Aluminium capillary tube is cold-drawn seamless tubing with an outside diameter of roughly 0.5 to 10 mm and a bore that can be well under 1 mm. It is made mainly from 1050, 1060, 1070 and 3003 for fluid and refrigerant lines and from 6063 where a little more strength is needed. This guide covers alloys, sizes, standards, manufacturing, applications and how aluminium compares with copper.
A capillary tube is a tube whose bore is small enough that its length and diameter, rather than a valve, control how much fluid passes and how much pressure is lost. The term is also used more loosely for any very fine, thin-walled tube. In aluminium, capillary tubes are usually produced by extruding a hollow shell and then cold drawing it through dies, with annealing between passes, until the tube reaches its final size.
Aluminium brings low weight, good thermal conductivity, resistance to corrosion in clean environments and easy bending and flaring. Its main limitations against copper are lower strength at the same wall thickness, more difficult brazing and soldering, and the need to avoid direct contact with copper in damp conditions. These points decide where aluminium capillary tubing is a good choice and where copper remains the default.
Between ultra-fine capillary sizes and ordinary small tube there is a grey zone. Tubes from about 4.8 mm up to 20 mm outside diameter are often called small aluminium tubes rather than capillaries; they use the same alloys and drawing route but need less precise bore control.
| Alloy | Character | Typical tempers | Common uses |
|---|---|---|---|
| 1050 / 1060 | 99.5 – 99.6 % aluminium; very ductile, high thermal and electrical conductivity | O, H14, H18 | Refrigerant and coolant lines, heat-exchange capillaries, sensor bulbs |
| 1070 | 99.7 % aluminium; highest purity of the group, very clean surface | O, H14 | Instrument tubing, laboratory and analytical lines, electrical uses |
| 1100 | 99.0 % aluminium with a little copper; slightly stronger than 1050 | O, H14 | General-purpose fine tubing, gas and fluid lines |
| 3003 | Al-Mn alloy; about 20 % stronger than 1xxx grades and suitable for brazing | O, H14, H18 | HVAC and appliance refrigerant circuits, brazed assemblies |
| 6063 | Heat-treatable Al-Mg-Si; higher strength and good surface | T4, T5, T6 | Small structural and guide tubes, antennas, decorative tubes |
For refrigerant and fluid service the soft 1xxx and 3003 alloys dominate, because the tube is bent and coiled during assembly and must not crack. 6063 is chosen when the tube is a mechanical part rather than a fluid line. Hard tempers (H14, H18) keep straight lengths stiff and straight; the annealed O temper is supplied for coils and for tubes that will be bent, flared or swaged.
Values are typical figures from Aluminum Association and ASM data, not guaranteed minimums. Very thin-walled drawn tube is normally certified to the tube standard named on the order, and the mill certificate gives tested results for each lot.
| Alloy / temper | Tensile strength (typical) | Thermal conductivity | Electrical conductivity |
|---|---|---|---|
| 1060-O | 70 MPa | About 234 W/m·K | About 62 % IACS |
| 1060-H18 | 130 MPa | About 230 W/m·K | About 61 % IACS |
| 1100-O | 90 MPa | About 222 W/m·K | About 59 % IACS |
| 3003-O | 110 MPa | About 193 W/m·K | About 50 % IACS |
| 3003-H14 | 150 MPa | About 159 W/m·K | About 41 % IACS |
| 6063-T6 | 240 MPa | About 200 W/m·K | About 53 % IACS |
The achievable combination of diameter, wall and tolerance depends on the alloy and drawing route; send your drawing to confirm.
Weight per metre comes straight from geometry: π × wall × (OD − wall) × density. The table shows calculated values in grams per metre for some common sizes.
| OD (mm) | Wall (mm) | Bore (mm) | Weight (g/m) |
|---|---|---|---|
| 1 | 0.2 | 0.6 | 1.4 |
| 1.5 | 0.3 | 0.9 | 3.1 |
| 2 | 0.3 | 1.4 | 4.3 |
| 2 | 0.5 | 1.0 | 6.4 |
| 3 | 0.5 | 2.0 | 10.6 |
| 4 | 0.5 | 3.0 | 14.8 |
| 5 | 0.8 | 3.4 | 28.5 |
| 6 | 1 | 4.0 | 42.4 |
| 8 | 1 | 6.0 | 59.4 |
| 10 | 1 | 8.0 | 76.3 |
| Standard | What it covers |
|---|---|
| ASTM B210 / B210M | Drawn seamless aluminium and aluminium-alloy tubes for general purposes |
| ASTM B483 / B483M | Drawn aluminium tube and pipe for general-purpose applications |
| ASTM B234 | Drawn seamless tubes for condensers, evaporators and heat exchangers |
| EN 754-7 | Cold-drawn seamless tubes: tolerances on dimensions and form |
| EN 754-2 | Cold-drawn rod, bar and tube: mechanical properties |
| EN 573-3 | Chemical composition of wrought aluminium alloys |
Standard tolerance tables were written for ordinary tube sizes, so capillary tubing is usually ordered against a drawing that sets the limits for outside diameter, bore or wall thickness, ovality and straightness. Tell the supplier which dimension controls function: for a flow restrictor it is the bore; for a tube that is pushed into a fitting it is the outside diameter. Holding both very tightly at once raises cost.
Expansion capillaries and refrigerant lines in all-aluminium circuits, sometimes bonded to an aluminium suction line to form a heat exchanger. Copper remains common because it is easier to braze and draw to very tight bores, so aluminium is chosen where the whole circuit is aluminium.
Small coolant and refrigerant lines, sensor tubes and thermal-management parts where weight counts.
Pressure-sensing lines, thermostat and thermometer capillaries, pitot and sampling tubes.
Low-pressure gas and fluid transfer lines where a clean, non-magnetic, light tube is needed.
Small heat pipes, cold-plate tubes and cooling loops embedded in plates.
Antenna elements, pins, sleeves, guide tubes and model-making components, usually in 6063.
| Property | Aluminium (1060 / 3003) | Copper (C12200) |
|---|---|---|
| Density | 2.70 g/cm³ | 8.94 g/cm³ |
| Thermal conductivity | About 190 – 235 W/m·K | About 340 W/m·K |
| Strength at equal wall | Lower | Higher |
| Brazing and soldering | Needs aluminium brazing alloys and fluxes; narrower process window | Easy with standard brazing alloys |
| Corrosion | Good in clean, dry environments; vulnerable when in contact with copper and moisture | Good, though formicary (ant-nest) corrosion can occur in some conditions |
| Tight bore tolerances | Achievable but more demanding | Long-established for restrictor service (ASTM B360) |
| Material cost per metre | Generally lower | Generally higher |
A practical rule: if the rest of the circuit is aluminium, use an aluminium capillary and avoid the copper-aluminium joint altogether. If the circuit is copper, keeping a copper capillary is usually simpler. Mixed joints need a proper transition fitting or a sealed, moisture-protected joint.
Drawn aluminium capillary tube can be made with outside diameters around 0.5 mm and bores of about 0.3 mm. Whether a particular combination is possible depends on the alloy and the tolerance required, so confirm with a drawing.
It can in an all-aluminium circuit, and some appliance designs use an aluminium capillary bonded to an aluminium suction line. In a copper circuit it is usually simpler to keep copper, because copper-aluminium joints need careful design to avoid galvanic corrosion.
1050, 1060 or 3003 in the annealed O temper. They bend to tight radii without cracking or collapsing; 3003 is a little stronger.
Precision capillary tube is normally seamless, made by extrusion followed by cold drawing. Welded tube is used for larger, less critical sizes.
In straight cut lengths, often end-capped, or in level-wound coils for long continuous runs. Cut pieces with deburred, flared or swaged ends are also possible.
An EN 10204 3.1 mill test certificate with chemical composition and, where specified, mechanical and dimensional results for the lot.
Share the alloy, size, tolerance and quantity. Metline will confirm what can be drawn, the certification and a delivered price.
