Research On Warm Forming Limit Of Automotive Lightweight Aluminum Alloy Sheet

In order to cope with the developing trend of automotive technologies, which is safety, energy saving, environmental protection, there appears lightweight technology, of which the key is lightweight materials. As well, forming technology is an important subject of lightweight materials. Application of new lightweight materials including aluminum alloy can reduce automobile weight, in order to achieve the purpose of energy saving. Therefore, the forming technology of aluminum alloy has broad prospect of technology development and practical application. Although aluminum alloy has high specific strength, good corrosion resistance, weldability and recyclability, the cold forming performance is relatively poor. Improving forming temperature enhances its plasticity and reduces its deformation resistance, as a consequence, the aluminum alloy warm forming technology arises at the historic moment.Automotive aluminum alloy sheet warm forming is a nonlinear process involves many parameters such as thermal, mechanical and micro parameters, its application is constrained by material mechanical properties and microstructure, stamping process parameters and tool shape design. In sheet metal plastic forming, the Forming Limit Diagram (FLD) is an important criterion of forming success or not. Experimental methods for FLD constructions of specific materials is complex and have many influence factors such as loading path, strain rate, deformation temperature, etc. Although many scholars have investigated the FLD of lightweight materials such as high strength steel and aluminum alloy at room temperature, the FLD of aluminum alloy sheet under warm forming temperature is rarely involved. Therefore, this paper focuses on the warm forming material constitutive relation, the anisotropic yield criterion and features of automotive lightweight6000series Al-Mg-Si alloy, investigates the Thermal Forming Limit Diagram (TFLD) with experimental method, theory prediction and finite element analysis simulation.Firstly, the uniaxial tensile test of6061-T6aluminum alloy sheet was carried out under different temperatures within25～400℃and two different strain rates, based on the test results the constitutive equation and anisotropic yield function of6061-T6considered temperature were established. Secondly, thermal FLD of6061-T6was constructed with hemispherical rigid punch bulging test. Based on the obtained test material parameters, predicted the6061-T6aluminum alloy sheet warm forming FLD with M-K theory. Using finite element analysis software DYNAFORM established finite element model of the bulging test. For non-isothermal conditions of aluminum alloy in actual stamping, the interface heat transfer was investigated. In order to verify the guiding role of FLD in sheet metal forming, the actual stamping of aluminum alloy with U-shape experiment was carried out.