Y含量对铸造Mg-Gd-Y-Nd-Zr合金组织与性能的影响

Effects of Y Content on Microstructures and Mechanical Properties of Mg-Gd-Y-Nd-Zr Casting Alloy

采用金相观察、硬度测试、扫描电镜观察、能谱分析、透射电镜观察、X射线衍射及室温拉伸等手段,研究了元素Y对铸造Mg-Gd-Y-Nd-Zr合金组织与性能的影响,结果表明:Y对该系合金的铸态组织无明显影响,在研究的成分范围内,不同成分合金的铸态组织均由α-Mg和非平衡共晶Mg5.05RE组成;经固溶处理后,非平衡共晶可溶入基体,但在晶界残留富稀土粒子,随着合金中Y含量降低,残留富稀土粒子的数量也降低;经T6处理后,合金中形成了大量的析出相β′,高Y含量合金中析出相的体积分数高于低Y含量合金,导致高Y含量合金T6态的硬度较高,但残留更多数量的富稀土粒子反而使高Y含量合金的拉伸强度和延伸率更低。经成分优化,较优的化学成分为Mg-5.5Gd-3.0Y-1.0Nd-1.0Zr,其铸造-T6态的抗拉强度为322 MPa,延伸率为4.0%,力学性能优于总稀土含量与之相当的商用WE54合金。

Effects of Y content on microstructures and mechanical properties of Mg-Gd-Y-Nd-Zr casting alloy were investigated by optical microscopy（OM）,hardness testing,scanning electron microscopy（SEM）,energy dispersive spectroscopy（EDS）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and tensile testing.The results indicated that the microstructure of the as-cast state was comprised ofα-Mg matrix and non-equilibrium eutectic Mg5.05 RE.The non-equilibrium eutectic was able to dissolve in the matrix after solution treatment,leaving some rare earth（RE）-rich particles.The quantity of the RE-rich particles decreased as the Y content decreasing.After ageing,the peak hardness of the alloy with high Y content was higher than that of the alloy with low Y content,which was ascribed to the higher volume fraction ofβ′precipitates formed in high Y containing alloy.However,the tensile strength of the high Y containing alloy was lower than that of the low Y containing alloy,which was ascribed to the residual RE-rich particles.The experimental results indicated that the superior chemical composition was Mg-5.5Gd-3.0Y-1.0Nd-1.0Zr.The ultimate tensile strength and the elongation for this alloy in cast-T6 state were 322 MPa and 4.0%,respectively.The mechanical properties were superior to that of the commercial alloy WE54,with a similar total rare earth content.