Effect Of Modification On Microstructure And Mechanical Properties Of Hypereutectic Mg-5Si Alloy

The inter-metallic compound Mg2 Si in the hypereutectic Mg-5% alloy exhibits many excellent properties such as high melting temperature, low density, high hardness,and low thermal expansion coefficient. Therefore, the hypereutectic Mg-5% alloy is used to be a potential structural material. However, under normal cast condition, the brittle primary Mg2 Si phase in the hypereutectic Mg-5% alloy could cause in the low strength and ductility of the alloys with its coarse dendrite or bulk shape. It is crucial to reinforce the primary Mg2 Si phase effectiveness with controlling and improving its morphology, size and distribution.The effect of Mg-30%(the mass fraction,the same as below)Er、Mg-30Gd、Mg-30Y、Mg-30Ca、Mg-30 Mn inter-metallic compound modify the primary Mg2 Si in the hypereutectic Mg-5% alloy with Optical Microcopy, Scanning Electron Microscopy,X-ray Diffraction and Mechanical Property Test. We have studied the modification effect of difference inter-metallic compound on the morphology, size and distribution of primary Mg2 Si phase in the hypereutectic Mg-5% alloy. In addition, We have thoroughly discussed its metamorphic mechanism through experimental tissue morphology.The result indicated that the type and content of modifier can modify and refine primary Mg2 Si phase effectively in the hypereutectic Mg-5% alloy. Mg-5% alloy presents the basic rules to modify from sub-metamorphism, metamorphose to metamorphic completely. The primary Mg2 Si phase can modify and refine effectively in the hypereutectic Mg-5% alloy with increasing the different inter-metallic compound modifier, Such as 2.0wt.%Mg-30%Er、2.0 wt %Mg-30Gd、1.0 wt %Mg-30Y、2.0 wt%Mg-30Ca、2.0 wt %Mg-30 Mn. The optimum solution to modify primary Mg2 Si phase shows Mg-30%Er as its content added to 2.0 wt %. Primary Mg2 Si phase transforms from coarse dendrite or bulk shape into fine polygon with increasing Mg-30%Er content to 2.0%. Meanwhile, the average size of Primary Mg2 Si phase turns into below 15 um and distribute evenly. The mechanical properties including tensile strength and elongation of Mg-5% alloy achieves 135 MPa and 3.0% induced by the 2.0wt %Mg-30 Ca. In addition to Mg-30 Ca inter-metallic compound, It is reasonable to conclude that the others becomes coarser again or over modification mechanism.