Microstructure And Mechanical Properties Of Mg-Ho Based Alloys

The addition of rare earth elements into Mg alloys are one of the most effective methods to imporve the mechanical properties of magnesium alloys at high temperature. The as-cast magnesium alloys containing rare earth take more than 50% in total magnesium alloys developed in the world, which makes the rare earth magnesium alloys take special place in the heat resistant magnesium alloys. There are plentiful magnesium and rare earth resourcces in China, which provides advantages in researching and developing excellent rare earth magnesium alloys with the acceptable cost.In the present work, Mg-10Ho-0.6Zr-xRE(x = 0 6, RE = Ce, Nd, Y) and Mg-3Zn-0.6Zr-xHo (x = 3, 5, 7) alloys were prepared by metal mould casting technique and the microstructures,age hardening behavior and mechanical properties were investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), inductively coupled plasma (ICP) and standard test machine etc.The results indicated that the grain size of Mg-xHo alloys decreased with increasing Ho content. Mg-10Ho alloy exhibits the best mechanical properties. Thus, the Mg-10Ho system is considered to develop new alloys. The effects of rare earth elements (Ce, Nd and Y) on microstructures and mechanical properties Mg-10Ho alloy are investigated. It can be seen that the maximum ultimate tensile strength and yield strength were obtained in the Mg-10Ho-0.5Ce-0.6Zr alloy at peak-aged state, and the values are 199 MPa, 132 MPa at room temperature. These values are about 1.1 times higher than that of as-cast alloy. The Mg-10Ho-3Nd-0.6Zr alloy set out the best heat resistant property and the Mg-10Ho-5Nd-0.6Zr alloy exhibit remarkable age hardening response and excellent mechanical properties. The ultimate tensile strength and yield strength at peak hardness of Mg-10Ho-5Nd-0.6Zr alloy are 323 MPa and 212 MPa at RT and about 258 MPa and 176 MPa at 250℃, respectively. These values are about 1.3 1.4 times higher than that of as-cast alloys.The effects of heavy rare earth element Y on microstructure and mechanical properties Mg-10Ho alloy are examined. The age hardening behavior is obvious but the ultimate tensile strength and yield strength at peak hardness changed slightly.The hardness of the as-cast Mg-3Zn-xHo-0.6Zr (x = 3, 5, 7) alloys are increased but the tensile strength and yield strength tended to reduce, which is mainly attributed to the distributed coarse and brittle Mg₃Ho₂Zn₃ phase.