Research On The Forming Limit Of 6060 Aluminum Alloy At Different Solution Temperatures

6××× series aluminum alloys,as heat-treatable strengthening alloys have different microstructures morphology and mechanical properties under different heat treatment regimes,and show different processing and forming abilities.This thesis takes 6060 aluminum alloy as the research object,and performs solution treatment at different temperatures,combined with M-K theoretical calculation,Dynaform numerical simulation and rigid die bulging experiments,the forming limit curves of the material at different solution temperatures are drawn respectively.The influence of solution temperature on the formability of aluminum alloy materials is systematically studied,and the influence of input parameters in theoretical calculation model on solving limit curve is analyzed.Combined with the numerical simulation and bulging experimental results,the accuracy of theoretical limit curve is discussed.The main research contents and conclusions of this thesis are as follows:1.Combined with the DSC test results,the solution treatment of 6060 aluminum alloy at different temperatures is carried out within the temperature range without overburning.Based on the uniaxial tensile experiment,the true stress-strain curve of the material after solution treatment was obtained,and the stress-strain curve was pushed back according to the hardening laws of the Hollomon,Voce and Kim-Tuan models.The tensile fracture morphology,microstructure and microhardness of the material were also measured.The results show that the strength and hardness of the material were positively correlated with the solution temperature,and the elongation after fracture decreased slightly with the increase of the solution temperature;The fracture showed obvious ductile fracture,the number of dimples in the tissue decreased with the increase of temperature,and the size of a single dimple increased.2.Based on the M-K theory,and considering the influence of Hill48 and Mises yield criteria and three hardening laws,the MATLAB calculation code was written.The theoretical limit strain of the material at different solution temperatures is solved,and the forming limit curve is drawn.In addition,the influence of solution temperature on the limit curve of the material is analyzed,and the difference of the limit curve under different hardening laws and theoretical model parameters(groove angle,initial thickness unevenness,and through-thickness stress)is discussed.By converting the formula,the ultimate strain is converted into the ultimate stress,the stress limit curve is drawn,and the influence of the model parameters on the stress limit curve is discussed.The results show that the theoretical limit curve moves downward with the increase of the solution temperature,and the forming limit curve is sensitive to the yield model and hardening law.In addition,the stress limit curve moves downward with the increase of the absolute value of the through-thickness stress.3.Through the Dynaform simulation platform,the bulging simulation was carried out,and the simulation prediction curves of the material’s ultimate strain and forming limit were obtained.The results show that the predicted trend of the forming limit at different solution temperatures is consistent with the trend of the theoretical calculation curve,and the best fit with the theoretical limit curve calculated by the Hollomon hardening law.4.The forming limit curve of the material was obtained by the rigid die bulging test,and compared with the limit curve obtained by theoretical calculation and simulation prediction.The results show that the limit curve solved by the M-K theory considering the Kim-Tuan hardening law has higher accuracy.Although the forming limit curve obtained by the simulation prediction can accurately judge the variation law with the solution temperature,the curves in the plane strain region and the double tension region of the forming limit diagram are quite different from those in the test,and the prediction accuracy of the curve in this region is lower than that in the tension and compression region.