22 Pages

Improved water-based silane pretreatment for hot-dip galvanized steel substrates

Abstract-Bis-silane films have proved to be environmentally benign, non-toxic and competent replacements for chromates as pre-treatments for corrosion protection of metallic substrates. So far the best performance has been shown by solvent-based silanes, having high volatile organic content (VOC). Amongst the water-based silanes, AV5, a 5:1 mixture of bis-[trimethoxysilylpropyl]amine (A1170) and vinyltriacetoxysilane, has shown great promise for aluminum-based alloys. However, its performance in case of more susceptible substrates, like hot-dip galvanized (HDG) steels and cold-rolled steels, is below par. The aim of this work was to improve the suitability of AV5 as a pretreatment for hot-dip-galvanized steel. This silane mixture was modified with an additive for crosslinking and toughening, and a corrosion inhibitor for self-healing. The concentration levels were optimized for the best performance after testing formulations with all the nine possible combinations of factor levels. Electrochemical Impedance Spectroscopy (EIS), Direct Current Polarization (DCP) and salt immersion were the performance tests utilized for this screening. The efficacy of corrosion inhibitive action was confirmed using the scratch cell test. The chemical nature of the improved system, vis-à-vis the base silane system (AV5), was investigated using IR spectroscopy. The optimized system showed enhanced corrosion protection, vis-à-vis the base silane system.