Tensile creep mechanisms of Al-Mn-Sc alloy fabricated by additive manufacturing

Abstract

The incorporation of Sc/Zr elements into aluminum (Al) alloys provides great opportunities for high temperature applications, due to the high coherency with the Al matrix, the high thermal stability and the high strengthening potentials of the generated Al3(Sc,Zr) precipitates. In this study, the microstructure, thermal stability, high temperature tensile and creep behaviors of additively manufactured Al-Mn-Sc alloy were systematically evaluated. The Al-Mn-Sc alloy demonstrated sound high temperature yield strength as compared with other reported Al alloys made by additive manufacturing. However, the formed large area fraction (approximately 60%) of fine grain boundaries significantly promoted the dislocation annihilation and reduced the creep threshold stress, though the inherent thermally stable solutes and/or precipitates contributed to its high creep activation energy. On the other hand, the primary Alx(Mn,Fe) and Aly(Sc,Zr) particles and the fine grain boundaries severed as the potential cavity nucleation sites, enhancing the cavity kinetics during creep loading. The cavity nucleation and coalescence process, which basically dominated the tertiary stage of the creep lifetime and led to the final fracture, were further revealed through a cavity evolution model. Future creep-resistant Al alloy design outlook, especially for the inoculates modified Al alloys with fine grain structures, were proposed based on the present findings.