Hydrogen embrittlement in Al–Zn–Mg alloys: Semispontaneous decohesion of precipitates

Our study investigates how hydrogen trapped at interfaces of MgZn₂ 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 MgZn₂ instigated a discernible transition in the quasicleavage and intergranular fractures. First-principles calculations revealed that the hydrogen trapping energy at semicoherent interfaces of MgZn₂ 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 MgZn₂ 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 MgZn₂ decreased the interfacial cohesive energy, causing semispontaneous decohesion and quasicleavage fracture in the Al–Zn–Mg alloys.