CN111378869B

CN111378869B - Fine-grain reinforced brass strip for connector and processing method thereof

Info

Publication number: CN111378869B
Application number: CN202010216403.5A
Authority: CN
Inventors: 华称文; 巢国辉; 傅杰
Original assignee: Ningbo Jintian Copper Group Co Ltd
Current assignee: Ningbo Jintian Copper Group Co Ltd
Priority date: 2020-03-25
Filing date: 2020-03-25
Publication date: 2021-06-01
Anticipated expiration: 2040-03-25
Also published as: CN111378869A

Abstract

The invention relates to a fine-grain reinforced brass strip for a connector, which is characterized by comprising the following components in percentage by mass: 63-67 wt%, Sn: 0.01 to 0.3 wt%, and the balance of Zn and inevitable impurities; the grain diameter of the structure of the fine-grain reinforced brass strip is less than or equal to 10 mu m, wherein the grain diameter ratio of the minimum grain diameter to the maximum grain diameter is more than or equal to 0.85. The small structure crystal grains can improve the strength, meet the requirements of stamping and bending processing, simultaneously keep good plasticity, and also can enhance the elastic property of the strip; the uniformity of the structure crystal grains ensures the stability of the hardness, the strength and the plasticity of a final product while controlling the fineness of the structure crystal grains, and avoids the problems that the bending surface is easy to hair and even cracks and the like during bending.

Description

Fine-grain reinforced brass strip for connector and processing method thereof

Technical Field

The invention relates to a copper alloy, in particular to a fine-grain reinforced brass strip for a connector and a processing method thereof.

Background

With the continuous development of the communication, automobile and electrical industries, the copper strip used for the connector also puts higher material requirements. For example, the copper strip used in the wire harness connector product is required to meet the requirements of both the plasticity during stamping and the strength and elasticity during plugging. In addition, as connector products are miniaturized and lightened, the bending conditions of copper strip products are more strict for customers. Copper tape for connectors is typically tin phosphor bronze tape and H65 brass tape, but brass tape for connectors has become a trend in recent years due to cost considerations. However, even if the conventional brass band meets the indexes of high tensile strength and high elongation, the bending performance of the conventional brass band still has a large improvement space (the 90-degree bending performance is excellent, and the R/t value of the relative bending radius in a good direction is required to be less than or equal to 1, and the R/t value of the relative bending radius in a bad direction is required to be less than or equal to 2).

The invention patent CN108057999A discloses a production process method of a double-strength copper strip for an automobile connector, wherein a rough rolling procedure adopts 84% of processing rate, a subsequent processing procedure comprises 4 rolling procedures, 4 annealing procedures and 4 cleaning procedures, sulfuric acid pickling is adopted after annealing, the mass concentration of sulfuric acid is 4-12%, and finally the performance of the material is controlled by the bottom processing rate, so that the performance requirements of 500-520 MPa of tensile strength and 15-18% of elongation of the material are met. However, the material strength in the processing technology is difficult to meet the use of the connector with higher requirements, and the connector with the future miniaturization development will need higher tensile strength.

The invention patent CN106636731B discloses a processing technology of a high-strength high-elongation brass alloy strip, 2 lanthanide series rare earth metals, manganese and iron are added in a smelting mode, the cold processing adopts finish rolling with a small processing rate of less than 20%, the intermediate annealing temperature is 500-600 ℃, the low-temperature annealing temperature of a finished product is 270-300 ℃, and the performance result that the tensile strength of brass is more than or equal to 580 and the elongation is more than or equal to 10% is obtained. However, the processing method has adverse effect on the structural uniformity of the material, and is unstable for bending processing under high requirement conditions, and the bent part of the strip in the bad direction is easy to crack.

Disclosure of Invention

The first technical problem to be solved by the invention is to provide a fine-grained reinforced brass strip for a connector, which has high strength, high elongation and excellent bending performance, aiming at the current state of the prior art.

The technical scheme adopted by the invention for solving the first technical problem is as follows: the fine-grain reinforced brass strip for the connector is characterized by comprising the following components in percentage by mass: 63-67 wt%, Sn: 0.01 to 0.3 wt%, and the balance of Zn and inevitable impurities; the grain diameter of the structure of the fine-grain reinforced brass strip is less than or equal to 10 mu m, wherein the grain diameter ratio of the minimum grain diameter to the maximum grain diameter is more than or equal to 0.85.

When the amount of Sn is less, Sn is not dissolved in Zn in a solid manner, part of Sn is dissolved in Cu in a solid manner, and the rest of Sn and Cu form an intermetallic compound which can be used as a nucleation mass point, so that the nucleation rate is improved, the growth of crystal grains is inhibited, and the effect of refining the crystal grains is achieved. Meanwhile, due to the difference of atom sizes, Sn is not dissolved in Zn in a solid solution manner, the phenomenon of lattice distortion is caused by the solid solution strengthening effect, the resistance of dislocation movement is increased, and slippage is difficult to carry out, so that the strength and the hardness of the alloy are improved, and the plasticity and the toughness of the alloy are reduced. According to the invention, a certain content of Sn is added to achieve the effect of fine grain strengthening, when the content of Sn is 0.01-0.3 wt%, the structure grain diameter of the material can be controlled to be less than or equal to 10 mu m, and the grain diameter ratio of the minimum grain diameter to the maximum grain diameter is greater than or equal to 0.85. When the content of Sn is increased to exceed 0.3%, the structure thinning effect is weakened, and simultaneously Sn begins to segregate in the grain boundary, so that the bonding strength of the grain boundary is reduced, the toughness and the plasticity of the alloy are reduced, and the hardness is improved. Therefore, a proper amount of Sn may refine the structure grains while enhancing the strength of the alloy.

The brass strip for the connector meets the requirements of high strength and high elongation and simultaneously has good plasticity, the grain diameter is controlled to be less than or equal to 10 mu m, the fine structure grains meet the requirements of stamping and bending processing while improving the strength, and simultaneously keep good plasticity, and the fine structure grains can also enhance the elastic property of the strip; while controlling the fineness of the structure crystal grains, the uniformity of the structure crystal grains is a key factor influencing the performance stability of the brass strip, the uniformity of the structure can influence the hardness, the strength and the plasticity stability of a final product, and meanwhile, the bending surface is easy to hair and even cracks when the structure is not uniform in size during bending, so that the grain diameter ratio of the minimum crystal grain diameter to the maximum crystal grain diameter in the structure crystal grains is more than or equal to 0.85.

Preferably, the alloy also comprises at least one selected from rare earth elements Y, Sc with the total weight of 0.001-0.3 wt%.

The alloy of the invention can be selectively added with rare earth Y, Sc on the basis of brass, and the rare earth is beneficial to increasing nucleation cores in the crystallization process, refining as-cast structure and providing basic conditions for subsequent fine-grained strengthening. However, the addition of excessive thinning results in a decrease in the effect and an increase in the production cost.

Preferably, the weight percent of Y + Sc is more than or equal to 0.05 and less than or equal to 0.15, and the weight percent of Sn: 0.25 wt% -0.3 wt%.

Preferably, the tensile strength of the fine-grain reinforced brass strip is 550-620 MPa, the Vickers hardness is 170-190 HV, the elongation is more than or equal to 15%, the 90-degree bending R/t is less than or equal to 0.5 at GW and less than or equal to 1.5 at BW.

The second technical problem to be solved by the invention is to provide a preparation method of the fine-grain reinforced brass strip for the connector, which has short production process and is beneficial to fine-grain reinforcement.

The technical scheme adopted by the invention for solving the second technical problem is as follows: the preparation method of the fine-grain reinforced brass strip for the connector comprises the following processing technological processes:

casting → hot rolling → face milling → rough rolling → intermediate annealing → thick shearing → cleaning → finish rolling → bottom annealing → cleaning → finished product rolling → low temperature annealing → cleaning → straightening; the casting adopts a semi-continuous casting and pulling casting flat ingot mode, the thickness of the ingot is 160-240 mm, and the width of the ingot is 400-630 mm; the hot rolling procedure adopts a rolling process with multiple passes and small processing rate of each pass, the total number of rolling passes is 9-15, and the processing rate of each pass is less than or equal to 32%; the rough rolling process adopts a large processing rate mode for rolling, and the processing rate is 85-92%.

In order to obtain excellent fine grain effect, the casting of the ingot meeting the requirements is also the key point for realizing the invention, the brass ingot casting adopts a semi-continuous casting flat ingot mode, and compared with a square ingot, the flat ingot has shorter distance from the surface to the center of the ingot in the thickness direction due to thinner thickness in the casting process, has better contact cooling effect with the cooling wall of the crystallizer, and is beneficial to increasing the supercooling degree, improving the nucleation rate and refining the casting state structure. The thickness of the cast ingot of the invention is 160-240 mm, and the width is 400-630 mm. The flat ingot is heated easily and uniformly when being heated in the stepping furnace, and is beneficial to hot rolling and rolling. The hot rolling is carried out by combining a mode of hot rolling with multiple passes and small processing rate of each pass, the total hot rolling passes are 9-15, the processing rate of each pass is less than or equal to 32%, compared with the traditional hot rolling mode of adopting few passes and large processing rate of each pass for cast ingots with the thickness of more than 260mm, the defects of surface peeling, cracks and the like generated in the hot rolling process are reduced, the quality of the hot rolling surface is ensured to be stable, and meanwhile, favorable conditions are provided for the rough rolling process in the subsequent cold working to adopt large processing rate rolling. The invention adopts rough rolling with high processing rate, and the rough rolling processing rate reaches 85-92%. The rough rolling with large processing rate is carried out under the conditions of pulling and casting a flat ingot and hot rolling with small processing rate of each pass, so that the plasticity of the material and the rolling capability of rolling mill equipment are fully utilized, favorable conditions are created for reducing the working procedures and shortening the delivery period of subsequent processing, most importantly, the sufficient crushing and refining of tissue grains are facilitated, the synchronous improvement of the strength and the plasticity of the material is realized, and the purpose of fine grain strengthening is achieved. Moreover, the method ensures that the structure crystal grains of the product are fine, can also improve the bending stamping performance of the strip, and can also avoid the problem of rough surface caused by coarse structure crystal grains.

Preferably, the intermediate annealing temperature is 470-490 ℃, the annealing time is 2-12 h, and the grain size of the annealed structure is 5-15 μm.

The size control of the structure grains does not leave the control of the annealing process. Different from the conventional copper strip intermediate annealing production process, the low-temperature annealing process is adopted according to the incomplete recrystallization mode, the intermediate annealing temperature is 470-490 ℃, the annealing time is 2-12 hours, the intermediate annealing process at the temperature enables the tissue crystal grains not to fully and completely grow under the condition that the crystal grains are completely crushed after the rough rolling with large processing rate, and the grain size of the annealed tissue is 5-15 mu m. The final fine grain strengthening can be ensured by controlling the grain size of the structure after the intermediate annealing within the range.

Preferably, the bottom annealing temperature is 400-430 ℃, the annealing time is 3-6 h, and the grain size of the annealed structure is 5-15 μm.

After finish rolling, the original incomplete recrystallization structure is completely crushed again, a large number of slip bands and twin bands appear in crystal grains, and the crystal grains are elongated and flattened to form a processed fiber structure. Under the action of bottom-retaining annealing at lower temperature, the processed fibrous tissue is subjected to recovery recrystallization, but due to the lower temperature, the tissue grows up in an incomplete recrystallization mode. Therefore, the grain size of the structure after bottom annealing is 5-15 μm, and a foundation is provided for fine grains of a finished product.

Preferably, the processing rate of the finished product rolling is 22-35%, and the texture grain size of the rolled finished product is less than or equal to 10 microns; the finished product low-temperature annealing process comprises the following steps: the annealing temperature is 230-260 ℃, and the heat preservation time is 2-6 h.

The invention controls the hardness and the strength of the product by adopting the finished product processing rate and ensures the qualified elongation rate of the final product by combining the low-temperature annealing process of the product. Because the connector is used for the brass performance requirement, the hardness and the strength of the connector accord with the EH performance requirement, and the elongation accords with the H performance requirement. The product performance is controlled simply through the finished product processing rate, and the obtained elongation is low, and belongs to an EH state. Therefore, when EH state performance with lower limits of hardness and strength is obtained, the low-temperature annealing process is combined to improve the elongation. The invention combines the structure and performance before and after low-temperature annealing, refers to a brass work hardening curve, and formulates a specific finished product rolling rate and a low-temperature annealing process according to the mechanical properties of a finished product to be obtained. Annealing below the recrystallization temperature, also known as stress relief annealing. In terms of structure and properties, the structure does not change under annealing conditions at a temperature lower than the recrystallization temperature, and the elongation can be appropriately increased. In addition, the residual stress in the strip can be released by stress relief annealing, and the problems of warping and twisting in the stamping process of a client are reduced. The processing rate of rolling the finished product is 22-35%, and the low-temperature annealing temperature of the finished product is controlled at 230-260 ℃. The rolling rate is lower than 22%, the low-temperature annealing temperature is higher than 260 ℃, and the mechanical property cannot be met; the rolling rate is higher than 35%, the low-temperature annealing temperature is lower than 250 ℃, the material is processed and hardened, and the elongation is reduced.

Compared with the prior art, the invention has the advantages that:

1) on the basis of the traditional brass, a proper amount of Sn is added, part of Sn is dissolved in Cu in a solid solution mode, and the rest of Sn and Cu form an intermetallic compound which can be used as nucleation particles, so that the nucleation rate is improved, the growth of crystal grains is hindered, and the effect of refining the crystal grains is achieved. The structure grain diameter of the material can be controlled to be less than or equal to 10 mu m, and the grain diameter ratio of the minimum grain diameter to the maximum grain diameter is more than or equal to 0.90. The small structure crystal grains can meet the requirements of stamping and bending processing while improving the strength, and simultaneously keep good plasticity, and the small structure crystal grains can also enhance the elastic property of the strip; the uniformity of the structure crystal grains ensures the stability of the hardness, the strength and the plasticity of a final product while controlling the fineness of the structure crystal grains, and avoids the problems that the bending surface is easy to hair and even cracks and the like during bending.

2) The tensile strength of the fine-grain reinforced brass strip is 550-620 MPa, the Vickers hardness is 170-190 HV, the elongation is more than or equal to 15%, the R/t of 90-degree bending is less than or equal to 0.5 at GW, less than or equal to 1.5 at BW, and the elastic modulus is more than or equal to 110GPa, so that the performance requirement of the copper strip for the connector is met.

Drawings

FIG. 1 is a metallographic photograph (magnified 500 times) of example 1 of the present invention.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.

Selecting 14 example alloys to prepare according to the preparation method of the invention, casting → hot rolling → face milling → rough rolling → intermediate annealing → thick shear → cleaning → finish rolling → bottom annealing → cleaning → finished product rolling → low temperature annealing → cleaning → straightening. The specific component ratio is shown in table 1, and the key process control is shown in table 2.

Comparative example brass C2680 process flow: batching → casting → hot rolling → face milling → rough rolling → intermediate annealing → thick shearing → acid washing → intermediate rolling → acid washing → finish rolling → bottom annealing → acid washing → finished product rolling → degreasing and water washing → straightening → shearing → packaging and warehousing.

The prepared strip samples of 14 example alloys and 1 comparative example alloy were respectively tested for mechanical properties, bending properties and structure grain diameter, and the specific test results are shown in table 3.

Tensile test at room temperature according to GB/T228.1-2010 Metal Material tensile test part 1: room temperature test method, a test was conducted on an electronic universal mechanical property tester using a 20mm wide tape head specimen with a drawing speed of 5 mm/min.

And (3) metallographic structure grain size test according to JIS H0501: the product finding method in 1986 stretched copper product crystal size test method tests the grain size in a 500-time metallographic microscope photograph. The sample had a width of 10mm and a length of 10 mm.

And (4) carrying out a texture grain uniformity test, selecting grains with the minimum diameter and the maximum diameter on a gold phase picture, and measuring the diameter size of the grains. The uniformity of the crystal grains is expressed by the ratio of the minimum crystal grain diameter to the maximum crystal grain diameter of the structure.

The bending performance test is carried out on a universal testing machine through a corresponding bending die according to GB/T232-2010 metal material bending test method, and the sample width is 10mm and the length is 50 mm.

The table 3 shows that the tensile strength of the fine-grain reinforced brass is 550-620 MPa, the Vickers hardness is 170-190 HV, the elongation is more than or equal to 15%, the 90-degree bend R/t is less than or equal to 0.5 at GW, and less than or equal to 1.5 at BW, so that the connector material meets the performance requirements of the connector material used in the industries of electricity, automobiles, communication and the like, the strength, hardness, bending and plasticity are superior to C2680 processed by adopting the traditional process, the structure grain size of the connector is controlled to be less than or equal to 10 mu m, and the grain diameter ratio of the minimum grain diameter to the maximum grain diameter is more than or equal to 0.85, so the fine-grain reinforced brass is more suitable for connector processing.

TABLE 1 ingredients of examples and comparative examples

Claims

1. The preparation method of the fine-grain reinforced brass strip for the connector is characterized in that the processing technological process of the fine-grain reinforced brass strip is as follows:

casting → hot rolling → face milling → rough rolling → intermediate annealing → thick shearing → cleaning → finish rolling → bottom annealing → cleaning → finished product rolling → low temperature annealing → cleaning → straightening; the casting adopts a semi-continuous casting and pulling casting flat ingot mode, the thickness of the ingot is 160-240 mm, and the width of the ingot is 400-630 mm; the hot rolling procedure adopts a rolling process with multiple passes and small processing rate of each pass, the total number of rolling passes is 9-15, and the processing rate of each pass is less than or equal to 32%; the rough rolling process adopts a large processing rate mode for rolling, and the processing rate is 85-92%;

the fine-grained reinforced brass strip comprises the following components in percentage by mass, Cu: 63-67 wt%, Sn: 0.01 to 0.3 wt%, and the balance of Zn and inevitable impurities; the grain diameter of the structure of the fine-grain reinforced brass strip is less than or equal to 10 mu m, wherein the grain diameter ratio of the minimum grain diameter to the maximum grain diameter is more than or equal to 0.85;

the tensile strength of the fine-grain reinforced brass strip is 550-620 MPa, the Vickers hardness is 170-190 HV, the elongation is more than or equal to 15%, the 90-degree bend R/t is less than or equal to 0.5 at GW and less than or equal to 1.5 at BW, wherein GW is a good direction, and BW is a bad direction.

2. The method of producing a fine grained reinforced brass strip for connectors as set forth in claim 1 wherein: and at least one rare earth element Y, Sc with the total weight of 0.001-0.3 wt%.

3. The method of producing a fine grained reinforced brass strip for connectors as set forth in claim 2 wherein: the weight percentage of Y + Sc is more than or equal to 0.05 percent and less than or equal to 0.15 percent, and the weight percentage of Sn: 0.25 wt% -0.3 wt%.

4. The method of producing a fine grained reinforced brass strip for connectors as set forth in claim 1 wherein: the intermediate annealing temperature is 470-490 ℃, the annealing time is 2-12 hours, and the grain size of the annealed structure is 5-15 μm.

5. The method of producing a fine grained reinforced brass strip for connectors as set forth in claim 1 wherein: the bottom annealing temperature is 400-430 ℃, the annealing time is 3-6 h, and the grain size of the annealed structure is 5-15 mu m.

6. The method of producing a fine grained reinforced brass strip for connectors as set forth in claim 1 wherein: the processing rate of rolling the finished product is 22-35%, and the grain size of the rolled structure of the finished product is less than or equal to 10 mu m; the finished product low-temperature annealing process comprises the following steps: the annealing temperature is 230-260 ℃, and the heat preservation time is 2-6 h.