Key factors and tools to minimize hydrogen embrittlement during Zn-Ni coating on ultra-high-strength steels

This study focuses on hydrogen embrittlement in ultra-high-strength steels used in aerospace applications, particularly in critical components such as landing gear. The initial challenge is that these steels require anti-corrosion coatings to operate in aggressive environments; however, the associated electrodeposition processes introduce hydrogen into the material, creating a risk of embrittlement. Traditionally, cadmium has been used due to its excellent protection and low hydrogen generation, but its toxicity and regulatory restrictions have driven the transition toward Zn-Ni coatings—an area in which AZTERLAN has been working within the H2Free project.

Miguel presented the results of the research, which focused on analyzing how different Zn-Ni coating conditions affect hydrogen content and mechanical properties. The AZTERLAN researcher described how different coating morphologies (closed, semi-open, and open) were generated by varying current density and rotating electrode speed. Subsequently, steels such as E35 and Custom 465 were tested by combining hydrogen measurements with mechanical testing using the Small Punch Test technique, as well as applying thermal dehydrogenation treatments to evaluate hydrogen desorption.

The results obtained show a clear relationship between morphology, hydrogen content, and mechanical strength. The open structure exhibits higher hydrogen uptake and greater variability, although it also degasses more quickly, whereas the closed structure maintains the lowest hydrogen levels and provides higher mechanical strength in both steels. Among the conclusions, it was highlighted that although thermal treatments partially reduce hydrogen content, they do not eliminate the differences between morphologies. Therefore, coating morphology is a critical factor in hydrogen embrittlement, with more closed structures being the most favorable for safe industrial applications.