Electrochemical investigation of corrosion and repassivation of structural aluminum alloys under permanent load in bending

Abstract

This work reports an electrochemical investigation of corrosion and repassivation in NaCl solutions of structural Al 7075-T6 and Al 2024-T3 as a function of permanent load in bending by means of single-cycle anodic polarization. Experimental variables other than the load level were the extent of corrosion, chloride ion concentration and initial pH of the test solution, in addition to the pre-exposure in the aggressive environment and of the viscosity of the test solution for Al 7075-T6. The susceptibility to local stress during corrosion and repassivation depends on the alloy microstructure and corrosion mechanisms. In the case of Al 2024-T3, the mechanical activation is driven by cathodically controlled dissolution of this alloy at open circuit in concentrated NaCl, being indicative of a chemomechanical effect. Conversely, for Al 7075-T6, the effect of applied load is better discerned from the repassivation response. Film rupture/formation sequence and related interfacial (electro)chemical processes determine the stress-enhanced metastable repassivation of this alloy

Stress Corrosion Cracking of Friction Stir-Welded AA-2024 T3 Alloy

“…Similar effect was observed on the same alloy by Ferri et al on 4PBB loaded in elastic field during potentiodynamic tests [45]. This was attributed to dissolution mechanism assisted by the mechanical stress, according to the chemomechanical theory of Gutman [46].…”

The repassivation response from single cycle anodic polarization: The case study of a sensitized Al-Mg alloy

“…therein]. The localization of anodic processes during repassivation is enhanced with β phase precipitation at lattice defects [ [17,20] and refs. therein].…”

“…The opposite has been found for Al 2024-T3 subjected to residual elastic compressive stresses after removal of uniaxial tensile load [13]. A recent study with Al 2024-T3 and Al 7075-T6 under permanent load in bending has indicated that the effect of local stresses below the yield strength is enhanced with anodic processes localization during repassivation [17]. Al-Mg alloys are of special interest from the prospective of the understanding and achievement of the balance between mechanical performance and corrosion resistance.…”

“…Single cycle anodic polarization has been widely used for investigating the repassivation behaviour of Al and alloys in chloride containing solutions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A potential drop at high currents during the potential scan into the negative direction has been frequently detected [1][2][3][4][6][7][8][9][10][12][13][14][15][16][17].…”

“…The response to repassivation in aftermath of microstructural effects (e.g. impurities, precipitate phase, solute-depleted region) [6,10,12] and of mechanical deformation (residual [13] and applied [9,16,17] stresses) is not fully clear. The not distinguishable inflection detected for commercially pure Al 1050 exhibiting either etched or crystallographic pits [10] suggests that the presence of a salt layer in mass-transport limited repassivation is not mandatory.…”