Corrosion analysis of bare and open-air plasma-assisted organosilicon-coated aluminum alloy 7075 using electrochemical polarization

Abstract A novel open-air plasma jet process was used to deposit organosilicon corrosion barrier coating on aluminum alloy 7075-T6 (Al 7075); its protection effect was evaluated by electrochemical polarization and ASTM B117 salt spray exposure tests. Three independent processes (P/a, P/b, and P/c conditions) produced continuous and dense coating with representative thicknesses of approximately 780, 1380, and 1630 nm, respectively, and similar Si, O, and C contents in the examined STEM-EDS regions. To set a reasonable basis for electrochemical corrosion evaluation, a localized corrosion stabilization potential of uncoated Al 7075 was investigated by analyzing current transients at different anodic overpotentials in 3.5% NaCl, revealing a marginal passive regime of <54 mV for Al 7075. Under a 60 mV anodic overpotential, the approximately 1630 nm P/c-coated specimens maintained low currents in all four tests, suggesting corrosion-protection performance that may be comparable to the approximately 19 µm anodized condition within the limited dataset in the present testing conditions. In the ASTM B117 exposure tests conducted only for the uncoated and down-selected P/c-coated Al 7075, the organosilicon layer exhibited only minor corrosion damage compared to the uncoated Al 7075 that suffered from severe corrosion attack after 962 h. This work reports a novel corrosion barrier coating and a method for determining the localized corrosion stabilization potential of Al 7075.