Hydrogen trapped at intermetallic particles in aluminum alloy 6061-T6 exposed to high-pressure hydrogen gas and the reason for high resistance against hydrogen embrittlement Junichiro Yamabe a,b,c,* , Tohru Awane b,d,** , Yukitaka Murakami e a International Research Center for Hydrogen Energy, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan b Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan c Hydrogen Materials Laboratory (HydroMate), Research Promotion Division of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST), 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan d Kobe Material Testing Laboratory Co., Ltd., 47-13 Nii-jima, Harima-cho, Kako-gun, Hyogo 675-0155, Japan e Kyushu University, Japan article info Article history: Received 19 June 2017 Received in revised form 2 August 2017 Accepted 3 August 2017 Available online 31 August 2017 Keywords: High-pressure hydrogen gas Aluminum alloy Secondary ion mass spectrometry Thermal desorption analysis Intermetallic particle abstract Hydrogen ( 1 H) trapped at intermetallic particles (IPs) in an aluminum alloy, 6061-T6, was visualized with secondary ion mass spectrometry (SIMS) by precisely excluding the false signal which is caused by background hydrogen (H BG ). The interference of the H BG was avoided by a unique continuous pre-sputtering (pre-digging) by a primary ion beam of SIMS into a sample in combination with silicon sputtering prior to the SIMS measurement of the sample and we succeeded in visualizing the exact signal of 1 H trapped by IPs at subsurface layer of the sample charged in high-pressure hydrogen gas. The thermal desorption analysis clarified that the desorption energy (E d ) of the IPs was 200 kJ/mol or higher, which was extremely higher than E d for lattice interstice, dislocations, and vacancies. High density hydrogen was concentratedly trapped at IPs in the subsurface layer in contact with the hydrogen gas. This nature causes an extremely low effective hydrogen diffusivity of 6061-T6 of the order of 10 14 m 2 /s even at 200  C and may eventually give a high HE resistance to 6061-T6. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction The hydrogen atom easily invades into metals and interacts various lattice defects, such as dislocations, grain boundary, and secondary particles [1e4], causing degradation of the mechanical properties, well-known as hydrogen embrittle- ment (HE) [5e17]. According the NASA database [18], aluminum alloys, 6061-T6 and 7075-T73, are categorized into “negligibly embrittled”. However, the detailed mechanism of a * Corresponding author. International Research Center for Hydrogen Energy, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan. ** Corresponding author. Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan. E-mail addresses: yamabe@mech.kyushu-u.ac.jp (J. Yamabe), awane.toru.438@m.kyushu-u.ac.jp (T. Awane). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 42 (2017) 24560 e24568 http://dx.doi.org/10.1016/j.ijhydene.2017.08.035 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.