The Research On Process Parameters And Growth Mechanism Of Magnesum Alloys Micro-arc Oxidation

Micro-Arc Oxidation is a new surface treatment technique, developed from anodic oxidation. In this paper, a silicate electrolyte system components and its corresponding process parameters for the Micro-Arc Oxidation technique on magnesium alloy AZ91D was studied. Their effects on the sparking voltage,thickness,surface morphologies,composition and phase constitution of the ceramic coating were investigated by means of Energy Dispersive Spectrometer (EDS).Furthermore, their influences to the ceramic coating formation course and mechanics were discussed.An optimized silicate electrolyte system compounds and its corresponding process parameters, which could fast prepare a high quality ceramic coating on the magnesium alloy AZ91D were obtained as follows: Na₂SiO₃13g/L, NaOH12g/L, KF4g/L, impulse frequency 700Hz, oxidization time 10min.The experiment results have shown that, the electrolyte component affects its conductance, which causes variety of the coatings breakdown voltage, and causes the change of ceramic coating growth rate. The impulse frequency affects the ceramic coating surface quality. The oxidation time is related to increasing coatings thickness, improving the homogeneous simultaneity.Experiment results show that the ceramic coating on the magnesium alloy is mainly compose of MgAl₂O₄ phase, Mg₂SiO₄ phase and MgO phase, which mass percents are influenced by the voltages significantly but individually. And the ceramic coating can be approximately divided to the dense layer and the loose layer. The boundaries between the dense layer and the loose layer are not clear. The ceramic coating possesses good compactness, adhesion, integrity and protective ability, can enhance wear-resistance of magnesium alloy.Based on the experiment results, according to the change of process parameters, build micro-arc oxidation model.