Comparative corrosion inhibition of friction surfaced aluminium composite coatings for mild steel

This study extends the earlier report on friction-surfaced aluminium composite coatings over mild steel (AISI 1020) by adding the AA7075-15Ni coating to those already studied: Al-2Si-15SiC, Al-19Zn, and Al6082-T6 systems. Immersion corrosion experiments performed in acidic (pH3, 5), neutral (pH7), and alkaline (pH9) media were further supplemented by electrochemical testing in 3.5 wt.% NaCl solution to determine corrosion potential and current density. The uncoated mild steel experienced a maximum weight loss of 0.023 grams at pH 3 and an initial corrosion rate of approximately 7 mm/year at 24 h, which reduced to 1.30 mm/year at 120 h because of partial passivation. The Al–19Zn coating demonstrated the least mass loss, which measured about 0.001 g at pH 9, while AA7075–15Ni and Al–2Si–15SiC followed behind this coating to protect against corrosion at a rate below 1.0–1.5 mm/year after 72 h. The AA7075-15Ni coating showed stable passivation at 113 μm/year by formation of Al₃Ni intermetallics. The post-corrosion testing revealed that aluminium-based coatings experienced less corrosion damage. Overall, FS aluminium coatings achieved up to a 90% reduction in corrosion-rate due to dense, self-repairing Al₂O₃ and Zn-based layers across varying pH conditions.