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

7xxx aluminum alloys are representative high-strength aluminum alloys; however, mechanical property degradation due to hydrogen hinders further strengthening. We have previously reported that hydrogen embrittlement in 7xxx alloys originates from trapped hydrogen at the MgZn₂ precipitate interface, providing high hydrogen trapping energy. 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. Although no significant differences appear between the two alloys regarding the initiation of quasicleavage cracks, the area fractions of final quasicleavage fractures are 16.5% and 1.0% for 0.0%Mn and 0.6%Mn alloys, respectively; this finding indicates that the Mn addition reduces hydrogen-induced fractures. 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. The results of an original hydrogen partitioning analysis show that the dispersion of Mn-based particles (Al₁₂Mn₃Si) with high hydrogen trapping abilities reduces the hydrogen concentration at the semicoherent MgZn₂ interface and suppresses hydrogen embrittlement.