Effect of surface morphology on the adhesion of silicone elastomers on AA6061 aluminum alloy

Abstract In this study, different primer formulations were used for enhancing the adhesion between a high consistency methyl phenyl vinyl silicone rubber (HCR) and AA6061 aluminum alloy. These formulations were selected on the basis of their different chemical composition. One contains only silanes and a titanate catalyst, a second contains only reactive macromolecular polysiloxane chains and a third contains both silanes and reactive macromolecular polysiloxane chains as the main components. The effect of the metal surface topography on the efficiency of the primers was investigated. The condensation reactions in the primers were followed by Fourier Transform Infrared Reflexion Absorption (FTIR-RA) spectroscopy and rheological measurements. 90° peel test was used to measure the adhesive strength of the silicone on metal and the fracture surfaces after peeling were analysed using SEM-EDS to determine the loci of failure. Cure monitoring of the silane based formulations showed that hydrolysis/condensation of silanes occur rapidly after their application on AA6061 surfaces and lead to a high degree of crosslinking even in the formulations with PDMS additives. The heat cure of the formulation based on a one-component addition curing system (SiH oligomer, vinylated-PDMS with a platinum catalyst) resulted in a film with a high cohesive strength. The primer formulation containing silanes and reactive PDMSs as the main components resulted in the best adhesion of the silicone elastomer with a dominant cohesive failure. However, a weaker adhesion was obtained at a high roughness of the substrate due to a weak adhesive strength at the metal/primer interface. A pretreatment composed of a first layer of activated silanes and a second layer of reactive silicone chains gave a good adhesion both at low and high roughness of the aluminum substrate. Roughening of the metal surface did not improve the adhesion of silicone elastomers on the primed metals in any of the studied treatments, indicating that mechanical interlocking and increase in contact area do not contribute to adhesion. The results were discussed based on the different chemical composition and rheological properties of the primer formulations.