OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 Introduction Technologies based on the use of plasma effects on the material are widely used for product processing [1], surface modification and coating formation [2], spray coating [3] and many other areas of industrial production of products from metals, alloys, ceramics, polymers and others. The high energy density of the plasma jet allows it to be used both for materials with a high melting point and to increase the productivity of processes associated with it. In particular, the high power of the plasma jet allows it to be used to obtain cut-pieces for subsequent industrial production. In modern industrial production, plasma cutting, along with laser and waterjet cutting, is one of the most widely used methods for producing metal and alloy cut-pieces [4]. Plasma cutting has the advantage of high productivity and the ability to cut thick sheets [5]. However, despite the widespread use of plasma technology, there are still a number of aspects that require further research. These include reducing the roughness of the cutting surface [6–8], reducing the influence of the cutting process on the structure of the material [9–11], and increasing the productivity and accuracy of the cutting process. In the domestic industry, another task is to obtain analogues of the currently used foreign equipment. The cut quality can be achieved by optimizing the cutting process parameters [12–14], the most important being the current and the arc voltage [15–17]. The thickness of the sheet used also has a significant influence on the cutting process and the quality of the cut surface [18]. Plasma cutting of heavy plates using direct polarity plasmatrons is potentially difficult due to cathode insert run-out or temperature operation [19, 20], which is especially important in the growing need for import substitution of components. Plasma cutting of rolled sheet using reverse polarity currents is of great importance and potentially allows for a better quality cut surface. In connection with the above, at present “ITS-Siberia” and ISPMS SB RAS jointly develop modern equipment for plasma cutting at reverse polarity currents. In this case it is important to determine the influence of energy impact during plasma cutting, determined by process parameters, on morphology, structure and mechanical properties of surface layers of billets. Such studies in relation to rolled aluminum and titanium alloy sheets are the purpose of this work. Materials and methods Experimental studies were carried out at the production site of LLC ITS-Siberia and on the experimental equipment of ISPMS SB RAS. The cutting was carried out on a plasmatron with reverse polarity. The scheme of the plasma cutting process is shown in fig. 1, a. The general view of the plasma cutting unit is shown in fig. 1, b. The unit consists of a worktable, a plasmatron, a gas treatment unit, a moving carriage and guides. In the experiment, the unit with a reverse-polarity plasmatron was used. The cutting of aluminum alloys was performed using plasma gas in the form of air. Nitrogen was used as a shielding and plasma forming gas when cutting titanium alloy. The cutting of the specimen 1 was performed by a plasma jet 2 formed by an arc between a water-cooled electrode 3 and the inner body of the plasmatron, in which a flow of plasma-forming gas 4 was constantly flowing. For cutting titanium alloy, a shielding gas in the form of nitrogen 5 was used, which was supplied in the outer circuit of the plasmatron. The molten metal 6 was blown out of the cutting zone by the gas flow. As a result of cutting, an area of thermally degraded material (or heat affected zone) 7 and a layer of molten metal (or fusion zone) 8 were formed on the surface of the specimens. As an experimental material, rolled aluminum alloy AA2024, AA5056 and titanium Grade2 alloy sheets with a thickness of 10 mm were used. The cutting process parameters used in the study were adjusted to achieve different linear energy of the process. The main cutting parameters were arc current and arc voltage, which were 170 A and 125 V, respectively. The adjustable parameter was mainly the cutting speed (table). Metallographic sections were cut from the obtained experimental specimens using the electric discharge sawing (DK7750 machine) to study the structure and to identify features of changes in the mechanical properties of the near-surface zone. Structural studies were carried out using an Altami MET 1C optical
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