Er-Ba复合变质对Mg-2.5Si-4Zn铸造合金组织及性能的影响

Effect of Er-Ba Composite Modification on Microstructure and Mechanical Properties of Mg-2.5Si-4Zn Cast Alloy

摘要:

镁合金中的强化相Mg₂Si可以显著提高合金的硬度、耐磨性，特别是耐高温蠕变性。但铸态过共晶Mg-Si合金中初生Mg₂Si棱角粗糙，共晶Mg₂Si具有复杂的汉字形态，会严重割裂合金基体。为了改善Mg-2.5Si-4Zn合金的性能，进行了添加Er/Er-Ba的变质实验，并通过光学显微镜（OM）、扫描电子显微镜（SEM）、能量色散光谱仪（EDS）和X射线衍射仪（XRD）研究了Er/Er-Ba对合金组织和Mg₂Si相的影响。利用计算机辅助电子加载拉伸试验机对力学性能进行了测试和分析。结果表明，在Mg-2.5Si-4Zn合金中加入0.6%（质量分数）的Er，其组织中的初生Mg₂Si从粗大的树枝状转变为规则的四方块状，而共晶Mg₂Si则从粗大的汉字状转变为更复杂的短棒状。随后加入0.8%的Ba后，初生Mg₂Si从规则的四边形块状进一步转变为带有沟槽和孔洞的不规则细小块状，共晶Mg₂Si在尺寸上细化效果显著，呈点线状弥散分布在合金基体中。当加入0.6%Er和0.8%Ba时，变质效果最佳。经Er-Ba复合变质的Mg-2.5Si-4Zn合金的力学性能得到显著改善，抗拉强度σ_b和伸长率δ分别提高到168 MPa和5.04%。

Abstract:

The enhanced phase Mg₂Si in the magnesium alloy can significantly improve the hardness, wear resistance, especially high temperature creep resistance. But the Mg₂Si phase of the as-cast hyper-eutectic Mg-Si alloy will seriously cut the alloy matrix because of the coarse angular shape of the primary Mg₂Si and complex Chinese script morphology of the eutectic Mg₂Si. In order to improve the properties of Mg-2.5Si-4Zn alloy, the modification experiments of adding Er/Er-Ba were performed and the effects on the alloy microstructure and Mg₂Si phase were investigated by the optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffractometer (XRD). The mechanical properties were measured and analyzed by the computer-aided electric-loaded tensile tester. The results show that with the addition of 0.6wt% Er to the Mg-2.5Si-4Zn alloy, the primary Mg₂Si in the microstructure transforms from a coarse dendritic shape into a regular tetragonal block shape, while the eutectic Mg₂Si transforms from a coarse Chinese script type to a more complex short rod shape. When adding 0.8wt% Ba subsequently, the primary Mg₂Si further transforms from a regular tetragonal bulk shape to an irregular fine bulk shape with grooves and holes, and the eutectic Mg₂Si has an obvious refining effect and is diffusely distributed with the dot/short-line shape in the alloy matrix. The best metamorphic effect is obtained by adding 0.6wt% Er and 0.8wt% Ba. The mechanical properties of the Mg-2.5Si-4Zn alloy modified by Er-Ba composite modifier are significantly improved, with the tensile strength σ_b and elongation δ increasing to 168 MPa and 5.04%, respectively.