The influence of Si, Cu, B, and trace alloying elements on the conductivity of aluminum die cast 12 (ADC12) alloy was investigated. The conductivity decreased linearly with increasing volume fraction of the Si phase attributed to a linear decrease of the volume of the more conductive Al phase through a rule of mixtures. The conductivity also decreased with increasing Cu content, between 0~3%. The conductivity increased with increasing B content, reached the peak at 0.02% B and thereafter decreased somewhat. The mechanism was that B reacted with the transition element in the Al phase to form boride, decreasing the transition element concentration in the Al lattice, and decreasing the lattice constant. The thermal conductivity, λ, was related to the electrical conductivity, $\sigma$, by means of $\mathsf{\lambda }=\mathrm{LT}\mathsf{\sigma }+{\mathsf{\lambda }}_{\mathrm{g}}$, where L is the apparent Lorentz constant, 1.86 × 10⁻⁸; T is the absolute temperature, 293 K; λ_g is the lattice conductivity, 42.3 W/(m·K).

During friction stir welding (FSW) of Al-Zn-Mg alloys, the grain size of the welded material significantly affects its mechanical properties. In this study, the FSW process was simulated using the finite element method (FEM). Subsequently, the Zener-Hollomon parameters and grain size were calculated using the results of the stimulation of the temperature and strain rate fields. Also, the accuracy of numerical simulation was proved by experiments. It was found that the Zener-Hollomon relationship correctly predicted the grain size for the weld stirring zone (SZ) and thermal-mechanical affected zone (TMAZ), and we concluded that low rotating and high welding speeds resulted in smaller grain sizes for the SZ. Moreover, the high welding speed could effectively improve the grain condition at the edge of the TMAZ and the specific relationship between Zener-Hollomon parameters and the average grain diameter of SZ can be expressed as: Z = 9.09 × 10¹³ d ^−4.74.