Editors’ Choice—Dealloying-Driven Cerium Precipitation on Intermetallic Particles in Aerospace Aluminium Alloys

Abstract

Cerium-based compounds have been studied for decades as non-toxic candidates for the protection of aerospace aluminium alloys (AAs) like AA2024-T3. However, the complex heterogeneous microstructure of these alloys has hindered a thorough understanding of the subsequent stages of corrosion protection provided by this class of inhibitors. Thus, this work is devoted to unravelling the interaction mechanisms of different intermetallic particles (IMPs) in AA2024-T3 with cerium nitrate at the nanoscopic scale. This has been fulfilled through detailed top-view and cross-sectional analytical TEM investigations along with electrochemical evaluations. In line with our recent findings, we here report dealloying of IMPs as the main factor governing the rate of local cerium precipitation in contrast to micro-galvanic corrosion between IMPs and the surrounding matrix. Furthermore, we discuss a connection between the electrochemical response of the AA2024-T3 system and the morphological and compositional evolutions of individual IMPs including

Corrosion of Synthetic Intermetallic Compounds and AA7075-T6 in Dilute Harrison’s Solution and Inhibition by Cerium(III) Salts

“…The magnesium in the Al 2 CuMg strongly determines its dissolution behavior in chloride solutions; it is selectively dissolved, leaving the IMP enriched in Cu. 48,60 In DHS, MgZn 2 was the only IMC that did not have a potential range that established a passive region (ΔE) in the anodic curve. For Al-Cu-containing IMCs ΔE spanned between 230 mV and 380 mV (Fig.…”

“…The thickness of the precipitates depends on the type of IMP. 40,48 It was shown recently that deposition of the Ce-rich layer initiates at large Cu-containing Al(Fe,Cu)Si IMPs and proceeds to grow laterally across the surface. Dealloying of IMPs was found to be the governing mechanism for the precipitation of large Ce-rich deposits; the outward dissolution of Al and Mg and simultaneous precipitation of Ce led to the formation of a mixed Ce-Al hydroxide.…”

“…40,47,49,50 Al 7 Cu 2 Fe(Mn) particles are either discretely or fully covered with a thin cerium-based layer, depending on immersion time. 40,48 The effects of the type of associated anions nitrate NO 3 -, 9,51 sulfate SO 4 2-43-45,51 and acetate CH 3 COO -9,52 and their potential synergistic effect on corrosion inhibition were studied as well. 44,45 The NO 3 − can passivate the aluminum surface, 39,53 SO 4 2can be adsorbed, 54 and CH 3 COOacts as a buffer.…”

“…The corrosion phenomena such as pit initiation, pit propagation, and inhibitor deposition are often localized within the micro or even nanometer range. 9,48 To characterize such processes, measurements should be performed locally 6,7,55 to allow only a small part of the sample area to be exposed to the corrosive solution. The corrosion mechanisms of AA2xxx and AA7xxx in chloride solutions were studied in detail using the microcell technique on the bulk alloys 39 and also on specific intermetallic compounds (IMCs) typical for these alloys.…”

Tuning homogenization of high-strength aluminum alloys through thermodynamic alloying approach

“…For the Al-Zn-Mg-Cu alloys, the coarse residual phases (M/T/S) along grain boundaries (mostly) or in the matrix (few) may highly affect the corrosion resistance. On the one hand, they may act as a typical ''variable polarity" phase to form the corrosion electrochemical microcell due to the active Mg/Zn atoms with the cathode matrix and the dealloying reaction [88,89], leading to the dissolution of active Mg/Zn atoms and the remaining Cu-enriched phase in the initial anode sites. As such, the electrochemical activity of the residual Cu-enriched phase is reduced and become noble relative to the surrounding active grain boundaries or the matrix, and this residual Cu-enriched phase can further act as the cathode together with the anodic grain boundaries and/or matrix to form the electrochemical microcell and promote the dissolution or pitting/intergranular corrosion [88,89].…”