Assessment of hydrogen embrittlement susceptibility of an Al-Cu-Mg alloy in humid air

¹ Department of Environmental Materials Engineering, National Institute of Technology (KOSEN), Niihama College, 7-1 Yagumo-cho, Niihama, Ehime 792-8580 Japan
² Undergraduate Student, Department of Mechanical System Engineering, College of Engineering, Ibaraki University, 4-12-1, Nakanarusawa-Cho, Hitachi, Ibaraki 316-8511 Japan
³ Graduate Student, Major in Mechanical Systems Engineering, Graduate School of Science and Engineering, Ibaraki University, 4-12-1, Nakanarusawa-Cho, Hitachi, Ibaraki 316-8511 Japan
⁴ Department of Mechanical Systems Engineering, College of Engineering, Ibaraki University, 4-12-1, Nakanarusawa-Cho, Hitachi, Ibaraki 316-8511 Japan

^* Corresponding author: manaka@mat.niihama-nct.ac.jp

Abstract

In the present study, we investigated the hydrogen embrittlement susceptibility of Al-4%Cu-1.5%Mg alloys subjected to several heat treatments by means of SSRT tensile test and humid gas stress corrosion cracking(HG-SCC) test. For SSRT tensile test, the tensile test pieces were cut from cold-rolled sheets of 1mm thickness. The test pieces were solution-treated at 500 °C for 1h, water-quenched and aged at 140oC for 72h or 360h. SSRT tensile test was performed in two environments, humid air (HA) and dry nitrogen gas (DNG) at a strain rate of 1.39×10^-6s^-1. Fracture surfaces were observed with a scanning electron microscopy(SEM). For HG-SCC test, compact tension(CT) test pieces were cut from hot-rolled plate of 6mm thickness. The CT test pieces were solution-treated, water-quenched and aged at 190 °C for 9h, 50°C for 96h or 140°C for 72h. HG-SCC test was carried out based on High Pressure Institute of Japan standards; HPIS E103:2018. The pre-cracked CT specimens with stress loading were kept for 90 days in two environments, HA and DNG. After 90 days, in order to observe whether cracks propagated due to HG-SCC, the specimens were loaded up to fracture rapidly, followed by SEM observation. Tensile properties obtained by SSRT tensile tests were almost the same in two environments. Also, fracture surfaces were not affected by test environments. Moreover, in HG-SCC tests, crack propagation was not observed at each test conditions. Therefore, Al-4%Cu-1.5%Mg alloy had high-resistance to hydrogen embrittlement.