About the role of the hydrogen during stress corrosion cracking of a low-copper Al-Zn-Mg alloy

This study provides some clarifications about the influence of microstructural parameters on the susceptibility of low-copper Al-Zn-Mg alloy to stress corrosion cracking (SCC). Tensile tests in air were carried out on AA7046 in T4 and T4 aged at 150 degrees C (named 150/20) metallurgical states after pre-exposure of the specimens to a chloride solution under mechanical loading. The results showed the predominant role of the corrosion-induced hydrogen during SCC process on the loss of elongation to failure. Scanning kelvin probe force microscopy (SKPFM) measurements were performed for the T4 specimens as well as for a 530 degrees C heat-treated T4 specimen with a coarse-grained microstructure; this allowed the contribution of hydrogen diffusion at the grain boundaries on the hydrogen distribution to be highlighted. The analysis of the fracture modes after tensile tests and hydrogen diffusion profiles obtained by SKPFM in the framework of previous studies investigating the microstructure-hydrogen and plasticity-hydrogen relationships allowed to propose a qualitative model to describe SCC phenomena. The detrimental role of hydrogen at the grain boundaries on the mechanical behaviour was highlighted; the outcome of the evaluation of results from the present study in combination with our previous studies and literature data suggested that it can be limited by hydrogen trapping on intragranular eta-MgZn2 precipitates. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study clarified the influence of microstructural parameters on the susceptibility of low-copper Al-Zn-Mg alloy to stress corrosion cracking. The predominant role of hydrogen diffusion at grain boundaries on hydrogen distribution was highlighted, and a qualitative model to describe SCC phenomena was proposed. The detrimental role of hydrogen at grain boundaries on mechanical behavior was emphasized, and it was suggested that hydrogen trapping on intragranular eta-MgZn2 precipitates could limit this effect.