Influence of subsurface microstructure variations on bending ductility of Aural™-2 HPVDC thin-walled components

High pressure die casting is widely employed in the automobile industry for its ability to mass produce intricate aluminium parts, including sizable structural components made of specialized alloys. However, the size and complexity of the castings, combined with the current understanding of the rapid solidification process, can limit our control over the microstructure. More specifically, the fast turbulent flow of material during filling leads to the formation of distinct subsurface microstructure variants, often visible within one casting. Given that bending ductility is generally a key performance indicator for high-integrity castings, and is expected to be largely influenced by near-surface microstructure, this paper aims to characterize the observed microstructure variations in die cast aluminum specimens and assess their impact on local bending behaviour. The microstructure variations were characterized using optical microscopy on representative specimens, revealing distinct types of subsurface microstructure variants. Samples from region expected to present different types of subsurface microstructure variants underwent VDA bending tests. Mechanical testing demonstrated that these subsurface variants influence the bending behaviour. Considering these results, a deeper understanding of the mechanisms involved in the filling process could improve die design practices. Furthermore, this knowledge could facilitate the control of microstructure formation and enhance the overall homogeneity of mechanical performances throughout HPVDC components.