CLADDING TECHNOLOGY SHANXI CO., LTDManufacturing Steel-Copper Bimetallic Plate Using Plasma Powder Cladding
Literature Overview
This 1997 study by Ji Jie, Dong Xiaoqiang, Zhang Shusheng, and Su Yongqing from Fuxin Industrial Equipment Installation Company, published in the Journal of Shenyang University of Technology, presents a process for manufacturing steel-copper bimetallic plates using plasma transferred arc (PTA) powder cladding. The work addresses the manufacturing of copper-clad steel plates used in applications requiring both structural strength from the steel substrate and excellent electrical conductivity or corrosion resistance from the copper overlay layer.
Technical Background
Copper-clad steel plates are widely used in electrical engineering (bus bars, transformer components), marine applications (seawater heat exchangers), and chemical processing equipment. Traditional manufacturing methods for copper-steel bimetallic plates include explosion cladding, roll bonding, and conventional welding overlay. Each method has limitations:
- Explosion cladding: High cost, limited to specific alloy combinations, difficult to achieve uniform thickness.
- Roll bonding: Requires rolling mill capacity, limited to continuous production of large quantities.
- Conventional welding overlay (GMAW/SAW): High dilution at the steel-copper interface due to the large difference in melting points and thermal conductivity, leading to intermetallic compound formation and reduced bond strength.
PTA cladding offers a superior alternative because the plasma arc provides a concentrated, high-temperature heat source that melts the powder feedstock and a controlled depth of the substrate, resulting in a dilution rate that can be precisely managed.
Process Description and Key Parameters
The PTA process involves directing a high-velocity plasma jet onto the steel substrate surface while simultaneously feeding copper or copper-alloy powder into the plasma arc. The powder is melted and deposited onto the substrate, forming a metallurgical bond with controlled dilution.
| Parameter | Value / Range | Rationale |
|---|---|---|
| Plasma arc current | 200–400 A | Sufficient to melt substrate surface |
| Arc voltage | 25–35 V | Controls arc length and penetration |
| Powder feed rate | 200–500 g/min | Depends on current and travel speed |
| Travel speed | 100–300 mm/min | Controls dilution and bead geometry |
| Shielding gas | Argon | Prevents oxidation of molten copper |
| Powder composition | Cu / CuCrZr / CuSn | Depends on application requirements |
| Substrate material | Q235 / 45 steel | Structural base plate |
| Overlay thickness | 1.5–5 mm | Multi-pass build-up |
| Preheat temperature | 100–200 °C | Reduces cracking tendency |
Metallurgical Analysis of the Interface
The steel-copper interface is the critical zone in any bimetallic product. The key metallurgical considerations include:
- Intermetallic compound formation: The Cu-Fe system forms brittle intermetallic compounds (FeCu, Fe₃Cu, Fe₅Cu₂) that reduce ductility and fatigue resistance. The thickness of the intermetallic layer must be controlled to less than 50 μm for acceptable mechanical performance.
- Dilution control: The dilution rate (substrate material dissolved into the overlay) must be kept below 15–20% to maintain the electrical conductivity and corrosion resistance of the copper layer. PTA allows dilution rates as low as 5–10% with proper parameter optimization.
- Residual stress management: The coefficient of thermal expansion mismatch between steel (~12 × 10⁻⁶/K) and copper (~17 × 10⁻⁶/K) generates significant residual stresses during cooling. Multi-pass deposition with alternating directions helps mitigate these stresses.
Performance Comparison with Other Methods
| Method | Dilution Rate | Bond Strength (MPa) | Surface Quality | Cost | Flexibility |
|---|---|---|---|---|---|
| PTA Cladding | 5–15% | 200–350 | Excellent | Medium | High |
| GMAW Overlay | 20–40% | 150–250 | Good | Low | Medium |
| Explosion Cladding | < 5% | 250–400 | Good | High | Low |
| Roll Bonding | < 5% | 300–450 | Excellent | Medium | Low (continuous only) |
Engineering Applications and Quality Control
For pressure vessel and heat exchanger applications, the quality of the steel-copper clad plate must be verified through:
- Bond strength testing: Shear test per ASTM A263/A264 requirements, minimum 200 MPa for most applications.
- Penetration test (PT): Surface inspection of the overlay for cracks, porosity, and incomplete coverage.
- Ultrasonic testing (UT): Detection of subsurface defects and bond quality at the interface.
- Metallurgical examination: Cross-sectional analysis to measure intermetallic layer thickness and confirm proper fusion.
Study Insights and Reflections
This 1997 study was ahead of its time in promoting PTA cladding for bimetallic plate production in China. The key insight is that PTA provides the best balance between dilution control, productivity, and cost-effectiveness for copper-on-steel cladding. From my engineering practice, I have found that the powder feed system reliability is often the limiting factor in PTA cladding — powder bridging, inconsistent feed rates, and nozzle clogging can all compromise quality. Modern PTA systems with dual-nozzle powder feeders and real-time monitoring have significantly improved process stability. For pressure vessel applications, the clad plate must also comply with the requirements of NB/T 47002 and ASME VIII Div. 1 regarding qualification of the cladding weld procedure and the qualification of the welder. The study's emphasis on parameter optimization through systematic experimentation is a methodology that remains relevant today, though modern approaches would supplement it with thermal simulation and process modeling to predict dilution and residual stress distributions more accurately.