Si solution in θ-Al13Fe4 from first-principles

θ-Al13Fe4 forms as a primary Fe-intermetallic compound (Fe-IMC) in the casting processes of most Al alloys. Si is added to Al alloys to improve the mechanical performance of products. Fe-IMCs including (Si doped) θ-Al13Fe4 have nontrivial impacts on the mechanical performances of the solidified Al-based components. Here, we investigate systematically Si solution in θ-Al13Fe4 using ab initio density functional theory (DFT). We reveal that Si prefers substitution on two Al sites (Al9 and Al8) in θ-Al13Fe4, forming θ-Al70(Si,Al)IX4(Al,Si)VIII4Fe24 (the Roman numerals represent the Al sites (Grin et al., 1994) [13]). The calculations identify a linear relation between the lattice parameters of the unit cell and the Si content. The knowledge obtained here is useful to get insight into the formation and structural and chemical properties of the Fe–Al–Si intermetallic compounds and to optimize the microstructures and properties of the solidified Al based alloys. •Si prefer on the Al8 and Al9 sites, forming θ-Al70(Si,Al) IX4(Al,Si)VIII4Fe24.•Lattice parameters and volume of the unit cell decrease linearly with Si content.•The calculated results agree with the experimental data in the literature.•θ-(Al, Si)13Fe4 exhibits ionic, covalent and metallic triple nature.