Polystyrene Coating on APTES-Primed Hydroxylated AA2024-T3: Characterization and Failure Mechanism of Corrosion

Abstract

Polystyrene has limited adhesivity to inorganic materials such as metals. However, the inorganic surface can be treated to enhance bonding to energetically stable polystyrene. This concept is verified in this paper with organosilane aminopropyltriethoxysilane (APTES) as the coupling agent primed on hydroxylated aluminum alloy AA2024-T3. We characterize the structural integrity and electrical impedance of the polystyrene coating on APTES-primed surfaces with different cured conditions after exposure to 3.5 wt.% NaCl solution for seven days. The results show that top-coated polystyrene on APTES is more structurally intact and less electrically conductive than the polystyrene coating alone. The coating layer made of top-coating polystyrene on a curing APTES film has the largest water uptake rate in the early stage of immersion in the corrosion solution. In the later stage, all coating layers tested regained their impedance while losing structural integrity. The charge transfer in the double layer of coated specimens for all types of coatings tested is predominantly through capacitance-based charging/discharging, presumably governed by the adsorption mechanism of ions at the coating/substrate interface.