Microstructure And Deformation Properties Of Severely Plastic Deformed Magnesium Alloy

At present,there has been a lot of research on one of the main methods of severe plastic deformation of magnesium alloys-equal channel angular pressing(ECAP),which is mainly to accumulate strain through multiple passes to achieve grain refinement and improve mechanical properties.The severe plastic deformation of magnesium alloy can induce large strain,which is difficult to deform at room temperature.It usually needs to be completed at a temperature above 200°C.In addition,it needs multiple passes to achieve significant results,which is difficult to achieve its economic application in the engineering field.Therefore,how to simplify the ECAP process and further improve the mechanical properties of magnesium alloys to meet the requirements in engineering field has become an urgent problem.V-bending is a common process in sheet metal forming.Due to the strong texture in rolled magnesium alloy,the V-bending formability at room temperature is poor.Regarding how to improve the room-temperature V-bending formability of AZ31 magnesium alloy,there are relatively few related studies.In this paper,through the combination of pre-compression deformation and severe plastic deformation ECAP,the effects of pre-twinning on the mechanical properties and bending deformation properties of ECAP after processing are analyzed.And the samples are analyzed by optical microscope and EBSD.The conclusions are as follows:(1)Along transverse direction(TD)of AZ31 magnesium alloy rolled sheet was subjected to plane strain compression with the strain of 8%,and then annealed at 200°C to eliminate internal stress.The results show the tensile yield strength of the pre-compressed followed by annealed(RPCA)sample has been improved dramatically.The tensile strength are 140.8MPa and 272.5MPa,respectively,which are 55%and 12%higher than the original rolled sheet.The average microhardness of RPCA sample is 65.9HV,which is 16%higher than the original rolled sheet.{10^<sub>12}extension twins appeared in the RPCA sample,and most of the grains were rotated by 86°to form a new orientation.(2)ECAP is performed at 250°C after 8%pre-compression,and the maximum fracture elongation of the sample after deformation reaches 35.7%,which is 76%higher than that of the original rolled sheet.Compared with the ECAP of the rolled sheet,the mechanical properties of all parts of the sample obtained by RPCEA were improved.And the Schmid factor of the basal slip was significantly improved compared to the rolled sheet.(3)V-bending experiments were performed on samples in different states.It was found that the limiting bending depth of the pre-compressed followed by annealed sample(RPCA)was increased by 39%compared to the original rolled sheet,and the maximum bending force was increased by 20%.The limiting bending depth of the RPCEA specimen has been increased by 54%.Through metallographic analysis and EBSD analysis,it is found that the dominant deformation mechanism in the inner region of the RPCA bending sample is{10^<sub>12}extension twinning,and the outer region is mainly detwinning.The main deformation mechanisms in the inner and outside region are{10^<sub>12}extension twinning and basal slip.