Molten pool thermodynamics in laser-powder-bed-fusion aluminum alloys and thermal strengthening mechanisms of ceramic particles

Abstract

Laser Powder Bed Fusion (LPBF) of aluminum alloy 6061 (AA6061) faces serious challenges including poor processability and defect formation, which significantly degrade mechanical properties. This study investigates the unique effects of incorporating 5 vol% low-cost, micron-sized TiCN particles to AA6061 through LPBF experiments and numerical simulations. The experiments reveal that TiCN significantly improves printability and reduces defects. The simulations reveal that increasing scanning speed shifts molten pool dynamics from keyhole mode to conduction mode, with transitional states in between. It is identified that unstable flow and strong reverse motion of the melt pool cause deep keyhole truncation, forming isolated spherical voids. In addition, the insufficient laser energy leads to poor molten pool wetting and spreading, resulting in defects like necking, fracture, and balling. Thermodynamic analysis of the metal-ceramic composite molten pool clarifies the TiCN strengthening mechanism. TiCN particles increase the local molten pool’s temperature, velocity, and heat flux. They also intensify re-circulation zones and velocity gradients around themselves, while reducing overall flow velocity and re-circulation strength. This enhances central thermal transfer efficiency and stabilizes flow. The heat storage and buffering of TiCN particles, along with their absorption and dissipation of turbulent motion, help stabilize molten pool dynamics and suppress printing defects. This study offers a versatile material design strategy and effective simulation method for LPBF processing of high-strength aluminum alloys.