Effects of Si additions and heat treatment on the thermal characteristics of Al–Si–Mg alloys

In the present work, the thermal properties and heat treatment effect of an ingot metallurgy hypereutectic Al–Mg–Si alloy with extra Si are studied. The alloy is produced by gravity casting using 99.8% pure Al, 98.5% Si, and 99.9% pure Mg pellets. Thermal diffusivity, thermal conductivity, specific heat, and thermal expansion analyses are performed both after solid solution and after various aging treatments. The heat flow curve reveals a correlation between the precipitation reactions and the thermal diffusivity behaviors. In particular, the thermal characteristics of the Al–Mg–Si alloy are determined by the precipitation of the β″ and β′ phases, and the precipitation and re-dissolving of Si. Interestingly, the effect of Si precipitation upon the thermal diffusivity and expansion is greater than that of meta-stable β-phase precipitation.