OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Introduction Selective laser melting (SLM) is an additive manufacturing (AM) technology in which metal powder is melted by a laser beam along a given trajectory to make products layer by layer. Compared with traditional manufacturing technologies, SLM has a number of advantages, such as rapid prototyping, production of complex-shaped parts and reduced lead time. The technology is developing towards synthesizing new powder compositions for SLM units, studying the influence of mode parameters upon the stable quality of the products, repeatability and reproducibility of the process on different devices [1]. Aluminum and aluminum-based powders are some of the most common materials in the automotive, aerospace and aviation industries due to its excellent strength-to-weight ratio, good thermal and electrical conductivity, and corrosion resistance. Recently, aluminum-based powder has also been the object of research for use in selective laser melting units [2]. This technology allows not only to shorten the design and production cycle, but also to obtain an alloy with a unique structure as metal powder is rapidly melted and cooled [3]. Currently, there are many studies concerning production of various items from aluminum-based powders using the SLM technology [4–6], and recommendations are given to improve the quality of the resulting products. Thus, when determining the SLM conditions, the following physical properties of aluminum are taken into account: high thermal expansion coefficient, high shrinkage during solidification, low level of laser energy absorption, formation of strong oxide layer, high thermal conductivity, relatively wide range of solidification temperatures [7–9]. Defects of the surface and internal structure, such as porosity, layer distortion, cracking, low dimensional accuracy and surface roughness occurred in the process of selective laser melting of aluminum-based powders [10]. These defects are often associated with development of uneven temperature gradients along the fused surface, with contamination of powder by oxides, with inhomogeneity of surface tension which prevents the adhesion of the melt to the substrate and interlayer bonding [11]. All the studies were completed on the specimens produced from the special spherical powders of the necessary alloys which cost a lot. The relative density of the specimens made from spherical powders is over 99.5 %. It was obtained by optimizing laser scanning parameters from AlSi10Mg [12], [13], Al12Si [14] and AlSi7Mg [15] alloys. In addition, these specimens showed excellent mechanical properties of the formed fine cellular dendrite microstructure, which results from the SLM process [16]. Despite the advances in the field of additive technologies, only a limited number of aluminum alloys can be used to produce a high-quality product using the SLM method [17]. Completely dense and crack-free specimens from aluminum-based powders can be produced using SLM in a narrow range of modes [18, 19], which is selected experimentally for each material. The research for non-spherical powders has not been described by scientists. The SLM conditions include over 120 parameters that, to one degree or another, affect the quality of the resulting product. Beside the selective laser melting mode the scanning strategy is also one of the processing parameters that affects the microstructure formation and the properties of the resulting products. By controlling the direction of the heat flow between the layers through the laser beam scanning strategy it is possible to form various grain structures and change the direction of the interlayer grains growth [20]. High energy consumption and uneven temperature distribution lead to huge temperature gradients, high thermal stresses and deformation. Thermal temperature gradients, direction of the heat flow and the cooling rate have a very important influence upon the dislocation density, grain size and texture of the manufactured products. The purpose of the given paper is to study the influence of the scanning strategy on the microstructure, elemental composition, porosity and density of the specimens produced by selective laser melting from non-spherical powders (Al – 91 wt. %, Si – 8 wt. %, Mg – 1 wt. %) specially prepared as described in the previously published papers [21] to determine optimal SLM conditions. This purpose requires solving the following problems: producing specimens from the prepared powder composition [21] using the selective laser melting method with different scanning strategies; identifying of the optimal scanning strategy, which allows producing a specimen with the lowest porosity without changing other melting parameters; determining the density of the specimens, studying the structural and phase composition of the specimen using the transmission microscopy method.
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