Thermal and electrical conductivity in Al–Si/Cu/Fe/Mg binary and ternary Al alloys

Abstract

This study investigated 30Al–Si, Al–Cu, Al–Fe, Al–Mg, Al–10Si–Cu, Al–10Si–Fe, and Al–10Si–Mg binary and ternary Al alloys, which are among the most commonly used commercial alloys. The thermal and electrical conductivity of the gravity castings of these alloys were measured. The results indicated that when 1 wt% Si, Cu, or Fe was mixed with commercial Al with 99.8 % purity, the thermal conductivity decreased from 213.5 Wm⁻¹ K⁻¹ to approximately 190–210 Wm⁻¹ K⁻¹. The thermal conductivity remained at a nearly constant level of 154–157 Wm⁻¹ K⁻¹ when the Si concentration exceeded 6 wt% in the Al–Si alloys. Regarding the Al–Mg alloys, the thermal conductivity did not change when the concentration of Mg was increased to 1 wt%. When the concentration of Mg exceeded 1 wt%, the thermal conductivity decreased greatly from 212.1 Wm⁻¹ K⁻¹ in the Al–1wt%Mg to 124.1 Wm⁻¹ K⁻¹ in the Al–5wt%Mg. This decrease occurred because the Mg-rich phase continuously impeded heat transfer at the grain boundaries. For the ternary Al alloys, when 0–1 wt% Fe or Cu was added to Al–10Si, the thermal conductivity increased slightly from 154 Wm⁻¹ K⁻¹ in Al–10Si to 162.7 Wm⁻¹ K⁻¹. The increase was due to the inclusion of Fe, which led to the formation of an Al _x Fe _y Si phase, reducing the solutes in the matrix phase. When the composition, morphology, amount, and distribution of all precipitates along with the matrix phase were taken into account, the effective medium approximations accurately interpreted the thermal conductivities of the Al alloys. Electrical conductivities were also measured and compared with thermal conductivities estimated using the Wiedemann–Franz law, and the results indicated close agreement. The Wiedemann–Franz law, however, often underestimates the thermal conductivity in Al alloys containing a high level of Si.