Study On As-Cast Mg-Bi And Mg-Bi-Sn Heat-resistant Magnesium Alloy

At present, magnesium alloy is one of the most important lightest alloys in industrial production. Its application and development potential breadth are important no less than aluminum. It has a low density, easy thermal conductivity, high strength, good mechanical properties and processing advantages of strong electromagnetic shielding capability. Thus magnesium alloys in the automotive industry, aerospace industry, the communications industry has been widely applied. Mg-Bi Bi alloy because alloying elements harmful to humans, strengthening good phase stability, known as the green metal, with good development potential in the development of new biomaterials and heat-resistant magnesium alloy aspects. Mg-Bi alloy is one of the new magnesium alloy has great potential for development, but the alloy low hardness, brittleness. For these shortcomings Mg-Bi alloys in the presence of the processing and use, we use alloying and extrusion methods to improve the mechanical properties of Mg-Bi alloys. At the same time, the effect of heat treatment on microstructure and mechanical properties of Sn on Microstructure of Mg-Bi alloy has been studied in this passage. This article studied the Sn and refinement of the principle of Mg-Bi alloy, the alloy alloy phase formation and strengthening principle and the principle of heat-treated alloy refining organization.Results show that:1) Binary Mg-Bi alloy mainly composed of a-Mg phase and Mg3Bi2composition, morphology Mg3Bi2phase is continuous or semi-continuous network and strip.2) Bi alloy grain refinement is added, the alloy significantly improved, and when the content of bismuth is3%wt, most of fine grain alloy, Mg3Bi2phase is not too thick, then the alloy mechanical achieve the best performance. When the Bi content is further increased, the start of the alloy increases the grain, the second phase also coarsening.3) Mg-Bi-xSn ternary alloy mainly composed of α-Mg, Mg3Bi2and Mg2Sn phase. Mg2Sn phase as the main rule is present in the spherical a-Mg matrix.4) In the Mg-Bi alloy appears after adding Sn to Mg2Sn regular spherical phase, the spherical phase and with increasing Sn content increases. As the grain size of the alloy after the first increase in Sn content decreases while increases. No Sn maximum grain size of the alloy, Sn content of4%, the smallest grains. When the Sn content of6%, slightly coarse grain alloy, but still less than the binary alloy.5) at room temperature and high temperature (200℃), the mechanical properties of tensile strength of two yuan Mg-Bi alloy, elongation and hardness with increasing Bi content with the first and then decreased while, when the content of bismuth mechanical properties for the best3%.6) increase in Sn content, the mechanical properties of tensile strength of Mg-Bi-xSn alloys, elongation and hardness are presented after the first increased and then decreased. With increasing Sn content, the hardness of the alloy showed a decreasing trend after the first rise, reaching the highest value53HV when Sn element content of4%, the further increase of Sn content in the alloy hardness began to decrease in the Sn content of6%When reduced51.9HV; under normal condition, with the increasing of Sn content, the tensile strength and elongation of the alloy are presented after the first increased and then decreased. In the Sn content of4%, the tensile strength and elongation of the alloy reached the maximum131MPa and6.3%, respectively. Compared with the matrix alloy, increased by51MPa,2.8%, performance is improved significantly. Under200℃, Sn is added in an amount of4%optimum tensile properties, a tensile strength of112MPa, the relative increase of the matrix alloy44MPa, elongation, but did not change significantly. Based on the above analysis, the addition of Sn element for optimum mechanical properties4%. This is the grain boundary strengthening, the results of the second phase precipitation strengthening of the role.7) tensile fracture alloy analysis showed that:Mg-Bi alloy and tensile fracture mode of Mg-Bi-Sn alloys are subject to cleavage fracture;morphology of the fracture is determined by the dissociation step, cleavage crack,tear edge, and together constitute the dimple quasi-cleavage fracture. Sn alloy elements join, significantly improved the tensile fracture morphology of Mg-Bi alloy, and when Sn element content of4%, the most significant improvement in results. Mg-Bi-xSn alloy high temperature tensile fracture surface relative to the room temperature tensile fracture, the level was significantly higher.