Investigations On Formability Of 5000 Series Aluminum Alloy Sheets For Automotive Application

In order to reduce fuel consumption and emission, lightweight vehicles are more and more popular in addition to the development of new energy. Aluminum alloys, with the advantages of lightweight, high erosion resistance, good processibility and weldability, can be well applied to lightweight vehicles, especially for body panels. In the current study, the mechanical properties, forming limits and lubrication conditions Al 5182-0 are analyzed through theoretical analysis, experimental study and finite element method (FEM). The servo press is utilized to study the effects of multiple process parameters on the drawability of Al 5182-O sheets. The main research and achievement are as follows:(1) The flow stress curves for Al 5182-O were characterized using standard tensile test and Viscous Pressure Bulge (VPB) test. It was found that the deviation of the flow stress curves was up to 10%. Since the deformation of sheets in the VPB test was more closer to stamping condition, it was suggested to obtain flow stress curves by using VPB test or similar tests in sheet metal forming study.(2) The performance of 14 lubricants and 2 surface morphologies for drawing of Al alloys were evaluated by using Cup Draw Test. It was found that one of the dry film lubricants could provide best lubrism. The effects of Electric Discharge Texturing (EDT) and Mill Finish (MF) were also evaluated. It was found that the EDT surface could provide better lubrication condition during cup drawing. The coefficient of friction was calculated by proposed inverse analysis in FEM.(3) Combined experimental and numerical analysis was conducted to determine the forming limits of Al 5182-O. Forming processes in different strain status, including tensile test, cup drawing test and dome test, were simulated by FEM. The onset of necking and fracture based on ductile fracture were defined by the second derivative of principal strains in the critical regions in the parts. The forming limit curves for necking and fracture were obtained, verified and applied to FE simulation of forming process of more complex part.(4) The experiments and FE analysis were carried out to study the drawability of 5182-0 by using a servo press. The effects of different forming conditions, including variable blank holder force, forming speed and heat generation, on the drawability and parts quality, were studied. It was found that, increasing BHF could help avoid the wrinkle issue on the flanges, however could lead to early fracture on the corners. The forming speed curves were well designed and controlled by the servo press. Results showed higher forming speed could enhance the drawability via the changed friction condition on the contact interface. The temperature filed of room temperature stamping was accurately predicted by using mechanical-thermal FE model.