CLADDING TECHNOLOGY SHANXI CO., LTDThick Plate Aluminum Alloy MIG Plus TIG Dual-Gun Welding Process
Literature Overview
This 2016 study by Li Boqiang, Jia Xinyu, Lei Qiang, and Tan Qianqian from Xi'an XD Switchgear Electric Co., Ltd. addresses the welding of thick aluminum alloy plates using a MIG+TIG dual-gun configuration. The research is particularly relevant to the fabrication of large electrical equipment housings, switchgear enclosures, and other thick-section aluminum alloy components where single-process welding may be insufficient to achieve full penetration and adequate mechanical properties.
Technical Background
Thick aluminum alloy plates, typically defined as those with thicknesses exceeding 20 mm, present unique welding challenges. The high thermal conductivity of aluminum causes rapid heat dissipation, making it difficult to achieve full penetration in a single pass. Additionally, the wide solidification range of many aluminum alloys increases the susceptibility to hot cracking. The MIG+TIG dual-gun configuration was investigated as a means to overcome these challenges by combining the high deposition rate of MIG welding with the deep penetration and stable arc of TIG welding.
The MIG torch provides the bulk of the metal deposition, while the TIG torch acts as a "penetration" torch that ensures full root penetration and stabilizes the melt pool. This configuration is analogous to the plasma-MIG hybrid approach discussed in the previous literature, but uses TIG instead of plasma as the second heat source.
Process Configuration and Parameters
The dual-gun configuration involves two welding torches mounted on a single welding head, with the MIG torch positioned to deposit the bulk of the weld metal and the TIG torch positioned to provide additional heat input and penetration. The following table summarizes the typical parameter ranges used in this configuration:
| Parameter | MIG Torch | TIG Torch | Combined Effect |
|---|---|---|---|
| Current | 250–400 A | 80–150 A | Total current 330–550 A |
| Voltage | 22–28 V | 12–18 V | Combined heat input |
| Travel speed | 150–350 mm/min | Same as MIG | — |
| Wire diameter | 1.2–1.6 mm | — | Deposition rate |
| Shielding gas | Ar or Ar+He | Ar | Combined shielding |
| Nozzle to arc distance | 10–15 mm | 8–12 mm | Arc stability |
The TIG torch typically uses a tungsten electrode with a diameter of 3.2–4.0 mm, depending on the current level. The tungsten electrode is positioned slightly behind the MIG torch in the direction of travel, allowing it to refine the solidifying melt pool and improve the weld bead appearance.
Weld Quality and Mechanical Properties
The study evaluated the weld quality of the MIG+TIG dual-gun configuration through visual inspection, radiographic testing (RT), ultrasonic testing (UT), and mechanical property testing. The results demonstrated that the dual-gun configuration produced welds with excellent full penetration, low defect density, and mechanical properties comparable to or better than those of single-process welds.
The mechanical properties of the weld metal and heat-affected zone (HAZ) were evaluated through tensile testing, hardness testing, and impact testing. The following table summarizes the typical results:
| Property | Weld Metal | HAZ | Base Metal | Acceptance Criteria |
|---|---|---|---|---|
| Tensile strength (MPa) | 280–320 | 240–280 | 300–350 | ≥90% of base metal |
| Yield strength (MPa) | 180–220 | 150–200 | 200–250 | ≥80% of base metal |
| Elongation (%) | 12–18 | 10–15 | 14–20 | ≥10% |
| Hardness (HV) | 80–110 | 70–95 | 90–120 | — |
The HAZ properties are typically lower than the base metal properties due to the thermal effects of welding. For aluminum alloys, the HAZ is often the weakest region of the weld joint, and the mechanical properties of the HAZ must be considered in the design and qualification of welded structures.
Application to Bimetal and Cladding Applications
While the primary focus of this study is on structural welding of thick aluminum alloy plates, the MIG+TIG dual-gun configuration has potential applications in cladding and overlay welding. For example, in the fabrication of aluminum-clad steel pressure vessels or heat exchangers, the dual-gun configuration could be used to deposit a thick aluminum overlay layer with excellent bonding to the steel base.
The TIG torch, with its stable arc and low spatter, is particularly well-suited for the first pass of overlay welding, where precise control of the melt pool is essential to ensure bonding to the base metal. The MIG torch can then be used for subsequent passes to build up the overlay layer thickness efficiently. This sequential use of TIG for the first pass and MIG for subsequent passes is a common strategy in overlay welding, and the dual-gun configuration allows both processes to be performed simultaneously, improving productivity.
Common Defects and Quality Control
The following defects are commonly encountered in thick plate aluminum alloy welding, and their countermeasures are summarized below:
| Defect | Cause | Countermeasure |
|---|---|---|
| Hot cracking | Wide solidification range; impurity segregation | Use appropriate filler metal; control travel speed; preheat |
| Porosity | Hydrogen absorption from moisture | Dry shielding gas; clean base metal; use gas lens |
| Lack of fusion | Insufficient heat input; improper joint fit-up | Increase current; reduce travel speed; ensure tight fit-up |
| Undercut | Excessive arc energy; improper gun angle | Reduce current; increase travel speed; adjust gun angle |
| Distortion | Thermal expansion mismatch; restraint | Use backing plates; apply welding sequence to minimize distortion |
Study Insights and Engineering Implications
The research by Li and colleagues demonstrates that the MIG+TIG dual-gun configuration is a viable and effective approach for welding thick aluminum alloy plates. The combination of high deposition rate from MIG and deep penetration from TIG provides a synergistic effect that exceeds what either process alone could achieve.
For engineers working on bimetal pressure vessel fabrication, this research highlights the importance of process innovation in overcoming the inherent challenges of welding dissimilar materials and thick sections. The dual-gun configuration offers a practical solution for situations where single-process welding is insufficient, and the approach can be adapted for cladding and overlay applications with appropriate parameter optimization.
The study also underscores the importance of quality control in aluminum alloy welding. The susceptibility of aluminum alloys to porosity, hot cracking, and other defects requires rigorous non-destructive testing and mechanical property verification. Engineers must ensure that welding procedures are qualified in accordance with applicable standards such as NB/T 47014 or ASME IX, and that welders are certified through practical performance testing.
In conclusion, the MIG+TIG dual-gun welding process for thick aluminum alloy plates represents a significant advancement in welding technology that has direct applications in the fabrication of bimetal products and pressure vessels. The synergistic combination of high deposition rate and deep penetration makes this configuration particularly suitable for thick-section cladding operations where both productivity and weld quality are critical requirements.