Stress corrosion cracking induced by the combination of external and internal hydrogen in Al-Zn-Mg-Cu alloy

Tang, J.*; Wang, Y.*; Fujihara, Hiro*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Ebihara, Kenichi; Takeuchi, Akihisa*; Uesugi, Masayuki*; Toda, Hiroyuki*

Scripta Materialia, 239, p.115804_1 - 115804_5, 2024/01

https://doi.org/10.1016/j.scriptamat.2023.115804

Stress corrosion cracking (SCC) behaviors induced by the combination of external and internal hydrogen (H) in an Al-Zn-Mg-Cu alloy were systematically investigated via in situ 3D characterization techniques. SCC of the Al-Zn-Mg-Cu alloy could initiate and propagate in the potential crack region where the H concentration exceeded a critical value, in which the nanoscopic H-induced decohesion of -MgZn precipitates resulted in macroscopic cracking. External H that penetrated the alloy from the environment played a crucial role during the SCC of the Al-Zn-Mg-Cu alloy by generating gradient-distributed H-affected zones near the crack tips, which made Al alloys in water environment more sensitive to SCC. Additionally, the pre-existing internal H was driven toward the crack tips during plastic deformation. It was involved in the SCC and made contributions to both the cracks initiation and propagation.

Hydrogen embrittlement and its prevention in 7XXX aluminum alloys with high Zn concentrations

Shimizu, Kazuyuki*; Toda, Hiroyuki*; Fujihara, Hiro*; Yamaguchi, Masatake; Uesugi, Masayuki*; Takeuchi, Akihisa*; Nishijima, Masahiko*; Kamada, Yasuhiro*

Corrosion, 79(8), p.818 - 830, 2023/08

https://doi.org/10.5006/4300

7xxx aluminum alloys are representative high-strength aluminum alloys; however, mechanical property degradation due to hydrogen hinders further strengthening. We propose the dispersion of Mn-based second-phase particles as a novel technique for preventing 7xxx aluminum alloy hydrogen embrittlement. In this study, the deformation and fracture behaviors of high hydrogen 7xxx alloys containing 0.0% Mn and 0.6% Mn are observed in situ using synchrotron radiation X-ray tomography. The obtained macroscopic hydrogen embrittlement is quantitatively analyzed based on hydrogen partitioning in alloys. Adding 0.6% Mn, generating second-phase particles with high hydrogen trapping abilities, significantly suppresses hydrogen-induced quasicleavage fracture.

Spontaneous debonding behaviour of reinforcement fine particles in aluminium; Toward high-strength metallic materials development

Toda, Hiroyuki*; Tsuru, Tomohito; Yamaguchi, Masatake; Matsuda, Kenji*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*

Kagaku, 75(10), p.48 - 53, 2020/10

Highly-concentrated precipitations play therefore dominant role in mechanical properties and hydrogen embrittlement of aluminum alloys. It has been considered that the coherent interface between matrix and precipitation does not contribute to the crack initiation and embrittlement due to its coherency. Here, we discovered the origin of unprecedented quasi-cleavage fracture mode. Hydrogen partitioning at various defect sites is investigated comprehensively combined with experiment, theory and first-principles calculations. We demonstrate that despite low excess free volume, the aluminum-precipitation interface is more preferable trap site than void and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy while hydrogen atoms are trapped stably up to extremely high occupancy equivalent to spontaneous cleavage.

The Possible transition mechanism for the meta-stable phase in the 7xxx aluminium

Bendo, A.*; Matsuda, Kenji*; Nishimura, Katsuhiko*; Nunomura, Norio*; Tsuchiya, Taiki*; Lee, S.*; Marioara, C. D.*; Tsuru, Tomohito; Yamaguchi, Masatake; Shimizu, Kazuyuki*; et al.

Materials Science and Technology, 36(15), p.1621 - 1627, 2020/09

https://doi.org/10.1080/02670836.2020.1821323

Metastable phases in aluminum alloys are the primary nano-scale precipitates which have the biggest contribution to the increase in the tangible mechanical properties. The continuous increase in hardness in the 7xxx aluminum alloys is associated with the phase transformation from clusters or GP-zones to the metastable phase. The transformation which is structural and compositional should occur following the path of the lowest activation energy. This work is an attempt to gain insight into how the structural transformation may occur based on the shortest route of diffusion for the eventual structure to result in that of phase. However, for the compositional transformation to occur, the proposed mechanism may not stand, since it is a prerequisite for the atoms to be at very precise positions in the aluminum lattice, at the very beginning of structural transformation, which may completely differ from that of the GP-zones atomic arrangements.

An Unreported precipitate orientation relationship in Al-Zn-Mg based alloys

Bendo, A.*; Matsuda, Kenji*; Lervik, A.*; Tsuru, Tomohito; Nishimura, Katsuhiko*; Nunomura, Norio*; Holmestad, R.*; Marioara, C. D.*; Shimizu, Kazuyuki*; Toda, Hiroyuki*; et al.

Materials Characterization, 158, p.109958_1 - 109958_7, 2019/12

https://doi.org/10.1016/j.matchar.2019.109958

Characterization of precipitates in Al-Zn-Mg alloys, using a combination of electron diffraction, bright field transmission electron microscopy and atomic scale scanning transmission electron microscopy imaging revealed the presence of an unreported orientation relationship between the -MgZn phase and the Al lattice with the following orientation relationship (0001) (120) and () (001), plate on (120). The precipitate interfaces were observed and analyzed along two projections 90 to one-another. The precipitate coarsening was through the common thickening ledge mechanism. The ledges were significantly stepped along one lateral direction. An interface relaxation model using density functional theory was carried out to explain the precipitate behavior.

Effect of copper addition on precipitation behavior near grain boundary in Al-Zn-Mg alloy

Matsuda, Kenji*; Yasumoto, Toru*; Bendo, A.*; Tsuchiya, Taiki*; Lee, S.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Marioara, C. D.*; Lervik, A.*; Holmestad, R.*; et al.

Materials Transactions, 60(8), p.1688 - 1696, 2019/08

https://doi.org/10.2320/matertrans.L-M2019828

no abstracts in English

Abnormally enhanced diamagnetism in Al-Zn-Mg alloys

Nishimura, Katsuhiko*; Matsuda, Kenji*; Lee, S.*; Nunomura, Norio*; Shimano, Tomoki*; Bendo, A.*; Watanabe, Katsumi*; Tsuchiya, Taiki*; Namiki, Takahiro*; Toda, Hiroyuki*; et al.

Journal of Alloys and Compounds, 774, p.405 - 409, 2019/02

https://doi.org/10.1016/j.jallcom.2018.10.037

First-principles calculation of multiple hydrogen segregation along aluminum grain boundaries

Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito; Matsuda, Kenji*; Toda, Hiroyuki*

Computational Materials Science, 156, p.368 - 375, 2019/01

https://doi.org/10.1016/j.commatsci.2018.10.015

The segregation of multiple hydrogen atoms along aluminum (Al) grain boundaries (GBs) and fracture surfaces (FSs) was investigated through first-principles calculations considering the characteristics of GBs. The results indicate that hydrogen segregation is difficult along low-energy GBs. The segregation energy of multiple hydrogen atoms along GBs and FSs and the cohesive energy was obtained for three types of high-energy Al GBs. With increasing hydrogen segregation along the GBs, the cohesive energy of the GB decreases and approaches zero with no decrease in GB segregation energy. The GB cohesive energy decreases in parallel with the volume expansion of the region of low electron density along the GB.

First-principles study of hydrogen segregation at the MgZn precipitate in Al-Mg-Zn alloys

Tsuru, Tomohito; Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Shiihara, Yoshinori*; Matsuda, Kenji*; Toda, Hiroyuki*

Computational Materials Science, 148, p.301 - 306, 2018/06

https://doi.org/10.1016/j.commatsci.2018.03.009

Hydrogen embrittlement susceptibility of high strength 7xxx series Al alloys has been recognized as the critical issues in the practical use of Al alloys. Focusing on the interface between MgZn precipitates and an Al matrix, which is considered as one of the important segregation sites in these alloys, we investigated the stable -MgZn-Al interface, and the possible hydrogen trap sites in MgZn and at the -MgZn-Al interface via first-principles calculation. Most of the interstitial sites inside the MgZn crystal were not possible trap sites because their energy is relatively higher than that of other trap sites. The trap energy of the most favorable site at the -MgZn-Al is approximately -0.3 eV/H, which is more stable that of the interstitial site at the grain boundary. The interface between MgZn and Al is likely to be a possible trap site in Al alloys.

Mitsubishi activities for advanced reactor development; Sodium-cooled Fast Reactor

Ito, Takaya*; Sato, Hiroyuki*; Usui, Yukinori*; Toda, Mikio*

Mitsubishi Juko Giho, 43(4), p.45 - 49, 2006/12

http://www.mhi.co.jp/technology/review/abstractj-43-4-45.html

MHI has participated in the FBR development that is a national project from an initial stage as a member of fabricators. Aiming at FBR commercialization until 2050, MHI has actively contributed to "Feasibility Studies on Commercialized Fast Reactor Cycle System" performed mainly by JAEA from 1999. This time, the Sodium-cooled Fast Reactor was chosen at a national level as the main concept. This Sodium-cooled Fast Reactor is proposed by MHI, and for an economy improvement innovation technologies (reduction of the number of the loops, shortening of piping systems, integrated IHX/Pump component and so on) are adopted in this concept. From now on, research and development for FBR commercialization will be accelerated at a national level toward realization of a demonstration reactor until about 2025. MHI also challenges the project as a proposer of this concept.