OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 1 2024 When a laser interacts with the powder composition, a number of complex physical and chemical phenomena occur on the surface of the specimen in the process of rapid melting and solidifi cation. The phenomena include absorption and scattering of laser energy, heat transfer, phase transition and melt fl ow. The thermodynamic and kinetic behavior of the melt pool can be changed by adjusting the processing parameters. The work establishes optimal processing conditions including: laser power of 90W, the scanning speed of 225 mm/s, the scanning step of S = 0.08 mm to make products from the powder composition with aluminum powder size of 20 to 64 μm. Porosity analysis revealed the area of high consolidation without signifi cant metallurgical defects. Less laser power result in reduced energy input causing disordered surface solidifi cation due to low wettability of aluminum. The liquid phase is not enough to fi ll the cracks [17, 21]. High energy input is required for rapid propagation of heat and cooling due to the high thermal conductivity and high refl ectivity of aluminum [19]. Increasing the laser power to 90 W and more improves the wettability of the powder and reduce the dynamic viscosity of the molten aluminum-based material [23]. As a result, the liquid melt fi lls the pores compacting the structure, which leads to optimal fusion. The scanning speed is the second important parameter of the SLM mode; increasing it can signifi cantly reduce the product manufacturing time. In experiments with the powder composition under consideration, its increase to 300 mm/s reduces the eff ect of laser energy on the processed layer of powder and its wettability, resulting in the gradual growth of porosity. Setting the scanning speed of less than 225 mm/s and the laser power of more than 90 W leads to the growth of the thermal conductivity eff ect, but it also increases the cooling time. Long-term interaction between the laser and metal powder occurs under the low scanning speed and high power, and pores are formed [23]. In addition, increasing the laser power and decreasing the scanning speed enhances the evaporation of molten low-temperature materials, which leads to the change in the proportion of alloy elements, reduces the stability of the resulting fusion tracks and aff ects dispersion strengthening [24]. As a result, at the end of the laser scanning tracks there appear round pores fi lled with vapors or gases [17], which are trapped in the melt pool due to the non-equilibrium convection fl ow associated with ultra-high energy input. For the samples built under the optimal conditions from the powder composition with aluminum powder size from 20 to 64 μm, the laser energy input was suffi cient to achieve complete melting of the metal a b Fig. 9. Light-fi eld images on various parts of the specimen
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