OBRABOTKAMETALLOV TECHNOLOGY Vol. 26 No. 4 2024 metal combustion products accumulated around the cutting zone, which were displaced by the protective gas fl ow (Fig. 1, e). The arc current during cutting ranged from 350 to 370 A, with a voltage ranged from 370 to 400 V. The height of the plasma torch above the plate surface during cutting was from 16 to 25mm. Gas pressure ranged from2.0 to 4.0 bar, andwater pressure in the systembefore entering the plasma torch cooling circuit was 6 bar. The gap between the nozzle and electrode was between 0.5 and 2.0 mm. The cutting speed varied from 250 to 3,000 mm/min. Air was used as both the plasma-forming and protective gas. After obtaining the experimental samples, metallographic sections for structural analysis were cut from it using electrical discharge machining (DK7750 machine). Structural and morphological studies of the cut surface were conducted using an optical microscope Altami MET 1C, Olympus LEXT 4100 laser scanning microscope, and Zeiss LEO EVO 50 scanning electron microscope equipped with a system for micro-X-ray spectral analysis. The distortion of the cut geometry was determined by the maximum deviation of the cut surface from perpendicularity, using macrostructural images obtained through optical microscopy. The most pronounced edge distortion for the aluminum and copper alloys occurred in the central region (II in Fig. 2, b, c), whereas for the titanium alloy, the greatest distortion was observed at the lower edge (III in Fig. 2, d). The roughest surface texture for all alloy samples was seen at the bottom of the plate (III), while the most uniform cut surface was in the upper region (I). In the subsurface structure of all three alloy types, there were regions of molten metal, a heat-aff ected zone (HAZ), and the base metal with an unchanged structure. The structure of the Cu-9Al-2Mn bronze was the least aff ected by thermal exposure, while the Ti-5Al-5Mo-5V alloy exhibited the largest HAZ, and the Al-6Mg alloy had the thickest molten metal zone. As will be discussed later, these diff erences are due to the thermal conditions, alloy composition, melting temperatures, and thermal conductivity. Results and discussion During plasma cutting of 100 mm thick plates, a specifi c structure formed near the cut surface, along with a characteristic macroscopic relief typical of plasma cutting (Fig. 2). The cut surfaces of the aluminum alloy and bronze exhibited numerous fl ow marks from the metal along the cut edge during the cutting process (Fig. 2, a, c). The cut surface of the titanium alloy, however, showed fewer signs of metal fl ow and was characterized by the presence of microcracks (Fig. 2, e). The most pronounced edge distortion for the aluminum and copper alloys occurred in the central region (II in Fig. 2, b, d), whereas for the titanium alloy, the greatest distortion was observed at the lower edge (III in Fig. 2, e). The roughest surface texture for all alloy samples was seen at the bottom of the plate (III), while the most uniform cut surface was in the upper region (I). In the subsurface structure of all three alloy types, there were regions of molten metal, a heat-aff ected zone (HAZ), and the base metal with an unchanged structure. The structure of the Cu-9Al-2Mn bronze was the least aff ected by thermal exposure, while the Ti-5Al-5Mo-5V alloy exhibited the largest HAZ, and the Al-6Mg alloy had the thickest molten metal zone. As will be discussed later, these diff erences are due to the thermal conditions, alloy composition, melting temperatures, and thermal conductivity. The surface of the Al-6 Mg aluminum alloy after cutting exhibits diff erent structures in the upper, central, and lower parts of the cut (Fig. 3, a–c). The upper part is more uniform, while the lower part contains a higher number of pores and oxidation marks. Microstructural analysis revealed the formation of microcracks (1 in Fig. 3, d) and small spherical pores (2 in Fig. 3, d). Energy-dispersive spectroscopy (EDS) indicated a signifi cant amount of oxygen in the surface layers. The surface layer structure (Fig. 4, a–e) shows distinct regions: the fusion zone (FZ), the heat-aff ected zone (HAZ), and the base metal (BM). The depth of the heat-aff ected zone (HAZ) and base metal (BM) does not exceed 1 mm in the central part. The fusion zone (FZ) contains a large number of coarse secondary phase particles (1 in Fig. 4, d), pores (2 in Fig. 4, f, g), and discontinuities (3 in Fig. 4, g). According to energy-dispersive spectroscopy (EDS) analysis, the fusion zone contains only a small amount of oxygen, but there is a signifi cant change in magnesium content, as shown in Fig. 5, b. The depletion of magnesium in Al-6 Mg -type alloys is expected
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