Microscopic corrosion behavior and first-principles calculations of interfacial diffusion layers of the Cu–Al composite plate

This work studies the corrosion behavior of the interfacial diffusion layers of the Cu-Al composite plate through microstructure observation, Electrostatic Force Microscopy (EFM), and First-principles calculations. The results show that there are three diffusion layers at the interface of the Cu–Al composite plate, which are composed of Al2Cu, AlCu, and Al4Cu9 from the Al side to the Cu side respectively. After being corroded by the 1% NaCl salt spray, the diffusion layer Al2Cu corrodes firstly, followed by AlCu and finally Al4Cu9 in sequence. Through the calculations of surface energy, electronic work function, and the intrinsic potential difference between different Cu-Al intermetallics at the interface, it is found that the relatively stable plane is Al2Cu (110), AlCu (111), and Al4Cu9 (100), and the order of intrinsic potential difference between Al substrate is Al4Cu9 > AlCu > Al2Cu. Al2Cu has a smaller Fermi energy level, and its crystal faces have a smaller electronic work function and potential difference. Therefore, Al2Cu has a greater tendency to be corroded in the corrosion environment and is corroded at first. AlCu is second, and Al4Cu9 as the diffusion layer with the largest electronic work function and intrinsic potential difference, is corroded at last.