Mechanism of corrosion and corrosion fatigue of 2024-T3 aluminum alloy in hydrochloric acid solutions.

摘要

In order to understand the corrosion mechanism of aluminum copper alloys, the morphological changes of a 2024-T3 aluminum alloy have been studied in different concentration of hydrochloric acid by in situ atomic force microscopy. This aluminum copper alloy has been found to be susceptible to intergranular corrosion in hydrochloric acid solutions. Severe intergranular damage is a result of a difference between the dissolution rates of copper depleted regions in the vicinity of second phase precipitates along grain boundaries and grain bodies.; The mechanism of corrosion fatigue of this alloy during cyclic fatigue in distilled water and 0.1 M HCl has also been investigated during free corrosion and under cathodic polarization. Both anodic dissolution and hydrogen embrittlement mechanisms appear to cooperate and result in a significant reduction of the observed cycle life as compared to that observed in air. Intergranular cracking is observed in early stages of crack nucleation and propagation, and transgranular fracture in the later stages.; In order to investigate the role of hydrogen during fatigue of the 2024-T3 aluminum alloy in hydrochloric acid media, fatigue cycling has been performed in 0.1 M HCl solutions containing either a hydrogen combination poisoning agent, arsenic, or a copper complexing agent, ammonium chloride. Shortening of cycle life in these solutions as compared to that observed in 0.1 M HCl with no additives clearly shows that the 2024-T3 aluminum alloy is susceptible to hydrogen embrittlement and that the most important factor controlling the hydrogen uptake by this alloy is the presence of metallic copper in a surface layer formed during the corrosion experiments.; Metallic copper acts as a preferential site for proton reduction during corrosion fatigue; however, due to very low hydrogen diffusivity in copper, hydrogen ions reduced at these sites do not contribute to hydrogen embrittlement. When copper is complexed by solution ions and is not present in its metallic form at the surface film, e.g., in a solution containing arsenic or ammonium ions, the hydrogen uptake is enhanced and significant reduction of cyclic life is observed. The significant role of re-deposited metallic copper in this alloy and its role in hydrogen embrittlement/fatigue is emphasized by a series of investigations performed on pre-corroded specimens from which the copper-containing film, formed during pre-exposure, either remained on or was removed from the sample surface prior to the corrosion fatigue experiments.