Understanding Keyhole Induced-Porosities in Laser Powder Bed Fusion of Aluminum and Elimination Strategy

Abstract

Laser powder bed fusion (LPBF) technology has the potential to revolutionize the fabrication of complex metal components in the aerospace, medical and automotive industries. However, keyhole pores may be induced during the rapid laser-metal interaction (~ 10-5s) of LPBF. Those inner porosities can potentially affect the mechanical properties of the fabricated parts. Here, based on the experimental observed keyhole-penetration pore (KP-pore) led by keyhole splitting the molten pool in LPBF, we first built a multi-physics finite volume model to reveal this mechanism, where keyhole penetrated the molten pool due to their instability and the keyhole tip was captured by the solidification interface prematurely. We compared the formation mechanisms of KP-pore, rear-front pore (RF-pore) and rear pore (R-pore), and found that they could be attributed to different keyhole fluctuation modes. We investigated the effects of powder on the characteristics of keyhole and molten pool, as well as pore formation, and found that pore counts increased while the pore size decreased, which was due to that powder promoted the keyhole and molten pool oscillation. In addition, the relationship map between the input energy density and the pore number was built via the high-throughput simulation, which provided a strategy to reduce or remove the pore in laser powder bed fusion.

Keywords: laser powder fusion, simulation, keyhole pore, mechanism