MIG Brazing Cladding of Copper Strip Technology

Literature Overview

The 2006 publication by Ma Wangzhe, Zhang Shanbao, Yang Yongbo, Zheng Yonggang, Wang Lianyi, and Yuan Fanhua in the journal Welding presents a practical investigation into MIG (Metal Inert Gas) brazing cladding of copper strip onto steel substrates. This work addresses a specific industrial need for producing bimetallic components where a copper layer provides corrosion resistance, electrical conductivity, or thermal conductivity while the steel substrate provides structural strength. The authors represent a collaboration between the Harbin Welding Research Institute, Heilongjiang Hua'an Industry Group, and Factory 123, reflecting the integration of academic research with industrial application in Chinese welding technology development.

Technical Background and Process Fundamentals

MIG brazing cladding differs fundamentally from fusion welding overlay in that the base metal substrate remains solid throughout the process, with only the filler material melting to form the cladding layer. This distinction has profound implications for process control, joint quality, and application scope. In conventional arc welding overlay, the substrate melts and dilutes with the filler, creating a fusion zone that is metallurgically bonded but introduces dilution concerns. In brazing cladding, the bond is achieved through capillary action and wetting of the clean substrate surface, producing a diffusion bond without substrate melting.

Process Parameters and Their Interactions

Parameter	Typical Range	Effect on Bond Quality	Effect on Layer Properties
Arc voltage	18-28 V	Controls heat input to substrate	Affects melting pool geometry
Wire feed speed	4-8 m/min	Determines deposition rate	Controls layer thickness per pass
Travel speed	0.2-0.6 m/min	Affects heat distribution	Influences solidification rate
Shielding gas	Ar or Ar/CO₂ mix	Prevents oxidation	Minor effect on composition
Substrate preheat	100-300°C	Promotes wetting	Prevents thermal shock cracking
Filler composition	Cu or Cu-P, Cu-Ag	Determines wetting behavior	Sets final layer properties

Substrate Preparation Requirements

The success of MIG brazing cladding depends critically on substrate surface preparation. Unlike fusion welding where surface contamination is consumed in the molten pool, brazing requires the substrate surface to be chemically clean and oxide-free to achieve proper wetting. The recommended preparation sequence includes:

Mechanical cleaning by grinding or wire brushing to remove gross contamination
Chemical degreasing using alkaline cleaners or solvent-based degreasers
Application of flux (typically solid or paste flux containing borax, fluorides, or chlorides)
Controlled heating to activate the flux and promote wetting

The flux serves multiple functions: it removes residual oxides during heating, prevents re-oxidation during the brazing process, and promotes capillary flow of the molten copper into the substrate surface. For copper strip cladding specifically, the flux composition must be carefully selected to avoid excessive corrosion of the copper layer during subsequent service.

Application Scope and Industrial Relevance

The MIG brazing cladding of copper strip technology finds application in several industrial sectors:

Electrical engineering: Production of copper-clad steel busbars, transformer components, and electrical contact strips where copper provides conductivity while steel provides mechanical strength
Heat exchangers: Manufacturing of copper-clad steel tubes for evaporators and condensers where copper offers superior thermal conductivity and corrosion resistance in refrigerant environments
Marine applications: Production of copper-clad steel components for seawater service where copper provides cathodic protection and corrosion resistance
Aerospace: Fabrication of copper-clad structural components requiring both strength and electrical grounding capability

Comparison with Alternative Cladding Methods

Method	Bond Strength	Substrate Dilution	Layer Thickness Control	Production Rate	Equipment Cost
MIG brazing cladding	Moderate-High	None	Good (0.5-5 mm)	High	Low-Moderate
ESW overlay	High	20-30%	Moderate (1-10 mm)	High	Moderate
SAW overlay	High	25-40%	Moderate (1-8 mm)	High	Moderate
Explosive cladding	Very High	Minimal	Good (0.5-10 mm)	Low (single shot)	High
Roll bonding	Very High	None	Limited (0.1-3 mm)	Very High (continuous)	Very High

Quality Control and Defect Prevention

The primary quality concerns in MIG brazing cladding include incomplete wetting, voids, cracks, and insufficient bond strength. Each defect has distinct root causes and corresponding countermeasures:

Common Defects and Countermeasures

Defect Type	Root Cause	Detection Method	Countermeasure
Incomplete wetting	Insufficient flux, oxide contamination	Visual, PT	Improve surface preparation, increase preheat temperature
Void formation	Gas entrapment, flux decomposition	UT, RT	Optimize travel speed, use vacuum brazing if critical
Cracking	Thermal stress, incompatible materials	MT, PT	Reduce cooling rate, use intermediate alloy layer
Insufficient bond	Low heat input, poor wetting	Peel test, shear test	Increase heat input, verify flux activation
Excessive substrate penetration	Excessive heat input	Visual, UT	Reduce arc voltage, increase travel speed

The peel test and shear test are the standard methods for evaluating bond strength in brazed cladding joints. For copper-clad steel joints, acceptable bond strength typically exceeds 15 MPa in shear and 10 MPa in peel, depending on the specific application requirements and applicable standards.

Engineering Practice Considerations

Several practical considerations emerge from the application of MIG brazing cladding technology in production environments. First, the process is highly sensitive to operator skill and technique, particularly in maintaining consistent arc characteristics and travel speed. Semi-automated or fully automated systems significantly improve consistency and reduce defect rates. Second, the flux management is critical: flux must be applied in the correct quantity (typically 200-500 g/m²) and must be activated at the correct temperature range. Under-fluxing leads to poor wetting, while excessive fluxing can cause corrosion issues in the final product.

Third, the process is limited in terms of achievable layer thickness per pass. For thicker copper layers, multiple passes may be required, with each subsequent pass brazing onto the previous copper layer rather than the steel substrate. This creates a layered structure where the interlayer bonds between successive copper passes must be carefully managed to ensure uniform properties throughout the thickness. The interpass temperature must be maintained within a narrow window (typically 400-550°C) to ensure proper wetting without excessive grain growth in the previously deposited layer.

Study Insights and Conclusions

The work by Ma Wangzhe and colleagues demonstrates that MIG brazing cladding offers a practical, cost-effective solution for producing copper-clad steel components in industrial settings. The technology bridges the gap between the high-quality but expensive explosive cladding and roll bonding methods and the lower-quality fusion welding overlay approaches. The key advantage is the absence of substrate dilution, which preserves the mechanical properties of the steel substrate while providing a pure copper surface layer.

For engineers specifying copper-clad components, this study reinforces that process control parameters must be tightly managed to ensure consistent bond quality. The flux system is the critical enabling technology that makes brazing cladding viable, and its selection must account for both the brazing process requirements and the service environment of the final component. The technology is particularly well-suited for strip and plate production where consistent geometry facilitates automated processing, and it represents a mature technology with well-established quality control practices that can be readily implemented in production facilities with moderate capital investment.