Numeral Simulation and Experimental Verification of Ti-Al Explosion Welding Interface Formation Mechanism

1. Definition and Fundamental Principles

1.1 Overview of Ti-Al Explosion Welding

Titanium-aluminum (Ti-Al) explosion welding is a solid-state joining process in which a titanium flyer plate is accelerated to high velocity (typically 300–600 m/s) and collides with an aluminum base plate at a controlled oblique angle (usually 10°–15°). The kinetic energy of impact is converted into intense plastic deformation, shock compression, and jet formation at the interface, resulting in a metallurgical bond without melting. The resulting clad product combines the high specific strength and corrosion resistance of titanium with the thermal conductivity, formability, and cost-effectiveness of aluminum, making it highly valuable in aerospace, marine, and chemical processing industries.

1.2 Interface Formation Mechanism

The interface in Ti-Al explosion welding is formed through a complex sequence of physical phenomena including:

• Shock compression: The incident and reflected shock waves generate hydrodynamic pressures exceeding the yield strength of both materials, enabling plastic flow at the collision zone.
• Tangential velocity jetting: Material ejected from the collision point forms a characteristic "jet" that seals the interface against oxidized surface films.
• Vortex instability (Kelvin-Helmholtz): The high-velocity shear between the flyer and base materials generates periodic vortex structures, producing the characteristic wavy interface morphology.
• Dynamic recrystallization: Severe plastic deformation at the interface induces grain refinement and the formation of intermetallic compounds (e.g., TiAl, TiAl₂, Ti₃Al) in a controlled manner.

Understanding these mechanisms is critical because the wavy interface geometry, vortex amplitude, wavelength, and intermetallic layer thickness directly govern the mechanical properties, fatigue resistance, and corrosion performance of the final clad product.

1.3 Role of Numerical Simulation

Numerical simulation—primarily using Arbitrary Lagrangian-Eulerian (ALE) or Smoothed Particle Hydrodynamics (SPH) methods—enables engineers to model the full dynamic process from initial acceleration through collision, interface formation, and post-impact relaxation. Simulation provides:

• Visualization of subsurface stress fields, strain rates, and temperature distributions inaccessible to direct measurement.
• Parametric studies on collision angle, flyer velocity, material properties, and explosive charge configuration.
• Predictive capability for interface morphology (vortex amplitude, wavelength, phase) as a function of process parameters.
• Optimization of window sizes, overlap ratios, and charge distributions prior to physical trials.

2. Category and Business Positioning

2.1 Technical Knowledge Base Development

This entry represents a foundational R&D capability within Cladding Technology Shanxi Co., Ltd.'s explosion welding technology route. It is not merely a process execution capability but a mechanistic understanding capability that underpins:

• Process qualification and WPS development for novel material combinations.
• Defect root-cause analysis and corrective action in production.
• Technical proposals and feasibility studies for customer-specific clad products.
• Training and knowledge transfer within the engineering team.

2.2 Strategic Value in the Company's Technology Portfolio

The company operates three distinct technology routes: TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding. The Ti-Al explosion welding interface study sits at the intersection of scientific rigor and manufacturing practicality, providing the theoretical grounding that differentiates the company from purely empirical competitors. This knowledge asset is particularly valuable for:

• Qualification of new material systems (e.g., Ti-6Al-4V / 6061-T6, Ti-Gr.2 / 5083-O) without prohibitive trial-and-error costs.
• Responding to customer inquiries with data-driven justification for process capability.
• Supporting NDT interpretation by correlating interface morphology with ultrasonic and radiographic signals.

3. Technical Purpose and Value

3.1 Primary Objectives

1. Establish a validated simulation model that accurately reproduces the interface morphology observed in physical Ti-Al explosion welds.
2. Identify critical process parameters (collision velocity, angle, material temperature) that govern interface quality and mechanical performance.
3. Define acceptance windows for vortex amplitude, wavelength, and intermetallic thickness that ensure bond strength meets or exceeds applicable standards.
4. Reduce qualification cost and timeline by using simulation to narrow the experimental search space before physical trials.

3.2 Value to Product Delivery

By correlating simulation predictions with experimental results, the company can:

• Predict bond quality prior to full-scale production runs, minimizing scrap rates.
• Justify design margins in clad component specifications with quantitative interface data.
• Provide customers with technical documentation demonstrating process understanding beyond mere compliance testing.
• Accelerate the qualification of new material combinations for emerging applications (e.g., hydrogen storage vessels, cryogenic heat exchangers).

4. Key Process and Implementation Points

4.1 Numerical Simulation Methodology

The numerical simulation of Ti-Al explosion welding interface formation typically involves the following stages:

1. Material constitutive modeling: Selection of appropriate plasticity models (Johnson-Cook, modified Cowper-Symonds, or split-Hopkinson pressure bar calibrated models) for both titanium and aluminum, accounting for strain rate sensitivity and adiabatic heating.
2. Mesh generation: ALE or SPH discretization with sufficient resolution at the collision interface (element size ≤ 0.1 mm at the interface zone).
3. Boundary conditions: Flyer plate initial velocity (300–600 m/s), collision angle (10°–15°), and explosive charge pressure profile.
4. Time integration: Explicit dynamic solver with time step controlled by Courant criterion (CFL ≤ 0.9).
5. Post-processing: Extraction of interface trajectory, stress/strain fields, temperature distributions, and vortex morphology metrics.

4.2 Critical Simulation Parameters

Parameter	Typical Range	Effect on Interface	Verification Method
Flyer collision velocity	300–600 m/s	Higher velocity → increased vortex amplitude, potential over-bonding	Hopkinson bar, photonic streak camera
Collision angle	10°–15°	Lower angle → longer interface, higher jet velocity; too low → poor bonding	High-speed photography, X-ray tomography
Strain rate at interface	10³–10⁵ s⁻¹	Governs adiabatic shear localization and intermetallic formation	FEA post-processing, TEM analysis
Peak contact pressure	5–20 GPa	Determines plastic flow extent and oxide film disruption	Shock impedance matching, FEA
Interface temperature	200–600 °C (adiabatic)	Controls intermetallic growth kinetics (Ti-Al phase formation)	Thermocouple (limited), simulation, DSC
Overlap ratio	1.0–1.5 (flyer/base width)	Affects stress distribution and residual deformation	Geometric measurement, simulation

4.3 Experimental Verification Protocol

Physical verification of the simulation model requires a systematic experimental campaign:

1. Flat-bar qualification welds: Standardized coupon dimensions (typically 200 mm × 50 mm × 3–6 mm) welded at controlled parameters matching simulation inputs.
2. Interface morphology characterization: Metallographic cross-sectioning with optical microscopy (OM) and scanning electron microscopy (SEM) to measure vortex amplitude (A), wavelength (λ), and amplitude-to-wavelength ratio (A/λ).
3. Mechanical property testing: Shear strength (per ASTM E203 or equivalent), peel strength, tensile bond strength, and fatigue performance.
4. Microstructural analysis: Energy-dispersive X-ray spectroscopy (EDS) mapping for intermetallic identification; transmission electron microscopy (TEM) for grain structure and phase identification at the interface.
5. Model validation: Comparison of simulated interface trajectory (vortex amplitude, wavelength) with measured metallographic data; acceptable deviation typically ≤ 20% for qualitative agreement and ≤ 10% for quantitative model qualification.

4.4 Interface Morphology Acceptance Criteria

Morphology Parameter	Acceptance Range	Indication	Related Standard/Method
Vortex amplitude (A)	5–50 μm (material-dependent)	Confirms adequate plastic flow and jet formation	ASTM E203, internal specification
Wavelength (λ)	50–500 μm	Indicates stable Kelvin-Helmholtz instability	SEM measurement, FEA correlation
A/λ ratio	0.05–0.3	Optimal bonding efficiency indicator	Internal qualification criteria
Intermetallic layer thickness	≤ 5 μm (for Ti/Al, unless designed)	Excessive intermetallic → embrittlement risk	SEM/EDS, XRD
Unbonded area (per unit length)	≤ 5% (per applicable standard)	Direct measure of bond quality	ASTM E203, GB/T 15174
Shear strength	≥ 100 MPa (material-specific)	Confirms mechanical integrity of bond	ASTM E203, GB/T 15174

5. Applicable Standards and Acceptance Criteria

5.1 Welding and Cladding Standards

• GB/T 15174-2016 — Welded and cladded steel plates, pipes and fittings — Terminology (Chinese national standard for clad product definitions)
• GB/T 18106-2008 — Explosion welded plates — Technical conditions
• ASTM E203 — Standard Test Method for Bond Strength of Clad Materials by Shear
• ASTM A414/A414M — Specification for Composite Plate of Steel with Clad
• ASME BPV Section II, Part D — Material specifications for clad components in pressure vessels
• ASME BPV Section VIII, Div. 1, UCS-66 — Clad materials qualification requirements
• NB/T 47014 — Qualification rules for welding procedures and welders in pressure vessel fabrication
• ISO 18263 — Explosion welding — Vocabulary
• ISO 18265 — Explosion welding — General requirements

5.2 Material-Specific Standards for Ti/Al Systems

• ASTM B265 — Specification for Titanium and Titanium Alloy Flat, Sheet, and Strip
• ASTM B348 — Specification for Wrought Titanium and Titanium Alloy Products
• GB/T 3621 — Forged products of titanium and titanium alloys
• ASTM B209 — Specification for Aluminum and Aluminum Alloy Sheet and Plate
• GB/T 3880 — Wrought aluminum and aluminum alloy products

5.3 Non-Destructive Testing Standards

• GB/T 15174 — NDT methods for clad products (ultrasonic, radiographic)
• ASTM E164 — Standard specification for liquid penetrant inspection materials
• ASME BPV Section V — Non-destructive examination methods for pressure vessels
• NB/T 47013 — Non-destructive testing methods for pressure vessels and components

5.4 Simulation and Computational Standards

• ISO 10993 — General requirements for finite element analysis in structural engineering (analogous application to dynamic simulation validation)
• ASTM E290 — Standard practice for evaluating computer programs used for engineering calculations

6. Common Risks and Controls

6.1 Technical Risks in Simulation and Experimentation

Risk	Description	Mitigation/Control
Constitutive model inaccuracy	Material models not calibrated for high strain rates (10³–10⁵ s⁻¹) lead to incorrect prediction of interface morphology	Calibrate models using Split Hopkinson Pressure Bar (SHPB) data; perform sensitivity analysis on model parameters
Mesh dependency in ALE simulations	Artificial stress concentrations at element boundaries may distort predicted vortex morphology	Perform mesh convergence studies; use SPH as complementary method; validate against known experimental data
Intermetallic overgrowth prediction	Simulation may underestimate or overestimate Ti-Al intermetallic formation, leading to incorrect brittleness assessment	Incorporate diffusion kinetics models; validate with heat treatment experiments; maintain intermetallic thickness ≤ 5 μm
Simulation-experiment mismatch	Predicted interface morphology does not match measured results, invalidating model predictions	Establish quantitative acceptance criteria (≤ 20% deviation); iterate model parameters; document all assumptions
Scale-up errors	Parameters validated on coupon scale may not translate directly to production-scale plates	Perform scale-up studies; account for charge distribution non-uniformity; maintain qualification welds at production scale
Environmental contamination	Oxide films on flyer/base surfaces disrupt bonding and create unbonded zones	Implement surface preparation protocols (grinding, cleaning); include oxide layer in simulation model; monitor cleanliness

6.2 Quality and Compliance Risks

• Inadequate WPS qualification: Without validated simulation-to-experiment correlation, Welding Procedure Specifications may not be robust across the full parameter window. Control: Require simulation support for all new WPS submissions per NB/T 47014.
• Insufficient NDT coverage: Interface defects (unbonded areas, cracks) may be missed if NDT methods are not calibrated to the specific interface morphology. Control: Develop NDT procedures specific to Ti-Al interfaces, validated against destructive test coupons.
• Traceability gaps: Simulation models and experimental data must be traceable to specific production batches. Control: Implement document control per ISO 9001 requirements; maintain simulation input/output archives linked to production records.

7. Application Across the Company's Three Technology Routes

7.1 Explosion Welding Route (Primary Application)

This is the direct application domain. The simulation and experimental verification of Ti-Al interface formation mechanisms directly supports:

• Process optimization: Determining optimal collision velocity and angle for specific Ti/Al material combinations to maximize bond quality while minimizing intermetallic formation.
• Window and overlap design: Predicting the required overlap ratio and charge distribution to achieve uniform bonding across the full plate width.
• Defect prediction and prevention: Identifying process parameter combinations that lead to over-bonding, under-bonding, or excessive intermetallic growth before physical trials.
• New material qualification: Rapidly extending knowledge from well-characterized Ti-6Al-4V/6061 systems to novel combinations (e.g., Ti-Gr.2/7075, Ti-α-β/2024) using validated simulation models.

7.2 Hydraulic Explosive Bonding Route (Secondary Application)

While hydraulic explosive bonding (HEB) uses water as the explosive medium rather than chemical explosives, the fundamental interface formation mechanisms are analogous. The Ti-Al interface knowledge contributes to:

• Water jet velocity optimization: Understanding the minimum velocity required for plastic flow and oxide disruption at the Ti-Al interface.
• Interface morphology prediction: Applying vortex instability principles from explosion welding to predict HEB interface characteristics.
• Material compatibility assessment: Determining whether Ti-Al combinations are suitable for HEB based on interface formation criteria established through explosion welding research.
• Comparison and selection: Providing data-driven basis for customers to select between explosion welding and HEB for specific Ti/Al applications based on predicted interface quality.

7.3 TIG/MIG Weld Overlay Route (Tertiary Application)

While weld overlay is fundamentally a melting-based process, the Ti-Al interface formation knowledge contributes indirectly:

• Intermetallic understanding: Knowledge of Ti-Al intermetallic formation kinetics from explosion welding research informs the selection of filler metals and heat input parameters for TIG/MIG overlay of Ti on Al or vice versa.
• Transition layer design: Understanding of diffusion and reaction layers at the Ti-Al interface guides the design of multi-layer transition weld overlays to manage intermetallic thickness.
• Post-weld heat treatment: Knowledge of intermetallic growth kinetics from explosion welding supports the development of post-weld heat treatment schedules to control brittle phase formation.
• Cross-contamination control: Understanding of how Ti and Al interact under thermal cycling informs dilution control strategies in weld overlay applications.

8. Contribution to Qualification Building and Customer Value

8.1 Qualification Building

The systematic study of Ti-Al explosion welding interface formation mechanisms directly supports the company's qualification infrastructure:

1. WPS Development: Each new Ti/Al material combination requires a qualified Welding Procedure Specification. Simulation reduces the number of physical trials needed from 15–20 to 5–8, accelerating qualification timelines by 40–60%.
2. Equipment Qualification: Understanding of how collision parameters affect interface quality enables the definition of equipment acceptance criteria (velocity control accuracy, angle stability, charge uniformity).
3. Personnel Qualification: The knowledge base derived from this study supports the training and certification of engineers and technicians in Ti-Al explosion welding, meeting NB/T 47014 requirements for qualified welding procedure designers.
4. Product Certification: For pressure vessel and nuclear applications (ASME BPV, RCC-M), documented process understanding with simulation support is increasingly required to demonstrate process control capability.

8.2 Customer Value Proposition

This technical capability translates directly into customer value:

• Reduced time-to-market: Simulation-guided process development accelerates product qualification, enabling customers to bring Ti/Al clad components to production faster.
• Enhanced reliability: Mechanistic understanding of interface formation enables the design of clad products with guaranteed bond quality, reducing field failure risk.
• Technical partnership: The ability to provide simulation-based design support positions the company as a true engineering partner rather than a pure manufacturer.
• Cost optimization: By predicting the optimal process window, the company can minimize material waste and rework, passing cost savings to customers.
• Customization capability: Simulation enables the tailoring of interface morphology (vortex amplitude, wavelength) to specific customer requirements for fatigue, corrosion, or thermal cycling performance.

8.3 Competitive Differentiation

In the global explosion welding market, most competitors rely on empirical trial-and-error approaches. The company's investment in numerical simulation and experimental verification of interface formation mechanisms provides:

• A predictive capability that reduces qualification risk and cost.
• A knowledge moat that is difficult for competitors to replicate without sustained R&D investment.
• A technical credibility that supports premium positioning in high-value markets (aerospace, nuclear, defense).
• A scalable methodology that can be extended to other material systems (steel/Ti, steel/Al, Cu/Al, etc.) to build a comprehensive simulation library.

9. Implementation Recommendations

9.1 Short-Term Actions (0–6 Months)

1. Complete the simulation model validation against existing Ti-6Al-4V/6061-T6 explosion weld data.
2. Establish quantitative acceptance criteria for simulation-experiment correlation (target: ≤ 15% deviation in vortex amplitude prediction).
3. Develop a standardized simulation input template and output reporting format for all Ti/Al qualification projects.
4. Train 2–3 engineers in ALE/SPH simulation methods specific to explosion welding.

9.2 Medium-Term Actions (6–18 Months)

1. Extend the validated model to additional Ti/Al material combinations (Ti-Gr.2/5083, Ti-α-β/7075).
2. Develop a parametric database linking process inputs to interface morphology outputs for rapid WPS development.
3. Integrate simulation capabilities with the company's NDT procedures to predict detectability of interface defects.
4. Pursue publication of simulation methodology in peer-reviewed journals to establish technical authority.

9.3 Long-Term Actions (18–36 Months)

1. Develop a proprietary simulation software module optimized for explosion welding qualification.
2. Extend simulation capabilities to multi-layer clad structures and complex geometries (pipes, shells).
3. Establish a simulation-based digital twin of the explosion welding process for real-time process monitoring and control.
4. Build a comprehensive material interaction database covering all commercially relevant metal combinations.

10. Conclusion

The study of Ti-Al explosion welding interface formation mechanisms through numerical simulation and experimental verification represents a critical intellectual asset for Cladding Technology Shanxi Co., Ltd. It transforms the company's explosion welding capability from a purely empirical, trial-based process into a scientifically grounded, predictively capable engineering discipline. This capability directly supports qualification building, product delivery reliability, and customer value creation across all three technology routes—explosion welding, hydraulic explosive bonding, and TIG/MIG weld overlay. By maintaining and extending this knowledge base, the company positions itself as a technology leader in the global explosion welding and cladding market, capable of delivering high-reliability Ti/Al clad products for the most demanding industrial applications.