Tailoring the mechanical properties of Al₄Ca intermetallic by doping M (M = Cu, Zn, Mg, Fe and Mn) from DFT calculations

As an important strengthening phase in Al-Ca eutectic alloy, the mechanical properties of Al4Ca phase are important for its engineering application. The effects of Cu, Zn, Mg, Fe and Mn doping on mechanical properties and electronic structures of Al4Ca phase are investigated in detail based on DFT calculations. The negative mixing enthalpy and cohesive energy of all Al-4(Ca,m) phases show that the substitution of Ca by m (m = Cu, Zn, Mg, Fe and Mn) is energetically favorable at 0 K. The modulus and hardness values of Al-4(Ca,m) are improved from 43.3, 2.73 GPa to 47.4, 2.99 GPa, 52.3, 3.3 GPa, and 70.6, 4.45 GPa by Mg, Fe and Mn doping, while they are decreased to 35.1, 38.2 and 2.21, 2.4 GPa by Cu and Zn doping. Based on Pugh ratio (B/G, 1.75) and Poisson's ratio (sigma, 0.26) criteria, all Al-4(Ca,m) phases are ascertained as ductile materials. Cu and Zn can increase the ductility of Al4Ca and the situation is in contrary after doping of Mg, Fe and Mn. Mn is the ideal element for increasing fracture toughness and decreasing the mechanical anisotropy of Al4Ca among these elements from calculation results. The calculated electronic structures show that the mechanical properties evolution of Al-4(Ca,m) phases are primarily attribute to the variation of Al-m bonds.