Composition Design And Microstructure,Properties Evaluation Of Ductile Magnesium Alloy Sheets

Magnesium alloy is a promising green material with lightweight structure.However,due to its hexagonal close packed crystal structure,the slip system that can be operated at room temperature is insufficient,and the formability is not ideal.In addition,because the base slip is easy to be activated,the strength of magnesium alloy is low.The application field of magnesium alloy is very limited,which is not conducive to its popularization and application,and restricts the application of magnesium alloy.In order to expand the application scope of magnesium alloy,this paper firstly the effect of recrystallization annealing on the microstructure,macrotexture,mechanical properties and stretch formability of Mg-1.5Y alloy sheet was studied.Secondly,the effect of Y addition and recrystallization annealing on the microstructure,texture,mechanical properties and stretch formability of Mg-3Y alloy sheet was studied.Finally,the effect of Sn addition on the microstructure,texture and mechanical properties of Mg-3Y alloy was studied.The main conclusions are as follows:Short time high temperature annealing promoted strong static recrystallization?SRX?of as-rolled Mg-1.5Y sheet,which transformed the deformed structure into complete recrystallization structure.The strong SRX changed the texture type of the sheet,which made the texture orientation of the sheet more dispersive and randomized,and further improved the plasticity and stretch formability of the sheet.The elongation to fracture and index of Erichsen test reached 30.5%and 4.4mm respectively.The solidification segregation behavior of Y element resulted in the micro-nano coexistence of?-Mg₂₄Y₅ phase in Mg matrix,which made the deformation structure of as-rolled Mg-3Y sheet more uniform.A large number of kink bands induced strong SRX during annealing,which made the bimodal texture evolved into a further weakened multi-modal texture.And the maximum polar density of?0002?plane further decreases from5.2 to 3.1.The plasticity and stretch formability were improved simultaneously.The elongation to fracture and index of Erichsen test reached 25.6%and 6.2mm respectively.The addition of Sn significantly changed the precipitation behavior of Mg-3Y alloy.The added Sn element preferentially combines with Y element to form Sn₃Y₅ phase and MgSnY phase,thus inhibiting the precipitation and growth of Mg₂₄Y₅ phase.During the rolling process,(Sn₃Y₅+Sn-Mg₂₄Y₅)and(MgSnY+Sn-Mg₂₄Y₅)composite phase structures which existed in the growth process of Sn₃Y₅ and MgSnY phases were easily to be broken,thus forming the“comet tail”shape feature,which greatly improved the rolling formability and plasticity of the sheet and weakened the texture intensity of the alloy.Especially for the alloy with 0.3wt.%Sn addition,the elongation of the as-rolled and as-annealed sheets reached19.8%and 28.3%respectively,and the strength is higher than that of the matrix alloy.The strength and elongation of the sheet were improved at the same time.