New environmental regulations have led to major changes in aluminum corrosion protection by prohibiting, for example, Cr(VI). Thus, the assessment of the corrosion behavior of Cr-free systems under atmospheric conditions is a major topic of interest for the aerospace industry. One major difficulty in this task is the lack of robust and reliable accelerated corrosion test(s) in this field. The aim of the present study is to compare the results of various accelerated corrosion standards (ASTM B117, ISO 4623-2, VCS 1027,149) to results obtained after 5 years of exposure at a marine atmospheric site in Brest, France. Additional accelerated corrosion tests were designed by varying several parameters in the VCS 1027, 149, such as the salt concentration, the time of wetness, and the relative humidity. The different modes of failure obtained in accelerated corrosion tests on the painted samples were then compared to field exposures in a marine atmospheric site. The first results obtained showed that the developed tests are more representative of service conditions than standard tests. © 2024 by the authors.

Aluminum alloys are not immune to corrosion which can take the form of localized corrosion. Thus, the assessment of the corrosion behavior of aluminum alloys under atmospheric conditions is a major topic for the aerospace industry. One major difficulty in this task is the lack of robust and reliable accelerated corrosion test(s) in this field. Indeed, several tests as the neutral salt spray test (ASTM B117) are used to assess the general corrosion resistance of aluminum, but these tests were not developed specifically for the aerospace industry and are not representative of service conditions. The aim of the present study was to compare the results of various accelerated corrosion test conditions (ASTM B117, VDA 233-102, Volvo STD 423-0014) with newly developed test conditions. Hence, different accelerated corrosion tests were designed by varying several parameters in the Volvo STD 423-0014 such as the salt concentration, time of wetness, and relative humidity. The results obtained on eight aluminum alloys (2xxx, 7xxx, and Al-Li alloys) were then compared to marine exposures. From the results, one test provides the same type of corrosion attacks on the different alloys under atmospheric exposures in the marine site and a good acceleration factor.

Cr-free paints applied on different aluminum alloys were exposed for 5 years at different atmospheric weathering sites worldwide. By image analysis, the extent, and the type of corrosion (filiform or blistering) were determined after 1, 2, and 5 years. In that way, it was possible to rank the different systems as a function of their resistance to corrosion. The kinetics of degradation of each system at all sites was also determined. From the results, it is shown that the kinetics of degradation is system dependent. It is also shown that it is the combination of several climatic parameters which contributes to the corrosivity of the site and not only one single parameter such as chloride deposition, relative humidity, and so on. 

Aluminum alloys are known to have many advantages (e.g., light weight and low cost) but they are not immune to corrosion. So, it is important to assess their corrosion behavior, in particular under atmospheric conditions. To protect aluminum alloys against corrosion, paints are generally applied onto the materials. Corrosion protection in the aerospace industry consists of a conversion or anodized coating, an inhibited primer, and a top-coat. Chromate conversion coating (CCC) and primers containing chromate pigments have been widely used in the aerospace industry over the last decades. However, new environmental regulations have led to major changes for aluminum corrosion protection. By limiting or prohibiting some chemicals, for instance Cr(VI), the European regulation REACH (Regulation on Registration Evaluation, Authorization and Restriction of Chemicals) has induced major changes to some of the finishing processes of aluminum alloys (e.g., chromate conversion, chromic acid anodizing, and chromate sealing). Interesting results have been obtained while seeking replacements for Cr(VI), for example, with the incorporation of cerium, lithium salt, or nanocontainers loaded with corrosion inhibitors in organic coatings. For several years, hybrid sol–gel coatings able to replace the pre-treatment and primer steps have been under development, showing interesting results. New prospects for the future involve the use of photo-polymerization to reduce the energy-intensive heat treatment needed in sol–gel technology. It will also be necessary to test these new technologies in service conditions or in accelerated corrosion tests before being able to conclude on the real effectiveness of these coatings. This review summarizes the recent developments in Cr-free coatings for aluminum alloys. Their advantages and draw-backs are also discussed. 

Specimens of AA2099-T8 were immersed for different times ranging from 2 to 180 min in 0.1M NaCl. The development of corrosion around intermetallic particles was studied by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDXS). The degradation evolution of each major intermetallic particle after exposure of the alloy to electrolyte allowed to determine which particle corroded during the first stages of immersion. The corrosion of lithium-containing particles was also investigated by transmission electron microscopy (TEM). The earliest stages of attack started with localised corrosion of Al2CuMg (S-phase) particles resulting in dealloying which was followed by trenching around these particles. After 10 min, trenching was observed around Al7Cu2Fe(Mn) particles and then progressed to AlCuFeMnSi particles after 90 min. 

In this study, the use of electrical resistance (ER) sensors to monitor the corrosion of Al94Cu6 alloy is assessed and compared with 2024-T3 coupons. Under uniform corrosion, a good correlation was found between the ER sensors and mass loss on coupons. Three different chloride depositions are studied: (i) pre-contamination with dry/wet cycles, (ii) Volvo standard accelerated corrosion test and (iii) neutral salt spray test. The obtained results show good reproducibility of the ER sensors under all tested conditions. This suggests that ER sensors more levelled the effect of localised corrosion through a large surface evaluation compared with cross-sections. The corrosion thickness obtained with the ER sensors does not correspond to the mean depth obtained by cross-sections. This can be explained by the distribution and size of the localised corrosion events according to a finite element model proposed. The ER method allows obtaining useful real-time corrosion data for the understanding of the corrosion mechanisms and the development of accelerated tests. The chloride concentration, the frequency of salt application and wet/dry cycles have a strong influence on the corrosion rate of aluminium alloys. © 2021 The Authors.