Preparation of cerium oxide based environment-friendly chemical conversion coating on magnesium alloy with additives

Ce(SO4)2-H2O2 solution was adopted to prepare a chemical conversion coating on AZ91D magnesium alloy. Additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate were applied to improving the coating formation. SEM, EDS, XRD and GIXD were adopted to study the coating morphology, structure and composition, and the potential change curve in the treating solution was recorded to study the coating growth. Sodium dodecyl benzene sulfonate makes a remarkable improvement in the coating compactness, and shortens the time in the second stage of the coating formation from 5 min to 2 min. Compared to Ni(NO3)2, sodium dodecyl benzene sulfonate makes the more remarkable effect on the corrosion resistance improvement, since it can decrease the current density of corrosion from 7.41×10−5 A/cm2 to 2.20×10−5 A/cm2. The additives of Ni(NO3)2 and sodium dodecyl benzene sulfonate can enhance the Ce content from 18.92% to 22.32% and 25.08% in the coating, respectively. The XRD and GIXD results indicated that all the conversion coating formed in different solutions exhibit amorphous structure.