# Investigation of Laser Polishing of Four Selective Laser Melting Alloy Samples
## 2 Materials and Methods  
### Sample Fabrication  
Four typical alloys were selected in the present study, namely, Ti6 Al4V, AlSi10 Mg, 316L and IN718. The samples, all of which measured 40 mm \(\times\) 40 mm \(\times\) 5 mm, were fabricated using SLM equipment (SLM 125, SLM Solutions NA, Inc., Lubeck, Germany). The square plate-shaped samples were printed at the center of the build plate. The structure of the samples was simple and the height was very low, so the position may have a little influence on the global geometry. Therefore, a systematic compensation approach from forming technology presented by [PERSON] et al. [29] has not been considered. The particle diameter of the metal powders (Advanced Powders and Coatings Inc., Boisbriand, Quebec, Canada) used in the present study was 15-45 \(\upmu\)m. Figure 1 shows scanning electron microscope (SEM, FEI Inspect F50, Thermo Fisher Scientific Inc., Waltham, MA, USA) images of the particles of the four typical alloy powders, showing the particle size range and that most of the powder particles are spherical.  
Each of the four kinds of powders exhibits a good size distribution and surface roughness. [PERSON] et al. confirmed that these powder characteristics have a great impact on the performance of the samples [30], such as their mechanical strength, porosity and surface finish. As such, the virgin powder that was selected in the experiment can greatly reduce printing problems caused by powder quality, including oxidation and particle adhesion. All of the above factors affect the surface quality and mechanical properties of the printed parts and, sometimes, could lead to printing failures. In fact,powders are often reused. Although they are screened, the powder quality will degrade during the recycling.  
A continuous wave fiber laser (IPG YLR-400, IPG Photonics Corporation, Oxford, MA, USA) with a wavelength of 1060 nm, a nominal output power of 400 W and a spot size of 100 \(\upmu\)m was used in the sample fabrication process. The specific printing process parameters are optimized and they are empirical values of the SLM equipment, shown as Table 1. After the printing was completed, the samples were not taken out of the chamber. Rather, a laser-polishing experiment was performed under an argon atmosphere with an oxygen content of \(<\)0.1%, which was the same as that of the printing processing environment, in which almost no oxidation occurs. The experimental setup used to perform the polishing experiments is shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Ti6 Al4V** & **AlSi10 Mg** & **316L** & **IN718** \\ \hline Power (W) & 276 & 350 & 320 & 175 \\ Feed rate (m/s) & 0.76 & 1.15 & 0.65 & 0.60 \\ Layer thickness (\(\upmu\)m) & 50 & 50 & 50 & 50 \\ Hatch spacing (\(\upmu\)m) & 120 & 170 & 140 & 140 \\ \hline \hline \end{tabular}
\end{table}
Table 1: SLM parameters of four typical alloys.  
Figure 1: SEM images of four powder particles: (**a**) Ti6 Al4V, (**b**) AlSi10 Mg, (**c**) 316L and (**d**) IN718.  
Figure 2: Experimental setup.  
The sample surface was divided into nine areas, each measuring 10 mm \(\times\) 10 mm. The laser-polishing experiment was performed using the same laser equipment but laser parameters were adjusted for laser polishing. The experimental parameters corresponding to eight regions are listed in Table 2. In addition, the scanning path of the laser is the same as that of the printing process, the hatch spaces of the 316L and IN718 alloys are adjusted to 80 \(\mu\)m, and the others remained unchanged. Subsequently, the sample was cut from the build plate using electrospray wire-electrode cutting equipment (FH-020C, Suzhou Xingjie CNC Technology Co., Ltd., Suzhou, China). The initial and post-processed surfaces of the four typical alloys are shown in Figure 3.