CLADDING TECHNOLOGY SHANXI CO., LTDManufacturing Steel-Copper Bimetallic Plate by Plasma Powder Cladding Process
Literature Overview
This 1997 paper published in the Journal of Shenyang University of Technology, authored by Ji Jie, Dong Xiaoqiang, Zhang Shusheng, and Su Yongqing from Fuxin Industrial Equipment Installation Company, addresses the fabrication of steel-copper bimetallic plates using the plasma transferred arc (PTA) powder cladding technique. The work represents an early systematic investigation into applying PTA cladding for producing functional bimetallic components where a copper-rich surface layer is deposited onto a carbon steel substrate to achieve enhanced electrical conductivity, thermal conductivity, or wear resistance while maintaining the structural strength of the steel base.
Core Technical Content
The fundamental challenge in steel-copper bimetallic fabrication lies in the metallurgical incompatibility between the two materials. Iron and copper exhibit limited mutual solubility, and direct welding often produces brittle intermetallic compounds such as Fe-Cu phases that severely degrade mechanical properties. The PTA plasma powder cladding method circumvents this issue by controlling the dilution ratio and solidification conditions to produce a near-pure copper overlay layer with a sound metallurgical bond to the steel substrate.
The plasma arc provides a concentrated, high-energy heat source with temperatures exceeding 10,000 K at the arc center. The powder feedstock—typically electrolytic copper or a copper-alloyed powder—is introduced into the plasma arc via a gas stream and melts in the arc zone before depositing onto the substrate. The key advantage over conventional arc welding methods is the precise control over heat input, dilution, and layer composition.
Process Parameters and Their Significance
| Parameter | Typical Range | Effect on Cladding Quality |
|---|---|---|
| Plasma arc current | 100–300 A | Controls melting capacity and dilution rate |
| Powder feed rate | 100–400 g/min | Determines deposition rate and layer thickness |
| Shielding gas (Ar or Ar+H2) | 15–40 L/min | Prevents oxidation of molten copper |
| Travel speed | 50–200 mm/min | Affects heat input per unit length |
| Powder-to-gas ratio | 0.5–2.0 | Controls powder entrainment efficiency |
| Layer thickness per pass | 1–3 mm | Multi-pass builds required total thickness |
Metallurgical Analysis
The bonding mechanism between the copper cladding layer and steel substrate involves a thin diffusion zone at the interface. Under optimal PTA conditions, the dilution ratio can be maintained below 5–10%, producing a copper layer with purity exceeding 99%. The interface typically shows a narrow transition zone (50–200 μm) where limited iron dissolution occurs, but the bulk of the cladding retains its copper composition.
The solidification microstructure of the PTA copper layer is characterized by columnar dendrites growing epitaxially from the substrate interface. Each subsequent pass remelts the top of the previous layer, producing a layered columnar structure that is advantageous for fatigue resistance in the through-thickness direction. The grain orientation in PTA deposits differs significantly from cast or rolled copper, which has implications for anisotropic mechanical properties.
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Porosity | Gas entrapment from powder moisture or shielding gas | Dry powder storage; adequate shielding gas coverage |
| Cracking at interface | Thermal mismatch and rapid cooling | Preheating substrate to 150–250°C; controlling cooling rate |
| Incomplete bonding | Insufficient melting of previous layer | Increase current or reduce travel speed for interpass bonding |
| Excessive dilution | Too high heat input or low powder feed rate | Reduce current; increase powder feed rate; use lower arc voltage |
| Oxidation | Inadequate shielding gas | Increase gas flow; use nozzle extension; consider H2 addition |
Engineering Practice Integration
In industrial applications, steel-copper bimetallic plates fabricated by PTA cladding find use in electrical contact plates, heat exchanger tube sheets, and wear-resistant components in mining and cement industries. The technique offers significant advantages over explosive cladding or roll-bonding for small to medium production volumes and for complex geometries where mechanical bonding methods are impractical.
The economic comparison is noteworthy: while the material cost of copper powder is higher than that of rolled copper strip, the overall fabrication cost for PTA cladding can be competitive for specialized components. The process eliminates the need for intermediate bonding operations, reduces material waste, and allows for localized cladding on complex shapes.
Key Insights and Reflections
The 1997 study by Ji Jie and colleagues is historically significant as it demonstrates the maturity of PTA cladding technology in China for bimetallic fabrication during the late 1990s. The work bridges the gap between laboratory-scale research and industrial application, providing practical process windows that can be directly applied in production environments.
From a modern perspective, the fundamental principles established in this work remain valid. Contemporary PTA systems with computerized powder feeders and multi-axis robotic positioning can achieve even tighter control over dilution ratios and layer uniformity. However, the core understanding of thermal management, powder selection, and interface metallurgy remains essential for quality production.
The study also highlights an important engineering consideration: the selection of PTA over alternative cladding methods (such as laser cladding or hot-wire TIG) should be based on a comprehensive evaluation of production volume, required layer thickness, equipment availability, and cost structure. For thick copper overlays (greater than 5 mm), PTA remains economically advantageous over laser cladding due to higher deposition rates.
This literature provides a solid foundation for engineers tasked with specifying or implementing steel-copper bimetallic components through PTA cladding, and its process recommendations remain relevant for current industrial practice.