Crevice corrosion sequentially leading to pitting, intercrystalline and delaminating corrosion of AMg6 aluminum alloy in tap water

• О.V. Volkova¹, Т.V. Shibaeva², А.G. Rakoch¹, А.V. Dub¹ and Ye.P. Monakhova¹

¹ Department of Metallurgy of Steel, New Production Technologies & Protection of Metals, College of Environmentally Sound Technologies & Engineering, National University of Science and Technology MISiS, Leninsky prosp., 4, 119049 Moscow, Russian Federation
² A.A. Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninsky pr. 49, 119334 Moscow, Russian Federation

Abstract: The study covers the corrosion behavior of industrial aluminum alloy AMg6 in crevice-like gaps after various one-week exposures in tap water at a temperature of 60°C. Using the metallographic analysis and scanning electron microscopy methods, it was found that in addition to the main intermetallide Al₃Mg₂, this magnalium also comprises Al₆(Fe,Mn) and Mg₂Si particles. It has been shown that local types of corrosion damage in the zone of crevice-like gaps develop with an increase in the duration of tests in the following stages: 1) active dissolution of the metal base in contact with the passive sections of the alloy and Al₆(Fe,Mn) cathodic particles, which leads to the formation of hemispherical pits; 2) intercrystalline and delaminating corrosion after additional precipitation of intermetallides along the grain boundaries. The number of damages in the surface layers of the medium-alloyed magnalium for each of these local types of corrosion depends on the location of Al₃Mg₂ intermetallide particles released from the solid solution of magnesium in aluminum as discontinuous lines at the grain boundaries. If, prior to corrosion tests, these particles are located at the grain boundaries that are extended along the rolling direction, delaminating corrosion occurs, whereas if they do not have a distinct orientation, then intercrystalline corrosion occurs.

Keywords: aluminum alloy AMg6, intermetallides, gaps, crevice, intercrystalline and delaminating corrosion, tap water

Int. J. Corros. Scale Inhib., 2022, 11, no. 4, 1483-1495
doi: 10.17675/2305-6894-2022-11-4-4

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