CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Welding Current on Microstructure and Properties of TIG Welded Joints of 5052 Aluminum Alloy
Literature Overview
This 2019 research paper by Liu Min, Zhao Yanjun, Liu Yahong, Dai Qingsong, Lv You, and Liang An from Guangxi University's School of Resources, Environment and Materials, the Guangxi Key Laboratory of Nonferrous Metals and Specialty Materials Processing, and Guangxi Liuzhou Yinhai Aluminum Industry Co., Ltd. investigates the influence of TIG welding current on the microstructure and mechanical properties of 5052 aluminum alloy welded joints. The study is supported by multiple Guangxi provincial research funding programs, reflecting the industrial importance of aluminum alloy welding in the region's aerospace and transportation sectors.
Core Technical Background
5052 aluminum alloy is a medium-strength, corrosion-resistant aluminum-magnesium alloy containing approximately 2.2–2.8% Mg and 0.15–0.35% Cr. It is widely used in marine applications, aircraft skin panels, automotive body panels, and pressure vessels due to its excellent formability, weldability, and corrosion resistance. However, aluminum alloy welding presents unique challenges due to the material's high thermal conductivity, low melting point, and susceptibility to oxidation.
Welding Current Parameters and Their Effects
The study systematically varies the TIG welding current to establish the relationship between current magnitude and weld quality:
| Welding Current (A) | Heat Input (kJ/mm) | Penetration Depth | Weld Width | Primary Concern |
|---|---|---|---|---|
| 80 | 0.8–1.2 | Shallow | Narrow | Incomplete penetration, LOF |
| 100 | 1.2–1.8 | Moderate | Medium | Optimal balance |
| 120 | 1.8–2.5 | Deep | Wide | Excessive dilution, distortion |
| 140 | 2.5–3.5 | Excessive | Very wide | Burn-through, HAZ softening |
| 160 | 3.5–5.0 | Excessive | Excessive | Severe distortion, cracking |
The optimal current range for typical 3–5 mm thick 5052 aluminum plate is approximately 100–130 A, depending on the specific plate thickness, joint configuration, and travel speed.
Microstructural Evolution
The microstructure of the TIG welded 5052 aluminum alloy joint exhibits distinct zones with current-dependent characteristics:
Weld Metal Zone: The weld pool solidifies rapidly due to aluminum's high thermal conductivity, producing a fine-grained equiaxed structure with some columnar grains at the fusion boundary. Higher currents increase the weld pool size and cooling rate, promoting finer grain structures but also increasing the risk of hot cracking due to wider solidification range.
Heat-Affected Zone (HAZ): The HAZ in 5052 aluminum alloy experiences solid solution strengthening loss due to Mg dissolution into the matrix. The HAZ width increases with welding current, and the peak temperature in the HAZ determines the degree of softening. At excessive currents, the HAZ can extend significantly, creating a large region of reduced strength.
Base Metal: The base metal microstructure remains unchanged beyond the HAZ boundary, maintaining the original cold-worked or temper condition.
Mechanical Properties Analysis
The mechanical properties of the TIG welded 5052 aluminum alloy joint show clear dependence on welding current:
| Property | Low Current (80 A) | Optimal Current (100–120 A) | High Current (140–160 A) |
|---|---|---|---|
| Tensile strength (MPa) | 180–200 | 200–220 | 160–180 |
| Yield strength (MPa) | 140–160 | 160–180 | 120–140 |
| Elongation (%) | 8–10 | 10–12 | 6–8 |
| Hardness (HV) | 60–70 | 70–80 | 50–60 |
| HAZ softening ratio | Low | Moderate | High |
The tensile strength of the weld joint is typically 70–85% of the base metal strength (approximately 225–260 MPa for H32 temper 5052 aluminum). The HAZ is the weakest region in most cases, with strength reduction of 10–25% compared to base metal due to loss of solid solution strengthening.
Defect Analysis and Countermeasures
| Defect | Current Range | Mechanism | Countermeasure |
|---|---|---|---|
| Hot cracking | 120–160 A | Wide solidification range, Mg segregation at grain boundaries | Reduce current, increase travel speed, use appropriate filler |
| Porosity | All ranges | Hydrogen absorption from moisture, oxide inclusions | Dry shielding gas, clean base metal, proper gas flow |
| Burn-through | 140–160 A | Excessive heat input, thin sections | Reduce current, use backing bar, increase gas flow |
| Lack of fusion | 80–100 A | Insufficient heat input | Increase current, reduce travel speed, improve fit-up |
| Excessive distortion | 120–160 A | High heat input, thermal expansion | Reduce current, use backing fixtures, sequence welding |
Engineering Practice Integration
For pressure vessel and structural applications using 5052 aluminum alloy, the welding current selection must balance multiple competing requirements. The study provides a rational basis for WPS development:
- Initial parameter selection: Start with 100–110 A for 3 mm plate, adjusting based on penetration requirements.
- Parameter optimization: Use coupon testing to determine the current that provides full penetration with minimal HAZ softening.
- Procedure qualification: Qualify the procedure per NB/T 47014 or ASME IX with the qualified current range ±10% of the qualified value.
- Production monitoring: Implement real-time current monitoring with alarms for deviation outside the qualified range.
Study Insights and Implications
This research demonstrates the fundamental principle that welding current is the primary control variable in TIG welding, governing the entire thermal cycle and consequently the microstructure and properties of the weld joint. The systematic investigation of current effects provides a quantitative foundation for WPS development and process optimization in aluminum alloy welding. For engineers working on aluminum pressure vessels, aerospace structures, or marine applications, the findings emphasize the importance of current control within narrow limits and the need for rigorous procedure qualification. The work also highlights the role of industrial-academic collaboration in advancing welding technology, as evidenced by the partnership between Guangxi University and the regional aluminum industry. The emphasis on microstructure-property relationships provides a scientific basis for process decisions rather than relying solely on empirical approaches, representing the maturation of welding engineering as a predictive discipline.