Titanium Clad Copper Plates: Explosion Bonding vs Extrusion Manufacturing Methods

What titanium-clad copper is

Titanium-clad copper (Ti-clad Cu) plate is a bimetallic composite plate consisting of:

• Cladding layer: Titanium (typically CP Grade 1 or Grade 2 per ASTM B265), 1-6 mm thick

• Base layer: Copper (C11000 electrolytic tough pitch, C12200 DHP, or C70600 Cu-Ni), 5-50 mm thick

• Bond: Metallurgical bond at the interface, formed by one of the production methods below

The composite combines the properties of both metals:

For applications that need both corrosion resistance and conductivity (or thermal conductivity), Ti-clad Cu is the cost-effective solution. Using solid titanium would be 5-10x more expensive for the same corrosion coverage. Using solid copper would fail in months for most chemical service.

Where Ti-clad Cu is used

The Ti-clad Cu plate market is driven by a few specific applications:

1. Electrochemical industry (largest market)

• Electrolytic copper refining (anode/cathode plates)

• Electrowinning of zinc, nickel, cobalt, manganese

• Chlor-alkali membrane cells (cathode side)

• Electrogalvanizing lines (anode)

• Electroplating anode baskets (in some designs)

The copper conducts current efficiently; the titanium resists the corrosive electrolyte (H₂SO₄ for zinc electrowinning, HCl for chlor-alkali).

2. Cathodic protection

• Impressed current cathodic protection (ICCP) anodes for marine structures

• Pipeline anode beds

• Offshore platform anode systems

The Ti-clad Cu plate provides the anode current distribution (copper conductor) with the anode-active Ti surface.

3. Chemical process equipment

• Heat exchanger tube sheets (Ti-clad Cu replacing solid Ti)

• Reactor covers and internals for sulfuric acid service

• Electrolysis cells for water treatment

• Pickling equipment for metal finishing

4. Power electronics and battery manufacturing

• Bipolar plates for fuel cells and electrolyzers (Ti-clad Cu)

• Battery can materials

• Cooling plates for power electronics

The bipolar plate application is emerging rapidly due to hydrogen economy growth. Ti-clad Cu replaces expensive Pt-coated Ti with cost-effective Ti-Cu composite.

The titanium-copper interface problem

Titanium and copper form a series of brittle intermetallic compounds in the Ti-Cu binary system:

These intermetallics make fusion welding of Ti-Cu essentially impossible. The melt pool during TIG, MIG, or laser welding of Ti-Cu always forms some intermetallic phase, which cracks under thermal stress on cooling. Even electron beam welding (which minimizes the heat-affected zone) cannot avoid intermetallic formation.

This is why Ti-Cu cannot be welded by conventional fusion processes. The bonding methods that work are those that either:

1. Avoid melting: Solid-state bonding (explosion bonding, roll bonding, diffusion bonding) — no melt pool, no intermetallic formation in the bulk bond

2. Minimize time at temperature: Very brief contact (explosion bonding with jet-cleaned surfaces, milliseconds of contact)

Four production methods compared

For Ti-Cu plate specifically, explosion bonding is the dominant process because:

1. It can join Ti-Cu without the intermetallic cracking that fusion welding produces

2. It produces plate sizes larger than standard mill rolling capability

3. It allows custom plate thicknesses not available in standard mill stock

4. The wavy interface provides mechanical interlocking in addition to metallurgical bond

Hot and cold roll bonding are used for smaller standard plate sizes where economics favor mill production.

Explosion bonding in detail

Explosion bonding (also called explosion welding or EXW) is a solid-state welding process that uses controlled explosive force to create a metallurgical bond between dissimilar metals.

Process

1. Preparation: Ti plate and Cu substrate surface prepared — typically shot blasted or machined to remove scale and oxides, then degreased

2. Assembly: Ti plate positioned parallel to Cu substrate, separated by a standoff distance (typically 1-3× the thinner plate thickness). Explosive powder or sheet placed on top of the Ti plate

3. Detonation: Explosive detonated at one edge of the Ti plate. The detonation wave propagates across the surface at 2,000-3,000 m/s

4. Collision: Ti plate is accelerated by the explosion toward the Cu substrate. The collision angle and velocity create a high-velocity oblique impact

5. Jet formation: The collision creates a metal jet that strips surface oxides and contaminants, exposing clean metal surfaces

6. Bond formation: Behind the jet, the clean metal surfaces come into contact under high pressure, forming a metallurgical bond

7. Wave formation: The bond interface has a characteristic wavy morphology due to the hydrodynamic instability of the collision process

Bond zone characteristics

• Wavy interface: Wavelength typically 0.5-5 mm, amplitude 0.05-0.5 mm. Provides mechanical interlocking.

• Melted zones: Small pockets (10-100 μm) of melted material trapped in the wave troughs. Cool rapidly to form fine-grained microstructure.

• Intermetallic layer: 1-5 μm thin layer at the bond interface, composed of Ti-Cu intermetallics. Brittle but very thin — does not compromise mechanical properties.

• Heat-affected zone: Minimal — the bulk material away from the bond is essentially unaffected by heat.

Process parameters

Parameter selection is critical. Wrong parameters produce:

• Too low velocity: No jet, no bond, plates separate

• Too high velocity: Excess melting, large brittle intermetallic zones, possible cracking

• Too low standoff: Insufficient jet formation, poor bond

• Too high standoff: Excessive deformation of flyer plate

Hot roll bonding

Hot roll bonding produces clad plate by heating both the cladding and base materials to elevated temperature, then passing them through a rolling mill together under high pressure.

Process

1. Surface preparation: both Ti and Cu surfaces cleaned and deoxidized (chemical or mechanical)

2. Assembly: Ti plate placed on Cu substrate (typically with spacer pins or edge welding)

3. Heating: assembly heated to 700-900°C in inert atmosphere or reducing atmosphere furnace

4. Rolling: heated assembly passed through roll stand. Reduction per pass 20-40%. Multiple passes may be used.

5. Bond formation: heat + pressure + deformation creates diffusion bond at interface

6. Cooling: controlled cooling to room temperature

Bond characteristics

• Bond strength: 180-250 MPa shear

• Interface: relatively flat (not wavy), with diffusion zone 5-20 μm thick

• Intermetallics: thicker than explosion bond (5-20 μm) due to higher temperature and longer time

• Heat-affected zone: significant (mm-scale in both Ti and Cu)

Limitations for Ti-Cu

Hot roll bonding of Ti-Cu is challenging because:

• Ti-Cu eutectic temperature is ~880°C. Above this, the interface melts.

• Rolling must be done at temperatures below the eutectic (typically 700-850°C)

• Intermetallic formation is significant at these temperatures

• Bond quality is variable and depends on precise temperature control

For Ti-Cu plate, hot roll bonding is less reliable than explosion bonding. It is used when plate sizes are within standard mill capability and cost pressure exists.

Cold roll bonding

Cold roll bonding produces clad plate at room temperature using high reduction in a single pass or few passes.

Process

1. Surface preparation: critical step. Both surfaces degreased and brushed to create a "fresh" surface layer

2. Assembly: Ti and Cu surfaces brought into contact

3. Rolling: assembly passed through roll stand with high reduction (50-70% in single pass)

4. Bond formation: the high reduction breaks up surface oxides and exposes fresh metal; the clean metal surfaces bond under pressure

5. Annealing: optional heat treatment at moderate temperature (300-500°C) to strengthen bond via diffusion

Bond characteristics

• Bond strength: 140-180 MPa shear (lower than explosion or hot roll)

• Interface: relatively flat

• Intermetallics: minimal (cold working limits diffusion)

• Heat-affected zone: minimal

• Work hardening: significant (cold rolling hardens both metals)

Limitations for Ti-Cu

Cold roll bonding of Ti-Cu is difficult because:

• Ti has limited ductility at room temperature compared to Cu

• High reduction in single pass can crack Ti

• Multiple passes with intermediate annealing are needed

• Bond strength is lower than other methods

For Ti-Cu plate, cold roll bonding is used for thin sheets (typically < 3 mm total thickness) where economics favor mass production and bond strength requirements are modest.

Extrusion cladding

Extrusion cladding produces clad products by heating a clad billet and forcing it through a die. The process is used for tube and rod products, not plate.

Process

1. Billet preparation: Ti tube inserted into Cu billet (or vice versa, depending on design)

2. Heating: assembly heated to 700-850°C

3. Extrusion: billet forced through die using hydraulic press (typical pressure: 700-1500 MPa)

4. Bond formation: pressure + temperature + reduction creates metallurgical bond

5. Cooling: controlled cooling to room temperature

Bond characteristics

• Bond strength: excellent in extrusion direction (200-300 MPa shear)

• Anisotropic: bond may be weaker in transverse direction

• Interface: relatively flat with diffusion zone 5-15 μm

• Limited to tube, rod, and simple profile shapes

For Ti-Cu plate, extrusion cladding is not applicable. It is used for Ti-Cu tube products (e.g., for chemical processing heat exchangers).

ASTM B898 and specifications

The primary specification for reactive and refractory metal clad plate in the US is:

ASTM B898 requirements for Ti-Cu clad plate

• Base metal: Must meet base metal specification (e.g., ASTM B152 for C110 copper)

• Cladding metal: Must meet cladding specification (e.g., ASTM B265 Grade 2 titanium)

• Bond integrity: 100% ultrasonic testing of bond area per ASTM A578 or equivalent

• Shear strength: Minimum 140 MPa (20 ksi) per ASTM A264 or equivalent

• Bend test: 180° bend around 3× thickness mandrel without bond separation

• Dimensional tolerances: Per base metal spec unless otherwise agreed

A real Ti-clad Cu case

Scenario

A zinc refinery was replacing the cathodes in its electrowinning cells. The original design used solid titanium cathode plates (3 mm thick). The new design considered Ti-clad Cu plate (2 mm Ti on 8 mm Cu) as a cost reduction alternative.

The decision

The refinery performed qualification testing on Ti-clad Cu plates from three suppliers:

• Supplier A: Explosion bonded plate, ASTM B898 compliant, $1,200 per plate

• Supplier B: Hot roll bonded plate, modified B898, $950 per plate

• Supplier C: Explosion bonded plate, B898 with extra UT inspection, $1,450 per plate

Testing included:

1. Bond shear strength per ASTM A264

2. Ultrasonic bond inspection per ASTM A578

3. Bend test per ASTM B898

4. Service simulation: 30-day test in actual zinc electrowinning electrolyte (ZnSO₄/H₂SO₄, 35°C, 500 A/m²)

Results

• Supplier A passed all tests with margin

• Supplier B failed bend test (bond separation at 4× thickness bend radius)

• Supplier C passed all tests with significant margin (highest bond strength)

The refinery selected Supplier A based on value (acceptable quality, lower cost than C). The qualification cycle took 12 weeks.

Outcome

After 18 months of service:

• Zero Ti-clad Cu plate failures

• Cost savings: $1,800 per cathode vs solid Ti (refinery has 4,000 cathodes)

• Total savings: $7.2 million on the cathode replacement

• Service life projection: 8-12 years (vs 6-8 years for previous solid Ti)

The Cu base provides structural rigidity that the thinner Ti alone could not — improving cathode flatness and reducing zinc deposit irregularities.

Frequently asked questions

What is titanium clad copper plate?

Titanium clad copper plate is a composite plate consisting of a titanium layer metallurgically bonded to a copper substrate. The titanium provides corrosion resistance in chloride and oxidizing environments; the copper provides electrical and thermal conductivity, structural strength, and cost reduction. The bond is metallurgical (atomic-level diffusion), not just mechanical, which is essential for service under thermal cycling, mechanical load, and electrical current. Common configurations: titanium 2-6 mm on copper 5-50 mm thick, in plate or sheet form.

What is explosion bonding of titanium to copper?

Explosion bonding (also called explosion welding or EXW) uses the energy of a controlled explosion to drive the titanium plate into the copper substrate at high velocity. The collision creates a jet of metal that strips surface oxides and contaminants, exposing clean metal that bonds under pressure. The result is a metallurgical bond with characteristic wavy interface morphology. Explosion bonding can join dissimilar metals that cannot be welded by fusion processes (because of brittle intermetallic formation), including titanium to copper, titanium to steel, and aluminum to steel.

What is ASTM B898 for clad plate?

ASTM B898 is the Standard Specification for Reactive and Refractory Metal Clad Plate. It covers titanium-clad steel, titanium-clad copper, zirconium-clad steel, and other reactive/refractory metal clad combinations. The standard specifies base metal, clad metal, bond integrity requirements, mechanical properties, and testing (ultrasonic bond testing, shear strength). Most industrial and chemical process specifications reference B898 for clad plate requirements.

Can titanium and copper be welded together?

Not by conventional fusion welding (TIG, MIG, laser). Titanium and copper form brittle intermetallic compounds (TiCu2, TiCu, Ti2Cu) in the melt pool. These crack under thermal stress on cooling, making fusion welds unreliable. Solid-state bonding methods (explosion bonding, hot/cold roll bonding, diffusion bonding) avoid the melt pool and produce reliable metallurgical bonds. For joining clad plate components, the titanium layer is welded to other titanium and the copper layer to other copper — never trying to weld across the Ti-Cu interface.

What is the cost of Ti-clad Cu vs solid titanium?

For the same corrosion coverage, Ti-clad Cu plate (3 mm Ti on 20 mm Cu) costs 50-60% of solid titanium plate (23 mm thick). The savings come from the lower-cost copper replacing the majority of the section thickness. For applications needing only 2-3 mm of Ti corrosion coverage, the savings are even larger — clad plate can be 30-40% of solid Ti cost. The trade-off is more complex supply chain (specialized clad plate manufacturer vs Ti mill).

Where can I buy titanium-clad copper plate?

Ti-clad Cu plate is produced by specialized clad metal manufacturers who operate explosion bonding facilities. Major suppliers include: DMC (Dynamic Materials Corporation, US), AMETEK (US), Baoji Clad Metals (China), and several European and Japanese suppliers. Lead times for non-standard sizes are typically 8-16 weeks; standard sizes may be available in 4-8 weeks. Specify ASTM B898 compliance and request ultrasonic bond inspection, shear strength, and bend test reports with each shipment.