Investigation of Cracking Susceptibility and Porosity Formation and Its Mitigation Techniques in Laser Powder Bed Fusion of Al 7075 Alloy

The processing of high-strength Al7075 alloy through the laser powder bed fusion process is challenging because of cracking susceptibility. In this work, an experimental study has been carried out to understand the defects formation and to predict the optimum conditions for defect-free parts by varying process parameters such as laser power, scanning speed, base-plate heating temperature, remelting speed, and powder composition. A detailed mechanical and microstructural characterization has been carried out to investigate porosities, cracks, microstructure, grain structure, and mechanical properties. It was observed that the single-melting-based fabrication of Al7075 samples results in excessive porosities and solidification cracks along the build direction. The cracks are due to the insufficient liquid back-filling of the long columnar-dendritic grains during the solidification. The ramped-down high-speed remelting eliminates the balling defect, decreases the porosity percentage, and reduces surface roughness. The base plate heating of 473 K and 573 K reduces the extent of porosity and crack formation. Adding 4 wt% nano-TiC reinforcement to the Al7075 matrix eliminates the porosity and solidification cracks due to the very fine equiaxed grain because of heterogeneous nucleation.