Method for manufacturing cold-forged, extruded aluminum alloy tube

A method for manufacturing a cold-forged, extruded aluminum alloy tube having two opposite open ends, consisting of-the steps of:

• (A) providing a primary material having a hollow columnar shape and made of an aluminum alloy material, and a first cold extrusion apparatus including a first cold extrusion die, and a first ram and a first plunger corresponding in position to the first cold extrusion die, the first plunger extending downwardly from the first ram;
• (B) processing the primary material to form a preform that extends along an axis and that has a first end surface and a second end surface opposite to each other along the axis, an inner circumferential surface between the first end surface and the second end surface and defining a central bore, and an outer circumferential surface opposite to the inner circumferential surface, the preform further having an original length extending from the first end surface to the second end surface, and an original outer diameter measured across the outer circumferential surface, each of the first end surface, the second end surface and the outer circumferential surface having a surface roughness controlled at less than 0.4 μm Ra, each of the original outer diameter and the original length having a tolerance of less than 0.01 mm;
• (C) subjecting the preform to a homogeneous annealing which involves heating the preform in a furnace to a temperature of about 410° C. to 510° C., and then removing the preform from the furnace after the furnace is cooled to a temperature of about 160° C. to 200° C. at a cooling rate of 10° C. per hour;
• (D) testing the hardness of the preform, the hardness being 60±5 degrees measured on Rockwell Hardness F scale;
• (E) immersing the preform in a tank containing a lubricant at a working temperature ranging from 80° C. to 100° C. for a predetermined time;
• and
• (F) subjecting the preform to cold extrusion which involves positioning the preform in the first cold extrusion die, after which the first cold extrusion apparatus is operated to strike the first ram against the preform with the first plunger extending through the central bore of the preform to thereby form the cold-forged, extruded aluminum alloy tube, the cold-forged, extruded aluminum alloy tube having a first end surface and a second end surface opposite to each other, an outer circumferential surface between the first end surface and the second end surface of the cold-forged, extruded aluminum alloy tube, and an inner circumferential surface opposite to the outer circumferential surface of the cold-forged, extruded aluminum alloy tube and defining a central bore, the cold-forged, extruded aluminum alloy tube having a length that extends between the first end surface and the second end surface of the cold-forged, extruded aluminum alloy tube and that is longer than the original length of the preform.