A nickel/bayerite bilayer coating for enhanced corrosion resistance of aluminum alloys

Purpose This study aims to propose a new type of double-layer coating system composed of an electroplating nickel layer and a hydrothermally grown bayerite [ß-Al(OH)3] coating on a 1060 aluminum alloy substrate, aiming to enhance the corrosion resistance of aluminum alloys in the application environments of aerospace, automotive and marine industries. Design/methodology/approach The nickel layer was obtained via constant current electrodeposition, and then the bayerite layer was grown in situ through hydrothermal treatment at 125 °C with different durations (3, 6, and 12 h). The microstructure and chemical composition of the Ni layer and bayerite layer were investigated by scanning electron microscope, energy dispersive spectroscopy, X-ray diffractometer and X-ray photoelectron spectroscopy. Their corrosion resistance was verified using electrochemical impedance spectroscopy and immersion tests. Findings Electrochemical tests in 3.5 Wt.% NaCl solution revealed that the Ni/Bayerite-6h coating exhibited the highest corrosion resistance, with a corrosion current density of 4.42 × 10−7A·cm−2 (three orders of magnitude lower than the Ni layer) and a polarization resistance of 513951 Ω·cm2. Long-term immersion tests showed that the Ni/Bayerite-6h coating delayed corrosive medium penetration for up to five days and can still prevent galvanic corrosion between the nickel layer and the aluminum substrate after seven days, significantly suppressing galvanic corrosion at the nickel–aluminum interface. The bayerite coating effectively isolates the pinholes and grain boundary gaps in the Ni layer and forms a dual-layer structure with it, providing a strong barrier against the intrusion of chloride ions. Originality/value This work demonstrates a viable strategy to enhance the durability of aluminum alloys through engineered multilayer coatings.