A defect-induced property degradation map for high-pressure die-cast aluminum structure based on 3D porosity and mechanical property heterogeneity

Large aluminum structures can be manufactured by HPDC with a large-tonnage clamping force. However, reliability cannot be ensured by geometric filling alone, because defects and properties vary along the flow path. In this study, a 3800 mm S-shaped thin-wall aluminum casting was used to reveal the link between process attenuation, porosity, and mechanical property degradation. Samples were taken at flow lengths of 1000, 2000, and 3000 mm. Computational fluid dynamics simulation, OM/SEM, micro-CT, pore classification, finite-element analysis, and tensile testing were combined. Progressive pressure loss and flow instability were predicted from the near-gate region to the flow end. A clear transition in pore population was identified. Sparse regular pores were replaced by gas-dominated irregular pores and mixed gas-shrinkage defects. Strength was only moderately reduced. Elongation was much more sensitive to pore volume fraction and volume-weighted sphericity. A defect-induced property degradation map was then constructed by using porosity fraction and volume-weighted sphericity as defect coordinates. Safe, transitional, and critical regimes were defined by property retention. The map was further validated using an integrated rear-floor casting. It provides a practical basis for property zoning and local quality assessment of long-flow HPDC aluminum structures. This framework supports local quality assessment in industrial castings.