Effects Of Secondary Bending And Straightening On Microstructure And Mechanical Properties Of AZ31 Plate

Magnesium alloys have broad application prospects in the field of manufacturing industry in China.They are used in automobile frame,high-speed EMU train body,aerospace equipment and so on.It is the lightest metal engineering material with the greatest potential.Magnesium alloys are widely used as light metal materials,which exhibit low strength,low stiffness and difficulty in plastic forming.These shortcomings limit the application of magnesium alloys in practical industrial production.In actual production,cast magnesium alloys are the most widely used but have poor comprehensive mechanical properties.Therefore,improving the comprehensive mechanical properties of magnesium alloys has become an urgent problem to be solved.Twin deformation is an important deformation mechanism of hexagonal magnesium alloys at room temperature.Twin plays an important role in improving the mechanical properties of materials.Firstly,in the process of twinning,the grains rotate at a certain angle.The grain orientation of some grains is not conducive to the improvement of material plasticity.After twinning makes the grains rotate,the grain orientation of this part becomes conducive to the improvement of material plasticity.In addition,the occurrence of dynamic recrystallization can also be induced by the formation and growth of twins,which can refine the grains of materials by inducing dynamic recrystallization,thus improving the comprehensive mechanical properties of materials.And twins can also be used as an obstacle to dislocation movement in materials,which makes dislocation difficult to move.The work hardening of the material increases the strength of the material.Tensile twins can be preset in magnesium alloys by compression.This paper proposed a method of bending and straightening.Through the bending and straightening process,the tensile twin crystals were pre-arranged inside the AZ31 magnesium alloy plate,and the changes in the microstructure and mechanical properties of the plate after a bending and straightening were analyzed.On the basis of a bending and straightening,After annealing the sheet after a bending and straightening at different temperatures,the bending and straightening paths are further increased,and the microstructure and mechanical properties of the sheet after the second bending and straightening at different intermediate annealing temperatures are discussed.The effects of different intermediate annealing temperatures on the microstructure and mechanical properties of the plates after secondary bending and straightening were studied.The findings indicate that:(1)After the original sheet is straightened by one bend,a certain number of twins are formed on both the RD plane and the TD plane.After annealing and straightening the sheet after annealing at 250?,the annealed twins appear in large quantities,and as the annealing temperature increases,the number of annealed twins decreases.The RD plane is consistent with the TD plane.After the original sheet is straightened by one bend,the tensile strength and elongation of the RD direction and the TD direction sheet are increased.The tensile strength and elongation of the TD direction are the best after the bending and straightening,the tensile strength is 283.1MPa,and the elongation is 18.6%.The TD direction is more sensitive to twinning,and the presence of twins is more conducive to the improvement of the comprehensive mechanical properties of TD-directional plates.After one straightening of the straightening,the hardness of the sheet is improved significantly.However,the hardness decreases after annealing,and as the annealing temperature increases,the hardness of the sheet gradually decreases due to the disappearance of the residual stress inside the sheet.The TD plane is consistent with the law obtained by the RD plane.(2)After annealing at different temperatures,tensile twins are generated inside the plate after secondary bending and straightening,and the amount of tensile twins increases first and then decreases with the increase of annealing temperature.The intermediate annealing temperature in the TD direction is 250?,being 13.6%.When the intermediate annealing temperature in the RD direction is 350?,the twin ratio is the most,which is 20%.The effect of secondary bending straightening on the mechanical properties of the sheet is obvious.When the intermediate annealing at 350? in the TD direction,the tensile rate of the sheet reached 16.8%,and when the intermediate annealing at 450?,the tensile strength of the sheet was the best,which was 222.4 MPa.When the RD direction is 350?,the same tensile rate of the sheet reaches the maximum,which is 20.2%.When the intermediate annealing at 150?,the tensile strength of the sheet is the largest,reaching 267.1 MPa.The intermediate annealing will reduce the comprehensive mechanical properties of the sheet after the secondary bending is straightened.In the TD direction,the tensile strength and elongation of the sheet after intermediate annealing are decreased,while in the RD direction,the elongation of the sheet during annealing at 350? is greater than the elongation of the sheet after annealing,in the middle of other temperatures.After annealing,the tensile strength and elongation of the sheet decreased.(3)With the increase of bending straightening pass,the proportion of twins in the plate increases gradually,and the comprehensive mechanical properties of the plate are improved.With the increase of the intermediate annealing temperature,the proportion of twins in the plate increases first and then decreases.The trend of comprehensive mechanical properties shows a trend of improvement and then deterioration.