Aluminium brazing strip is clad brazing material slit into narrow coils, typically 0.15 – 3 mm thick, that feeds tube mills, folding lines and progressive presses. Most of it becomes high-frequency welded or folded flat tubes for radiators, heater cores and charge-air coolers, or headers and side plates. This guide explains the clad structures, how strip is turned into tubes, what to specify and how to avoid common problems.
Brazing strip is the same roll-bonded composite as brazing sheet, a higher-melting core with an aluminium-silicon filler layer on one or both faces, but supplied as narrow, precision-slit coil. Its job is to feed continuous forming lines without stopping.
In a heat exchanger, the strip usually becomes the tube. A narrow coil is roll-formed into a flat or round tube and either welded along its seam by high-frequency (HF) welding, or folded into a "B" profile that is closed during brazing. The outside of the tube carries filler that will braze to the fins and headers; the inside is often lined with 7072 to protect it from coolant corrosion.
Strip also feeds presses that stamp headers, side plates, turbulators and small plates. Compared with cut sheets, coil feeding lets these parts be made at high speed with minimal scrap. For thin fin material, see our brazing foil guide; for wide sheet and plate, the brazing sheet guide.
| Structure | Where used | Why |
|---|---|---|
| 4343 / 3003 / 7072 | HF-welded radiator, heater and charge-air cooler tubes | Filler outside brazes to fins and headers; 7072 inside protects the coolant side |
| 4343 / 3003 + Zn | Tubes and plates needing an anodic core | Zinc-bearing core resists perforation by making corrosion spread sideways |
| 4343 / 3003 / 4343 | Folded B-tubes, plates and turbulators brazing on both faces | Filler on both sides closes the fold and joins internal webs |
| 4045 / 3003 | Single-side clad headers and side plates | More fluid filler for wide or uneven header joints |
| 4343 / long-life 3xxx core / 7072 | Tubes for long-life radiators and heater cores | Modified core resists silicon penetration and pitting |
| 4343 / 6951 / 4343 | High-strength plates and side supports | Heat-treatable core regains strength after brazing; check flux compatibility |
| Bare 3003 or 3102 | Tube or plate stock where filler is supplied by the mating part | Lower cost when fins or headers are clad |
Magnesium-bearing cores such as 6951 or 6061 do not braze reliably with standard potassium fluoroaluminate flux in CAB. Use caesium-modified flux or vacuum brazing, and confirm by trial.
The strip is roll-formed into a tube, its edges heated by high-frequency current and forged together, the outer weld bead is scarfed off, and the tube is sized to a flat oval. Requires very consistent width, edge condition and thickness.
Double-clad strip is folded so that a central web is formed and the edges overlap; the tube is closed and the web joined during brazing. Allows very thin walls and internal reinforcement.
Clad strip formed and welded into round tube for heat exchangers, connection tubes and manifolds.
Strip fed from coil into progressive dies to make header plates, end plates and turbulators.
Each route places different demands on the strip. HF welding is sensitive to edge burrs and to variation in width, because the seam must meet evenly. Folded tubes need good elongation and accurate clad ratios on both faces. Deep-drawn headers need O or H24 temper. Tell your supplier which route the strip is for, not just its dimensions.
| Alloy | Role | Main alloying | Approx. melting / solidus |
|---|---|---|---|
| 4343 | Filler | Si 6.8 – 8.2 % | 577 – 613 °C |
| 4045 | Filler | Si 9.0 – 11.0 % | 577 – 591 °C |
| 4047 | Filler | Si 11.0 – 13.0 % | 577 – 582 °C |
| 3003 | Core | Mn 1.0 – 1.5 % | Solidus about 640 °C |
| 3102 | Core | Mn 0.05 – 0.40 % | High conductivity, lower strength |
| 6951 | Core | Mg 0.40 – 0.8 %, Si 0.20 – 0.50 % | Solidus about 615 °C; heat-treatable |
| 7072 | Liner | Zn 0.8 – 1.3 % | Sacrificial; not a filler |
Values are Aluminum Association composition limits and published melting ranges. Many radiator tube cores are proprietary long-life variants of 3003; specify the corrosion and post-braze strength performance you need, and the core chemistry can be matched.
Weight per metre of strip is width × thickness × density. With a composite density of about 2.73 g/cm³:
| Thickness × width (mm) | kg per metre | metres per kg |
|---|---|---|
| 0.20 × 30 | 0.0164 | 61.1 |
| 0.25 × 40 | 0.0273 | 36.6 |
| 0.27 × 50 | 0.0369 | 27.1 |
| 0.30 × 60 | 0.0491 | 20.4 |
| 0.40 × 50 | 0.0546 | 18.3 |
| 0.50 × 80 | 0.1092 | 9.2 |
| 1.00 × 100 | 0.2730 | 3.7 |
| 1.50 × 120 | 0.4914 | 2.0 |
| 2.00 × 150 | 0.8190 | 1.2 |
| Problem | Possible cause | What to check |
|---|---|---|
| Weld defects on HF tube | Burrs, width variation, camber | Slitting quality and width tolerance |
| Tube leaks after brazing | Core erosion by filler; thin spots | Clad ratio, braze cycle time and temperature |
| Fin joints weak on tube surface | Filler on wrong face, oil residue, low flux | Clad side marking, cleanliness, flux load |
| Early coolant-side pitting | No or thin 7072 liner; aggressive coolant | Liner ratio, coolant quality, core alloy |
| Cracking when folding or forming | Temper too hard for the forming route | Order O or H24 for severe forming |
Mainly for making heat exchanger tubes by HF welding or folding, and for stamping headers, side plates and turbulators. The clad filler brazes the tubes to fins and headers in the furnace.
7072 contains about 1 % zinc, which makes it anodic to the core. It corrodes preferentially and sideways, protecting the core from pitting through the tube wall on the coolant side.
Welded tubes are formed from single- or three-layer strip and seam-welded before brazing. Folded B-tubes use double-clad strip folded into shape and closed during brazing, which allows thinner walls and an internal web.
It depends on the forming route. HF tube mills commonly run H14 or H24 strip; severe folding and deep-drawn headers need O or H24. Agree the temper with your tube mill operator.
Not reliably with standard flux, because magnesium poisons potassium fluoroaluminate flux. Use caesium-modified flux, a low-Mg core, or vacuum brazing.
Give the nominal width and tolerance, the camber limit and the required edge condition, plus the coil inner and outer diameter and winding type for your line.
Send the clad structure, thickness, slit width, temper, coil size and forming route. We reply with supply options, certification and delivery terms.
