PSI - Issue 30

E.G. Grigoryev et al. / Procedia Structural Integrity 30 (2020) 33–39 Grigoryev E.G. et al. / StructuralIntegrity Procedia 00 (2020) 000–000

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1. Introduction The creation of products of general engineering and instrumentation by the methods of resistance welding from non-ferrous metals in a heterogeneous combination is associated with a difference in the physical and chemical properties of materials, which contributes to the formation of an unfavorable structure, intermetallic compounds, during the thermal deformation cycle. To minimize the processes of structural-phase transforomations, it is necessary to reduce the duration of the alloys at the eutectic transformation temperatures by using of concentrated sources of the thermo-deformation cycle in the joint zone. The main sources of concentrated energy (localized) in the connection zone are the energy accumulated during the charging of capacitor banks and the energy released during chemical reactions of explosives. As a rule, explosives are used in explosion welding to obtain broadband bimetallic compounds, for miniature compounds it is of little use. The electric energy accumulated in capacitor banks is used in contact capacitor welding, seam welding, relief welding. The process parameters (the steepness of the rise and fall of the front of the discharge of the current, its duration and pause) depend on the control equipment, the energy stores and switching devices used. In most cases, for the lap joints, the discharge current does not exceed 20-50 kA, the current flow time (1/2 period) is not more than 40 ms, and the compression force of the parts is up to 5000N. Metallographic studies of the joint zone showed that, depending on the modes, a welded joint can be formed in both solid and liquid phases (Martynenko, 1984). To obtain miniature t-shaped welded joints, the Paton Institute of electric Welding developed and studied shock capacitor welding (SCW) with a spring drive under atmospheric conditions and in a protective environment (vacuum) by Paton (2012), Kaleko (2013). When welding wires with a diameter of up to 2 mm, the compression force of the spring of two parts does not exceed 30 N, and the current flow time is 0.06-0.25 ms. When welding studs with a diameter of up to 6 mm with sheet parts, the spring compression force of the two parts is increased to 200 N, and the current flow time varies in the range of 2-12 ms. An analysis of the microstructures of the fusion zone of welded joints during SCW from dissimilar alloys showed that the structure contains brittle intermetallic compounds or quenching structures, pores, shrink shells, or cracks. This is due to the technological difficulties of regulating the mechanical impact, as well as its inertia and insufficient created by the force of the spring mechanism. Foreign sources present the results of studies of capacitor welding of studs according to the CD Stud Welding technology, which is classified as follows: welding of studs by discharge of capacitor banks - SD, electric short arc with a short technological cycle - SC, electric arc - ARC by Strizhakov (2017). The presented CD Stud Welding technologies differ in the following process parameters: arc burning duration at CD (1 ÷ 5) ms, at SC (3 ÷ 500) ms, and at ARC (100 ÷ 2000) ms, respectively. The clamping force of the parts does not exceed 180 N. Microstructural analysis of welded joints performed by CD Stud Welding technology showed that the welded joint is formed in the liquid phase. The difference in the liquid phase is associated with the duration of the arc burning and, accordingly, with the volume of molten metal. A comparative analysis of the dependences of the welding current on the time of its flow with various methods of capacitor welding showed that they relate to the rigid parameters of the exposure modes, because characterized by a short duration of the current flow and increased values of the welding current. The employees of Don State Technical University (DSTU) proposed minimizing the processes of atomic heterodiffusion or reactive diffusion in the solid phase, through the use of thermomechanical effects in superhard conditions, using high-voltage capacitor welding (HVCW) with an induction-dynamic drive (IDD), see Fig. 1d, obtained by Strizhakov (2019). Superhard modes are characterized by a discharge of current I d > 100 kA, its flow time t f = 100-400 μ s, pressure on the connection zone P d = 10 5 ÷ 10 6 MPa. Implementation of synchronous thermomechanical action allows to: minimize the oxidation of microroughness (or particles) of the metal in the contact zone; displace molten metal from the joint zone; provide continuous protection of the connection zone; reduces porosity in powder compositions. Technological methods were developed and studied to expand the capabilities of HVCW with IDD for welding non-ferrous alloys in homogeneous and heterogeneous combinations and for the compaction of powder compositions, see Fig. 1, obtained by Strizhakov (2015).