挤压铸造AZ81镁合金均匀化热处理工艺研究

Investigation on Homogenization Heat Treatment of Squeeze Casting AZ81 Magnesium Alloy

为改善挤压铸造AZ81镁合金组织的不均匀性,对铸态试样进行均匀化热处理。采用金相显微镜、X射线衍射仪和扫描电镜对AZ81镁合金的组织与性能进行分析。结果表明:经400℃、8h均匀化处理后,AZ81合金有效地消除了枝晶偏析,改善了材料的组织状态;合金硬度由HRE73.72下降到HRE57.68,屈服强度由130MPa增加到138MPa,抗拉强度由226MPa增加到258MPa,伸长率则由7.6%增加到13.6%;试样的室温拉伸断口均为准解理断裂,经均匀化处理后断裂方式由沿晶界的脆性断裂转变为韧性穿晶断裂。

To improve the organization heterogeneity of the squeeze casting magnesium alloy AZ81, the homogenization heat treatment to as-cast sample was carried out. The microstructure and performance of AZ81 magnesium alloy was analyzed by metallographic observation, X-ray diffraction and SEM. The results showed that after 400 ℃ x8 h homogenization, the dendrite microsegregation of AZ81 alloy was effectively eliminated and the material status of the organization was improved. The hardness of alloy decreases from as-cast alloy HRE 73.72 to HRE 57.68, and a slight decrease in yield strength; tensile strength increases from 226 MPa of the as-cast alloy to 258 MPa, and the elongation increases from 7.6% to 13.6%. The room temperature tensile fracture is based on quasi-cleavage fracture. After homogenization heat treatment, the fracture mode translates from brittle fracture along the grain boundary into ductility transgranular fracture.