| With good characteristics, aluminum alloys are widely used in light industry andconstruction materials, aerospace, electronic communications and many other fields.However, easily corroded in the process of production and use, Al alloys are oftentreated by chromate treatment technology which is economic and effective in order toimprove their anti-corrosion performance. Because of carcinogen, Cr(VI) was limited touse in the metal surface treatment by the European Union RoHS Directive (Restrictionof certain hazardous substances in electrical and electronics equipment) as early as2006,and “Heavy metal pollution comprehensive prevention and control12thfive year plan”,the first12th five year plan, was put forward in2011, giving strict control requirementsto the five heavy metals including hexavalent Cr. Therefore, an alternative to chromateconversion coating is urgently needed.Because of its simple, convenient, easy to operate? low cost, non-toxic,environmentally friendly?sodium silicate sealing treatment was used to further improvethe corrosion resistance of fluoroaluminate conversion coating in the thesis. The processconditions of single sodium silicate sealing solution were studied. The single factorexperimental results indicated that the neutral salt spray time of fluoroaluminateconversion coating sealed with12g/L Na2SiO3, pH12,40?50?,30min?was up to360h, far more than168h industrial application requirement.The research results from SEM?EDS and electrochemical polarization measu-rements showed that the composition of Al alloy surface changed from50.75%F?16.89%Na?32.32%Al?0.17%Si before sealing to42.21%F?12.17%Na?37.88% Al?1.47%Si?6.27%O after sealing with Na2SiO3solution. After sealing?alumin-osilicate and silicon-oxide polymer were formed among ordered and uniform granularfluoroaluminate conversion coating, which made the corrosion potential244mVhigher. Therefore?the corrosion resistance of Al alloy was evidently increased. |
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