Scrutinizing the importance of surface chemistry versus surface roughness for aluminium / sol-gel film adhesion

•Significant increase in adhesion strength of epoxy bonded commercially pure aluminium by the application of a hybrid sol-gel film has observed•Pre-treatment of aluminium strongly affect the surface morphological and surface chemical properties•Statistical analysis enabled distinction between individual contributions of surface roughness and surface chemistry•A strong correlation was found between surface hydroxyl fraction and adhesion strength, evidencing the effect efficient interactions across the aluminium/sol-gel interface on the properties of the sol-gel•The relation of roughness and water contact angle to interfacial adhesion were found to be non-significant The sol-gel synthesis process is a versatile method used to produce a wide diversity of materials and is being increasingly used as a surface modification method to alter porosity, wettability, catalytic activity, biocompatibility and corrosion performance of underlying substrates. Silane sol–gel films deposited on aluminium and aluminium alloys have been widely studied as chemical conversion coatings and as coupling agent between the substrate and organic layers. This study set out to investigate the effect of the surface chemical treatment prior to sol-gel application on the interfacial adhesion properties of a hybrid sol-gel film. Different surface pre-treatments, including two abrasive treatments and three chemical surface pre-treatments were used and their effect on surface chemistry and surface roughness was assessed. Surfaces were characterized by scanning electron microscopy, x-ray photoelectron spectroscopy, roughness measurements and static contact angles. Cerium nitrate loaded hybrid sol-gel films were deposited and adhesion on commercially pure aluminium was evaluated using pull-off testing. Statistical analysis revealed that, although highest adhesion values were obtained on rougher surfaces, the strongest correlation exists between the surface hydroxyl fraction and adhesion strength. [Display omitted]