Evaluation of the role of surface pretreatments on the corrosion process. Correlation between conventional and electrochemical tests

The influence on the anticorrosion properties of three different pretreatments applied on steel panels, before being powder‐paint coated, is investigated both by conventional tests (cross cut, impact resistance, and neutral salt spray tests) and electrochemical tests (electrochemical impedance spectroscopy (EIS) and accelerated cyclic electrochemical technique (ACET)). Amorphous phosphate, microcrystalline phosphate, and a sol‐gel, based on 3‐aminopropyltriethoxysilane (APTES), were the different pretreatments that were analyzed. All of them were compared with a non‐pretreated coated carbon steel panel. The microcrystalline phosphate, followed by the sol‐gel surface treatments, showed the best system properties. These good results are attributed to PO4−3 ions available at the interface, and to covalent bonds generated by the silicon network and the substrate surface, respectively. It has been observed that phosphate molecules enhance the characteristics of coatings on steel. The more ordered the structure of the layer, the better improvement on properties. It has been confirmed that electrochemical tests lead to similar results than conventional measurements and give more accurate and deep information. But, in all cases, it is difficult differentiating close behaviors.