Effect of Nd and Yb on the Microstructure and Mechanical Properties of Mg-Zn-Zr Alloy

摘要:

研究了稀土元素Nd、Yb对Mg-5.5Zn-0.6Zr合金组织与性能的影响。结果表明：单独添加Nd或Yb元素后，试验合金的组织明显细化，同时在晶界处形成了γ ((Mg, Nd)Zn2) 或γ ((Mg, Yb)Zn2) 三元稀土相；而复合添加Nd和Yb元素后，试验合金的组织不但没有细化，而且在晶界处形成了呈网状分布的γ ((Mg, Nd+Yb)Zn2) 四元稀土相，并且晶界变宽。经过T4固溶处理后，Mg-5.5Zn-0.6Zr合金中的共晶组织完全溶入基体，而添加Nd、Yb元素后的Mg-5.5Zn-0.6Zr合金晶界处仍有未溶的化合物相存在。其中，添加Yb元素后的Mg-5.5Zn-0.6Zr合金经固溶处理后在晶界处形成了一种新的Mg-Zn-Yb三元球状颗粒相，其常温下的抗拉强度、屈服强度和伸长率分别达到了255.6 MPa、163.6 MPa和17.4%，这主要是因为加入稀土元素Yb后固溶处理产生了复合强化效果。在高温条件下，复合添加稀土元素Nb、Yb后的试验合金具有很好的热稳定性，但其高温塑性比较差。

Abstract:

The effects of neodymium (Nd) and ytterbium (Yb) on the microstructures and tensile properties of Mg-5.5Zn-0.6Zr alloy were investigated. Results show that an addition of Nd or Yb both brings about the precipitation of a new γ (Mg, Nd) Zn2 or γ (Mg, Yb) Zn2 eutectic phase and results in a refinement in dendritics. However, the combination addition of Nd and Yb has an opposite effect on dendritics and leads to the formation of γ (Mg, Nd+Yb) Zn2 eutectic phases in the shape of network-like, even the lamellar eutectics are somehow thickened. After T4 solution treatment, the eutectic structure in Mg-5.5Zn-0.6Zr alloy is fully dissolved into the matrix while there are still some undissolved compounds at grain boundaries in Mg-5.5Zn-0.6Zr alloy with Nd and Yb addition. A new ternary phase Mg-Zn-Yb appears in Mg-5.5Zn-0.6Zr alloy containing Yb, which is formed at dendrite boundaries after solution treatment. The tensile test results indicate that the tensile strength, yield strength and the elongation are about 255.6 MPa, 163.6 MPa and 17.4%, respectively, at room temperature. This is mainly attributed to combined strengthening factors induced by Yb addition. At the elevated temperature, the Mg-5.5Zn-0.6Zr alloy with addition combination of Nd and Yb has a good performance in thermal stability, but inferiority in elongation.