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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The kinetics of the HVCW process without an initial clearance, with a protrusion at the end face of the rod element and with a powder composition is carried out as follows, Fig. 2a. When a high voltage is applied, the electric circuit between the statically pressed welded surfaces (or the powder composition) closes, the discharge current I d flows, heating microroughnesses to the melting point, evaporation. An arc discharge is excited in the formed gap Δ R-G , the vapor pressure of the metal of microroughnesses P pm occurs, which counteracts the approach. Depending on the thermo-physical properties of the welded alloys, P pm reaches 2•10 4 MPa or more. When HVCW with preliminary contact, the protrusion of the rod element and with a preliminary clearance, the pressure drop of the metal vapor P pm is an order of magnitude higher, because there are no restrictions on the release of metal vapor into the environment. The magnetic pressure generated on adjacent surfaces is 1-2 orders of magnitude higher than the vapor pressure of the metal. When HVCW powder composition, the pressure drop is much lower and its speed depends on the technological gaps in the equipment used. In the absence of the initial clearance, the thermal effect is limited by the height of the microprotrusions and most of the energy stored in the capacitive storage device U IVD is spent on the force effect and the plastic deformation of the surfaces to be welded. The voltage U supplied to the parts to be welded should be sufficient for ionization of the initial gap between the surfaces to be welded due to field emission at HVCW with the initial gap Δ I-C . In the experiments carried out, as a rule, Δ I-C was (0.1-1)•10 -3 m. Exceeding Δ I-C led to increased deformation and deterioration of the appearance of the obtained compounds, Fig. 2b. At the breakdown of the Δ I-C , the circuit closes, there are conduction channels, which over time merge into a single one, contributing to the excitation of the pulse arc. Thermal action is carried out, leading to the destruction of surface films, contaminants, and it is characterized by electroerosive cleaning of the connected surfaces. The rapprochement of the connected surfaces during the flow of the current discharge I d carries out an IDD, consisting of a flat inductor and a pusher. An induced current is generated in the IDD pusher. The interaction of the current with the magnetic field of a flat inductor leads to the appearance of a magnetic pressure P m (dynamic action). Under the influence of this pressure, overcoming the vapor pressure of the metal Р pm , the pusher brings the mating surfaces closer together, the initial or formed gap decreases, and when the surfaces collide, the molten metal is displaced from the joint zone to the periphery, jointly deforming the surfaces being welded, realizing solid-phase interaction. 3. Experimental methods with results and discussions The results of an energy spectral analysis of the distribution of chemical elements of the weld zone during the interaction of dissimilar alloys using SEM Quanta 200, see Fig. 3-6 by Larikov (1975) were one of the proofs of minimizing the processes of atomic heterodiffusion or reactive diffusion in the solid phase during HVCW with IDD. The analyzed samples were obtained by statistical and regression analysis during experimental studies by Nescoromniy (2018). The parameters of the HVCW modes that have the greatest impact on the strength of welded joints in the modes are the storage unit capacity C and the operating voltage U, which together determine the input energy W. The studied samples obtained by HVCW were obtained at the following energy: AlMg2.5 + Cu01 - 8100J, AlMg2.5 + Br63 - 6900J, HfC (powder) - 12200J, Fig. 7 and 8. Experimental samples were obtained using a PCG 16-1 pulse current generator with a discharge circuit inductance L = 2100 nH; capacitance of the storage block C = 2400 μ F; the frequency of the current discharge f = 4000 Hz, the diameter of the rod elements 10 mm, the diameter and length of the protrusion at the end of the rod element d l / l l = 1.3 / 1.5 mm, the thickness of the substrate is 0.8 mm. An analysis of the joint zone showed that between the two alloys there is a thin transition layer of two alloys, the width of which depends on the HVCW regimes, Fig. 3 and 5. The energy-dispersive analysis of the distribution of chemical elements in the joint zone showed the absence of diffusion and mass transfer when using super-hard exposure modes, Fig. 4 and 6.