The Research Of Tension Straightening Process Optimization And Plastic Deformation Mechanism For Magnesium Alloy Profile

In this paper,The AZ31 alloy and Mg-Gd-Y-Zn-Mn high-strength magnesium alloy bars were extruded as the research objects.The influence of drawing temperature,straightening speed and straightening passes on the straightening effect of the two alloys was studied systematically.Through the establishment of two expressions for evaluating the straightening effect,Which are the residual deformation rate ? and the bending degree a,the straightening effect under different straightening parameters is directly reflected,thus the optimal straightening process parameters of the alloy are established.On this basis,the warm tensile tests of the two alloys were carried out at different temperatures and speeds,in order to obtain the constitutive model of the two alloys with the change of strain,so as to grasp the deformation characteristics under the warm stretching straightening.The main results are as follows:?The test results of tension straightening after pre bending of AZ31 alloy and Mg-Gd-Y-Zn-Mn high strength alloy extrusion bar show that there is a function relationship between the bending degree a after tension straightening and the residual elongation ? of tensile deformation of the test piece,"the relationship between the residual deformation rate ?-the bending degree a after straightening”can conform to the single exponential decay model ?-A1×exp(-?/ti)+y0,The correction determination coefficients of ?l6mm and ?l2mm AZ31 and ?l2mm Mg-Gd-Y-Zn-Mn high-strength alloys fitting are close to 1,It shows that the fitting effect is good.indicating that the model can fit the relationship between ? and ? of different alloy and shape bending samples after tension straightening.?For the ?l2mm extruding bar of conventional AZ31 alloy and high-strength Mg-Gd-Y-Zn-Mn alloy,the uniform shape pre bent specimen should reach the expected flatness after tension straightening(the curvature after straightening is equal to or less than 0.2%),and the required residual deformation rate ? value is different:tension correction at 3.0mm/s speed,AZ31 alloy need ? value is 2.42%,3.18%and 3.72%at 160?,200? and 240?,Mg-Gd-Y-Zn-Mn alloy need ? value is 3.41%at 200?;at the speed of 0.3mm/s,when AZ31 alloy is at 160? and 200?,and Mg-Gd-Y-Zn-Mn alloy is at 200?,the ? value above 4.50%can not make a below 0.2%.The same degree of ? value of the two alloys is divided into two times of tension straightening,which is not conducive to a reduction.Therefore,the lower the tension straightening temperature,the faster the speed and the more passes are,the better to obtain a sufficiently small bending degree a with a smaller residual deformation rate ?,and the smaller ? is,the better to change the shape and size of the cross section of the products after tension straightening.But when AZ31 alloy is above 160?,Mg-Gd-Y-Zn-Mn alloy is above 200?,it can ensure that the clamped end is not easy to crack.? Based on the Arrhenius constitutive equation,according to the experimental data of two kinds of alloys under the condition of 160??240?,0.001s-1?0.1s-1,the constitutive parameters of two kinds of alloys are calculated by the Marquardt algorithm.The maximum relative errors between the calculated results and the experimental results of the constitutive models of AZ31 and Mg-Gd-Y-Zn-Mn alloys are 6.27%and 2.59%respectively.The model can reflect the flow stress and true strain relationship well.It is found by comparison that when the same strain is stretched,the stress index n of AZ31 is much lower than that of Mg-Gd-Y-Zn-Mn alloy,but the deformation activation energy Q is higher than that of Mg-Gd-Y-Zn-Mn alloy.? The experimental data of warm tensile test in the range of deformation temperature 160??240? and strain rate 0.001s-1?0.1s-1 show that the flow stress of AZ31 will gradually decrease after stretching to a certain stress variable,and the deformation activation energy Q will generally decrease with the increase of the stress variable,indicating that the dynamic recovery gradually counteracts the work hardening,while the flow stress and hot deformation activation energy Q of Mg-Gd-Y-Zn-Mn high strength alloy will gradually decrease with the strain The increase of the total amount has been on the rise,and the dynamic recovery only eliminates part of the work hardening.