Cerium-based modification treatment of Mg-Al hydrotalcite film on AZ91D Mg alloy assisted with alternating electric field

An environment-friendly cerium-based conversion coating (CeCC) was prepared by alternating electric field assisted treatment for the modification of magnesium-aluminum (Mg-Al) hydrotalcite (HT) film on AZ91D Mg alloy. The influence of cerium nitrate (Ce(NO3)3) concentration was evaluated in terms of morphology, composition, and corrosion resistance. The results showed that deposition behavior (including deposition amount and sealing effect) of CeCC was controlled by Ce(NO3)3 concentration. The HT film treated with 10 g/L Ce(NO3)3 was better sealed; the HT film immersed in 30 g/L Ce(NO3)3 displayed larger deposition amount of CeCC. With the increase in concentration from 5 to 40 g/L, the corrosion resistance exhibited a waving trend. The treated HT film with better sealing effect or larger deposition amount revealed superior corrosion resistance.