Influence of laser surface polishing on surface topology and residual stress in laser powder bed fusion additively manufactured aluminium-12 silicon part Einfluss des Laserstrahloberflächenpolierens auf die Oberflächentopologie und die Eigenspannungen in einem durch Laserstrahl-Pulverbettschmelzen additiv gefertigten AlSi12-Bauteil

Abstract

Laser-assisted additive manufactured surfaces are more often inherently associated with surface and subsurface defects such as poor surface texture, high surface roughness, high tensile residual stress, porosity etc. Depending on the design and methodology adopted, these factors entail limitations in improving the functional properties of additively manufactured parts. Post-processing often becomes mandatory to improve surface finish, residual stresses and other surface-dependent properties. Nowadays, aluminium alloys are widely used for lightweighting in aerospace, aircraft and automotive industries with special emphasis on manufacturing complex design and multi-functional components employing additive manufacturing routes (both laser and non-laser based). The present work aims to demonstrate laser surface polishing (by remelting) of laser-assisted powder bed fusion aluminium-12silicon additively manufactured parts as a viable post-processing technique to improve surface properties. Aluminium-12 silicon cubes printed by laser powder bed fusion at optimum processing conditions having high relative density were stress-relived and subjected to laser surface polishing employing a multi-mode square-beam diode laser under varying energy densities. Results indicated a profound influence of energy density on resulting surface roughness, remelted depth, residual stress and microstructure of laser-assisted powder bed fusion additive manufactured parts. At optimum energy density, the surface roughness of the additive manufactured part was reduced by 82 % with smoothing of initial chaotic texture and reduction in residual tensile stress to zero-level. Indeed, laser surface polishing at optimum energy density enhanced surface and subsurface micro-hardness to 75 HV 0.5 – 100 HV 0.5 from 65 HV 0.5 – 75 HV 0.5 in the initial additive manufactured part on account of refined rapidly solidified structure.