Aluminium Brazing Sheet & Clad Coil

What is aluminium brazing sheet?

Brazing sheet was developed so that a whole heat exchanger can be joined in one furnace cycle. Instead of adding filler at each joint, the filler is rolled onto the sheet itself. Parts are stamped, formed and assembled, then heated to about 600 °C; the cladding melts, runs into every joint by capillary action, and solidifies into fillets.

The core alloy melts at a higher temperature than the cladding, typically about 615 – 655 °C depending on alloy, so it stays solid and carries the load. The cladding, with 7 – 13 % silicon, begins to melt at 577 °C. That narrow gap between filler melting and core melting is why aluminium brazing needs accurate furnace control.

This page covers the thicker end of the range: sheet and coil from roughly 0.4 mm upwards, used for headers, manifolds, tanks, plates, side supports, flat-tube stock and cold plates. Thin fin foil has its own considerations, covered in our brazing foil guide; narrow slit material is covered under brazing strip.

Single, double and three-layer structures

7072 is a sacrificial liner (Al-1 % Zn), not a filler. Structures are written from one face to the other.

Core and cladding alloys

Composition values are Aluminum Association limits for the main alloying elements. Many heat exchanger makers use modified, proprietary "long-life" cores with controlled copper, titanium and manganese to resist pitting and silicon penetration; specify the properties you need and the supplier proposes a matching core.

How brazing sheet is made

Brazing sheet starts as separate slabs. A thick core ingot is scalped, and thinner liner plates of filler alloy (and of 7072 where needed) are rolled to a precise thickness. The liner plates are laid on the core, strapped or welded at the edges, preheated and hot-rolled. The first passes press the layers together so hard that the oxide films break and the metals bond across the interface, forming a single composite slab.

The composite is then hot-rolled to coil and cold-rolled to final gauge, with intermediate and final anneals to set the temper. Because every layer is reduced in the same proportion, the clad ratio set by the starting plate thickness is carried through to the finished sheet. That is why clad ratio is specified as a percentage rather than as an absolute thickness: a 10 % clad 1.0 mm sheet carries about 0.1 mm of filler per clad face.

Edge trimming removes the zone where the cladding thins at the slab edges, and finished coils are slit or cut to length. Quality checks on the cross-section confirm that the clad layer is continuous and within tolerance across the width.

Mechanical and thermal properties before and after brazing

A brazing cycle at about 600 °C fully anneals non-heat-treatable cores. Whatever temper the sheet arrives in, a 3003 core ends up close to its O-temper properties after brazing, so design strength should be based on post-braze values. Heat-treatable 6951 cores are different: they are solution-treated by the brazing cycle and gain strength by natural or artificial ageing afterwards.

Typical values for unclad 3003 from ASM data. Clad composites differ slightly; supplied properties are reported on the mill certificate, and post-braze properties can be tested on request after a simulated brazing cycle.

Common delivery tempers are O (for deep drawing and complex stamping), H24 (partially annealed, a balance of strength and elongation) and H14 (half-hard, for flat parts and better handling). Because brazing anneals the core anyway, choose the temper for how the part is formed, not for final strength.

Supply range and weights

Weight is calculated with a composite density of 2.73 g/cm³, close for 3xxx cores with Al-Si cladding.

How to select brazing sheet, step by step

1. Identify faces that brazeOne face, both faces, or one braze face plus a coolant face. This sets single, double or three-layer structure.
2. Match the brazing processCAB with standard flux needs a low-magnesium core and 4343 or 4045 cladding. Vacuum brazing uses Mg-bearing 4004 or 4104 cladding and tolerates 6951 cores.
3. Plan corrosion protectionFor coolant circuits, a 7072 liner or zinc-bearing core makes the inner surface sacrificial and slows pitting through the wall.
4. Size for post-braze strengthUse post-braze properties for burst and fatigue calculations. If 3003 is too weak, consider 3005, long-life cores or 6951.
5. Set clad ratioThicker plates with larger joints often use 10 – 15 %; thinner tube stock uses less to limit erosion of the core.
6. Choose temper for formingO for deep draws, H24 for moderate forming, H14 for flat or lightly formed parts.

Tolerances, testing and common mistakes

• Thickness and flatness to EN 485-4 / ASTM B209 or tighter by agreement
• Clad ratio per side with tolerance, measured on metallographic cross-sections
• Chemistry of core and cladding on the EN 10204 3.1 mill certificate
• Mechanical properties as delivered, plus post-braze tests if required
• Brazeability, erosion and sag tests on request for critical parts
• Surface cleanliness: low residual oil for consistent flux adhesion

Where brazing sheet is used

Related brazing materials

Aluminium (aluminum) brazing sheet: frequently asked questions