Effect of Er-Ba Composite Modification on Microstructure and Mechanical Properties of Mg-2.5Si-4Zn Cast Alloy

The enhanced phase Mg2Si in the magnesium alloy can significantly improve the hardness, wear resistance, especially high temperature creep resistance. But the Mg2Si phase of the as-cast hyper-eutectic Mg-Si alloy will seriously cut the alloy matrix because of the coarse angular shape of the primary Mg2Si and complex Chinese script morphology of the eutectic Mg2Si. In order to improve the properties of Mg-2.5Si-4Zn alloy, the modification experiments of adding Er/Er-Ba were performed and the effects on the alloy microstructure and Mg2Si phase were investigated by the optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffractometer (XRD). The mechanical properties were measured and analyzed by the computer-aided electric-loaded tensile tester. The results show that with the addition of 0.6wt% Er to the Mg-2.5Si-4Zn alloy, the primary Mg2Si in the microstructure transforms from a coarse dendritic shape into a regular tetragonal block shape, while the eutectic Mg2Si transforms from a coarse Chinese script type to a more complex short rod shape. When adding 0.8wt% Ba subsequently, the primary Mg2Si further transforms from a regular tetragonal bulk shape to an irregular fine bulk shape with grooves and holes, and the eutectic Mg2Si has an obvious refining effect and is diffusely distributed with the dot/short-line shape in the alloy matrix. The best metamorphic effect is obtained by adding 0.6wt% Er and 0.8wt% Ba. The mechanical properties of the Mg-2.5Si-4Zn alloy modified by Er-Ba composite modifier are significantly improved, with the tensile strength s b and elongation d increasing to 168 MPa and 5.04%, respectively.