Effect Of Pre-Deformation On Mechanical Properties And Microstructure Of AZ31 Magnesium Alloy

In recent years,light metals have played an important role in high-end fields such as national defense and military industry.Magnesium alloy is a lightweight metal that is currently used in various engineering fields.However,due to the hexagonal close-packed(HCP)crystal structure of magnesium alloys,the number of activated slip systems is limited,which usually results in their poor ductility and strength.Pilger cold rolling is prone to defects due to multi-pass deformation,so it is combined with pre-deformation to strengthen the billet to effectively reduce the number of deformation passes to obtain high-performance alloys.Based on the stress characteristics of the instantaneous deformation of the cross section of the wall reducing section of Pilger rolled pipe,the die is designed to carry out room temperature pre-deformation experiments on AZ31 magnesium alloy along the parallel ED direction and vertical ED direction,so as to analyze the microstructure characteristics after pre-deformation.Then the room temperature secondary compression experiment is carried out.According to the VPSC model,the relatively accurate stress-strain curve is obtained by adjusting the parameters,the relative activity and texture evolution of different deformation mechanisms are analyzed,and the influence of pre-deformation on the macro mechanical properties and microstructure of AZ31 Magnesium Alloy during plastic deformation is analyzed by EBSD,which provides a theoretical basis for the design and optimization of Pilger cold rolling process.The main results are as follows:(1)The pre-deformation direction is of great significance to improve the secondary compressive yield strength of magnesium alloys.When the predeformation direction is ∥ED,the yield strength of 3% and 5% pre-deformation increases by 66.7% and 130%,respectively.For the pre-deformation direction of⊥ED,the yield strength of 3% and 5% pre-deformation increases by 6.6% and46.3%,respectively.Besides grain refinement and increased dislocation density dominating secondary compressive yield strength,basal texture weakening(or twinning texture enhancement)may play a more important role in improving the mechanical properties of AZ31 magnesium alloy.(2)The VPSC simulation results show that the pre-deformation in the ∥ED(⊥ED)direction makes the {0001} basal texture gradually disappear,which is more favorable for the extreme density of the {0001} basal texture to the positive direction of ED(TD).The twinning texture in the c-axis ∥ED(TD)direction is gradually enhanced;when the secondary compression is 8%,the twinning texture has been completely transformed into the c-axis ∥ED(TD)direction.This is mainly due to the change of the grain orientation of the pre-deformed samples after a certain amount of twinning,which makes the orientation of the basal plane more conducive to slip,resulting in the enhanced slip activity of the basal plane<a>.(3)The high ductility of magnesium alloys can be achieved by activating more cone <c+a> slip or suppressing {101?1} compression twinning.Pre-deformation leads to the suppression of the activity of the <c+a> slip system on the cone surface and the activation of the {101?1} compression twinning activity,which is less plastic than the unpre-deformed specimen.Therefore,magnesium alloys with high strength and good plasticity can be obtained by activating more cone <c+a>slip and suppressing {101?1} compression twinning to adapt to plasticity in magnesium alloys.