Influence Of Sm、Bi、Zn And Die-casting Process On Microstructures And Mechanical Properties Of Mg-6Al Magnesium Alloy

The purpose of the research is to develope of a new low-cost, high-strength rare-earth heat-resistant magnesium alloy by improving the heat resistance of Mg-Al based alloys. The effect of Bi、Zn and rare earth Sm on microstructures and mechanical properties of Mg-6Al magnesium alloy have been investigated by optical microscopy, scanning electron microscopy, X-ray diffractometer and electronic tensile test.And the effect of the die-casting on microstructure and mechanical properties of the cast alloys has been investgated. The results show that:The appropriate amount addition of Sm, Bi, and Zn has significantly improved the as-cast microstructures and mechanical properties of Mg-6A1alloy at room temperature and high temperature. The die-casting has improved the microstructures and mechanical properties of Mg-6A1alloy.For the Mg-6A1magnesium alloy with0.5wt%-3.0wt%Sm, cast microstructures appear dispersed phase Al2Sm, distributing in the grain boundary and grain interior. With increasing content of Sm, the tensile strength and elongation first increase, then decrease. At room temperature, when content of Sm is1.Owt%, the mechanical properties and elongation are up to the maximum,i.e.220MPa、12.5%. At high temperatures, when the content of Sm is1.Owt%, the mechanical properties and elongation are169MPa and25.5%,respectively.For Mg-6Al-1Sm alloy with0.5～1.5wt%Bi, the Mg17Al12phase reduces, and Mg3Bi2and Al2Sm phases have formed. With increasing content of Bi, Mg3Bi2and Al2Sm phases become thick, produce segregation partly. At room temperature, the effect of Bi on tensile strength and elongation is not obvious. At high temperature (150℃), Bi significantly improves tensile strength and elongation. When content of Bi is0.75wt%,the tensile strength and elongation reaches maximum184MPa and23.5%For the Mg-6Al-1Sm alloy with0.5～1.5wt%Zn, Mg17Al12phases have incresed, and distrubuted along the grain boundaries. Zn solid solution in the matrix or other second phases. At25℃and150℃, with increasing content of Zn, tensile strength first increase, then decrease. At25℃, the mechanical properties of the cast-alloy which added0.5wt%Zn are up to its maximum235MPa; At150℃, the mechanical properties and elongation reaches their maximum175MPa and20.0%. The elongation is improved abviously.Die-cast alloy tissue is more dense than the cast alloy, the finer the grain, the higher tensile strength. Sm element can effectively reduce the number of pores and inclusions in the alloy die-casting. Mg-6Al-1Sm alloy has the best room temperature tensile properties, i.e. tensile strength285MPa, elongation16.5%. At150℃Mg-6Al-1sm-0.5Zn have the best comprehensive properties, and its elongation is17.5%, which increased by118%.The flow properties of the experimental cast alloys are better than AZ91D, Mg-6Al-1Sm-1.0Zn has the best liquidity,up to520mm. Flow properties of die-cast alloy are close to AZ91D, the flow length of Mg-6Al-1Sm-0.5Bi and Mg-6Al-1Sm-1.0Bi are2420mm and2390mm respectively.