微量Gd元素对ZK60铸造镁合金微观组织及拉伸性能的影响

Effect of trace Gd on microstructure and tensile property of ZK60 cast magnesium alloy

摘要

本工作系统研究ZK60镁合金微量添加0.5%（质量分数，下同）与1.0%的Gd元素对其组织及拉伸性能的影响。通过光学显微镜、扫描电镜、能谱分析、差热分析、X射线衍射分析等技术对ZK60、ZVK600、ZVK610合金试样铸态与固溶态微观组织进行表征，测试合金的室温拉伸性能。结果表明，铸态ZK60合金晶粒尺寸为95 μm，在晶界处存在粗大的块状MgZn相和少量Zn₂Zr₃相颗粒，微量添加Gd元素会导致第二相比例增加，MgZn相转变为Mg₃GdZn₆相，但晶粒尺寸未发生细化。3种合金铸态下的室温拉伸性能较为接近，铸态ZVK610合金的屈服强度和塑性相对较低，这与其相对较大的晶粒尺寸和较多晶界第二相有关。经过T41阶梯化固溶处理后，ZK60合金的晶粒粗大，第二相基本消除，合金塑性显著提升，但晶粒尺寸长大导致屈服强度略有下降，而ZVK600和ZVK610合金仍有少量晶界第二相残留。延长高温固溶时间或提升固溶温度设计的T42和T43工艺，虽然可以进一步降低基体中第二相比例，但是由于晶粒长大，合金屈服强度进一步下降，塑性也没有明显提升，因此推荐采用T41固溶热处理工艺。

Abstract

This study systematically investigates the effects of trace Gd additions of 0.5% (mass fraction, the same hereinafter) and 1.0% on the microstructure and tensile property of ZK60 magnesium alloy. The as-cast and solution-treated microstructures of ZK60, ZVK600, and ZVK610 alloys are characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, differential scanning calorimetry, and X-ray diffraction. The tensile properties of the alloy specimens are measured and analyzed via room-temperature tensile tests. The results show that the as-cast ZK60 alloy has grain size of 95 μm, with coarse blocky MgZn phases and a small number of Zn₂Zr₃ particles present at grain boundaries. Trace Gd addition increases the fraction of secondary phases and transforms the MgZn phase into the Mg₃GdZn₆ phase, but does not refine the grain size. The room-temperature tensile properties of the three as-cast alloys are relatively close. The as-cast ZVK610 alloy exhibits lower yield strength and ductility, which is associated with its relatively large grain size and increased grain-boundary secondary phases. After T41 step solution treatment, the grain of ZK60 alloy become oarse, the secondary phases are nearly eliminated, and the ductility is significantly improved. However, the yield strength decreases slightly due to grain coarsening. In contrast, a small amount of grain-boundary secondary phases remains in ZVK600 and ZVK610 alloys. T42 and T43 processes, designed with prolonged high-temperature solution time or elevated solution temperature, further reduce the secondary phase fraction in the matrix but lead to additional grain coarsening, resulting in further reduced yield strength and no obvious improvement in ductility. Therefore, T41 solution heat treatment process is recommended.

关键词

ZK60镁合金 / 塑性 / 微观组织 / 析出相

Key words

ZK60 magnesium alloy / plasticity / microstructure / precipitated phase

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基金资助

国家自然科学基金(52371037)

国家自然科学基金(52171055)

国家自然科学基金(52171121)

国家自然科学基金(51971151)