In situ imaging of precipitate formation in additively manufactured al-alloys by scanning X-ray fluorescence

Abstract

Al-alloys incorporating Mn, Cr and Zr, tailored for powder bed fusion-laser beam processes with solubilities three times equilibrium have recently been developed that yield a high strength. Mn and Cr-enriched precipitates that form during printing and heat treatment influence the material’s mechanical properties hence making it important to understand their kinetics. In this study, direct imaging of these precipitates was accomplished through the utilisation of in situ synchrotron-based scanning X-ray fluorescence. During heat treatment, a selective accumulation of Cr and Mn in two distinct types of precipitates at grain boundaries was observed. Additionally, the microstructure at the melt-pool boundary, containing precipitates found in the as-printed state, remains thermally stable during the heat treatment. Both these results shed light on the active role Cr plays in the precipitation kinetics of the material. The study also demonstrates the significant value of employing high-sensitivity in-situ X-ray fluorescence microscopy in exploring the kinetics of sub-micrometre scale precipitation.