Views: 0 Author: Site Editor Publish Time: 2026-03-17 Origin: Site
Low-temperature high-speed extrusion is a manufacturing process that combines relatively low billet temperatures with rapid extrusion rates. This technique features an inverse relationship between "low temperature" and "high speed" —as the billet temperature decreases, the extrusion speed can be increased. For typical extruded alloys like 6063 aluminum alloy, the low-temperature extrusion temperature range is typically maintained at approximately 440–460°C, while the extrusion speed can reach up to 30–50 meters per minute.
The core principle of low-temperature high-speed extrusion lies in how lower temperatures suppress overheating during deformation, creating optimal conditions for rapid extrusion. It's crucial to note that the term' low temperature 'specifically refers to the billet temperature at the die inlet, while the extruded product at the die outlet must still reach the optimal temperature range for solid solution treatment (e.g., 515–525°C for 6063 alloy) to ensure the product's mechanical properties.
High-temperature low-speed extrusion, on the other hand, refers to a production process combination where the extrusion speed is slowed down under higher billet temperatures. The temperature range for high-temperature extrusion is typically controlled between 500-520°C, and the extrusion speed must be strictly limited to a slower rate.
The basic logic of high temperature and low speed extrusion is that higher temperature reduces the deformation resistance of metal, making it easier to form but it also brings the risk of overheating, so it is necessary to reduce the speed to control the temperature rise and ensure the uniform flow of metal.
Technological Parameter | Low Temperature High Speed Extrusion | High Temperature Low Speed Extrusion |
Billet Temperature | 440~460℃（Lower） | 500~520℃（Higher） |
Extrusion Speed | 30~50m/minute（Fast） | significantly lower than low-temperature high-speed (slow) |
Outlet Temperature | The temperature must reach 515–525°C (by heating through deformation) | 550~575℃ |
Primary Applicable Alloy | Alloys with good extrusibility (e.g., 6063) | Alloys with poor extrusibility (e.g., Group 2 and Group 7 high-strength aluminum alloys) |
Technical Difficulty | Precise temperature control is required, with stringent equipment specifications. | Relatively mature but inefficient |
Characteristics:
Exceptionally high production efficiency: The extrusion speed can reach 2-3 times that of conventional processes, significantly boosting production capacity.
Relatively low energy consumption: The heating temperature of the billet is low and the energy cost is saved.
Using deformation heat to increase temperature: The deformation heat from high-speed extrusion is skillfully utilized to achieve the solid solution treatment temperature at the exit of the profile without additional heating.
Technical challenges:
Quenching capability matching issue: High-speed extrusion requires subsequent online quenching equipment (air-cooled, spray, water-cooled) to have sufficient capacity; otherwise, the profiles cannot achieve the required basic mechanical properties.
Tail overheating risk: During high-speed extrusion, especially in the tail stage, the billet temperature may rise rapidly due to intense deformation heat, potentially causing metal overheating and burn-through. This can lead to surface cracks or even "pull-out" defects on the profile, resulting in increased scrap rate.
Mold cooling demand: In order to solve the problem of overheating caused by high-speed extrusion, liquid nitrogen cooling technology is often introduced. Liquid nitrogen is injected into the working area of the mold to reduce the temperature of the deformation area and take away the deformation heat. At the same time, nitrogen can also protect the surface of the profile and reduce oxidation.
Characteristics:
The deformation resistance is small: The metal has good fluidity at high temperature, the extrusion pressure is reduced and the equipment capacity is relatively low.
Suitable for hard deformation alloys: For high-strength aluminum alloys such as 2-series and 7-series, high temperature is a necessary condition for their extrusibility.
Technical Risk:
The risk of grain coarsening: When the mold temperature exceeds 525℃ and the cooling is not sufficient, the product is prone to produce coarse grain structure, which seriously affects the mechanical properties.
Insufficient solid solution: If the temperature is too high but not properly controlled, it may result in incomplete solid solution of alloy elements such as magnesium and silicon, thereby reducing the hardness and strength of the alloy.
Loose flow lines: For hollow profiles extruded using flow combing die, if the extrusion speed is too fast or the temperature is excessively high, insufficient metal supply may lead to the formation of loose structures along the flow lines. During subsequent alkaline cleaning, these defects are prone to corrosion exposure, affecting surface quality and post-processing results.
Extrusion temperature and extrusion speed are not independent variables, they exhibit a coupled relationship, as shown in the figure below.
Excessive low compression temperature or excessively slow compression rate → Compression force exceeds the equipment capacity → Compression is difficult to achieve
Excessive extrusion speed or elevated temperature → Defects such as surface cracks and adhesion appear on the product → Non-compliance with quality standards
Therefore, the extrusion temperature and extrusion speed must be controlled in the region between the extrusion capacity curve and the product surface quality curve, which is the feasible process window.
Research demonstrates that extrusion speed significantly impacts metal flow uniformity more than temperature. Taking automotive sunroof guide rail profiles as an example, when the extrusion speed increases from 4mm/s to 6mm/s, the standard deviation of velocity (SDV) at the die exit profile cross-section rises sharply from 10.56mm/s to 24.11mm/s, indicating intensified flow velocity irregularities. Studies on 7-series high-strength aluminum alloys further confirm that low-speed extrusion (<0.3mm/s) results in minimal temperature rise and uniform flow, whereas speeds exceeding 0.3mm/s cause a dramatic increase in frictional heat, which may lead to cross-sectional velocity irregularities and profile bending.
Different alloys have their optimal temperature ranges. For high-strength Al-Zn-Mg-Cu-Zr alloys, the 390-430℃ range provides optimal material plasticity and moderate extrusion pressure. Temperatures below 350℃ result in excessive resistance, while those above 470℃ carry the risk of overburning. In contrast, the 6063 alloy employs both low-temperature high-speed processing (440-460℃ for billets) and high-temperature low-speed processing (500-520℃), with the former representing a more advanced production philosophy.
Recent studies have provided quantitative data on the effectiveness of two processes. Research on machining AA6063 aluminum alloy using the novel torsion channel self-bending process (TCSE) demonstrates that:
Performance Index | Effect of improving billet temperature | Effect of increasing extrusion speed |
Average Hardness | An increase of 55.9% | An increase of 19.5% |
Ultimate Tensile Strength(UTS) | An increase of 12.5% | An increase of 7.1% |
Applicable Scene | Preferred when high curvature (≥328.67 mm) is required | Preferred when low curvature (≤328.67 mm) is required |
This demonstrates that under specific product requirements, increasing temperature can significantly enhance mechanical properties more effectively than increasing speed. However, it is also important to note that excessively high temperatures may lead to grain coarsening—when the temperature difference between the deformation zone and its surroundings exceeds 31K, coarse grain layers approximately 400μm in size tend to form at the edges, resulting in reduced hardness.
Whether low-temperature high-speed or high-temperature low-speed, the traditional constant-speed extrusion is difficult to avoid the problem of uneven temperature distribution in the profile. During the extrusion process, the friction between the ingot and the extrusion barrel, as well as the deformation heat, gradually increase the temperature of the billet, leading to uneven microstructural properties in the front and back of the profile.
To address this issue, isothermal extrusion technology was developed. Its core principle involves real-time control of extrusion speed to maintain a constant temperature at the die outlet (typically within ±10°C). Methods to achieve isothermal extrusion include:
Billet gradient heating/cooling method: The billet is subjected to a temperature gradient along its length, with higher temperatures at the front end and lower temperatures at the rear end, thereby offsetting the temperature rise caused by deformation heat.
Online closed-loop control of extrusion speed: The Optalex constant-temperature extrusion control system developed by Alumac (Denmark) achieves 8%-10% higher average productivity and 2%-3% lower scrap rate by continuously monitoring extruded profiles' outlet temperature and dynamically adjusting extrusion speed.
Temperature Control in Mould and Tooling: Technologies include zoned heating/cooling of extrusion cylinders and liquid nitrogen cooling for moulds. The introduction of isothermal extrusion technology effectively combines the advantages of low-temperature high-speed and high-temperature low-speed processes. It allows for low-speed operation during the initial extrusion phase (when the blank temperature is high) and automatically reduces speed during the mid-to-late stages (when the blank temperature rises due to deformation heat), thereby achieving constant-temperature extrusion throughout the entire process. This ensures product quality uniformity while maximizing average extrusion speed.
