In situ Imaging of Precipitate Formation in Additively Manufactured Al-Alloys by Scanning X-ray Fluorescence

A new family of high-strength Al-alloys has recently been developed, tailored for the powder bed fusion-laser beam process. In these alloys, Mn, Cr and Zr are incorporated in solid solution at amounts up to three times that of equilibrium in the as-printed state. Mn and Cr-enriched precipitates that form during printing and heat treatment influence the material's mechanical properties. 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. The study demonstrates the significant value of employing high-sensitivity in-situ X-ray fluorescence microscopy in exploring the kinetics of sub-micrometre scale precipitation.