Anticorrosive Performance Approach Combining an Epoxy Polyaminoamide–Zinc Phosphate Coatings Applied on Sulfo-tartaric Anodized Aluminum Alloy 5086

Abstract

This study focused on developing an effective anticorrosive formulation for selected sulfo-tartaric anodized aluminium alloy (Al-alloy AA5086) to withstand harsh marine environment. The developed formulation was based on an epoxy resin bisphenol A diglycidyl ether (DGEBA) that is cured with polyaminoamide. Two sets of coated Al-alloy AA5086 samples were prepared using the epoxy resin formulation; a standard and ER–EZ. The formulation for making the ER samples included zinc phosphate (ER–ZP). Zinc phosphate was added to the formulation in about 5 wt%. The coated samples of Al-alloy AA5086 were evaluated by exposing them to a salt spray test chamber for various periods of time. The test was carried out according to an ISO 7253 standard test. The anticorrosive performance of the two epoxy coatings, the standard and ER–ZP were monitored by an electrochemical impedance spectroscopy (EIS). According to the EIS results, ER–ZP exhibited superior anticorrosive performance. The surface morphology analysis of the ER–ZP sample as shown by scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) stayed smooth with minor roughness even after exposure to the harsh environments for 4392 h. The Bode and Nyquist plots showed that the ER–ZP coating has an outstanding barrier property in protecting Al-alloy AA5086 in marine environment against corrosion. The superior performance of the ER–ZP could be attributed to the presence of zinc phosphate which enhanced the adhesion properties of the coating and made it a more effective barrier.