Study On The Microstructures And Mechanical Properties Of Mg-Zn-Y-Zr-xSb Alloys

The microstructure and mechanical properties of the as-cast and heat-treatedMg-Zn-Y-Zr-xSb alloys were investigated in this paper, through optical microscope（OM）, scanning electron microscope （SEM）, tensile testing et al. The casting ofmagnesium alloys is casted via suction casting. Element Sb and Y play a key role on themicrostructure and mechanical properties of Mg-6Zn-Y-0.6Zr-xSb alloys. They can alsochange the formation of the main second phase.The grain size of Mg-6Zn-1Y-0.6Zr-xSb alloy, comparing with gravity casting, isgreatly refined. Its grain size decreased from200μm to40μm. The results show that themicrostructures of Mg-6Zn-1Y-0.6Zr-xSb alloys are mainly composed of α-Mg matrix,I-phase （Mg₃YZn₆） and Mg₃Sb₂-phase. With the adding of Sb, these grain boundaryprecipitates are breaked and likely to refined into sphericals, and become short. Theseprecipitates distribute in the structure. The tensile strengths and yield strengths areimproved with the adding of element Sb. The failure mode of the facture surface isbrittle cleavage fracture.The microstructure of Mg-6Zb-3Y-0.6Zr-xSb alloys is mainly composed of α-Mgmatrix, I-phase （Mg₃YZn₆）, W-phase （Mg₃Y₂Zn₃） and Mg₃Sb₂-phase. Comparing withMg-6Zn-1Y-0.6Zr-xSb alloys, w-phase is newly formed, and YSb-phase is found inMg-6Zb-3Y-0.6Zr-1.4Sb alloy. Grain boundary precipitates of Mg-6Zb-3Y-0.6Zr-xSballoys are coarsened, comparing with those of Mg-6Zb-1Y-0.6Zr-xSb alloys. The effectof Sb on the microstructure of Mg-6Zb-3Y-0.6Zr-xSb alloys is similar to that ofMg-6Zb-1Y-0.6Zr-xSb alloys.After T6heat-treated, grain boundary precipitates of these magnesium alloys arepartially melting, refined and are soluted in the α-Mg matrix. Grain sizes are increasedquickly and obviously. Although the phase composition of T6heat-treated magnesiumalloy is the same to that of the as-cast magnesium alloys, XRD peaks of the secondphases are decreased. As to Mg-6Zn-1Y-0.6Zr-1.4Sb alloy, after T6heat treatment, itstensile strength reaches238.2MPa, the yield strength166.9MPa.After T6heat-treated， the magnesium alloy， its mechanical properties areobviously improved. Of Mg-6Zn-3Y-0.6Zr-1.2Sb alloy, the tensile strength ofMg-6Zn-3Y-0.6Zr-1.2Sb alloy reaches250.5MPa, the yield strength reaches172.6MPa,whereas, the elongation of Mg-6Zn-3Y-0.6Zr-1.2Sb alloy is decreased. The fracture mechanisms are brittle fractures.