선택적 레이저 용융 공정을 이용한 Al-Si계 합금분말 3차원 조형체 제조 및 특성연구

Abstract

Selective laser melting (SLM) is one of the additive manufacturing technologies, which allows the fabrication of 3D parts through the use of focused laser energy to powder beds directly from user defined 3D CAD models. Generally, this technology is considered as one of the most promising manufacturing techniques for metallic materials due to its ability to produce complex geometries with unique design and high accuracy that can be used not only for the prototyping step but also for small series productions. During the process, the metallic powders are completely molten by highly localized laser energy, which enables the production of individual parts with high density and excellent mechanical properties. Therefore, the laser energy is a critical factor that plays a decisive role in the porosity and microstructural development in SLM process. In this study the densification behavior and microstructural development of AlSi10Mg parts fabricated by selective laser melting (SLM) were investigated with variation of the applied laser scan speed, laser power, overlap ratio and heat treatment. The starting materials of AlSi10Mg powder particles were prepared using a gas atomization process showing uniform size distribution with high flowability. The atmosphere in the chamber in which the process proceeds is performed in an Ar atmosphere. The laser power was changed to 90W, 180W, 270W and 360W, and the laser speed varied from 100mm/s to 4000mm/s. In order to confirm the microstructures and mechanical properties of the laser beam overlap, the specimens were fabricated with 10%, 30%, 50%, and 70% Generally, in the selective laser melting process, Mg2Si appears in 3D fabrication of AlSi10Mg alloy, but XRD analysis showed no peaks other than Al and Si peaks. The changes of microstructure and relative density with the variation of laser power and scan speed were proportional to the size and number of pores. The relative density increased as the laser scan speed increased, but decreased again after a certain period. The microstructure was also densified as the relative density, and then the pore was again generated. At the same laser speed, relative density increased with increasing laser power. We can confirm that the laser output energy is important as the density decreases after a certain period. Under all conditions, the microstructure of AlSi10Mg alloy was confirmed that Si was segregated around Al and appeared dendrite. This dendrite shape appears because the selective laser melting process is a rapid solidification. The analysis of the characteristics of 3D parts produced by selective laser melting was also confirmed by heat treatment condition. First, as-built state, Si was segregated and microstructure was observed. It was confirmed that Si coalesced in the annealing. Especially, it was confirmed that the size of furnace cooling Si precipitate is smaller than water cooling. The elongation was highest for furnace cooling specimens, while yield strength and UTS were highest for as-built specimens. Vickers hardness value was as high as 142.41Hv in the hardness value of the as-built specimen, similar to the tensile property, and the second highest in 81.5Hv of the sample subjected to age hardening treatment after water cooling.73Hv for water cooling and 52Hv for furnace cooling. Analysis of specimens prepared under each condition showed that optimum conditions were found..