Silicate Passivation Treatment On Aluminum Surface

Aluminum has low density, high specific strength and good corrosion resistance; it has been used in many industries. Because the standard electrode potential of aluminum is low, it is easy to corrode. In order to improve its corrosion resistance, we have used the chromate passivation treatment. Because the carcinogenicity of hexavalent chromium, China has begun to execute the EU RoHS directive since the March 1,2007 and abolished the metal surface chromate treatment which has a century-old traditional. It is very eager to develop the alternative technologies for our scientists.Based on the experiments of aluminum surface treatment’s conversion liquid composition and film-forming reaction conditions, we gained the optimum reaction conditions is 15g/L silicate,25g/L EDTA, disodium in the pH:11.5,65℃, reaction time is 10min, neutral salt spray time can be reached 10 hours. After the Sodium silicate treatment, corrosion resistance of aluminum alloy increased, and the coating is colorless. The reason is that, SiO32- which is hydrolyzed from the sodium silicate reacts with the Al3+ which is from conversion reaction. Aluminum surface is covered by the alumina-silicate. Experimental results show that the appropriate pre-and post-treatment can further improve the alloy’s corrosion resistance.