OBRABOTKAMETALLOV Vol. 24 No. 4 2022 technology Fig. 9. Macro- and microstructure of typical specimen of aluminum alloy with a thickness of 40 mm after plasma cutting: a – macrostructure; b, c – enlarged images of the upper and lower parts of cut zone; d–f – microstructure of specific zones; g, h – microhardness variation; 1 – base metal; 2 – heat-affected zone; 3 – melting zone; 4 – defects; 5, 6 – areas of microhardness testing size of the heat-affected zone are characteristic for the mode No. 8, for which the size of the heat-affected zone is 4.0 mm in the upper part of the cut and 8.0 mm in the bottom part. For these specimens the deviation of cut geometry in the upper part, which is from 0.7 to 5.2 mm, is very important. Studies of the structure of the specimens under higher magnification show that the structure of the material in different parts of the cutting zone is represented by structures quite similar to those identified for 12 mm thick specimens (Fig. 9, d–e). In the melting zone, the structure is represented by dendritic structure with a large number of pores and discontinuities. The heat-affected zone is characterized by increased etchability compared to the base metal; it can be further divided into two parts, also different in the degree of etching. With the initial value of the microhardness of the material in 1.25–1.35 GPa, in the heat-affected zone, it is possible to reduce the microhardness to values of the order of 0.85–1.15 GPa (Fig. 9, g, h). According to changes in microhardness the heat-affected zone is also divided into two separate parts.
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