JP2009079283A - High-strength, high-conductivity two phase copper alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength, high-conductivity two phase copper alloy having excellent strength and bending workability. <P>SOLUTION: The high-strength, high-conductivity two phase copper alloy includes, by mass%, 4 to 10% Fe, 0.01 to 0.5% Mg which dissolves in an alloy, and the balance Cu with unavoidable impurities; and is formed of a Cu mother phase and a second phase. When the second phase is viewed from the cross-section orthogonal to the rolling direction, thicknesses of the second phase are 1 μm or less and distances between adjacent second phases are 1 μm or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-strength and highly conductive two-phase copper alloy that is excellent in strength and bending workability and can be suitably applied to, for example, a spring material for electronic equipment.

  As the density and miniaturization of connector products has progressed dramatically, connector materials must have sufficient contact pressure and a small bending radius, that is, both strength and bending workability must be achieved. Yes.

  In general, when a strengthening element is added to Cu to increase the strength, the electrical conductivity decreases, while on the other hand, increasing the Cu purity has a relationship of decreasing the strength to increase the electrical conductivity. Therefore, an alloy system (double phase alloy) was developed in which the second phase was crystallized in the Cu matrix. This alloy has a second phase dispersed in a fiber form by strong processing and has the same strength as phosphor bronze, but the parent phase is Cu, so the conductivity is 60% IACS (international annealed copper standard, annealed) A highly conductive material exceeding the ratio of electrical conductivity to standard annealed copper has been obtained. As this multiphase alloy system, Cu—Cr, Cu—Ag, and the like are known (see, for example, Patent Documents 1 to 3). A Cu—Fe alloy has also been reported (see Patent Document 4).

JP-A-9-249925 Japanese Patent Laid-Open No. 06-279894 Japanese Patent Laid-Open No. 10-53824 Japanese Patent Laid-Open No. 11-213761

However, in the case of a conventional multiphase copper alloy, the material strength is improved by the effect of the second phase, but the bending workability is not sufficient. In addition, the multiphase alloy is excellent in strength and workability in the working direction, that is, in the drawing direction of the second phase, so that there is no problem in strength when the multiphase alloy is used for the wire. On the other hand, when a multiphase alloy is used as a rolled material, sufficient bending workability is required in both the rolling direction and the direction perpendicular to the rolling in order to perform processing such as press punching.
However, a rolled material of a multiphase alloy has a problem that bending workability in the direction perpendicular to rolling is inferior to that in the rolling parallel direction. This is due to the relationship (anisotropy) between the stretching direction and strength of the second phase described above. In particular, when a multiphase alloy is strongly processed for the purpose of finely dispersing the second phase and improving the strength, the anisotropy of the material structure becomes remarkable and the bending workability decreases.
Therefore, the conventional multiphase alloy cannot achieve both strength and bending workability.

In addition, when using a Cu-Fe alloy as described in Patent Document 4, it is necessary to add Fe in excess of 10% by mass in order to obtain a strength as high as that of a general copper alloy. There is a problem that the melting temperature is much higher than that of a general copper alloy (Cu-15% Fe has a melting temperature of 1450 ° C or higher). In this case, since the alloy is cast by cooling the high-temperature molten metal, the cooling time becomes long and the Fe crystallized material obtained by casting becomes coarse, so that the characteristics of high strength and high conductivity cannot be obtained.
That is, it is said that the Cu—Fe-based multiphase alloy is difficult to melt and also does not provide sufficient characteristics, and is actually difficult to manufacture. Conventionally, it has been said that the strength of a general copper alloy cannot be obtained unless Fe is added in excess of 10%. However, when a large amount (about 15%) of Fe is added, the melting temperature becomes high, there are few suitable furnace materials, and there is a problem that the Fe crystallized material becomes coarse due to the long cooling time, Cu-Fe In fact, it is difficult to manufacture a base alloy. On the other hand, to reduce the melting temperature, it is effective to reduce the amount of Fe added to about 4-6%. However, in this case, the effect of improving the strength by the second phase is insufficient.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a Cu—Fe-based high-strength, high-conductivity, two-phase copper alloy excellent in strength and bending workability.

  As a result of various investigations, the present inventors have adopted a Cu-Fe-based two-phase alloy, and by dissolving Mg in the alloy, the Fe concentration is high even when the Fe addition amount is 10% or less (10 -30%) succeeded in improving the strength of the alloy. This is because the crystallized material becomes finer due to Mg and the interfacial area between phases becomes larger than that of conventional double-phase alloys, and Mg is mainly dissolved in the copper matrix and the Cu matrix is strengthened. Is stretched and refined to become high strength.

  In order to achieve the above object, the high-strength, high-conductivity, two-phase copper alloy of the present invention contains 4% to 10% Fe by mass, and 0.01 to 0.5% Mg is dissolved in the alloy. It consists of the remainder Cu and inevitable impurities, and consists of a Cu matrix and a second phase.

It is preferable that the thickness of the second phase is 1 μm or less when viewed from a cross section perpendicular to rolling.
When viewed from a cross section perpendicular to rolling, the interval between the adjacent second phases is preferably 1 μm or less.

  According to the present invention, a Cu—Fe-based high-strength and highly conductive two-phase copper alloy excellent in strength and bending workability can be obtained.

  Hereinafter, embodiments of the high-strength, high-conductivity two-phase copper alloy according to the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.

[Fe]
The copper alloy contains 4% to 10% Fe. When Fe is contained in an amount of 4% or more, it is crystallized as a second phase in the Cu matrix and constitutes a so-called “double phase alloy”. When the Fe content is less than 4%, Fe does not crystallize at all, and the effect of composite strengthening by the second phase is small.
In addition, in the literature reported as a Cu-Fe-based alloy, there are almost cases where Fe is added up to 10-30%, and the strength tends to increase in proportion to the Fe concentration. However, as the Fe concentration increases, the melting temperature increases and the crystallization phase becomes coarse, so even if the Fe concentration exceeds 10%, the strength is hardly improved and the effect is saturated.

Conventionally, it has been said that the strength of a general copper alloy cannot be obtained unless Fe is added in an amount of 10% or more. However, when a large amount (about 15%) of Fe is added, the melting temperature becomes high, there are few suitable furnace materials, and there is a problem that the Fe crystallized material becomes coarse due to the long cooling time, Cu-Fe In fact, it is difficult to manufacture a base alloy. On the other hand, to reduce the melting temperature, it is effective to reduce the amount of Fe added to about 4-6%. However, in this case, the effect of improving the strength by the second phase is insufficient.
Therefore, in the present invention, the strength and bending workability of the alloy were successfully improved by dissolving Mg in the alloy.

[Second phase]
The second phase is obtained by crystallizing these elements from a molten alloy containing Cu and other chemical components during casting, and a large amount of Fe is distributed to the second phase during the crystallization. Cu and Fe are elements that dissolve in each other, and the second phase that crystallizes in the Cu matrix contains Cu and Fe. According to the qualitative analysis by X-ray, the Fe concentration in the second phase is about 80%. It is considered to be more than%. However, it is not limited to this.
The second phase is crystallized, for example, in a needle shape in the Cu matrix, but the crystallization form is not limited to this. The second phase can be observed as a composition different from the parent phase by a BSE (backscattered electron) image of an SEM (scanning electron microscope) after polishing the cross section of the rolled structure after the final step. If the structure is difficult to observe, etching or electropolishing may be performed.

[Mg]
When 0.01 to 0.5% of Mg is added to the alloy, Mg mainly dissolves in the Cu matrix and refines the crystallization phase during melt casting. The refined crystallized phase is stretched by processing, and the interfacial area between the phases is increased to obtain high strength. At that time, the dissolved Mg has an effect of facilitating the stretching of the second phase. As seen from the phase diagram, Mg was hardly dissolved in the second phase, and when the alloy of the present invention was actually subjected to characteristic X-ray analysis using EPMA, the inventors found that Mg was below the detection limit. Have confirmed. Mg refines the Fe crystallized product (second phase). The additive concentration of Mg is 0.01 to 0.5%. If the additive concentration of Mg is less than 0.01%, the effect of refining the Fe second phase cannot be obtained, and if it exceeds 0.5%, Mg hardly dissolves in the Cu matrix and becomes an oxide (such as MgO). Crystallize. Note that if the Mg concentration exceeds 0.3%, coarse particles (oxides, noro) are generated, leading to deterioration of bending workability, and the particle size of the coarse particles is larger than the interval between the second phases. Since the second phase is divided and as a result, the extension of the second phase is suppressed, the strength decreases. Therefore, the Mg content is preferably 0.3% or less.

  Furthermore, Mg strengthens the copper alloy in solid solution and raises the recrystallization temperature of the copper alloy, so that the heat resistance (semi-softening temperature) is improved.

  As described above, by adding Mg, high strength can be obtained even when the Fe concentration of the Cu—Fe alloy is reduced to 10% or less. In particular, in the range of 4 to 7% Fe concentration, the strength required as a spring material, strength of 700MPa or more can be obtained with 0.2% proof stress, and high conductivity of 40% IACS or more can be obtained.

The method for measuring the content ratio of the solid solution element in the alloy can be obtained, for example, by analyzing the surface or cross section of the obtained material by Auger Electron Spectroscopy (AES) and performing element quantification. . In this case, a calibration curve may be created in advance for the pure substance of each element, and quantification may be performed.
Further, quantitative analysis of an alloy can be performed using a wavelength dispersive spectroscopy (WDS) EPMA.
In addition, even in the same specimen, the content ratio of precipitates varies. Therefore, for example, the content ratio of the solid solution element can be measured for 50 points in one alloy sample, and the maximum value can be set as the content ratio of the solid solution element.

In the present invention, Fe added to the alloy forms a two-phase alloy with Cu. Usually, heat treatment (aging treatment) for precipitating Fe into the Cu matrix may not be required, but unintentional precipitates precipitate during cooling in high-temperature processes such as melt casting and hot rolling without aging treatment. Sometimes. However, these precipitates are few and do not affect the properties. When Fe crystallizes as the second phase, Fe is dissolved in the Cu matrix at a predetermined concentration. In this case, according to the phase diagram, the solid solubility limit of Fe dissolved in Cu is about 3.8% in an equilibrium state at 1094 ° C. However, the amount of Fe crystallized and precipitated varies depending on the cooling rate during melt casting. According to the study by the present inventors, it has been confirmed that a two-phase alloy is formed at an Fe concentration of substantially 4% or more.
Note that, as described above, in the present invention, sufficient strength and conductivity can be obtained by the refinement effect by Mg.

The content of inevitable impurities in the copper alloy is preferably the same as oxygen-free copper specified in JIS. For example, it can be made equivalent to the content of impurities in oxygen-free copper C1011 standardized to JIS H2123.
Examples of these impurities include Gd, Y, Yb, Nd, In, Pd, and Te.

  By the way, the multiphase alloy is an alloy that is strengthened by using the composite law or increasing the area of the heterogeneous interface, and the effect by increasing the area of the heterogeneous interface is great. For this reason, i) the more the second phase is dispersed in the alloy (the more the same volume fraction, the more finely dispersed), ii) the easier the second phase is stretched, and iii) the greater the degree of work. Increased strength. For these reasons, higher strength can be obtained by controlling the shape and size of the second phase.

The above item i) can be realized by adding Mg to the alloy to refine the crystallized product during melting and casting. The inventors have observed that the dendrite arm space during melt casting is 1 μm or less. As for ii), Mg dissolves in the copper matrix phase, so that the second phase is easily stretched and the Fe phase is refined.
With regard to iii), the degree of work should be increased as in the case of conventional multiphase alloys, and sufficient strength can be obtained with the degree of work normally used for multiphase alloys. For example, if the processing degree is 80% or more, the strength is increased to about 700 MPa with 0.2% proof stress. However, in the present invention, high strength can be obtained even at a low degree of processing due to the refinement effect of the crystallized material by Mg.

  Next, the form of the second phase will be described. FIG. 1 schematically shows the rolled material structure of the alloy of the present invention. In this figure, in the rolled material structure, the second phase 4 is dispersed in the matrix of the Cu matrix 2. Then, “the width direction of the plate is defined as“ a perpendicular direction T of rolling ”and the longitudinal direction of the plate is defined as“ the parallel direction L of rolling ”. In the present invention, the second phase preferably has a length in the rolling parallel direction of 10 times or more of the thickness t, and shows, for example, a ribbon shape (tongue piece shape).

[Thickness of the second phase]
In FIG. 1, when viewed from a cross section perpendicular to rolling, the thickness of the second phase (corresponding to the second phase length in the rolling direction) is t1, and the interval between adjacent second phases (distance in the rolling direction) is d. The rolling perpendicular section refers to a section when the rolled material is cut along a plane perpendicular to the rolling surface along the rolling perpendicular direction T. The rolling parallel direction may be determined, for example, as the rolling parallel direction of the rolls formed on the rolling surface.
The strength increases as the thickness t1 of the second phase decreases. Moreover, d can be reduced by increasing the rolling degree. However, in the present invention, it is not necessary to excessively increase the workability due to the refinement effect of the crystallized product by Mg, but a greater effect can be obtained by increasing the workability.
In the case of the alloy of the present invention, by setting t1 to 1 μm or less, higher strength can be obtained, and t1 is further preferably set to 0.3 μm or less.

  The reason why the strength is improved by reducing t1 will be further described. A multiphase alloy is a strengthening mechanism using a composite law. In general, the strength (σ: stress) of a material depends on the volume fractions of the first and second phases (V1 and V2 respectively). (Σ = V1σ1 + V2σ2), rather than the volume fraction of the second phase, the distance between the dispersed second phases contributes more to the strength. That is, when the interval between the second phases is narrowed by processing, that is, the area of the heterophase interface between the Cu matrix and the second phase is increased, that is, the thickness of the Cu matrix is thinned, the highest strength is obtained.

  And in order to narrow the space | interval of 2nd phases, it is necessary for each 2nd phase to become fine and the thickness to also become small. That is, in order to strengthen the multiphase alloy, it is important to make the initial crystallized product of the second phase fine, and further deform the second phase by subsequent processing to reduce the thickness so that they are close to each other. .

[Interval between adjacent second phases]
Further, as described above, when viewed from the cross section perpendicular to the rolling direction, the smaller the distance d between the adjacent second phases, the higher the strength is obtained. Therefore, d is preferably 1 μm or less. For the same reason that the thickness t1 decreases, the strength depends on the interfacial area. That is, when a line is drawn perpendicularly to the stacking direction of the second phase on the structure photograph (the direction of rolling reduction), the number of interfaces between the parent phase and the second phase (ribbon-like structure) passing through this line Strength depends. And the intensity | strength which only the 2nd phase is sheared when processing shows the intensity | strength of this material, and it is thought that intensity | strength becomes high, so that there are many said interfaces.
It is more preferable that d is 0.2 to 0.65 μm or less.

  The values of t1 and d can be controlled by the amount of Mg added.

  As described above, a copper alloy having a 0.2% proof stress of 700 MPa or more can be obtained by setting the distance d between the second phases to 1 μm or less and precipitating fine precipitates in the mother phase.

[Manufacturing]
An ingot is prepared by melting a composition in which electrolytic copper or oxygen-free copper is used as a main raw material and adding the above chemical components and the like in a melting furnace. A rolled material is obtained by sequentially performing, for example, homogenization annealing, hot rolling, cold rolling, annealing, cold rolling, and annealing (distortion annealing) on the ingot. Cold rolling is preferably performed, for example, at a total workability of 95% or more. However, the manufacturing method is not limited to the above.

In addition, this invention is not limited to the said embodiment.
The copper alloy of the present invention can be in various forms such as spring materials (strips) and foils. For example, when the copper alloy of the present invention is used for the spring material, it can be applied to electronic devices such as connectors. The connector can be applied to all known forms and structures, but usually consists of a male (jack, plug) and a female (socket, receptacle). For example, the terminals may be arranged like a spring, with a number of skewered pins arranged side by side and appropriately bent so that the terminals come into electrical contact with each other when fitted to other connectors. And the terminal of a connector is normally comprised with the said copper alloy for electronic devices.
As described above, the copper alloy of the present invention is effective as a spring material for electric / electronic devices such as terminals, connectors, switches, and relays.

  EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these.

1. Preparation of sample Ingot was cast by adding elements of the composition shown in Tables 1 and 2 to electrolytic copper, and melted in vacuum, and this was homogenized and annealed at a temperature of 800 ° C for 3 hours. After the solution treatment, hot rolling was performed. Further, chamfering was performed, cold rolling was performed, and finish cold rolling was performed to prepare a spring material sample having a plate thickness of 0.080 mm. The total degree of cold rolling was 99.7%. In addition, strain relief annealing was finally performed as necessary (at 500 ° C. for 15 seconds). Bending workability is improved by performing strain relief annealing.
The form of the second phase (thickness t1, d) was determined from the BSE image of the cross section SEM of the sample. The grain size of the precipitate was determined by cutting the alloy strip before the final cold rolling in a direction perpendicular to the thickness parallel to the rolling direction, and observing the precipitate in the cross section with 10 fields of view using a scanning electron microscope or a transmission electron microscope.
The measurement method of the content ratio of the solid solution element in the alloy was obtained by analyzing the cross section of the sample with a wavelength dispersive (WDS) EPMA (FE-EPMA manufactured by JEOL Ltd.). In this case, a calibration curve was prepared in advance for the pure substance of each element, and quantification was performed.

<Sample evaluation>
(1) Strength evaluation
According to JIS-Z2241, the tensile strength of the sample was measured to obtain 0.2% yield strength (YS). The sample was produced according to JIS.
(2) Evaluation of conductivity The conductivity of the sample was determined by the four probe method. The unit% IACS (international annealed copper standard) is the ratio of electrical conductivity to annealed standard soft copper. However, the conductivity decreases when the alloy contains the above additive elements (Sn, etc.). Therefore, if the additive element is not included, the conductivity is 50% IACS or more. If the additive element is contained, the conductivity is 45% IACS or more. Was evaluated as being good.

(3) Evaluation of bending workability A W bending test was performed according to the Japan Copper and Brass Association Technical Standard (JBMA T307). The minimum bending radius (MBR) was determined for a 10 mm wide sample (t: sample thickness) extending in the direction perpendicular to the rolling. The MBR / t of the reference example is about 1, and the smaller the MBR / t value, the better the bending workability.

  The obtained results are shown in Tables 1 and 2.

As is apparent from Tables 1 and 2, in each example, the 0.2% proof stress was improved to 700 MPa or more, and the conductivity was 40% IACS.
In particular, in Examples 1, 9, 10, 14, and 15 in which strain relief annealing was finally performed, bending workability in the direction perpendicular to the rolling was remarkably improved.

On the other hand, in the case of Comparative Examples 1, 3, and 4 in which the Fe content was less than 4%, a two-phase alloy was not obtained and the strength was lowered.
In the case of Comparative Example 2 not containing Mg, the second phase was coarsened (thickness of 3.4 μm or more), and the strength decreased.
In the case of Comparative Examples 5 and 7 in which the Mg content exceeded 0.5%, a large amount of oxide was generated, and coarse grains exceeding 100 nm were precipitated, resulting in a decrease in bending workability.
In the case of Comparative Example 6 that did not contain Mg, the strength decreased.

It is the figure which showed typically the rolling material structure | tissue of the alloy of this invention.

Explanation of symbols

2 Cu parent phase 4 Second phase

Claims (3)

  High-strength, high-conductivity consisting of Cu and inevitable impurities, and Cu parent phase and second phase. Two-phase copper alloy.   2. The high-strength, high-conductivity, two-phase copper alloy according to claim 1, wherein the second phase has a thickness of 1 μm or less when viewed from a cross-section perpendicular to rolling.   3. The high-strength, high-conductivity, two-phase copper alloy according to claim 1, wherein when viewed from a cross-section perpendicular to rolling, an interval between the adjacent second phases is 1 μm or less.