JP2020158818A - Cu-Co-Si BASED COPPER ALLOY STRIP EXCELLENT IN BENDABILITY AND SMOOTH FLEXURE SKIN - Google Patents

Abstract

To provide a Cu-Co-Si based copper alloy strip capable of improving bendability and the rough surface (flexure skin) of a flexure portion.SOLUTION: The Cu-Co-Si based copper alloy strip excellent in bendability and flexure skin includes Co of 0.5-3.0 mass%, Si of 0.1-1.0 mass% and the remainder consisting of copper and inevitable impurities; and when setting an average grain size by a cutting method specified in JIS-H3130 to Gs (μm) and a plate thickness to t (μm), Gs/t is 0.30 or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to Cu—Co—Si based copper alloy strips suitable for materials such as connectors, terminals, relays, switches and the like.

In recent years, along with the miniaturization of electronic devices, the miniaturization of electrical and electronic components has progressed. The copper alloy used for these parts is required to have good strength and conductivity. In response to this demand, precipitation-strengthened copper alloys such as Corson alloys having high strength and conductivity have been used in place of conventional solid-melt reinforced copper alloys such as phosphor bronze and brass, and the demand for them is increasing.
Among Corson alloys, Cu-Co-Si-based copper alloy is an alloy-based alloy that has relatively high strength and high conductivity, and its strengthening mechanism is that Co-Si-based intermetallic compound particles are precipitated in the Cu matrix. By doing so, the strength and conductivity are improved.

In general, strength and bending workability are contradictory properties, and it is desired to improve bending workability while maintaining high strength even in Cu—Co—Si based copper alloys.
Here, in the terminal manufacturing process, poor contact contact is one of the main defects, and not only the terminal is broken due to insufficient bendability, but also the contact resistance is increased due to the rough surface of the terminal and the continuity is poor. It is mentioned as a cause. Therefore, it is desired that the bent portion not only has no cracks but also has a smooth surface as much as possible.

As a method for improving the bending workability of the Cu—Co—Si based copper alloy, there is a method for controlling the crystal orientation as described in Patent Documents 1 to 3. Patent Documents 1 and 2 describe that the area ratio of {001} <100> is 50% or more. Further, in Patent Document 3, the area ratio of {110} <112> is 20% or less, the area ratio of {121} <111> is 20% or less, and the area ratio of {001} <100> is 5 to 60%. It is stated that it should be done.

Further, as a method for improving the bending surface, Patent Document 4 states that the formation of a shear band on the surface layer is suppressed as compared with the central portion of the plate thickness, the number of precipitates on the surface layer of the material Ns, and the number of precipitates on the central portion of the plate thickness. It is described that the ratio Ns / Nc of Nc is 1.0 or less.

Japanese Unexamined Patent Publication No. 2006-283059 Japanese Unexamined Patent Publication No. 2006-152392 Japanese Unexamined Patent Publication No. 2011-017072 Japanese Unexamined Patent Publication No. 2012-207264

However, with the above technique, it has been difficult to achieve both bending workability and smoothness of the bent skin.
In view of these circumstances, the present invention has been made to solve the above problems, and provides Cu—Co—Si copper alloy strips having improved bending workability and rough skin (bending surface) of bent portions. With the goal.

The present inventors have focused on reducing the number of wrinkles on the bent skin as a measure for improving the rough skin (bent skin) on the bent portion.
Since wrinkles on the bent skin occur at the grain boundaries, it is conceivable to make the crystal grains as fine as possible in order to reduce the wrinkles. However, even if the crystal grains are made finer, fine wrinkles are generated at the grain boundaries at the micro level, and in addition, non-uniform crystal grains due to variations in the cooling rate in the plate thickness direction during copper strip production. Wrinkles may occur locally due to the arrangement and distribution.

Therefore, the present inventors have found that wrinkles hardly occur when the average crystal grain size is 1/3 or more of the plate thickness. By doing so, it is considered that the crystal grains on the surface of the material become close to a single crystal and the number of crystal grain boundaries is significantly smaller than that of the conventional copper strip, so that the starting point where wrinkles occur is reduced.
Further, it has been found that in this way, even a radius smaller than the minimum bending radius at which wrinkles occur in the conventional copper strip can be bent without wrinkles, which contributes to the improvement of bendability.

In order to achieve the above object, the Cu—Co—Si based copper alloy strip of the present invention contains 0.5 to 3.0% by mass of Co and 0.1 to 1.0% by mass of Si. The balance is composed of copper and unavoidable impurities. When the average crystal grain size by the cutting method specified in JIS-H3130 is Gs (μm) and the plate thickness is t (μm), Gs / t is 0.30 or more. A Cu—Co—Si copper alloy strip having excellent bending workability and bending surface.

Further, it is preferable to contain 0.005 to 2.5% by mass in total of one or more selected from the group of Sn, Zn, Mg, Fe, Ti, Zr, Cr, Al, P, Mn, Ni and Ag.

According to the present invention, a Cu—Co—Si based copper alloy strip having improved bending workability and rough skin (bending surface) of a bent portion can be obtained.

It is a figure explaining the method of measuring the number of W bending and bending wrinkles. It is a figure which shows the bending wrinkle.

Hereinafter, Cu—Co—Si based copper alloy strips according to the embodiment of the present invention will be described. In the present invention,% means mass% unless otherwise specified.

(composition)
[Co and Si]
The Cu—Co—Si based copper alloy strip according to the embodiment of the present invention contains 0.5 to 3.0% by mass of Co and 0.1 to 1.0% by mass of Si, and the balance is copper and Consists of unavoidable impurities.
Co and Si are precipitated as Co—Si-based intermetallic compounds by aging treatment. This compound improves the strength, and by precipitating, Co and Si dissolved in the Cu matrix are reduced, so that the conductivity is improved.
However, when the Co concentration is less than 0.5% or the Si concentration is less than 0.1%, the strength decreases. On the other hand, if the Co concentration exceeds 3.0% or the Si concentration exceeds 1.0%, the hot workability deteriorates.

[Additional elements]
The alloy further contains at least one selected from the group of Sn, Zn, Mg, Fe, Ti, Zr, Cr, Al, P, Mn, Ni and Ag in a total amount of 0.005 to 2.5% by mass. You may.
These elements contribute to increasing the strength of the alloy strips. Further, Zn is effective in improving the heat-resistant peeling property of the plating layer when the alloy strip is Sn-plated. Mg is effective in improving stress relaxation characteristics. Zr, Cr, and Mn are effective in improving hot workability.
If the total content of the elements is less than 0.005%, the above effects cannot be obtained, and if it exceeds 2.5%, the conductivity may decrease and the material may not be suitable as an electric / electronic component material.

[Gs / t]
When the average crystal grain size by the cutting method specified in JIS-H3130 is Gs (μm) and the plate thickness of the alloy strip is t (μm), Gs / t is 0.30 or more.
As described above, when the average crystal grain size Gs is 1/3 or more of the plate thickness t, the crystal grains on the surface of the material become close to a single crystal, and the number of crystal grain boundaries is significantly smaller than that of the conventional copper strip. As a result, the starting point where wrinkles occur is reduced. It is preferable that Gs / t is 0.50 or more.

It is preferable that Gs is 3 μm or more and the plate thickness is t (μm) or less. It is preferable that t (μm) is 9 to 1000 (μm).
If Gs is less than 3 μm, many cracks may occur from the grain boundaries when the strips are bent, and the number of wrinkles may increase.

The 0.2% proof stress of the alloy strip is preferably 500 to 950 MPa, more preferably 600 to 950 MPa in the rolling direction. The 0.2% proof stress is obtained by a tensile test according to JIS-Z2241. The conditions of the tensile test were a test piece width of 12.7 mm, room temperature (15 to 35 ° C.), a tensile speed of 5 mm / min, and a gauge length of 50 mm.
The conductivity (% IACS) of the copper alloy strip is preferably 50% IACS or higher, more preferably 60% IACS or higher. For the sample in the rolling parallel direction, the conductivity (% IACS) was calculated from the volume resistivity obtained by the four-terminal method using a double bridge device in accordance with JISH0505.

<Manufacturing method>
The Cu—Co—Si based copper alloy of the present invention can usually be produced by performing an ingot in the order of hot rolling, cold rolling, solution heat treatment, aging treatment, and final cold rolling. Strain removal annealing may be performed after the final cold rolling.
In order to control the average crystal grain size, it is effective to adjust the temperature and heating time of the solution. In the solution treatment, the added element is dissolved and a calorific value is given so that Gs / t becomes 0.30 or more. The solution temperature is not particularly specified, and it is important to add enough heat to recrystallize the ingot at a temperature below the melting point. You may refer to the state diagram.
Considering that the recrystallization temperature increases from 500 to 600 ° C when an additive element is added to copper (Colson alloy) and that the melting point of copper is around 1350 ° C, the higher the solution temperature, the higher the heating. Since the time is short, it is preferable that the solution treatment temperature is 900 to 1300 ° C. for 60 to 300 seconds.

The aging treatment can be carried out at 400 to 600 ° C. for 2 to 20 hours, and the final cold rolling can be carried out at a working degree of 5 to 40%, for example.
The strain-removing annealing can usually be carried out at 250 to 600 ° C. for 5 to 300 seconds in an inert atmosphere such as Ar. Cold rolling may be performed between the solution treatment and the aging treatment in order to further increase the strength. Further, after the solution heat treatment, the final cold rolling and the aging treatment may be performed in this order, and the order of these steps may be changed.

2.50 kg of electrolytic copper was dissolved in an alumina or magnesia crucible having an inner diameter of 110 mm and a depth of 230 mm in an argon atmosphere in a high-frequency melting furnace. Elements other than copper are added according to the composition shown in Table 1, and the molten metal temperature is adjusted to 1300 ° C. Then, the molten metal is cast into an ingot of 30 × 60 × 120 mm with a mold (material: cast iron), and a copper alloy is formed in the following steps. A strip was made.

(Step 1) After heating at 950 ° C. for 3 hours, hot rolling to a thickness of 10 mm was performed, and then water cooling was performed.
(Step 2) The oxide scale on the plate surface after hot rolling was ground and removed with a grinder.
(Step 3) Cold rolling was performed to a plate thickness of 0.235 mm at a rolling reduction of 70%.
(Step 4) As a solution treatment, the mixture was heated in the air at the temperature shown in Table 1 for 180 seconds and rapidly cooled in water.
(Step 5) As an aging treatment, an electric furnace was used and heated at 550 ° C. for 5 hours in an Ar atmosphere.
(Step 6) The final cold rolling was performed to a plate thickness of 0.20 mm.
(Step 7) For strain removing annealing, the mixture was heated at 400 ° C. for 10 seconds in an Ar atmosphere.

The following characteristics of the sample prepared in this manner were evaluated.
(1) Crystal structure For the strips obtained in step 7, the structure of the cross section parallel to the rolling direction and parallel to the plate thickness direction is etched (water-NH ₃ (40vol%) -H ₂ O ₂ (0.6vol%)). The crystal grain size was measured using an optical microscope by a cutting method based on JIS-H3130.

(2) 0.2% proof stress and conductivity 0.2% proof stress was measured as described above using a tensile tester.
The conductivity was measured as described above.
(3) Bendability As shown in FIG. 1, as an evaluation of bendability, 90 ° W bending was performed in a rolling parallel direction (Bad Way direction) with a bending radius of 0.2 mm in accordance with JIS-H3130. A cross section S parallel to the rolling direction L of the bent portion and parallel to the plate thickness direction was finished to a mirror surface by mechanical polishing and buffing, and observed with an optical microscope (magnification 50 times) in a field of view of 0.32 mm ² . The number of bending wrinkles was counted.
As shown in FIG. 2, the bending wrinkles appear as streaks bending from the rolling direction L.
When the number of bending wrinkles is 5 or less, the bending workability and the rough skin of the bent portion are improved.

The results obtained are shown in Table 1.

As is clear from Table 1, in the case of each example, Gs / t was 0.30 or more, and the rough skin of the bent portion was improved.
On the other hand, in the case of Comparative Example 1 in which both the Co and Si concentrations were less than the specified range, the 0.2% proof stress was reduced to less than 500 MPa. In the case of Comparative Example 2 in which both the Co and Si concentrations exceeded the specified range, cracks occurred during hot rolling.
In the case of Comparative Example 3 in which the total amount of the added elements exceeded the specified range, the conductivity was reduced to less than 50% IACS, and Gs / t was less than 0.30, resulting in deterioration of rough skin at the bent portion. When the amount of added elements exceeds the specified value, it is presumed that the precipitate has a pinning effect of suppressing the particle size.
In the case of Comparative Example 4 in which the temperature of the solution treatment was high, the material was deformed at a high temperature during solution formation, and evaluation was not possible.
In the case of Comparative Example 5 in which the temperature of the solution treatment was low, Gs / t was less than 0.30, and the rough skin of the bent portion deteriorated. It is considered that this is because the number of crystal grain boundaries increased compared with the thickness and many cracks from the grain boundaries occurred.

Claims (2)

Containing 0.5 to 3.0% by mass of Co and 0.1 to 1.0% by mass of Si, the balance is composed of copper and unavoidable impurities, and average crystals by the cutting method specified in JIS-H3130. A Cu—Co—Si copper alloy strip having excellent bending workability and bending surface, having Gs / t of 0.30 or more when the particle size is Gs (μm) and the plate thickness is t (μm). Further, claim 1 contains 0.005 to 2.5% by mass in total of one or more selected from the group of Sn, Zn, Mg, Fe, Ti, Zr, Cr, Al, P, Mn, Ni and Ag. The Cu—Co—Si based copper alloy strip described.