Hydrogen embrittlement in Al–Zn–Mg alloys: Semispontaneous decohesion of precipitates
Kazuyuki Shimizu, Hiroyuki Toda, Kyosuke Hirayama, Hiro Fujihara, Tomohito Tsuru, Masatake Yamaguchi, Taisuke Sasaki, Masayuki Uesugi, Akihisa Takeuchi
Abstract
Our study investigates how hydrogen trapped at interfaces of MgZn 2 precipitates affects hydrogen embrittlement in Al–Zn–Mg alloys. Al–Zn–Mg alloys featuring various aged microstructures were prepared, and their hydrogen embrittlement behaviors were monitored in situ during tensile tests via synchrotron radiation X-ray microtomography. The changes in the interfacial properties of MgZn 2 instigated a discernible transition in the quasicleavage and intergranular fractures. First-principles calculations revealed that the hydrogen trapping energy at semicoherent interfaces of MgZn 2 is significantly high at 0.56 eV/atom, and multiple hydrogen trapping leads to a substantial reduction in interfacial cohesive energy. Hydrogen partitioning analysis of all trapping sites, including vacancies, grain boundaries, and MgZn 2 interfaces, demonstrated that in overaged alloys, more than 90% of the hydrogen was trapped at semicoherent interfaces. The hydrogen trapped at the semicoherent interface of MgZn 2 decreased the interfacial cohesive energy, causing semispontaneous decohesion and quasicleavage fracture in the Al–Zn–Mg alloys. • MgZn 2 semicoherent interfaces is a hydrogen trapping site of 0.56 eV/atom. • Hydrogen reduces the interfacial cohesive energy of MgZn 2 interfaces. • Quasicleavage fracture originates from decohesion of MgZn 2 by hydrogen.