Effect of Energy Density on Defect Characteristics of Ti6Al4V Alloy Formed by Selective Laser Melting

This study investigates the formation mechanisms and suppression strategies for common metallurgical defects—including balling, porosity, powder adhesion, and spatter—in Ti6Al4V alloys fabricated by selective laser melting (SLM). A comprehensive numerical framework linking process parameters, molten pool dynamics, and defect evolution is developed to optimize linear and volumetric energy densities. This research further proposes actionable guidelines aimed at achieving high-quality manufacturing outcomes in SLM processes. A three-dimensional transient thermal-fluid flow model for SLM-processed Ti6Al4V powder was established to elucidate molten pool dynamics under controlled processing conditions. Utilizing dimensionless numbers to quantify dynamic behaviors, the simulations were optimized to accurately capture molten pool evolution. Defect formation mechanisms, particularly for balling and porosity, were thoroughly examined through integrated numerical modeling and experimental validation, emphasizing the critical impact of linear and volumetric energy densities. The analysis revealed that thermal convection predominantly governs heat transfer within the molten pool, driven primarily by evaporation recoil pressure, surface tension, and Marangoni shear stress. A reduction in energy density adversely affects molten pool fluidity, promoting porosity formation as molten metal solidifies into spherical shapes driven by surface tension. This resultant porosity significantly deteriorates the mechanical properties of fabricated parts, underscoring the necessity for meticulous control over energy density. Optimizing key processing parameters, such as laser power, scanning speed, and scanning spacing, enables the formation of high-quality components. The proposed “process parameters‒molten pool characteristics‒forming quality” analytical framework provides robust guidance for parameter optimization. Application of this framework effectively mitigates metallurgical defects, thereby enhancing the density and mechanical performance of parts manufactured through SLM.