Preparing an Environment-Benignly Rare-Earth Based Chemical Conversion Coatings on 6063 Aluminium Alloy

In order to develop an environment-benignly chemical conversion process to substitute the toxic hexavalent chromium treatment on Al alloy surface, a new surface treatment technology based on rare-earth element, which is to form chemical conversion coating on 6063 Al alloy was presented. In this process, Ce(NO3)3 was adopted in the chrome-free preparing solution, and KMnO4 was used as oxidant to accelerate the coating formation on 6063 Al alloy. Furthermore, an L16(43) orthogonal experiment was carried out to examine the effect of Ce(NO3)3, KMnO4 and solution temperature on the coating growth on 6063 Al alloy. Accelerants of SrCl2 and NH4VO3 were added to the preparing solution to improve the coating performance. XRD, SEM and EDS were used to analyse the coating surface structure, morphology and composition. It was found that a good anti-corrosion coating which is mainly composed of the elements of Al, Ce, O, Mn, Mg could be formed in the optimal preparing solution of 5g/L Ce(NO3)3 , 4g/L KMnO4, 1.4g/L SrCl2 at the temperature of 20°C.