OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Therefore, these technologies change the framework for the automobile, aerospace and mechanical engineering industries [1]. In spite of the intense introduction of additive technologies (AT) and industrial investments into it [2] there are difficulties that prevent the enormous potential of these methods from realizing. Many alloys, which possess perfect mechanical properties when being treated according to traditional production techniques, are prone to significant cracking when hardening during the laser melting [3]. The large gap in the scientific knowledge concerning the microstructures is also an obstacle limiting the use of SLM methods. The gap occurs due to the complex nonequilibrium processes associated with laser melting [4]. Currently, only a small number of aluminum alloys is used as basic materials for additive manufacturing [5], [6]. The most widely used ones are the hardening alloy AlSiMg [7, 8] and the eutectic alloy AlSi12. The mechanical properties of AT components produced from these two alloys compare well with those of cast or die-cast samples but it is definitely far below the properties of the deformed items produced from high-strength aluminum alloys, such as Al7075 (Zn – 5.5 wt. %, Mg – 2.5 wt. %, Cu – 1.5 wt. %), which yield strength exceeds 500 MPa and its plasticity is 3–9 % [9]. Unfortunately, SLM of the last-named alloy is difficult due to its low weldability as well as due to its high reflectivity and low viscosity (an inherent disadvantage of most conventional aluminum alloys). To be more precise, thermal compression of the item when treated leads to its cracking [10]. Besides, the evaporation of the low-melting alloying elements, such as Zn, in the process of laser melting is crucial for the formation of strengthening phases, so it also results in mechanical properties deterioration. Literature analysis shows that the composition of the alloy plays an important role in determining the final microstructure and the mechanical properties of the SLM-produced composites [11, 12]. Al-Si-Mg (Al – 91 wt. %, Si – 8 wt. %, Mg – 1 wt. %) alloy is close to the eutectic composition. It has perfect castability due to little change in volume when solidifying, which makes it suitable for manufacturing thin complex shape casts and a promising material for SLM-produced items with improved mechanical properties [13]. An increase in mechanical properties occurs due to an increase in the solids solubility and a decrease in the grain size of Al-Si-Mg alloys due to high rates of the powder material melting, cooling and solidification during the SLM process. Currently, globular powders produced from Al-Si-Mg alloy are used in SLM units [14, 15]. In the given paper the method of layer-by-layer laser synthesis will be applied to solve a fundamental problem – the possibility of synthesizing items and alloy of Al-Si-Mg system from the powder composition of aluminum, silicon and magnesium having principal difference in melting temperatures, density, thermal conductivity, etc. Two methods are usually used to prepare mixtures of powdered metals: direct blending and mechanical alloying with a globe mill. Mechanical alloying is a nonequilibrium solid-state treatment method which can be used for preparing a powder composition at room temperature. The repeated deformation and destruction taking place under high-energy ball-milling lead to the change of morphology, size and microstructure of metal powders [16]. As the globe mill introduces a lot of energy into the powder mixture (in comparison to direct mixing), it can significantly influence the properties of the composite material after the laser treatment [17], that is why research is required to determine the powder morphology, the size and the sizewise distribution characteristics of particles in the initial powder. The aim of the given study is to determine the requirements for the structural-phase state and element composition of aluminum, silicon and magnesium powders; further preparation of the mixture of Al-Si-Mg (Al – 91 wt. %, Si – 8 wt. %, Mg – 1 wt. %) powder composition to be used for the laser synthesis. Based on the purpose of the study, the following tasks were formulated: to study the initial powders and the powder composition by the methods of X-ray diffraction and X-ray phase analysis, scanning electron microscopy; prepare a powder composition for the SLM process and conduct an experiment of laser synthesis of the powder composition to determine the possibility of the process. Study methods The powders of aluminum, silicon, and magnesium were used as initial materials for creating the powder composition. Aluminum powder PA-4 (produced according to GOST 6058–73), silicon powder
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