半固态AlSi7Mg合金二次加热工艺与组织转变机制

REHEATING PROCESS AND STRUCTURAL EVOLUTION OF SEMI-SOLID AlSi7Mg ALLOY

采用电阻炉对用电磁搅拌方法制备的半固态ＡｌＳｉ１７Ｍｇ合金二次加热，结合金相分析研究了半固态组织的转变机制．实验发现，共晶相中的Ｓｉ相通过向 相中扩散溶解，其形状从片层状断裂成点链状颗粒，并随着温度升高颗粒细化球化，片层越薄。这一过程发生的温度越低，速度越快。Ｓｉ溶解到一定程度后共晶部分熔化，初生 相形状、尺寸开始变化，树枝状 相和蔷薇花状 相球化，但前者变大，后者变小为原始尺寸的１／２－１／４．

Reheating experiments of semi-solid AlSi7Mg alloy produced by electromagnetic stirringhave been carried out using resistance furnace. The structural evolution during reheating was also studiedby optical metallograph. It was found that, the Si-phase in eutectic dissolved in a way of diffusion toward -phase, its appearance changed from flake to dot-like, and tended to be fine and spheroidal with increasein treating temperature. The thinner the Si flake, the lower the temperature for the occurrence of thisprocess, and the higher the transforming speed. The eutectic melted partially when Si-phase dissolved tosome extent, and the morphology and size of primary -phase began to change. The dendrite and rosette -phases tended to sphericize. The size of the former became larger, while the size of the latter reducedto be 1/2- 1/4 of the original size. The primary sheroidal-like -phase had a tendency of growth.