Study on 5A06 Aluminum Alloy Variable Polarity Pulse AC Argon Arc Welding Process
August 16 18:00:49, 2025
1. Introduction
With the rapid advancement of science and technology, lightweight and high-strength metal materials have become increasingly important across various industries. Among these, aluminum alloys are widely used in aerospace, automotive, and civil engineering due to their excellent properties such as low weight, high strength, and good thermal characteristics. In industrial applications, they have become a key material for manufacturing. To meet the demands of the modern aerospace industry, achieving defect-free connections—especially with rust-proof aluminum 5A06—has become a critical focus.
Aluminum alloys tend to oxidize easily when exposed to air, forming a dense and refractory oxide layer on the surface that protects the underlying metal from further oxidation. However, this oxide layer can interfere with welding processes. To remove it effectively and reduce electrode burn-off, alternating current TIG (Tungsten Inert Gas) welding is commonly used. Despite its advantages, this method often leads to welding porosity defects, which can compromise the quality and integrity of the weld.
This paper explores the use of a variable polarity pulsed AC arc welding power source to investigate how changes in pulse frequency and mixed gas ratios affect the formation of welding porosity. The results obtained were promising and offer valuable insights into improving the quality of aluminum alloy welds.
2. Test Conditions
The test involved studying the effects of pulse frequency and mixed gas ratio on porosity defects during the welding of 5A06 aluminum alloy. The test specimens had dimensions of 390 mm × 240 mm × 1.5 mm and 390 mm × 84 mm × 1.5 mm. A 5356 filler wire with a diameter of 2 mm was used. The chemical compositions of both the base metal and the filler wire are listed in Table 2.
The welding torch nozzle had a diameter of 10 mm, and the tungsten electrode used was 2.4 mm in diameter. A custom-made welding fixture was designed and shown in Figure 1. During the welding process, a pressure plate made of phenolic laminated cloth board was placed on the aluminum sheet. This material has low thermal conductivity, helping to retain heat and improve the welding process.
3. Influence of Pulse Frequency and Mixed Gas Ratio on Welding Porosity
(1) **Effect of Pulse Frequency**
Before butt welding the test plates, the surfaces were pickled, but no mechanical polishing was performed. The argon gas ratio, AC frequency, welding speed, duty cycle, base current ratio, and wire feed rate remained constant throughout the welding process. Experiments were conducted at pulse frequencies of 10 Hz, 50 Hz, 100 Hz, 150 Hz, 250 Hz, and 350 Hz, with X-ray inspection used to evaluate penetration.
From the data in Table 3, it's clear that increasing the pulse frequency does not necessarily reduce the tendency for pore formation. Instead, the smallest number of pores was observed at intermediate frequencies between 10 Hz and 50 Hz. This is because at these frequencies, the welding speed and pulse frequency align well, enhancing the shrinkage effect of the molten pool and accelerating gas escape, thus reducing porosity.
However, when the pulse frequency reaches 100 Hz or higher, the arc becomes continuous, increasing arc force and penetration while reducing the required welding current. As the frequency increases, the size of the molten pool decreases significantly. At 350 Hz, the molten pool size is only about 70% of what it is at 10 Hz.
(2) **Effect of Helium-Argon Gas Mixture**
The helium-argon gas ratio was varied from 0:10 to 10:0, and the 1.5 mm thick test plates were welded under conditions ensuring full penetration. X-ray inspection was used to evaluate the results.
As shown in Table 4, the porosity tendency initially decreases with an increase in helium content, reaching a minimum at a 4:6 helium-argon ratio. Increasing the helium proportion raises the arc voltage, reduces the welding current, and improves arc stability. The arc becomes more concentrated, and the molten pool size gradually decreases. When pure helium is used, arc ignition and maintenance are easier, and the molten pool size is reduced by half compared to pure argon shielding gas.
4. Conclusion
(1) For thin 5A06 aluminum alloy welding, the tendency for pore formation is minimized when the pulse frequency is between 10 Hz and 50 Hz.
(2) At pulse frequencies of 100 Hz or higher, the arc becomes continuous, increasing arc force and penetration while reducing the required welding current.
(3) The lowest porosity tendency occurs when the helium-argon gas ratio is 4:6.
(4) As the helium proportion increases, arc voltage rises, welding current decreases, arc stability improves, and the molten pool size gradually reduces.
Applying these findings in the production of a specific type of aluminum alloy tank diaphragm weld has led to a significant reduction in porosity and an increase in the welding pass rate from 60% to over 90%. These results demonstrate the practical value of optimizing pulse frequency and gas mixture in improving weld quality.