Influence of Paint Baking Process on the Fracture Initiation of an Al-Mg-Si Alloy Sheet

Some of the aluminium alloy sheets widely employed in the light weight automotive body are well known to have hardening mechanism originating from precipitation. Sensitive to heat treatment process, variation of precipitation status induces change of mechanical properties f the aluminium sheets. In this study, fracture phenomenon of a paint bake-hardenable Al-Mg-Si alloy sheet was investigated. As a paint baking process of the aluminium sheet, the heat treatment was isothermally performed on the sheet at 180°C for 20 minutes, i.e., artificial ageing. The mechanical properties especially for the flow curve and the ductile fracture criterion were characterized by conducting different types of tensile tests for variation of loading path and by analytical analysis of hybrid method. Furthermore, the effect of the baking process on fracture initiation was also quantitatively evaluated by comparison between fracture strain of the aluminium sheet before and after ageing.