Cold Finished Aluminium Rod & Bar

What does "cold finished" mean?

"Cold finished" (CF) describes how the bar reaches its final size. Instead of using the bar as it comes off the extrusion press, the mill draws it at room temperature through a precision die, sometimes in more than one pass. The drawing step sizes the bar accurately and gives it a smooth, bright surface.

In ASTM language, cold finished bar is covered by ASTM B211 ("rolled or cold finished bar, rod and wire"), while extruded bar falls under ASTM B221. The aerospace equivalent of B211 is AMS-QQ-A-225, which replaced the old US federal QQ-A-225 specification and is divided into slash sheets by alloy. In Europe, cold drawn bar is ordered to EN 754.

For machine shops the difference is practical. A Swiss-type or multi-spindle automatic lathe feeds bar through a collet or guide bush with very little clearance. Bar that is oversize, out of round or bent will jam, chatter or produce scrap. Cold finished bar is made for exactly this kind of work: it feeds smoothly, holds a consistent diameter from bar to bar and often needs no skimming cut on the outside diameter.

Grades of cold finished bar and AMS-QQ-A-225 sheets

For high-volume screw-machine work, 2011 and 6262 are chosen for machinability; 6061 when corrosion resistance and anodising matter; 2024 and 7075 when strength is critical. Lead-free versions of free-machining grades (for example 2011 variants with bismuth and tin instead of lead, and 6xxx free-machining grades) are increasingly specified to meet RoHS and end-of-life vehicle rules.

Minimum mechanical properties (ASTM B211)

The table lists commonly published specified minimums for cold finished rod and bar in the most used tempers, for moderate diameters. Limits can change with diameter, so check the standard for your size and the certificate for the lot.

Specified minimums summarised from ASTM B211. Typical delivered values usually exceed these figures.

The T3, T8 and T9 tempers are worth understanding. T3 means solution treated, cold worked and naturally aged; T8 means solution treated, cold worked and then artificially aged; T9 means solution treated, artificially aged and then cold worked. The cold-work step in these tempers is often the drawing operation itself, which is why they appear mainly on cold finished products. T651 and T351 indicate bar stretched to relieve stress, which reduces distortion during heavy machining.

How cold finished bar is produced

1. Cast and homogenise billetThe alloy is cast to billet and homogenised so that the structure is uniform.
2. Extrude redraw stockBillet is extruded to a round, hex or square slightly larger than the finished size.
3. Draw coldThe bar is pulled through a hardened die, in one or more passes, to reduce and size the section and improve the surface.
4. Heat-treat and ageHeat-treatable alloys are solution treated, quenched and aged to the required temper; for T8 and T9 tempers the order of cold work and ageing is controlled.
5. StraightenRoll or rotary straightening brings the bar within straightness limits; stretched tempers are stretched by a controlled amount.
6. Finish and inspectBars are cut to length, ends chamfered if required, and checked for diameter, roundness, straightness, surface and properties; eddy-current or ultrasonic testing on request.

Some precision bar is centreless ground after drawing to achieve even tighter tolerances and a finer surface. Ground bar is a separate product, used where the outside diameter is a finished, functional surface, such as pistons, guide rods and shafts.

Tolerances, straightness and surface

Standard tolerances for cold finished bar come from ANSI H35.2 (ASTM and AMS orders) and EN 754-3 to -6 (round, square, rectangular and hexagonal bar for EN orders). Cold finished tolerances are substantially tighter than extruded tolerances for the same size, and they are normally specified as a plus-or-minus or a minus-only band on diameter.

A useful rule is to order only the tolerance the process needs. If the outside diameter is turned in every part, standard cold finished tolerance is usually enough. If the bar OD becomes a finished surface or the feeder is very tight, ask for a defined ISO tolerance or ground bar.

Cold finished versus extruded bar

Above about 100 mm diameter, cold finishing becomes impractical and extruded or forged bar is used, often peeled or turned to size. Below that, cold finished bar usually pays for itself in less scrap, fewer stoppages and fewer machining passes, even though the material costs more per kilogram.

Size range and weight per metre

Cold finished bar is commonly available in metric and inch sizes, in round, hexagonal (measured across flats), square and rectangular sections. The table gives weights per metre for a density of 2.70 g/cm³; 2xxx and 7xxx alloys are 2.78 – 2.81 g/cm³, so add about 3 – 4 % for those grades.

Machining cold finished aluminium bar

Where cold finished bar is used

• Automotive: brake pistons and valves, fuel-system fittings, ABS and transmission components
• Aerospace: fasteners, bushings, hydraulic fittings and pins in 2024, 7075 and 6061
• Fluid power: hydraulic and pneumatic fittings, valve spools and manifold parts
• Electronics: connector bodies, standoffs, heat-dissipating inserts and housings
• Medical and optics: instrument components, lens mounts, precision spacers
• Automation: rollers, shafts, guides and fixture parts
• Consumer products: camera, bicycle and sporting hardware, knobs and trim

How to order cold finished bar

1. Alloy, temper and shapeFor example 6061-T6 round, 2011-T3 hex or 7075-T651 round.
2. Size and toleranceDiameter or across-flats size, tolerance standard or ISO band, and straightness if critical.
3. StandardASTM B211, AMS-QQ-A-225 slash sheet, an AMS material spec or EN 754.
4. Length and endsRandom or fixed lengths, chamfered or square-cut ends.
5. Documents and packingEN 10204 3.1 mill certificate; bundles or boxes with protective wrapping; EXW, FOB, CIF or DAP delivery.

Related bar grades and guides

Cold finished aluminium (aluminum) bar: FAQ