Extrusion is the core technology in metal plastic processing, where pressure is applied to force the blank to flow out of die holes, resulting in profiles with the desired cross-sectional shape. Aluminum alloy extrusion primarily employs forward hot extrusion, operating at temperatures of 400–500°C, with an extrusion ratio typically ranging from 10 to 100.
The complete process includes:Casting Ingot heating (gradient heating temperature control), die preheating, extrusion deformation, online quenching, stretching straightening and artificial aging. Key parameters include extrusion ratio λ, extrusion temperature, extrusion speed and extrusion force, which are intercoupled and collectively determine product quality.
Casting Ingot Heating
Ingot heating is a critical pre-treatment step in the extrusion process, aimed at achieving the required temperature for plastic deformation (typically 400–500°C) and eliminating casting segregation while homogenizing the microstructure.
The heating method primarily employs industrial frequency induction heating, offering advantages such as rapid temperature rise and uniform heat distribution. Resistance furnace heating is suitable for mass production. Process specifications require radial temperature differences ≤±5°C and axial temperature differences ≤±10°C. Gradient heating technology is commonly adopted, where the front end of the ingot (near the die side) maintains a temperature 10–30°C lower than the rear end to balance deformation heat and frictional heat during extrusion, thereby preventing outlet overheating.
Die heating
Die heating is a crucial preparatory step in the extrusion process, aimed at matching the die temperature with the ingot temperature to prevent excessive cooling due to significant temperature differences during metal flow through the die holes, which could impair fluidity and weld quality.
The heating method employs a resistance heating furnace, with the die preheating temperature typically maintained at 450–500°C and a holding time of no less than 2 hours to ensure uniform through-burn. Key process requirements: The die temperature should be slightly higher than the front end temperature of the ingot (10–30°C) to compensate for heat loss during metal flow through the die.
Temperature matching between dies, extrusion cylinders and cast ingots is critical. Excessively low die temperatures can lead to increased pressing peak values, reduced metal fluidity, poor welding quality or even die blockage; conversely, excessively high temperatures may compromise the strength and wear resistance of die steel, accelerating die failure. Precise temperature control (±5°C) and thorough burn-through are key to ensure extrusion stability and surface quality of profiles.
Extrusion deformation
Extrusion deformation is the core process of plastic forming in which metal flows through die holes under high pressure. The ingot is driven by the extrusion shaft within the extrusion cylinder, generating a triaxial compressive stress state. The metal enters the die holes either through a diversion bridge (hollow profile) or directly, thereby achieving the transformation of cross-sectional shape.
Key process parameters include extrusion ratio λ (typically 10–100), extrusion temperature (400–500°C), extrusion speed (axial velocity 2–15 mm/s) and extrusion force. Deformation heat and frictional heat generated during extrusion can cause metal temperature rise of 30–80°C, which requires balance through gradient heating or speed control.
Online Quenching
Online quenching serves as a seamless integration between extrusion processes and heat treatment. It utilizes residual heat from the extrusion die holes to achieve rapid cooling, solidifying the dissolved strengthening phases (e.g., Mg₂Si) at elevated temperatures down to room temperature, thereby creating favorable conditions for subsequent aging.
The cooling method is selected based on alloy properties: air cooling is suitable for alloys with low quenching sensitivity such as 6063; water mist cooling is the most commonly used method for 6xxx series alloys, offering controllable cooling rates and minimal deformation; water immersion cooling is employed for high quenching sensitivity alloys like 7xxx series, with cooling rates ≥50°C/s.
Critical process requirements: The profile temperature must exceed the alloy solid solution temperature (typically ≥500°C) prior to quenching. Cooling must be uniform and sufficient in speed to prevent localized cooling deficiency that could lead to strengthening phase precipitation.
Stretch Rolling
Stretch Rolling serves as a critical finishing process after extrusion. By applying axial tension to the profiles, it eliminates bending, twisting and residual stresses generated during extrusion and quenching processes, while simultaneously fine-tuning dimensional accuracy.
Key technical points: The stretching amount should be controlled within 0.5% to 2.0% (depending on the profile shape, wall thickness and precision requirements). Excessively low stretching cannot achieve effective straightening, while excessive stretching may lead to cross-sectional narrowing, dimensional deviations or even fracture. During the stretching process, ensure uniform clamping and force line alignment to prevent additional bending.
Artificial Aging
Artificial aging is a critical heat treatment process for imparting final mechanical properties to extruded profiles. After quenching, the profiles are heated and held in an aging furnace to promote uniform precipitation of strengthening phases (e.g., Mg₂Si in the 6xxx series) from the supersaturated solid solution, forming nanoscale dispersed precipitates that significantly enhance hardness and strength.
Typical process parameters: The aging temperature for the 6xxx series is 180–200°C with a holding time of 2–4 hours; the 7xxx series employs two-stage aging with more complex temperature and time combinations. During the aging process, strict control of furnace temperature uniformity (within ±3°C) is required to prevent localized overaging or underaging.
Andoic Oxidation
Electrophoretic Coating
Powder Coating
Hot Rolling
Hot rolling is a forming process in which metal billets are heated above the recrystallization temperature for rolling deformation. The heating temperature typically ranges from 0.6 to 0.9 times the metal melting point, with aluminum alloy hot rolling temperatures generally set at 350–450°C.
During hot rolling, metals undergo both work hardening and dynamic recrystallization simultaneously, resulting in significantly improved plasticity and reduced deformation resistance, making them suitable for high reduction production. The primary equipment includes hot rolling mills (two-roll, four-roll or multi-roll), which apply pressure to the billet through rotating rolls to reduce its thickness and increase its width.
The primary function of hot rolling is to transform cast ingots (flat or round ingots) into sheet metal, strip or bar billets; to break down the casting structure, eliminate pores and shrinkage cavities; and to refine grain size while improving mechanical properties.
Cold Rolling
Cold rolling is a rolling deformation process performed below the metal recrystallization temperature, typically conducted at room temperature. Prior to cold rolling of aluminum alloys, hot-rolled billets must undergo annealing to soften, eliminate the hot-rolled microstructure, and reduce deformation resistance.
Cold rolling is characterized by significant work hardening, where metals exhibit increased strength and reduced plasticity during deformation. With minimal single-pass reduction (typically 10%–30%), achieving target thickness requires multiple passes combined with intermediate annealing. Cold-rolled products demonstrate excellent surface quality and high dimensional accuracy (with thickness tolerances as low as ±0.01 mm), while their mechanical properties can be precisely controlled through work hardening degree adjustment.
Specifications and Tolerances
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