Zhuojin Pipe Fitting Co., LtdEffect of Weld Wire Composition on Microstructure and Properties of 5E61 Aluminum Alloy TIG Welded Joints
Literature Overview
The paper by Mao Xiaodong, Gu Ningjie, Song Xiaoyu, Ren Simeng, Lu Liying, and Li Hutian, published in Transactions of the China Welding Institution (Vol. 43, No. 4, 2022, pp. 86-93), investigates the influence of weld wire composition on the microstructure and mechanical properties of TIG welded joints in 5E61 aluminum alloy ship plate. Funded by the National Key R&D Program of China (Project No. 2021YFB3704200), this research addresses the practical challenge of selecting appropriate filler metals for marine aluminum alloy structures.
Core Technical Content
5E61 aluminum alloy (equivalent to 5083-H116) is widely used in shipbuilding due to its excellent combination of strength, corrosion resistance, and weldability. The study compares three filler wires—Wire-1561, Wire-5B71, and Wire-5E61—for TIG welding of 4 mm thick 5E61-H116 aluminum alloy ship plate. The investigation encompasses weld appearance, formation quality, microstructure, and mechanical properties.
Weld Wire Composition Comparison
| Wire Designation | Primary Alloying Elements | Intended Application |
|---|---|---|
| Wire-1561 | Al-Mn-Si system | General purpose aluminum welding |
| Wire-5B71 | Al-Mg-Zn system | Higher strength welding |
| Wire-5E61 | Al-Mg-Zr system | Matched composition welding |
Microstructural Analysis Results
| Parameter | Wire-1561 | Wire-5B71 | Wire-5E61 |
|---|---|---|---|
| Weld grain size | Largest | Smallest | Medium |
| Weld hardness | Lowest | Medium | Highest |
| Tensile strength (MPa) | 322 | 323 | 338 |
| Welding coefficient | 0.83 | 0.84 | 0.88 |
| Elongation (%) | 13.0 | 14.5 | 14.5 |
| Fracture location | Near fusion line | Near fusion line | Near fusion line |
Strengthening Mechanisms
The superior performance of Wire-5E61 can be attributed to two strengthening mechanisms:
- Solid solution strengthening: The Mg element in the filler metal provides significant solid solution strengthening in the weld metal, increasing both strength and hardness.
- Grain refinement: The Zr element (as Zr) promotes grain refinement through heterogeneous nucleation during solidification, resulting in finer weld grains and improved mechanical properties.
Process Quality Assessment
Weld Formation Quality
All three wires produced acceptable weld formation with no visible porosity at the weld center. However, the grain structure differences indicate varying solidification behaviors:
- Wire-1561: Larger grains suggest slower nucleation rates and potentially higher susceptibility to hot cracking.
- Wire-5B71: Smallest grains indicate effective grain refinement, likely due to the Zn addition promoting nucleation.
- Wire-5E61: Medium grain size with the best mechanical properties, suggesting an optimal balance between nucleation and growth.
Fracture Analysis
The consistent fracture location near the fusion line across all three wires indicates that the fusion line region is the weakest link in the joint. This is attributed to:
- Columnar grain structure in the fusion line region
- Lowest hardness at the fusion line
- Potential microsegregation of alloying elements
- Residual stress concentration at the fusion boundary
Engineering Practice Recommendations
For shipbuilding applications involving 5E61 aluminum alloy, the following recommendations are derived from this study:
| Application Consideration | Recommendation |
|---|---|
| Wire selection | Wire-5E61 preferred for maximum strength and welding coefficient |
| Acceptance criteria | Welding coefficient ≥0.85 for critical structural applications |
| NDT requirements | Dye penetrant testing (PT) for surface defects; UT for volumetric inspection |
| Joint design | Avoid stress concentrations at fusion line; consider joint geometry optimization |
| Post-weld treatment | Stress relief annealing may improve fatigue performance |
Standards Compliance
The welding process must comply with relevant marine standards:
- EN ISO 14343: Welding of aluminum and aluminum alloys
- AWS D10.1/D10.2: Welding of aluminum and its alloys
- CCS Rules: China Classification Society requirements for aluminum structures
- NORSOK M-501: Material requirements for offshore structures
The welding coefficient values reported (0.83-0.88) should be evaluated against the specific requirements of the applicable classification society for the intended application.
Study Insights and Implications
This research provides practical guidance for filler metal selection in marine aluminum alloy welding. The finding that Wire-5E61 achieves the highest welding coefficient (0.88) while maintaining good ductility (14.5% elongation) makes it the preferred choice for critical ship structural applications. The consistent fracture location near the fusion line across all wire compositions highlights the need for future research into fusion line strengthening techniques, such as local grain refinement or post-weld heat treatment. The study also demonstrates that grain refinement through appropriate alloying (Zr in this case) is an effective strategy for improving weld metal properties without sacrificing ductility.