OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 2 2022 Further studies were done in intermediate conditions, since compared with others, it makes it possible to obtain a stable distribution of vibrations over the plate. The results of preliminary experiments showed a better effect on the weld structure. Low-amplitude conditions show almost no effect, and high-amplitude conditions may cause heavy splashing of dropping metal (ultrasonic spatter) and a signifi cant number of pores. Microstructural changes The application of ultrasonic vibrations during welding leads to changes in the microstructure of the weld (Figs. 6 and 7). a b Fig. 6. Microstructures of the weld metal of steel St3: a – without vibrations applied; b – with vibrations applied а b Fig. 7. Microstructures of the fusion zone of the AMg4 alloy: a – without vibrations applied; b – with vibrations applied The vibrations cause a decreased proportion of dendritic segregation for steel St3 and a decreased height of the dendrite zone for alloy AMg4. A different nature of effects is associated with a longer steel crystallization time as compared to aluminum, which allows vibrations to have a greater effect. Microstructure changes are caused by effects occurring in the molten metal when ultrasonic vibrations are applied to it. Phenomena having a signifi cant effect on crystallization kinetics include sound pressure, cavitation and acoustic streams.
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