Effect of Electrolyte Composition on Properties of Phosphoric Acid Anodization Film on Aluminum Alloy Surface

2124 aluminum alloy was anodized by using phosphoric acid as the base electrolyte.The effect of electrolyte composition on properties of alumina film was investigated.The results indicated that with the increase of phosphoric acid concentration,the thickness of alumina film increased,and hardness of alumina film decreased,when phosphoric acid was in the range of 10~40 g/L.And the film was of high quality when film forming additive was added into phosphoric acid electrolyte.The optimum formula of phosphoric acid composite electrolyte was selected.The results were significant to synthesize alumina film with large aperture,high thickness and high hardness.