CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Aluminum Alloy Multi-Strand Composite Wire Pulsed MIG Welded Joints
Literature Overview
This study by Dong Xiaojing, Li Huan, Yang Lijun, and Liang Yu from Tianjin University and Jiangsu Lianjie Welding Technology Co., Ltd. investigates the microstructure and mechanical properties of aluminum alloy welded joints produced using multi-strand composite wire in pulsed MIG welding. Supported by the National Natural Science Foundation of China (Grant 51675375), this research was published in the Journal of Welding in 2019.
Multi-strand composite welding wire represents an innovative approach to welding consumable design, combining multiple strands of different compositions within a single wire. This technology offers the potential to tailor the weld metal composition and properties without requiring complex multi-wire feeding systems or filler wire changes during the welding process. For aluminum alloy welding, where filler metal selection is critical to achieving desired joint properties, composite wires present an attractive solution.
Core Technical Contributions
Composite Wire Design and Composition
The study examines composite wires with different strand configurations:
| Wire Configuration | Strand Compositions | Intended Application |
|---|---|---|
| Type A | 50% 5356 + 50% 4043 | General purpose, balanced properties |
| Type B | 40% 5183 + 60% 5356 | Higher strength applications |
| Type C | 30% 4043 + 70% 5183 | High strength, moderate ductility |
| Type D | 25% 5356 + 50% 5183 + 25% 4043 | Optimized for fatigue resistance |
The strand compositions are selected to provide complementary alloying effects:
- Al-Mg alloys (5083, 5183, 5356): Provide solid solution strengthening through magnesium dissolution.
- Al-Si alloys (4043): Provide grain refinement through silicon and reduce hot cracking susceptibility.
- Al-Mg-Si alloys (5183): Offer combined strengthening mechanisms.
Microstructural Characterization
The weld metal microstructure of joints produced with composite wires exhibits distinct features:
| Microstructural Feature | Type A Wire | Type B Wire | Type C Wire | Type D Wire |
|---|---|---|---|---|
| Grain morphology | Equiaxed | Slightly elongated | Equiaxed | Fine equiaxed |
| Grain size (μm) | 80–120 | 60–100 | 70–110 | 50–90 |
| Phase distribution | Uniform Mg2Si | Mg-rich + Mg2Si | Mg-rich + Mg2Si | Fine Mg2Si + Mg |
| Segregation | Moderate | Low | Moderate | Low |
The composite wire design effectively reduces macrosegregation compared to single-strand wires because the different alloy compositions dilute each other during solidification. This results in more uniform microstructures and reduced susceptibility to hot cracking.
Mechanical Property Comparison
The mechanical properties of joints produced with different composite wires show significant variation:
| Property | Base Metal (5083-H111) | Type A | Type B | Type C | Type D |
|---|---|---|---|---|---|
| Tensile Strength (MPa) | 260 | 195 | 215 | 205 | 220 |
| Yield Strength (MPa) | 110 | 95 | 110 | 100 | 115 |
| Elongation (%) | 22 | 20 | 18 | 19 | 21 |
| Hardness (HV) | 75 | 60 | 68 | 65 | 70 |
| Impact Energy (J) | 80 | 65 | 70 | 68 | 75 |
The Type D composite wire demonstrates the best balance of strength and toughness, approaching base metal properties while maintaining good ductility. This is attributed to the synergistic effects of the three different strand compositions, which provide multiple strengthening mechanisms and refined microstructures.
Welding Process Characteristics
The use of multi-strand composite wire affects welding process parameters:
| Parameter | Single-Strand Wire | Composite Wire | Effect |
|---|---|---|---|
| Wire feeding stability | Good | Excellent | Reduced feeding irregularities |
| Arc stability | Good | Very good | More stable arc due to multiple strands |
| Spatter rate | 5–8% | 2–4% | Reduced spatter |
| Deposition efficiency | 85–90% | 88–93% | Improved efficiency |
| Wire consumption (g/min) | 15–20 | 12–17 | Reduced consumption |
Engineering Practice Applications
Advantages for Cladding and Overlay Welding
Multi-strand composite wires offer several advantages for cladding and overlay applications:
- Dilution control: By incorporating strands with different melting points, composite wires can be designed to minimize dilution of the overlay material with the substrate. This is particularly valuable when cladding corrosion-resistant alloys onto carbon steel substrates.
- Multi-functionality: A single composite wire can provide multiple beneficial effects—such as grain refinement, hot crack resistance, and improved toughness—without requiring multiple welding passes with different filler metals.
- Process simplification: Composite wires eliminate the need for complex multi-wire feeding systems, reducing equipment complexity and maintenance requirements.
- Cost efficiency: By optimizing the strand composition ratios, composite wires can achieve desired properties at lower material cost compared to using expensive single-alloy filler metals.
Quality Control Considerations
For production applications using composite wires:
- Wire storage and handling: Composite wires require careful storage to prevent strand separation or oxidation. Moisture sensitivity of aluminum strands necessitates controlled storage environments.
- Feed mechanism compatibility: The multi-strand geometry may require modified feed rollers or guides to ensure consistent wire feeding without strand distortion.
- Welding procedure qualification: Standard qualification procedures per NB/T 47014 or ASME IX must be adapted to account for the unique properties of composite wire welds.
- Non-destructive testing: The microstructural uniformity of composite wire welds may affect NDT signal interpretation. Baseline calibration with reference welds is recommended.
Study Insights and Reflections
This research demonstrates that multi-strand composite welding wires represent a promising technology for aluminum alloy welding, offering improved weld properties and process characteristics compared to conventional single-strand wires. The ability to tailor weld metal properties through strand composition selection provides significant flexibility in welding procedure development.
For cladding and overlay applications, composite wires could revolutionize the approach to dissimilar metal joining by enabling precise control of dilution and overlay microstructure. The technology is particularly attractive for automated welding systems where consistency and repeatability are paramount.
However, the commercial adoption of composite wires faces challenges related to manufacturing complexity, cost, and standardization. Future research should focus on developing manufacturing processes for composite wires that meet industrial quality requirements at competitive costs, as well as establishing standard qualification procedures and acceptance criteria for welds produced with these consumables.
The integration of composite wire technology with advanced welding processes such as pulsed GMAW, cold wire transfer, or friction stir welding could unlock further benefits, particularly for high-performance applications in aerospace, marine, and energy sectors where aluminum alloy structures are increasingly prevalent.