First-Principles Investigation of the Properties of Copper–Aluminum Intermetallic Compounds

After copper and aluminum are connected friction stir welding(FSW), the primary intermetallic compounds formed in the joint are Al₄Cu₉, Al₂Cu, and AlCu. To further analyze the influence of intermetallic compounds on the properties of Cu/Al joints, the mechanical, electronic, and thermodynamic properties of Al₄Cu₉, Al₂Cu, and AlCu in Cu/Al joints were calculated using first-principles methods. Based on the calculated cohesive energy and formation enthalpy, the stability order of the compounds is Al₄Cu₉ > Al₂Cu > AlCu. The energy band structure and density of states indicate that these compounds predominantly form covalent bonds while exhibiting conductive properties. The single-crystal elastic constants and polycrystalline elastic moduli, including bulk modulus, Young’s modulus, and shear modulus were calculated, and the melting points were predicted to understand their respective thermal expansion coefficients.