| Magnesium alloys are widely used in aerospace,medical,electronic products and other fields due to their outstanding performance advantages.The production of magnesium alloy plates by rolling can not only obtain good mechanical properties and meet the needs of various specifications,but also has high production efficiency,which is an inevitable choice for large-scale production.However,the magnesium alloy plate is prone to edge cracks during the rolling process,resulting in an increase in production costs and a low yield rate.In this paper,through compression experiment,vertical roll pre-rolling,flat rolling experiment and finite element simulation,the process parameters for preparing extension twins of magnesium alloy,the influence of different process conditions on magnesium alloy plate edge cracking and the mechanism of edge crack suppression by vertical roll pre-rolling were systematically studied.The microstructure and texture evolution of the samples under different deformation conditions were analyzed by EBSD.The main conclusions are as follows:(1)Preparation and Effect Analysis of {10-12} Extension Twins at the Edge of AZ31 Magnesium Alloy Plate.At room temperature and 250°C,compression experiments were performed on rolled magnesium alloy plates to guide the vertical roll pre-rolling process parameters.The results show that when the compressive strain along the RD was small at the edge of the rolled piece at room temperature,a large number of extension twin layers were generated.Grain matrix and twins coexisted.As the strain increased to 8.19%,the grains completely transformed into extension twins.Along with the generation of extension twins,hard-oriented grains were consumed in large quantities and the weakening effect of the basal texture was proportional to the volume fraction of the extension twins,while at 250°C,the slip dominated the plastic deformation process.(2)Analysis of improving edge crack damage of AZ31 magnesium alloy hot-rolled plate by vertical roll pre-rolling.At room temperature,4%,6% and8% were pre-rolled by vertical rolls along the transverse direction of the rolled magnesium alloy plate.Then single pass flat rolling was carried out at 350°C with 30%,40% and 50% reduction rates,respectively.The results show that{10-12} primary twin and {10-12}-{10-12} secondary twin dominate the edge deformation,while {10-12} primary twin dominates the middle deformation.With the increase of vertical roll pre-rolling reduction,the twin volume fraction of edge and middle increased,and the difference between the two decreased gradually.After heating,the elongation of PRA sample along ND compression was greatly improved.When the flat rolling was 30%,cracks appeared at the edge of the initial plate,while the vertical roll pre-rolled sample showed extremely high rolling performance.When the flat rolling was 50%,the 8PR sample still had no crack initiation.Moreover,after 50% flat rolling,the initial plate showed strong basal texture with the maximum pole density of 13.18.While the maximum pole density at the edge of the 8PR sheet is only 5.24,and the texture distribution is very scattered,showing weak orientation characteristics.(3)Mechanism analysis of vertical roll pre-rolling weakening edge damage of as-cast magnesium alloy plate.At 350°C,4%,7% and 10% vertical roll pre-rolling and single pass flat rolling numerical simulations were carried out for as-cast magnesium alloy sheets.The results show that the tensile stress on the edge was too large in the rolling process,resulting in the edge damage of the plate.The vertical roll pre-rolling improved the stress state of the edge metal in the rolling deformation zone,effectively reduced the tensile stress of the edge along the rolling direction,and transformed some areas into compressive stress,which was beneficial to the reduction of edge damage.Reasonable vertical roll pre-rolling reduction reduced the maximum edge damage value from 0.21 in direct rolling to 0.168. |
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