The Role of Silicon Morphology in the Electrical Conductivity and Mechanical Properties of As-Cast B319 Aluminum Alloy

Abstract

The enhanced performance of automotive B319 aluminum alloys can be realized via the improvement of both strength and conductivity. Yet, vastly dissimilar mechanisms are responsible for each property, and the incomplete understanding of their respective dominant microstructural features impedes effective alloy design. In this study, permanent mold cast B319 alloy was systematically produced with total solidification rates between 0.14 and 5.89 °C s−1 and strontium contents up to 300 ppm to isolate their respective effects on material properties. The as-cast samples were characterized by their dendritic structure, eutectic silicon morphology, porosity content, hardness, tensile strength, ductility, and electrical conductivity. With increasing solidification rate, the refinement of microstructure considerably improved all mechanical properties analyzed. Nonetheless, these properties were found to be independent of strontium content, attributed to the role of the coarse and brittle intermetallic phases in fracture initiation. In contrast, conductivity was minimally affected by solidification rate in the unmodified condition. However, the synergistic silicon modification promoted by increasing both solidification rate and strontium enhanced conductivity by up to 3 pct IACS. The correlations developed with the quantified silicon characteristics establish this phase as dominant in the conductivity of B319 alloy, and they elucidate opportunities for the further enhancement of automotive materials.