Effect Of Equal Channel Angular Pressing On Microstructure And Properties Of ZA52-2Sn Alloys

The wrought magnesium alloy can achieve better comprehensive performance than the as-cast magnesium alloy by dynamic recrystallization,and can meet the performance requirements of different fields,such as automobile,aerospace industry and other fields.The solid solubility of Sn in Mg varies greatly with temperature,forming a thermally stable Mg₂Sn phase,which makes Sn-containing magnesium alloy have great potential in developing high strength properties.In this paper,Mg-5Zn-2Al-2Sn?ZAT522?alloy was prepared by conventional casting method.The microstructure characteristics of as-cast alloy were studied.The as-cast alloy was homogenized with different process parameters to determine the optimal homogenization treatment process.On this basis,the homogenized ZAT522 alloy was subjected to hot extrusion at different temperatures,and the microstructure and properties of the extruded alloy were characterized.Finally,on the basis of hot extrusion,the extruded ZAT522 alloy was subjected to?220?+2 passes?+?130?+2 passes?to realize low temperature ECAP extrusion deformation,and the microstructure and structure of the alloy after cooling deformation were studied.The characteristics of texture change,and the grain refinement mechanism of Mg2Sn phase and alloy.The research shows that the as-cast ZAT522 alloy is a typical dendritic structure,which is mainly composed of a-Mg,Mg2Sn and Mg₃₂?Al,Zn?₄₉phases.Mg₃₂?Al,Zn?₄₉9 is a continuous network structure distributed at the grain boundary.Most of the Mg₂Sn phase is mixed with Mg₃₂?Al,Zn?₄₉.After homogenization treatment at different temperatures,the homogenization treatment effect at 350?for 40 h was completed,and there was no over-burning phenomenon.The Mg2Sn and Mg₃₂?Al,Zn?₄₉9 phases were basically dissolved in a-Mg.After extrusion at 300?and 325?,the alloy is completely dynamic recrystallized,the grains are remarkably refined,and the dynamic recrystallized grains with fine grain size and fine dynamic recrystallized grains are pressed along the extrusion.The orientation distribution is shown as a typical bimodal distribution with an average grain size of 2.25?m and 11.2?m,respectively.The nano-sized Mg₂Sn phase is precipitated in the as-extruded alloy.When extruded at 300?,the precipitated phase in the alloy is mainly nano-sized Mg₂Sn phase.When extruded at 325?,there is a larger size than the Mg₂Sn nano-scale precipitate.The Mg₃₂?Al,Zn?₄₉9 phase exists,and the average size thereof is0.30?mand 0.52?m,respectively.Extrusion alloys all exhibit strong basal fiber texture.Due to the higher extrusion temperature at 325?,there are{10-10}<0002>textures in the extruded alloy.Compared with the 325?extruded alloy,the 300?extruded alloy has excellent comprehensive properties,and its tensile strength,yield strength and elongation reach 320 MPa,180 MPa and 33.4%.The increase in strength is mainly due to the strengthening of the grain boundary and the dislocation strengthening caused by the incompatibility of the second phase with the matrix.Since the grain size of extruded alloy at 325?is larger than that of extruded alloy at 300?,the number and size of deformation twins formed during the process of extruding alloy at 325?are larger than that of extruded alloy at 300?,which makes the elongation of the alloy lower than that of extruded alloy at 300?.After 300?extrusion of ZAT522 alloy,the grain of the alloy is significantly refined after ECAP deformation at?220?+2 passes?,from the original 2.25?m to 1.4?m,after?220?+2 two passes?+?130?+2 two passes?ECAP deformation,the grains were further refined to 1.18?m.After the ECAP extrusion deformation,the number of the second phase of the alloy increased significantly from 11.20%of the initial alloy alloy to 16.1%after ECAP deformation?220?+2 passes?,and the average size was broken due to precipitation and deformation shear.The effect is refined to 0.21?m;after?220?+2 two passes?+?130?+2 two passes?ECAP deformation,there is basically no precipitation of new Mg₂Sn phase due to lower deformation temperature,and the second phase size is further Refined to 0.17?m.After the ECAP extrusion deformation,the alloy has a large change in the texture type.After?220?+2 passes?the ECAP deformation,the extruded alloy still retains the micrograin of the 300?extruded alloy base.Features;after?220?+2 two passes?+?130?+2 two passes?ECAP deformation,the deformed alloy is formed along the shear plane and the extrusion direction is45^?.The new texture type completely replaces the original Texture.Compared with the 300?extruded alloy,the yield strength of the ECAP deformed alloy is significantly improved.The UTS of the?220?+2 two passes?alloy is increased to 245 MPa,which is mainly the grain boundary strengthening caused by grain refinement;the UTS of the?220?+2 two passes?+?130?+2 two passes?alloy is increased to 335 MPa,mainly due to fine grain strengthening and substructure strengthening.