Effect of sol-gel layers obtained from GLYMO/MTES mixtures on the delamination of a cataphoretic paint on AA1050

In this study, the performance of different sol-gel layers produced from different mixtures of silicon alkoxides precursors (gamma-glycidoxypropyltrimethoxysilane, GLYMO, and methyltriethoxysilane, MTES) applied on AA1050 aluminum alloy as a pretreatment prior to depositing an electrophoretic paint (polyether-polyamine polymeric blend) is investigated. The structure of the sol-gel coatings was characterized by means of ATR FTIR, while the corrosion protection properties were assessed by polarization curves. Accelerated laboratory tests, such as exposure in both neutral and acetic salt spray chambers and filiform corrosion tests, were employed to investigate the corrosion protection properties of the cataphoretic paint-coated samples. The failure mechanisms of the different coatings were investigated. The experiments revealed that the presence of GLYMO in the sol-gel coating seems not to be suitable for acting as a coupling agent between the paint and the aluminum substrate. On a positive note, this work shows that the filiform corrosion test seems to be the most appropriate test to evaluate the efficiency of sol-gel layers employed as pretreatment to enhance the corrosion protection provided by a paint on an aluminum substrate.