Microstructure and hardness behaviours of Ti-containing Al-Si alloys

The microstructures and microhardnesses of Al-12 wt% Si and Al-17.5 wt% Si alloys, with Ti contents up to 4 wt%, prepared by rapid cooling, were investigated. An extension of Si solubility in Al as a result of rapid cooling was measured. The addition of Ti to Al-12 wt%Si alloy led to the precipitation of the intermetallic compound Al3Ti which dissolves up to 13.12 at.% Si, while its addition to Al-17.5 wt% Si alloy led to the precipitation of the ternary compound AlSi2Ti. The microhardness of both as-cast alloys increased with increase in Ti content as a result of the precipitated phases. During isothermal heat treatment, the as-cast alloys showed some response to age hardening at 200degreesC, but a decrease in the microhardness was measured at 400degreesC.