Effect of Rare-Earth Element Y on the Microstructure and Mechanical Properties of the Mg-6.0wt.%Zn-0.5wt.%Zr Alloy

The extruded Mg-6.0wt.%Zn-0.5wt.%Zr (ZK60) alloys with 0.5wt.% and 1.0wt.% Y additions were prepared. The microstructures and tensile properties of the alloys aged in different conditions were investigated. The results show that the specimen with 1.0wt.% Y additions and aged at 453K for 15 h had the best tensile strength. The ultimate tensile strength and yield strength reached 365MPa and 352MPa, respectively. The grain refinement, the formation of the fine dispersed Mg-Zn particles and the W-Mg3Zn3Y2 ternary phase may be the main reasons for the improvement. The average grain size reached to ~ 3μm. The size of the fine and dispersed particles was only several nanometers and the particle number density (Nv) was very high. The crystallographic characteristics of the ternary W-Mg3Zn3Y2 phase were studied by the transmission electron microscope and selected area electron diffraction techniques. The crystallographic orientation relationship between the W phase and the α-Mg matrix is identified as: [2 0]α//[ ]w, (0002)α plane near parallel to the (220)w plane with a 3.5 degree angle difference. This orientation relationship has rarely been studied and reported.