SEM was employed to characterize the surface morphology evolution of coatings prepared by micro-arc oxidation on magnesium alloy in silicate solution. The possible growth mechanism of micro-arc oxidation coatings was proposed. The results showed that the coating grew by the following steps : the stage of anodic deposition, micro-arc oxidation and local arc light. In the stage of anodic deposition, the flocculent oxidation film deposits and extends on the surface of MB8 magnesium alloy. The next stage of mi...