Correlation between microstructure, tensile properties, and thermal conductivity of non-heat-treated Al-Si casting alloys fabricated by high-pressure die-casting

This study analyzed the thermal conductivity and mechanical properties of non-heat-treated Al–Si based high-pressure die-casting (HPDC) alloys, based on microstructural analysis according to the alloying elements. Each Al–Si-based alloy containing various alloying elements was systematically investigated, and thermodynamic simulations were performed to predict the formation of intermetallic compounds (IMCs). The simulation results were subsequently validated through comprehensive microstructural analyses. Thermal conductivity was primarily determined by the matrix solute content, and a consistent trend was observed between the calculated and experimental results. As the contents of Mg and Cu increased, thermal conductivity tended to decrease. From a mechanical perspective, the combined effects of solid solution and precipitation strengthening were consistent with matrix hardness. However, overall hardness and yield strength exhibited different trends, suggesting that the contribution of IMCs to yield strength should be considered. The increased dislocation density around IMCs, particularly the accumulation of geometrically necessary dislocations (GNDs), induced back stress and activated hetero-deformation-induced (HDI) strengthening, thereby improving yield strength and significantly enhancing work-hardening capability. Meanwhile, a high volume fraction of brittle Fe-rich IMCs tended to reduce elongation. However, even when the amount of Fe-IMCs was similar, alloys with a higher volume fraction of IMCs exhibited improved elongation due to enhanced work-hardening capability. Although many studies have focused only on varying the contents of a limited number of alloying elements, this study is distinguished by its investigation of the combined effects of various alloying elements on the properties of HPDC alloys.