Modification Of Fluoroaluminate Conversion Coating On Al Alloy6063

With good characteristics, aluminum alloys are widely used in air transportation,light industry and construction materials, electronic communications and many otherfields. However, easily corroded in the process of production and use, Al alloys areoften treated by chromate treatment technology which is economic and effective inorder to improve their anti-corrosion performance. Because of carcinogen, Cr(VI) waslimited to use in the metal surface treatment by the European Union RoHS Directive(Restriction of certain hazardous substances in electrical and electronics equipment) asearly as2006, and “Heavy metal pollution comprehensive prevention and control12thfive year plan”, the first12thfive year plan, was put forward in2011, giving strictcontrol requirements to the five heavy metals including hxavalent Cr. Therefore, analternative to chromate conversion coating is urgently needed.Aimed at the problem of low anti-corrosion properties of fluoroaluminateconversion coating from our previous research, the coating was modified with Na2SiO35g/L,(NaPO3)6, NH4VO3by single factor experiment method firstly. Then, thecomponents and the operation conditions of the conversion solution were furtheroptimized. The results showed that under the condition of NaF7.5g/L, Na2SiO35g/L,(NaPO3)63g/L, NH4VO35g/L, pH3.0~4.0, room temperature and20minutes, the saltspray time of the conversion coating obtained could increase to264h from24h beforemodification, which was much larger than the industry use requirement of96h.The results from SEM and EDS analysis showed that the conversion coatingconsisted of5.22%O、47.63%F、20.37%Na、20.79%Al、1.15%Si、3.88%P and0.79% V. After modification，the conversion coating was still made of granular fluoroaluminatecoating, but the gap of particular skeleton was precipitated with Al2(Na4P6O18)3andsilicon, vanadium oxides. Therefore, the coating was more denser, Al alloys’corrosionpotential about70mV more positive, corrosion current density nearly90％lower, andthe corrosion resistance ofAl alloy6063was significantly improved.