Improvement in the corrosion resistance by Ce–Mo chemical conversion treatment in Al–Mg alloys with Cu addition by electron beam process

Abstract

We investigated the corrosion resistance of Al–Mg(5052) alloys by means of the electro-chemical measurement, the immersion test and the observation of structures. The surface of alloys were modified by adding Cu with electronbeam melting method, and then coated with the oxide film contained Ge and Mo elements by three chemical treatments. The corrosion resistance of the alloy coated with the oxide film by immersing in the 4×10⁻³ kmol·m⁻³ Ce (CH₃CO₂)₃ boiling aqueous solution for 5.4 ks was improved more than by the other chemical treatments. The small Ge and Mo were in the oxide film and the distribution of these element is not uniform. Especially the concentrations of Ge and Mo were high in the vicinity of the intermetallic compound (Al₂Cu) . Micro voids and the other defects in the oxide films were increased with the increase in the intermetallic compound Al₂Cu existing as secondary phase, and those defects affected as a corrosion initiation.