Cathodic electrodeposition of hybrid silane pre-treatment on mild steel to improve adhesion and protection of epoxy coatings

In this article, hybrid silane coatings were applied on mild steel via dip-coating and electrodeposition methods. Different cathodic potentials of −0.3, −0.5, −1, and −1.5 V/SCE were applied for electrodeposition. Based on scanning electron microscopy (SEM) and water contact angle results, respectively, the more uniformity and hydrophobicity were obtained when the silane film was applied via electrodeposition at cathodic potential of −0.5 V/SCE. The findings of electrochemical impedance spectroscopy (EIS) and Tafel polarization test implied that the sample treated with −0.5 V/SCE exhibited the most superior anti-corrosion performance among the different sol-gel coated samples. Compared with dip-coated sample, the R_f improved from 6.8 to 16.2 kΩ.cm² and consequently R_ct enhanced from 45.6 to 92.2 kΩ.cm². Similarly, i_corr reduced from 0.263 to 0.070 µA.cm⁻². Subsequently, organic coating of epoxy was applied on the dip-coated, electrodeposited silane pretreatment at cathodic potential of −0.5 V/SCE as well as untreated mild steel substrate to figure out how silane film affected the dry and wet adhesion characteristics of the covering epoxy via pull off test. Comparing the outcomes revealed that the modification of the carbon steel substrate resulted in improved adhesion strength when it treated through electrodeposition at cathodic potential of −0.5 V/SCE. It was followed the sequence of untreated substrate < dip-coating < electrodeposition pretreatment.