AZ91D真空低压消失模铸造组织特性分析

Microstructure of AZ91D Magnesium Alloy in Low Pressure Lost Foam Casting

利用真空低压消失模铸造新工艺浇注AZ91D镁合金试样,通过金相显微镜、扫描电镜、电子探针分析组织结构,并与其他铸造工艺的组织、性能进行比较。结果表明,AZ91D镁合金真空低压消失模铸造组织主要由初生相α-Mg和晶界不连续骨骼状离异共晶相β-Mg17Al12组成,富Al的共晶相在α区附近析出二次β-Mg17Al12沉淀相。Al大多分布在晶界,形成β-Mg17Al12,少部分Al固溶于基体α-Mg中;Zn和Si弥散分布于α和β相中;Mn集中分布于晶界。其组织、性能比粘土砂型铸造和重力消失模铸造好,基本达到金属型铸造的强度,而伸长率较高则是由于低压状态凝固补缩好,提高了组织致密度。

The microstructure of AZ91D magnesium alloy in low pressure lost foam casting was observed by OM(optical microscope),SEM(scanning electron microscope) and EPMA(electron probe micro-analysis),which was compared with that of ones in other casting methods.The results reveal that the micro-structure of AZ91D magnesium alloy in low pressure lost foam casting is composed of primary AAAAAAAA-Mg phase and divorced eutectic β-Mg17Al12 phase with discontinuous skeleton shape distributed along grain boundary.A little amount of secondary precipitates β-Mg17 Al12 phase is precipitated from near eutectic α-Al-rich zone.Major Al is distributed along grain boundary to create the β-Mg17 Al12 phase,and minor Al is dissolved into the α-Mg matrix.Zn and Si elements were dispersively distributed in a-Mg and β-Mg17 Al12 phase and Mn elements are aggregated on the grain boundary.The microstructure of AZ91D magnesium alloy in low pressure lost foam casting is superior to that in sand casting and in gravity lost foam casting,and is equivalent to that in permanent mold.In addition,the improvement of elongation is attributed to better feeding effects in low pressure improving the compactness of microstructure.