Effect of Pulse Current Density on Microstructure of Ti-6Al-4V Alloy by Laser Powder Bed Fusion

This work thoroughly investigated the microstructure of laser powder bed fusion (LPBF) Ti64 alloy induced by electropulsing (ECP) with different current densities. The results show that as the electric current density increases, the small-sized (<10 mu m) alpha ' martensites increase and the large-sized (>10 mu m) alpha ' martensites decrease, resulting in a typical grading microstructure treated by the ECP treatment. The thermodynamic barrier was found to decrease as the electric current passed, recrystallization occurred, and the percentage of small-sized alpha ' martensites increased. At the same time, the unique electrothermal coupling effect of ECP treatment acted on the needle-like alpha ' martensites, causing an energy concentration on the tip to break the adjacent alpha ' martensite and the percentage of large-sized alpha ' martensites to decrease. When the current density of ECP treatment was 48.37 A/mm(2), the grading phenomenon of acicular alpha ' martensites was the most obvious and its size distribution changed significantly, which simultaneously improved the strength and elongation of LPBF-Ti64 alloy. Thus, the typical grading phenomenon of the alpha ' martensites plays a decisive role in improving the mechanical properties of the LPBF-Ti64 samples induced by the ECP treatment. The present results provide new information on the ECP processing additive manufacturing metallic materials.