Formation and influence mechanism of metal vapor on the powder spatter and denudation in laser additive manufacturing of Al alloys

The ejection of high-flux metal vapor and its entrained flow are primary factors causing the formation of spatter and denudation phenomena in the laser additive manufacturing process. This work develops a multiphase flow model by bi-directionally coupling computational fluid dynamics-discrete element methods to reveal the influence mechanism of metal vapor from different Al alloys on the stability of the powder bed in the laser powder bed fusion (LPBF) process. The simulation results indicate that the metal vapor generated from the evaporable Mg constituent dominates the formation of powder spatter and denudation in the LPBF processing of Al alloys. The number of spattered powder particles and the width of powder bed denudation are ∼991 and 800 μm for the AlMg5 alloy and ∼904 and 720 μm for the AlMn5 alloy, respectively. This is closely correlated to the composition, diffusion and dynamic behaviors of the metal vapor formed from these two alloys. Investigations on the corresponding surface morphology and roughness are conducted to indirectly verify the simulation results. Good surface quality with a surface roughness of ∼6.7 μm for the AlMn5 alloy is obtained with respect to that of the AlMg5 alloy (∼13.5 μm). This corresponds well to significantly reduced spattered powder and denudation phenomena for the AlMn5 alloy, further confirming the accuracy of the proposed model.