1 Introduction
The innovation of arc ultrasound is to achieve the concept of “arc not only as a heat-generating mechanism but also as an ultrasonic transmitterâ€. Its basic principle is to excite arc ultrasound using the arc's variable resistive load characteristics. This method overcomes the disadvantages of the conventional ultrasonic generation method such as the difficulty of coupling and the difficult adjustment of parameters, so that the application of power ultrasound in engineering practice develops in the direction of self-coupling, frequency and energy real-time adjustment, and uses ultrasonic sound current and cavitation, etc. The effect improves the quality of the process.
At present, broadband high-power arc ultrasonic excitation devices (including continuous wave and pulse wave excitation methods) have been successfully developed, arc excitation and control characteristics have been studied, and this technology has been successfully applied to welding, spraying, and surface modification. In the field of material processing, such as sex, a national invention patent “a method of exciting an ultrasonic wave with an arc†was applied and is about to be authorized.
2 Application Description
â— Application of arc ultrasonic technology in welding
In welding, coarse grains in the weld zone, large heat-affected zone structures, large residual stress in the welds, stress concentration, and reduced weld toughness are common phenomena in the welding process. Limited to one or more materials and welding methods. The generation of arc ultrasound is independent of the welding material and the welding method and is only affected by the characteristics of the external excitation source and the high frequency characteristics of the arc plasma. Through arc ultrasonic welding experiments on a variety of materials (A3, 45, 16MnDR, 09MnNiDR, 1Cr18NiTi, TC4, etc.) and various welding methods (hand arc welding, CO2 gas shielded welding, submerged arc welding, TIG, MIG, etc.), Arc-ultrasonics is proved as a universal method, which is not limited by welding materials and welding methods. It has a significant effect on improving the overall performance of weld joints and provides a new and effective method for improving the performance of welded joints. method.
(1) Carbon Steel Welding
Experiments on a variety of steels show that the introduction of arc ultrasound has a significant effect on refining the grain structure of welded joints, improving the heat affected zone structure, and improving the stress distribution in the weld zone, greatly improving the comprehensiveness of the welded joint organization. Performance; At the same time, many new phenomena that are difficult to achieve under conventional welding conditions have also been discovered.
For A3 AC AC submerged arc welding, under the effect of arc ultrasonic, significant changes have occurred in the heat affected zone of the welded joint structure. The frequency of excitation ultrasound increased, the width of the "heat affected zone" increased, and was distributed in fingers. Microscopic metallographic analysis showed that under the effect of arc ultrasound, the organization of “heat affected zone†is no longer the weak link of grain growth, but a small equiaxed crystal, showing the excellent characteristics of normalizing structure.
After manual arc welding of 45 steel, 50 kHz arc ultrasonic was added, the microstructure of the weld zone was significantly refined. Arc-electrical ultrasound has an inhibitory effect on the growth of columnar crystals in the weld and causes significant changes in the microstructure of the weld joint. During the conventional welding, the microstructure of the weld is more pro-eutectoid ferrite and side-striped ferrite; when the center frequency of the excitation source is about 50 kHz, the coarse co-crystal structure is significantly refined, and the weld metal is More acicular ferrite is formed.
(2) Low temperature steel welding
For the submerged arc automatic welding of low temperature steel 09MnNiDR, through the morphological analysis of the fusion zone and heat affected zone of the welding sample, it was observed that the columnar crystal growth in the weld was inhibited, the microstructure was refined and the distribution was uniform. The specimens were subjected to low temperature impact toughness tests, which confirmed that the impact toughness of the weld zone and the heat affected zone were improved to varying degrees. In particular, at 50kHz excitation frequency, the impact toughness of the 09MnNiDR weld zone increased by nearly 50%, and the heat affected zone increased by 80. %the above.
(3) stainless steel welding
The austenitic stainless steel 1Cr18Ni9Ti was tested by manual arc welding and build-up welding. The results show that the introduction of arc ultrasound has a great influence on the microstructure of the weld zone of the stainless steel. The original strip-like structure becomes a network structure and crystal. The particle size decreases, and as the frequency increases, the tissue becomes more uniform. It can be seen that arc ultrasonic welding has a significant effect on the refinement of the grain structure in the stainless steel weld zone.
(4) Titanium alloy welding
The series of AC/DC/pulse TIG welding of the most widely used α+β duplex Ti-6Al-4V (TC4) alloy in the aerospace industry was tested. After adding arc ultrasound, columnar grains in the weld zone were refined to a certain extent. At the excitation frequency of 50 kHz, the morphology of the grain in the weld zone has changed significantly, and the weld zone is almost completely composed of fine equiaxed crystal grains. The boundaries between the regions are not obvious. This will greatly improve the performance of titanium alloy welded joints.
(5) Improve weld stress distribution
Using A3 steel oblique Y-groove welding specification, ultrasonic energy was directly introduced into the welding process through the arc, and a comparative experiment was conducted. The stress distribution of the weld seam and its surrounding area was measured by both the small hole method and the magnetic memory method. Without arcing, the stress distribution around the weld is extremely uneven, and the maximum stress is also high. After adding arc ultrasonic, the stress distribution is obviously improved. When the excitation frequency is 50 kHz, the average value of the stress is reduced by about 40%, and the fluctuation range of the stress value is also small. At the same time, the introduction of arc ultrasound can add compressive stress on the weld. , thereby improving the performance of the weld joint.
â—Application of Arc Ultrasonic Technology in Arc Spraying
Under the effect of arc ultrasound, pure zinc was used for spraying, and the metallographic test, micro Vickers hardness test, and corrosion resistance test were performed on the sample. It was proved that the effect of arc ultrasonication was to reduce the particle size and porosity of the coating. Oxide reduction, micro-Vickers hardness, corrosion resistance in alkaline environment and salt water environment have been significantly improved, especially 50 kHz arc ultrasound to improve the corrosion resistance of the best.
Through tensile tests on chromium coatings sprayed at different ultrasonic frequencies and ultrasonic excitation voltages, the bond strength of the coatings has been significantly improved, and the bond strength of the sample coatings has generally risen by more than 12%, demonstrating the introduction of ultrasound. It has a significant effect on improving the bonding strength of the coating. With the increase of ultrasonic frequency and ultrasonic excitation voltage, the bond strength also increases, which fully reflects the corresponding relationship between frequency and energy.
3 Benefit Analysis
As a general field method, Arc Ultrasonic has the characteristics of real-time controllable parameters such as frequency and power, self-coupling through the arc to the workpiece, and high coupling efficiency.
Introducing arc ultrasonic to the welding process can refine the grain of the welded joint structure, improve the stress distribution of the joint structure, and improve the joint strength, toughness, etc., and provide a new and effective welding method for comprehensively improving the structural properties of the welded joint.
The introduction of arc ultrasound into the arc spraying process can reduce the particle size and porosity of the coating, reduce the oxides, improve the bonding strength and corrosion resistance of the coating, and provide a new and effective arc spraying method for improving the coating performance. .
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