| Magnesium alloys have many excellent properties and broad application prospects.But in the actual industrial production,a lot of edge cracks often occur when magnesium alloy sheets are processed by rolling.In this paper,based on the process of vertical crown pre-rolling and longitudinal rolling,the theoretical system of edge crack control is further improved by means of experiment and finite element simulation.The effect of reduction on the rolling of AZ31 magnesium alloy sheet with prefabricated crown was studied experimentally,and the feasibility of restraining edge cracking of AZ31 magnesium alloy sheet with prefabricated crown was verified.On this basis,the optimum mathematical model of rolling crown for magnesium alloy plates with thickness from 10 mm to 50 mm is established by numerical simulation.Firstly,the AZ31 magnesium alloy sheet with the same thickness and the same edge pre-cast convexity was rolled by multi-pass rolling with different reduction schemes.The first reduction was 10%,15%,20%,25%,respectively.The effects of different reduction schemes on the edge crack depth of AZ31 magnesium alloy sheet during rolling and the effects of multi-pass rolling on its microstructures and mechanical properties were analyzed.The experimental results show that the edge crack of AZ31 magnesium alloy sheet can be significantly inhibited by multi-pass rolling of the sample with pre-crown edge.Under the same rolling conditions,the first pass reduction should not be too large for the specimen with certain prefabricated crown,and the edge cracking is closely related to the first pass reduction.Taking the sample with 10 mm thickness as an example,the prefabricated convexity at the edge is 3.3 mm,and the first reduction is 15%.There is no obvious crack at the edge after multi-pass rolling,and the shape of the plate is the closest to the rectangle.Moreover,the yield strength of the sample is the largest,which is obviously superior to other samples.At the same time,the difference of mechanical properties between the middle and the edge of the sample is the smallest.In addition,the microstructure of the middle and the edge of the sample is more uniform and fine than that of other samples,and a large number of equiaxed grains appear,which is better than that of other samples.The tensile fracture also shows obvious plastic fracture characteristics,so it has good plasticity.For a certain thickness of magnesium alloy billet,it is very important to determine its pre-crown measurement when adopting vertical rolling pre-crown + longitudinal rolling process.Therefore,the crown process of AZ31 magnesium alloy sheet in vertical rolling was simulated by finite element method.In the postprocessing of finite element simulation,the damage value,equivalent strain,temperature value and surface expansion ratio of the simulated results were analyzed.The convexity data obtained by numerical simulation of AZ31 magnesium alloy sheet vertical rolling were fitted by Origin processing.A total of 54 sets of convexity mathematical models with 9 groups of sheet thickness under 6 different reduction values were obtained.The sum of squares of correlation coefficients and the adjusted sum of squares of correlation coefficients are all above 0.95,and the maximum sum of residual squares is 0.99998.The formulae coefficients of different reduction are treated as mathematical models with ?h as independent variable,and the formulae coefficients of each group of plate thickness and the basic models of 9 groups of different plate thickness are obtained.Combining with the experimental results,these models are further modified,and finally three sets of optimal models describing pre-rolling crown of vertical rolling with thickness of 10 mm to 50 mm are established.In order to provide theoretical support for industrial production and further improve the theoretical system of prefabricated crown rolling process. |
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