Change in microstructural characteristics of laser powder b e d fuse d Al-Fe binary alloy at elevated temperature

The present study addressed the change in the microstructure of Al-2.5 wt% Fe binary alloy produced using laser powder bed fusion (L-PBF) technique by thermal exposure at 300 degrees C, and the associated mechanical and thermal properties were systematically examined as well. Multi-semi-cylindrical patterns corresponding to melt pools in the microstructure were macroscopically observed for the asmanufactured sample. No change in the melt-pool morphology was observed after thermal exposure for 10 0 0 h. Inside the melt pools, a large number of the nanoscale metastable Al 6 Fe phase particles were uniformly distributed inside columnar grains of the alpha-Al matrix containing concentrated solute Fe in supersaturation. The sequential formation and coarsening of stable theta-Al 13 Fe 4 phases were observed upon exposure to a 300 degrees C environment, but a considerable amount of nano-sized metastable Al 6 Fe phases remained even after 10 0 0 h. Furthermore, the thermal exposure continuously reduced the concentration of solute Fe atoms in the alpha-Al matrix. No significant grain growth was found in alpha-Al matrix after 10 0 0 h owing to the pinning effect of the dispersed fine particles on grain boundary migration. These results demonstrate a sluggish change in microstructural morphologies of the Al-2.5 wt% Fe alloy. The quantified microstructural parameters addressed dominant strengthening contributions by the solid solution of Fe element and Orowan strengthening mechanism by fine Al-Fe intermetallics in the L-PBF-produced alloy. The high strength level was sustained even after being exposed to 300 degrees C for long periods. The superior balance of mechanical properties and thermal conductivity can be achieved in the experimental alloys by taking advantage of the various microstructural parameters related to the Al-Fe intermetallic phases and alpha-Al matrix. (c) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

This study demonstrated that the microstructural morphologies of the Al-2.5 wt% Fe alloy undergo a sluggish change, dominated by the solid solution of Fe element and the Orowan strengthening mechanism by fine Al-Fe intermetallics. The high strength level of the alloy is sustained even after long-term exposure to 300 degrees C, with no significant grain growth in the α-Al matrix.