Environmental corrosion in industrial-marine atmosphere at qingdao of 7050 Al-alloy anodized in boric- and sulfuric-acid electrolyte

Corrosion behavior of 7050 Al-alloy, which was pre- anodized in electrolyte of boricand sulfuric-acid, was assessed through field exposure in industrial-marine atmosphere for 2 a at Qingdao area. The corrosion rate was acquired from the relevant mass-lost data. The surface morphology, distribution of elements and the phase compositions of corrosion products were characterized by SEM, EDS and XRD, as well as the protectiveness of product scale and anodic film was evaluated by using EIS. It is indicated that the bare Al suffered from severe exfoliation corrosion with annual corrosion rate of 5.92 µm·a^-1, and its corrosion product mainly consists of Al(HSO₄)₃·6H₂O, Al₄SO₄(OH)10·5H₂O and NaAlSi₃O₈; the formed corrosion product scale on the bare Al can provide protectiveness to the substrate to some extent, however, the anodized film can provide much better protectiveness in comparison with the formed oxide scale on bare Al.