A complex component multi-phase synergistic high-strength and high-conductivity copper alloy and its preparation method

Abstract

The present invention belongs to the technical field of materials and their preparation and processing, and particularly relates to a complex-component multi-phase synergistic high-strength and high-conductivity copper alloy and a preparation method thereof. By mass percentage, the alloy components are as follows: Cr is 0.5-0.9%, Zr is 0.08-0.25%, Ni is 0.4-0.7%, Si is 0.05-0.15%, Co is 0.1-0.2%, Zn is 0.05-0.1%, and the balance is matrix Cu. The alloy can be prepared by two short-process preparation methods: (1) vacuum induction melting and casting → homogenization treatment → double-side milling → hot rolling → solution treatment → cold rough rolling → primary aging → cold finish rolling → secondary aging; (2) downward continuous casting → continuous extrusion of plates → cold rough rolling → primary aging → cold finish rolling → secondary aging. The complex-component multi-phase synergistic high-strength and high-conductivity copper alloy of the present invention has many advantages such as high strength, high conductivity, heat resistance, corrosion resistance, and stress relaxation resistance, and not only meets the use requirements of lead frames for large-scale and ultra-large-scale integrated circuits and high-end electronic component connectors, but also can be applied to special environments such as high temperature and corrosion.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials and their preparation and processing, and particularly relates to a complex-component multiphase synergistic high-strength and high-conductivity copper alloy and a preparation method thereof. Background Art

[0002] The rapid development of the electronic information industry and the new energy vehicle field has greatly promoted the rapid development of related industrial chains. With the rapid advancement of integrated circuits towards large-scale and ultra-large-scale, the lead frame, as the skeleton of integrated circuits and the bridge connecting semiconductor chips and external circuits, requires its materials to have high strength and high conductivity characteristics. As the core component of electrical connectors, electronic component connectors mainly function for energy transmission and information exchange, and are widely used in almost all scenarios of optical and electrical signal transmission and interaction. Higher requirements are imposed on the materials for high-end electronic component connectors. In addition, some special environments such as high temperature and corrosive environments also pose higher and more stringent requirements on the service performance of materials. Copper alloys have good electrical and thermal conductivity, strong tensile strength and hardness, and good plastic processing performance, which are one of the important reasons for gradually becoming the main materials for lead frames and electronic component connectors. By microalloying and adding complex components to introduce multiple precipitation phases, copper alloys can also achieve excellent service effects in harsh special environments, and the regulation of copper alloy properties by adding alloying elements has been increasingly favored by domestic and foreign scholars in the industry. For example:

[0003] Patent application: "A multi-element composite precipitation-strengthened high-strength and high-conductivity copper alloy and a preparation method thereof (Publication No. CN108823466A)" proposed adding Zn, Cr, and P elements to the Cu-Ni-Si-based copper alloy, and obtained a lead frame copper alloy with easy melting, composite precipitation strengthening, high tensile strength, and high electrical conductivity through a preparation method of melting → homogenization → hot rolling → double-sided milling → rough cold rolling → trimming → first online quenching → pre-finishing rolling → second online quenching → first finishing rolling → first aging → second finishing rolling → second aging.

[0004] Patent application: "A multi-element copper alloy material for lead frame materials and a preparation method thereof (Publication No. CN106756202A)" proposed adding Fe, Ni, Sn, P, B, and Co elements to copper, and obtained a tensile strength of 450 - 520 MPa, electrical conductivity greater than 75% IACS, thermal conductivity of 313 W / (m·k), elongation greater than or equal to 3%, and stress relaxation rate (H state, temperature 100 °C, time 100 h) reaching 20% after processing treatments such as melting and casting, hot rolling, primary rolling, intermediate annealing, pickling, medium rolling, online solution treatment, finishing rolling, and low-temperature annealing treatment.

[0005] Patent application: "A multi-element copper alloy strip for power battery connectors and its preparation method (Publication No. CN106636729A)" proposes adding elements such as Sn, P, Fe, Zn, Mg, B, Cr, and Gd to copper alloys. The resulting material has high strength, a high yield ratio, excellent electrical conductivity, and stress relaxation resistance, and can meet the usage requirements of power battery connectors for high conductivity, high frequency, and high-power transmission.

[0006] Patent application: "Cu-Ni-Si-Co-Cr alloy system for electronic materials (Publication No. CN101983249A)" proposes that, based on the Cu-Ni-Si base alloy system, adding Co and Cr elements results in a copper alloy for high-strength and high-conductivity electronic materials. Patent application: "Cu-Ni-Si alloy system for electronic materials (Publication No. CN101270423A)" proposes a Cu-Ni-Si-Cr copper alloy system, and similarly obtains a copper alloy for electronic materials with a yield strength greater than 750 MPa and a conductivity greater than 50% IACS.

[0007] Although the above research has obtained copper alloy materials for lead frames and electronic connectors with good performance through adding alloy strengthening elements and corresponding preparation means, the service performance of copper alloys and industrial short-process preparation means in special complex environments have been increasingly emphasized with the wide application of electronic technology and the improvement of industrial production efficiency. Summary of the Invention

[0008] For the above reasons, the purpose of the present invention is to provide a complex-component multi-phase synergistic high-strength and high-conductivity copper alloy and its preparation method. It can, while ensuring that the high-strength and high-conductivity performance requirements of large-scale and ultra-large-scale lead frames and high-end electronic component connectors are met, give play to the characteristics of multi-phase synergistic high-strength and high-conductivity, enabling it to also achieve good service performance in extreme special environments such as high temperature and corrosion. By reasonably configuring alloy strengthening elements and shortening the process flow, low-cost, low-energy consumption, low-emission, and high-performance short-process preparation of copper alloys for lead frames and electronic component connectors under conventional and special environments is realized.

[0009] To achieve the above purpose, the technical solution of the present invention is:

[0010] A complex-component multi-phase synergistic high-strength and high-conductivity copper alloy, by mass percentage, the alloy components are as follows: Cr is 0.5 - 0.9%, Zr is 0.08 - 0.25%, Ni is 0.4 - 0.7%, Si is 0.05 - 0.15%, Co is 0.1 - 0.2%, Zn is 0.05 - 0.1%, and the balance is matrix Cu.

[0011] For the complex component multi-phase synergistic high-strength and high-conductivity copper alloy described above, preferably, by mass percentage, the alloy components are as follows: Cr is 0.7 - 0.75%, Zr is 0.12 - 0.16%, Ni is 0.51 - 0.55%, Si is 0.09 - 0.1%, Co is 0.1 - 0.15%, Zn is 0.06 - 0.07%, and the balance is matrix Cu.

[0012] The complex component multi-phase synergistic high-strength and high-conductivity copper alloy described above comprises the following steps:

[0013] (1) Vacuum induction melting and casting;

[0014] (2) Homogenization treatment;

[0015] (3) Double surface milling;

[0016] (4) Hot rolling;

[0017] (5) Solution treatment;

[0018] (6) Cold rough rolling: The total cold rough rolling deformation is 70% - 90%, and the thickness after cold rough rolling is 0.5 mm - 2 mm;

[0019] (7) Primary aging: The aging temperature is 360°C - 560°C, and the aging time is 0.5 h - 16 h;

[0020] (8) Cold finish rolling: The total cold finish rolling deformation is 40% - 95%, and the thickness after cold finish rolling is 0.1 - 0.3 mm;

[0021] (9) Secondary aging: The aging temperature is 350°C - 550°C, and the aging time is 0.5 h - 16 h.

[0022] For the complex component multi-phase synergistic high-strength and high-conductivity copper alloy described above, the characteristics of vacuum induction melting and casting are as follows: Weigh electrolytic Cu with a purity above 99.96 wt%, electrolytic Ni with a purity above 99.96 wt%, polycrystalline Si with a purity above 99.99 wt%, Cr with a purity above 99.96 wt%, Co with a purity above 99.96 wt%, and Zn with a purity above 99.96 wt% in proportion. After charging and evacuating, start heating to melt. After all the metals in the crucible are melted, adjust the temperature to 1150°C - 1250°C, refine for 15 min - 20 min. After refining, fill the vacuum furnace with argon and put in pure Zr wrapped in copper foil or Cu-Zr master alloy through the secondary feeding bin. Wait until the liquid surface is calm and no bubbles escape, which means it is completely melted. Stir evenly, and during casting, carry out charged casting with the temperature controlled at 1150°C - 1200°C.

[0023] For the complex component multi-phase synergistic high-strength and high-conductivity copper alloy described above, the characteristics of homogenization treatment are as follows: The ingot is held at a temperature of 900°C - 1100°C for 1 - 6 hours.

[0024] For the described complex component multi-phase synergistic high-strength and high-conductivity copper alloy, the double milling surface feature is as follows: Double-sided milling is performed as required to remove the defects on the surface of the hot-rolled plate, and the milling depth is 0.1 - 0.5 mm.

[0025] For the described complex component multi-phase synergistic high-strength and high-conductivity copper alloy, the hot rolling feature is as follows: The starting rolling temperature is ≥850 °C, the final rolling temperature is ≥700 °C, the single-pass hot rolling deformation is 10% - 35%, the total hot rolling deformation is 70% - 85%, and the thickness after hot rolling is 5 - 8 mm.

[0026] For the described complex component multi-phase synergistic high-strength and high-conductivity copper alloy, the solution treatment feature is as follows: The solution treatment temperature is 800 °C - 1000 °C, and the solution treatment time is 1 - 5 h.

[0027] The described complex component multi-phase synergistic high-strength and high-conductivity copper alloy includes the following steps:

[0028] (1) Downward continuous casting;

[0029] (2) Continuous extrusion of the plate;

[0030] (3) Cold rough rolling: The single-pass cold rough rolling deformation is 15% - 30%, the total cold rough rolling deformation is 83% - 90%, and the thickness after cold rough rolling is 0.5 mm - 1.2 mm;

[0031] (4) First aging: The aging temperature is 360 °C - 560 °C, and the aging time is 0.5 h - 16 h;

[0032] (5) Cold finish rolling: The total cold finish rolling deformation is 40% - 92%, and the thickness after cold finish rolling is 0.1 - 0.3 mm;

[0033] (6) Second aging: The aging temperature is 360 °C - 560 °C, and the aging time is 0.5 h - 16 h.

[0034] The design concept of the present invention is:

[0035] Utilize the characteristic that strengthening phases precipitate during the aging process of the copper alloy. By adding several elements, the purpose of multi-phase synergistic strengthening of the copper alloy is achieved. At the same time, according to the characteristics exhibited by each precipitated phase, control the specific precipitation size, distribution, and size so that it can meet the usage requirements in high-temperature and corrosive environments.

[0036] In the alloy composition design of the present invention, it is preferably to control the alloy element composition as follows: Cr is 0.7 - 0.75%, Zr is 0.12 - 0.16%, Ni is 0.51 - 0.55%, Si is 0.09 - 0.1%, Co is 0.1 - 0.15%, and Zn is 0.06 - 0.07%. Among them:

[0037] The role of Cr is as follows: It forms an fcc Cr phase at the nanoscale and forms a stable Cr3Si phase with Si, reducing the concentration of Si in the matrix, enhancing the electrical conductivity, and improving the thermal stability of the overall microstructure and properties. When Cr < 0.7 wt%, or the amount is too small to form a stable Cr3Si, the attraction to Si is weakened; when Cr > 0.75 wt%, due to the high melting point of Cr, when an excessive amount of Cr is introduced, Cr cannot be dissolved into the matrix, and large-scale elemental Cr points are formed during melting and solidification, affecting the strength.

[0038] The role of Zr is as follows: It forms a Ni2SiZr phase with Ni and Si elements to enhance the electrical conductivity. When Zr < 0.12 wt%, there is not enough Zr element to form a concentration gradient to attract Ni and Si to react; when Zr > 0.16 wt%, excessive Zr will attract excessive Ni and Si elements, resulting in insufficient quantity of nanoscale Ni2Si to play the role of precipitation strengthening, and thus reducing the strength of the copper alloy.

[0039] The role of Ni is as follows: It is a key element for multiple elements to form nanoscale alloy phases. When Ni < 0.51 wt%, there is not enough nano-strengthening phase provided for the alloy; when Ni > 0.55 wt%, due to the infinite solid solubility of Ni and Cu, excessive Ni will be dissolved in the Cu matrix, and when the precipitation driving force is insufficient, it cannot precipitate sufficiently, thereby affecting the lattice and shear modulus mismatch of the Cu matrix and the electrical conductivity of the Cu alloy.

[0040] The role of Si is as follows: It forms stable precipitation phases of different scales with Ni, Zr, Cr, and Co, and is one of the most important elements for strengthening copper alloys. When Si < 0.09 wt%, there are not enough elements to form a large number of precipitation strengthening phases; when Si > 0.1 wt%, it cannot precipitate sufficiently from the matrix, thus affecting the strength and electrical conductivity.

[0041] The role of Co is as follows: It has the same role as Ni but a higher strengthening effect than Ni. It is one of the key elements for realizing short-process preparation when forming (Ni, Co)2Si with Ni and Si elements to promote the further precipitation of Ni and Si. When Co < 0.1 wt%, nano-strengthening phases cannot be formed sufficiently; when Co > 0.15 wt%, the solid solution of elements in Cu is aggravated, affecting the electrical conductivity.

[0042] The role of Zn is as follows: It improves the welding performance of the alloy. When Zn < 0.06 wt%, Zn cannot segregate at the solder interface and cannot affect the aggregation of Cu elements towards the solder, deteriorating the welding performance; when Zn > 0.07 wt%, due to the solid solution problem of the element in the copper matrix, its electrical conductivity is reduced.

[0043] The advantages and beneficial effects of the present invention are as follows:

[0044] 1. It can give full play to the characteristics of multi-phase synergistic high strength and high conductivity while ensuring that the requirements of high strength and high conductivity of copper alloys for large-scale, ultra-large-scale lead frames and high-end electronic component connectors are met, enabling it to achieve good service performance even in extreme special environments such as high temperature and corrosion. By reasonably configuring alloy strengthening elements and shortening the process flow, the short-process preparation of copper alloys for lead frames and electronic component connectors with low cost, low energy consumption, low emissions, and high performance under conventional and special environments is realized.

[0045] 2. During the primary aging and secondary aging treatment processes of the present invention, a variety of stable and metastable strengthening phases are formed, enabling the alloy to have a multi-phase strengthening effect. At the same time, the elements dissolved in the Cu matrix precipitate during the competition between precipitations, improving the conductivity of the alloy. After cold precision rolling, the thickness of the strip is 0.1 - 0.3 mm. The tensile strength of the alloy in the secondary peak aging state is greater than 700 MPa, and the conductivity is greater than 70% IACS. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of the preparation method of the first complex component multi-phase synergistic high strength and high conductivity copper alloy.

[0047] Figure 2 It is a flow chart of the preparation method of the second complex component multi-phase synergistic high strength and high conductivity copper alloy. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In the specific implementation process, the complex component multi-phase synergistic high strength and high conductivity copper alloy of the present invention can be prepared by two short-process preparation methods. The specific processes are as follows: (1) Vacuum induction melting and casting → Homogenization treatment → Double milling → Hot rolling → Solution treatment → Cold rough rolling → Primary aging → Cold precision rolling → Secondary aging; (2) Downward continuous casting → Continuous extrusion of plates → Cold rough rolling → Primary aging → Cold precision rolling → Secondary aging.

[0049] Hereinafter, the embodiments of the present invention will be further described in detail with reference to the accompanying drawings.

[0050] Example 1:

[0051] In this example, a complex component multi-phase synergistic high strength and high conductivity copper alloy (wt%) that meets the requirements of high strength and high conductivity for large-scale, ultra-large-scale lead frames and high-end electronic component connectors under conventional and special environments is designed and developed: Cr is 0.71%, Zr is 0.15%, Ni is 0.52%, Si is 0.093%, Co is 0.14%, Zn is 0.067%, and the balance is matrix Cu.

[0052] As Figure 1 shown, the preparation method of the above complex component multi-phase synergistic high strength and high conductivity copper alloy is specifically described as follows:

[0053] (1) Vacuum induction melting and casting: Weigh electrolytic Cu with a purity above 99.96 wt%, electrolytic Ni with a purity above 99.96 wt%, polycrystalline Si with a purity above 99.99 wt%, Cr with a purity above 99.96 wt%, Co with a purity above 99.96 wt%, and Zn with a purity above 99.96 wt% according to the proportion. After charging and evacuating, start heating up to melt. After all the metals in the crucible are melted, adjust the temperature to 1200 ± 10 °C, refine for 20 min. After refining, fill the crucible with argon and input pure Zr wrapped with copper foil or Cu-Zr master alloy through the secondary feeding bin. When the liquid surface is calm and no bubbles escape, that is, when it is completely melted, stir evenly. During casting, carry out electrocasting, and control the temperature at 1150 ± 10 °C.

[0054] (2) Homogenization treatment: Keep the ingot at 960 °C for 4 h and then cool it to room temperature in the furnace.

[0055] (3) Double milling: Remove the defects on the as-cast surface, and the milling depth is 0.2 mm.

[0056] (4) Hot rolling: The starting rolling temperature is 900 ± 10 °C, the final rolling temperature is 750 ± 10 °C, the single-pass deformation of hot rolling is 20%, the total deformation of hot rolling is 80%, and the thickness after hot rolling is 6 mm.

[0057] (5) Solution treatment: The solution temperature is 860 ± 10 °C, the solution time is 1 h, and it is water-cooled to room temperature.

[0058] (6) Cold rough rolling: The total deformation of cold rough rolling is 83.3%, and the thickness after cold rough rolling is 1 mm.

[0059] (7) First aging: The aging temperature is 460 °C, the aging time is 2 h, and it is air-cooled to room temperature.

[0060] (8) Cold finish rolling: The total deformation of cold finish rolling is 70%, and the thickness after cold finish rolling is 0.3 mm.

[0061] (9) Second aging: The aging temperature is 410 °C, the aging time is 2 h, and it is air-cooled to room temperature.

[0062] In this example, after the second aging, the tensile strength of the alloy reaches 826 MPa, and the conductivity reaches 79% IACS.

[0063] Example 2:

[0064] In this example, a complex component multi-phase synergistic high-strength and high-conductivity copper alloy (wt%) that meets the high-strength and high-conductivity performance requirements of large-scale, ultra-large-scale lead frames and high-end electronic component connectors under conventional and special environments is designed and developed: Cr is 0.72%, Zr is 0.13%, Ni is 0.54%, Si is 0.096%, Co is 0.11%, Zn is 0.065%, and the balance is matrix Cu.

[0065] As Figure 2 shown, the preparation method of the above-mentioned complex component multiphase synergistic high-strength and high-conductivity copper alloy is specifically described as follows:

[0066] (1) Downward continuous casting.

[0067] (2) Continuous extrusion of sheet.

[0068] (3) Cold rough rolling: The single-pass deformation amount of cold rough rolling is 15% - 20%, the total deformation amount of cold rough rolling is 83.3%, and the thickness after cold rough rolling is 1 mm.

[0069] (4) First aging: The aging temperature is 460 ± 10 °C, the aging time is 2 h, and it is air-cooled to room temperature.

[0070] (5) Cold finish rolling: The total deformation amount of cold finish rolling is 70%, and the thickness after cold finish rolling is 0.3 mm.

[0071] (6) Second aging: The aging temperature is 410 ± 10 °C, the aging time is 2 h, and it is air-cooled to room temperature.

[0072] In this embodiment, after the second aging, the tensile strength of the alloy reaches 754 MPa, and the conductivity reaches 81% IACS.

[0073] The results of the embodiment show that the complex component multiphase synergistic high-strength and high-conductivity copper alloy of the present invention has many advantages such as high strength, high conductivity, heat resistance, corrosion resistance, and stress relaxation resistance. It not only meets the use requirements of large-scale and ultra-large-scale integrated circuit lead frames and high-end electronic component connectors, but also can be applied to special environments such as high temperature and corrosion.

[0074] The above-mentioned embodiments are only preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of technical solutions that can be obviously obtained by those skilled in the art within the technical scope disclosed by the present invention all fall within the protection scope of the present invention.

Claims

1. A complex component multi-phase synergistic high-strength and high-conductivity copper alloy, characterized in that, By mass percentage, the alloy components are as follows: Cr is 0.5 - 0.9%, Zr is 0.08 - 0.25%, Ni is 0.4 - 0.7%, Si is 0.05 - 0.15%, Co is 0.1 - 0.2%, Zn is 0.05 - 0.1%, and the balance is matrix Cu; among them, Cr forms a nanoscale fcc Cr phase and forms a stable Cr3Si phase with Si, Zr forms a Ni2SiZr phase with Ni and Si elements, and Co generates (Ni, Co)2Si with Ni and Si elements.

2. The complex component multi-phase synergistic high-strength and high-conductivity copper alloy according to claim 1, characterized in that By mass percentage, the alloy components are as follows: Cr is 0.7 - 0.75%, Zr is 0.12 - 0.16%, Ni is 0.51 - 0.55%, Si is 0.09 - 0.1%, Co is 0.1 - 0.15%, Zn is 0.06 - 0.07%, and the balance is matrix Cu.

3. The preparation method of the complex component multi-phase synergistic high-strength and high-conductivity copper alloy according to claim 1 or 2, characterized in that, It includes the following steps: (1) Vacuum induction melting and casting; (2) Homogenization treatment; (3) Double milling; (4) Hot rolling; (5) Solution treatment; (6) Cold rough rolling: The total cold rough rolling deformation is 70% - 90%, and the thickness after cold rough rolling is 0.5 mm - 2 mm; (7) Primary aging: The aging temperature is 360°C - 560°C, and the aging time is 0.5 h - 16 h; (8) Cold finish rolling: The total cold finish rolling deformation is 40% - 95%, and the thickness after cold finish rolling is 0.1 - 0.3 mm; (9) Secondary aging: The aging temperature is 350°C - 550°C, and the aging time is 0.5 h - 16 h.

4. The preparation method of the complex component multiphase synergistic high-strength and high-conductivity copper alloy according to claim 3, wherein The characteristics of vacuum induction melting and casting are as follows: Weigh electrolytic Cu with a purity above 99.96 wt%, electrolytic Ni with a purity above 99.96 wt%, polycrystalline Si with a purity above 99.99 wt%, Cr with a purity above 99.96 wt%, Co with a purity above 99.96 wt%, and Zn with a purity above 99.96 wt% in proportion. After charging and evacuating, start heating to melt. After all the metals in the crucible are melted, adjust the temperature to 1150°C - 1250°C, refine for 15 min - 20 min. After refining, fill the vacuum furnace with argon and put in pure Zr wrapped in copper foil or Cu - Zr master alloy through the secondary feeding bin. When the liquid surface is calm and no bubbles escape, it means complete melting. Stir evenly, and during casting, carry out charged casting with the temperature controlled at 1150°C - 1200°C.

5. The preparation method of the complex component multi-phase synergistic high-strength and high-conductivity copper alloy according to claim 3, characterized in that, The characteristics of homogenization treatment are as follows: The ingot is held at a temperature of 900°C - 1100°C for 1 - 6 hours.

6. The preparation method of the complex component multiphase synergistic high-strength and high-conductivity copper alloy according to claim 3, characterized in that, The characteristics of double milling are as follows: Carry out double - side milling as needed to remove the defects on the surface of the hot - rolled plate, and the milling depth is 0.1 - 0.5 mm.

7. The preparation method of the complex component multi-phase synergistic high-strength and high-conductivity copper alloy according to claim 3, characterized in that, The characteristics of hot rolling are as follows: The starting rolling temperature ≥850°C, the final rolling temperature ≥700°C, the single - pass hot - rolling deformation is 10% - 35%, the total hot - rolling deformation is 70% - 85%, and the thickness after hot rolling is 5 - 8 mm.

8. The preparation method of the complex component multi-phase synergistic high-strength and high-conductivity copper alloy according to claim 3, characterized in that, The characteristics of solution treatment are as follows: The solution temperature is 800°C - 1000°C, and the solution time is 1 - 5 h.

9. The preparation method of the complex component multiphase synergistic high-strength and high-conductivity copper alloy according to claim 1 or 2, characterized in that, It includes the following steps: (1) Down - casting continuous casting; (2) Sheet continuous extrusion; (3) Cold rough rolling: The single-pass deformation of cold rough rolling is 15% - 30%, the total deformation of cold rough rolling is 83% - 90%, and the thickness after cold rough rolling is 0.5 mm - 1.2 mm; (4) First aging: The aging temperature is 360°C - 560°C, and the aging time is 0.5 h - 16 h; (5) Cold finish rolling: The total deformation of cold finish rolling is 40% - 92%, and the thickness after cold finish rolling is 0.1 - 0.3 mm; (6) Second aging: The aging temperature is 360°C - 560°C, and the aging time is 0.5 h - 16 h.

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