Effects of Continuous and Pulsed Ultrasonic Treatment on Microstructure and Microhardness in Different Vertical Depth of ZL205A Castings

In this paper, in order to improve the performance of the ZL205A castings, continuous ultrasonic and pulsed ultrasonic treatments were applied to the melted alloy to study the effect of ultrasound propagation distance on microstructure and microhardness. The results indicated that ZL205A grains were significantly refined by ultrasonic vibration, but the refinement effect became weak gradually with the increase of sampling depth. The minimum grain sizes were 103.2 μm and 122.5 μm respectively in continuous and pulsed ultrasonic treatment. Grain boundary segregation also became more serious and coarser with the increase of vertical depth. In addition, microhardness and vertical depth are not positively correlated linearly. As the vertical depth increased, microhardness first decreased and then increased, the maximum hardnesses were 73.9 HV and 72.84 HV, respectively, in the two process modes. According to the experiment results and available studies, the mechanism of ultrasonic treatment maybe that: the cooling rate of solidification interface front increased by cavitation and streaming, thus changing the solute redistribution behavior of the ZL205A melt.

Characteristics of Arc and Metal Transfer in Pulsed Ultrasonic-Assisted GMAW

Pulsed ultrasonic-assisted gas metal arc welding (PU-GMAW) is a newly developed welding method. Pulsed frequency is one of the most important parameters in the PU-GMAW process. In this paper, the influence of pulsed frequency on the GMAW of aluminum alloy was studied. The results showed that the conventional GMAW process was improved significantly by adding different pulsed frequencies. The pulsed arc length, which was the change of arc length with the change of pulsed frequency, was obtained when the pulsed frequency ranged from 1 to 10 Hz. The stable compression arc length was obtained when the pulsed frequency exceeded 20 Hz. The metal transfer frequency in PU-GMAW in-creased compared to conventional GMAW. The increase of burning arc space pressure in PU-GMAW was mainly the reason for the change of the arc length. The increase in electro-magnetic force and acoustic radiation force was the fundamental reason for the increase in droplet frequency.

ДОСЛІДЖЕННЯ ПРОХОДЖЕННЯ УЛЬТРАЗВУКОВИХ ХВИЛЬ КРІЗЬ ДВОШАРОВИЙ МАТЕРІАЛ ІЗ СКЛАДНОЮ СТРУКТУРОЮ ПРИ КОНТРОЛІ ЙОГО ТЕХНОЛОГІЧНИХ ПАРАМЕТРІВ

Investigate the passage of ultrasonic waves through a two-layer material with a complex structure with non-contact control of its technological parameters. A non-contact ultrasonic method was used in the work to control technological parameters of materials with a complex structure, which takes into account the attenuation of ultrasonic waves. It is substantiated that the attenuation of an ultrasonic signal for a material with significant pores during its transverse sounding can be neglected compared to attenuation in a material without through pores. The results of studies of the influence of the thickness of a material with pores on the amplitude ratios of ultrasonic waves are presented. The dependences of the amplitudes of ultrasonic waves are obtained, one of which passes through a two-layer continuous material, and the other passes through a two-layer material with pores, taking into account the dependence of their attenuation on the thickness of the material. In this work, we obtained the dependences of the phase shift of ultrasonic waves, which were reflected from a two-layer material without pores, and waves reflected from a two-layer material with pores, on the total thickness of the controlled material, if we compare the phase of these waves with incident vibrations. Also obtained are the dependences of the change in wave amplitudes over time for a pulsed ultrasonic signal passing through a controlled material. It is proposed to use a pulsed ultrasonic signal for operational non-contact control of technological parameters of bilayer materials with a complex structure. The analysis showed that the obtained expressions for pulsed ultrasonic signals that can interact with porous materials can be used to create new methods and means of non-destructive non-contact control of technological parameters of materials with a complex structure. The aforementioned will make it possible to create complex integrated and universal contactless control devices for various technological parameters for composite materials with pores, which today are subjected only to destructive contact control, which does not allow operational monitoring directly at the plant.