Microstructure And Properties Of High-Strength As-cast Magnesium Alloys

Two sets of alloy were designed in this paper. The first set of alloy are Mg-2Cu-7Zn-0.7Mn-ωY (ω= 0,1,3), the second set of alloy are Mg-3Cu-6Al-8Zn-1.5Mn-3Ca-Si, Mg-3Cu-6Al-8Zn-1.5Mn-5Ca-Si and Mg-6Al-8Zn-1.5Mn-5Ca-Si.The alloys were prepared by DSL-300 vacuum induction furnace under the argon atmosphere.The microstructure and phase constituent were examined by optical microscopy(OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The Vickers-hardness of the alloys were tested by digital Vickers-hardness tester. The mechanical properties of the alloys were tested by universal electronic material testing machine. The important results are summaried as following:(1) With the content of Y increases, the microstructure of Mg-Cu-Zn-Mn-Y alloys are optimized. It shows that Y has a better effect on grain refinement. The second phase of natural cooling Mg-2Cu-7Zn-0.7Mn alloy are mostly coarse CuMgZn phase, which is continuous network. The phases of natural cooling Mg-2Cu-7Zn-0.7Mn-3Y alloy are:α-Mg, Mg3Y2Zn3 and Mg2Zn3. Mg3Y2Zn3 phase, which exist in natural cooling alloy, rapid quenching alloy and alloy after aging treatment, improved the morphology and mechanical properties of alloys. The addition of Y element can also improve the hardness, tensile strength and plasticity. When aging time is 50h, the HV value of Mg-2Cu-7Zn-0.7 Mn-3Y alloy is the maximal,95. Tensile strength and elongation are 348MPa and 10.2%, respectively.(2) In the series of natural cooling Mg-Zn-Al-Cu-Ca-Mn-Si alloys, the second phase is tough CaMgSi phase. The phase composition of natural cooling Mg-8Zn-6Al-3Cu-3Ca-1.5Mn-1Si are:a-Mg, Mg2Cu6Al5, CaMgSi and Mg2Zn3. After aging treatment, small blocky CaMgSi phase precipitate. As the aging time increase, the Vickers-hardness of three kinds of alloys all firstly increase and then decrease. When aging for 10 hours, the HV value of Mg-8Zn-6Al-3Cu-3Ca-1.5Mn-1Si alloy reaches the highest-111. When aging for 50h, the highest HV value of Mg-8Zn-6Al-3Cu-5Ca-1.5Mn-1Si and Mg-8Zn-6Al-5Ca-1.5Mn-1Si alloy are 107 and 103, respectively. When aging for 10 hours, the tensile strength and elongation of Mg-8Zn-6Al-3Cu-3Ca-1.5Mn-1Si are the highest in the three alloys, they are 380 MPa and 8.6%, respectively.