What is CUPAL?

CUPAL definition {#cupal-definition}

CUPAL is a cold-roll-bonded copper-aluminum bimetal composite material: 70% aluminum (AL 99.5 / Werkstoff-Nr. 3.0255) and 30% copper (E1-Cu58 / Werkstoff-Nr. 2.0065), diffusion-welded into one inseparable layer. Not an alloy — each metal layer retains its own physical and chemical properties. Density 4.6 g/cm³, electrical conductivity 41.9 m/(Ω·mm²), bond strength 70–110 N/cm band-width. CUPAL eliminates galvanic corrosion at bolted joints where aluminum and copper conductors meet.

The name CUPAL comes from CU (copper) and AL (aluminum). The material is supplied through our German source partner, WMH Westdeutscher Metall-Handel GmbH (ISO 9001:2015 certified). The two metal layers are inseparably cold-roll-bonded and diffusion-welded, yet each retains its own physical and chemical properties.

Why it matters

When copper and aluminum conductors are joined directly, the electrochemical potential difference between the two metals causes galvanic corrosion. This corrosion loosens the joint over time, raises contact resistance, can cause temperature rise, and in the extreme can become a fire risk.

CUPAL solves this by placing the dissimilar-metal interface inside the composite, where it is protected from environmental exposure. Each outer face contacts its own metal — copper face to copper conductor, aluminum face to aluminum conductor.

Composition and structure

CUPAL consists of 70% aluminum (carrier layer) and 30% copper (clad layer). The aluminum component is AL 99.5 (Werkstoff-Nr. 3.0255, Alloy 1050A); the copper component is E1-Cu58 (Werkstoff-Nr. 2.0065, Cu 99.9% purity).

The two metal layers cannot be separated — the bond strength achieved during manufacturing is 70–110 N/cm band-width, an exceptionally strong, permanent connection.

Manufacturing process: cold-roll-bonding

CUPAL production proceeds in multiple stages:

1. Surface preparation: both the aluminum and copper surfaces are conditioned for optimal adhesion.
2. Cold-roll-bonding (Kaltwalzplattieren): the prepared sheets pass through a rolling stand under extreme pressure, bonding at room temperature. This cold process distinguishes CUPAL from hot-rolled bimetal products.
3. Stress relief: high-pressure rolling causes significant work-hardening in both metals; controlled heat treatment restores the desired material properties and formability.
4. Diffusion welding: during heat treatment, a diffusion-welding process occurs at the Al–Cu interface, substantially improving bond strength.
5. Controlled intermetallic layer: annealing time and temperature are precisely limited to prevent uncontrolled formation of an alloy layer (Legierungsschichtbildung). The resulting intermetallic layer is only sub-microscopic in thickness, preventing layer separation during cold forming.

Technical properties

Surface hardness

Key benefits

Weight savings

At 4.6 g/cm³, CUPAL is approximately 49% lighter than pure copper (8.96 g/cm³). This is a significant advantage wherever weight matters — switchgear, EV fast-charger Cu/Al transitions, overhead-line applications.

Galvanic corrosion prevention

CUPAL solves the galvanic-corrosion problem of direct copper–aluminum contact. The dissimilar-metal interface lives inside the composite, protected from atmospheric exposure.

Excellent conductivity

At 41.9 m/(Ohm·mm²), CUPAL needs only a 1.41× cross-section relative to pure copper to deliver equivalent ampacity. At high frequencies the difference shrinks further due to skin effect.

Broadly machinable

CUPAL accepts almost every cold-forming process: bending, deep drawing, riveting, stamping, profiling. The copper side is soft-solderable and accepts standard galvanic coatings.

Application areas

• Switchgear and distribution boards: washers and transition plates between Al busbars and Cu cable lugs.
• Cable lugs and connectors: CUPAL washers M6–M20.
• Lightning protection: CUPAL strips for transitions between dissimilar metals.
• Renewable energy: Cu/Al transition points in PV inverters, wind-turbine generator cabinets, BESS systems.
• EV infrastructure: Cu/Al transition elements in EV fast-charger cabinets (not cell-level use).
• High-frequency engineering: components in capacitors and transmitter/receiver assemblies.
• Machinery and equipment manufacturing: enclosures, vessels, piping.

Available product forms

CUPAL sheet is available in 0.5, 1.0, 1.5, and 2.0 mm thicknesses, in the standard 500 × 2000 mm size. Pre-cut washers (M6–M20), strips (500 × 40 mm) and custom shapes (discs, strips, rectangles, arbitrary contours) are also available.

CUPAL material is supplied by our German partner, WMH Westdeutscher Metall-Handel GmbH — ISO 9001:2015 certified supplier quality management, consistent material quality across shipments.

Further questions? Request a quote or write to us via chat — we respond within minutes on business days.