The influence of laser direct energy deposition processing parameters on Al7075 alloy and Zr-modified Al7075 alloy

Abstract

The Laser Directed Energy Deposition (LDED) technique in metal additive manufacturing (MAM) offers intricate geometries while maintaining material properties akin to cast and wrought components. However, challenges persist in fabricating high-strength aluminum alloys like 2xxx, 6xxx, and 7xxx series due to hot cracking during rapid solidification in LDED. This study addresses Al7075 hot cracking issue by introducing 1 wt% Zr. To evaluate this novel approach, the influence of process parameters on track geometry, porosity, microstructure, hardness, and tensile properties of both Al7075 and modified Al7075 (with 1 wt% Zr) was examined using an L<inf>27</inf> orthogonal array of experiments. Findings indicate that increased laser power widens bead width and wetting angle. Conversely, higher scan speeds reduce bead height but marginally increase width, impacting wetting angle. Notably, the addition of Zr decreased porosity from 0.07 to 0.032%, indicating enhanced material quality. Microstructural analysis reveals Zr’s role in preventing solidification cracking by enhancing molten metal fluidity during solidification, transitioning the microstructure from columnar to equiaxed fine grain due to Al<inf>3</inf>Zr precipitates, and promoting grain refinement. This addition of Zr also improved hardness and tensile strength by 11% and 10%, respectively, attributed to Al<inf>3</inf>Zr precipitates’ role in grain refinement and precipitation strengthening within Al7075. In summary, incorporating 1 wt% Zr into Al7075 via LDED demonstrates promising improvements in microstructure, reducing porosity, enhancing mechanical properties, and mitigating solidification cracking, thereby offering potential enhancements in the fabrication of high-strength aluminum alloys. © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2024.