Damage micromechanisms of stress corrosion cracking in Al-Mg alloy with high magnesium content. (15th May 2021)

• Record Type: Journal Article
• Authors: Hirayama, Kyosuke; Toda, Hiroyuki; Fu, Dongsheng; Masunaga, Ryohei; Su, Hang; Shimizu, Kazuyuki; Takeuchi, Akihisa; Uesugi, Masayuki
• Is Part Of: Corrosion science. Volume 184(2021)
• Publication Date: 2021-05-15
• Subjects: Stress corrosion cracking -- Al-Mg alloy -- Hydrogen embrittlement -- Nanotomography -- Phase-contrast imaging; Corrosion and anti-corrosives -- Periodicals; 620.11223
• DOI: 10.1016/j.corsci.2021.109343
• Languages: English
• ISSNs: 0010-938X

Abstract

Graphical abstract: Highlights: SCC was directly observed with a recently realized high-energy and ultra-high resolution X-ray CT. Dissolution of b phase along GB and incidental IG and TG fracture have been observed in 3D. Drastic effects of pre-existing and external H on SCC revealed by measuring crack-tip plasticity. Catastrophic failure was observed when GB b film is combined with interconnected b in grain interior. Local H content at crack-tip is measured for the first time to discuss quantitative criterion for SCC. Abstract: Al-10Mg alloys, which are highly susceptible to SCC, were prepared with various β precipitate morphologies. Interrupted in-situ tensile tests were conducted under synchrotron X-ray radiation, employing a recently developed X-ray microtomography technique that combines high-energy, applicability to metallic materials, and ultra-high resolution. Preferential dissolution of the β phase along grain boundaries, and incidental intergranular and transgranular fracture, were observed in 3D. A drastic decrease in SCC resistance was measured after hydrogen charging. The additional effect of external hydrogen absorbed from an aqueous solution during loading was also revealed, by directly measuring crack-tip plasticity. The aquatic environment, one of the most extreme conditions for hydrogen uptake, caused continuous crack-tip corrosion. Catastrophic failure was observed when an alloy had both a relatively high areal grain boundary coverage by film-like β phase, and a reticulately interconnected plate-like β phase in the grain interior. Hydrogen bubble formation was also observed, in relation to the progress of crack-tip corrosion. The main corrosion product was identified as Al(OH)3, based on its linear absorption coefficient. The respective amounts of corrosion products and hydrogen gas in the gas bubbles, and the pH value of the aqueous solution, were accurately measured during in-situ tensile testing, enabling estimation of the local elevation of hydrogen content in the crack-tip vicinity. Finally, a quantitative criterion for the occurrence of hydrogen embrittlement in inter-β ligaments is discussed, together with the applicability of the findings to the prevention of SCC.