TSA anodising voltage effects on the near-surface coarse intermetallic particles in the AA2024-T3 and AA2198-T8 alloys

Abstract

In this study, the behaviour of the micrometric particles of the AA2198-T8 alloy during anodising at various voltages and the effect of anodising voltage on the anodised surface morphology have been investigated in a tartaric-sulfuric acid anodising solution. The results were compared with that of the AA2024-T3 alloy. For the AA2198-T8 alloy, partial dissolution of these particles occurred at 0, 3 and 4 V. Besides, for potentials above 5 V, there is a preferential dissolution of the intermetallic particles. For the AA2024-T3 alloy, the results indicated a total dissolution of the micrometric particles at 0 V and a partial dissolution at 3 V, whereas above 4 V total dissolution occurred. Between 1 and 2 V, no dissolution was observed for both alloys. The preferential dissolution of the micrometric particles resulted in defects in the anodic film and cavities on the anodised surfaces.

An assessment of pitting corrosion in anodized aluminum alloys: It might not be what it seems

“…[ 55 ] In fact, during the anodizing process, IMPs tend to dissolve and form voids on the surface of the anodic layer, as indicated by the red arrows in Figure 2e–g. [ 42,56 ] Saenz De Miera et al [ 57 ] reported similar results when studying the behavior of IMPs in the AA7075‐T6 aluminum alloy during sulfuric anodizing. In addition, changes in the morphology of the film have been reported.…”

“…It is noteworthy that IMPs have a different electrochemical potential compared to Al matrix due to their chemical composition; thus, the connection between matrix and IMPs might lead to galvanic microcells that promote corrosion initiation. [55] In fact, during the anodizing process, IMPs tend to dissolve and form voids on the surface of the anodic layer, as indicated by the red arrows in Figure 2e-g. [42,56] Saenz De Miera et al [57] reported similar results when studying the behavior of IMPs in the AA7075-T6 aluminum alloy during sulfuric anodizing. In addition, changes in the morphology of the film have been reported.…”

“…[ 1,5,40 ] In this work, metallographic surface preparation was used to compare our results with those of works already reported in the literature. [ 41,42 ]…”

“…[1,5,40] In this work, metallographic surface preparation was used to compare our results with those of works already reported in the literature. [41,42] Anodizing was performed in TSA solution composed of 0.46 mol L −1 sulfuric acid and 0.53 mol L −1 tartaric acid at 37 ± 1°C using a potentiostat (SP-300 from BioLogic). The area exposed to the TSA electrolyte was 1 cm 2 .…”

“…Another point that must be taken into account is that initiation of pitting in anodized alloys occurs in the defects of the anodic layer due to dissolution associated with micrometer IMPs during anodizing process. [41,42,58,75] Currently, Takahashi et al, [13,14] Zuo et al, [15] and Ren and Zuo [16] focused their studies on pure Al, while only the works of Moutarlier et al [17] and Ma et al [41] reported findings from commercial alloys.…”