The Anti-corrosion Modification Of Sodium Dodecyl Benzene Sulfonate On Vanadate Conversion Coating On Mg Alloy

Magnesium alloys, which has a relatively low density, high strength, impact resistance, good machining performance, wear-resistant, etc., are widely used in the automotive, aviation, light industry and other fields, known as the "21st century green engineering material." However, compared with aluminum and steel, magnesium alloys have low chemical stability and poor corrosion resistance. The traditional chromate conversion processing technology can prepare good corrosion resistance conversion coating on Mg alloy surface. However, due to their strong carcinogenicity, chromates cause serious harm to humans and the environment. In2011, China' s "Heavy metal pollution comprehensive prevention and control12th five year plan" clearly limits the use of five kinds of heavy metals including chrome. Therefore, the research for non-chromate conversion treatment technology is progressing in the world.In this paper, in order to solve the problem of poor corrosion resistance of vanadate conversion coating on Mg alloy, sodium dodecyl benzene sulfonate was to change the corrosion resistance of vanadate conversion coating. The research results showed that under the condition of sodium dodecyl benzene sulfonate1.2g/L, vanadate2.2g/L, pH4.0,15min,30?, a conversion coating was prepared on AZ31B Mg alloy. Its neutral salt spray time was up to72h, which was60h more than that before modification and higher than8h industrial application requirements.The results from SEM, EDS, Fourier transform infrared spectroscopy and polarization curve test showed that the modified conversion coating was the amorphous structure and contained10.82%C,0.83%V,28.50%O,1.57%F,56.30%Mg and absorption peaks relating with organic function group of SDBS. The corrosion potential of Mg alloy was-1.263V and-1.246V, the corrosion current density was1.50×10-5A/cm2and5.99×10-6A/cm2bafore and after modification, respectively. The corrosion potential of Mg alloy increased17mV and the corrosion current density decreased60%compared with the un-modified sample. The corrosion resistance of Mg alloy significantly enhanced. The binding force was strong between the modified conversion coating and Mg alloy substrate...