Aluminum alloy conductor gradient annealing method

Abstract

The application provides an aluminum alloy conductor gradient annealing method, comprising the following steps: (1) the cold-drawing wire-formed single wire is loaded into a wire reel and then is placed into an annealing furnace to be kept at a temperature of 300-340 DEG C for 4-6 hours, and after the keeping, the temperature is reduced to room temperature at a cooling rate of 5-8 DEG C / min; (2) the annealed single wire is stranded to form a conductive core, the conductive core is loaded into a wire reel and then is placed into an annealing furnace to be kept at a temperature of 280-300 DEG C for 6-8 hours, and after the keeping, the temperature is reduced to room temperature at a cooling rate of 3-5 DEG C / min; (3) the annealed conductive core is compacted, the compacted conductive core is placed into an annealing furnace to be kept at a temperature of 320-360 DEG C for 8-10 hours, and after the keeping, the temperature is reduced to room temperature at a cooling rate of 4-6 DEG C / min. Through three-stage gradient temperature regulation, the application realizes the accurate balance between the conductivity and the tensile strength, and the treated conductor meets the national standard requirements.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy conductor processing technology, and relates to a gradient annealing method for aluminum alloy conductors. Background Technology

[0002] Driven by the "aluminum-for-copper" strategy, aluminum alloy conductors have become a core alternative material in the power transmission field due to their resource endowment and cost advantages. Annealing, as a key process in the manufacturing of aluminum alloy conductors, plays a crucial role in eliminating residual stress from cold working and optimizing the microstructure through recrystallization, thereby achieving a balance between conductivity and mechanical properties. However, traditional aluminum alloy conductor annealing processes have the following prominent drawbacks: Temperature control defects: Traditional processes use a single annealing temperature, which cannot adapt to the microstructure requirements of aluminum alloy conductors at different processing stages. Too high a temperature (>380℃) will cause abnormal grain growth, and the tensile strength retention rate will drop to below 85%. Too low a temperature (<300℃) will result in incomplete precipitation of solid solution atoms, and the conductivity will be below 60% IACS, making it difficult to simultaneously meet the dual requirements of conductivity and mechanical properties in GB / T 31840-2015 standard.

[0003] Stress relief defects: Traditional annealing uses a "one-size-fits-all" heat preservation time design (mostly a fixed 24-hour cycle), which does not take into account the difference in stress distribution before and after conductor stranding, resulting in incomplete residual stress relief (residual stress > 50MPa). This leads to easy loosening of the conductor during laying, shortened bending fatigue life, increased contact resistance at connection points during long-term operation, and potential overheating safety hazards.

[0004] Batch stability defects: Traditional processes lack precise control over the amount of material loaded onto trays. When the difference in the amount of material loaded onto trays in a single furnace exceeds 15%, the temperature uniformity deviation inside the furnace can reach ±8℃, resulting in a conductivity fluctuation of ±1% IACS or more in the same batch of conductors, which cannot meet the quality consistency requirements of large-scale production.

[0005] Process synergy defects: Traditional annealing processes do not synergize with preceding drawing and pressing processes. The drawing deformation amount (30%-50%) does not match the annealing parameters, which can easily lead to insufficient elongation (<3%) due to "excessive deformation + insufficient annealing", or insufficient strength due to "insufficient deformation + over-annealing". Summary of the Invention

[0006] The purpose of this invention is to provide a gradient annealing method for aluminum alloy conductors, addressing the problems existing in the prior art.

[0007] Therefore, the present invention adopts the following technical solution: A gradient annealing method for aluminum alloy conductors includes the following steps: (1) The cold-drawn aluminum alloy monofilament is loaded into the wire spool and then placed in the annealing furnace at a temperature of 300-340℃ for 4-6 hours. After the heat preservation is completed, the temperature is reduced to room temperature at a cooling rate of 5-8℃ / min. (2) Twist the annealed monofilaments to form a conductive wire core, load it into a wire spool, and then place it in an annealing furnace at a temperature of 280-300℃ for 6-8 hours. After the heat preservation is completed, cool it down to room temperature at a cooling rate of 3-5℃ / min. (3) Press the annealed conductive core tightly, place the pressed conductive core into the annealing furnace and keep it at 320-360℃ for 8-10 hours. After the heat preservation is completed, cool it down to room temperature at a cooling rate of 4-6℃ / min.

[0008] Furthermore, the cold drawing deformation of the monofilament in step (1) is 35%-40%.

[0009] Furthermore, the density of the monofilament after being loaded into the tray in step (1) is 50-80 kg / m³.

[0010] Furthermore, in step (3), the compaction coefficient during the compaction of the conductive wire core is ≥0.92.

[0011] Furthermore, during the annealing process in steps (1)-(3), an inert gas protective atmosphere is preset in the annealing furnace, and the oxygen content in the annealing furnace is ≤0.1%.

[0012] The beneficial effects of this invention are as follows: (1) Excellent performance balance: Through three-stage gradient temperature control, the conductivity and tensile strength are precisely balanced. After treatment, the volume conductivity of the conductor is ≥61% IACS, the tensile strength is ≥190MPa (up to 195±2MPa), and the elongation is ≥3%, which fully meets the requirements of national standards such as GB / T 31840-2015 and GB / T 30552-2014. (2) Thorough stress elimination: residual stress is reduced to ≤35MPa, creep resistance is significantly improved, conductor connection points do not loosen during long-term operation, contact resistance is stable, overheating failure is avoided, and bending fatigue life is increased by more than 1.5 times compared with traditional process; (3) Strong batch stability: Through the control of the loading quantity and the protection of inert gas, the temperature uniformity deviation in the furnace is ≤±3℃, the conductivity fluctuation of the same batch of conductors is ≤0.5% IACS, and the finished product qualification rate is increased from 85% of the traditional process to more than 98%; (4) High efficiency of process synergy: It is highly compatible with drawing and pressing processes, shortening the overall production cycle (the total annealing time is optimized from 24 hours to 18-24 hours, which can be flexibly adjusted according to specifications), and the average monthly production efficiency of a single production line is increased by 20%; (5) Significant economic benefits: Inert gas protection reduces oxidation loss on conductor surface and increases material utilization by 5%; gradient temperature control reduces energy consumption by 30%. Detailed Implementation

[0013] The present invention will be described in detail below with reference to embodiments: A gradient annealing method for aluminum alloy conductors includes the following steps: (1) Aluminum alloy monofilaments are produced by cold drawing. A 13-die high-precision wire drawing machine is used to draw the monofilaments, which have a diameter of 2.18 mm. The cold drawing deformation is 35%-40%. In this embodiment, the cold drawing deformation is 35%. The aluminum alloy monofilaments are then loaded into a wire spool with a diameter of 2000 mm. The density of the aluminum alloy monofilaments after loading is 50-80 kg / m³, and the weight after loading is no more than 10 tons. This ensures uniform airflow in the furnace. The wire spool is then placed in an annealing furnace and heated and annealed at a temperature of 300-340℃ for 4-6 hours. An inert gas protective atmosphere is preset in the annealing furnace during annealing. Specifically, nitrogen is introduced into the annealing furnace during annealing to replace the air in the furnace, so that the oxygen content in the furnace is ≤0.1%. In this embodiment, the furnace is heated and held at a temperature of 320℃ for 5 hours. The residual stress generated during the drawing process can be released by the first annealing, providing a single wire substrate with good plasticity for the stranding process, and avoiding wire breakage due to stress concentration during stranding. After the heat preservation is completed, the temperature is cooled to room temperature at a cooling rate of 5-8℃ / min. In this embodiment, the temperature is cooled to room temperature at a cooling rate of 6℃ / min. After cooling to room temperature, the residual stress is 42MPa and the conductivity is 59.8% IACS.

[0014] (2) The annealed monofilaments are twisted together to form a conductive core. Specifically, the pitch ratio during the twisting process is 11, the tension is controlled by multi-axis servo, and the fluctuation is <3%. The conductive core is loaded into the coil. The density of the conductive core in the coil is also 50-80 kg / m³. The weight after loading the coil is no more than 10 tons. Then the coil is placed in the annealing furnace and kept at 280-300℃ for 6-8 hours. After the heat preservation is completed, the temperature is reduced to room temperature at a cooling rate of 3-5℃ / min. In this embodiment, the annealing is carried out at 290℃ for 7 hours to eliminate the circumferential and radial stress generated during the twisting process, promote the uniform precipitation of strengthening phases such as Al3Zr inside the aluminum alloy, and initially balance the conductivity and mechanical properties. After the heat preservation is completed, the temperature is reduced to room temperature at a cooling rate of 4℃ / min. After the temperature is reduced to room temperature, the residual stress is 38 MPa and the conductivity is 60.5% IACS. The annealing process is also carried out in the annealing furnace with a pre-set inert gas protective atmosphere. The specific method is the same as step (1).

[0015] (3) The annealed conductive core is compacted to obtain the finished product. The compaction coefficient during compaction is ≥0.92. In this embodiment, the compaction coefficient is 0.93. The conductor cross-section filling rate is 92.5%, and there are no exposed wires or bulging defects. The compacted conductive core is loaded into a wire spool. The density of the finished product in the spool is also 50-80 kg / m³. The spool is placed in an annealing furnace at a temperature of 320-360℃ and kept at that temperature for 8-10 hours. In this embodiment, the temperature is 340℃ and kept at that temperature for 8-10 hours. After 9 hours of heat treatment, the conductor was completely recrystallized, the grain size was refined (grain size ≤ 50 μm), and the balance between conductivity and tensile strength was optimized. After the heat treatment, the temperature was reduced to room temperature at a cooling rate of 4-6℃. In this embodiment, the temperature was reduced to room temperature at a cooling rate of 5℃ / min. The annealing process was also carried out in an inert gas protective atmosphere in the annealing furnace. The specific method was the same as step (1). After cooling to room temperature, the surface of the finished product was blown to remove a small amount of oxide dust and ensure that the surface roughness Ra ≤ 0.8 μm. Final test results: residual stress 32 MPa, volume conductivity 61.5% IACS, tensile strength 193 MPa, elongation 3.2%, straightness error 0.4 mm / m. All indicators met the requirements of GB / T 31840-2015 and GB / T 30552-2014 standards.

[0016] This method was continuously operated for eight months on two aluminum alloy cable production lines at Jinchuan Group Wire & Cable Co., Ltd. The defect rate of conductors with specifications such as 120mm², 300mm², and 630mm² decreased from 15% with traditional processes to 1.2%, with no performance issues caused by the annealing process. The average monthly capacity of a single production line increased by 25%, energy costs decreased by 32%, and the product's operational stability in new energy power plant projects was comparable to that of copper cables, reducing the total project cost by more than 50%. Market feedback has been positive.

Claims

1. A gradient annealing method for aluminum alloy conductors, characterized in that, Includes the following steps: (1) The cold-drawn aluminum alloy monofilament is loaded into the wire spool and then placed in the annealing furnace at a temperature of 300-340℃ for 4-6 hours. After the heat preservation is completed, the temperature is reduced to room temperature at a cooling rate of 5-8℃ / min. (2) Twist the annealed monofilaments to form a conductive wire core, load it into a wire spool, and then place it in an annealing furnace at a temperature of 280-300℃ for 6-8 hours. After the heat preservation is completed, cool it down to room temperature at a cooling rate of 3-5℃ / min. (3) Press the annealed conductive core tightly, place the pressed conductive core into the annealing furnace and keep it at 320-360℃ for 8-10 hours. After the heat preservation is completed, cool it down to room temperature at a cooling rate of 4-6℃ / min.

2. The gradient annealing method for aluminum alloy conductors according to claim 1, characterized in that, The cold drawing deformation of the monofilament in step (1) is 35%-40%.

3. The gradient annealing method for aluminum alloy conductors according to claim 1, characterized in that, The density of the monofilament after being loaded into the tray in step (1) is 50-80 kg / m³.

4. The gradient annealing method for aluminum alloy conductors according to claim 1, characterized in that, In step (3), the compaction coefficient of the conductive wire core is ≥0.

92.

5. The gradient annealing method for aluminum alloy conductors according to claim 1, characterized in that, In steps (1)-(3), an inert gas protective atmosphere is preset in the annealing furnace during annealing, and the oxygen content in the annealing furnace is ≤0.1%.