Effect Of Sn, Pb And Zr Elements On Microstructures And Mechanical Properties Of Magnesium Alloy

In this paper, the development of high formability of magnesium alloy for research background, based on both the existing research results and existing problems, and in order to improve the strength and toughness of magnesium alloys as the main line to proceed from the control of alloy composition, microstructure and properties, the gas stir melting process and method of metal type casting were used to produce magnesium alloys of Mg-Sn system, Mg-Sn-Pb system and Mg-Sn-Pb-Zr system. The effect of Sn, Pb, and Zr elements on microstructure and mechanical properties of magnesium alloy at room temperature were studied, and fracture mechanism of experiment alloys were also studied. The Gleeble-3500 thermal-mechanical simulation tester was used to study thermal compressive deformation behavior of experiment magnesium alloys, and the plastic deformation behavior of the alloy were comparison analyzed.As-cast organization of Mg-x Sn(x=2,4,6,8) alloys were composed by α-Mg and Mg2 Sn phase. The microstructure of pure magnesium was changed by the addition of Sn. The microstructure and properties of Mg-4Sn alloy were most optimal, its tensile strength and elongation rate reached 112.9 MPa and 10%, respectively. The fracture mode of Mg-4Sn alloy exhibited the characteristic of quasi-cleavage fracture.After Pb element was added into Mg-4Sn alloy, the microstructure of as-cast alloys consist of α-Mg and Mg2 Sn phase. The addition of Pb element can inhibit the precipitation of Mg2 Sn phase on the boundary, reduce the amount of Mg2 Sn phase and change the morphology of Mg2 Sn phase to short rod-shaped. Pb element dissolves in α-Mg matrix and exists in the Mg2 Sn phase. When the Pb content is 2.5%, the tensile strength and elongation rate of the test alloy are better than that of Mg-4Sn alloy, reached 114.05 MPa and 12.48%, respectively, while the hardness of Mg-4Sn alloy is reduced by addition of Pb,the fracture mode of Mg-4Sn-2.5Pb alloy exhibited the characteristic of quasi-cleavage fracture.After Zr element was added into Mg-4Sn-2.5Pb alloy, the microstructure of as-cast alloys consist of α-Mg, Mg2 Sn and Zr phase. The addition of Zr element did not significantly refine the grain size, and there were trend that make precipitates along the grain boundary precipitate like mesh. When the Zr content is 1.0%, the grain size of magnesium alloy were slightly refined, and the tensile strength and hardness of the alloy were improved, while the elongation dropped significantly, the fracture mode of Mg-4Sn-2.5Pb-1.0Zr alloy exhibited the characteristic of cleavage fracture.The results of hot compression experiment showed that high temperature compression flow process of Mg-4Sn、Mg-4Sn-2.5Pb and Mg-4Sn-2.5Pb-1.0Zr alloy all can be described as work hardening and dynamic softening stage, and the same change trend were presented between peak stress and strain rate, deformation temperature: With the increase of strain rate increases, and decreases with the increase of temperature, showing the characteristics of positive negative temperature-sensitive strain rate. The constitutive relations of three kinds of alloys can be described by the hyperbolic sine function including Z parameter. The apparent activation energy of Mg-4Sn-2.5Pb alloy were higher than the other two, which is 171.2 k J/mol.