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

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• 作者：N.J.H. Holroyd^a ; ^b ; ^{henry.holroyd@luxfer.net} ; T.L. Burnett^c ; M. Seifi^a ; J.J. Lewandowski^a
• 关键词：Environment-enhanced-cracking ; Stress ; corrosion cracking 3-D tomography ; Aluminum-magnesium alloys
• 刊名：Materials Science and Engineering: A
• 出版年：2017
• 出版时间：13 January 2017
• 年：2017
• 卷：682
• 期：Complete
• 页码：613-621
• 全文大小：2342 K
• 卷排序：682

文摘

Two mechanistically different modes of EIC 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 UTS 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.