Rare earth microalloy semi-hard flat copper coil and preparation method and application thereof

Abstract

The invention provides a rare earth microalloy semi-hard flat copper coil and a preparation method and application thereof, and belongs to the technical field of lead frame materials. The rare earth microalloy semi-hard flat copper coil comprises the following elements in percentage by mass: 0.05% of La, 0.01% of Zr, 0.04% of Y, 0.02% of Te, 0.005% of Ag and the balance of copper and inevitable impurities. Under the working condition of a high-frequency transformer of a charging pile, the resistance loss (copper loss) of the coil is obviously increased due to a skin effect and a proximity effect, so that the material mainly solves the problems of ensuring the ultrahigh conductivity, improving the mechanical strength, avoiding the stress deformation of the winding and improving the short-circuit resistance of the winding coil. By controlling the component proportion of the rare earth microalloy semi-hard flat copper coil, improving the conductivity and considering the yield strength and elongation performance, the high-strength and high-conductivity characteristics of the winding wire are achieved, and the performance index of the high-power charging pile high-frequency transformer flat copper coil is met.

Description

Technical Field

[0001] This invention relates to the field of conductor frame materials technology, and in particular to a rare earth microalloyed semi-hard flat copper coil, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles, electric vehicle charging stations are evolving towards higher power and higher voltage. The coils (windings) of the high-frequency transformer in charging stations are the core components for energy transfer, voltage ratio, and electrical isolation. Their materials must be adapted to the high-frequency, high-voltage, and high-power operating characteristics. During operation, the high-frequency transformer causes a significant increase in coil resistance loss (copper loss) due to the skin effect and proximity effect, leading to winding damage. Therefore, the mechanical and conductive properties of the copper wires in high-frequency transformers for charging stations are subject to stricter requirements. With the development of high-power electric vehicle charging stations such as supercharging and liquid cooling, the market urgently needs semi-hard flat copper wires with strong short-circuit withstand capabilities to manufacture the coils. The yield strength of the wire has a significant impact on the coil's short-circuit withstand capability and is a crucial performance indicator. This places higher demands on the copper wires used for windings; therefore, achieving semi-hard, high-strength, and high-conductivity copper wires is a critical problem that urgently needs to be solved.

[0003] Existing technologies that rely solely on increasing the purity of industrial electrolytic copper and adding trace elements to improve conductivity, or simply adjusting production processes to enhance the conductivity and strength of winding coils, have reached their limits. They cannot address the high strength and high conductivity requirements of semi-hard flat copper coils in high-frequency transformers (100~300kHz). Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a rare-earth microalloyed semi-hard flat copper coil, its preparation method, and its application. The rare-earth microalloyed semi-hard flat copper coil provided by this invention achieves high strength and high conductivity characteristics of the winding conductor.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a rare earth microalloy semi-hard flat copper coil comprising the following elements by mass percentage: 0.05% La, 0.01% Zr, 0.04% Y, 0.02% Te, 0.005% Ag, with the remainder being copper and unavoidable impurities.

[0006] This invention also provides a method for preparing the rare-earth microalloyed semi-hard flat copper coil described in the above technical solution, comprising the following steps: A mixed powder was obtained according to the element ratio; The mixed powder is then vacuum melted to obtain an ingot; The ingot is refined and solution treated before being cast into a mold to obtain an intermediate alloy ingot. The intermediate alloy ingot is subjected to cold rolling and extrusion followed by stress-relief annealing to obtain the rare earth microalloy semi-hard flat copper coil.

[0007] Preferably, the mixed powder is wrapped in copper foil before being vacuum melted.

[0008] Preferably, the vacuum melting temperature is 1200~1300℃ and the time is 1~2h.

[0009] Preferably, the vacuum melting is carried out by electromagnetic stirring, wherein the frequency of the electromagnetic stirring is 20~30Hz, the current is 200~300A, and the time is 15~30min.

[0010] Preferably, the refining-solidification treatment is carried out at a temperature of 930~960℃ for 1~2 hours.

[0011] Preferably, the cold rolling extrusion temperature is 800~850℃, the holding time is 1~2h, and the extrusion pressure is 20MPa.

[0012] Preferably, the stress-relief annealing temperature is 600~700℃ and the time is 1~2h.

[0013] Preferably, the first cold drawing is performed after the cold rolling extrusion and before the stress-relief annealing, and the second cold drawing is performed after the stress-relief annealing.

[0014] This invention also provides the application of the rare earth microalloy semi-hard flat copper coil described in the above technical solution or the rare earth microalloy semi-hard flat copper coil prepared by the preparation method described in the above technical solution in the field of charging pile transformers.

[0015] This invention provides a rare earth microalloy semi-hard flat copper coil comprising the following elements by mass percentage: 0.05% La, 0.01% Zr, 0.04% Y, 0.02% Te, 0.005% Ag, with the remainder being copper and unavoidable impurities.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: Under the operating conditions of high-frequency transformers in charging piles, the resistive loss (copper loss) of the coil increases significantly due to the skin effect and proximity effect. Therefore, the material needs to focus on ensuring ultra-high conductivity, improving mechanical strength, avoiding winding deformation under stress, and improving the short-circuit withstand capability of the winding coil. In this invention, the micro-alloyed semi-hard flat copper coil, after adding rare earth elements, exhibits a significantly increased yield strength and elongation compared to pure copper. At the same time, its conductivity not only does not decrease but actually increases compared to pure copper wire. This invention improves conductivity by controlling the composition ratio of rare earth micro-alloyed semi-hard flat copper coils, while considering yield strength and elongation performance, achieving high strength and high conductivity characteristics of the winding wire, meeting the performance indicators of flat copper coils in high-power charging pile high-frequency transformers (100~300kHz).

[0017] This invention also provides a method for preparing the rare earth microalloy semi-hard flat copper coil described in the above technical solution. The preparation method of this invention is simple to operate and suitable for industrial application. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation of a rare-earth microalloyed semi-hard flat copper coil in Example 1; Figure 2 The images show the metallographic structures of pure copper and the rare earth microalloy semi-hard flat copper coil of Example 1, where (a) is the metallographic structure of pure copper and (b) to (d) are the metallographic structures of the rare earth microalloy semi-hard flat copper coil of Example 1 at different magnifications. Detailed Implementation

[0019] This invention provides a rare-earth microalloyed semi-hard flat copper coil, comprising the following elements by mass percentage: 0.05% La, 0.01% Zr, 0.04% Y, 0.02% Te, 0.005% Ag, with the remainder being copper and unavoidable impurities. Adding appropriate proportions of trace alloys (Zr, Te, and Ag) can improve the mechanical strength of the copper alloy, while adding appropriate proportions of rare-earth elements (La and Y) can purify, remove impurities, and refine grains, resulting in rare-earth microalloyed semi-hard copper wires with higher strength and toughness than pure copper wires, while simultaneously reducing resistivity. Excessive addition of rare-earth elements will exist as impurities in the copper matrix, thus reducing the conductivity of the copper wire. The resistivity of the copper wire is the result of the competition between the rare-earth purification effect and the grain refinement effect; the former reduces the resistivity of pure copper, while the latter, due to increased grain boundaries, may increase the resistivity of pure copper. La has a stronger effect on the resistivity and elongation of the copper wire than Y, mainly because La has higher reactivity and readily reacts with many harmful impurities in the alloy solution. Rare earth elements such as oxygen, sulfur, hydrogen, nitrogen, and some low-melting-point metallic elements such as Pb, Sb, or Bi react, and the reaction products sink or float to form slag, reducing the harmful effects of these elements on copper alloys. This process deoxidizes, desulfurizes, dehydrogenates, denitrifies, and purifies the melt, with a stronger purification ability than Y. It can significantly improve the resistivity and elongation of rare earth copper alloys. Te and Zr mainly play a role in precipitation strengthening and solid solution, with little or no effect on the conductivity and elongation of copper alloys, or even a negative effect. Y has the greatest impact on the yield strength of the alloy, mainly because Y can make the dendritic mesh of the copper alloy casting structure smaller and the grain structure significantly refined, playing a certain role in grain refinement strengthening. Trace amounts of Te and Zr mainly play a role in dispersion strengthening and solid solution, but due to their small amount, their effect on yield strength is not as significant as the grain refinement strengthening effect of Y. La mainly plays a role in purifying the melt, while trace elements of Ag mainly play a role in reducing resistivity. The interaction of these elements makes the strength and conductivity of the material reach the optimal effect.

[0020] In this invention, the thickness of the rare earth microalloy semi-hard flat copper coil is preferably 0.8~5.6mm, specifically 0.8, 1.6, 2.4, 3.2, 4, 4.8 or 5.6mm, and the width is preferably 2.0~16mm, specifically 2, 4, 6, 8, 10, 12, 14 or 16mm.

[0021] In this invention, the yield strength of the rare earth microalloy semi-hard flat copper coil is preferably 220~260 N / mm². 2 The elongation is preferably ≥30%, and the resistivity is preferably ≤0.017150Ω·mm. 2 / m.

[0022] This invention also provides a method for preparing the rare-earth microalloyed semi-hard flat copper coil described in the above technical solution, comprising the following steps: A mixed powder was obtained according to the element ratio; The mixed powder is then vacuum melted to obtain an ingot; The ingot is refined and solution treated before being cast into a mold to obtain an intermediate alloy ingot. The intermediate alloy ingot is subjected to cold rolling and extrusion followed by stress-relief annealing to obtain the rare earth microalloy semi-hard flat copper coil.

[0023] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0024] The present invention obtains a mixed powder according to the element ratio.

[0025] In this invention, the particle size of the mixed powder is preferably 100~500nm, specifically 100, 200, 300, 400 or 500nm.

[0026] The present invention preferably places the raw materials in a high-energy ball mill for ball milling and mixing to obtain the mixed powder.

[0027] In this invention, the ball mill jar is preferably subjected to vacuum treatment before ball milling and mixing, so that the vacuum degree is preferably less than 29 Pa.

[0028] After obtaining the mixed powder, the present invention performs vacuum melting on the mixed powder to obtain an ingot.

[0029] In this invention, it is preferable to wrap the mixed powder with copper foil before vacuum melting. The wrapping forms a sealed "protective layer" that completely isolates residual gas, prevents powder oxidation and failure, and the copper foil wrapping can slow down the direct contact rate between the powder and the high-temperature melt, reduce volatilization loss, and ensure the accuracy of rare earth and trace metal composition in the copper ingot.

[0030] In this invention, the thickness of the protective layer is preferably 0.05~0.1mm.

[0031] In this invention, the vacuum melting temperature is preferably 1200~1300℃, specifically 1200, 1250 or 1300℃, and the time is preferably 1~2h.

[0032] In this invention, the vacuum melting is preferably carried out by electromagnetic stirring. The frequency of the electromagnetic stirring is preferably 20~30Hz, specifically 20, 25 or 30Hz, the current is preferably 200~300A, specifically 200, 250 or 300A, and the time is preferably 15~30min, specifically 15, 20, 25 or 30min. The electromagnetic stirring makes the mixed powder evenly distributed in the copper liquid.

[0033] After obtaining the ingot, the present invention refines and solidifies the ingot and then casts it into a mold to obtain an intermediate alloy ingot.

[0034] In this invention, the refining-solidification treatment temperature is preferably 930~960℃, specifically 930, 940, 950 or 960℃, and the time is preferably 1~2h.

[0035] In this invention, the refining-solidification process is preferably carried out in a vacuum induction melting furnace.

[0036] After the refining-solidification process is completed, it is preferably cooled to the casting temperature before casting.

[0037] In this invention, the pouring temperature is preferably 1150~1200℃.

[0038] In this invention, the casting mold for ingot molding is preferably a cast iron mold.

[0039] In this invention, the intermediate alloy ingot is preferably a cylinder with a diameter of 60 mm.

[0040] After obtaining the intermediate alloy ingot, the present invention sequentially performs cold rolling extrusion and stress-relief annealing on the intermediate alloy ingot to obtain the rare earth microalloy semi-hard flat copper coil.

[0041] In this invention, the preferred temperature for cold rolling extrusion is 800~850℃, specifically 800, 835, or 850℃, the preferred holding time is 1~2 hours, and the preferred extrusion pressure is 20MPa. Cold rolling extrusion has a dual function of "forming + strengthening," satisfying the dimensional / surface requirements of parts through cold precision forming and improving the mechanical properties of materials through work hardening. It is particularly suitable for the mass production of copper alloy / rare earth copper alloy parts with high precision and strength requirements, and is an important processing technology for key components in the new energy field. Cold rolling extrusion can improve the plasticity of billets: copper and copper alloys change from brittle to plastic at high temperatures (above the recrystallization temperature), avoiding cracking during extrusion. Pure copper recrystallizes at 200℃, and is in a fully austenitic state at 800~850℃, exhibiting optimal plasticity. It also reduces deformation resistance: at high temperatures, metal atoms have strong mobility, reducing flow resistance and minimizing extrusion pressure consumption, thus preventing overloading of the hydraulic press or damage to the die. Furthermore, it ensures uniform microstructure: heat preservation keeps the billet at a consistent temperature inside and out, resulting in uniform metal flow during extrusion and guaranteeing the dimensional accuracy of the finished product (e.g., uniform wall thickness of copper profiles).

[0042] Before cold rolling and extrusion, the copper alloy intermediate alloy ingot is preferably machined to remove surface impurities and defects, and then placed in an electric furnace for cold rolling and extrusion.

[0043] In this invention, the extrusion die for cold rolling extrusion is preferably preheated. The preheating temperature is preferably 500~600℃, specifically 500, 550, or 600℃, and the holding time is preferably 1~2 hours. If the preheating temperature of the extrusion die is too low (<500℃), the die will experience severe thermal shock, which can easily lead to microcracks. The surface of the billet will cool down quickly, forming a hard shell, resulting in a rough surface of the extruded part. If the temperature is too high (>600℃), the die strength will decrease, the cavity will be easily deformed, leading to out-of-tolerance dimensions of the finished product. The die oxidation will be accelerated, and the surface accuracy will be reduced.

[0044] The present invention preferably uses a 300t vertical hydraulic press for the cold rolling extrusion.

[0045] In this invention, the copper rod with a Φ of 8.0~8.5mm is preferably obtained after cold rolling and extrusion.

[0046] In this invention, the stress-relief annealing temperature is preferably 600~700℃, specifically 600, 650 or 700℃, and the time is preferably 1~2h.

[0047] In this invention, after cold rolling and extrusion and before stress-relief annealing, a first cold drawing is preferably performed, and after stress-relief annealing, a second cold drawing is preferably performed.

[0048] In this invention, the copper rod with a diameter of 8.0~8.5mm is preferably pickled to remove the surface oxide layer and oil stains, then cold-drawn to a diameter of 7.5~8.0mm, placed in a box-type annealing furnace for stress relief annealing, then pickled again and cold-drawn again to obtain a semi-hard copper alloy material with a diameter of 5.0~5.5mm. Finally, according to the winding power requirements, it is drawn into the rare earth microalloy semi-hard flat copper coil suitable for different power and size requirements.

[0049] In this invention, the purpose of the first cold drawing and the second cold drawing is to eliminate internal stress, prevent cracking, stabilize dimensional accuracy, and at the same time retain the original mechanical properties of the material to the greatest extent.

[0050] In this invention, the cold working deformation of the first cold drawing and the second cold drawing is preferably 10% to 30%, which does not reach the high deformation of the hard state (60% to 90%), and retains some plasticity, which is a semi-hard alloy.

[0051] This invention obtains high-strength, high-conductivity microalloyed rare-earth high-frequency transformer winding flat copper wire material by adding specific trace alloying elements and rare earth elements to pure copper, combined with high-energy ball milling and mixing, electromagnetic stirring vacuum melting, refining-solidification treatment, cold rolling extrusion, and stress-relief annealing processes. Compared with conventional motor winding copper wire material production processes, it has two advantages: First, the appropriate proportion of added trace alloying and rare earth elements increases both the conductivity of the copper material and the strength and hardness of the coil winding; second, the specific high-energy ball milling and mixing, electromagnetic stirring vacuum melting, refining-solidification treatment, cold rolling extrusion, and stress-relief annealing processes ensure the formation of a high-density, high-purity crystalline structure in the copper material. The density of the copper alloy obtained by conventional processes (atmospheric melting + hot rolling) is 8.70~8.85 g / cm³. 3 (Relative density of 97.1%~98.8%), the density of the rare earth microalloyed semi-hard flat copper coil obtained by this invention is 8.85~8.91 g / cm³. 3 (The relative density is 98.7%~99.5%. The high-purity crystalline structure in this invention refers to the composite structure of "ultrafine crystalline matrix + dispersed second phase + directional fiber structure", which can refine grains, improve strength, ensure conductivity (no impurities scattering electrons at grain boundaries), hinder dislocation movement (precipitation strengthening), improve high-temperature stability, improve tensile strength along the extrusion direction, and is suitable for stress scenarios such as charging pile copper busbars.)

[0052] This invention also provides the application of the rare earth microalloy semi-hard flat copper coil described in the above technical solution or the rare earth microalloy semi-hard flat copper coil prepared by the preparation method described in the above technical solution in the field of charging pile transformers.

[0053] The present invention does not impose any special limitation on the specific method of application, and any method known to those skilled in the art can be used.

[0054] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0055] Example 1 Preparation of rare earth microalloyed semi-hard flat copper coils. Figure 1 The flowchart for the preparation of rare-earth microalloyed semi-hard flat copper coils in Example 1 includes the following steps: 1) Ball milling and powder mixing: Rare earth powder and high-purity trace metal powder are placed in a high-energy ball mill for ball milling and powder mixing. The ball milling time is 30 min and the rotation speed is 200 r / min. The ball milling jar is vacuum treated, and the vacuum degree is required to be less than 29 Pa to obtain mixed powder with a particle size of 500 nm.

[0056] 2) Vacuum melting and casting: The mixed powder is wrapped in 0.05mm copper foil and then put into a vacuum melting furnace containing pure copper. During the melting process, electromagnetic stirring technology (frequency 20Hz, current 300A, time 30min) is used to make the mixed powder evenly distributed in the copper liquid. The vacuum melting temperature is 1300℃ and the vacuum melting time is 1h.

[0057] 3) Refining-solidification treatment: Refining and solidification treatment is carried out in a vacuum induction melting furnace at a solidification temperature of 960℃ for 2 hours. After refining, the mixture is cooled to the casting temperature (1150℃) and then rapidly poured. The ingot mold is a cast iron mold, which is then left to stand before being poured into an intermediate alloy ingot, which is a Φ60mm cylinder.

[0058] 4) Cold rolling extrusion: Before extrusion, impurities and defects on the surface of the copper ingot are removed by machining. Then, it is placed in an electric furnace and held at 835℃ for 1 hour. The extrusion die is held at 550℃ for 1 hour. A 300t vertical hydraulic press is used for extrusion with an extrusion pressure of 20MPa.

[0059] 5) Stress-relief annealing: The extruded copper rod has a diameter of 8.0 mm. After pickling to remove the surface oxide layer and oil, it is cold-drawn to a diameter of 7.5 mm. Then, it is placed in a box annealing furnace and annealed at 650℃ for 1 hour. After pickling, it is cold-drawn to obtain a semi-hard copper alloy material with a diameter of 5.0 mm. Then, according to the winding power requirements, a rare earth microalloy semi-hard flat copper coil with a thickness of 0.8 mm and a width of 2.0 mm is obtained. The rare earth microalloy semi-hard flat copper coil contains the following elements by mass percentage: 0.05% La, 0.01% Zr, 0.04% Y, 0.02% Te, 0.005% Ag, with the remainder being copper and unavoidable impurities.

[0060] Table 1 shows the mechanical and electrochemical properties of the rare-earth microalloyed semi-hard flat copper coil and pure copper prepared in Example 1. The microstructure of the samples was observed using a DM4000M metallurgical microscope and a Phenom ProX scanning electron microscope. The mechanical properties of the samples were tested using a WDW-100 electronic universal testing machine. The resistivity of the samples was measured using a QJ84 digital bridge at room temperature (20℃) with a measurement accuracy of 10 Ω·cm. -6 Ω. The numbers in Table 1 represent three repeated experiments performed in Example 1. It can be seen that the rare earth microalloy semi-hard flat copper coil prepared by this invention improves conductivity by controlling the component ratio, while also improving strength and elongation performance, thus achieving high strength and high conductivity characteristics of the winding conductor.

[0061] Table 1. Test results of mechanical and electrochemical properties of rare earth microalloyed semi-hard flat copper coils and pure copper in Example 1.

[0062] Figure 2 The images show the metallographic structures of pure copper and the rare-earth microalloyed semi-hard flat copper coil of Example 1, where (a) is the metallographic structure of pure copper, and (b) to (d) are the metallographic structures of the rare-earth microalloyed semi-hard flat copper coil of Example 1 at different magnifications. Figure 2 As can be seen in (b), the metallographic structure of the sample after adding other elements is significantly finer than that of pure copper. Figure 2 As can be seen in (d), a small amount of particulate matter exists in the grains after the addition of other elements, forming a small amount of second-phase matter, which is dispersed in the copper grains.

[0063] Comparative test of performance parameters of rare earth microalloyed copper with different proportions The rare earth microalloyed copper material was prepared by designing and determining the alloy composition through orthogonal experiments. The preparation process was the same as in Example 1, except that the element content was different.

[0064] The optimal addition ratio of La, Y, Te, Zr, and Ag is considered, with Ag effectively reducing resistivity and improving the conductivity of copper alloys. However, from a cost control perspective, the Ag content should not be too high; therefore, the Ag addition amount is fixed at 0.005 wt%. The orthogonal experiment only considers the variations of the other four elements, using 9 groups (3... 4 The alloying schemes for La, Y, Te, and Zr are shown in Table 2.

[0065] Table 2. Copper alloy element addition ratio (wt%)

[0066] The orthogonal experimental results of preparing rare earth microalloyed copper wires with different compositions are shown in Table 3. The orthogonal experimental results were analyzed by the orthogonal experimental intuitive analysis method. (1) For yield strength, the influence of each element is C(Y)>B(Zr)>D(Te)>A(La), and the preferred factor level is A3B2C3D3. (2) For elongation, the influence of each element is A(La)>C(Y)>D(Te)>B(Zr), and the preferred factor level is A2B2C2D1. (3) For resistivity, the influence of each element is A(La)>C(Y)>D(Te)>B(Zr), and the preferred factor level is A2B1C2D1. A comparative analysis of the performance parameters of rare earth microalloyed copper with different proportions reveals that La (La) has a stronger effect on the resistivity and elongation of copper conductors than Y (Y). This is mainly due to La's higher reactivity, making it more readily reacted with numerous harmful impurities in the alloy solution, such as oxygen, sulfur, hydrogen, nitrogen, and some low-melting-point metals like Pb, Sb, or Bi. The reaction products either settle or float to form slag, reducing the harmful effects of these elements on the copper alloy. La effectively deoxidizes, desulfurizes, dehydrogenates, denitrifies, and purifies the melt, with a stronger purification capacity than Y, significantly improving the resistivity and elongation of rare earth copper alloys. Te (Te) and Zr mainly play a role in precipitation strengthening and solid solution, having little or even a negative impact on the conductivity and elongation of copper alloys. Y has the greatest impact on the yield strength of the alloy, primarily because Y can refine the dendritic mesh of the copper alloy casting structure, significantly refining the grain structure and providing a certain degree of grain refinement strengthening. Trace amounts of Te and Zr mainly function as dispersion strengthening and solid solution, but due to their small amounts, their impact on yield strength is not as significant as the grain refinement strengthening effect of Y. La mainly purifies the melt, while trace elements of Ag primarily reduce resistivity. When the elements are properly proportioned and interact, the material achieves optimal strength and conductivity. Based on the above analysis, the optimal numbering group is A2B1C2D1, that is, the proportions (mass fractions) of each element are 0.05%La, 0.01%Zr, 0.04%Y, 0.02%Te, and 0.005%Ag, with the remainder being industrial electrolytic pure copper (99.9%). The corresponding sample exhibits the best performance.

[0067] Table 3. Orthogonal Experiment Grouping Table and Mechanical and Electrical Properties of the Obtained Samples

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A rare-earth microalloy semi-hard flat copper coil, characterized in that, It includes the following elements by mass percentage: 0.05% La, 0.01% Zr, 0.04% Y, 0.02% Te, 0.005% Ag, with the remainder being copper and unavoidable impurities.

2. The method for preparing the rare earth microalloyed semi-hard flat copper coil according to claim 1, characterized in that, Includes the following steps: A mixed powder was obtained according to the element ratio; The mixed powder is then vacuum melted to obtain an ingot; The ingot is refined and solution treated before being cast into a mold to obtain an intermediate alloy ingot. The intermediate alloy ingot is subjected to cold rolling and extrusion followed by stress-relief annealing to obtain the rare earth microalloy semi-hard flat copper coil.

3. The preparation method according to claim 2, characterized in that, The mixed powder is wrapped in copper foil and then vacuum melted.

4. The preparation method according to claim 2 or 3, characterized in that, The vacuum melting temperature is 1200~1300℃, and the time is 1~2h.

5. The preparation method according to claim 4, characterized in that, The vacuum melting is carried out by electromagnetic stirring, with a frequency of 20~30Hz, a current of 200~300A, and a time of 15~30min.

6. The preparation method according to claim 2, characterized in that, The refining-solidification treatment is carried out at a temperature of 930~960℃ for 1~2 hours.

7. The preparation method according to claim 2, characterized in that, The cold rolling extrusion temperature is 800~850℃, the holding time is 1~2h, and the extrusion pressure is 20MPa.

8. The preparation method according to claim 2, characterized in that, The stress-relief annealing temperature is 600~700℃, and the time is 1~2h.

9. The preparation method according to claim 2 or 8, characterized in that, The first cold drawing is performed after cold rolling and extrusion and before stress-relief annealing, and the second cold drawing is performed after stress-relief annealing.

10. The application of the rare earth microalloy semi-hard flat copper coil according to claim 1 or the rare earth microalloy semi-hard flat copper coil prepared by the preparation method according to any one of claims 2 to 9 in the field of charging pile transformers.

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