Extrusion temperature is the most basic and critical process factor for extrusion production. Extrusion temperature has a great impact on product quality, production efficiency, mold life, energy consumption and so on.
The most important problem of extrusion is the control of the temperature of the metal. From the start of the ingot heating to the quenching of the extruded profile, it is ensured that the dissolvable phase structure does not precipitate out of the solid solution or exhibits the dispersion of small particles.
The heating temperature of 6063 alloy ingot is generally set in the temperature range of precipitation of Mg2Si. The heating time has an important influence on the precipitation of Mg2Si. The rapid heating can greatly reduce the time of precipitation. In general, the heating temperature of the 6063 alloy ingot can be set as: unhomogenized ingot: 460-520 ° C; homogenized ingot: 430-480 ° C.
The extrusion temperature is adjusted during operation depending on the product and unit pressure. The temperature of the ingot in the deformation zone changes during the extrusion process. As the extrusion process is completed, the temperature of the deformation zone gradually increases and increases as the extrusion speed increases. Therefore, in order to prevent the occurrence of crush cracks, the extrusion speed should be gradually lowered as the extrusion process progresses and the temperature of the deformation zone increases.
The extrusion speed must be carefully controlled during the extrusion process. The extrusion speed has an important influence on the deformation heat effect, deformation uniformity, recrystallization and solid solution process, mechanical properties of the product and surface quality of the product.
If the extrusion speed is too fast, there will be a tendency for pitting, cracking, etc. on the surface of the product. At the same time, the extrusion speed is too fast, which increases the unevenness of metal deformation. The rate of outflow during extrusion depends on the type of alloy and the geometry, size and surface condition of the profile.
The extrusion speed of the 6063 alloy profile (metal outflow speed) can be selected from 20 to 100 m/min.
With the advancement of modern technology, the extrusion speed can be controlled by program control or simulation program, and new technologies such as isothermal extrusion process and CADEX are also developed . By automatically adjusting the extrusion speed to maintain the temperature of the deformation zone within a certain constant range, rapid extrusion without cracking 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 . When the extrusion is performed, the high temperature end faces the extrusion die, and the low temperature end faces the pressing pad to balance a part of the deformation heat. The water-cooled die is extruded, that is, forced cooling at the back end of the mold, and the test proves that the extrusion speed can be increased by 30%-50%.
In recent years, the mold (extrusion die) has been cooled with nitrogen or liquid nitrogen abroad to increase the extrusion speed, improve the life of the mold and improve the surface quality of the profile. During the extrusion process, nitrogen is introduced to the exit of the extrusion die, which can rapidly shrink the cooled product, cool the extrusion die and the deformation zone metal, and the deformation heat is taken away, while the mold outlet is surrounded by nitrogen atmosphere. Control, reducing the oxidation of aluminum, reducing the bonding and accumulation of alumina, so the cooling of nitrogen improves the surface quality of the product, which can greatly increase the extrusion speed. CADEX is a new extrusion process recently developed. The extrusion temperature, extrusion speed and extrusion force in the extrusion process form a closed loop system to maximize extrusion speed and production efficiency while ensuring the best. Performance.
3. Onboard quenching
The 6063-T5 quenching is to preserve the Mg2Si dissolved in the base metal at a high temperature and then rapidly cooled to room temperature. The cooling rate is often proportional to the strength of the strengthening phase. The 6063 alloy has a minimum cooling rate of 38 ° C / min and is therefore suitable for air-cooled quenching. Changing the fan and fan revolutions can change the cooling intensity to reduce the temperature of the product to below 60 °C before tension straightening.
4. Tension straightening
After the profile is punched out, it is usually pulled by a tractor. When the tractor is working, the traction product is given a certain traction tension, and simultaneously moves with the product outflow speed. The purpose of using the tractor is to reduce the length and unevenness of the multi-line extrusion, and also to prevent the profile from being twisted and bent after the die hole, which brings trouble to the tension straightening. Tension straightening not only eliminates the longitudinal shape of the article, but also reduces its residual stress, improves strength properties and maintains its good surface.
5. Aluminum artificial aging
The aging treatment requires uniform temperature and the temperature difference does not exceed ±3-5 °C. The artificial aging temperature of 6063 alloy is generally 200 °C. The aging time is 1-2 hours. In order to improve the mechanical properties, it is also effective at 180-190 ° C for 3-4 hours, but the production efficiency will be reduced.
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