Experimentally and Numerical Study on Deep Drawing Process for Magnesium Alloy Sheet at Elevated Temperatures

Abstract

Recently, magnesium alloys have been considered as a promising alternative for high-strength steel and aluminum in some applications because of its advantages such as low density, high specific strength etc. However, the application of formed magnesium wrought alloys components is restricted due to lack of knowledge for processing magnesium alloys at elevated temperatures. In this study, the deformation behavior of a cylindrical deep drawing of magnesium alloy sheets at elevated temperatures are simulated by using a non-isothermal finite element based on DEFORM 3D commercial software. In order to validate the finite element analysis, deep drawing test of cylindrical cup of AZ31 and AZ52 rolled sheets at given conditions was also performed. The experimental results show a good agreement with the finite element simulation predictions. The optimal forming temperature, thickness distribution of the cup and punch force were determined for the process. (doi:10.2320/matertrans.MC200761) Weight reduction has long been identified as a key priority for improving automotive fuel economy, and many studies often suggest substituting lightweight materials for typical steel applications. In recent years, magnesium alloys have been paid much attention due to its advantages such as low density, high specific strength etc. Therefore, magnesium alloys have been considered as a promising alternative for high-strength steel and aluminum in some applications and expected to be widely used for structural components, notably in the automotive and aerospace industry in the near future. 1-3) The application of formed magnesium wrought alloys components, however, is restricted due to lack of knowledge for processing magnesium alloys, especially forming process, at elevated temperatures. Traditionally, forming processes are usually carried out in isothermal conditions. In other words, the processes are conducted under the conditions of constant and homogeneous temperatures of tools and workpiece. However, deep drawing tests with magnesium alloy sheets show that the drawability of sheets can be improved by local heating based on the change of material property with respect to temperatures. 4-6) This means the process is ultimately non-isothermal. Moreover, during the forming process, heat is generated by plastic deformation and the heat loss by conduction and by radiation and convection to the punch as well as to the environment can result in several property changes of the workpiece. There- fore, this underscores the need for accurate methods to investigate a forming process of magnesium alloy not only deformation behavior but also heat transfer process, a task to which the finite element method is well suited. In this study, a thermo-rigid-viscoplastic FEM, based on DEFORM 3D codes, with anisotropic Hill's non-quadratic yield criterion is applied to analyze the warm deep drawing of AZ31 and AZ52 rolled sheets. The load-stroke curves, optimal process parameters and temperature distribution in the sheets obtained in the FE simulation were compared with experimental results for various forming conditions. 2. Experimental Procedure The magnesium alloys used in this study are AZ31 and AZ52 rolled sheets with a thickness of 0.83 mm. The chemical composition and microstructure images of the sheets are shown in Table 1 and Fig. 1, respectively.