For the extrusion production of aluminum metal, extrusion temperature is the most basic and most critical process factor. Extrusion temperature has a great impact on product quality, production efficiency, die life, energy consumption, etc.
The most important issue in extrusion is the control of metal temperature. From the beginning of heating of the ingot to the quenching of the extruded profile, it is necessary to ensure that the soluble phase structure does not precipitate from the solid solution or show the dispersion and precipitation of small particles.
Taking 6063 aluminum alloy plate as an example, the heating temperature of 6063 aluminum alloy profile ingot is generally set within the temperature range of Mg2Si precipitation. The heating time has an important influence on the precipitation of Mg2Si. Rapid heating can greatly reduce the possible precipitation time. . Generally speaking, the heating temperature of 6063 aluminum alloy profile ingots can be set as: non-homogenized ingots: 460-520 °C; homogenized ingots: 430-480 °C.
The extrusion temperature is adjusted according to different products and unit pressure during operation. During the extrusion process, the temperature of the ingot in the deformation zone varies. With the completion of the extrusion process, the temperature of the deformation zone gradually increases, and it increases with the increase of the extrusion speed. Therefore, in order to prevent extrusion cracks, the extrusion speed should be gradually reduced as the extrusion process progresses and the temperature of the deformation zone increases.
Control the extrusion speed of industrial aluminum profiles
The extrusion speed must be carefully controlled during extrusion. The extrusion speed has an important influence on the thermal effect of deformation, the uniformity of deformation, the recrystallization and solid solution process, the mechanical properties of the product and the surface quality of the product. If the extrusion speed is too fast, there will be pitting and cracks on the surface of the product. At the same time, the extrusion speed is too fast to increase the non-uniformity of metal deformation. The outflow rate during extrusion depends on the type of aluminum alloy profile and the geometry, size and surface condition of the profile.
The extrusion speed of the 6063 aluminum alloy profile (the outflow speed of the metal) can be selected as 20-100 m/min.
With the advancement of modern technology, the extrusion speed can be controlled by program or simulated program, and new technologies such as isothermal extrusion process and CADEX have also been developed. By automatically adjusting the extrusion speed to keep the temperature of the deformation zone within a certain constant range, the purpose of rapid extrusion without cracks can be achieved.
In order to improve production efficiency, many measures can be taken in the process. When induction heating is used, there is a temperature gradient of 40-60 °C (gradient heating) along the length of the ingot. During extrusion, the high temperature end faces the extrusion die, and the low temperature end faces the extrusion pad to balance part of the deformation heat; For water-cooled die extrusion, that is, forced cooling with water at the back end of the die, tests have shown that the extrusion speed can be increased by 30%-50%.
In recent years, nitrogen or liquid nitrogen has been used in foreign countries to cool the die (extrusion die) to increase the extrusion speed, increase the life of the die and improve the surface quality of the profile. During the extrusion process, nitrogen gas is introduced to the outlet of the extrusion die to be released, which can make the cooled product shrink rapidly, cool the extrusion die and the metal in the deformation zone, so that the deformation heat is taken away, and the outlet of the die is surrounded by nitrogen atmosphere. Control, reduce the oxidation of aluminum, reduce the adhesion and accumulation of alumina, so the cooling of nitrogen improves the surface quality of the product, which can greatly improve the extrusion speed. CADEX is a new extrusion process developed recently. The extrusion temperature, extrusion speed and extrusion force during the extrusion process form a closed-loop system to maximize the extrusion speed and production efficiency, while ensuring the best quality performance.
On-machine quenching
The quenching of 6063-T5 is to keep the Mg2Si dissolved in the base metal at high temperature out of the die hole and then rapidly cooled to room temperature. The cooling rate is often proportional to the strengthening phase content. The minimum cooling rate that can be strengthened for 6063 aluminum alloy profiles is 38°C/min, so it is suitable for air-cooled quenching. Changing the fan and fan revolutions can change the cooling intensity, so that the temperature of the product before tension straightening drops below 60°C.
Tension straightening
After the profile is out of the die hole, it is generally pulled by a tractor. When the tractor is working, it gives a certain traction tension to the extruded products, and at the same time moves synchronously with the outflow speed of the products. The purpose of using the tractor is to reduce the uneven length and smear of the multi-line extrusion, and also prevent the profile from twisting and bending after the die hole is released, which will bring trouble to the tension straightening. In addition to eliminating the longitudinal shape irregularity of the product, tension straightening can also reduce its residual stress, improve its strength properties and maintain its good surface.
artificial aging
Aging treatment requires uniform temperature, and the temperature difference does not exceed ±3-5℃. The artificial aging temperature of 6063 aluminum alloy profiles is generally 200 ℃. The aging holding time is 1-2 hours. In order to improve the mechanical properties, aging at 180-190 °C for 3-4 hours is also used, but the production efficiency will be reduced at this time.