Microstructural Evolution And Mechanical Properties Of Wrought ATZ821-Y Alloy

As the promising lightest engineering structural metallic material,magnesium and its alloys have many excellent properties such as low density,high specific strength,high specific stiffness,good damping performance and easy recovery,which have attracted significant attention in aerospace,automobile,communication fields and in terms of energy conservation,environmental protection.Compared with cast magnesium alloys,wrought magnesium alloys have more excellent mechanical properties.Among the wrought magnesium alloys developed up to now,AZ80 wrought magnesium alloy have been widely used in industrial applications due to their relatively low cost,moderate strength and ductility.However,compared with the wrought aluminum alloys that have been widely commercial applied,there is still a large gap in the comprehensive mechanical properties of the AZ80 wrought magnesium alloy.Recent studies have found that the addition of proper amount of Sn can significantly improve the strength of Mg-Al-Zn alloys.Moreover,the addition of rare earth elements and non-rare earth elements can effectively weaken the texture of wrought magnesium alloys and improve the ductility of alloys.Therefore,through the design and optimization of alloy composition,the Mg-AI-Sn-Zn-Y wrought magnesium alloy with high strength and ductility was successfully prepared by traditional extrusion and new hard plate rolling(HPR)process in the present work.In this study,the influence of Y addition on the microstructural evolution and mechanical properties of extruded and HPRed ATZ821 alloy was studied;the alloy composition and HPR process were optimized;the relationship between microstructure and mechanical properties was discussed;and the intrinsic mechanism of high strength and ductility wrought ATZ821-Y alloy was revealed.The main conclusions of this study are as follows:(1)The influence of Y addition on the microstructural evolution and mechanical properties of extruded ATZ821 alloy was studied.It was found that Y addition has a certain refinement effect on the microstructure;the grain size was refined form～35μm to～24 μm,and effectively weakened basal texture,improved comprehensive mechanical properties of the alloy.In particular,when 1.0 wt.%Y was added,the optimized comprehensive mechanical properties of the alloy was achieved,where the yield strength,ultimate tensile strength and elongation were 201 MPa,355 MPa and 27%,respectively.(2)It was revealed that the increased yield strength of extruded ATZ821-1.0Y alloy was mainly attributed to the relatively fine grain size and the dispersed high volume fraction second phases(Mg17Al12,Mgzsn and Al2Y);in addition,the high ductility was the main result of grain refinement,second phase strengthening and texture weakening.(3)The influence of Y addition on the microstructural evolution and mechanical properties of cast-HPRed ATZ821 alloy was studied.It was found that the microstructure of the alloy gradually evolved from a mixed crystal structure to a uniform crystal structure with increasing Y content.In particular,when 1.0 wt.%Y was added,the yield strength,ultimate tensile strength and elongation reached 208 MPa,360 MPa and 19.8%,respectively.It was revealed that the excellent comprehensive mechanical properties should be attributed to the grain boundary strengthening,second phase strengthening,and texture weakening.(4)The influence of Y addition on the microstructural evolution and mechanical properties of extruded-HPRed ATZ821 alloy was studied.It was found that the microstructure gradually evolved from a mixed crystal structure to a uniform fine grain crystal structure with increase of Y content.Especially,when 1.0 wt.%Y was added,the yield strength,ultimate tensile strength and elongation increased to 248 MPa,385 MPa and 19.6%,respectively.The excellent comprehensive mechanical properties was mainly the result of the combination of finer grains,dispersed fine Mgl7Al12,MgZSn and Al2Y second phases and the basal texture weakening.