| Abstract Scope |
Directed energy deposition (DED) of Al6061 is limited by a narrow processing window, in which both insufficient and excessive heat inputs can lead to defect formation. In this work, multilayer Al6061 deposits were fabricated by varying energy density to investigate the development of crack networks, porosity, and microstructural features. Cumulative crack density and pore morphology were quantitatively evaluated from metallographic cross sections using image-based analysis. Cracks were primarily observed in reheated partially melted zones, at melt pool boundaries, and within solute-enriched interdendritic regions. These results demonstrate that both liquation during layer reheating and solidification cracking due to limited interdendritic feeding contribute to crack formation. In the conduction-mode regime, the optimized window appeared near the threshold beyond which higher heat input promoted keyhole-mode instability and increased porosity. In Al6061, these thermal conditions promote cracking and porosity by limiting interdendritic feeding and gas escape, thereby defining the reduced-defect processing window during DED. |