The Role of Silicon Morphology in the Electrical Conductivity and Mechanical Properties of As-Cast B319 Aluminum Alloy
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, BERNOULLI ANDILAB
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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 s1 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. https://doi.org/10.1007/s11661-020-05650-2 The Minerals, Metals & Materials Society and ASM International 2020
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INTRODUCTION
AUTOMOTIVE powertrain components are typically subjected to non-uniform temperature distributions during operation, due to their complex geometries and high heating loads. Consequently, uneven expansion rates within the material induce thermal stresses that can be detrimental to the performance and life of the part. This issue can be mitigated via two main strategies of alloy enhancement. First, by improving its mechanical properties, the strengthened part becomes capable of sustaining higher thermal stresses prior to failure. Second, by improving its conductivity, the material enables a more uniform internal distribution of heat, thereby proactively reducing the developing stresses. Thus, for cast 319-type Al-Si-Cu alloys, which
are commonly-used in the production of engine blocks and cylinder heads, the maximization of both strength and conductivity is imperative for the achievement of optimal component performance. Unfortunately, these two properties are affected by dissimilar microstructural mechanisms. Improving mechanical properties relies on effectively impeding the motion of dislocations through the material, which is classically accomplished via grain refinement.[1] In contrast, improving conductivity requires facilitation of the motion of thermal energy carriers through the material. In ambient-temperature metals and alloys, free electrons are primarily responsible for the conduc
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