Clad Aluminium HF Welded Tubes for Vehicle Heat Exchangers
Clad HF welded tube is the flat or oval tube that carries coolant, oil or charge air through a brazed radiator, oil cooler or intercooler. It is roll-formed from brazing sheet, typically a 3003 core with a 4343 or 4045 filler layer and an optional zinc-bearing 7072 liner, and seam-welded by high-frequency induction. Metline supplies these tubes and the clad strip they are made from to heat-exchanger builders worldwide.
- Core alloys
- 3003, 3005
- Clad layers
- 4343, 4045, 7072
- Tempers
- H14, H16, H18
- Wall
- about 0.22 – 0.80 mm
How a clad welded tube works
A modern aluminium radiator is a single brazed block: tubes, corrugated fins, headers and side plates are assembled and passed through a controlled-atmosphere (CAB) or vacuum brazing furnace at about 590 – 610 °C. Only the thin silicon-rich clad layer melts, flows by capillary action into every tube-to-fin and tube-to-header joint, and solidifies into a fillet.
Welded tube is made by forming clad strip through a series of rolls into a flat or oval section and joining the edges with a high-frequency weld. Compared with extruded multiport tube, HF welded tube carries its own braze filler on the outside, so the fins can be bare, and walls can be thinner for a given burst pressure. It is the standard tube for engine radiators, heater cores, oil coolers and charge-air coolers.
Clad alloy combinations and tempers
| Construction | Outside layer | Core | Inside layer | Typical use |
|---|---|---|---|---|
| 4343 / 3003 | 4343 filler | 3003 | — | Radiator and heater tube with bare fins |
| 4343 / 3003 / 4343 | 4343 filler | 3003 | 4343 filler | Tubes with internal turbulators or inserts that must braze inside |
| 4343 / 3003 / 7072 | 4343 filler | 3003 | 7072 (Al-1 % Zn) | Radiator tube in contact with coolant; 7072 corrodes sacrificially |
| 4343 / 3005 / 7072 | 4343 filler | 3005 | 7072 | Higher post-braze strength for thinner walls |
| 4045 / 3003 (/ 4045, / 7072) | 4045 filler | 3003 | none, 4045 or 7072 | Charge-air and oil coolers; 4045 has more silicon and flows more freely |
Tubes are supplied in H14, H16 or H18 temper. The temper matters mainly for forming and handling, because the brazing cycle anneals the core; post-braze strength comes from the core alloy itself, which is why manganese-rich 3003 and 3005, or proprietary long-life cores, are used. Clad ratios of about 5 – 15 % per side are common, and zinc additions to the outer or inner layer are made where extra sacrificial protection is needed.
Typical tube sections and tolerances
| Tube type | Major axis (mm) | Minor axis (mm) | Wall (mm) | Typical tolerance |
|---|---|---|---|---|
| Radiator flat / oval tube | 12 – 42 | 1.35 – 2.7 | 0.22 – 0.45 | Width ±0.05; height ±0.10; wall ±0.01 – 0.02 |
| Oil cooler oval tube | 12 – 80 | 2.7 – 6.0 | 0.40 – 0.80 | Width ±0.05; height ±0.10; wall ±0.02 |
| Charge-air cooler rectangular tube | 25 – 120 | 4.0 – 11.0 | 0.40 – 0.60 | Width ±0.05; height ±0.25; wall ±0.02 |
| Round header / manifold tube | OD 18 – 34 | — | 1.0 – 1.6 | OD ±0.05; wall ±0.05 |
Typical acceptance values
- Burst pressure
- Agreed per drawing; radiator tube is commonly specified at about 14 MPa (140 kg/cm²) minimum
- Tensile strength (as supplied)
- ≥ 120 MPa typical requirement
- Elongation
- ≥ 2 % in hard tempers
- Inside weld bead
- ≤ 0.3 mm
- Cut-end burr
- ≤ 0.10 mm
- Camber and bow
- ≤ 1 mm per metre
Special sections, dimpled tubes and tubes with inserted turbulators are made to drawing; cut lengths are agreed with each order.
Quality checks that matter for brazing
- Clad thickness and uniformity: checked by cross-section; too little filler gives weak fillets, too much erodes thin cores.
- Weld integrity: eddy-current testing in line, plus burst and flattening tests on samples.
- Cleanliness: rolling oil and forming lubricant must be low-residue or evaporative, or flux will not wet the surface in CAB brazing.
- Post-braze properties: sag resistance and post-braze strength of the core, and SWAAT or OY-water corrosion tests for long-life tubes.
- Geometry: width and height control the fit into header slots; a few hundredths of a millimetre decide whether the joint seals.
How to order clad welded tube
- SectionSend the tube drawing: major and minor axis, wall, corner radius, any dimples or inserts, and cut length or coil form.
- MaterialState the clad combination (e.g. 4343/3003/7072), clad ratio per side, zinc content if required, and delivery temper.
- PerformanceGive burst-pressure, post-braze strength and corrosion-test requirements, and the brazing process (CAB or vacuum).
- QuoteWe confirm the specification, inspection plan and delivery terms (EXW, FOB, CIF or DAP).
- ShipTubes are packed in clean, dry, moisture-protected cases to keep the brazing surface free of contamination, with an EN 10204 3.1 certificate.
References and standards
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- EN 573-3 – Chemical composition and form of wrought products (3003, 3005, 4343, 4045, 7072)
- ASTM B313 – Standard Specification for Aluminum and Aluminum-Alloy Round Welded Tubes
- American Welding Society AWS C3.7 – Specification for Aluminum Brazing
- IATF 16949 – Quality management system requirements for automotive production and relevant service parts organisations
Clad welded radiator tube: FAQ
What is the difference between welded tube and extruded microchannel tube?
Welded tube is roll-formed from clad brazing sheet and carries its own filler, so the fins can be bare. Extruded multiport tube is made from unclad alloy and needs clad fins or a zinc-sprayed, flux-coated surface. Welded tube dominates engine radiators; extruded microchannel dominates air-conditioning condensers.
Why is a 7072 inner layer used?
7072 contains about 1 % zinc, which makes it electrochemically more active than the 3003 core. In contact with coolant it corrodes first and spreads corrosion sideways, protecting the core from pitting through the thin wall.
Which temper should I order?
H14 is the usual choice for good formability in the tube mill; H16 or H18 is used for thin walls that need extra handling stiffness. Because brazing anneals the core, the delivery temper has little effect on final strength.
Can you supply the clad strip instead of finished tube?
Yes. We supply slit brazing strip in the same clad combinations for customers who run their own tube mills, with clad ratio, thickness and width to order.
What certificates come with the tubes?
An EN 10204 3.1 certificate with chemistry of core and clad, mechanical properties, dimensions and burst-test results where specified.
Need clad welded tube for heat exchangers?
Send the section drawing, clad combination, temper and volume. We will confirm the specification and quote delivered to your plant.
