CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Mechanical Properties of 1561 Aluminum Alloy Double-Sided Double-Arc TIG Welded Joints
Literature Overview
This study, published in the Chinese Journal of Nonferrous Metals in 2016 by Yan Dejun, Han Duanfeng, Wang Yi, Luo Jiuqiang, Liu Xiaoli, and Liang Zhimin, investigates the microstructural evolution and mechanical performance of 1561 aluminum alloy welded joints produced using a double-sided double-arc TIG (gas tungsten arc) welding technique. The research was supported by international cooperation projects and national defense science and technology basic research programs, indicating its significance in shipbuilding and marine applications. The 1561 aluminum alloy is a high-strength Al-Cu-Mg-Si system alloy widely used in naval hull structures where both strength and corrosion resistance are critical.
Core Technical Points
The double-sided double-arc TIG welding process represents an advanced approach to achieving full-penetration welds in thick aluminum alloy plates without the need for backing gas or backing strips, which are common challenges in single-sided TIG welding of aluminum. The key innovation lies in simultaneously applying heat input from both sides of the workpiece, which helps to:
- Achieve complete penetration through thick sections (typically 10-25 mm)
- Reduce distortion and residual stress by symmetric heat distribution
- Eliminate the need for expensive helium backing gas
- Improve weld quality and reduce porosity formation
Microstructural Characteristics
The weld metal in 1561 alloy TIG joints typically exhibits a columnar dendrite structure with inter-dendritic segregation of Al2Cu and Al2CuMg phases. The heat-affected zone (HAZ) undergoes precipitation dissolution and re-precipitation, leading to significant softening in the T6 temper condition. The double-sided double-arc approach creates a more uniform thermal cycle on both surfaces, potentially reducing the width of the severely softened zone compared to single-sided welding.
| Parameter | Single-Sided TIG | Double-Sided Double-Arc TIG |
|---|---|---|
| Typical plate thickness | 3-6 mm | 10-25 mm |
| Backing gas required | Yes (He or Ar) | No |
| Heat input symmetry | Asymmetric | Symmetric |
| HAZ softening width | 3-5 mm per side | 2-4 mm per side |
| Distortion control | Poor | Improved |
| Productivity | Lower | Higher |
Mechanical Performance
The welded joint of 1561 aluminum alloy typically shows a strength ratio (weld strength / base metal strength) of approximately 0.75-0.85 in the as-welded condition. The double-sided double-arc technique may improve this ratio by reducing the extent of over-aging in the HAZ. Tensile tests reveal that the weakest link is usually in the HAZ rather than the weld metal itself, consistent with the precipitation-free zone formation characteristic of Al-Cu-Mg-Si alloys.
Engineering Practice Integration
In shipbuilding applications, 1561 aluminum alloy is specified for hull structures in the splash zone and submerged areas where high strength and excellent corrosion resistance are demanded. The double-sided double-arc TIG process offers particular advantages for:
- Repair welding of hull structures where access is limited to one side
- Welding of thick plate sections in shipblock assembly
- Joining of dissimilar thickness plates where single-sided welding would be impractical
From a quality control perspective, the double-sided approach facilitates visual inspection of the root side and allows for more effective non-destructive testing (NDT) using ultrasonic testing (UT) from both sides. The symmetric heat input also reduces the risk of hot cracking, which is a common concern in Al-Cu-Mg-Si alloys due to their wide solidification range.
Key Reflections and Study Insights
The double-sided double-arc TIG welding technique for 1561 aluminum alloy represents a practical solution to the long-standing challenge of welding thick aluminum sections in shipbuilding. The key insight is that symmetric thermal cycling not only improves weld quality but also reduces post-weld treatment requirements. However, the process requires precise coordination between the two arcs, which demands skilled operators or mechanized equipment. The research contributes valuable data for process qualification under standards such as AWS D1.2 and EN 1090, which govern aluminum welding in structural applications.
For pressure vessel engineers working with aluminum alloy vessels, this technology offers a pathway to fabricating thick-walled components without resorting to expensive friction stir welding (FSW) equipment. The mechanical property data obtained from this study can be directly applied to joint efficiency calculations per ASME Section VIII Division 1, where the weld joint efficiency factor depends on the measured strength of the qualified procedure.
The study underscores the importance of understanding the relationship between welding process parameters, microstructural evolution, and final mechanical properties in high-strength aluminum alloys. Process optimization should focus on minimizing the width of the precipitation-free zone in the HAZ, which can be achieved through controlled heat input and appropriate interpass temperature management.