Powder Plasma Surfacing of Steel-Copper Composite Plate

Literature Overview

The paper by Ji Jie et al., published in the Journal of Shenyang University of Technology (1997, Vol. 19, No. 2, pp. 52–55), reports on the application of powder plasma surfacing to manufacture steel-copper composite plates by depositing a white copper alloy onto 16Mn steel substrates. The authors from Fuxin Industrial Equipment Installation Company investigated the cracking and deformation issues encountered during the surfacing process and proposed effective solutions.

Process Description and Technical Challenges

Powder plasma surfacing is a high-energy welding process that uses a plasma arc to melt a metal powder feedstock and deposit it onto a substrate. The process is characterized by high deposition rates, low dilution, and precise control of the deposit composition. In this application, the goal was to create a composite plate combining the strength of 16Mn steel with the electrical conductivity and thermal conductivity of white copper alloy.

The two primary challenges identified in the study were:

1. Cracking: The surfacing layer was prone to cracking, attributed to the mismatch in thermal expansion coefficients between steel and copper, as well as the presence of impurities in the surfacing material.
2. Deformation: The asymmetric thermal input from one-sided surfacing caused significant warping and distortion of the plate.

Cracking Prevention

The study found that using surfacing material with low impurity content and enhancing the shielding gas protection were effective measures to prevent cracking. The impurities, likely sulfur and phosphor, act as crack-initiating sites during solidification. By reducing these impurities, the solidification cracking susceptibility is significantly lowered. Enhanced shielding gas protection prevents atmospheric contamination of the molten pool, which can also introduce crack-initiating elements.

From a metallurgical perspective, the steel-copper interface is inherently challenging due to the limited mutual solubility of iron and copper. The formation of brittle intermetallic compounds (such as Fe-Cu phases) at the interface can promote cracking. The plasma surfacing process, with its high energy density and rapid cooling, tends to limit the thickness of the intermetallic layer, but the residual stresses at the interface remain a concern.

Deformation Control

The dual-sided symmetric welding approach is a well-established technique for minimizing warping in composite plate fabrication. By depositing material on both sides of the plate in a balanced sequence, the thermal inputs are partially self-canceling, reducing the net bending moment that causes warping. The post-weld stress relief treatment, typically involving furnace heating to 600–650°C for 16Mn steel, further reduces residual stresses and improves dimensional stability.

The combination of these two measures—symmetric welding and stress relief—provides a robust solution to the deformation problem. The symmetric welding reduces the magnitude of the initial deformation, while the stress relief treatment eliminates the residual stresses that could lead to delayed deformation during subsequent machining or service.

Interface Microstructure and Bonding

Although the paper does not provide detailed microstructural analysis of the steel-copper interface, the quality of the bonding is critical for the performance of the composite plate. The interface microstructure typically consists of a gradient of Fe-Cu intermetallic phases, with the composition transitioning from pure iron on the steel side to pure copper on the surfacing side. The thickness and morphology of this intermetallic layer directly affect the bonding strength and ductility of the composite.

For engineering applications, the bonding strength should be verified through shear or tensile tests, and the interface should be examined microscopically to ensure there are no cracks or voids. The powder plasma surfacing process, with its controlled melt pool and rapid solidification, is generally well-suited for producing high-quality interfaces in dissimilar metal joining.

Application and Engineering Relevance

Steel-copper composite plates find applications in heat exchangers, electrical busbars, and other components where both mechanical strength and electrical or thermal conductivity are required. The powder plasma surfacing method offers advantages over explosive cladding or explosion welding in terms of equipment simplicity, scalability, and the ability to produce plates of various sizes and thicknesses. The method is particularly suitable for manufacturing medium to large plates where explosive cladding may be impractical.

The engineering lessons from this study include:

• Material purity is critical in dissimilar metal surfacing applications.
• Symmetric welding strategies are effective for deformation control in composite fabrication.
• Post-weld stress relief is essential for dimensional stability and long-term performance.
• Plasma surfacing is a versatile process for producing composite plates with tailored surface properties.

Study Insights and Implications

This paper, though published in 1997, remains relevant as a foundational study on the practical challenges of producing dissimilar metal composite plates through surfacing. The solutions proposed—material purity control, symmetric welding, and stress relief—are timeless engineering principles that continue to be applied in modern manufacturing. The work underscores the importance of addressing both metallurgical and mechanical aspects of composite fabrication, as neglecting either can lead to premature failure in service. For engineers involved in the design and manufacture of composite components, this study serves as a practical guide to overcoming the inherent challenges of joining dissimilar materials.

In conclusion, these five literature studies collectively demonstrate the breadth and depth of surfacing welding technology across diverse engineering applications, from large hydraulic components and pressure vessels to automotive molds and composite plates. Each study addresses specific technical challenges through systematic process development, metallurgical analysis, and practical engineering solutions. The common thread throughout all five papers is the emphasis on process optimization, quality control, and the integration of metallurgical understanding with manufacturing practice. For engineers in the field of steel pipe, pipe fitting, and welding technology, these studies provide valuable references for tackling similar challenges in their own work, reinforcing the principle that successful surfacing operations require a holistic approach encompassing material selection, process design, thermal management, and rigorous quality assurance.