Stretchability Research Of Al-Mg-Si Based Alloy Auto Body Sheet

Al-Mg-Si based alloy auto body sheet will be used widely in the future, but, in the recent, one of the difficulty in practice is its poor formability. It's one of the main problems that fracture always occurs during sheet metal forming processes. In this paper such original research as analyzing the strechability of Al-Mg-Si based alloy auto body sheet was done through physical experiment and numerical simulation.In this paper, firstly the processing technology of Al-Mg-Si based alloy auto body sheet was optimized, and its mechanical properties were tested. Then the stretchability of Al-Mg-Si based alloy sheet was also tested by using FLD experiment. Testing result indicates that Al-Mg-Si based alloy sheet has not only good mechanical properties but also favorable stretchability, and that its forming limit is higher than that of AA61111. This show the comprehensive properties of Al-Mg-Si based alloy sheet are excellent.Secondly, this paper studied the stretchability of of Al-Mg-Si based alloy sheet using FEM in numerical simulation view, FE stretching test model with hemispherical punch was constructed. Barlat yield criteria and arc-length analytical method is applied in order to describe Al alloy sheet stretching test. Diverse strain state changes though different friction and the dimension of sample according to the thought of the physics test, the result was revealed: Strain history can retain proportional loading way. The character of strain concentration and plasticity local buckling can be judged at the time which major strain occur apex point. Analytical FLD was constructed with major strain and minor strain of the node which was judged fracture, Analytical FLD is good coincident with FLD experiment.Effect of the sheet properties group on FLD of Al-Mg-Si based alloy sheet show that the shape of FLD depends on sheet properties group, but the height of FLD can be judged by the value of n; Effect of the properties group caused by thickness on FLD of Al-Mg-Si based alloy sheet indicate that relatively amplitude which be improved of FLD decrease with increasing thickness of sheet. The rule in theory was validated by using FEM.At last, this paper use FLD obtained from experimentation as fracture criterion in numerical simulation. The result of simulation of the forming limit of the cylinder drawingand box drawing indicates the position of fracture accord with experimental rules. Forming processes of door panel was also simulated using FLD as fracture criterion, through which the adaptability for forming of Al-Mg-Si based alloy sheet was studied.