Understanding hydrogen permeation in zinc flake coatings for hydrogen embrittlement mitigation

Zinc flake coatings offer a viable alternative to conventional zinc applications like hot-dip galvanizing or electroplating, especially for high-strength steels prone to hydrogen embrittlement. Unlike electroplated coatings, they do not generate hydrogen during application, providing cathodic protection without compromising safety. However, under real-world conditions, hydrogen uptake can still occur due to corrosion processes, as for all zinc systems. This study examines the hydrogen permeation behavior of zinc flake-coated interstitial-free steel. Comparative analyses are conducted on two different zinc flake coatings containing either pure Zn flakes or alloyed ZnAlMg flakes, with a focus on their characteristics regarding corrosion-induced hydrogen permeation. Electrochemical techniques, including linear sweep voltammetry, and permeation tests using a Devanathan-Stachurski cell, are carried out to evaluate permeation behavior and calculate the diffusion coefficients of the coated and uncoated steel samples. Experimental data were compared and fit with a constant flux and a constant concentration boundary condition. The alloyed ZnAlMg flake system shows higher permeation than the Zn flakes at the same hydrogen generation current. Both have a lower overall diffusion coefficient during hydrogen generation than the bare steel, with the Zn flake system exhibiting the lowest. The findings contribute to a deeper understanding of the influencing factors of corrosion-induced hydrogen permeation mechanisms in zinc flake-coated steel. This knowledge facilitates the optimization and development of zinc flake systems tailored to minimize hydrogen permeation risks while maintaining superior corrosion resistance.