凝固速率对压铸态AZ91-1.5Si-0.4Ca镁合金组织和性能的影响

Effect of solidification rate on microstructure and mechanical properties of die casting AZ91-1.5Si-0.4Ca magnesium alloy

摘要:

以AZ91-1.5Si-0.4Ca为对象(以AZ91为参照),通过设计并压铸成型4种厚度的板状试样获得了4个凝固速率。首先对各壁厚试样的凝固速率进行了数值模拟,并对两种合金试样的显微组织、常温和180℃高温拉伸性能、拉伸断口形貌进行了对比研究。结果表明：1)AZ91-1.5Si-0.4Ca中的Si与Mg生成Mg₂Si,Ca主要以固溶的形式存在；Si和Ca有一定的晶粒细化效用。2)随着凝固速率增加,AZ91-1.5Si-0.4Ca中的Mg₂Si相由粗大的多边形及汉字状向细小的多边形颗粒及短棒转变。3)随着凝固速率增加,两种合金试样的常温和高温力学性能提高,AZ91-1.5Si-0.4Ca常温和高温强度受凝固速率影响大于AZ91,伸长率受凝固速率影响则小于AZ91。当壁厚低于2.5mm时,AZ91-1.5Si-0.4Ca的中温强度高于AZ91；当壁厚低于3mm时,AZ91-1.5Si-0.4Ca的常温强度高于AZ91。

Abstract:

Specimens of AZ91-1.5Si-0.4Ca and AZ91 with different section thicknesses were prepared by HPDC(high pressure die-casting). The solidification rate of the HPDC specimens was numerically simulated. The microstructure, tensile properties and the fracture morphologySat the ambient temperature and 180_oC of the specimens were investigated. The results show that: 1) Si and Mg form Mg₂Si phase and Ca mainlySdissolves in the matrix. Besides, Si and Ca have some effect of grain refinement on the Mg matrix. 2) The increase of solidification rate causes that the Mg₂Si phase in AZ91-1.5Si-0.4Ca turn from bulky polygons and Chinese script type to fine polygons and short rod. 3)The mechanical properties of AZ91-1.5Si-0.4Ca and AZ91 at ambient temperature and 180_oC increase with the increase of solidification rate. The influence of section thickness on tensile strength of AZ91-1.5Si-0.4Ca is greater than that of AZ91, but the influence on elongation is less than that of AZ91. Furthermore, the tensile strength of AZ91-1.5Si-0.4Ca at 180_oC is higher than that of AZ91 when the section thickness is less than 2.5mm, and the tensile strength of AZ91-1.5Si-0.4Ca at ambient temperature is higher than that of AZ91 when the section thickness is less than 3mm.