Study On Large Plastic Deformation Process Of AZ31 Magnesium Alloy

Magnesium alloys have the advantages of low density,high specific strength and abundant resources in the crust.They are known as "green engineering materials in the21 st century".They are widely used in many fields such as 3C electronics,aerospace,automobile manufacturing and so on.However,magnesium alloys are dense hexagonal structure with few slip systems and poor forming ability.It is of great significance to explore the preparation technology of high strength and high plasticity magnesium alloys.A large number of studies have shown that grain refinement can improve the strength and plasticity of materials at the same time.The structure of magnesium alloys can be refined effectively by large plastic deformation processing.In this paper,friction stir processing,surface mechanical grinding treatment,rolling and other processing technologies and their composite treatment are studied respectively.The effects of rotating speed,feed speed and cooling conditions on the structure and mechanical properties of AZ31 magnesium alloy in the stirring zone were studied.After friction stirring,a "pot" shaped stirring zone is formed on the TD-ND surface,and the stirring zone is fine and uniform equiaxed crystal structure.The bigger the rotating speed is,the bigger the grain size of magnesium alloy is,and the worse the mechanical properties of the material are.Feed rate has little effect on the structure and mechanical properties of the material.Compared with air-cooling,water-cooling can refine the structure of the material obviously,and at the same time,the tensile strength and plastic shape are better.Surface mechanical abrasion(SMAT)treatment can produce a dense and defect-free fine grain layer on the metal surface,and there is no interface barrier with the metal matrix,which can make the material produce obvious strengthening effect.SMAT treatment at different time has obvious difference on the structure of magnesium alloy.The surface mechanical grinding treatment of 1mmAZ31 magnesium alloy sheet was carried out for 15min,30min,60min,90min and 120min,respectively.The thickness of fine grain layer increased from 9 micron to 171 micron.After surface mechanical abrasion treatment,the microhardness of material cross-section changes gradiently,the microhardness of metal is lower,and the closer to the surface the microhardness is,the higher the microhardness is.With the increase of treatment time,the tensile yield strength increases and the plasticity decreases.A large number of compression twins will be formed in 2mm plate after rolling.These twins will increase the compression yield strength of the material.After annealing at 100,180 and 250 degrees centigrade for 1h,dynamic recrystallization of magnesium alloy occurs,twin structure disappears gradually,yield strength decreases and plasticity increases.At the same time,this paper explores new processing technologies such as friction stir processing,surface mechanical abrasion(SMAT)and rolling composite processing.