Aluminum Tube Surface Composite Passivation And Corrosion Resistance

The silane-rare earth cerium composite coatings on the aluminum-tube used in evaporator of refrigerators were prepared by immersion in the workable solution in the paper. The best process conditions of coatings formed that the time of silane hydrolyzing is 40h at room temperature, passivation temperature of silane and rare earth cerium solution are 30℃and 60℃respectively, passivation time and temperature of coatings formed are 60s and 100℃respectively, were obtained by optimizing preparation process. Anionic surfactant sodium dodecyl sulfonate SDS used as additive to prepare modified silane-rare earth cerium composite coatings was selected by means of linear sweep voltammetry. The corrosion resistance of the two coatings was assessed by copper sulfate dropping test, alkaline leaching weight loss, collecting hydrogen experiment, neutral salt spray test and electrochemical methods. Scanning Electron Microscope(SEM) and X-ray Energy Dispersive Spectroscopy(EDX) were used to analysis morphology and composition of the coatings.The results of testing indicate that corrosion resistance of the composite coatings greatly improved compared with blank sample. The time of copper sulfate dropping is 56"50, loss weight rate is 0.0006261 W/S-h(g/cm2·h), releasing hydrogen's time is 3.5h, the anti-pitting corrosion time is 226h, the self-corrosion current and impedance value are 7.2991E-6A/cm2and 12586Ωrespectively, which show that the composite coatings is less effective than the coatings with Cr. However, the results of corrosion resistance showed that the composite coatings modified with SDS are better than the coatings with Cr, which The time of copper sulfate dropping is 1'04"48, loss weight rate is 0.0001657 W/S·h(g/cm2·h), releasing hydrogen's time is 4.5h, the anti-pitting corrosion time is 252h, the self-corrosion current is 4.9582E-7A/cm2. SEM observation showed that the modified composite conversion coat is much more uniform and dense than the composite coatings; EDX test showed that the complex coat is mainly composed of N, O, Si, Al and Ce and the content of S and Si increased greatly because of SDS adding. The coatings formed and corrosion protection mechanisms of the composite coatings were also analyzed in the paper.SDS modified silane-rare earth cerium composite coatings, which can be well used to replace the chromate treatment, is expected to be a practical passivation technology of the aluminum and aluminum alloy because of simple process, environmental friendly and excellent corrosion resistance.