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Selective Laser Melting (SLM) is a promising manufacturing technique for aluminium. However, the strength of AlSi10Mg is relatively low for applications such as automotive industries. The addition of copper, as a common practice to obtain higher strength, is investigated in this study. The post-SLM heat treatments were also investigated to further improve the mechanical properties. Simultaneously, the thermal gradient during manufacturing is high and directional due to the high energy density provided by the laser beam, resulting in preferentially growth of crystals and thus unique microstructure and texture. Therefore, the present work investigated the effect of alteration of scanning strategies on the formation of texture. In this study, the selective laser melting technique is applied on the AlSi10Mg and AlSi10Mg + 4wt% Cu alloys, with conventional casting and T6 process as a reference, in order to investigate the influence of copper addition and different scanning strategies on the mechanical properties. The optimal scan speed and laser power have been determined as 1500mm/s and 300W, respectively, with the relative density higher than 99.0% for both AlSi10Mg and copper-modified AlSi10Mg alloys. Finer microstructure and better mechanical properties compared with the casting followed by T6 heat treatment sample were obtained. The Copper addition improved the ultimate tensile strength and the yield strength of the AlSi10Mg alloy, with a sacrifice on the ductility. The T6 heat treatment further improve the tensile strength of the AlSi10Mg+Cu alloy, with comparable ductility compared to the SLM as-built state. The bidirectional scanning without and with 90° rotation result in weak anisotropy on the mechanical properties of the AlSi10Mg + 4wt% Cu alloy.

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Selective laser melting (SLM) is a new method to produce complex 3D shaped metallic objects in a layer-by-layer fashion. A wide range of electrical, electromagnetic and thermal applications demand complex shaped copper parts with an excellent combination of conductivity and quasi-static mechanical properties. More conventional copper manufacturing technologies face shaping limitations and therefore often time and material consuming joining and machining operations are required to produce the final parts. SLM allows to produce these parts on-site, in a single processing step and with a miminum amount of generated metal scrap. However, the intrinsic low laser absorption of copper at the wavelength of the currently applied fiber lasers inhibits SLM processing of dense copper parts not to mention their inferior properties, compared to conventionally manufactured copper parts. The first purpose of this thesis is trying to produce dense and crack free copper alloy samples using the selective laser melting method. The second goal is to achieve a good combination of electrical conductivity and mechanical properties. Within this context, special attention will be paid to the influence of post heat treatments on the property combination obtained within SLM processed copper alloy parts Five alloy powders are selected for SLM processing: two binary alloys in the Cu-Cr systems and three ternary alloys within the Cu-Cr-C system. In all cases, the maximum content of alloying elements is below 1.5 wt%. The Cu-Cr system is a prototype example of a precipitation hardening system. The strengthening effect of Cr was investigated in both a Cu-0.3Cr (wt%) and Cu-1Cr (wt%) alloy. Different amounts of carbon (C) (0.05 and 0.1 wt%) were added to the Cu-1Cr alloy. The influence of carbon on the optical properties of the Cu-Cr powder beds as well as the chemical interaction with other elements such as Cr and O will be investigated in detail. Special attention will be paid to the powder characteristics, especially the powder preparation method and its link with powder bed properties such as optical absorption, chemistry and flow behavior. Cube shaped samples were processed by SLM in order to define an optimum combination of SLM processing parameters (laser power, scan speed, hatch spacing). In all cases, the powder layer thickness and laser beam diameter were fixed. A combination of microscopy techniques and density measurements was used to determine the SLM processing window to obtain nearly fully dense and crack-free SLM parts. Using the optimized set of SLM processing conditions, heat treatments were performed on SLM processed samples. A conventional heat treatment, comprising a solutionizing step at 1015°C for 1.5h, followed by water quenching and subsequent aging at 400°C for different times was compared with direct aging at 500°C. Tensile bars, processed with optimized SLM and heat treatment parameters, were prepared. Their strength and elongation properties were analyzed and discussed. In case of the Cu-0.3Cr and Cu-0.3Cr-0.05C alloys, nearly fully dense and texture-free samples with relative densities above 98.9% were obtained. Carbon addition increased the electrical conductivity (80 vs 69% IACS), due to its de-oxidizing effect, and resulted in a marginal increase in hardness (82 vs 77 HV-0.3kg) and tensile strength (221 vs 242 MPa σUTS). The tensile elongation, however, decreased due to the carbon addition (29 vs 43%). Direct aging was preferred over

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Laser powder bed fusion (LPBF) is one of the most common additive manufacturing (AM) ‎techniques for fabricating various components in different industries. In recent years, ‎fabricating a single component with a multi-material structure has become increasingly ‎prevalent. It allows a combination of dissimilar materials with different properties into one ‎component to obtain a unique function. However, the fabrication of multi-material parts with ‎complex geometries via conventional methods is difficult due to their inherent limitations. ‎Multi-material LPBF offers a new route for producing 3D objects with tailored properties. ‎Despite its numerous advantages, the achievement of a free-defect interface between ‎dissimilar materials can be the main challenge.‎ Among multi-metallic materials, the stainless steel (SS)-copper (Cu) combination is very ‎attractive due to the excellent thermal conductivity of Cu combined with the good mechanical ‎properties and corrosion resistance of SS. This study explores the multi-material LPBF of 316L-‎CuCrZr components. The LPBF fabrication of SS-Cu multi-material parts is very challenging ‎because of their significant difference in properties such as solubility, laser absorptivity, ‎melting points, and thermal expansion coefficient, resulting in defects such as cracks and ‎pores at the interface after LPBF processing. ‎ In this work, two potential techniques for resolving the interfacial defect issues were ‎investigated. ‎ The first potential solution was surface modification of CuCrZr powder by chromium diffusion ‎in a nitrogen atmosphere to increase the laser absorptivity of the copper-rich powder. The ‎‎316L-modified CuCrZr samples were printed in various conditions. Some SS-Cu samples were ‎stacked horizontally with different scanning sequences and with different Cu printing ‎parameters. In addition, some SS-Cu samples were stacked vertically with different CuCrZr ‎LPBF scanning parameters, different interface designs and strategies, as well as the application ‎of interface remelting strategies. In all samples, however, microcracks were observed at the ‎interface between SS and Cu near the SS side, originating from Fe-rich regions. ‎ Another novel method to resolve the cracking problem was introducing a Ni-based interlayer. ‎In this thesis, an Inconel 625 interlayer with variable thickness was deposited between the ‎‎316L and CuCrZr alloys. The microstructure, elemental distribution, and grain size and ‎orientation of the multi-metallic samples were characterized. The results exhibited that the ‎addition of a 40 µm thick interlayer does not have a tangible effect on eliminating crack ‎formation. When increasing the interlayer thickness to 80 and 160 µm the number and size of ‎microcracks significantly decreased in the Cu-Ni-Fe intermixing zone. The microcracks were ‎mainly located at high-angle grain boundaries (>15°) and partially filled with copper. Finally, ‎applying a Ni-based interlayer with a thickness of 240 µm could successfully eliminate the ‎formation of microcracks. A further increase of the interlayer thickness to 320, 400, and 480 ‎‎µm, still guaranteed the formation of crack-free interfaces. In all samples with Ni-based ‎interlayers of at least 240 µm, no Fe was found near the interface between the Ni and Cu ‎alloys, indicating that the interlayer thickness in crack-free samples was sufficient to avoid the ‎presence of Fe-rich regions near the interface.