Effects Of Y, Bi Elements On Microstructure And Properties Of Sn-containing AZ80 Magnesium Alloys

In this paper, the development of low cost, high strength of AZ series wrought magnesium alloys as the experimental research background. AZ80-2Sn alloy as the base alloy, Y and Bi elements were added in the base alloy by using the method of alloying, then conducts the research on the microstructure and mechanical properties of as cast and extruded alloy, and with the help of OM, SEM, EDS, XRD and mechanical property test to further explore its influence mechanism, to look forward to design and development of high strength wrought magnesium alloy research group need.The results of the study show that, by adding appropriate amount of Y and Bi elements not only can improve the microstructure of the as cast and extruded alloy, but also can significantly improve the mechanical properties of as cast and extruded alloy.The microstructure of as cast AZ80-2Sn alloy is mainly consisted of α-Mg phase, Mg17Al12 phase and Mg2 Sn phase. The addition of Y element in the alloy, the emergence of a new Al2 Y phase, with the increase of Y content, the amount of Al2 Y phase is increased and the dimension of that is enlarged. At the same time, Mg17Al12 eutectic phase in the alloy by semicontinuous network becomes discontinuous dispersed phase, the marked decrease in the number, dimension is also reduced. But there has no obvious effect on grain refinement with Y addition. With the increase of Y content, the tensile strength and elongation of the as cast alloy are showing a trend of increased first and then decreased. When the adding amount of Y element in the alloy is 0.5%, the tensile strength and elongation reaches the maximum value, 215.1MPa and 8.2% respectively. Compared with the AZ80-2Sn alloy without addition of Y element, the tensile strength of AZ80-2Sn-0.5Y alloy is improved by 18.9%, and the elongation is increased by 49%.The microstructure of as-extruded AZ80-2Sn alloy is mainly consisted of α-Mg phase and a small amount of Mg17Al12 phase. And the microstructure of Y-containing extruded alloy is mainly composed of α-Mg phase, Al2 Y phase and a small amount of Mg17Al12 phase. Microstructure after hot extrusion significantly smaller than grains of as cast. When the Y content is 0.5%, the microstructure of the as-extruded AZ80-2Sn-0.5Y alloy is uniform and the average grain size is the minimum. With the increase of Y content, the tensile strength, yield strength and elongation of the as-extruded alloy are showing a trend of increased first and then decreased. When the Y content is 0.5%, the tensile strength and elongation of alloy reached the best value, 368.1MPa and 12.9% respectively, while the yield strength was raised to 241.3MPa. Compared with the AZ80-2Sn alloy without Y, the tensile strength, yield strength and elongation of the as-extruded AZ80-2Sn-0.5Y alloy were improved by 5.8%, 5.3% and 33.7% respectively, which reached the optimal comprehensive mechanical properties.The addition of Bi element in the alloy, the emergence of a new Mg3Bi2 phase, then the test alloy is mainly consisted of a-Mg matrix, Mg17Al12 phase, Mg2 Sn phase and Mg3Bi2 phase. At the same time, after the addition of Bi element, microstructure can be effectively refined, and with the increase of Bi content, the average grain size of the alloy decreases. In addition, after the addition of Bi element, the amount of semicontinuous network Mg17Al12 phase is decreased and the amount of discrete Mg17Al12 phase is increased. With the increase of Bi content, the tensile strength, yield strength and elongation of the as-extruded alloy are showing a trend of increased first and then decreased. When the adding amount of Bi element is 1%, the comprehensive mechanical properties of the test alloys is the best, the tensile strength, yield strength and elongation were 225.4MPa, 116.2MPa and 8.8% respectively. Compared with the AZ80-2Sn alloy without addition of Bi element, the tensile strength of AZ80-2Sn-1Bi alloy increase rate is 22.9%, the yield strength increased by 11.2%, and the elongation increases reached 69.2%.The microstructure of Bi-containing extruded alloy is mainly consisted of α-Mg phase, Mg17Al12 phase and Mg3Bi2 phase. When the Bi content is 0.5%, the microstructure of extruded alloy is uniform, grain is significantly refined, and the average grain size is about 12μm. In addition, squeezed broken fine Mg17Al12 phase and Mg3Bi2 phase is dispersed in the matrix. When the adding amount of Bi element in the alloy is 0.5%, the comprehensive mechanical properties of extruded alloy achieve the best, the tensile strength, yield strength and elongation were 379.6MPa, 247.1MPa and 14.8% respectively. Compared with the as-extruded AZ80-2Sn alloy without addition of Bi element, tensile strength of AZ80-2Sn-0.5Bi alloy is increased by 8.7%, the yield strength increased by 7.5%, and the elongation increases reached 54.2%.