Abstract
In the presented research effort, cyclic polarization tests were conducted coupled with acoustic emission measurements, in order to monitor the corrosion phenomena. Previous studies have shown that epoxy composite coatings offer satisfactory corrosion protection to aluminum substrates minimizing and even eliminating some degradation phenomena. In the present effort, acoustic emission was applied during potentiodynamic cyclic polarization testing on as received, anodized and carbon epoxy coated aluminum substrates in order to correlate corrosion phenomena, like oxide layer development and localized corrosion, with characteristic acoustic emission signal descriptors. The epoxy coating was used both as received and as reinforced with various carbon fillers i.e. carbon nano-tubes, amorphous graphite or a combination of them. Acoustic emission detected signals due to hydrogen bubble related processes during cathodic polarization and signals due to deposition of thick soluble films during the final stage of anodic polarization. The acoustic profile between coated and uncoated aluminum substrates, exhibited substantial changes dependent both on the surface preparation and the employed reinforcing filler. The overall outcome of the experimental results, indicate that with further research, acoustic emission can be employed as an Aluminum Corrosion Monitoring tool.
Highlights
Aluminum 2024-T3 (Al2024-T3) alloy is one of the most widely used aluminum alloys in the aerospace industry due to its relatively low weight, high strength and fatigue resistance
The anodization process enhances the adhesion between the aluminum substrate and the epoxy coating, due to electrical conductivity mismatches, in the event of a coating failure, aluminum corrosion can initiate and proceed notably fast leading to catastrophic failures [3]
Apart from the improved adhesion, carbon nano tubes (CNTs) can reduce the ingress of water in the epoxy due to their hydrophobic nature and the water affected specific area resulting in more tortuous paths for the absorption and diffusion of water, further enhancing the performance of the joint structure [9,10,11]
Summary
Aluminum 2024-T3 (Al2024-T3) alloy is one of the most widely used aluminum alloys in the aerospace industry due to its relatively low weight, high strength and fatigue resistance. A major disadvantage of Al2024-T3 is its low corrosion resistance; in aerospace applications, it is used after an anodizing treatment followed by sealing with epoxy paints/coatings [1,2]. The anodization process enhances the adhesion between the aluminum substrate and the epoxy coating, due to electrical conductivity mismatches, in the event of a coating failure (scratches), aluminum corrosion can initiate and proceed notably fast leading to catastrophic failures [3]. In order to further enhance adhesion and alleviate the mismatches, several studies have been conducted on nano-modified epoxies employing mainly graphitic structures like carbon nano tubes (CNTs) [4,5,6,7,8]. AG is combined with CNTs, with the objective to explore such synergistic effects that could further improve the corrosion protection of the aluminum substrates
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