The dissolution mechanism of S-phase particles in 2024-T351 aluminum alloy at open-circuit potential in chloride-containing sulfate solutions was investigated using atomic force microscopy (AFM), scanning Kelvin probe force microscopy (SKPFM), and secondary ion mass spectroscopy (SIMS). The combination of the three techniques allowed the correlation between SKPFM measurements and the corrosion behavior of AA2024 to be confirmed, leading to a better understanding of the electrochemical behavior of S-phase particles. A three-step mechanism for the dissolution and accompanying processes occurring near <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">S</mml:mi></mml:mrow></mml:math>S particles was proposed: <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mi>i</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math>(i) preferential aluminum and magnesium dissolution, <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mi>i</mml:mi><mml:mi>i</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math>(ii) galvanic coupling between the copper-enriched particles and the surrounding matrix, leading to an increased passivity of the matrix around the particles, and <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:mi>i</mml:mi><mml:mi>i</mml:mi><mml:mi>i</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:math>(iii) copper deposition around the corroded particles.

The corrosion behavior of a Friction Stir Welding joint in 2050-T3 Al-Cu-Li alloy was studied in 1 M NaCl solution and the influence of T8 post-welding heat treatment on its corrosion susceptibility was analyzed. After exposure to 1 M NaCl solution, the heat affected zone (HAZ) of the weld without post-welding heat treatment was found to be the most extensively corroded zone with extended intergranular corrosion damage while, following T8 post-welding heat treatment, no intergranular corrosion was observed in the HAZ and the global corrosion behavior of the weld was significantly improved. The corrosion damage observed on the welded joints after immersion in 1 M NaCl solution was compared to that obtained after 750 h Mastmaasis Wet Bottom tests. The same corrosion damage was observed. Various stationary electrochemical tests were carried out on the global welded joint and/or each of the metallurgical zones of the welded joint to understand the corrosion damage observed. TEM observations helped in bringing meaningful elements to analyze the intrinsic electrochemical behavior of the different zones of the weld related to their microstructure. However, galvanic coupling tests showed that galvanic coupling effects between the different zones of the weld were at least partially responsible for its corrosion behavior.

The corrosion behavior of a pure aluminum/pure magnesium couple in a weakly conductive sodium sulfate solution was investigated. Potential and current distributions on the surface of the model couple at the beginning of immersion were obtained by solving the Laplace equation using a finite element method algorithm. Magnesium acted as the anode of the system while oxygen and water were reduced on aluminum. Calculations predicted a large current peak at the <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Al</mml:mi><mml:mo>∕</mml:mo><mml:mi mathvariant="normal">Mg</mml:mi></mml:mrow></mml:math>Al∕Mg interface related to a local increase in both Mg dissolution and oxygen and water reduction on aluminum, leading to a local pH increase. Optical and scanning electron microscope observations confirmed the strong dissolution of magnesium concomitantly with depassivation of aluminum at the <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Al</mml:mi><mml:mo>∕</mml:mo><mml:mi mathvariant="normal">Mg</mml:mi></mml:mrow></mml:math>Al∕Mg interface. Local electrochemical impedance spectroscopy showed the detrimental effects of the galvanic coupling both on aluminum and magnesium.

Experiments were performed to determine the propagation kinetics of intergranular corrosion on 2024 aluminum alloy immersed in 1 and <mml:math display="inline"><mml:mrow><mml:mn>3</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">M</mml:mi></mml:mrow></mml:math>3M chloride solutions. Tests consisting of immersion in a corrosive solution followed by optical observations on sectioned samples were carried out. This method was found to be time consuming and led to a lack of reproducibility due to the random nature of the corrosion attacks. Another method proved to be more efficient; it consisted of measuring the load to failure on precorroded tensile specimens vs preimmersion time in an aggressive environment. This method was found to allow the mean depth of the corrosion defects to be determined. Further, in 1 and <mml:math display="inline"><mml:mrow><mml:mn>3</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">M</mml:mi></mml:mrow></mml:math>3M chloride solution, intergranular corrosion led to the formation of a nonbearing zone, the thickness of which was equal to the mean depth of the corrosion defects. This corroded zone explained the premature failure of the specimens when a uniaxial tensile stress was applied.