Atmospheric plasma treatment for improved epoxy coating performance on aluminium alloys

Achieving strong adhesion of polymer coatings like epoxy, acrylic, and polyurethane to aluminium surfaces is a crucial focus in materials research, given its importance across the automotive, aerospace, marine, and construction sectors. Current adhesion-promoting surface treatments like anodizing, electropolishing, phosphate and chromate conversion coatings are environmentally problematic due to their chemical processes, necessitating the development of alternative solutions. With the goal of enhancing coating performance on aluminium alloys, we introduce atmospheric pressure plasma jet technology to improve the adhesion, mechanical performance, and corrosion resistance of epoxy coatings. This study investigates the impact of atmospheric pressure plasma treatment on the adhesion, scratch resistance, and corrosion resistance of graphene-reinforced epoxy (EP/G) composite coatings applied to aerospace aluminium alloy AA7075. Contact angle measurements, FTIR spectroscopy, and surface free energy (SFE) analysis were used to characterize the resulting surfaces. Test specimens were plasma-treated before applying the coating. The impact of the plasma treatment on surface wettability was studied by analyzing its effect on the dispersive ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mi>γ</mml:mi> <mml:mi>L</mml:mi> <mml:mi>D</mml:mi> </mml:msubsup> </mml:math> ) and specific polar ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mi>γ</mml:mi> <mml:mi>L</mml:mi> <mml:mrow> <mml:mi>S</mml:mi> <mml:mi>P</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) components of surface free energy. The removal of surface contaminants and weak boundary layers by plasma treatment increased surface reactivity, directly leading to a significant increase in surface free energy (SFE) from 43.49 mJm 2 to 142.34 mJm 2 . This improved the surface wettability. Potentiodynamic polarization analysis revealed that the composite coating's oxidation resistance was significantly enhanced by the surface cleaning process using ionized argon ions prior to coating. This was evidenced by a shift in the E corr value from – 1.28 V to 0.31 V. Further, supporting the protective effect of coatings, electrochemical impedance spectroscopy (EIS) results indicated superior corrosion resistance for EP/G coating on plasma treated AA7075 than coating on untreated samples.