Characterization of hot-dip galvanized (HDG) steel treated with γ-UPS, VS, and tetrasulfide

The aim of this work was to study the suitability of silane treatments for hot-dip galvanized (HDG) steel. Silane coupling agents are used as adhesion promoters between paint and galvanized steel. The focus in this paper is on the characterization of the silane-treated surfaces. The adhesion and corrosion performance of the selected silanes in painted galvanized steel systems are reported separately. In this work, HDG steel was treated with γ-ureidopropyltrimethoxysilane (γ-UPS), vinyltrimethoxysilane (VS), and bis-(3-[triethoxysilyl]-propyl)-tetrasulfide (A-1289), and the samples were characterized by surface analytical methods. The treatment technique and the deposition pH affected the amount of silane that could be adsorbed onto HDG steel from the solutions of γ-UPS and VS. The results show that more ureido groups are present on the surface side of the γ-UPS film than near the silane-zinc interface. Better coverage of the treated surface was obtained at the higher pH studied, i.e. pH 8. According to the surface energy results, the γ-UPS films are stable in air. The VS films consisted mainly of low-molecular-weight siloxanes. The rinsed VS films were shown to be stable, whereas a sudden change in the surface basicity was detected in the unrinsed films within 24 h from treatment. The results of A-1289 differed from those obtained with the water-soluble silanes. The chemical and structural compositions of the unrinsed and rinsed films of A-1289 were similar. The films could not be rinsed off by water and were thermodynamically stable.