by adding Mg-25%Sr master alloy. The effect of Sr addition on the modification of the primary Mg2Si phases and the modification mechanisms were investigated. The results show that the primary Mg2Si phases were effectively modified by Sr addition. The size of the primary Mg2Si phases was clearly decreased by Sr addition （average size from about 50 μm to about 20μm）, and the primary Mg2Si phases change from coarser dendrites to finer dendrites, the shapes of the primary Mg2Si particles from the irregular shapes to relatively regular shapes. The shapes of the eutectic Mg2Si particles change from obvious Chinese characters shapes to fine short rod shapes. There are two modification mechanisms, First, more primary Mg2Si growth due to Sr-rich particles as heterogeneous nucleation sites. Secondly, Sr enriched in growth surface of eutectic Mg2Si phase inhibits the preferred growth manner of the eutectic.