Effect of morphology and precipitation of Si phase on thermal properties of Al–Si–Mg–Cu foundry alloy

The objective of this study was to investigate effects of morphology and precipitation on thermal properties of Al-9.8%Si-0.4%Mg-0.7%Cu (in mass%) alloys using a laser flash apparatus, differential scanning calorimetry, and a thermomechanical analyser. Results revealed that mean particle size and shape of Si depended on mould temperature. Specimens with higher mould temperature had long and needle-like eutectic Si. As-cast specimens were solid solution treated at 535 °C for 6 h and then quenched in warm water of 80 °C. As-solution specimens were then aged at 180 or 190 °C for 1, 5, and 10 h. After artificial ageing treatment, the long needle-like eutectic silicon phase was split into smaller particles. It then gradually became spherical. When the shape of Si phase became similar after artificial ageing treatment, thermal diffusivity and thermal conductivity had similar values. It was found that shape change of Si particles greatly influenced thermal diffusivity and thermal conductivity.