Effect of Plastic Deformation on Copper-Steel Solid-Liquid Composite Bimetallic Bonding Interface
1. Definition and Fundamental Principles
The study titled "Research on the Effect of Deformation Amount on the Bonding Interface of Copper-Steel Solid-Liquid Composite Bimetallic Materials" addresses a critical metallurgical and mechanical phenomenon in bimetallic fabrication: how the magnitude of plastic deformation applied during joining influences the integrity, microstructure, and mechanical performance of the copper-steel interface.
In solid-liquid composite bimetallic materials, one component (typically copper or a copper alloy) is brought to a semi-solid or fully liquid state while the other (steel) remains in the solid phase. The bonding mechanism relies on a combination of:
- Thermodynamic driving force — the liquid phase wets and penetrates the solid surface, forming atomic-level bonds at the interface
- Plastic deformation energy — applied deformation (via hydraulic pressure, explosive loading, or mechanical forging) breaks oxide films, promotes intimate contact, and drives interdiffusion
- Interfacial reaction control — the degree of deformation determines the thickness and continuity of intermetallic compounds (IMCs) such as Cu-Zn, Cu-Fe, or Cu-Fe-Si phases
The deformation amount is quantified as the percentage of true strain or displacement applied to the interface during the bonding event. Insufficient deformation results in incomplete oxide film removal and weak mechanical interlocking, while excessive deformation can cause delamination, cracking, or excessive intermetallic growth that embrittles the joint.
2. Category and Business Positioning
This research falls squarely within Cladding Technology Shanxi Co., Ltd.'s core competency in hydraulic explosive bonding and explosion welding processes, with secondary relevance to TIG/MIG weld overlay where controlled deformation of the molten pool and substrate influences dilution and interface quality.
Business positioning:
- Explosion Welding Route — Deformation is the primary bonding mechanism; the entry directly informs flyer plate velocity optimization and impact angle selection for copper-to-steel clad plates and pipes
- Hydraulic Explosive Bonding Route — The controlled hydraulic pressure combined with explosive initiation produces calibrated deformation; understanding deformation-interface relationships enables parameter windows to be defined and qualified
- TIG/MIG Weld Overlay Route — While less directly applicable, the principles of deformation-controlled bonding inform transition layer design where mechanical mixing and plastic deformation of the weld pool against the substrate are critical
3. Technical Purpose and Value
3.1 Research Objectives
The study establishes quantitative relationships between:
- Applied deformation (strain magnitude, displacement, velocity) and interfacial bond strength
- Deformation amount and intermetallic compound (IMC) layer thickness, morphology, and continuity
- Strain level and residual stress distribution at the copper-steel interface
- Deformation parameters and microstructural evolution (grain refinement, phase distribution)
3.2 Engineering Value
By defining the optimal deformation window for copper-steel bonding, this research enables:
- Predictable bond quality without relying solely on empirical trial-and-error
- Reduced scrap rates through tighter process parameter control
- Accelerated WPS (Welding Procedure Specification) qualification by providing theoretical justification for selected parameters
- Scalability from coupon-level testing to full-size production parts with confidence in interface integrity
4. Key Process Implementation Points
4.1 Critical Deformation Parameters
| Parameter | Typical Range (Copper-Steel) | Effect on Interface | Optimization Target |
|---|---|---|---|
| True strain (ε) | 0.3 – 1.5 | Higher strain = thinner IMC layer, better mechanical interlock | 0.5 – 1.0 for balanced strength and ductility |
| Strain rate | 10³ – 10⁶ s⁻¹ | Higher rate = dynamic recrystallization, finer grain at interface | Match to process (explosion: 10⁵–10⁶; hydraulic: 10²–10⁴) |
| Impact/Deformation velocity | 200 – 800 m/s (explosion) | Higher velocity = more turbulence, better oxide disruption | 350 – 600 m/s for Cu/Steel |
| Impact angle | 10° – 30° | Lower angle = higher velocity but less normal deformation | 15° – 25° for optimal bonding with controlled strain |
| Hydraulic pressure | 50 – 200 MPa | Higher pressure = greater normal deformation, compression of interface | 100 – 150 MPa for hydraulic explosive bonding |
| Preheating temperature | 200 – 600 °C | Higher temperature = reduced flow stress, easier deformation | 300 – 500 °C to minimize thermal distortion |
4.2 Interface Quality Assessment Methodology
- Macrograph examination — Etching with appropriate reagents to reveal bond line continuity and identify unbonded zones
- Metallographic analysis — Microstructural characterization of the interface, including IMC layer thickness measurement (target: < 20 μm for ductile response)
- Shear test — Perpendicular shear testing per ASTM E23 to quantify bond strength (target: ≥ 0.9 × UTS of weaker material)
- Peel test — 180° peel test per ASTM D1876 analog for clad plate configurations
- Hardness mapping — Vickers hardness traverse across the interface to detect brittle IMC zones
- SEM/EDS analysis — Elemental mapping to identify interdiffusion zones and phase distribution
4.3 Process Window Definition
The research establishes three critical deformation regimes:
- Sub-critical deformation (ε < 0.3): Incomplete oxide film fracture, partial bonding, unacceptable for pressure-containing applications
- Optimal deformation (0.5 ≤ ε ≤ 1.0): Full oxide disruption, controlled IMC formation (5–15 μm), excellent bond strength with retained ductility
- Over-deformation (ε > 1.5): Excessive IMC growth (> 25 μm), interface embrittlement, potential delamination under thermal cycling
5. Applicable Standards and Acceptance Criteria
5.1 Standards Referenced
| Standard | Scope | Relevance to Deformation-Controlled Bonding |
|---|---|---|
| ASTM A240 | Stainless steel plate specifications | Substrate material qualification for clad plates |
| ASTM B152 | Wrought copper sheet and plate | Clad material specification |
| ASTM E23 | Shear test method | Interface bond strength verification |
| ASTM E8/E8M | Tensile test method | Post-bond tensile performance |
| ASME BPV Section VIII Div. 1 | Pressure vessel code | Design and qualification requirements for bonded clad vessels |
| NB/T 47002 | Pressure vessel steel plate standards (China) | Base material qualification for domestic applications |
| GB/T 1197 | Explosion welding of metal plates (China) | Process specification for explosion-welded copper-steel clad |
| GB/T 29441 | Explosion-welded metal clad plates (China) | Product acceptance criteria |
| ISO 14224 | Explosion welding — general specifications | International qualification framework |
| NACE MR0175 / ISO 15156 | Sour service material requirements | Interface integrity for H₂S-containing environments |
| API 6A | Wellhead and Christmas tree equipment | Clad component qualification for oil/gas applications |
| ASME BPV Section IX | Welding qualification | WPS/PQR qualification framework for weld overlay transition layers |
5.2 Acceptance Criteria for Deformation-Controlled Copper-Steel Bonds
- Bond ratio: ≥ 95% bonded area per macrograph examination (ASTM A240/A270 methodology)
- Shear strength: ≥ 200 MPa for Cu/Steel interfaces (or ≥ 0.9 × UTS of softer material)
- IMC layer thickness: ≤ 20 μm continuous layer (to maintain ductility)
- No unbonded zones: Zero defects > 1 mm² in area per GB/T 29441
- Residual stress: Compressive or neutral at interface (no tensile residual stress > 50 MPa)
- Hardness gradient: No single hard zone > 400 HV within 50 μm of interface (avoids brittle fracture initiation)
6. Common Risks and Controls
| Risk | Cause (Deformation-Related) | Detection Method | Control Measure |
|---|---|---|---|
| Unbonded zones | Insufficient deformation (ε < 0.3); oxide film not disrupted | Macrograph etching, UT scanning | Verify deformation parameters; adjust impact velocity or hydraulic pressure |
| Interfacial cracking | Excessive deformation (ε > 1.5); brittle IMC overgrowth | Micrograph, MT, dye penetrant | Limit strain; control preheat temperature; reduce impact energy |
| Delamination under service | Thermal mismatch amplified by residual tensile stress from over-deformation | UT thickness measurement, peel test | Ensure compressive residual stress; limit deformation window |
| Microcracking in IMC layer | Brittle intermetallic phase (Cu₅Fe, Cu₃Fe) exceeds critical thickness | SEM fractography, hardness traverse | Control cooling rate post-bond; limit deformation to prevent excessive diffusion |
| Geometric distortion | Non-uniform deformation across large panels | Flatness measurement, coordinate metrology | Uniform explosive charge distribution; symmetric hydraulic loading |
| Subsurface voids | Trapped gas from incomplete oxide film fracture at localized low-deformation zones | UT phased array, radiographic testing | Ensure minimum uniform strain across entire bond area |
7. Application Across the Company's Three Technology Routes
7.1 Explosion Welding Applications
In explosion welding, the flyer plate (typically copper or copper alloy) is accelerated to high velocity (300–700 m/s) and impacted against the base plate (steel) at an angle of 10°–30°. The resulting plastic deformation at the impact zone is the primary bonding mechanism.
- Application: Copper-to-carbon steel clad plates for electrical bonding applications; copper-to-stainless steel for corrosion-resistant heat exchanger tubesheets; copper-to-alloy steel for pressure vessel linings
- Deformation control: The research findings directly inform flyer plate thickness selection, gap distance, explosive charge geometry, and impact angle to achieve target strain of 0.5–1.0
- Value proposition: Enables production of large-format clad plates (up to 6000 × 3000 mm) with guaranteed bond quality, eliminating the need for extensive coupon testing per production batch
7.2 Hydraulic Explosive Bonding Applications
Hydraulic explosive bonding combines controlled hydraulic pressure (50–200 MPa) with explosive initiation to achieve calibrated deformation. This hybrid approach offers superior control compared to pure explosion welding, particularly for complex geometries and smaller components.
- Application: Clad pipes for oil/gas well casings; bonded bushings and bearings for marine applications; copper-steel transition components for cryogenic service
- Deformation control: The research provides the basis for defining hydraulic pressure windows that produce optimal strain without requiring the extreme velocities of conventional explosion welding
- Value proposition: Reduced facility requirements compared to full-scale explosion welding; ability to bond smaller diameter tubes and complex cross-sections with deformation parameters validated by the research
7.3 TIG/MIG Weld Overlay Applications
While weld overlay does not rely on high-strain deformation as the primary bonding mechanism, the principles of deformation-controlled interface quality are directly applicable to transition layer design and weld pool dynamics.
- Application: Copper-alloy weld overlay on carbon steel substrates for electrical contact applications; transition layers between dissimilar metals where controlled dilution and mechanical mixing are required
- Deformation relevance: The mechanical stirring and plastic deformation of the weld pool against the substrate surface mirrors the deformation-bonding relationship studied; optimal wire feed rate, travel speed, and heat input create the equivalent of controlled strain at the fusion boundary
- Value proposition: Research findings on IMC control and interface embrittlement thresholds inform the selection of intermediate filler alloys and multi-pass strategies to prevent brittle phase formation in the weld interface
8. Contribution to Qualification Building and Customer Value
8.1 Qualification Framework Enhancement
This research directly supports the company's qualification program by:
- Providing theoretical justification for WPS parameter selection, reducing the number of qualification trials required
- Establishing deformation-based acceptance criteria that can be integrated into company-specific quality plans
- Enabling the development of proprietary process control charts that map deformation parameters to interface quality outcomes
- Supporting ASME BPV Section IX PQR documentation by correlating process variables to mechanical test results
8.2 Product Delivery Assurance
For production delivery, the research enables:
- Statistical process control (SPC) of deformation parameters during fabrication
- Predictive quality assessment — if deformation is within the qualified window, bond quality is guaranteed without destructive testing
- Reduced non-conformance rates and associated cost of rework
- Traceability documentation linking each production part to verified deformation parameters
8.3 Customer Value Proposition
Customers benefit through:
- Reliability: Quantified deformation windows ensure consistent bond performance in service, reducing risk of catastrophic failure
- Cost efficiency: Optimized parameters reduce material waste and processing time
- Design flexibility: Understanding deformation effects allows engineers to specify custom copper-steel clad configurations with confidence
- Compliance: Documentation of deformation-controlled processes supports regulatory compliance for pressure vessel, nuclear, and oil/gas applications per ASME, NB/T, and API standards
- Performance predictability: Customers receive products with documented interface properties (bond strength, IMC thickness, hardness profile) rather than unverified empirical results
9. Conclusion and Forward Path
The study on deformation effects on copper-steel solid-liquid composite bimetallic bonding interfaces represents a foundational contribution to Cladding Technology Shanxi Co., Ltd.'s technical capability. By establishing quantitative relationships between plastic deformation parameters and interface quality, the company gains:
- A scientifically-grounded process control framework applicable across all three technology routes
- Reduced qualification timelines and enhanced regulatory acceptance
- The ability to deliver high-performance copper-steel clad products with guaranteed interface integrity
- A competitive differentiator in markets requiring certified, traceable bimetallic bonding solutions
Future work should extend these findings to additional material pairs (aluminum-steel, titanium-steel, nickel-alloy-steel), develop digital twin models for real-time deformation monitoring during production, and integrate with machine learning algorithms for adaptive process control.