1 Introduction
The innovation of arc ultrasound lies in the concept that "an arc is not only a heat source but also an ultrasonic transmitter." Its fundamental principle involves exciting ultrasonic waves by utilizing the variable resistive characteristics of the arc. This method overcomes the limitations of traditional ultrasonic generation techniques, such as poor coupling and difficult parameter adjustment, enabling power ultrasound to develop toward self-coupling, real-time frequency and energy control. It leverages ultrasonic current and cavitation effects, significantly enhancing the quality of the process.
Currently, broadband high-power arc ultrasonic excitation devices—covering both continuous and pulsed wave methods—have been successfully developed. Research on arc excitation and control characteristics has been conducted, and this technology has been applied in welding, spraying, and surface modification. In material processing, a national invention patent titled “A Method for Exciting Ultrasonic Waves with an Arc†has been submitted and is expected to be granted soon.
2 Application Description
â— Application of Arc Ultrasonic Technology in Welding
In welding, issues such as coarse grains in the weld zone, large heat-affected zones, residual stresses, stress concentration, and reduced toughness are common. These problems are often influenced by the materials and welding methods used. However, arc ultrasound generation is independent of these factors and depends mainly on the external excitation source and the high-frequency properties of the arc plasma.
Experiments on various materials (including A3, 45, 16MnDR, 09MnNiDR, 1Cr18NiTi, TC4, etc.) and different welding techniques (such as manual arc welding, CO2 gas shielded welding, submerged arc welding, TIG, MIG, etc.) have demonstrated that arc ultrasound is a universal technique. It is not restricted by the type of material or welding method and has proven highly effective in improving the overall performance of weld joints, offering a new and efficient approach for enhancing weld quality.
(1) Carbon Steel Welding
Studies on different steels show that the introduction of arc ultrasound significantly refines the grain structure of the weld joint, improves the microstructure of the heat-affected zone, and enhances stress distribution in the weld area, leading to better mechanical performance. Many new phenomena that are hard to achieve under normal welding conditions have also been observed.
For example, in submerged arc welding of A3 steel, the heat-affected zone underwent significant structural changes under the influence of arc ultrasound. The ultrasound frequency increased, the width of the heat-affected zone expanded, and it appeared in a finger-like pattern. Microscopic analysis revealed that the heat-affected zone no longer acted as a weak point for grain growth but instead formed small equiaxed crystals, showing a normalized structure.
When 50 kHz arc ultrasound was introduced during manual arc welding of 45 steel, the weld zone microstructure was significantly refined. The columnar crystal growth was inhibited, and the weld microstructure changed dramatically. Under conventional welding, the weld contained more pro-eutectoid ferrite and side-striped ferrite. However, at around 50 kHz, the coarse co-crystal structure was refined, and more acicular ferrite was formed.
(2) Low Temperature Steel Welding
In submerged arc automatic welding of low-temperature steel 09MnNiDR, morphological analysis showed that the columnar crystal growth in the weld was suppressed, the microstructure was refined, and the distribution became uniform. Low-temperature impact tests confirmed improved impact toughness in both the weld and heat-affected zones. At 50 kHz, the impact toughness of the weld zone increased by nearly 50%, while that of the heat-affected zone rose by over 80%.
(3) Stainless Steel Welding
Austenitic stainless steel 1Cr18Ni9Ti was tested using manual arc and build-up welding. The results showed that arc ultrasound significantly altered the weld microstructure. The original strip-like structure transformed into a network-like structure, with smaller grain sizes. As the frequency increased, the microstructure became more uniform, indicating the effectiveness of arc ultrasound in refining the grain structure of stainless steel welds.
(4) Titanium Alloy Welding
Tests were conducted on AC/DC/pulse TIG welding of Ti-6Al-4V (TC4), a widely used α+β titanium alloy. After introducing arc ultrasound, the columnar grains in the weld zone were refined. At 50 kHz, the grain morphology changed significantly, and the weld zone was almost entirely composed of fine equiaxed grains, with less distinct boundaries. This greatly improves the performance of titanium alloy welded joints.
(5) Improving Weld Stress Distribution
Using A3 steel oblique Y-groove welding, ultrasonic energy was directly introduced through the arc. Stress distribution in the weld and surrounding area was measured using the small hole method and magnetic memory method. Without arc ultrasound, the stress distribution was uneven with high peak values. With arc ultrasound, the stress distribution improved significantly. At 50 kHz, the average stress decreased by about 40%, and the fluctuation range was smaller. Additionally, arc ultrasound introduced compressive stress into the weld, further improving the joint performance.
â— Application of Arc Ultrasonic Technology in Arc Spraying
Under the influence of arc ultrasound, pure zinc was sprayed, and the samples were analyzed using metallographic testing, micro Vickers hardness, and corrosion resistance tests. Results showed that arc ultrasound reduced particle size and porosity in the coating, decreased oxide content, and significantly improved micro-Vickers hardness and corrosion resistance in both alkaline and saltwater environments. Notably, 50 kHz arc ultrasound provided the best improvement in corrosion resistance.
Tensile tests on chromium coatings sprayed at different ultrasonic frequencies and voltages showed a significant increase in bond strength. Coating bond strength generally increased by over 12%, demonstrating the positive impact of ultrasound on coating adhesion. As the ultrasonic frequency and voltage increased, so did the bond strength, reflecting the direct relationship between frequency and energy.
3 Benefit Analysis
As a versatile technique, arc ultrasound offers real-time controllable parameters like frequency and power, enables self-coupling through the arc to the workpiece, and ensures high coupling efficiency. Integrating arc ultrasound into the welding process can refine the microstructure of the weld joint, improve stress distribution, and enhance joint strength and toughness, providing a new and effective method for improving the overall performance of welded joints. Similarly, introducing arc ultrasound into arc spraying reduces coating particle size and porosity, minimizes oxides, and enhances bonding strength and corrosion resistance, offering a novel and effective approach to improve coating performance.
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