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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 metamorphic Mg-Si alloy was modified by Mg-25% Sr master alloy to study the metamorphic effect (mainly including morphology and size) of alkaline earth element Sr on the Mg2Si primary crystal and to discuss its metamorphic mechanism. The results show that alkaline earth element Sr can effectively degrade Mg2Si primary crystals in the hypereutectic Mg-Si alloy. The size of primary Mg2Si decreases obviously (the average size decreases from about 50μm to about 20μm), and its morphology changes from coarse dendrites and irregular shape particles to relatively regular shape particles. Eutectic Mg2Si by the obvious change from the Chinese character was thin rod shape. The metamorphic mechanism has two main points: one is Sr enrichment particles as heterogeneous nucleation sites to induce more primary Mg2Si growth; the other is that Sr is enriched in the eutectic Mg2Si phase growth surface, inhibiting the growth of its preferential growth direction .