OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 The etchability of the heat affected zone increases as a result of overaging of the material caused by excessive precipitation of alloying elements from the solid solution. This behavior is characteristic of heat treatable alloy A2024 that is subjected to excessive heat treatment, such as welding. When cutting specimens of titanium Grade2 alloy, the structure of the cutting zone is characterized by low values of macro distortions, except for modes No. 1 and No. 5, characterized by the maximum and minimum cutting speed (fig. 7, a–d). At an average cutting speed of 3.0 m/min and an energy input of 7.1 kJ/m in mode No. 3, specimens with the smallest deviation of the cut geometry, which is about 450–500 μm, are formed. Fig. 7. The structure in the cutting zone of the Grade2 titanium alloy: the macrostructure of the cut (a–d); the initial structure of the base material (f); the fusion zones and the heat affected zone (g, h) a b c d e f g h The fusion zone for Grade2 alloy specimens is represented by a dendritic structure (fig. 7, g, h); its thickness can reach 150–200 μm. The heat affected zone tends to form a needle-like structure (fig. 7, g), which significantly differs from the base metal (fig. 7, f). However, the heat affected zone for this alloy is rather thin. Closer to the cutting surface of the Grade2 alloy specimens, thin layers (up to 10 μm thick) are formed (fig. 7, h), presumably containing titanium oxides, which, as will be shown later, leads to a sharp increase in the microhardness of the surface layers of the specimens. Mechanical properties in the cutting zone of the specimens are consistent with structural changes (fig. 8). The A5056 alloy specimens are characterized by a decrease in microhardness from an average in the base metal of 0.83–0.84 GPa to 0.70–0.75 GPa near the surface in the fusion zone. In the heat affected zone, the microhardness values are intermediate and close enough to the microhardness of the base metal. The total size of the heat affected zone and the fusion zone is about 500–1,000 µm, depending on the cutting mode. For the specimens obtained in optimal mode No. 2, the total value of macro-distortion of the geometry and heat affected zone and fusion zone is about 1,400 µm (1.4 mm), which determines the
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