Extreme wet adhesion of a novel epoxy-amine coating on aluminum alloy 2024-T3

Amine-epoxy polymer systems are widely used, for example as matrix materials for structural composites employed in aerospace industry and in industrial coatings on metal substrates for corrosion protection. This work focuses on the investigation of different epoxy-amine coatings on the adhesion performance on aluminum AA-2024 substrates. Two different epoxies (Epikote 828 (aromatic) and Eponex 1510 (aliphatic)) and four different amines (1,8-diaminooctane, Dytek A, Jeffamine EDR148 and Jeffamine D230) as curing agent were used in different stoichiometric ratios. These different epoxy-amine coatings were characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile tests (pull-off) and water-uptake measurements. Pull-off tests in dry conditions showed comparable adhesion of the coatings. Surprisingly, pull-off results showed after water soaking a higher wet adhesion of the coatings prepared with Eponex 1510 as compared to coatings prepared with Epikote 828. Moreover, the combination of Eponex 1510-Jeffamine EDR148 coatings resulted in high adhesion values (∼7 MPa) with pull-off tests and these values did not change after immersion for two weeks in water. This combination shows extreme good wet adhesion performance as compared to any other epoxy-amine coating. Complete recovery was demonstrated of the adhesion of Eponex 1510-Jeffamine D230 coating after being immersed for two weeks in water and dried for two weeks. Furthermore, in contrast with Epikote 828 water uptake measurements showed almost nil water uptake for all coatings prepared with Eponex 1510. Optical microscopy investigations on the residues of the coatings after pull-off tests revealed adhesive failure in wet condition for Epikote 828, while coatings prepared with Eponex 1510 showed cohesive failure.