Ce Magnesium Alloy Micro-arc Oxidation And Corrosion Behavior Of Influence

Micro-arc oxidation (MAO) as a new and promising magnesium alloy surface treatment technology, can produce a ceramic oxide coating with higher wear resistance and corrosion resistance by anodic discharge deposition under higher applied voltage and current density. However, it is necessary to research on the complex oxidation growth process and the corrosion process of MAO coating under harsh conditions for further improving its corrosion resistance and eliminating the impact of the porous structure of MAO coating.Rare earth element is well applied in material and its surface modification because of its special electronic structure. This work was mainly focus on the effect of cerium on the coating growth and properties of MAO coating. The main work and reads as follow:Through the single factor experiment, effect of electrolyte, applied voltage, and treatment time on corrosion behavior of MAO coating was studied under constant voltage AC MAO process. The optimal MAO parameter was chosen to obtain the better corrosion resistance of MAO coating.It is well known that substrate is the main influencing factor on the MAO process and MAO coating's properties. Cerium added into AZ91D alloy can form new rare earth intermetal compounds and decrease the size of theαandβgrains. The effect of the composition and structure of substrate change on MAO process was investigated on magnesium alloy modified by Cerium. Further more, growth process of the MAO coating was advanced and the phase composition of MAO coating was changed. A more uniformed and compacted coating was obtained while its corrosion resistance was largely improved.On account of the side effect of cerium on the performance of MAO coating by adding Ce3+ into oxidation electrolyte, a novel kind of MAO coating was prepared on magnesium alloy surface coated with rare earth conversion film (RE-film) in an alkaline aluminum oxidation electrolyte. As the pretreatment of magnesium alloy with RE-film, the cerium oxides can be incorporated into the MAO coatings, reduce porosity of the MAO coating surface and enhance the thickness of MAO coating. These structure features and the cerium oxides incorporated into the MAO coating result in greatly improved corrosion resistance.In terms of corrosion resistance and the corrosion behavior of MAO coating during immersion in 3.5 wt.% NaCl solution, electrochemistry impedance spectroscopy (EIS) measurement, the electronic structure and composition analysis of the MAO coating were analyzed. A double-layer structure, with a compact inner layer and a porous outer layer, of the coating was proposed for understanding its corrosion process. The corrosion process comprised two stage:the initial stage of interlayer broken then the corrosion of substrate in the broken interlayer area.