| The AlSi10Mg alloy is widely used in the fields of aerospace,automobile lightweighting,and others due to its excellent casting performance.However,the coarse primary α-Al dendrites and needle like eutectic silicon in the alloy result in poor mechanical properties of AlSi10Mg castings.Selective laser melting(SLM)technology,which uses high-energy lasers as heat sources,greatly improves the mechanical properties of AlSi10Mg formed parts.However,the low density and high laser reflectivity and thermal conductivity of aluminum alloys make SLM forming difficult,affecting the mechanical properties of the formed parts.In this study,we investigated the effect of process parameters on the quality and distribution of the melt pool for SLM forming of AlSi10Mg alloy and optimized the forming process parameters.The microstructure and distribution of the melt pool were controlled by in-situ re-melting process,which improved the strength of the formed parts.We also studied the variation of the powder after multiple cycles of use,compared the effects of different numbers of powder reuse on the mechanical properties of conventional formed parts and re-melted formed parts,and evaluated the stability of the reinforcement effect of the remelting process after multiple uses of the powder.The relationship between laser power,scanning speed,and the density,surface quality,and surface hardness of formed parts during SLM forming of AlSi10Mg was first studied.A density prediction model based on energy density was established.Using image recognition technology,the variation of pore shape under different process parameters was quantitatively analyzed to optimize the process parameter window.Ultimately,the best forming quality was achieved within the processing window range of laser power 300 W-350 W and scanning speed 750 mm/s-1650 mm/s.The formation mechanism of the melt pool was also investigated.Larger aspect ratio of the melt pool was obtained under high laser power,while smaller melt pools were obtained with higher scanning speeds.Analysis of the mechanical properties of the melt pool using nanoindentation technique revealed that both types of melt pools had higher strength and modulus compared to conventional melt pools.It was also found that elongated melt pools obtained under high laser power were often accompanied by keyhole defects.The presence of irregular metallurgical pores in small-sized melt pools obtained at higher scanning speeds resulted in a higher porosity rate,leading to an overall weaker mechanical performance of the formed parts.In order to obtain a more refined distribution of melt pool structure without affecting the forming quality,a re-melting process was introduced to control the microstructure of the melt pool.Different laser powers and scanning speeds were selected for single-track re-melting experiments of SLM-formed AlSi10Mg,and the geometric morphology changes of the melt pool and cross-section of the remelted track were statistically analyzed.It was found that the effect of scanning speed on the aspect ratio of the remelted melt pool was smaller than that of laser power,and compared with changes in scanning speed,the topography of the melt pool was less affected by laser power.Therefore,the re-melting laser power was determined as the variable,and the effect of re-melting laser power on the forming quality,microstructure,and mechanical properties of AlSi10Mg printed parts was studied.It was found that a high content of melt pool with fine microstructure distribution was achieved at a re-melting laser power of 250 W,and the best comprehensive mechanical properties were obtained.At this time,the yield strength,tensile strength,and elongation of the remelted sample were 250.82 MPa,421.83 MPa,and 6.79%,respectively,which were increased by 16.71%,7.57%,and decreased by 10.54%,respectively,compared with the unremelted sample.Finally,by observing the characteristics of AlSi10Mg powder with different recycling cycles,it was found that the proportion of cellular crystals in the powder increased and the powder variation degree intensified with the increase of recycling cycles.Comparing the mechanical properties of AlSi10Mg powder specimens with different recycling cycles and specimens treated with 250 W laser power re-melting,it was found that the elongation of both the molded and re-melted samples slightly decreased with the increase of powder recycling cycles,but the mechanical properties of the re-melted samples were better than those of the non-re-melted samples at different recycling cycles,indicating that the optimized re-melting process maintains a good and stable strength enhancement effect during powder recycling. |
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