The morphology of particles of minor phases in a commercial Al-7.12wt% Si alloy

Abstract

The morphology of particles of minor phases was monitored in an Al-7.12 wt% Si alloy in three different states: as-cast, hot isostatically pressed (HIPed) and heat-treated. In all of these states, the minor phases existing in this alloy were secondary silicon-rich particles and those which are iron-containing-Al₁₂Fe₃Si and (FeAl₆) Si. The major phase was primary silicon-rich particles. The HIPed and heat-treated materials contained an additional phase, the iron-containing particles Al₉Fe₂Si₂. It was found that secondary silicon-rich particles in the as-cast material were plate-like, spherical or fibrous. On the other hand, the few iron-containing particles in the as-cast material were needle-like. During HIPing or heat treatment, the iron-containing particles which precipitated also had a needle-like morphology. Most of the non-spherical secondary silicon-rich particles tended to spheroidize during HIPing or heat treatment. Fibrous secondary silicon-rich particles were not present in the HIPed or heat-treated materials.