Production and Manufacturing of Aluminum Tubes

Complete Process for Aluminum Tube Production and Manufacturing
Aluminum tubes are classified into four main types based on their forming process: hot-extruded aluminum tubes (the mainstream), cold-drawn and precision-rolled aluminum tubes, welded aluminum tubes, and impact-extruded pharmaceutical aluminum tubes. Among these, the most widely used in the industry is seamless or 分流模 (diverging‑die) extruded aluminum tubing.

I. Mainstream Process Route: Hot-Extruded Aluminum Tubing (Industrial‑Grade, using alloys such as 6061, 6063, and 7075)
Process Step 1: Melting and casting to produce aluminum round ingots (raw billets)
Ingredients: Electrolytic aluminum ingots plus alloying elements such as magnesium, silicon, manganese, and copper, blended according to specified grades (e.g., 6061, 6063, 5052, 7075, etc.).
Smelting and Refining
Melting temperature: 720–760°C
Argon rotary spray degassing and ceramic filtration to remove slag, with hydrogen content controlled to prevent porosity in the tubing.
Semi-continuous vertical casting: molten aluminum is cooled and cast into solid, large-diameter aluminum billets.
Homogenization annealing (key): Hold at 480–560°C to eliminate compositional segregation and reduce the risk of extrusion cracking.
Sawing: Cut the ingots to specified lengths according to the extruder’s stroke, and perform nondestructive testing to detect cracks and slag inclusions.
Process Step 2: Billet Heating + Die Preheating
Aluminum bar heating: 420–480°C (commonly 430–450°C for 6-series alloys)
The extrusion cylinder and die are preheated simultaneously to prevent surface scratches and uneven wall thickness caused by temperature differentials.
Process Step 3: Hot Extrusion Forming (the core process; two methods for forming aluminum tubes)
① Piercing needle extrusion → [Truly seamless aluminum tube]
Solid aluminum billets are fed into the extrusion cylinder, where a piercing mandrel at the front end first forms an internal bore, enabling high-pressure extrusion of hollow tubing; no weld lines are present. ✅ Applications: hydraulic pipelines, high-pressure fluids, aerospace, defense, and other high-pressure environments. Standards: GB/T 4437.1.

② Flow‑diverting combined die extrusion → [Flow‑diverting die for hollow aluminum tubes (seam‑welded extruded tubes)]
The metal is drawn into multiple strands by a die and then high-pressure welded in the welding chamber to form a tube; a weld line remains inside. ✅ Applications: structural supports, general-purpose fluids, decorative tubing; cost lower than perforated seamless tubing. Standard: GB/T 4437.2.

Many manufacturers commonly refer to it as a “seamless extruded tube,” but in reality, it is a分流模管 (diverging die tube), with a lower pressure rating than perforated seamless aluminum tubing.

Process Step 4: Online Cooling (Quenching)
T5 condition: air-cooled after extrusion (6063 architectural aluminum tube)
T6 condition: Strong air cooling / water‑mist quenching (for 6061 industrial tubing), rapidly locking in the supersaturated solid solution to prepare for age hardening.
Process 5: Stretching and Straightening
After cooling, the tubing exhibits bending and torsional distortion; a small‑strain stretch (elongation of 1%–3%) is applied to correct straightness and relieve internal extrusion stresses.

Process 6: Cut-to-length sawing
Cut to customer-specified lengths and deburr both ends.

Process Step 7: Heat Treatment (Age Hardening, Selected as Required)
Artificial aging T5: hold at 160–180°C for 2–4 hours, air-cool, medium strength.
Artificial aging T6: hold at 170–190°C for 4–8 hours, resulting in higher strength (6061‑T6 is the most common).
High-strength alloys of the 2xxx and 7xxx series (2024, 7075) typically require separate offline solution treatment followed by two-stage aging.
Process Step 8: Finishing and Inspection
Visual inspection, dimensional measurement, wall‑thickness testing, and hardness testing; for high‑pressure tubing, additional hydrostatic flaw detection and eddy‑current testing are performed.

Process Step 9: Surface Treatment (Optional)
Degreasing and polishing, sandblasting
Anodizing (natural color / colored), hard anodizing (wear-resistant hydraulic cylinder tubes)
Electrophoresis, powder coating, chromate conversion coating
Turning, boring, roll forming, and internal/external polishing (for precision hydraulic aluminum tubing)

II. Cold-drawn / Cold-rolled aluminum tubes (high-precision thin-walled aluminum tubes)

Process flow: Extrusion of rough tube → Annealing for softening → Multi‑pass cold drawing/cold rolling → Intermediate annealing → Finish precision drawing → Final annealing Characteristics:

Extremely high dimensional accuracy, uniform wall thickness, and smooth inner and outer surfaces;
Suitable for small-diameter, thin-walled precision tubing (heat exchangers, instrument tubing);
The deformation per pass is limited, requiring multiple annealing steps, which results in higher production costs compared to direct extrusion.

III. Welded Aluminum Pipes (Seam-Welded Pipes)

Process: Aluminum strip coil → Rolled into a cylinder by the forming unit → High-frequency welding / TIG welding → Sizing and drawing. Advantages: Low cost; suitable for large-diameter, thin-walled applications. Disadvantages: Weld seams are present, making it unsuitable for high-pressure service; commonly used for heat dissipation, decorative purposes, and low-pressure piping.

IV. Brief Comparison Table of Processes

V. Reference for Selecting Common Aluminum Alloy Grades

1060 pure aluminum tube: excellent electrical conductivity, corrosion resistance, and ductility, but low strength.
3003 aluminum-manganese alloy tube: rust-resistant aluminum, used for heat exchangers and refrigerant tubing.
5052 aluminum-magnesium alloy tube: excellent marine corrosion resistance and weldability.
6063-T5: Architectural structural and decorative aluminum tubing
6061-T6: General industrial structures and medium-pressure piping (the most widely used)
7075: Ultra-high strength, for high-end aerospace components.