Effect Of Y And Sm On Microstructure And Mechanical Properties Of Mg-7Al-1Ca Alloy

As a new structural material,magnesium alloy has a good application prospect in automobile,aerospace and other fields due to its low density and good specific strength and stiffness.However,compared with traditional steel materials,poor mechanical properties limit its wide application.Alloying is an effective way to solve these problems.In this study,Mg-7Al-1Ca-x Y-y Sm（x=0,0.4,0.7,1.0,1.3 wt.%）alloys with different states were prepared by adding rare earth elements Y and Sm（Y:Sm=2:1）to Mg-7Al-1Ca alloy in a medium proportion.The microstructure observation and mechanical properties test were carried out to analyze the mechanism of Y and Sm in it,and a new ratio and superior performance of rare earth magnesium alloy was explored.The results show that after the addition of Y and Sm in the as-cast Mg-7Al-1Ca magnesium alloy,the microstructure of the alloy changes and gradually changes to equiaxed grains.While the rare earth phases Al₂Y and Al₂Sm are formed,the appearance and number of the second phase have changed,and the grain size is also refined.After adding Y and Sm,the mechanical properties of as-cast alloy also change.When the total content of Y and Sm reaches 1.05 wt.%,the tensile properties and hardness of the alloy reach the best,the tensile strength is 187.7 MPa,the elongation is6.4%,and the microhardness is 69.92 HV.When the content exceeds 1.05 wt.%,the microstructure and properties of the alloy do not continue to improve,but have a tendency to deteriorate.The extruded Mg-7Al-1Ca-x Y-y Sm alloy is prepared by heat treatment and forward hot extrusion of the as-cast alloy.After analysis and testing,the average grain size of the extruded alloy is much smaller than that of the as-cast alloy.After adding Y and Sm,the grains of the alloy are further refined,the second phase changes significantly,and the rare earth phases Al₂Y and Al₂Sm are uniformly distributed after extrusion.When the total content of Y and Sm reaches 1.05 wt.%,the room temperature tensile properties and hardness of the alloy reach the best,the tensile strength is 285MPa,the elongation is 8.3%,and the microhardness is 78.03 HV.When exceeding this content,the extruded alloy shows a basically consistent trend with the as-cast alloy,and the microstructure and properties of the alloy do not continue to improve,but have a tendency to deteriorate.The tensile test of the extruded alloy is carried out at three temperatures（150°C,200°C,250°C）.The results show that the higher the temperature,the better the elongation and the worse the tensile strength of the alloy.Compared with the fracture morphology of room temperature tensile,the number of dimples increase significantly.The EBSD analysis of the extruded alloys with three components showed that the addition of Y and Sm has a certain influence on the Schmid factor,recrystallization degree and texture of the alloy.When the addition amount of Y and Sm is 1.05 wt.%,the recrystallization degree of the alloy is 82.5%,and the Schmid factor on the cylindrical surface increases,showing a better cylindrical slip system activation ability.According to the pole figure（PF）and inverse pole figure（IPF）,the addition of Y and Sm（1.05 wt.%）increases the basal texture intensity of the alloy and the average angle of local misorientation.When the content of Y and Sm reaches 1.95 wt.%,the basal texture begins to decrease.