Powder Plasma Surfacing Method for Manufacturing Steel-Copper Composite Plates

Literature Overview

The research paper by Ji Jie, Dong Xiaoqiang, Zhang Shusheng, and Su Yongqing, published in the Journal of Shenyang University of Technology (1997, Vol. 19, No. 2, pp. 52-55), presents the application of powder plasma surfacing technology for manufacturing steel-copper composite plates. The authors are affiliated with Fuxin Industrial Equipment Installation Company. This work addresses the manufacturing of bimetallic composite materials through advanced surfacing techniques, with particular focus on overcoming cracking and distortion challenges inherent in dissimilar metal joining.

Technical Background

Steel-copper composite materials find extensive applications in electrical engineering, marine engineering, and heat exchanger manufacturing, where the combination of mechanical strength (steel) and electrical/thermal conductivity (copper) is required. Traditional manufacturing methods for steel-copper composites include explosion welding, roll bonding, and forge bonding, all of which have limitations in terms of scale, thickness, and cost. Powder plasma surfacing offers an alternative approach with greater flexibility in component geometry and thickness.

Application Requirements

Powder Plasma Surfacing Process

Powder plasma surfacing utilizes a high-temperature plasma arc to melt and deposit powder material onto a substrate surface. The process offers several advantages over conventional surfacing methods:

Process Parameters

The powder plasma surfacing process involves the following key parameters:

• Plasma current - Controls heat input and melting capacity
• Powder feed rate - Determines deposition rate and dilution ratio
• Travel speed - Controls bead width and penetration
• Shielding gas flow - Provides protection of molten pool
• Powder composition - Determines final overlay properties
• Interpass temperature - Controls residual stress and cracking

Cracking Problem and Solutions

Cracking is the primary metallurgical challenge in steel-copper composite plate manufacturing through surfacing. The significant difference in thermal expansion coefficients between steel and copper creates substantial residual stresses upon cooling, which can exceed the fracture strength of the deposited layer.

Types of Cracks Observed

Solutions Implemented

The authors identified two primary strategies for crack prevention:

1. Use of high-purity surfacing materials - Impurities in the powder material, particularly sulfur, phosphorus, and oxygen, significantly increase hot cracking susceptibility. Using powder with minimal impurity content reduces segregation and improves crack resistance.
2. Enhanced gas protection - The plasma arc provides inherent protection, but additional shielding gas (argon or helium) is applied to the molten pool area. Enhanced protection minimizes oxygen pickup, which forms brittle oxides that promote cracking. The shielding strategy includes:

• Primary plasma gas for arc formation
• Secondary shielding gas for molten pool protection
• Tertiary trailing gas for solidifying deposit protection

Distortion Problem and Solutions

Distortion in surfaced composite plates results from the asymmetric heat input that creates non-uniform thermal expansion and contraction. For thick surfacing deposits, this can result in significant warping that compromises dimensional accuracy and bonding quality.

Distortion Mechanisms

1. Thermal gradient distortion - The heated side expands while the cooler side remains relatively unchanged, causing bending
2. Phase transformation distortion - Volume changes during phase transformations in the HAZ contribute to distortion
3. Residual stress relaxation - Plastic deformation during cooling leads to permanent distortion

Solutions Implemented

The authors proposed two effective approaches:

1. Double-sided symmetric surfacing - Depositing material on both sides of the base plate in a symmetric pattern ensures that thermal expansion occurs on both sides, canceling out the bending moment. This approach requires:

• Alternating surfacing passes on each side
• Matching deposition rates on both sides
• Coordination of multiple surfacing heads or sequential operations

1. Post-weld stress relief treatment - Heat treatment after surfacing to relieve residual stresses through:

• Stress relief annealing at 550-650°C
• Soaking time of 1-2 hours per 25 mm thickness
• Controlled cooling rate to prevent new residual stresses
• Optional solution treatment for the copper overlay

Metallurgical Analysis

The interface between the steel base and copper overlay is the critical region determining the performance of the composite plate. Key metallurgical features include:

• Bonding mechanism - Metallurgical bonding through interdiffusion at the interface
• Interface thickness - Typically 50-200 micrometers of interdiffusion zone
• Intermetallic phases - Formation of Fe-Cu intermetallic compounds at the interface
• Dilution zone - Transition region where steel and copper compositions mix
• Microstructure - Copper-rich dendrites in the overlay, with possible Cu-Fe compounds at the interface

The quality of the metallurgical bond is assessed through:

• Tensile bond strength testing
• Peel testing
• Microstructural examination of the interface
• Hardness profiling across the interface
• Corrosion testing to evaluate interface integrity

Process Optimization

Based on the experimental results, the following process optimization guidelines emerge:

Engineering Applications

The steel-copper composite plates manufactured through powder plasma surfacing find applications in:

• Electrical bus bars and connectors requiring both strength and conductivity
• Marine propeller shafts with copper overlay for corrosion resistance
• Heat exchanger plates combining structural steel with copper thermal conductivity
• Chemical equipment requiring copper alloy corrosion resistance on steel substrates
• Specialized tooling where combined properties are required

Study Insights and Implications

This research from 1997 demonstrates the maturity of powder plasma surfacing technology for dissimilar metal joining applications. The systematic approach to identifying and solving cracking and distortion problems provides a methodology that remains relevant for contemporary composite manufacturing challenges. The dual-sided symmetric surfacing approach is particularly elegant in its simplicity - it addresses distortion at its root cause rather than attempting to correct it after the fact. The emphasis on material purity as a crack prevention strategy underscores the fundamental principle that metallurgical cleanliness is essential for reliable surfacing operations. For modern engineers, this work highlights that plasma surfacing remains a viable and competitive technology for manufacturing functional composite materials, particularly where conventional manufacturing methods are limited by geometry, thickness, or cost constraints. The principles of crack prevention through material purity and enhanced protection, combined with distortion control through symmetric processing and post-weld treatment, form a comprehensive approach that can be adapted to various surfacing applications involving dissimilar metal combinations.