Corrosion behaviors and galvanic studies of microarc oxidation films on Al-Zn-Mg-Cu alloy

Corrosion-resistant films were fabricated by the microarc oxidation technique on the LC4 zinc-containing aluminum alloy in silicate electrolyte. The electrochemical corrosion behaviors of LC4 alloy, with and without films, were evaluated using potentiodynamic polarization curves. Galvanic currents and galvanic potentials of bare and coated alloys coupled with copper were measured using the zero-resistance technique. Scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) was used to analyze the microstructure of films and the corrosion morphology before and after corrosion testing. After microarc discharge treatment, the corrosion potential was increased and the corrosion current was significantly reduced. For a thin film sample, the galvanic current is similar to that of the bare alloy. However, a thick film can protect the LC4 alloy against galvanic corrosion.