镁合金半固态坯料及其部分重熔组织的显微分析

Micro-analyses of thixotropic magnesium alloy and its partial remelting microstructure

对AZ91镁合金的液相线铸造与两相区铸造半固态坯料及其部分重熔组织进行SEM,EPMA,XRD和EDAX分析.结果表明,两种制浆工艺的铸造前适当静置,除增加形核数量外,还有利于促进溶质元素扩散,减小显微偏析.初生α-Mg固相颗粒中固溶有部分A l,Ca和Zn,Mg17A l12和阻燃元素Ca形成的A l2Ca相主要存在于晶界上.坯料部分重熔开始时A l2Ca相在晶界上呈条状和块状的不连续分布,随后部分分解,逐渐形成A l2Ca和Mg17A l12与α-Mg形成的低熔点共晶组织;重熔时间过长加剧了A l和Ca等元素在液相中的偏聚程度.

The microstructures of liquidus or sub-liquidus casting AZ91 semi-solid slurrying billets were investigated together with their partial-remehed microstructures by SEM, EPMA, XRD and EDAX. The results indicate that, for the two slurrying methods, properly stewing before casting would increase the number of nucleating center, and also promote solute diffusion and relieve microsegregation in the meantime. Al, Ca and Zn solid soluted partially within α - Mg grains, and Al2Ca formed from Mg17TAl12 and fire-retardant Ca, were precipitated primarily in grain boundaries. During partial-remelting presented, Al2Ca present within grain boundary as discontinuous stick or block precipitation initially, and then decompose gradually and formed low - melting eutectic structure together with Mg17Al12 and α- Mg. The Al and Ca would aggregate locally as prolonging the partial-remelting holding time.