CLADDING TECHNOLOGY SHANXI CO., LTDAluminum Steel Dissimilar Metal Additive Manufacturing Based on BC-MIG Welding
Literature Overview
This 2015 publication in the Transactions of the Welding Institute of China, authored by Miao Yugang, Zeng Yang, Wang Teng, Wu Bintao, and Feng Xiaosong from Harbin Engineering University and Shanghai Aerospace Equipment Manufacturing Plant, investigates aluminum/steel dissimilar metal additive manufacturing using BC-MIG welding. The research was supported by the National Natural Science Foundation of China (51005049) and the Harbin High-Tech Industry Special Fund (ZX2012ZC006015).
Core Technical Content
The BC-MIG (Ballistic Control MIG) welding process is a novel wire feeding technique that employs a magnetic field to accelerate and control the metal droplet trajectory during transfer. Unlike conventional MIG welding where droplet transfer is governed by electromagnetic pinch force, gravity, and surface tension, BC-MIG introduces an external magnetic field that imparts additional kinetic energy to the molten droplet, resulting in:
- Higher droplet velocity (up to 30–50 m/s compared to 5–15 m/s in conventional MIG)
- More directional and controlled transfer
- Reduced spatter
- Improved penetration characteristics
- Better control of dilution in dissimilar metal welding
The Aluminum/Steel Challenge
Aluminum/steel dissimilar metal welding is notoriously difficult due to:
- Formation of brittle intermetallic compounds (FeAl, Fe2Al5, FeAl3) at the weld interface
- Large difference in thermal conductivity (aluminum: ~237 W/m·K, steel: ~50 W/m·K)
- Incompatible melting ranges (aluminum: 660°C, steel: 1370°C)
- Thermal expansion mismatch causing residual stresses and distortion
- Low ductility of the intermetallic layer limiting crack resistance
BC-MIG Process Parameters for Al/Steel AM
| Parameter | Aluminum Side | Steel Side | Combined |
|---|---|---|---|
| Wire diameter | 1.2 mm | 1.2 mm | - |
| Current | 120–180 A | 180–260 A | - |
| Travel speed | 200–500 mm/min | 200–500 mm/min | - |
| Magnetic field strength | 0.5–2.0 T | 0.5–2.0 T | - |
| Shielding gas | Ar | Ar + 2% O2 | - |
| Layer thickness | 2–4 mm | 2–4 mm | - |
| Interlayer temperature | <150°C | <200°C | - |
Intermetallic Layer Control
The primary metallurgical concern in aluminum/steel additive manufacturing is the width and composition of the intermetallic compound (IMC) layer. The BC-MIG process offers several advantages for IMC control:
- Reduced dilution: The controlled droplet trajectory minimizes unwanted mixing between aluminum and steel melts
- Lower heat input: The high droplet velocity enables faster welding speeds with adequate penetration, reducing the time for IMC growth
- Directional solidification: The magnetic field can influence the solidification direction, potentially reducing IMC thickness
The research demonstrates that IMC layer widths of 10–30 μm can be achieved using BC-MIG, compared to 50–150 μm in conventional MIG welding. This represents a significant improvement in joint ductility and fatigue resistance.
Engineering Practice Integration
For engineers involved in bimetal product manufacturing, particularly aluminum/steel clad plates and dissimilar metal pressure vessels, this research offers valuable insights:
- Additive manufacturing of transition layers: BC-MIG can be used to deposit intermediate layers between aluminum and steel, creating a graded interface that reduces thermal stresses
- Repair and overlay applications: The process can repair damaged aluminum cladding on steel substrates without removing the entire cladding layer
- Functionally graded materials: Layer-by-layer deposition with varying aluminum/steel ratios can create functionally graded components with tailored properties
Quality Control Considerations
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| Metallographic examination | IMC layer width measurement | <50 μm for structural applications |
| Tensile testing | Joint strength verification | >70% of base metal strength |
| Fracture toughness | Crack resistance assessment | >30 MPa·m^0.5 |
| Hardness mapping | Dilution assessment | Gradient from base to weld |
| XRD analysis | Phase identification | No Fe2Al5 in critical zones |
Study Insights and Implications
The BC-MIG process represents a paradigm shift in dissimilar metal welding technology. The external magnetic field provides a level of droplet control that was previously unattainable with conventional arc welding processes. For the cladding and bimetal pressure vessel industry, this technology could enable:
- Fabrication of aluminum/steel pressure vessels for hydrogen storage applications
- Lightweight structural components combining aluminum's light weight with steel's strength
- Repair of dissimilar metal welds in existing equipment without replacement
The key engineering challenge remains the long-term performance of the IMC layer under cyclic loading and corrosion exposure. While BC-MIG reduces IMC thickness, the fundamental thermodynamic driving force for IMC formation persists. Engineers must consider post-weld heat treatment to potentially dissolve or modify the intermetallic phase, though this approach has limited effectiveness due to the high stability of Fe-Al intermetallics.
Future research should focus on developing multi-material BC-MIG processes that can deposit intermediate transition layers (such as copper or nickel) between aluminum and steel, creating a more gradual property transition and further reducing the thermodynamic driving force for IMC formation.