Understanding hydrogen diffusion and trapping in overaged 7xxx series Al alloys using a reliable electrochemical hydrogen permeation method

Abstract

The diffusion and trapping of H in overaged commercial 7xxx series alloys of the second and third generation is first studied using an enhanced electrochemical permeation method involving sputter etching of the native oxide and hydrogen charging by alkaline corrosion at the open circuit potential. Proof of concept is provided demonstrating remarkable experimental reproducibility and addressing common experimental errors, such as native oxide films, localized corrosion and buildup of corrosion products. A commercial second and third generation 7xxx series alloy exhibit effective H diffusion coefficients of 1.6 ± 0.7 × 10^−10 cm2/s and 3.7 ± 0.3 × 10^−10 cm2/s, respectively. The different H diffusivities were explained by extensive H trapping in coarse intermetallic Al7Cu2Fe and S-phase particles, alongside potential trapping at the interface of quench-induced grain-boundary precipitates with lower Zn content.