| As a kind of metal structural material,duo toits light weight,good recyclability and high specific strength,magnesium alloy has attracted wide attention and has been used in aviation,automobile manufacturing and other fields.However,with the HCP crystal structure magnesium usually shows low plasticity,which limits its application as structural materials.In order to improve the plasticity of magnesium alloys,people have studied various methods,such as heat treatment,which can improve the plasticity of magnesium alloys,but at the cost of the strength.Therefore,it is of great significance for the application of magnesium alloys to improve the plasticity of magnesium alloys without sacrificing strength.Cryogenic treatment refers to the material in the environment of-130 °C to-190 °C to keep warm for a period of time to optimize the material structure and performance of the method.This method can not only improve the dimensional stability,wear resistance,corrosion resistance and other properties of the workpiece,but also extend the service life of the workpiece,so it is widely used in the production of tool steel,high-speed steel and cemented carbide.However,the study of the microstructure and property changes of magnesium alloy after cryogenic treatment is still in the exploratory stage,and there are relatively few existing results.In this paper,the extruded Mg-Sn-Ca-Mn-Zn/Al alloy was prepared by adding Zn/Al elements to the Mg-Sn-Ca-Mn-Mn-based alloy.The effect of cryogenic treatment(-196°C)on the microstructure and mechanical properties of the alloy was studied,and the influence of cryogenic treatment on the microstructure and properties of magnesium alloy was explored.The specific results were as follows:(1)By adding alloying elements,the influence of Al and Zn elements on the microstructure and mechanical properties of extruded Mg-Sn-Ca-Mn alloy was studied.The results show that the addition of an appropriate amount of Al/Zn elements can promote the precipitation of the second phase in the alloy,and the grain size of the alloy sample will decrease with the increase of Al addition,thereby improving the microstructure and mechanical properties of the alloy.After the addition of elements,the YS,UTS and EL of the alloy with an element addition amount of 1.5Al(wt.%)reached 273.5MPa,291.1MPa and 13.07%,respectively,and the YS,UYS and EL of alloys with 1.0Zn(wt.%)added elements reached 217.8MPa,254.2MPa and 22.38%,respectively.(2)The microstructure and mechanical properties of the alloy with the addition amount of 1.5Al(wt.%)after different cryogenic treatment times were studied,and it was found that after cryogenic treatment,the volume fraction of the second phase(Ca Mg Sn phase)in the alloy increased,the grain size was refined from 2.31μm to 1.86μm,and the grain orientation rotated from [112—0] to [101—0].After 18 h cryogenic treatment,the YS,UTS and EL of the alloy samples were 289.1MPa,304.3MPa and 19.15%,respectively,which were increased by 5.7%,4.5% and 46.5% compared with the alloy without cryogenic treatment.(3)The influence of cryogenic treatment on the microstructure and mechanical properties of alloy with an addition amount of 1.0Zn(wt.%)was preliminarily revealed.It is found that the volume fraction of the precipitated phase in the alloy increases after cryogenic treatment,and the alloy is mainly composed of Ca Mg Sn phase,nanoscale Mg2 Sn phase and nanoscale β-Mn phase.After cryogenic treatment,the diffraction peak intensity of the α-Mg matrix changed,and the grain orientation rotated from [101—0] to [112—0].As the cryogenic time increases,the grain size is refined from 3.28 μm to 2.81 μm.After 18 hours of cryogenic treatment,the tensile properties of the alloy samples were the best,and the YS,UTS and EL at this time were 222.6MPa,275.3MPa and 28.54%,respectively,which were 2.2%,8.3% and 27.5% higher than the alloy without cryogenic treatment.The analysis showed that the reduction of the grain size of the alloy and the precipitation of a large number of second phases after cryogenic treatment could make the alloy samples show better mechanical properties. |
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