Corrosion fatigue crack growth in A7N01S?T5 aluminum alloy MIG welded joints

This paper studies the corrosion fatigue crack growth (CFCG) in 3.5 wt% NaCl solution of the local zones of A7N01S-T5 aluminum alloy metal inert gas (MIG) welded joints cut from high-speed train underframes after service lives of 1.8 million km. The results show that the base metal (BM) region exhibits the highest rate of CFCG compared to both the heat-affected zone (HAZ) and the weld metal (WM) zone. Crack features suggest that the corrosion fatigue failure mode of the BM is hydrogen-assisted propagation and that the failure mode for both the HAZ and WM is anodic dissolution. We calculate that the multi-site adsorption and substitution of Cl- on the surface of the passivation film can make the oxygen and aluminum atoms detach from the surface of the passivation film, causing its destruction and allowing the cracks to expand further. Hydrogen is more likely to accumulate and diffuse along the grain boundaries, reducing their strength and causing them to become the most likely orientation for crack propagation. This study provides the new insight into the specific CFCG mechanisms of each zone in aluminum alloy welded joints.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigates the corrosion fatigue crack growth (CFCG) in the local zones of A7N01S-T5 aluminum alloy metal inert gas (MIG) welded joints from high-speed train underframes. The results indicate that the base metal (BM) region has the highest rate of CFCG compared to the heat-affected zone (HAZ) and the weld metal (WM) zone. The failure mode of the BM is hydrogen-assisted propagation, while the HAZ and WM exhibit anodic dissolution. The study provides insights into the specific CFCG mechanisms in each zone of aluminum alloy welded joints.