# Investigation of Laser Polishing of Four Selective Laser Melting Alloy Samples
## 1 Introduction
studied the evolution of the molten pool by applying a multiphysics simulation and experiments and analyzed the influence of the flow field on the surface morphology of a single track [14]. In addition, [PERSON] et al. undertook an investigation on the effect of three different powder granulations on the resulting part density, surface quality and mechanical properties of the resulting materials [15]. They were able to attain a low surface roughness by optimizing the powder material. [PERSON] et al. drew a conclusion that spatter, including powder spatter and droplet spatter, affected the SLM process and increased the surface roughness [16]. [PERSON] et al. studied the effects of powder spatter on the quality of parts at different positions on the manufacturing board [17]. The results showed that the surface roughness increased from 14.4 \(\upmu\)m to 28 \(\upmu\)m in the spatter-intensive areas of the board. Therefore, it is recommended that this area should not be used in the manufacture of high-quality parts. With a goal of better understanding these spatter phenomena, [PERSON] et al. used different technologies to prepare the powder so as to not only increase laser absorptivity but also greatly reduce the surface spheroidization phenomenon which can easily occur in metal powder printing [18], thus reducing the surface roughness. [PERSON] et al. presented a systematic approach to improve the surface profile of AM parts using a computational model and a multi-objective optimization technique [19]. All of the above studies aimed to optimize the SLM process parameters applied to the raw materials and printing process to obtain a smoother surface. However, the final product surface still exhibits a significant degree of roughness, which greatly affects the development of AM technology. In recent years, much research has addressed the post-processing of SLM products to obtain a smooth surface. [PERSON] et al. described a method to control the surface deformation during the SLM and found that increasing the magnetic field within a certain range decreased the impact of the Marangoni effect, resulting in a smoother surface [20]. [PERSON] et al. sand-blasted on the top and bottom surfaces of the sample in order to obtain lower surface roughness [21]. [PERSON] et al. applied electrochemical polishing (ECP) to Inconel 718 components fabricated by selective laser melting, significantly reducing the surface roughness as a result [22]. [PERSON] et al. demonstrated the utilization of a chemical polishing approach to improve the surface finish of as-produced metal additive manufacturing components [23]. Another post-processing method involves laser polishing. [PERSON] et al. hold that the method was mainly based on the melting caused by the thermal input of laser irradiation [24], accompanied by the solid-liquid-gas phase change. [PERSON] et al. presented a novel method for reducing the surface roughness of cobalt chromium (CoCr) components with a complex surface geometry by applying a polishing method [25]. They achieved a reduction in the surface roughness of up to 93% relative to the as-received samples. [PERSON] et al. carried out experimental studies to determine the influence of the different laser sources on the roughness reduction rate in laser polishing [26]. [PERSON] et al. presented a laser-polishing process for metallic sintered parts and the measured reductions were up to 80% reductions in \(R_{\text{a}}\) parameter [27]. [PERSON] et al. investigated laser polishing of 304 stainless steel using different process parameters such as laser output power, off-focus position, pulse frequency, scanning speed, and scanning strategy [28]. The present study focused on the influence of different laser-polishing strategies on the surface roughness of selective laser-melted samples. Typical alloys, commonly used in AM, namely, Ti6 Al4V, AlSi10 Mg, 316L and IN718, were studied. In addition, a 3D optical profiler was used to measure the surface roughness of the samples before and after polishing.