Application of Ti/Zr Chemical Conversion System on Several Aluminum Alloys and Galvanized Steel

The primer coating technology applicable to a variety of aluminum alloys and steel materials has become a key requirement for the manufacturing of lightweight body for new energy vehicles. In this paper, a study on chemical conversion of metal surfaces based on the titanium/zirconium composite system was carried out on 6061 and 7075 aluminum alloys and galvanized steel. The effects of H2TiF6 concentration, H2ZrF6 concentration and process parameters on the corrosion resistance of the coatings formed on the surfaces of the three metals were investigated through copper sulfate spot experiments, and the corrosion resistance of the coatings was verified by electrochemical testing. Moreover, the scanning electron microscope and the energy spectrometer were employed to observe and analyze the surface morphology and element composition of the conversion coatings. Results showed that after a conversion treatment under the conditions that the H2TiF6 concentration was 1.60～2.00 mL/L, the H2ZrF6 concentration was 0.80～1.30 mL/L, the conversion time was 90 ～ 150 s, the pH value was 3.5 ～ 4.5, and the temperature was 30～40 ℃, these three kinds of metal materials possessed good corrosion resistance. The Jcorr of three metal materials decreased significantly in comparison with that of the blank sample, and the Ecorr of the blank sample was significantly lower than that of the other samples. In addition, the EIS spectrum showed that the film resistance Rct of the three metal materials treated with chemical conversion was significantly higher than that of the blank sample. The differences in the surface microstructure of the samples at different times was observed by SEM, and there were significantly fewer micropores and cracks on the surfaces of 6061 and 7075 aluminum alloys and galvanized steel after a treatment for 120 s.