Abstract
Laser polishing is a widely used technology to improve the surface quality of the products. However, the investigation on the physical mechanism is still lacking. In this paper, the established numerical transient model reveals the rough surface evolution mechanism during laser polishing. Mass transfer driven by Marangoni force, surface tension and gravity appears in the laser-induced molten pool so that the polished surface topography tends to be smoother. The AlSi10Mg samples fabricated by laser-based powder bed fusion were polished at different laser hatching spaces, passes and directions to gain insight into the variation of the surface morphologies, roughness and microhardness in this paper. The experimental results show that after laser polishing, the surface roughness of Ra and Sa of the upper surface can be reduced from 12.5 μm to 3.7 μm and from to 29.3 μm to 8.4 μm, respectively, due to sufficient wetting in the molten pool. The microhardness of the upper surface can be elevated from 112.3 HV to 176.9 HV under the combined influence of the grain refinement, elements distribution change and surface defects elimination. Better surface quality can be gained by decreasing the hatching space, increasing polishing pass or choosing apposite laser direction.
Highlights
Additive manufacturing technology (AM), known as 3D printing technology, is an advanced material forming technology
They found that the surface roughness and the carbon concentration could be significantly reduced after laser polishing
The temperature distribution and the rough surface evolution process can be shown in Figures 3 and 4
Summary
Additive manufacturing technology (AM), known as 3D printing technology, is an advanced material forming technology. Temmler et al [13] selected four sets of experimental process parameters to investigate the effect of multi-steps laser polishing on the microstructural properties of tool steel H11. They found that the surface roughness and the carbon concentration could be significantly reduced after laser polishing. A numerical model was established to study the rough surface evolution mechanism and complex hydrodynamic behavior in the molten pool during laser polishing with consideration of the phase transitions, gravity, recoil pressure, surface tension and Marangoni effect. To account for the rough surface evoluZtion mechanism during laser polishing, the fsionfittwe aerleem(CeOnXtMmSOetLhomduwltia-sphuysesidcsin5.4th, Ce OthMeoSrOetLicIanlcHs.,tAXuStZdoyc.kIhnoltmBhai,ssSepwlaaepydeerern, )thweacsoemmmpleoryceiadl considering heat transfer, laminar flow, gravity, recoil pressure, surface tension and Marangoni effect. (2) The deformation of mechanical behavior has negligible effect on fluid field [27]. (3) The laser absorptivity of the material is assumed to be constant [27]. (4) The flow field in the molten pool is assumed as an incompressible Newtonian laminar flow [27]. (5) The material is isotropic and homogenous [27]. (6) The metal loss caused by evaporation during L-PBF is ignored [28]
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