A method for coating, a composition suitable for coating and a coating generated with the method of coating on anodizable metallic surfaces, especially on magnesium rich and aluminum rich surfaces, is disclosed. The composition is an aqueous solution including alkali metal or ammonium cations, phosphorus containing anions and silicon containing anions as well as optionally a peroxide or a compound of Al, Ti, Zr or any mixture of them. Preferably, the anodizing is carried out with a micro-arc oxidation process.