Abstract
Effect of various eco-friendly surface treatments based on Titanium conversion coatings (in the presence of molybdenum, nickel, phytic and hexaflourozirconic acid compounds) on electrochemical and surface properties of steel substrates was studied comprehensively. Moreover, chromate and tri-cationic phosphate conversion coatings were used as references. Tungsten micro-electrode was used to study the film formation mechanism of conversion coatings and obtained results indicated that an increase in local pH (about 4 units) is responsible for the precipitation of coatings. FE-SEM and AFM images revealed that modification by Ni ions results in formation of uniform and pack layer structure which improves barrier properties of conversion coating. Moreover, the interaction of conversion coatings with epoxy coating was evaluated with respect to anti-corrosion and adhesion performance. Obtained results indicated that Ti-based surface treatments modified by nickel ions and phytic acid, have better adhesion strength to epoxy coating (4.2 and 4 MPa respectively) and indicated better anti-corrosion performance (according to EIS and salt-spray tests) compared to traditional chromate and phosphate conversion coatings.
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