The in-situ formation of Al3Ti reinforcing particulates in an Al-7wt%Si alloy and their effects on mechanical properties

Abstract

The formation of in-situ Al3Ti particulates (5 vol %) in an Al-7%Si alloy and their effects on the mechanical properties of the alloy with either the addition of Sr or not were studied under both as-cast and heat treated conditions. The in-situ Al3Ti particulates are having a blocky morphology with an average size of ∼3.5 μm. The major contribution of Sr addition is on modifying coarse plate-shaped eutectic Si-phase to a fine globular-fibrous morphology without a noticeable influence on the Al3Ti particulates. Energy dispersive X-Ray spectroscopic (EDS) analysis revealed the existence of Si in the blocky Al3Ti particulates as, most likely, (Al,Si)3Ti in the as-cast composites. Solutionization at 540 °C for 4 h resulted in the formation of a Si-rich phase inside the Al3Ti particulates, raising a question about the stability of (Al,Si)3Ti, τ1 and τ2 phases as reported by others. The introduction of in-situ Al3Ti particles improved the yield strength of Al-7Si alloy but showed adverse effect on the elongation without Sr addition. In comparison, the tensile strength and ductility of the composites were simultaneous improved with the modification of Sr under both as-cast and heat treated states due to the modification of eutectic Si plates.