Forming mechanism of equilibrium and non-equilibrium metallurgical phases in dissimilar aluminum/steel (Al–Fe) joints

• Published in: Scientific reports Vol. 11; no. 1; p. 24251
• Main Authors: Shang, Shun-Li, Sun, Hui, Pan, Bo, Wang, Yi, Krajewski, Adam M., Banu, Mihaela, Li, Jingjing, Liu, Zi-Kui
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20.12.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 639/166/988; 639/301/1023/1026; 639/301/1034/1038; Aluminum; Equilibrium; Free energy; Humanities and Social Sciences; Intermetallic compounds; Learning algorithms; Machine learning; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-021-03578-0

Forming metallurgical phases has a critical impact on the performance of dissimilar materials joints. Here, we shed light on the forming mechanism of equilibrium and non-equilibrium intermetallic compounds (IMCs) in dissimilar aluminum/steel joints with respect to processing history (e.g., the pressure and temperature profiles) and chemical composition, where the knowledge of free energy and atomic diffusion in the Al–Fe system was taken from first-principles phonon calculations and data available in the literature. We found that the metastable and ductile (judged by the presently predicted elastic constants) Al 6 Fe is a pressure ( P ) favored IMC observed in processes involving high pressures. The MoSi 2 -type Al 2 Fe is brittle and a strong P -favored IMC observed at high pressures. The stable, brittle η-Al 5 Fe 2 is the most observed IMC (followed by θ-Al 13 Fe 4 ) in almost all processes, such as fusion/solid-state welding and additive manufacturing (AM), since η-Al 5 Fe 2 is temperature-favored, possessing high thermodynamic driving force of formation and the fastest atomic diffusivity among all Al–Fe IMCs. Notably, the ductile AlFe 3 , the less ductile AlFe, and most of the other IMCs can be formed during AM, making AM a superior process to achieve desired IMCs in dissimilar materials. In addition, the unknown configurations of Al 2 Fe and Al 5 Fe 2 were also examined by machine learning based datamining together with first-principles verifications and structure predictions. All the IMCs that are not P- favored can be identified using the conventional equilibrium phase diagram and the Scheil-Gulliver non-equilibrium simulations.