Zhuojin Pipe Fitting Co., LtdMIG Welding Process Development for Aluminum Busbar 6063
Literature Overview
The paper by Tang Yanling and Wang Zhihong, published in the Welding Machine journal in 2011 (Vol. 41, No. 3, pp. 83–84), presents a practical welding process development study for 6063 aluminum alloy busbar tubes used in power station and power transmission applications. The authors conducted their research at Shandong Electric Power School, focusing on the welding of φ250 mm × 10 mm 6063 aluminum busbar tubes in the horizontal fixed position using MIG welding. The study addresses the critical challenge of porosity formation during aluminum alloy welding and aims to establish a qualified welding procedure for use in welder training programs and field applications.
Weldability Analysis of 6063 Aluminum Alloy
6063 is a heat-treatable aluminum alloy belonging to the Al-Mg-Si system, widely used for structural applications due to its good combination of formability, corrosion resistance, and moderate strength. However, its weldability presents several challenges that must be carefully addressed in process development:
| Challenge | Mechanism | Consequence | Mitigation Strategy |
|---|---|---|---|
| Porosity | Hydrogen pickup from moisture in shielding gas or on the workpiece surface; low solubility of hydrogen in solid aluminum | Gas pores in the weld, reduced cross-sectional area, stress concentration | Dry shielding gas (dew point < -40°C), thorough surface cleaning, preheating |
| Oxide film formation | Rapid re-oxidation of molten aluminum; Al₂O₃ has a melting point of 2050°C, far above aluminum's 660°C | Slag inclusion, incomplete fusion, surface irregularity | High-frequency pulsed current to break oxide film, appropriate gas flow rate |
| High thermal conductivity | Rapid heat dissipation from the weld zone | Cold cracks, incomplete fusion, lack of penetration | Higher heat input, preheating, appropriate travel speed |
| Thermal cracking | Low solidification range but high thermal expansion coefficient | Transverse cracks in the weld | Appropriate filler metal selection (ER4043 or ER5356), controlled cooling rate |
| Distortion | Large coefficient of thermal expansion (23 × 10⁻⁶ /°C) | Dimensional inaccuracy, post-weld straightening required | Fixturing, balanced welding sequence, low heat input where possible |
The authors specifically identified porosity as the most urgent problem to solve in aluminum busbar welding. This is consistent with industry experience, as aluminum alloy welds are extremely susceptible to hydrogen porosity due to the unique solubility behavior of hydrogen in aluminum: hydrogen is highly soluble in molten aluminum but has very low solubility in the solid state, leading to rapid gas evolution during solidification.
Welding Process Parameters and Technique
The study focused on the horizontal fixed position welding of the φ250 mm × 10 mm busbar tube, which is a challenging position because gravity tends to cause sagging of the molten weld pool on the lower side of the joint. The authors developed a systematic approach to parameter optimization:
Welding Procedure Specification
| Parameter | Value | Rationale |
|---|---|---|
| Base material | 6063 aluminum alloy tube, φ250 mm × 10 mm | Typical busbar specification |
| Welding process | MIG (GMAW) | Suitable for aluminum alloys, good deposition rate |
| Shielding gas | Argon (100%) or Ar/CO₂ mix | Argon provides stable arc; CO₂ addition improves wetting |
| Filler metal | ER4043 or ER5356 aluminum alloy wire | ER4043 for general use; ER5356 for higher strength |
| Wire diameter | 1.2 mm or 1.6 mm | 1.6 mm preferred for thicker sections |
| Welding position | Horizontal fixed | Simulates field conditions |
| Preheating | As required (typically 100–150°C) | Reduces thermal gradient, minimizes cracking |
| Interpass temperature | Controlled below 150°C | Prevents over-tempering of the heat-affected zone |
The authors emphasized the importance of controlling the welding operation technique, particularly the torch angle and weaving pattern, to manage the molten pool in the horizontal position. The torch is typically held at a 10–20° forward angle from vertical, with the contact tip oriented toward the travel direction. A slight weaving motion is used to maintain even heat distribution and prevent sagging of the weld pool on the lower side.
Quality Verification and Training Application
The welded joints were subjected to a comprehensive series of inspections and tests in accordance with relevant codes and standards. Although the paper does not specify the exact standards followed, typical verification procedures for aluminum alloy busbar welds include:
- Visual inspection: Checking for surface defects such as porosity, undercut, excess reinforcement, and burn-through.
- Radiographic testing (RT): Detecting internal defects including porosity, lack of fusion, and slag inclusions.
- Ultrasonic testing (UT): Screening for volumetric and planar defects.
- Dye penetrant testing (PT): Detecting surface-breaking defects.
- Mechanical property testing: Tensile tests, hardness tests, and potentially impact tests.
- Electrical resistance testing: Critical for busbar applications, ensuring low electrical resistance across the weld joint.
- Hydrostatic testing: For pressure-containing busbar applications.
The successful qualification of the welding procedure and its subsequent adoption for welder training at Shandong Electric Power School represents a practical contribution to the industry. The training program provides welders with hands-on experience in aluminum busbar welding, building a skilled workforce capable of performing this specialized welding in power station installation and power transmission equipment maintenance.
Engineering Practice Integration
The development of welding procedures for aluminum busbar is particularly important in the power industry, where aluminum busbars are used extensively in substations, switchgear, and power distribution systems. The advantages of aluminum over copper for busbar applications include lower weight, lower cost, and adequate electrical conductivity (about 61% of copper's conductivity, but aluminum is only about 30% of copper's density). However, the welding of aluminum busbars requires specialized skills and procedures, and the availability of qualified welders is often a bottleneck in power station construction and maintenance projects.
The approach taken by Tang and Wang, which combines process parameter optimization with operator technique development, is a practical and effective methodology for welding procedure development. The emphasis on training application is particularly commendable, as it addresses the human factor in welding quality, which is often the weakest link in the quality assurance chain.
Study Insights and Conclusions
This paper provides a practical and accessible welding procedure development case study for aluminum alloy busbar welding. The systematic approach to parameter optimization, combined with emphasis on operator technique and comprehensive quality verification, offers a replicable methodology for other aluminum alloy welding applications. The identification of porosity as the primary defect concern is consistent with metallurgical theory and provides a clear target for process improvement. The integration of the qualified procedure into a welder training program demonstrates a commitment to building long-term welding capability, which is essential for maintaining welding quality in the power industry. For engineers involved in aluminum busbar welding projects, this study serves as a useful reference for procedure development and welder qualification, highlighting the importance of both technical parameters and operator skill in achieving reliable weld quality.