No Chrome Dacromet Preparation And Properties Of Coating Solution

Dacromet technology is a new metal surface anti-corrosion technology which has many advantages such as high corrosion resistance, no hydrogen embrittlement and small environmental pollution, it has been widely applied since it came out. However, it has some shortcomings and deficiencies need to be further studied and improved. From the environmental point of view, hexavalent chromium is the biggest problem for its high toxicity and carcinogenic effect. In the auto-industry of developed industrialized countries in the world, many famous brand vehicles have adopted chromium-free coating technical standard. In other industries adopting the low chromium and chromium-free standard is also the trend of the application of dacromet. Looking for the chromium-free substitutes which have superior performance in all aspects is an inevitable developmental direction of dacromet technology.The purpose of this paper is through experiment to find a chromium-free acid system which could instead of the chromic acid in the chromium dacromet liquid, and prepare a new kind of chromium-free dacromet liquid which has anti-corrosion performance.The main contents of this paper are to research the selection of chromium-free acid system and prepare chromium-free dacromet dope liquid. The selection of chromium-free acid system is basicd of acid or salt being similar to chromium, and is prepared by adding organic acids or inorganic acid. Through researching the compatibility and stability of acid system, we determined its composition, Through orthogonal testing ,we determine the composition of acid system. The results show that the chromium-free acid system is composed of Sodium molybdate and boracic acid and methanoic acid. The best composition is that the percentage of Sodium molybdate is 10%, the percentage of boracic acid is 1%, and the percentage of methanoic acid is 8%. Sodium molybdate has the greatest impact on the coating, the second is boracic acid and the third is methanoic acid.Adopting the orthogonal experiment to study the composition and craft of chromium-free dacromet dope liquid. The acid system, zinc powder, aluminum powder, polyethylene glycol, the sintering temperature and time as a factor to consider, the coating appearance, adhesion and 5% NaCl immersion testing as a factor to indicate, and using the orthogonal experiment by the table of L₂₇ ( 3¹³) to design the chromium-free dacromet dope liquid composition and craft. According to studying the dope liquid composition by orthogonal experiment and coating sinter craft, and examining the coating performance, and contrasting the chromium-free dacromet coating with the chromium daromet coating, all of analysis results indicate that the excellent composition of preparing the chromium-free decromet dope liquid is as follow, Zinc powder is 300g/L, Aluminium powder is 70g/L, the mixed acid is 40g/L, assemble glycol is 180g/L, technics agglomeration temperature is 300°C and time is 30 minute. The time of appearancing red rust is 1500h in 5%NaCl liquid and is 720h in the neutral salt mist.Using the metallographic microscope and scan electricity mirror to analyzing coating surface appearance and section appearance, the results show that the coating is uniformity and continuum, and which is tight combined with radicle object. Using the power spectrum analyzer and X beam diffraction instrument to analyzing coating element composition and appearance composition, the results show that costing consisted of a mass of Zn and Al, and the gross of Zn and Al is more than 70%, and the quality percentage of oxygen is about 20%, three substances form the oxide which has effective passivation action. In summary, those experiments made a chromium-free acid system and water-solubility chromium-free dacromet dope liquid, and the coating has excellent anti-corrosion performance. The study in this paper provides a new method of preparing chromium-free dacromet dope liquid, and has a reference value of researching and improving chromium-free dacromet dope liquid.