OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 2 2022 In this manner, for experimental studies, the vibration system end is fi xed at the distance of 7/8B, which corresponds to 36 mm, and the weld is located at the distance of 15/8B, which corresponds to 77.5 mm and is in the middle of the plate. As a result of similar calculations for steel St3, the plate with the length of 130 mm was selected, the vibration system fi xing point is 30 mm, and the weld location is 65 mm. The same dimensions were used during the second stage of the research, e.g., welding of two plates and defi ning the mechanical properties of the joints. The plate was cut in the middle, and then the plate parts were welded on the ends, so that 0.5 mm remained between it, with no edge preparation. In these conditions, the vibrations are transmitted to the second plate via welding points along ends and the distribution nature of the vibrations remains the same. The welding time was 3.5 sec for AMg4 and 16 sec for St3. Defi ning the structure and properties After welding the seam, specimens were cut out of plates for further examination of the surface. Specimens were selected so that the surface under examination is the cross-section in the middle of the weld. The micro- and sub-microstructure were studied. The specimens were prepared for analysis by pouring with protacryl, with microsections obtained after its cooling. The microstructure was examined using a METAM RV-22 metallographic microscope (AO LOMO, Saint Petersburg). After welding of two plates, the obtained joints were examined for defl ection caused by metal shrinkage. The joints corresponding in size to XII specimens under GOST 6996-66 were tested for tensile. A contour measuring station model 220 (AO Proton, Zelenograd) that is intended to measure geometric parameters of products of various shapes was used to measure defl ection. The operation of the device is based on the principle of feeling the irregularities of the measured surface using a feeler gage with an inductive sensor by moving the gage along the measured surface and then converting the resulting mechanical vibrations of the gage into a digital signal. Further, the necessary measurements are carried out in the program for processing the surface profi le. Tensile tests were carried out using a UTS-110M-50-0U tensile machine designed to measure the specifi ed value of the force during mechanical tests in the tension or compression mode of the structural materials specimens. Results and Discussion Effects of ultrasonic parameters on the nature of vibrations To evaluate the nature of vibrations during the experiment, the distribution of vibrations over the plate was imaged by applying a sodium hydrocarbonate powder over it (Fig. 5). When ultrasound is turned on, the powder is distributed over the plate in accordance with the vibration amplitude: it is displaced from the antinode zone and accumulated in the nodes. The resonance frequency was f = 21,800 Hz, which is 700 Hz less than the calculated one (3.2 % error). This is explained by mechanical losses when converting longitudinal vibrations of the source into bending vibrations of the plate and by the fact that the calculation was done in case of pointed application of vibrations, and the surfaces contact area in the studies equals the area of the waveguide end having the diameter of 30 mm. Since the frequency is constant, the processing conditions were defi ned by the change in the vibration amplitude. Three types of ultrasonic vibrations were compared: low-amplitude (m = 3–4 μm); intermediate (m = = 9–10 μm) and high-amplitude (m = 13–15 μm). The analysis of vibration distribution shows that the zones of maxima and minima of the amplitude are irregular in shape, which is related to a complex nature of the plate vibration: apart from bending vibrations
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