Improvement Mechanism of Thermal Conductivity in T6/T7-Treated Al-Si-Mg Cast Alloy: Experimental Studies and Density Functional Theory Calculations

In this article, high strength and high thermal conductivity are achieved in T6/T7-treated Al-9%Si-0.8%Mg alloy. The improvement mechanism of thermal conductivity is discussed by experimental studies and density functional theory calculations. The experimental results indicate that the T7-treated Al-9%Si-0.8%Mg alloy shows the good overall performances: thermal conductivity of 177.34 W m(-1)K(-1), yield strength of 288 MPa, tensile strength of 314 MPa, and elongation of 9.63%. The beta '' precipitates at peak-aged condition show higher strengthening effect than that of beta ' at overaged condition, while the overaged condition is more favorable for improvement of thermal conductivity. The decrease in concentration of solution atoms by precipitation of beta '' and beta ' enhances periodic field of localized matrix lattice and increases the relaxation time of free electrons in the localized lattice. The decrease in concentration of solution atoms and increase in the number density of beta '' and beta ' precipitates not only markedly strengthen the mechanical properties but also reduce the scattering positions in Al lattice, resulting in the improvement of thermal conductivity.