Forming Process of Rare Earth Conversion Coatings on LY12 Al Alloy

A Cu/Al galvanic couple was used to simulate the electrochemical behavior of LY12 aluminum alloy in cerium salt solutions. The galvanic current decreased with time from 0.08 mV to 0.005 mV after immersion in the solutions, which indicates that the corrosion was inhibited. The galvanic potential moved negatively, which shows the cerium film inhibits the cathodic reaction. After 8 h of immersion, a yellow layer was formed on the copper of the galvanic couple. SEM, EDX anslyses show that the layer has a dry mud appearance and contains a mess of Ce.