Compound additive for magnesium alloy micro-arc oxidation

The invention relates to a compound additive for magnesium alloy micro-arc oxidation, which consists of trivalent rare earth compound, silane coupling agent and multi-component carboxylate, wherein the rare earth compound is one, two or three of cerium nitrate, neodymium nitrate and lanthanum nitrate; the amount of the rare earth compound is 0.1 to 1 percent; the multi-component carboxylate is one or two of tartrate, citrate, phytate, lactate and oxalate; the amount of the multi-component carboxylate is 5 to 20 percent; a coupling-agent additive is silane with an organic functional group; and the amount of the coupling-agent additive is 1 to 8 percent. The compound additive can be used for various alkaline systems of magnesium alloy micro-arc oxidation of silicate, phosphate, aluminate and the like, and can perform magnesium alloy micro-arc oxidation at room temperature after full mixing. Under the same oxidation conditions, micro-arc oxidation film prepared by use of the additive can be soaked in 3.5 percent NaCl solution for 400 hours with no corrosion, and the hardness of the film remains unchanged.