Effects Of Alloy Elements On Microstructure And Mechanical Properties Of Mg-Sn Alloys

The microstructure and phase constituent of Mg-Sn-Ca-Cu and Mg-Sn-Zn-Ca alloys in as-cast condition and aging condition were examined by optical microscopy (OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The mechanical properties of the alloys were tested by Vickers-hardness tester and universal electronic material testing machine. The fracture surfaces were analysized by using SEM. The important results are summaried as following:After rapid quenching, the solidficiation structures of Mg-3Sn-2Ca-xCu (x=1,3,5) alloys are refined, the morphology of CaMgSn phase is changed from coarse long-bar to short strip; after rapid quenching and aging treatment, the morphology of CuMg2 phase at grain boundaries is changed from lath-shaped to round-shaped. After aging for 48h, CaMgSn phase in Mg-3Sn-2Ca-3Cu alloy become nearly spherical. When the Cu content increases to 5wt%, the matrix has been significantly refined, but the white circle CuMg2 phase grows up and the inoxidizability of alloy decreases. After rapid quenching and aging treatment, the Vickers-hardness value of Mg-Sn-Ca-Cu alloys increase and then decrease. The highest Vickers-hardness value are 85,76 and 79, respectively.The phases of as-cast Mg-5Sn-5Zn-xCa (x=3,5,7) alloys are:α-Mg, CaMgSn and Mg2Ca. Mg2Ca phase has two forms:intra-grain particle and the platelike phase at grain boundaries. With the increase of Ca, two forms of Mg2Ca phase both increase. The tensile strength of as-cast Mg-Sn-Ca-Cu alloys are 214 MPa,278 MPa and 254 MPa, respectively. The elongation of the alloys are 2.78%,4.54% and 3.97%, respectively. Mg-5Sn-5Zn-5Ca alloy has the highest tensile strength and elongation.After solution heat treatment at 400℃for 4h and aging treatment at 180℃for 16h, almost all the eutectic microstructure of Mg-5Sn-5Zn-xCa (x=3,5,7) alloys dissolve, Mg2Ca phase mainly become granular. CaMgSn phase mainly became bar. As the content of Ca increase, the microstructure of alloys are defined. Ca2Mg6Zn3 phase is precipitated from the grain boundaries of Mg-5Sn-5Zn-5Ca and Mg-5Sn-5Zn-7Ca alloy. After heat treatment, the tensile strength of Mg-Sn-Ca-Cu alloys are 240 MPa,296 MPa and 334 MPa, respectively. The elongation are 4.39%,8.56% and 7.40%, respectively. Mg-5Sn-5Zn-7Ca alloy shows ideal tensile strength and good deformation ability, it has the best comprehensive mechanical properties.