On the problem of tool destruction when obtaining fixed joints of thick-walled aluminum alloy blanks by friction welding with mixing

Introduction. Among the technologies for manufacturing rocket and aircraft bodies, marine vessels, and vehicles, currently, more and more attention is paid to the technology of friction stir welding (FSW). First of all, the use of this technology is necessary where it is required to produce fixed joints of high-strength aluminum alloys. In this case, special attention should be paid to welding thick-walled blanks, as fixed joints with a thickness of 30.0 mm or more are the target products in the rocket-space and aviation industries. At the same time, it is most prone to the formation of defects due to uneven heat distribution throughout the height of the blank. It can lead to a violation of the adhesive interaction between the weld metal and the tool and can even lead to a destruction of the welding tool. The purpose of this work is to reveal regularities of welding tool destruction depending on parameters of friction stir welding process of aluminum alloy AA5056 fixed joints with a thickness of 35.0 mm. Following research methods were used in the work: the obtaining of fixed joints was carried out by friction welding with mixing, the production of samples for research was carried out by electric erosion cutting, the study of samples was carried out using optical metallography methods. Results and discussion. As a result of performed studies, it is revealed that samples of aluminum alloy with a thickness of 35.0 mm have a heterogeneous structure through the height of weld. There are the tool shoulder effect zone and the pin effect zone, in which certain whirling of weld material caused by the presence of grooves on tool surface is distinctly distinguished. It is shown that the zone of shoulders effect is the most exposed to the formation of tunnel-type defects because of low loading force and high welding speeds. It is revealed that tool destruction occurs tangentially to the surface of the tool grooves due to the high tool load and high welding speeds.

Features of arc discharges and erosion phenomena

Low-voltage electrical appliances play an important role in ensuring the control of energy processes, protection and switching of electrical circuits. Problems that occur in low-voltage electrical devices at rated currents of 32 - 1000 A, relate to electrical contacts that determine the operation of electrical devices. The main contribution to the development of erosion of the working surface is made by an electric arc, which is formed in the inter-contact gap when opening electrical contacts. In world practice, existing solutions to increase the arc resistance of electrical contacts do not completely solve the problem of reducing erosion of their work surface. The use of additional devices in arc suppression systems leads to an increase in the size of electrical devices. The use of expensive and toxic elements in the compositions leads to an increase in the cost of electrical appliances and poisoning of the environment. Strengthening the composition of the contacts through the use of refractory elements leads to an increase in the transient resistance. The aim of the study was to substantiate and develop the main provisions of the theory of processes and phenomena that occur on the work surface and in the electrode areas of electrical contacts, and to create compositions of high arc contact compositions for switching electrical devices. The theory of the mechanism of movement of arc reference points on the working surface of electrical contacts is substantiated and the factors providing increased arc resistance due to thermoemission properties of contact composition compositions that control diffusion, migration and phase transformations during chemical reactions are obtained. It has been experimentally established and theoretically confirmed that electric erosion is mainly determined by the microstructure of the material and the change in the physical and mechanical properties of the ingredients on the working surface of the contact parts during current switching. Key words: anode, cathode, erosion, contact wear, working surface, arc column, arc resistance, transient resistance

EVALUATION AND SELECTION OF THE METHOD FOR CONTROL SYSTEM THE WIRE TENSION IN CUT-OUT ELECTRIC EROSION MACHINES

Variants of the electrode tension mechanism in an electric erosion machine are considered in order to ensure a quick change of the electrode thread and the required degree of tension.

Investigation of the microhardness of the W-Ni-Fe powder alloy used for the restoration of machine parts

The paper presents the results of a study of the microhardness of the WNF-95 sintered electroerosive powder alloy. Powder alloy W-Ni-Fe95 was obtained by electroerosive dispersion of tungsten-containing waste in a kerosene medium. The resulting electroerosive powder alloy W-Ni-Fe 95was pressed in a vacuum chamber and sintered by the method of spark plasma sintering. The aim of this work was to study the microhardness of the WNF-95 sintered powder alloy obtained by the electroerosive dispersion of tungsten-containing waste in a kerosene medium. It has been established that the microhardness of samples sintered by the method of spark plasma sintering from particles of W-Ni-Fe 95alloy dispersed by electric erosion obtained in lighting kerosene is 2185.8 MPa and 2268.0 MPa, indicating their suitability for the manufacture of tungsten-nickel-iron alloys.

Influence of metal impurities on erosis and wearing of composite contacts

The questions of influence of contact material, switching modes and environment with various impurity on electroerosion resistance of contact details of switching devices are considered. Substantiated possibilities and measures to increase the reliability and efficiency of relays in electrical installations through agriculture through the use of erosion-resistant contact materials based on the study of physical and mechanical properties of the components of the composite contact material in switching current; substantiated composition of ingredients in the new composite material for contact parts of switching devices. The results of researches of electro erosive stability of composite material depending on structure of ingredients and their physical and mechanical properties are resulted. It has been experimentally established and theoretically confirmed that electric erosion is mainly determined by the microstructure of the material and the change in the physical and mechanical properties of the ingredients on the working surface of the contact parts during current switching. Factors providing increased arc resistance due to thermoemission properties of contact compositions that control the processes of diffusion, migration and phase transformations in chemical reactions are obtained, and the theory of the mechanism of arc reference points movement on the working surface of electrical contacts is substantiated.

X-ray spectral microanalysis of hardened additive products made of electroerosion cobalt-chromium alloys

This article presents the results of an X-ray spectral microanalysis of cobalt-chromium alloys based on particles of the of the tungsten nickel iron alloy dispersed by electric erosion, obtained in alcohol. It has been experimentally proved that a part of oxygen is present in the cobalt-chromium alloy of particles of the cobalt-chromium-molybdenum alloy dispersed by electric erosion. All other elements are distributed relatively evenly over the volume of particles. It is shown that Co, Cr and Mo are the main elements of the (CoCrMo) alloy dispersed by electric erosion.

Deposition of amorphous hardening coatings by electrospark treatment in a crystalline granule mixture

The article focuses on the preparation of amorphous coatings on the Steel 1035 surface by electric spark treat the coating composition control by changing the granule mixture composition was studied. EDS analysis showed that the coatings obtained contain W, Mo, Co and Ni in different ratios. The weight of granules having different compositions decreased by 11–16 wt.% in 6 hours of treatment as a result of electric erosion. The mass transfer coefficient varied from 33 to 54 %. X-ray diffraction analysis showed the predominance of the amorphous phase in the composition of layers deposited. Annealing of the coatings at 1150 °C led to amorphous phase crystallization into M23(C,B)6 type borocarbide and α-Fe. The coatings had an increased microhardness of 10–15 GPa, and their wear resistance under dry sliding wear conditions at 10 and 50 N loads was 3,3 and 1,6 times higher, respectively, than in Steel 1035. The highest values at both loads were shown by samples without nickel, while samples without tungsten featured the lowest values. The coatings had a friction coefficient within 0,27–0,31 that is lower than for Steel 1035 by 13–30 %. Wear resistance of the coatings under dry abrasive wear conditions at the 25 N load was 3 to 5 times higher as compared to uncoated Steel 1035. Samples without nickel demonstrated the best performance, while samples without cobalt had the worst indicators. Thus, it was shown that tungsten and cobalt increase wear resistance of iron-based amorphous alloys, while nickel and molybdenum tend to worsen their tribotechnical behavior.