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Abstract
An environmentally friendly anodising electrolyte for the corrosion protection of magnesium alloy AZ31 was optimised using orthogonal experimental design of four factors with three levels. Electrochemical tests were conducted to determine the corrosion resistance of anodic film. The microstructure and phase composition of the optimised film were characterised by scanning electron microscope and X-ray diffraction respectively. The results show that the optimised electrolyte is composed of 60 g L−1 potassium hydroxide, 20 g L−1 sodium silicate, 30 g L−1 sodium tetraborate and 10 g L−1 sodium phosphate. The significance of electrolyte factors affecting the corrosion resistance of anodic film can be ranked as sodium phosphate>sodium silicate>sodium tetraborate>potassium hydroxide. The optimised film is porous like the basic film, but it is more compact and therefore more corrosion resistant than the basic film. The optimised film is mainly composed of MgO, Mg2SiO4 and MgP4O11.