Understanding the Al diffusion pathway during atmospheric corrosion of a Mg-Al alloy using atom probe tomography

Magnesium alloys continue to play a significant role in the context of lightweight structural materials, albeit that corrosion susceptibility remains a limit to their wider use. Most research to date has focused on aqueous corrosion of Mg alloys, whilst atmospheric corrosion remains poorly understood. Using atom probe tomography and a novel in-situ coating method, the native oxide layer in an additively manufactured Mg-Al alloy (AZ111) was investigated. Aluminum was found to diffuse outwards during oxidation and to be incorporated into a Mg-oxide/hydroxide rather than forming the postulated Al₂O₃ layer. This study advances the understanding of magnesium oxidation. • In-situ metal coating of APT specimens enable the analysis of the native oxide around the entire specimen of an AZ111 alloy. • Al-rich nanoclusters could be found in the LBPF produced AZ111 alloy – providing a short diffusion pathway for Al. • No evidence of the formation of an Al enriched layer (Al 2 O 3 ) at the oxide-metal interface during atmospheric corrosion. • Al incorporation was found in the surface layer of Mg hydroxide/oxide.