Application of Aluminium Brazing Sheet in Automobiles
Almost every heat exchanger in a modern car is made from aluminium brazing sheet: a core alloy clad with a thin layer of aluminium-silicon filler that melts in the brazing furnace and joins tubes, fins and headers into one leak-tight unit. This guide maps each automotive heat exchanger to the clad combinations, tempers and thicknesses typically used, and explains what drives the choice.
- Filler layer
- 4343, 4045, 4047, 4104 (Al-Si)
- Core
- 3003, 3003 mod, 6951, 6063
- Water-side liner
- 7072 (Al-Zn)
- Process
- CAB or vacuum brazing
Why vehicle heat exchangers are brazed aluminium
Aluminium has a density of 2.70 g/cm³, about 34 % of steel and 30 % of copper, while conducting heat well and resisting coolant and refrigerant corrosion. Brazing lets thousands of fin-to-tube joints be made in a single furnace pass, so a radiator or condenser core is joined in minutes. Since the switch from copper-brass radiators, brazed aluminium has become the standard for both combustion and electric vehicles.
Brazing sheet is the enabling material. Its core gives strength and corrosion resistance; its cladding, usually 5 – 15 % of the thickness per side, supplies the filler metal exactly where it is needed. Some designs add a zinc-bearing liner, such as 7072, on the coolant side so that it corrodes sacrificially and protects the core from pitting.
Brazing sheet layers and alloys
| Layer | Typical alloys | Function |
|---|---|---|
| Braze cladding | 4343, 4045 (CAB); 4047 (high fluidity); 4004, 4104 (vacuum) | Al-Si filler, melting roughly 577 – 615 °C, forms the joints |
| Core | 3003, modified 3003 (with Cu, Ti), 3005 | Strength, formability and corrosion resistance after brazing |
| High-strength core | 6951, 6063 and similar brazeable 6xxx alloys | Higher strength for oil coolers, battery plates and pressurised parts; can age-harden after brazing |
| Water-side liner | 7072 or other Al-Zn alloys | Sacrificial layer that protects the core from coolant-side pitting |
| Fin stock | 3003 with Zn additions, bare or clad | Thin, sag-resistant fins that are slightly anodic to the tube |
Combinations are written outer to inner, for example 4343/3003/7072: braze clad on the air side, 3003 core, and a 7072 liner facing the coolant. A two-sided clad sheet such as 4343/3003/4343 brazes on both faces, which is typical of intercooler plates and tube stock.
Brazing sheet by vehicle component
| Component | Typical material combinations | Temper | Typical thickness range | Notes |
|---|---|---|---|---|
| Engine radiator headers and tubes | 4343/3003, 4343/3003/7072 | O or H14/H24 | Tubes about 0.2 – 0.4 mm; headers about 1.0 – 2.0 mm | Liner protects against coolant corrosion |
| Radiator and condenser fins | 3003 + Zn (bare or clad) | H14 or similar | About 0.05 – 0.12 mm | Fins are made anodic to tubes |
| Air-conditioning condenser | Multiport extruded tubes with clad headers and fins | H14 fins, O headers | Fins about 0.06 – 0.10 mm | High refrigerant pressure; often zinc-sprayed tubes |
| Air-conditioning evaporator | Clad plates or tubes, 3003 fins | H14 / O | Plates about 0.4 – 0.6 mm | Condensate exposure needs good corrosion resistance |
| Oil cooler | 3003 or 6951 core, clad plates and turbulators | O | Inner fins about 0.2 – 0.3 mm | 6951 for higher strength and pressure |
| Heater core | 3003 tubes and fins, 4047 or 4343 clad | O, H16, H18 | Fins about 0.05 – 0.1 mm | Cabin heating from engine coolant |
| Charge-air cooler (intercooler) | 4343/3003/4343, 4045/3003/4045 | H14 | About 0.1 – 0.4 mm depending on part | Hot, pulsating boost air; fatigue resistance matters |
| EV battery cold plates | 4104/3003/4104, 4104/6063/4104, 4343/3003 mod | O / H temper | About 0.6 – 2.0 mm | Vacuum or CAB brazed flow channels under the cells |
| EV chillers and inverter coolers | Clad 3003 or 6xxx plates | O | About 0.3 – 1.0 mm | Compact plate heat exchangers |
Indicative ranges drawn from common industry practice. Final alloy, clad ratio, temper and gauge are set by each heat exchanger design and the customer specification.
Typical properties of 3003-core brazing sheet
| Temper | Tensile strength (MPa) | Yield strength (MPa) | Typical use |
|---|---|---|---|
| O (annealed) | About 95 – 135 | ≥ 35 – 45 | Deep-drawn plates, headers, complex formed parts |
| H14 / H24 | About 145 – 195 | ≥ 115 – 125 | Fins and tube stock needing stiffness for forming |
| H16 / H18 | About 165 – 220+ | Higher | Thin fins needing extra stiffness |
| After brazing (all) | Close to O-temper values | Close to O-temper values | The braze cycle anneals non-heat-treatable cores |
Because the brazing cycle at about 600 °C anneals 3xxx cores, designers work with post-braze properties. Long-life and modified 3003 cores add copper and titanium to raise post-braze strength and create a corrosion-resistant band beneath the cladding. Heat-treatable 6xxx cores such as 6951 regain strength by natural or artificial ageing after brazing.
CAB versus vacuum brazing
Controlled atmosphere brazing (CAB) uses a nitrogen furnace and a thin coat of non-corrosive fluoroaluminate flux. It is the dominant process for radiators, condensers, heater cores and intercoolers because it runs continuously at high volume. Clad alloys are 4343 or 4045, and the core must keep magnesium low because magnesium reacts with the flux.
Vacuum brazing needs no flux: magnesium in 4004 or 4104 cladding evaporates and disrupts the oxide. It is a batch process, suited to oil coolers, battery cold plates and parts with internal channels that cannot be cleaned of flux, and it accepts higher-magnesium, stronger cores.
How to specify automotive brazing sheet
- Layer structureClad, core and liner alloys in order, for example 4343/3003/7072, and whether one or both sides are clad.
- Clad ratioPercentage of total thickness per clad layer, commonly 5 – 15 %.
- Temper and gaugeTemper (O, H14, H24 and so on), thickness and tolerance, width and coil inner diameter.
- PropertiesPre- and post-braze mechanical requirements, sag resistance and corrosion test (for example SWAAT to ASTM G85).
- LogisticsCoil weight, packing, delivery terms and the EN 10204 3.1 mill certificate.
References and standards
- ASTM B209 – Aluminum and Aluminum-Alloy Sheet and Plate
- EN 573-3 – Chemical composition and form of wrought products
- ASTM G85 Annex A3 – Acidified synthetic sea water (SWAAT) testing
- AWS Brazing Handbook – aluminium brazing
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
Automotive aluminium (aluminum) brazing sheet: FAQ
What is aluminium brazing sheet?
It is a composite sheet with a core alloy such as 3003 and a thin cladding of Al-Si filler (for example 4343). In the furnace the cladding melts and forms the joints between tubes, fins and headers, while the core stays solid.
What does 4343/3003/7072 mean?
It describes the layers from outside to inside: 4343 braze cladding, 3003 core and a 7072 zinc-bearing liner that corrodes sacrificially on the coolant side.
Why is 6951 used instead of 3003 for some parts?
6951 is a brazeable heat-treatable alloy that regains strength after brazing by ageing, so it suits oil coolers, battery plates and other parts that need higher pressure resistance.
Which brazing sheet is used in EV battery cooling?
Cold plates commonly use 4104/3003/4104 or 4104/6063/4104 for vacuum brazing, or 4343-clad 3003 variants for CAB brazing, depending on the design and pressure.
Does brazing change the temper of the sheet?
Yes. The brazing cycle near 600 °C anneals non-heat-treatable cores, so final properties are close to O temper regardless of the delivered temper.
Need brazing sheet for vehicle heat exchangers?
Send the layer structure, clad ratio, temper, gauge and volume to sales@metline.in, and our team will respond with availability and certification.
