Influence of oxidant KMnO₄ on film-forming process of rare earth metal conversion coating on LY12 aluminum alloy

A Cu/Al galvanic couple was established to study the influence of the oxidant KMnO₄ on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminum alloy. It is found that the galvanic couple simulative experiment accords with the actual immersion, and it can be substantially used to simulate the behavior of LY12 aluminum alloy in the film-forming process. It is showed that the formation of the coating is quickened in CeCl₃ solution containing KMnO₄ compared with that not containing KMnO₄. XPS results reveal that the coating formed on cathode is composed of oxide or hydroxide of Ce and Mn, so the mechanism of formation of REM conversion coating changes when KMnO4 is added.