Research On The Warm Forming Of AZ31 Magnesium Alloy Double Curved Square Cup

As the lightest engineering metal material,magnesium alloy is praised as “green engineering material in the 21 st century” and has a broad application prospect in rail transportation,automobiles,aerospace,3C and other fields.Compared with the cast magnesium alloy,wrought magnesium alloy products have better comprehensive performance,especially the stamping products of magnesium alloy sheet show great potential for development,however,the poor plasticity of magnesium alloy at room temperature severely restricts its application in large scale.Studies have shown that the warm forming of magnesium alloy sheet can obtain thin-walled forming parts of high quality.The warm forming of magnesium alloy sheet is a non-linear thermo-mechanical coupled process.More and more people have explored and optimized the warm forming technology of magnesium alloy sheets by means of a combination of numerical simulation and experimental research,which has greatly promoted the application and development of wrought magnesium alloy products.In this thesis,the warm forming of AZ31 magnesium alloy double curved square cup was taken as the research project,the mechanical properties of magnesium alloys at different temperatures were obtained by uniaxial tensile test,the non-isothermal forming process was analyzed by finite element simulation software-ABAQUS,the temperature distribution,material fluidity and thickness distribution in the forming process were analyzed,the influence of various forming parameters on its formability was systematically studied.On this basis,the results were optimized by using orthogonal tests,and the die was designed and manufactured,and then relevant forming tests were conducted,and finally the square cup with good surface quality and high forming precision was achieved.The main research contents and conclusions are as follows:(1)The influence of different forming parameters on the formability of magnesium alloy double curved square cup was studied through a combination of numerical simulations and experiments.The results show that the forming temperature has a great influence on its formability,The critical forming temperature is 150°C,and the optimum forming temperature is 300°C;Too small die radius,die clearance,and blank-holder gap will cause over-thinning,die radius should be greater than 3mm,die clearance should be greater than 1mm,blank-holder gap should be greater than 1.04mm;Excessive friction coefficient will cause the double curved square cup to crack,the friction coefficient should be less than 0.25;Magnesium alloy is sensitive to the forming speed,and excessive forming speed tends to cause the double curved square cup to crack.so,a lower forming speed is suitable.The ultimate forming speed at 200°C is 0.3 mm/s,and the ultimate forming speed at 250°C is 1.2 mm/s.(2)The forming results were optimized by the orthogonal test,the influence degree of each forming parameter on the maximum thinning rate is: blank-holder gap> die radius> friction coefficient> die clearance,the optimum forming parameters were determined as follows: the die radius is 7mm,the die clearance is 1.05 mm,the blank-holder gap is 1.2mm,and the friction coefficient is 0.05.(3)Based on the optimum die parameters,the die for the double curved square cup was designed and manufactured,and then the forming tests were conducted,the test piece with good forming quality was achieved,and the thickness measurements,precision tests of the test piece and microstructural analysis were conducted.The thickness distribution trend of the test piece was consistent with the simulation results,the maximum 3D deviation of the test piece was only 0.86 mm,and it met the precision requirement,which verified the accuracy of the numerical simulation.The difference in temperature and deformation leads to the difference of dynamic recrystallization in different parts,and the grain size and morphology are different.