Effect Of Pre Deformation On Microstructure And Aging Hardening Of Mg-Zn-Y-Zr Alloy

Strengthening and toughening of magnesium alloys is the priority among priorities of magnesium alloy.Aging strengthening can effectively increase the hardness of magnesium alloy by precipitation phase.But the aging precipitation process of Mg-Zn alloy is slow and the precipitation phase is sparse.The pre deformation treatment of magnesium alloy results in the twinning and dislocation in the magnesium alloy.The aging precipitation meets the twin and dislocation as the nucleation position,which greatly accelerates the precipitation process.Moreover,the twins produced by pre deformation have the effect of refining grain and increase the hardness of magnesium alloy.In this paper,the pre deformation treatment of magnesium alloy and isothermal aging were carried out.The microstructure change was observed and analyzed.In this paper,the Mg-8.14Zn-1.44Y-0.47Zr alloy was used as the experimental material,the pre compression and pre stretching deformation treatment was carried out to different extent,and then the pre deformation alloy was treated with isothermal aging.This paper observe the pre deformation of alloy morphology by using optical microscope(OM);analysis of alloy microstructure by electron backscatter diffraction(EBSD);then determining phase combine with X ray diffraction and HRTEM;hardening curves of different processing production.The main research contents are:The hardness of magnesium alloy was increased by 0 to 15%different compression deformation.Pre compression deformation highest hardness appeared in the amount of compression 15%,alloy hardness up to 85.1HV,compared with the initial hardness of 64.6HV.On magnesium alloy 0 to 3%different amount of tensile deformation,hardness also increased significantly,the highest value of tensile 78HV of 3%.With the increase of pre compression,the twins will increase the number of different types of twins also increased a lot.After pre stretch,magnesium alloy only have {1012} twinning,twinning and deformation is proportional to the number.It is found that compression can only produce a variant tensile twin,which can produce various variant tensile twins.After pre compression,the alloy(0001)concentration in the direction of RD,(1120)in parallel to the preferred direction of TD-ND,(1010)is also preferred in parallel to the TD-ND direction.But tensile deformation twinning is not less preferred orientation.In the process of increasing compressive deformation,the grain boundary proportion of twin decreases,the proportion of small angle grain boundaries increases,and the number of small angle grain boundaries increases.In the process of stretching,the number of small angle grain boundaries also increases.The hardness of pre compression magnesium alloy increases firstly and then its will decreases.The highest value of the hardness is 109HV,which appears in the age of 4H compression of 15%.The highest value of the hardness is 109HV,which appears in the age of 4H pretension of 15%.During the aging process,the number of small angle grain boundaries will be significantly decreased,the number of twin boundaries will not change,and the percentage of grain boundaries will be increased.After aging for the pre deformation of magnesium alloy,granular phase attached to the twin boundary firstly.With the increase of aging time,the density of precipitates grow up.The rods and disks are separated in the twin interior and the matrix,and they can grown up in the same and their density is increased.The granular phase is Mg3Zn6Y phase,while both rod-shaped and discoid phase are MgZn2 phase.