Zhuojin Pipe Fitting Co., LtdAC TIG Welding Process Research for Pure Aluminum L2
Literature Overview
This paper by Pang Liang from Inner Mongolia Second Power Construction Engineering Co., Ltd., published in Inner Mongolia Petrochemical (Vol. 35, Issue 7, 2009), investigates the AC TIG welding process for L2 pure aluminum plate. The study analyzes common TIG welding faults, their causes, and preventive measures, then conducts systematic welding process trials using automatic pulsed AC TIG welding to optimize parameters for 3 mm thick L2 pure aluminum.
L2 pure aluminum (equivalent to AA1050 or similar) is widely used in power transmission and distribution applications, including busbars, cable trays, and electrical enclosures. The welding of pure aluminum presents unique challenges due to its low melting point, high thermal conductivity, and formation of a tenacious aluminum oxide film.
Core Technical Findings
The study identifies and addresses common TIG welding faults for aluminum, then establishes optimized welding parameters:
| Parameter | Optimized Value | Significance |
|---|---|---|
| Base current | 90 A | Maintains arc stability and prevents base metal melting |
| Pulse current | 170 A | Provides sufficient heat input for penetration |
| Welding speed | 178 mm/min | Balances heat input and travel efficiency |
| Wire feed speed | 0.9 m/min | Maintains appropriate deposition rate |
| Pulse frequency | 2 Hz | Controls heat input and allows oxide film disruption |
| Tensile strength | 86.0942 MPa (maximum) | Approaches base metal strength |
The study demonstrates that pulsed AC TIG welding produces welds with:
- Minimal porosity and inclusion content.
- Fine and uniform HAZ grain size compared to other parameter combinations.
- Tensile strength approaching that of the base metal.
AC TIG Welding Mechanism for Aluminum
The use of AC (alternating current) in TIG welding of aluminum is fundamental to overcoming the aluminum oxide problem. The AC cycle alternates between:
- Electrode negative half-cycle (EN): The electrode is negative, providing high current density at the tungsten tip. This produces intense heat for melting the base metal and filler wire. The high current density also prevents tungsten contamination by aluminum.
- Electrode positive half-cycle (EP): The electrode is positive, and the workpiece is negative. During this phase, the arc produces a "cathodic cleaning" effect, where high-velocity electrons bombard the workpiece surface, mechanically disrupting and removing the aluminum oxide film. This is critical for achieving good weld fusion.
The pulse modulation adds a third dimension to the process:
- Base current phase: Maintains the arc at a lower current level, allowing the weld pool to partially solidify and controlling heat input.
- Pulse peak phase: Provides a burst of high current for penetration and filler metal deposition.
- Pulse frequency: Determines the rate of heat input cycling, which influences solidification rate and microstructure.
Common TIG Welding Faults and Countermeasures
The study provides a systematic analysis of common TIG welding faults for aluminum:
| Fault | Cause | Preventive Measure |
|---|---|---|
| Excessive spatter | Excessive current, contaminated tungsten | Reduce current, dress tungsten electrode |
| Porosity | Oxide film contamination, insufficient shielding | Improve cleaning, increase gas flow |
| Tungsten inclusion | Tungsten contamination, arc too close | Dress electrode, increase torch angle |
| Undercut | Excessive travel speed, improper torch angle | Reduce speed, optimize torch angle |
| Excessive reinforcement | Slow travel speed, excessive wire feed | Increase speed, reduce wire feed |
| Burn-through | Excessive heat input, thin base metal | Reduce current, increase speed |
| Poor fusion | Insufficient heat, oxide film interference | Increase current, ensure cleaning |
Engineering Practice Integration
For power construction applications where L2 aluminum structures are welded, the following considerations are important:
- Surface preparation: Aluminum oxide must be completely removed prior to welding. Mechanical cleaning with stainless steel brushes (dedicated for aluminum) followed by chemical cleaning with appropriate etchants is essential. The cleaned surface must be welded within a short time window to prevent oxide reformation.
- Shielding gas selection: Pure argon is typically used for aluminum TIG welding. Flow rates of 15-20 L/min are recommended for adequate shielding of the weld pool and heat-affected zone.
- Tungsten electrode selection: Pure tungsten or thoriated tungsten electrodes are commonly used for AC TIG welding of aluminum. The electrode must be dressed regularly to maintain a consistent tip geometry and prevent contamination.
- Welding sequence: For multi-pass welds, the sequence should be planned to minimize distortion and residual stress. Back-step welding or stitch welding may be used for thin sections to control heat input.
Key Questions and Reflections
The study provides practical parameter values for 3 mm L2 aluminum, but the generalization to other thicknesses requires systematic scaling. The relationship between pulse parameters and base metal thickness should follow established heat input scaling laws, but validation through additional testing is recommended.
The tensile strength value of 86.09 MPa is notably close to the base metal strength, which is excellent for pure aluminum welds. However, the study does not report elongation or hardness data, which are important for assessing weld ductility and HAZ softening. For power transmission applications, the electrical conductivity of the weld joint is also critical, and this should be evaluated alongside mechanical properties.
The study's systematic approach to fault analysis and parameter optimization provides a useful framework for welding procedure development. However, the lack of microstructural characterization (grain size, phase composition) limits the ability to correlate process parameters with metallurgical outcomes.
Study Insights and Implications
The research demonstrates that pulsed AC TIG welding is an effective process for joining L2 pure aluminum, with optimized parameters producing welds with near-base-metal tensile strength and minimal defects. The systematic fault analysis provides practical guidance for welders and quality control personnel. For power construction engineers, the key takeaway is that careful parameter optimization and surface preparation are essential for achieving reliable aluminum welds. The study's parameter values serve as a useful starting point for WPS development, though additional testing for other thicknesses and joint configurations is necessary for comprehensive procedure qualification.