Polymer plating of 6-diallylamino-1,3,5-triazine-2,4-dithiol and 1,3,5-triazine-2,4,6-trithiol on magnesium alloys has been carried out to provide adhesion property with plastics. Magnesium alloys treated electrochemically with 1,3,5-triazine-2,4,6-trithiol adhered directly with poly(phenylene sulfide) during injection molding under conventional conditions. It is considered that the adhesions become possible for resulting in chemical bonds in the interface between plated magnesium alloy surfaces and polymer chains during molding.