Study On Microstructure And Properties Of Mg-3Sn-2Al-1Zn-0.6Sb Magnesium Alloy By Extrusion

Magnesium alloy has many excellent properties such as light weight,high specific strength,good heat dissipation and so on.It has been widely used in aerospace,transportation,electronic communication and other fields.However,it also has some defects such as poor corrosion resistance,poor mechanical properties at high temperature and low plasticity at normal temperature,which limits the application range of magnesium alloys.For a long time,people have been exploring ways to make up for the performance defects of magnesium alloys,such as heat resistant magnesium alloys,corrosion resistant magnesium alloys,deformed magnesium alloys,rare earth magnesium alloys,etc.,which is also the focus of magnesium alloy research.In this thesis,Mg-3Sn-2Al-1Zn-0.6Sb magnesium alloy was obtained by adding Sn and Sb elements on the basis of AZ series of deformed magnesium alloy.The as-cast samples were homogenized by heating at 400℃for 24h.The homogenized samples were subjected to positive extrusion with extrusion ratios of 2.78 and 4,and composite extrusion with internal angles of 90°and 105°,respectively.The extrusion temperature was 250℃and the extrusion speed was 2 mm/s.Then,the microstructures of the samples were studied by metallography,XRD,SEM,TEM and EBSD,and the mechanical properties of the samples were studied by hardness test and tensile test.The main conclusions are as follows:（1）The dendrite segregation of Mg-3Sn-2Al-1Zn-0.6Sb magnesium alloy was basically eliminated and the average grain size was 53.01μm after homogenizing heat treatment at 400℃for 24h.The second phase of the as-cast alloy is mainly Mg₂Sn and Mg₃Sb₂phases and a small amount of Mg₁₇Al₁₂.After homogenization,Mg₁₇Al₁₂ disappears,and the size and quantity of Mg₂Sn decrease significantly.The homogeneous alloy has a certain strength base texture,and the maximum pole density is 17.83.The microhardness of the as-cast alloy is53.2HV and that of the homogeneous alloy is 55.3HV.The yield strength,tensile strength and elongation after fracture are 73 MPa,130MPa and 4.71%,respectively.The tensile fracture type is dissociation fracture.（2）The dynamic recrystallization degree ofΦ10 FE is higher than that ofΦ12 FE,and the effect of grain refinement is stronger.The average grain size ofΦ12 FE alloy is 5.69μm,and the average grain size ofΦ10 FE alloy is 4.17μm.The texture orientation of the base plane is parallel to ED,and the maximum pole densities of the alloys withΦ12 FE andΦ10FE are 35.33 and 18.22,respectively.The average transverse and longitudinal hardness ofΦ12 FE alloy is 67.7HV and 64.5HV,respectively,which is 22.4%and 16.6%higher than that of the homogeneous alloy.The average hardness ofΦ10 FE alloy is 67.1HV and 62.1HV,respectively,which is 21.3%and 12.3%higher than that of the homogeneous alloy.The yield strength,tensile strength and elongation after fracture ofΦ12 FE are 173 MPa,266 MPa and11.56%,respectively,which are 136.9%,104.6%and 145.4%higher than that of the homogeneous alloy.The yield strength,tensile strength and elongation after fracture ofΦ10FE are 171 MPa,266 MPa and 14.23%,respectively,which are 134.2%,104.6%and 202.1%higher than that of the homogeneous alloy.The tensile fracture types ofΦ12 FE andΦ10 FE alloys are quasi-dissociation fracture and dimple fracture,respectively.（3）The plastic deformation and dynamic recrystallization of the composite extrusion are large,and the alloy microstructure is uniform and fine equiaxed.The average grain size of Mg-3Sn-2Al-1Zn-0.6Sb magnesium alloy after 90°FPE and 105°FPE is 2.94μm and 2.23μm.After composite extrusion,there is a certain incline Angle between the texture of the base plane and the ED direction,and the texture strength of the base plane of the alloy is significantly weakened compared with that of the uniform alloy and the alloy after positive extrusion.The maximum pole density of the alloy after 90°FPE and 105°FPE is 10.48 and6.94,respectively.The average hardness of 90°FPE alloy is 74.2HV and 72.9HV,respectively,which is 34.2%and 31.8%higher than that of the homogeneous alloy.The average transverse and longitudinal hardness of 105°FPE alloy is 74.7 HV and 73.8HV,respectively,which is35.1%and 33.5%higher than that of homogeneous alloy.The yield strength,tensile strength and elongation after fracture of 90°FPE are 158 MPa,265 MPa and 21.83%,respectively,which are increased by 116.4%,103.8%and 363.5%compared with the homogeneous alloy,respectively.The yield strength,tensile strength and elongation after fracture of 105°FPE are134 MPa,280 MPa and 23.82%,respectively,which are increased by 83.6%,115.4%and405.7%compared with homogeneous alloy,respectively.The fracture type of 90°FPE and105°FPE alloys is dimple fracture.