4D Characterization of the Stress Corrosion Cracking Behavior in Al-10Mg Aluminium Alloy via Synchrotron X-Ray Tomography
- Dongsheng Fu (Kyushu University) | Hiroyuki Toda (Kyushu University) | Hang Su (Kyushu University) | Kyosuke Hirayama (Kyushu University) | Kentaro Uesugi (Japan Synchrotron Radiation Research Institute) | Akihisa Takeuchi (Japan Synchrotron Radiation Research Institute)
- Document ID
- International Society of Offshore and Polar Engineers
- The 29th International Ocean and Polar Engineering Conference, 16-21 June, Honolulu, Hawaii, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. International Society of Offshore and Polar Engineers
- Synchrotron X-ray Tomography, 3D Strain Mapping, Stress Corrosion Cracking, Hydrogen Embrittlement, Al-Mg alloy
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Stress corrosion cracking (SCC) behavior of Al-10Mg aluminium alloys is studied with the help of the high resolution X-ray tomography in the present research. The SCC-induced crack is formed from the corrosion pit near the surface, and gradually propagates and coalescence with the voids due to the fracture of β phase ahead of the crack tip at low applied strain levels. In addition, hydrogen concentration in the ligament between the SCC-induced crack tip and voids accelerates the propagation of the crack, indicating that hydrogen concentration and partitioning among various trap sites dominates the SCC and entire fracture of Al-10Mg aluminium alloys.
Al-Mg aluminium alloys are widely used in the fields of marine and automobile due to its high strength and strength-to-weight ratio. Al-10Mg aluminium alloys that increase the content of Mg to 10 % are designed to satisfy the industrial requirement in recent years. However, the application of Al-10Mg aluminium alloys is undermined by stress corrosion cracking (SCC) arising from the high susceptibility of Al-10Mg aluminium alloys to degradation in aggressive environments. According to the previous research, it is reported that SCC-induced cracks lead to unexpected failure under applied strain levels far lower than the strain that materials can sustain, indicating that SCC is a formidable problem for the application of Al-10Mg aluminium alloys, especially in the fields of marine science and nuclear power.
The resistance to SCC is determined by the chemical composition, heat treatment technology and related microstructural features of materials. According to Goswami, Spanos, Pao, et al. (2010), β-phase (Al3Mg2) is mainly precipitated on the grain boundaries of Al-Mg aluminium alloys during a sensitization heat treatment process. Due to the initiation and growth of β-phase during the sensitzation heat treatment, Crane and Gangloff, (2016) proposed that the growth rate of SCC-induced intergranular crack increases with an increase in the sensitization time and sensitization temperatures during the heat treatment process, revealing that the content of β-phase plays a significant role in the initiation and propagation of SCC-induced intergranular cracks in AA 5083-H131 aluminium alloys. Jones, Vetrano, and Windisch, (2004) proposed that the open circuit potential (OCP) of β-phase and aluminium matrix is −1.120 Vsce and −0.800 Vsce, respectively, leading to the anodic dissolution of β-phase and accelerating the propagation of SCC-induced intergranular cracks in AA5083 aluminium alloys that exposed in 3.5 % NaCl+chromate solution. In addition, Tanguy, Bayle, Dif, et al. (2002) studied the effects of hydrogen to the propagation of SCC-induced intergranular cracks in Al-5Mg aluminium alloys, revealing that the β-phase dissolution triggers the dissolution of the Al-Mg solid solution, providing a high over potential for the production and uptake of the external hydrogen ahead of the SCC-induced intergranular crack tip. The authors also proposed that the external hydrogen is mainly trapped at the interface of β-phase/ matrix and constrained β-free ligament due to a high hydrostatic strain concentration, leading to the propagation of SCC-induced crack along grain boundaries in terms of hydrogen enhanced decohesion (HEDE) models. Furthermore, Burnett, Holroyd, Scamans, et al. (2015), reported that the applied stress is shared by a number of corrosion-induced cracks due to the crack branching behavior, leading to the limited SCC-induced intergranular crack propagation in aluminium alloys.
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