This paper presents a survey of corrosion potentials, pitting potentials, and electrochemical characteristics for intermetallic particles commonly present in high-strength aluminum-based alloys. Results from relevant pure metals and solid solutions are also presented. It is seen that corrosion potentials and pitting potentials vary over a wide range for various intermetallics. Elaboration of the results reveals that the electrochemical behavior of intermetallics is more detailed than the simple noble or active classification based upon corrosion potential or estimated from the intermetallic composition. Intermetallics capable of sustaining the largest cathodic current densities are not necessarily those with the most noble Ecorr, similarly those with the least noble Ecorr will not necessarily sustain the largest anodic currents. The data herein was collected via the use of a microcapillary electrochemical cell facilitating electrode investigations upon intermetallic particles in the micrometer-squared range. This survey may be used as a tool for clarification of localized corrosion phenomena in Al alloys.

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Electrochemical Characteristics of Intermetallic Phases in Aluminum Alloys An Experimental Survey and Discussion

The morphology of attack at and around the intermetallic compounds (IMC) present on bare AA 2024-T3 was studied in situ using confocal laser scanning microscopy. Exposures were conducted in 0.1 M Na 2 SO 4 + 0.005 M NaCI at pH 3, 6, and 10 as well as near-neutral 0.5 M NaCl. The types of attack observed could be categorized as matrix and IMC pitting, trenching adjacent to IMC, and matrix etching. The electrochemical behavior of bulk synthesized Al-Cu, Al-Cu-Mg, and Al-Cu-Fe-Mn intermetallic compounds as well as that of AA 2024-T3 was used to rationalize the observed attack metrology. The galvanic coupling between the AA2024-T3 matrix and the intermetallic particles controlled the attack rates. In Al-Cu-Mg, the strong polarization to the open-circuit potential of the alloy caused rapid dissolution (ca. 10 mA/cm 2 ), whereas for the Al-Cu-Fe-Mn the dissolution rates were on the order of 100 μA/cm 2 . The limited dissolution rates of the Al-Cu-Fe-Mn phase were due to the cathodic polarization of these particles by the matrix under open-circuit conditions. Several pits were initiated at large Al-Cu-Mg particles. These pits were stable within the Al-Cu-Mg phase, but could not form stable pits in the alloy matrix during open-circuit corrosion. Calculation of growth rates and pit stability products for the individual IMC emphasized the role of metastable pitting in the observed corrosion metrology, which developed on AA2024-T3 during open-circuit corrosion.

In Situ Confocal Laser Scanning Microscopy of AA 2024-T3 Corrosion Metrology I. Localized Corrosion of Particles

We report a new efficient method for fabricating a superhydrophobic oxidized surface of aluminum alloys with enhanced resistance to pitting corrosion in sodium chloride solutions The developed coatings are considered very prospective materials for the automotive industry, shipbuilding, aviation, construction, and medicine The method is based on nanosecond laser treatment of the surface followed by chemisorption of a hydrophobic agent to achieve the superhydrophobic state of the alloy surface We have shown that the surface texturing used to fabricate multimodal roughness of the surface may be simultaneously used for modifying the physicochemical properties of the thick surface layer of the substrate itself Electrochemical and wetting experiments demonstrated that the superhydrophobic state of the metal surface inhibits corrosion processes in chloride solutions for a few days However, during long-term contact of a superhydrophobic coating with a solution, the wetted area of the coating is subjected to corrosion processes due to the formation of defects In contrast, the combination of an oxide layer with good barrier properties and the superhydrophobic state of the coating provides remarkable corrosion resistance The mechanisms for enhancing corrosion protective properties are discussed

https://pubs.acs.org/doi/pdf/10.1021/acsami.5b06217

Synergistic Effect of Superhydrophobicity and Oxidized Layers on Corrosion Resistance of Aluminum Alloy Surface Textured by Nanosecond Laser Treatment

Stable pit formation on AA2024-T3 in a NaCl environment

The study of aluminium anodes for high power density Al/Air batteries with brine electrolytes

Effect of Iron-Containing Intermetallic Particles on the Corrosion Behaviour of Aluminium

The influence of MgSi particle reactivity and dissolution processes on corrosion in Al–Mg–Si alloys

AA5182 (Al-4.5 wt% Mg) can become susceptible to intergranular corrosion (IGC) with time at moderately elevated service temperatures owing to precipitation of Mg-rich β-phase at grain boundaries, which can lead to stress corrosion cracking (SCC). The IGC and SCC susceptibility of AA5182 was found to depend strongly on sensitisation heat treatments. AFM and TEM studies demonstrated that the degree of precipitation and thus susceptibility to attack for a boundary can be related to its crystallographic misorientation. Low angle boundaries (

Intergranular Corrosion and Stress Corrosion Cracking of Sensitised AA5182

AA5182 (Al-4.5 wt% Mg) can become susceptible to intergranular corrosion (IGC) with time at moderately elevated service temperatures owing to precipitation of Mg-rich β-phase at grain boundaries, which can lead to stress corrosion cracking (SCC). The IGC and SCC susceptibility of AA5182 was found to depend strongly on sensitisation heat treatments. AFM and TEM studies demonstrated that the degree of precipitation and thus susceptibility to attack for a boundary can be related to its crystallographic misorientation. Low angle boundaries (<20°) are most resistant to attack as they do not show β-phase precipitation. However, higher angle boundaries show highly variable precipitation and corrosion susceptibility: critical factors are the grain boundary plane and precipitate/matrix crystallographic relationship.

Andreas Afseth

Papers

Effect of Iron-Containing Intermetallic Particles on the Corrosion Behaviour of Aluminium

The influence of MgSi particle reactivity and dissolution processes on corrosion in Al–Mg–Si alloys

Intergranular Corrosion and Stress Corrosion Cracking of Sensitised AA5182

Intergranular corrosion and stress corrosion cracking of sensitized AA5182

Effect of thermo-mechanical processing on filiform corrosion of aluminium alloy AA3005.