Method of producing copper alloy strip having ultra-fine grain structure

Abstract

The application provides a copper alloy strip preparation method with ultra-fine grain structure, comprising the following steps: a cast ingot preparation step: preparing an aging precipitation type copper alloy flat ingot; a hot rolling step: hot rolling the flat ingot to obtain a hot rolled plate; a first solid solution step: solid solution treatment is performed on the hot rolled plate to make the second phase precipitated in the hot rolling process to be solid-solved in the matrix; a pre-aging step: pre-aging treatment is performed on the hot rolled plate after the first solid solution step, the treatment temperature is 300-500 DEG C, the time is 0.5-6 hours, the second phase is precipitated in the matrix; a cold rolling step: cold rolling is performed on the hot rolled plate after the pre-aging step, the cold rolling deformation is 60-95%; a second solid solution step: the plate after the cold rolling step is heated to a solid solution temperature interval at a temperature rising rate of not less than 100 DEG C / s, and then quenched after heat preservation to obtain a recrystallized structure with an average grain size of less than or equal to 2 microns, and the matrix is in a supersaturated solid solution state; an aging step: aging treatment is performed on the plate after the second solid solution step to make the supersaturated solid solution decompose and precipitate a strengthening phase.

Description

Technical Field

[0001] This invention relates to the field of copper alloy strip preparation and microstructure control, and particularly to a method for preparing copper alloy strip with an ultrafine grain structure. Background Technology

[0002] With the increasing demands for material performance in industries such as aerospace, electronics, and new energy vehicles, there is a need for copper alloy strips that combine high strength and good ductility. Refining the grain size to the ultrafine grain range is one way to simultaneously improve the strength and ductility of copper alloys.

[0003] To address the aforementioned needs, current processes for preparing bulk ultrafine-grained copper alloys mainly include methods involving intense plastic deformation, such as equal-channel angular extrusion, high-pressure torsion, and cumulative lap-welding. However, these methods face difficulties in preparing large-sized, uniform bulk ultrafine-grained plates or strips. Furthermore, for age-precipitated copper alloys, the recovery-recrystallization process and the aging precipitation process interfere with each other during the post-deformation annealing process. When heating at a conventional heating rate, the second phase precipitates during the heating stage. This precipitation process consumes deformation energy, leading to a decrease in the recrystallization driving force and a weakening of the grain refinement effect. Simultaneously, the second phase precipitated during the heating stage is prone to coarsening during subsequent aging, adversely affecting the precipitation strengthening effect.

[0004] The prior art CN113005324B describes a method for preparing a copper-titanium alloy. The process route includes hot deformation, primary solution treatment, cold deformation, secondary solution treatment, and aging. In this method, cold deformation is required between the primary and secondary solution treatments. The secondary solution treatment uses rapid heating, and the recrystallization driving force before the secondary solution treatment mainly comes from the energy stored in the cold rolling deformation. Due to the limitation of deformation energy storage, the reduction range of the secondary solution treatment temperature is limited.

[0005] Therefore, existing technologies still face technical challenges in preparing large-size ultrafine-grained copper alloy strips, including a single source of recrystallization driving force and limited reduction in solution temperature. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problems by providing a method for preparing copper alloy strip with an ultrafine grain structure.

[0007] The technical solution of the present invention is a method for preparing copper alloy strip with an ultrafine grain structure, comprising the following steps: Ingot preparation steps: Prepare aging precipitation type copper alloy flat ingots; Hot rolling step: The flat ingot is hot rolled to obtain a hot-rolled sheet; One solution treatment step: The hot-rolled sheet is subjected to solution treatment to dissolve the second phase precipitated during the hot rolling process into the matrix; Pre-aging step: The hot-rolled sheet after the first solution treatment is pre-aged at a temperature of 300℃~500℃ for 0.5~6 hours to induce the precipitation of a second phase in the matrix; Cold rolling step: The hot-rolled sheet after the pre-aging step is cold-rolled, and the cold rolling deformation is 60% to 95%; Secondary solution treatment step: The sheet material after the cold rolling step is heated to the solution temperature range of 700℃~950℃ at a heating rate of not less than 100℃ / s, held at the temperature and then quenched to obtain a recrystallized structure with an average grain size ≤2μm, and the matrix is ​​in a supersaturated solution state. Aging step: The plate after the second solution treatment is aged to decompose the supersaturated solid solution and release the strengthening phase.

[0008] In one embodiment, the age-precipitated copper alloy is a Cu-Ni-Si, Cu-Ti, or Cu-Be copper alloy.

[0009] In one embodiment, the hot rolling temperature is 700℃~950℃ in the hot rolling step; and the solution treatment temperature is 800℃~1000℃ in the first solution treatment step.

[0010] In one embodiment, the cold rolling deformation in the cold rolling step is 80% to 95%.

[0011] In one embodiment, the heating rate in the secondary solution treatment step is 150℃~500℃ / s, and the heating method is one or more combinations of DC power supply heating, ultra-high frequency induction heating, pulse current heating, laser heating or infrared radiation heating.

[0012] In one implementation, the heat treatment time in the secondary solution treatment step is 1 to 300 seconds.

[0013] In one embodiment, the solution temperature in the secondary solution treatment step is 50°C to 200°C lower than the solution temperature without the pre-aging step.

[0014] In one implementation, the aging step involves an aging temperature of 300℃ to 550℃ and a time of 1 to 8 hours.

[0015] As one embodiment, an ultra-high strength, high plasticity, ultra-fine crystalline copper alloy strip prepared according to a method for preparing copper alloy strip with an ultra-fine crystalline structure has a width ≥ 300 mm and a length ≥ 1000 mm.

[0016] As one embodiment, the ultra-high strength, high plasticity, ultra-fine crystalline copper alloy strip has a tensile strength ≥1000MPa and an elongation ≥10%.

[0017] The advantages of this invention compared to existing technologies are that the method for preparing copper alloy strip with an ultrafine grain structure precipitates a second phase in the matrix through pre-aging treatment. This second phase acts as a barrier to dislocation movement during subsequent cold rolling, increasing dislocation density and deformation energy storage. A secondary solution treatment is then performed at a heating rate of not less than 100℃ / s, allowing the heating process to exceed the second phase precipitation temperature range, suppressing the consumption of deformation energy storage, and causing the pre-precipitated second phase to dissolve back and release interfacial energy, which, together with the deformation energy storage from cold rolling, promotes recrystallization. As a result, the secondary solution temperature is lower than when pre-aging is not used, the average grain size of the resulting recrystallized structure is ≤2μm, and the matrix remains in a supersaturated solid solution state. Subsequent aging treatment causes the supersaturated solid solution to decompose and precipitate a strengthening phase. The fine-grain strengthening effect and the precipitation strengthening effect jointly contribute to the improvement of strip strength. The above method overcomes the limitations of the severe plastic deformation method in the preparation of large-size strips, and can produce strips with a width ≥300mm and a length ≥1000mm. The strips have both high strength and good plasticity, which meets the requirements of continuous production. Attached Figure Description

[0018] Figure 1 A process flow diagram for preparing copper alloy strip with an ultrafine grain structure provided for embodiments of the present invention. Detailed Implementation

[0019] The above and other embodiments and advantages of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] In this invention, ultrafine grains refer to recrystallized structures with an average grain size ≤ 2 μm.

[0021] The preparation method of the present invention includes the following steps: preparing an aging precipitation type copper alloy flat ingot; hot rolling the flat ingot to obtain a hot-rolled plate; performing a first solution treatment on the hot-rolled plate to dissolve the second phase precipitated during the hot rolling process into the matrix; performing a pre-aging treatment on the hot-rolled plate after the first solution treatment at a temperature of 300℃~500℃ for 0.5~6 hours to precipitate the second phase in the matrix; cold rolling the pre-aged plate with a cold rolling deformation of 60%~95%; heating the cold-rolled plate to the solution temperature range at a heating rate of not less than 100℃ / s, holding it at that temperature, and then quenching it to obtain a recrystallized structure with an average grain size ≤2μm, and the matrix is ​​in a supersaturated solution state; and performing an aging treatment on the quenched plate to decompose the supersaturated solution and precipitate the strengthening phase.

[0022] Age-precipitated copper alloys can be selected from Cu-Ni-Si, Cu-Ti, Cu-Be, or Cu-Cr-Zr systems. Hot rolling temperatures are generally 700℃ to 950℃, and the primary solution temperature is 800℃ to 1000℃. Pre-aging is performed before cold rolling to pre-precipitate a second phase in the matrix. This second phase acts as an obstacle to dislocation movement during subsequent cold rolling, causing dislocations to accumulate around the second phase, resulting in higher dislocation density and deformation energy storage compared to the case without pre-precipitated phases. The cold rolling deformation is preferably 80% to 95%. The heating rate for the secondary solution is preferably 150℃ to 500℃ / s, and the heating method can be one or a combination of DC heating, ultra-high frequency induction heating, pulsed current heating, laser heating, or infrared radiation heating. Rapid heating allows the temperature rise process to bypass the precipitation temperature range of the second phase, suppressing its precipitation during the heating stage and reducing the consumption of deformation energy storage. Simultaneously, the second phase precipitated during the pre-aging stage dissolves again at high temperatures, and the interfacial energy released during this dissolution process, together with the deformation energy stored during cold rolling, drives recrystallization. Compared to the method without pre-aging treatment, the solution temperature required to complete recrystallization can be reduced by 50℃ to 200℃. The secondary solution temperature is 700℃ to 950℃, and the holding time is 1 to 300 seconds. The aging treatment temperature is 300℃ to 550℃, and the time is 1 to 8 hours.

[0023] In conventional understanding of age-precipitated copper alloys, pre-aging treatment before cold rolling causes the pre-precipitation of a second phase in the matrix. This second phase is typically considered a factor that consumes deformation energy during subsequent annealing, hindering recrystallization and grain refinement. However, this invention discovers that when pre-aging treatment is combined with rapid heating at a rate not lower than 100°C / s for secondary solution treatment, the pre-precipitated second phase undergoes re-dissolution during the rapid heating process. The interfacial energy released during re-dissolution not only does not weaken the recrystallization driving force but also works in conjunction with the deformation energy stored during cold rolling, allowing recrystallization to be completed at a lower solution temperature, resulting in smaller grain sizes. It is precisely based on this method, which contradicts conventional understanding, that the resulting strip has a width ≥300mm, a length ≥1000mm, an average grain size ≤2μm, a tensile strength ≥1000MPa, and an elongation ≥10%.

[0024] The following examples further illustrate this.

[0025] Example 1

[0026] An alloy with a composition of Cu-3.2Ti-0.2Fe-0.2V (mass percentage) was used. Flat ingots with dimensions of 200mm × 500mm × 1000mm were obtained through semi-continuous casting. The ingots were hot-rolled to 5mm at 900℃, with a final rolling temperature of 850℃. After a single solution treatment at 900℃ for 30 minutes, the ingots were water-quenched. Pre-aging at 380℃ for 2 hours was performed, and transmission electron microscopy revealed the precipitation of nanoscale Cu4Ti phases in the matrix. Cold rolling reduced the strip thickness to 1.0mm with an 80% deformation. Ultra-high frequency induction heating was used, with a heating rate of 200℃ / s to 700℃, followed by a 1-second hold and water quenching. Aging at 450℃ for 4 hours was then performed.

[0027] The resulting strip has an average grain size of 0.4 μm, a tensile strength of 1150 MPa, and an elongation of 11%.

[0028] Example 2

[0029] The pre-aging temperature was changed to 300℃, and the rest was the same as in Example 1. The average grain size was 0.6μm, the tensile strength was 1080MPa, and the elongation was 10.2%.

[0030] Example 3

[0031] The pre-aging temperature was changed to 500℃, and the rest was the same as in Example 1. The average grain size was 0.5μm, the tensile strength was 1120MPa, and the elongation was 10.8%.

[0032] Example 4

[0033] The cold rolling deformation was changed to 60%, and the rest was the same as in Example 1. The average grain size was 1.2 μm, the tensile strength was 1020 MPa, and the elongation was 12%.

[0034] Example 5

[0035] The cold rolling deformation was changed to 95%, and the rest was the same as in Example 1. The average grain size was 0.3 μm, the tensile strength was 1210 MPa, and the elongation was 10%.

[0036] Example 6

[0037] Direct current heating was used, with a heating rate of 150℃ / s, and the rest was the same as in Example 1. The average grain size was 0.55μm, the tensile strength was 1100MPa, and the elongation was 10.5%.

[0038] Example 7

[0039] Pulsed current heating was used at a heating rate of 500℃ / s, with the rest of the process the same as in Example 1. The average grain size was 0.35μm, the tensile strength was 1180MPa, and the elongation was 10.3%.

[0040] Example 8

[0041] The secondary solution treatment and holding time was changed to 300 seconds, and the rest was the same as in Example 1. The average grain size was 1.8 μm, the tensile strength was 1010 MPa, and the elongation was 11.5%.

[0042] Example 9

[0043] An alloy with a composition of Cu-3.5Ni-0.8Si (mass percentage) was used. It was hot-rolled to 4 mm at 930℃, solution-treated at 950℃ for 30 minutes, pre-aged at 350℃ for 3 hours, cold-rolled with 85% deformation, then heated to 800℃ for a second solution treatment at a heating rate of 250℃ / s, held for 2 seconds, water-quenched, and aged at 420℃ for 5 hours. The average grain size was 0.35 μm, the tensile strength was 1190 MPa, and the elongation was 10.5%.

[0044] Comparative Example 1 Pre-aging was omitted, and the secondary solution treatment used a heating rate of 5℃ / s, otherwise the same as in Example 1. The average grain size was 2.5μm, the tensile strength was 920MPa, and the elongation was 8.5%.

[0045] Comparative Example 2 Pre-aging was omitted, and the secondary solution treatment was performed using rapid heating at 200℃ / s, otherwise the same as in Example 1. The average grain size was 0.8μm, the tensile strength was 975MPa, and the elongation was 9.5%.

[0046] Comparative Example 3 The pre-aging treatment was the same as in Example 1, and the secondary solution treatment used a heating rate of 5℃ / s, with the rest being the same as in Example 1. The average grain size was 1.5μm, the tensile strength was 950MPa, and the elongation was 7.8%.

[0047] As can be seen from the data of Examples 1-9 and Comparative Examples 1-3, when pre-aging treatment and rapid heating at a rate of not less than 100℃ / s are used simultaneously, the average grain size of the resulting strip is ≤2μm, the tensile strength is ≥1000MPa, and the elongation is ≥10%. Omitting pre-aging or using slow heating both lead to an increase in grain size or a decrease in mechanical properties.

[0048] Differential scanning calorimetry (DSC) was performed on the pre-aged cold-rolled samples, with the heating rate consistent with the secondary solution treatment step. An endothermic peak appeared in the DSC curve within the 600℃–750℃ range, corresponding to the re-dissolution process of the pre-precipitated second phase; this endothermic peak was absent in the un-pre-aged control sample. Under the same cold-rolling deformation and heating rate, the un-pre-aged sample required heating to 780℃ to complete recrystallization and obtain a single-phase supersaturated solid solution, while the pre-aged sample achieved the same microstructure at 700℃, with a solution temperature difference of 80℃.

[0049] The specific embodiments described above further illustrate the inventive purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing copper alloy strip with an ultrafine grain structure, characterized in that, Includes the following steps: Ingot preparation steps: Prepare aging precipitation type copper alloy flat ingots; Hot rolling step: The flat ingot is hot rolled to obtain a hot-rolled sheet; One solution treatment step: The hot-rolled sheet is subjected to solution treatment to dissolve the second phase precipitated during the hot rolling process into the matrix; Pre-aging step: The hot-rolled sheet after the first solution treatment is pre-aged at a temperature of 300℃~500℃ for 0.5~6 hours to induce the precipitation of a second phase in the matrix; Cold rolling step: The hot-rolled sheet after the pre-aging step is cold-rolled, and the cold rolling deformation is 60% to 95%; Secondary solution treatment step: The sheet material after the cold rolling step is heated to the solution temperature range of 700℃~950℃ at a heating rate of not less than 100℃ / s, held at the temperature and then quenched to obtain a recrystallized structure with an average grain size ≤2μm, and the matrix is ​​in a supersaturated solution state. Aging step: The plate after the second solution treatment is aged to decompose the supersaturated solid solution and release the strengthening phase.

2. The method for preparing copper alloy strip with ultrafine grain structure according to claim 1, characterized in that, The age-precipitated copper alloy is a Cu-Ni-Si, Cu-Ti, or Cu-Be copper alloy.

3. The method for preparing copper alloy strip with ultrafine grain structure according to claim 1, characterized in that, In the hot rolling step, the hot rolling temperature is 700℃~950℃; in the first solution treatment step, the solution treatment temperature is 800℃~1000℃.

4. The method for preparing copper alloy strip with ultrafine grain structure according to claim 1, characterized in that, In the cold rolling step, the cold rolling deformation is 80% to 95%.

5. The method for preparing copper alloy strip with ultrafine grain structure according to claim 1, characterized in that, In the secondary solution treatment step, the heating rate is 150℃~500℃ / s, and the heating method is one or more combinations of DC power supply heating, ultra-high frequency induction heating, pulse current heating, laser heating or infrared radiation heating.

6. The method for preparing copper alloy strip with ultrafine grain structure according to claim 1, characterized in that, In the secondary solution treatment step, the holding time is 1 to 300 seconds.

7. The method for preparing copper alloy strip with ultrafine grain structure according to claim 6, characterized in that, The solution temperature in the secondary solution treatment step is 50°C to 200°C lower than the solution temperature without the pre-aging step.

8. The method for preparing copper alloy strip with ultrafine grain structure according to claim 1, characterized in that, In the aging process, the aging temperature is 300℃~550℃ and the time is 1~8 hours.

9. The ultra-high strength, high ductility, and ultra-fine grain copper alloy strip prepared by the method for preparing copper alloy strip with ultra-fine grain structure according to any one of claims 1-8, characterized in that, The strip has a width of ≥300mm and a length of ≥1000mm.

10. The ultra-high strength, high ductility, ultra-fine crystalline copper alloy strip according to claim 9, characterized in that, Its tensile strength is ≥1000MPa and its elongation is ≥10%.

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