OBRABOTKAMETALLOV technology Vol. 24 No. 4 2022 Fig. 8. Macro- and microstructure of typical specimen of aluminum alloy with a thickness of 12 mm after plasma cutting: a – macrostructure; b, c – enlarged images of the upper and lower parts of cut zone; d–g – microstructure of specific zones; h, i – microhardness variation; 1 – base metal; 2 – heat- affected zone; 3 – melting zone; 4 – zone boundary; 5, 6 – areas of microhardness testing The changes in mechanical properties in the cutting zone were observed on the specimens by measuring its microhardness (Fig. 8, h, i). The average value of the microhardness of the base metal of the specimens ranges from 1.35 to 1.45 GPa. In heat-affected zone and melting zone there is a sharp decrease of microhardness to the values 0.95–1.2 GPa which shows fairly significant decrease of mechanical properties in these zones. The boundary between the heat-affected zone and the base metal zone in the upper part of the sample is sharper than in the bottom part. Macrostructure of AA2024 alloy specimens with a thickness of 40 mm obtained by different modes of plasma cutting is quite different from that described above (Fig. 9, a–c). The size of the heat-affected zone is significantly higher and amounts to 12–15 mm for most of the cutting modes. The smallest values of the
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