Enhanced pitting resistance of Al-based coating by synergistic passivation effect from different shapes of Ni/Cr powders

Cold-sprayed Al-based coatings are widely used in corrosion protection fields, but they are poor in pitting resistance. In order to enhance the pitting resistance of Al-based coatings, dendritic Ni and irregular Cr powders are co-doped into Al powders to prepare Al-Ni–Cr composite coatings by cold spraying. Their structure, composition, and corrosion behavior are characterized by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), dynamic potential polarization, and electrochemical impedance spectroscopy. The results show that the Al-Ni-30Cr coating exhibits the best corrosion resistance with high E_pit, small i_corr and i_pass, large R_ct, and superior self-healing ability. The protective corrosion products rapidly form in the early stage of corrosion, which can effectively fill corrosion pits and intrinsic pores in coatings, preventing further penetration of corrosive media and the continuation of auto-catalytic corrosion reaction of Cl⁻ in the pits. The excellent anti-corrosion performance and long service life of the Al-Ni-30Cr coating are attributed to the self-healing ability and the synergistic shielding effect of nickel and chromium.