Improved understanding of environment-induced cracking (EIC) of sensitized 5XXX series aluminium alloys

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:682

Article

Holroyd, N. J. H.¹  Burnett, T. L.²  Seifi, M.¹  Lewandowski, J. J.¹ 

[1] Case Western Reserve Univ, Dept Mat Sci & Engn, Cleveland, OH 44106 USA

[2] Univ Manchester, Sch Mat, Henry Mosely Xray Imaging Facil, Manchester, Lancs, England

关键词: Environment-enhanced-cracking;    Stress;    corrosion cracking 3-D tomography;    Aluminum-magnesium alloys;   

DOI  :  10.1016/j.msea.2016.11.088

来源: Elsevier

【 摘 要 】

Two mechanistically different modes of ETC have been identified using high-resolution X-ray computed tomography and scanning electron microscopy (SEM) in sensitized AA5083-H131 that had been pre-exposed to 0.6 M NaCl prior to interrupted slow strain rate testing (SSRT) in the short transverse direction while exposed to laboratory air (50% RH). One mode, shown to propagate when local stress intensity factors are in the range of 4-12 MNm(-3/2), is the well-known 'classic' form of intergranular stress corrosion cracking, Type-1 cracking, which would not initiate and propagate in dry air, irrespective of pre-exposure or sensitization. The second mode of cracking, identified presently as Type-2 cracking, is associated with sudden load-drops occurring after the TITS during SSRT. Type-2 cracking propagates at higher local stress intensity factors (above 12-15 MNm(-3/2)) with significantly higher average growth rates than Type-1 cracking, involves the sudden simultaneous mechanical linkage of multiple fully-isolated regions of damage, pre-determined during pre-exposure to NaCl solution and generated during straining in laboratory air. Differences in the extent of Type-2 cracking for pre exposed samples tested in 'dry' air compared to laboratory air (50% RH) were marked, with that in dry air being limited to isolated patches. High-resolution 3D tomography and detailed SEM has been used to distinguish these two mechanistically different modes of EIC. Implications for a role of hydrogen embrittlement during EIC are discussed.

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