Seamless aluminium tube heat treatment is a process in which the metal workpiece is heated in a certain medium to an appropriate temperature, and then cooled at different speeds after a certain period of time. Seamless aluminium tube heat treatment is one of the most important processes in material production. Compared with other processes, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but gives or improves the performance of the workpiece by changing the internal microstructure of the workpiece or the chemical composition of the workpiece surface. Its characteristic is to improve the internal quality of the workpiece, which is generally not visible to the naked eye.
"Four fires" in seamless aluminium tube heat treatment refers to annealing, normalizing, quenching (solution) and tempering (aging):
(1) Annealing refers to heating the workpiece to an appropriate temperature, using different holding time according to the size of the material and workpiece, and then cooling slowly. Its main purpose is to reduce the hardness and improve the plasticity of the material, so as to facilitate subsequent processing, reduce residual stress and improve the homogenization of the structure and composition. Annealing can be divided into recrystallization annealing, stress relieving annealing, spheroidizing annealing and complete annealing according to different purposes.
(2) Normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, but the structure obtained is finer. Normalizing is often used to improve the cutting performance of materials, and sometimes it is also used for the final heat treatment of parts with low requirements.
(3) Quenching is the rapid cooling of workpiece in quenching medium of water, oil or other inorganic salts or organic water solution after heating and insulation.
(4) after quenching materials for the unbalanced organization, usually very hard and brittle, the need for long time preservation in a temperature higher than room temperature, then cooling, this process is called tempering (aging).
From the above definition can be seen, whether annealing, normalizing and quenching or tempering heat treatment process to workpiece heating, insulation and cooling. Therefore, in metal heat treatment, heating speed, holding time and cooling speed become the most important process parameters.
"Fire", quenching and tempering (aging) is most closely related, often with the use of both. But in the actual production, in order to save cost, improve production efficiency, low requirement for performance products are often used instead of on-line quenching quenching furnace quenching, tempering with natural aging instead. For example, in 6060, 6063 Aluminum Alloy extruded aluminum tube, due to very low quenching sensitivity of these alloys, silicon and magnesium in the solution temperature above the solution quickly. So to ensure the extrusion outlet temperature is higher than the solution temperature, the air cooling can also obtain the solid solution degree of supersaturated solid solution.