A method for eliminating residual stress of copper alloy thin strip by pulse magnetic field treatment

Abstract

The application discloses a pulse magnetic field treatment method for eliminating residual stress of copper alloy thin strips and belongs to the technical field of alloy strip performance improvement. In view of the problem that the strength and conductivity of copper alloy strips cannot be balanced at present, residual stress of the copper alloy strips cannot be effectively reduced, and etching performance of the copper alloy strips cannot be improved, the pulse magnetic field treatment method can significantly reduce residual stress in the alloy and even eliminate the residual stress after multiple composite treatments in the processes of alloy casting, hot rolling, cold rolling and annealing, and can improve the strength and conductivity of the alloy strip to a certain extent, is suitable for the final etching process of the alloy strip, and meets the performance requirements of the copper alloy strip for lead frames.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloy strip performance improvement, and particularly relates to a pulsed magnetic field treatment method for eliminating residual stress of copper alloy thin strips. BACKGROUND

[0002] The integrated circuit industry is the focus of current and future global technology competition. At present, copper alloy lead frames, as chip carriers of integrated circuits, are channels for chip information to contact the outside world, and are very important basic materials in the semiconductor industry. The copper alloy thin strips used for lead frames are mainly produced by chemical etching. Although etching is a stress-free processing method, it can realize the production of high-density and multi-pin lead frames, but this method brings more stringent requirements for the internal stress, warping degree, surface quality and etching performance of the copper alloy thin strips. The rolled copper alloy thin strips will warp due to uneven stress release during etching, which seriously affects the subsequent use of the products. Therefore, with the continuous improvement of product performance requirements, how to effectively reduce the residual stress of the copper alloy strip while balancing the strength-conductivity of the copper alloy strip and improving the etching performance has become an important research topic.

[0003] It is well known that the plasticity of almost all metal materials in a magnetic field will change to some extent, thereby improving their performance such as the improvement of wear resistance, the extension of fatigue life and the change of resistivity. The pulsed magnetic field can effectively reduce the residual stress of the material and improve the performance of the material through various mechanisms such as affecting dislocation movement, magnetostriction effect, selective grain deformation, dislocation multiplication and stress relaxation, and homogenization of residual stress. Compared with the commonly used heat treatment method, the magnetization treatment has the characteristics of simple operation, low investment, quick effect and no pollution. Studies have shown that magnetic annealing has a significant influence on the texture and microstructure evolution of non-ferrous metal alloys. The influence and regulation of magnetic field annealing on the microstructure and texture of metal materials are still the focus of attention of many scholars. The influence of magnetic field annealing on texture, microstructure and magnetism is still an important direction of current scientists' research, and the exploration of its internal mechanism is still a heavy task. SUMMARY

[0004] In view of the problem that the strength-conductivity of the copper alloy strip cannot be balanced while effectively reducing the residual stress and improving the etching performance, the application provides a pulsed magnetic field treatment method for eliminating the residual stress of the copper alloy thin strip. By adding a magnetic field treatment process to the process optimization of some processes in the whole industry chain of the copper alloy thin strip, a copper alloy thin strip with excellent performance is prepared, which provides a reference for the breakthrough of the manufacturing technology of high-precision etching lead frame copper alloy thin strips required by integrated circuits and the development of the industry, and continuously improves the precision forming quality of the copper alloy thin strip.

[0005] In order to achieve the above object, the application adopts the following technical scheme:

[0006] A pulse magnetic field processing method for eliminating residual stress of copper alloy thin strip, comprising the following steps:

[0007] Step 1, alloy casting: under the action of the pulse magnetic field, melt the copper alloy material at a temperature of 1000-1300 DEG C to form an alloy melt, and then inject the melt into a mold to cool and cast to obtain an ingot; the whole casting process is carried out in a magnetic field, the pulse magnetic field treatment is carried out on the molten alloy to promote the uniform distribution of solute and temperature field, so that the solidification structure is more uniform and the grain is finer, and the hardness and strength of the ingot are improved to some extent.

[0008] Step 2, solution treatment: under the action of the pulse magnetic field, heat and keep the ingot at a temperature of 800-1350 DEG C for 0.5-24 hours to make the second phase in the alloy dissolve into the solid solution matrix as much as possible; the pulse magnetic field treatment is also carried out to make the second phase in the alloy dissolve into the solid solution matrix as much as possible. At the same time, the stress generated by cold and hot working can be eliminated, the alloy can be recrystallized, and the performance of the material can be significantly improved.

[0009] Step 3, hot rolling: under the action of the pulse magnetic field, the solution-treated ingot is hot-rolled to obtain a copper alloy slab with a thickness of 10-20 mm; and a magnetic field is introduced during the hot rolling to improve the alloy performance.

[0010] Step 4, cold rolling: under the action of the pulse magnetic field, the copper alloy slab is cold-rolled N times, N is any positive integer, until the thickness requirement is met, to obtain a copper alloy thin strip; the pulse magnetic field is introduced during the cold rolling to improve the alloy performance.

[0011] Step 5, tension annealing: under the action of the pulse magnetic field, the copper alloy thin strip is heated and annealed at a temperature of 100-400 DEG C for 30 seconds to 12 hours; through the combined treatment of heat treatment and magnetic field, a copper alloy thin strip sample with residual stress eliminated is obtained.

[0012] Further, the pulse magnetic field current is 20-100000 A, the frequency is 20-100 Hz, the duty cycle is 20-100%, and the magnetic induction intensity is 0-M, the value of M is determined according to the specific process, and M is less than the limit of the instrument.

[0013] Further, inert gas is continuously introduced during the step S2 solution treatment to prevent oxidation of the copper alloy ingot.

[0014] Further, the holding time in step S2 needs to be adjusted according to the specific size of the ingot to make the ingot evenly heated and the structure homogenized.

[0015] Further, the time interval for hot rolling of the solid solution treated ingot is not more than 30s.

[0016] Further, the pulse magnetic field device in steps S1, S2 and S3 should be reasonably installed according to the specific process to make the magnetic field evenly distributed in the preparation of the alloy.

[0017] Further, the plate should be pickled before and after steps S3 and S4 to remove the oxide scale and impurities to ensure the surface quality of the product.

[0018] Further, the cold rolling pass in step 4 is 10-30 passes.

[0019] Further, in step S4, intermediate annealing treatment is performed at the cold rolling gap of N times of cold rolling to further reduce the hardness of the alloy and facilitate further cold rolling of the copper alloy slab. The intermediate annealing temperature is 100-800℃, the holding time is 10min-12h, and the specific holding time should be adjusted according to the size of the plate, so the holding time is not limited.

[0020] Further, in step S4, a pulse magnetic field is introduced to the copper alloy strip subjected to multiple cold rolling. The number of times of pulse magnetic field implementation and the process should be determined according to the actual production process, i.e. the magnetic field treatment process can be moderately increased according to the needs after the actual cold rolling production process.

[0021] Further, in step 5, tension annealing process is used in the annealing process, and pulse magnetic field treatment is also added. The pulse magnetic field is performed simultaneously with the heating annealing or before and after the pulse magnetic field treatment. Through the comprehensive action of magnetic field, thermal field and force, the residual stress in the alloy is reduced and the alloy performance is improved.

[0022] Further, the direction of the magnetic field should be controlled during the treatment of the pulse magnetic field, and it is not limited to the relative relationship that the direction of the magnetic field is perpendicular to the rolling direction.

[0023] Further, in addition to the commonly used Cu-Fe system, the copper alloy material for lead frame should also include Cu-Cr system, Cu-Ni system and other etching type lead frame copper alloys.

[0024] Further, the application of pulse magnetic field is not limited to copper alloy for lead frame, and other processes that need to reduce residual stress and improve product performance can also be applied.

[0025] Further, further, the pulse magnetic field device is added to the existing production equipment to save cost and improve production efficiency.

[0026] Compared with the prior art, the application has the following advantages:

[0027] The application first introduces a pulse magnetic field in the production process of the copper alloy industry chain, and through the coupling of magnetic force, mechanical force and thermal field, the strength and conductivity of the alloy are improved while the internal residual stress of the alloy is reduced, which is beneficial to the final etching process of the lead frame forming and meets the performance requirements of the copper alloy strip for lead frame.

[0028] The pulse magnetic field technology introduced in the production process of the copper alloy industry chain is simple in equipment, convenient in operation, economical and efficient, green and environmentally friendly, and has strong applicability, which is not only suitable for performance improvement as a single process, but also can be combined with a thermal field to further reduce residual stress without affecting the performance of the original product, and does not have special requirements for alloy workpieces during processing, and is suitable for rapid processing of alloy workpieces of various sizes and complex structures, greatly reducing production costs, and is expected to be applied to processing of other types of alloy components. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1 Process flow chart of the treatment method of the application;

[0031] Figure 2 Schematic diagram of nanoindentation loading curve of the treatment method of the application;

[0032] Figure 3 Microstructure of the alloy (a) rolling sample (b) magnetic field and annealing treatment are carried out at the same time. DETAILED DESCRIPTION

[0033] In order to further understand the application, it will be described in detail. However, the application has multiple implementation ways and is not limited to the specific examples listed herein. The presentation of these examples aims to deepen the overall understanding of the disclosure of the application.

[0034] The material of the copper alloy ingot in each of the following embodiments is a copper alloy for lead frame, and Cu-0.23Fe-0.06P alloy is selected. In order to illustrate the magnetic field and the coupling of the magnetic field and the thermal field, the sample process flow is as shown in Figure 1 .

[0035] The pulse magnetic field control conditions of the embodiment include voltage, current, frequency and duty cycle, and the direction of the magnetic field should be controlled during the treatment process of the pulse magnetic field (the rolling direction is parallel to the direction of the magnetic field without special marking).

[0036] Example 1

[0037] The pulse magnetic field conditions of the embodiment are voltage 100V, peak current 100A, frequency 20Hz and duty cycle 20%.

[0038] A pulse magnetic field treatment method for eliminating residual stress of copper alloy thin strips, as shown in Figure 1 , comprising the following steps:

[0039] Step 1, alloy casting: under the action of the pulse magnetic field, melt the copper alloy material at a temperature of 1200℃ and carry out deoxidation to form an alloy melt, and then pour into a mold to cool the casting to obtain an ingot;

[0040] Step 2, solution treatment: under the action of the pulse magnetic field, heat and hold the ingot, the holding temperature is 1000℃, and the holding time is 12h, so that all or most of the second phase in the alloy is dissolved into the solid solution matrix; nitrogen gas is continuously introduced into the heating furnace during the solution treatment process;

[0041] Step 3, hot rolling: before the alloy is treated, pickling is carried out, and under the action of the pulse magnetic field, the solution treated ingot is hot rolled with a time interval of 20s, and finally the thickness of the copper alloy slab is 16.5mm;

[0042] Step 4, cold rolling: before the alloy is treated, pickling is carried out, and under the action of the pulse magnetic field, the copper alloy slab is cold rolled for 10 passes, and the cold rolling gap is subjected to intermediate annealing treatment at a temperature of 500℃ for 2h, until the thickness is rolled to 0.203mm, to obtain a copper alloy thin strip;

[0043] Step 5, tension annealing: before the alloy is treated, pickling is carried out, and at the same time that the pulse magnetic field is introduced, the copper alloy thin strip is heated and annealed at an annealing temperature of 200℃ for 3min; through the combined treatment of heat treatment and magnetic field, water cooling, the residual stress value is measured to be 9.8MPa, which has been changed from the initial compressive stress to a tensile stress state, and the residual stress of the copper alloy thin strip sample has decreased by 100%.

[0044] Example 2

[0045] The difference between the embodiment and example 1 is:

[0046] Step 4, cold rolling: before the alloy is treated, pickling is performed, and the copper alloy slab is cold-rolled for 30 passes under the action of a pulse magnetic field, and the cold-rolling gap is subjected to intermediate annealing treatment at a temperature of 100°C for 12h until the thickness is rolled to 0.203mm to obtain a copper alloy thin strip;

[0047] Step 5, tension annealing: before the alloy is treated, pickling is performed, and the copper alloy thin strip is heated and annealed while a pulse magnetic field is passed through, the annealing temperature is 100°C, and the holding time is 12h; through the combined treatment of heat treatment and magnetic field, water cooling, the residual stress value is measured to be-50MPa, and the residual stress of the copper alloy thin strip sample is reduced by 65%.

[0048] Example 3

[0049] The difference between this example and Example 1 is that:

[0050] The pulse magnetic field conditions of this example are a peak current of 100000A, a frequency of 100Hz, and a duty cycle of 100%.

[0051] Step 4, cold rolling: before the alloy is treated, pickling is performed, and the copper alloy slab is cold-rolled for 30 passes under the action of a pulse magnetic field, and the cold-rolling gap is subjected to intermediate annealing treatment at a temperature of 800°C for 10min until the thickness is rolled to 0.203mm to obtain a copper alloy thin strip;

[0052] Step 5, tension annealing: before the alloy is treated, pickling is performed, and the copper alloy thin strip is heated and annealed under the action of a pulse magnetic field, the annealing temperature is 400°C, and the holding time is 30s; through the combined treatment of heat treatment and magnetic field, water cooling, the residual stress value is measured to be 10MPa, and the residual stress of the copper alloy thin strip sample is reduced by 100%.

[0053] Example 4

[0054] The pulse magnetic field conditions of this example are a peak current of 100A, a frequency of 20Hz, and a duty cycle of 20%.

[0055] A pulse magnetic field treatment method for eliminating the residual stress of a copper alloy thin strip, comprising the following steps:

[0056] Step 1, alloy casting: under the action of a pulse magnetic field, the copper alloy material is melted at a temperature of 1300°C and is subjected to deoxidation to form an alloy melt, and then the alloy melt is poured into a mold for cooling and casting to obtain an ingot;

[0057] Step 2, solution treatment: the ingot is heated and held under the action of a pulsed magnetic field, the holding temperature is 1350°C, and the holding time is 0.5h, so that all or most of the second phase in the alloy is dissolved into the solid solution matrix; nitrogen is continuously introduced into the heating furnace during the solution treatment process;

[0058] Step 3, hot rolling: the alloy is pickled before being processed, the solution-treated ingot is hot-rolled under the action of a pulsed magnetic field, the time interval is not more than 30s, and finally a copper alloy slab with a thickness of 16.5mm is obtained;

[0059] Step 4, cold rolling: the alloy is pickled before being processed, the copper alloy slab is cold-rolled for 15 passes (N is an arbitrary positive integer) under the action of a pulsed magnetic field, the cold rolling gap is subjected to intermediate annealing treatment, the temperature is 400°C, the holding time is 3h, and the thickness is rolled to 0.203mm to obtain a copper alloy thin strip;

[0060] Step 5, magnetic field treatment: the alloy is pickled before being processed, and the copper alloy thin strip is treated only under the action of a pulsed magnetic field, water-cooled, the residual stress measurement value is -122MPa, and the residual stress of the copper alloy thin strip sample is reduced by 15.8%.

[0061] Example 5

[0062] The difference from Example 4 is that the following steps are further included:

[0063] Step 6, tension annealing: the copper alloy thin strip after magnetic field treatment is heated and annealed before the alloy is processed, the annealing temperature is 400°C, the holding time is 30s, the residual stress measurement value is -86.5MPa, and the residual stress of the copper alloy thin strip sample is reduced by 40%.

[0064] Example 6

[0065] The difference from Example 4 is that:

[0066] Step 5, tension annealing: the copper alloy thin strip is heated and annealed before the alloy is processed, the annealing temperature is 400°C, the holding time is 10min, the residual stress measurement value is -23.1MPa, and the residual stress of the copper alloy thin strip sample is reduced by 84%.

[0067] Example 7

[0068] The difference from Example 4 is that:

[0069] Step 5, tension annealing: the copper alloy thin strip is heated and annealed before the alloy is processed, the annealing temperature is 400°C, the holding time is 10min;

[0070] Step 6, magnetic field treatment: before the alloy is treated, pickling is performed, and the copper alloy thin strip after tension annealing is treated again by magnetic field treatment, the residual stress measurement value is -20 MPa, and the residual stress of the copper alloy thin strip sample is reduced by 86.2%.

[0071] Example 8

[0072] The difference from Example 4 is that:

[0073] Step 5, magnetic field treatment: before the alloy is treated, pickling is performed, and the copper alloy thin strip is treated only under the action of a pulsed magnetic field, and water-cooled, the residual stress measurement value is -134 MPa, and the residual stress of the copper alloy thin strip sample is reduced by 7.5%.

[0074] Example 9

[0075] The difference from Example 1 is that:

[0076] The material selected is Cu-0.45Cr-0.1Zr alloy.

[0077] The pulsed magnetic field conditions of this embodiment are voltage 100V, peak current 100A, frequency 20Hz, and duty cycle 20%.

[0078] A pulsed magnetic field treatment method for eliminating the residual stress of a copper alloy thin strip, as shown in Figure 1 , comprising the following steps:

[0079] Step 1, alloy casting: under the action of a pulsed magnetic field, the copper alloy material is melted at a temperature of 1200℃ and deoxidized to form an alloy melt, which is then poured into a mold to cool and cast to obtain an ingot;

[0080] Step 2, solution treatment: under the action of a pulsed magnetic field, the ingot is heated and held at a temperature of 1000℃ for 12h to dissolve all or most of the second phase in the alloy into the solid solution matrix; nitrogen gas is continuously supplied in the heating furnace during the solution treatment;

[0081] Step 3, hot rolling: before the alloy is treated, pickling is performed, and the solution-treated ingot is hot-rolled under the action of a pulsed magnetic field, with a time interval of 20s, and finally a copper alloy slab with a thickness of 16.5mm is obtained;

[0082] Step 4, cold rolling: before the alloy is treated, pickling is performed, and the copper alloy slab is cold-rolled 10 times under the action of a pulsed magnetic field, with intermediate annealing treatment at a cold rolling gap, at a temperature of 500℃ for 2h, until the thickness is rolled to 0.203mm, to obtain a copper alloy thin strip;

[0083] Step 5, tension annealing: before the alloy is treated, the copper alloy thin strip is heated and annealed while the pulse magnetic field is passed, the annealing temperature is 200℃, and the holding time is 3min; through the combined treatment of heat treatment and magnetic field, water cooling, the residual stress value is measured as 2.3MPa, which has been changed from the initial compressive stress to tensile stress state, and the residual stress of the copper alloy thin strip sample has decreased by 100%.

[0084] Comparative Example 1

[0085] The pulse magnetic field conditions of the embodiment are peak current 100A, frequency 20Hz, and duty cycle 20%.

[0086] A pulse magnetic field treatment method for eliminating residual stress of a copper alloy thin strip, comprising the following steps:

[0087] Step 1, alloy casting: under the action of a pulse magnetic field, the copper alloy material is melted at a temperature of 1200℃ and deoxidized to form an alloy melt, which is then poured into a mold for cooling and casting to obtain an ingot;

[0088] Step 2, solution treatment: under the action of a pulse magnetic field, the ingot is heated and held at a temperature of 1000℃ for 12h, so that all or most of the second phase in the alloy is dissolved into the solid solution matrix; inert gas is continuously introduced into the heating furnace during the solution treatment;

[0089] Step 3, hot rolling: under the action of a pulse magnetic field, the solution-treated ingot is hot rolled with a time interval not exceeding 30s, and finally a copper alloy slab with a thickness of 16.5mm is obtained;

[0090] Step 4, cold rolling: under the action of a pulse magnetic field, the copper alloy slab is cold rolled for 10 passes, and intermediate annealing treatment is performed at a temperature of 400℃ for 10min, until the thickness is rolled to 0.203mm to obtain a copper alloy thin strip; and the residual stress thereof is tested as -144.9MPa.

[0091] As can be seen from the comparison between Comparative Example 1 and Example 6, the residual stress value of the copper alloy thin strip after annealing treatment is reduced.

[0092] As can be seen from the comparison between Comparative Example 1 and Example 1, the residual stress of the copper alloy thin strip treated by the combined treatment of magnetic field and annealing is reduced by 100%, and the effect is significant.

[0093] At the same time, we also tested Cu-Cr copper alloy and Cu-Ni copper alloy, and the test results can achieve the above technical effects.

[0094] In summary, the heat treatment process in the magnetic field can significantly reduce the residual stress and improve the microstructure. The precipitation process is an atomic diffusion process, and the speed of atomic diffusion depends on the diffusion flux. The magnetic field can accelerate the diffusion process by disturbing the balance of vacancy concentration, increasing the number of vacancies and significantly activating their mobility, thus promoting uniform microstructure and ultimately reducing the residual stress in the alloy.

[0095] The residual stress calculation process is shown in Fig. 1, and the residual stress calculation results are shown in Table 1. Figure 2

[0096] Table 1 residual stress results of Comparative Example 1 and Examples 1 and 2

[0097] Group Residual stress (MPa) Residual stress reduction ratio (%) Comparative Example 1 -144.9 Example 1 9.8 100 Example 2 -50 65 Example 3 10 100 Example 4 -122 15.8 Example 5 -86.5 40 Example 6 -23.1 84 Example 7 -20 86.2 Example 8 -134 7.5 Figure 2 2.3 100

[0098] Figure 3 In the nanoindentation load displacement curves of the rolled sample, the annealed sample and the alloy sample treated by magnetic field and annealing at the same time, the residual stress value of the rolled sample calculated by the nanoindentation model is-144.9MPa, the residual stress value of the annealed sample is-23.3MPa, and the residual stress value of the alloy sample treated by magnetic field and annealing at the same time is 9.8MPa. It is proved that the application of magnetic field during annealing can reduce the residual stress.

[0099] ​ The microstructure of the alloy (a) rolled sample (b) alloy sample treated by magnetic field and annealing at the same time can be seen in the alloy sample treated by magnetic field and annealing at the same time. The appearance of the recovery structure is the main reason for the reduction of the residual stress value.

[0100] The contents not described in detail in the specification of the present application belong to the prior art known to those skilled in the art. Although the above describes the specific embodiments of the present application for the purpose of facilitating the understanding of the present application by those skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that all the inventions and creations utilizing the concept of the present application within the spirit and scope of the present application defined and determined by the appended claims are included in the protection.​

Claims

1. A pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips, characterized in that: Includes the following steps: Step 1, Alloy melting and casting: Under the action of a pulsed magnetic field, the copper alloy material is melted at a temperature of 1000℃~1300℃ to form an alloy melt, which is then poured into a mold for cooling and casting to obtain an ingot; Step 2, solution treatment: Under the action of a pulsed magnetic field, the ingot is heated and held at a temperature of 800℃~1350℃ for 0.5h~24h, so that the second phase in the alloy is completely or to the maximum extent dissolved into the solid solution matrix. Step 3, hot rolling: Under the action of a pulsed magnetic field, the solution-treated ingot is hot rolled; Step 4, cold rolling: Under the action of a pulsed magnetic field, the copper alloy slab is cold rolled N times, where N is any positive integer, until the thickness requirement is met, and a copper alloy strip is obtained. Step 5, tension annealing: Under the action of a pulsed magnetic field, the copper alloy strip is heated and annealed at a temperature of 100℃~400℃ and a holding time of 30s~12h; through heat treatment and magnetic field treatment, a copper alloy strip sample with residual stress eliminated is obtained.

2. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: The pulsed magnetic field in steps 1 to 5 has a current of 20A to 100000A, a frequency of 20Hz to 100Hz, a duty cycle of 20% to 100%, and a magnetic induction intensity of 0 to M. The value of M is determined according to the specific process, and M is less than the limit that the instrument can meet.

3. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: During the solution treatment in step S2, inert gas is continuously introduced to prevent oxidation of the copper alloy ingot.

4. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: The time interval between hot rolling of the solution-treated ingots shall not exceed 30 seconds.

5. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: The plate material should be pickled before and after steps S3 and S4 to remove oxide scale and impurities and ensure the surface quality of the product.

6. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: In step 4, intermediate annealing is performed during the interval between N cold rolling cycles to reduce the alloy hardness and facilitate further cold rolling of the copper alloy slab. The intermediate annealing temperature is 100–800°C and the holding time is 10 min–12 h.

7. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 6, characterized in that: In step 4, the number of cold rolling passes is 10 to 30.

8. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: In step 5, the pulsed magnetic field is performed simultaneously with the heating annealing or before and after the pulsed magnetic field treatment. The combined effect of the magnetic field, thermal field and force reduces the residual stress inside the alloy and improves the alloy performance.

9. The pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: The direction of the magnetic field should be controlled during the processing of the pulsed magnetic field.

10. A pulsed magnetic field treatment method for eliminating residual stress in copper alloy strips according to claim 1, characterized in that: The copper alloy material is a Cu-Fe copper alloy, a Cu-Cr copper alloy, or a Cu-Ni copper alloy.

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