Adsorption of BTSE and γ-APS organosilanes on different microstructural regions of 2024-T3 aluminum alloy

The adsorption of bis-1,2-(triethoxysilyl)ethane (BTSE) and γ-aminopropyltriethoxysilane (γ-APS) has been studied on 2024-T3 aluminum alloy samples using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The thickness and coverage of the BTSE film formed on a mechanically polished sample was found to be strongly affected by the distribution of second-phase particles on the alloy surface. Specifically, although the adsorption occurs on the alloy matrix away from the particles, and on the particles themselves, the regions immediately surrounding the particles had less BTSE. The amounts of this adsorption on an air-oxidized sample is increased on average, although the coating is non-uniform with regions (∼100 μm) of higher and lower coverages. There appears to be a competition between the silane deposition and etching of the underlying oxide film for the initially oxidized sample. The adsorption of γ-APS is different with films of relatively even thickness formed over large areas of the polished sample; hydrogen bonding through the amino groups probably helps the distribution in this case.