Correlation between ultimate tensile strength and solidification microstructure for the sand cast A357 aluminium alloy

Many studies have demonstrated a relationship between secondary dendrite arm spacing (SDAS) and the mechanical behaviour of cast aluminium–silicon alloys, both for tensile and fatigue strength. SDAS is related to the solidification time and can be predicted, with a good approximation, by finite-element simulation. However, other microstructural features can affect the tensile behaviour of cast aluminium alloys such as size and morphology of the eutectic Si particles, grain size, composition and morphology of the intermetallic compounds. The present investigation was aimed at finding valuable relationships between ultimate tensile strength and the previously mentioned microstructural parameters for the sand cast A357 aluminium alloy. The microstructural characterization was carried out by optical microscopy and image analysis on more than about 2500 micrographs. Starting from the microstructural parameters and taking into account the material hardness, a relationship able to predict the ultimate tensile strength of the alloy, with an error less than 5%, was found. This relationship can be used to evaluate the local values of the UTS in complex cast components knowing only the hardness and the microstructural parameters, even in positions where the extraction of tensile specimens is not possible.