[China Aluminum Network] 1 Introduction 6063 aluminum alloy is a kind of deformed aluminum alloy with wide application and large amount. It is widely used in extrusion building profiles and industrial profiles. At present, the heat-extrusion extrusion process of aluminum alloy in China has gradually matured, but there is still a big gap compared with developed countries.
With the development of high-speed, energy-saving, and continuous materials processing, many aluminum extrusion manufacturers in recent years are hoping to adopt new technologies for low-temperature rapid extrusion. Generally 6063 aluminum alloy extrusion speed solid profile between 15m/min-50m/min, hollow profile between 10m/min-35m/min, rapid extrusion is the extrusion product from the mold hole outflow speed at 60m /min or more.
Excessively fast extrusion products tend to have pits, cracks, etc. on the surface of the product, increasing the non-uniformity of metal deformation. How can we achieve rapid extrusion while ensuring product quality?
2 conditions to achieve rapid extrusion 2.1 rapid extrusion die design and ordinary aluminum extrusion die compared to the rapid extrusion requires a large diverter hole, which guarantees a sufficient amount of feed; thin upper die, that is, shorten the feeding stroke; The mold work has a short belt, that is, the resistance of the aluminum and the mold decreases; with the completion of the extrusion process, the temperature in the deformation zone increases, and the faster the extrusion speed, the faster the temperature in the deformation zone rises, so the mold should have a mold Cooling system to ensure that the extrusion die temperature is stable, low temperature and high speed, to achieve rapid extrusion, but also to ensure the life of the die and profile quality. In addition, rapid extrusion of mold materials is better.
2.2 Requirements for Aluminum Alloy Aluminum Rods For rapid extrusion, the requirements for aluminum rods are higher than those for ordinary extrusions. The aluminum rods must be completely homogenous, with no oil contamination or inclusion in the aluminum rods. The homogenizing treatment of the alloy can increase the extrusion speed, which can reduce the extrusion force by approximately 6% to 15% compared to the unhomogenized ingot. For the ingot after rapid cooling, the Mg2Si is almost completely dissolved in the matrix, and excess Si is also dissolved in solid solution or dispersed as fine particles.
Such ingots can be extruded rapidly at lower temperatures and achieve excellent mechanical properties and surface brightness. Magnesium is generally controlled at about 0.5%, and the total amount of Mg2Si is controlled at about 0.82%. When 0.01% excess silicon, the mechanical properties of the alloy σb is about 218Mpa, has greatly exceeded the national standard performance, and the excess silicon is increased from 0.01% to 0.13%, σb can be increased to 250Mpa, that is, increased by 14.6%.
To form a certain amount of Mg2Si, it is necessary to first consider the loss of silicon due to impurities such as Fe and Mn, that is, to ensure that there is a certain amount of excess silicon. In order to fully match the magnesium in the 6063 alloy with silicon, the actual compounding must be consciously made Mg:Si<1.73. Excess magnesium not only weakens the strengthening effect but also increases the product cost.
2.3 Requirements for extrusion equipment The extruder must have a control system for constant speed extrusion and isostatic extrusion. With the advancement of modern technology, the extrusion speed can achieve program control or simulation program control, as well as new technologies such as isothermal extrusion technology and CADEX.
By automatically adjusting the extrusion speed to maintain the temperature of the deformation zone within a certain constant range, the purpose of rapid extrusion without cracking can be achieved, and with the progress of extrusion, there is no isothermal extrusion control system, high-speed extrusion The actual temperature of the extrusion will be greatly increased, that is, there is no constant speed extrusion and isothermal extrusion control system, the product discharge speed is inconsistent, the surface of the extruded product will appear squeezing and even cracking extrusion defects, which can not be Realize rapid squeeze.
2.4 Requirements for the discharging method After the product flows out from the die outlet, in order to ensure that it can advance rapidly along the longitudinal balance of the extrusion centerline, it must be hauled by the tractor, preferably by double traction. Without tractor traction, the surface of the rapidly flowing product product may exhibit defects similar to water ripples, or it may locally bend the product and even block the discharge.
3 The extrusion speed of the high-speed extrusion process can be generally increased to 2-4 times the extrusion extrusion speed. After more than one year's efforts, a few mold extrusion speeds have reached 60m/min or more. To achieve rapid extrusion. Compared with general extrusion, the process of rapid extrusion is more stringent.
3.1 Heating of Aluminum Rods, Molds, and Extrusion Tubes In order to increase production efficiency, many measures can be taken in the process. With induction heating, 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 a portion of the heat of deformation.
For extrusion production, extrusion temperature is a more basic and critical process factor. Extrusion temperature has a great influence on product quality, production efficiency, die life, and energy consumption. The more important problem of extrusion is the control of the metal temperature. The heating from the beginning of the aluminum rod to the quenching of the extruded profile must ensure that the dissolvable phase structure does not precipitate out of the solid solution or shows the dispersion of small particles.
The heating temperature of 6063 alloy aluminum rod is generally set within the temperature range of precipitation of Mg2Si. The heating time has an important influence on the precipitation of Mg2Si, and rapid heating can greatly reduce the time for possible precipitation. The heating temperature of the aluminum bar is generally set at 430-460°C for the flat die and 440-470°C for the split die to achieve rapid extrusion at low temperatures.
Mold heating furnace temperature: flat die temperature 450-480 °C; split mold 460-495 °C; flat mold and split mold heating temperature 460-495 °C.
The heating temperature of the extruding barrel is about 50°C lower than the temperature of the aluminum rod, and gradually rises to a specified temperature when heated, so that the temperature of each part is uniform, and the temperature inside the squeezing tube heater is controlled at 380-420°C. The outside temperature is higher than the inside temperature, and the temperature difference is controlled within 50°C.
3.2 Rapid extrusion process process control At low temperature rapid extrusion, the extrusion temperature is lower than 450°C, and the discharge rate is higher than 60m/min, that is, under the condition that the outlet temperature of the profile reaches the direct air-cooling and quenching temperature, Reducing the heating temperature of aluminum rods and increasing the temperature of the products to increase the temperature of the products to compensate for the purpose of rapid extrusion at a low temperature. This will not only increase production efficiency, but also save energy.
Compared with the ordinary extrusion method, the low-temperature rapid extrusion method has its outstanding features: due to the low temperature during extrusion, the billet heating time is shortened correspondingly, the deformation speed is fast, and the billet deformation time is short, which not only saves energy consumption, but also greatly improves The production efficiency.
Bar length control: The use of long bar hot shear, according to the production order requirements as much as possible to lengthen the length of the aluminum bar heat shear, can improve the extrusion efficiency to a certain extent, improve the yield and save costs. Aluminum rods for rapid extrusion are not allowed to have sticks, because the distribution of impurity elements and inclusions at the interface of aluminum rods is concentrated, and the surface quality of the products will be defective; moreover, the stress is also concentrated, which is disadvantageous for the rapid extrusion of metal flowing products.
The control of the main system pressure: the system pressure is too large to cause the friction between the product and the mold to increase, affect the surface quality of the product, and even seriously damage the mold working belt. The main system pressure generally requires ≤ 21MPa.
Control of discharging mode: The double-pull machine is used to pull the extrusion product out of the discharge port to ensure that the product discharge can advance rapidly along the longitudinal balance of the extrusion centerline, and the traction force is synchronized with the extrusion speed to ensure the traction machine The speed is consistent with the extrusion speed. After the profile exits the hole, it is generally pulled by a tractor. When the traction machine is working, it takes a certain pulling tension on the extruding product and simultaneously moves with the unloading speed of the product.
The purpose of using the tractor is to reduce the length of the multi-line extrusion and scratches, but also to prevent the profile out of the hole after the twisting, bending, tension tension to bring trouble. Tension straightening can not only eliminate the longitudinal shape of the product, but also reduce the residual stress, improve the strength properties and maintain its good surface.
Temperature control: On-machine quenching of 6063 aluminum profile is to keep the Mg2Si solid solution in the matrix metal at high temperature and quickly cooled to room temperature. The cooling rate is usually proportional to the content of strengthening phase. The 6063 alloy can be strengthened with a smaller cooling rate of 38°C/min.
According to the on-site inspection, when the extrusion speed exceeds 60m/min, the temperature of the aluminum rod after extrusion can be increased by more than 70°C. In the extrusion process, the mold temperature rises. When the mold is over-temperature, the mold is annealed, the extrusion mold is easily deformed, and even the service life of the mold is affected, and the product discharge is also unstable. In the process of rapid extrusion, the temperature rise of the mold must be faster than that of the general extrusion mold, so the mold should have a mold cooling system to ensure the temperature of the extrusion mold is stable.
In recent years, nitrogen or liquid nitrogen has been used to cool molds (extrusion dies) in foreign countries to increase the extrusion speed, improve die life and improve the surface quality of profiles. In the extrusion process, nitrogen is introduced to the outlet of the extrusion die to rapidly shrink the cooled product, cool the extrusion die and the metal in the deformation zone so that the heat of deformation is taken away, and at the same time, the outlet of the die is exposed to the nitrogen atmosphere. The control reduces the oxidation of aluminum and the bonding and accumulation of alumina, so the cooling of nitrogen improves the surface quality of the product and can greatly increase the extrusion speed.
It is a new extrusion process that is developed more recently. It forms a closed-loop system with the extrusion temperature, extrusion speed, and extrusion force in the extrusion process, which greatly increases the extrusion speed and production efficiency, and ensures that Excellent performance. Can also be used water-cooled die extrusion, that is forced water cooling in the back end of the mold, the test proved to increase the extrusion speed 30% -50%.
Extrusion speed control: The extrusion speed has an important influence on the thermal effect of deformation, uniformity of deformation, recrystallization and solution process, the mechanical properties of the product and the surface quality of the product. When the mold is just on the machine, the extrusion speed setting should not be too fast. After the products are discharged smoothly, the extrusion speed can be gradually increased, and the extrusion can be achieved more quickly.
4. Concluding remarks Aluminum alloy extrusion is the major trend of extrusion in the future. Only by achieving rapid extrusion, increasing productivity, improving production efficiency, reducing energy consumption, and saving costs can it be invincible in the industry. This article only introduces the considerations and ideas for achieving rapid extrusion. The specific process scope is effective at Jingge Company, and the range of possible processes for different equipment, different operators, and different regions will change slightly. In continuous production attempts to improve the process, faster extrusion is achieved.
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