Mechanisms for pore evolution and heterogeneity in laser powder bed fusion aluminum elucidated through x-ray microscopy

Laser powder bed fusion (LPBF) of metallic components produces a unique combination of thermomechanical phenomena such as convection, vaporization, and keyholing. The resulting melt pool structure is not easily characterized in post-facto analysis of printed parts, making process-structure correlations very difficult. Here, structures produced by laser keyhole formation during LPBF of an aerospace aluminum alloy were studied through a simplified sample geometry and controlled remelting. The final distribution of pores within the solidified wall were imaged and quantified through high resolution x-ray microscopy and correlated to the remelted melt pool structure. Based on observations from this multimodal, quantitative analysis, a mechanism for the distribution of porosity is proposed. Novel effects of laser processing conditions on microstructures are thus described, highlighting a key source of heterogeneity across the scales of melt pools to thin 3D features.