Effect of Return Material Utilization in High-Pressure Die Casting on the Quality of Automotive Castings

Driven by the increasing demand for material efficiency and reduced environmental impact in automotive foundry production, this study addresses the industrial problem of determining the allowable content of internal return material in high-pressure die casting of EN AC-47100 aluminum alloy while maintaining the required quality of automotive castings. The aim was to determine how return material content and selected process parameters affect ultimate tensile strength, Brinell hardness, and internal porosity. In the regression model with interaction terms, high explanatory ability was achieved for ultimate tensile strength and internal porosity, with R2 values of 0.920 and 0.744, respectively. A full factorial experiment was performed using five levels of return material content, five levels of plunger velocity, and three levels of intensification pressure, resulting in 75 experimental settings. The data were analyzed using ANOVA, regression models with interaction terms, response surface methodology, and constrained multi-criteria optimization. Return material content was identified as the dominant factor affecting tensile strength and porosity. Increasing its proportion caused a systematic decrease in strength and an increase in internal porosity. Plunger velocity acted as a modifying factor, partially reducing porosity and improving strength response. The optimization showed that the maximum usable return material content was mainly limited by internal porosity. Under the most permissive scenario, a return material content of approximately 33.5% was achievable. The proposed scenario-based approach supports the selection of acceptable process settings that balance casting quality with return material utilization and provides a practical basis for increasing material circularity in industrial HPDC production without exceeding defined quality limits.