JP2012207264A - Cu-Co-Si-BASED ALLOY HAVING EXCELLENT BENDING WORKABILITY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength copper alloy having excellent external appearance after bending.SOLUTION: A Cu-Co-Si-based alloy strip having high strength and excellent external appearance after bending, being a Cu-Co-Si-based alloy composed of, by mass%, 0.2-3.5% Co and 0.02-1.0% Si, and the balance Cu with inevitable impurities, can contain, as a third element group, one or more kinds selected from a group composed of Mn, Fe, Mg, Ni, Cr, V, Nb, Mo, Zr, B, Zn, Sn, Ag, Be, Mischmetal and P in the range of ≤1.0 mass% in total, and is characterized in that the ratio of the number of lines in a shear zone on the surface layer to that in the shear zone at the center part of the sheet thickness is ≤1.0, and crystal grain size is ≤20 μm, and the number of precipitated grains having 1-10 μm grain size on the surface layer is ≤3.0×10pieces/mm. In the Cu-Co-Si-based alloy strip, preferably, the number of lines in the shear zone on the surface layer is ≤330 pieces/10,000 μmand the ratio of the number of the precipitated grains having 1-10 μm grain size on the surface to that at the center part of the sheet thickness is ≤1, and the Cu-Co-Si-based alloy is subjected to a solution heat treatment where the solution heat treatment temperatue is controlled within the solid solubility limit temperature +25°C.

Description

  The present invention relates to a high-strength copper alloy used for electronic materials such as lead frames and connectors, and terminals for in-vehicle connectors. Specifically, the present invention relates to a high-strength copper alloy that exhibits excellent bending workability and bending portion appearance that does not cause wrinkles or cracks in the bending portion appearance after bending.

  In recent years, electronic devices such as mobile phones, digital cameras, and video cameras, and in-vehicle connectors have been mounted with high density, and the components have become extremely light and thin. The material used is also prone to thinning, and a material with higher strength is required. In addition, the shape of parts is becoming more complex, and there are an increasing number of cases where stricter bending is applied than before, and even if the strength is increased, the bendability is equivalent to the conventional material, or not only box bending and 180-degree contact bending, Further superior bending workability has been demanded, such as bending after crushing to reduce the plate thickness and no cracks.

A Corson alloy (Cu—Co—Si-based alloy) generally deteriorates in bendability when the strength of the alloy is increased, and an alloy with good bendability has low strength. Accordingly, various improvements have been made to achieve both strength and bendability. The Corson alloy is an age-hardening type copper alloy. When a supersaturated solid solution of Co and Si, which are solute atoms, is formed by solution treatment, and heat treatment is performed at a low temperature for a relatively long time from this state, precipitates with high strength are precipitated due to the aging precipitation phenomenon, and the strength is improved. To do. At this time, the problem is that the strength and the bending workability are contradictory. That is, if the strength is improved, the bending workability is impaired, and conversely, if the bending workability is emphasized, a desired strength cannot be obtained. In general, the higher the rolling reduction in cold rolling, the more dislocations are introduced and the dislocation density is higher, so that the number of nucleation sites contributing to precipitation increases and the strength after aging treatment can be increased. However, if the rolling reduction is too high, the bending workability deteriorates. For this reason, it has been an object to achieve both strength and bending workability.
Patent Document 1 describes a Cu—Co—Si-based alloy developed for the purpose of realizing high strength, high conductivity, and high bending workability, and pays attention to crystal grain size and aspect ratio. . Patent Document 2 describes a Cu—Co—Si-based alloy that focuses on the size and total amount of inclusions precipitated in the copper alloy as well as the composition of the copper alloy. Patent Document 3 describes a Cu—Co—Si based alloy developed for the purpose of realizing high strength, high conductivity, high bending workability, and fatigue resistance, and includes a precipitation-free zone ( We pay attention to the width of (PFZ) and the particle diameter on the grain boundary. Patent Document 4 describes a Cu—Co—Si alloy developed for the purpose of realizing high strength, high conductivity, and high bending workability, and pays attention to the crystal grain size and the distribution of crystal grain size. ing. Patent Document 5 describes a Cu—Co—Si based alloy excellent in strength, electrical conductivity, and bending workability. In the paragraph “0018” of the same document, attention is paid to a temperature increase rate and a temperature decrease rate during heat treatment. Yes.

JP-A-9-20943 JP 2008-55977 A JP 2010-215976 A JP 2010-59543 A WO2009-116649

The appearance of the bent portion of the Corson alloy, particularly the appearance of the bending (particularly BW) in which the bending axis is orthogonal to the rolling direction, is inferior to that of phosphor bronze and has a feature that the skin is rough. If a crack occurs in the terminal, the electrical conductivity and spring properties required for the terminal are lost, and the reliability of the product is impaired. Therefore, the appearance inspection of the bent part of the product is usually performed. However, for example, it is difficult to check the appearance of the bending part of the most advanced ultra-small terminal with the naked eye. In the inspection process for checking the condition after the bending press, it is visually observed using a magnifying glass or by a CCD camera. We have to rely on jigs and machines, such as checking with surface inspection equipment. In this inspection, although it is not actually cracked, when the appearance of the bent portion is so rough that it is difficult to distinguish it from cracks, it takes time to check the inspection and the inspection efficiency is lowered. Therefore, a Corson alloy used for a material for a microelectronic device is not limited as long as cracks do not occur in a bent portion, and a material with a small rough surface of the bent portion is required.
The object of the present invention is to improve not only the excellent bendability of a Corson copper alloy, specifically cracking, but also roughening of the bent portion, which has not been noticed in the past, after bending of BW (bad way). .

As a result of studying for the purpose of improving the BW bendability and the rough surface of the bent portion in the Cu-Co-Si-based alloy, the present inventors have found a portion that becomes a starting point of non-uniform elongation such as foreign matter and defects from near the surface. Eliminating and suppressing the formation of a shear band on the surface layer (from the material surface to 1/6 depth of the plate thickness) compared to the plate thickness center portion (portion other than the following surface layer), the material's original tensile strength, 0.2 The present invention was completed by discovering that the rough surface of the bent portion of BW can be improved while maintaining the mechanical properties such as% proof stress and spring limit value.
The present invention has the following configuration.
(1) A Cu—Co—Si alloy strip containing 0.2 to 3.5% by mass of Co and 0.02 to 1.0% by mass of Si, the balance being copper and inevitable impurities, The total amount of one or more selected from the group consisting of Mn, Fe, Mg, Ni, Cr, V, Nb, Mo, Zr, B, Zn, Sn, Ag, Be, Misch metal and P as the three element group 1.0 mass% or less, and the number Ss of shear band lines from the material surface to 1/6 depth of the plate thickness (hereinafter referred to as “surface layer”), and other than the material surface layer The ratio Ss / Sc of the number Sc of the lines of the shear band of the portion (hereinafter referred to as “plate thickness central portion”) is 1.0 or less, the crystal grain size is 20 μm or less, and the precipitation is 1 to 10 μm in the material surface layer. number is 3.0 × 10 ⁴ cells / mm ² or less of a product, excellent in appearance after and high strength bending u-Co-Si-based alloy strips.
(2) The Cu—Co—Si-based alloy strip according to (1), wherein the number of shear band lines in the material surface layer is 330 / 10,000 μm ² or less.
(3) The ratio Ns / Nc of the number Ns of precipitates having a particle diameter of 1 to 10 μm in the material surface layer and the number Nc of precipitates having a particle diameter of 1 to 10 μm in the center of the plate thickness is 1.0 or less (1) Or (2) Cu—Co—Si alloy strip.
(4) The Cu—Co—Si-based alloy strip according to any one of (1) to (3), which is manufactured by a solution treatment with a solution treatment temperature within a solid solution limit temperature of + 25 ° C.

  INDUSTRIAL APPLICABILITY The present invention can provide a high-strength copper alloy that is suitable as a copper alloy for electronic materials such as terminals and connectors, and exhibits excellent bending workability even in the BW direction and a bent portion appearance without wrinkles.

It is a SEM photograph (1,000 times) which image | photographed the surface layer part of the sample surface before a bending deformation of the alloy strip manufactured in Example 1 and orthogonal to a plate | board thickness direction at right angles. It is a SEM photograph (1,000 times) which image | photographed the plate | board thickness center part of the sample surface before a bending deformation of the alloy strip manufactured in Example 1 and orthogonal to a plate | board thickness direction. It is a SEM photograph (1,000 times) which image | photographed the plate | board thickness center part of the sample surface before a bending deformation of the alloy strip manufactured in Example 9, and parallel to a rolling direction and perpendicular to a plate | board thickness direction.

-Composition of Cu-Co-Si alloy-
<Co content>
If the Co content is less than 0.2% by mass, a sufficient strengthening mechanism cannot be obtained due to the original precipitation strengthening of the Cu—Co—Si based alloy. If the Co content exceeds 3.5% by mass, Second phase particles containing coarse Co and additive elements tend to precipitate, and the strength and bending workability tend to deteriorate. Therefore, the content of Co in the copper alloy according to the embodiment of the present invention is 0.2 to 3.5 mass%, preferably 1.5 to 3.5 mass%, more preferably 1.5. It is -3.0 mass%. Thus, by optimizing the Co content, it is possible to achieve both strength and bending workability suitable for electronic components.

<Si content>
Si reacts with Co without adversely affecting the electrical conductivity to generate second phase particles and contributes to the strengthening mechanism. From the knowledge of the test by the inventor, the content of Si is theoretically optimal in terms of the relationship between conductivity and strength in order for Co: Si = 4.2: 1 to fully exert the strengthening mechanism by precipitation strengthening. Was found. Si is difficult to add at the time of dissolution, and even if it is a little larger than Co, there is almost no effect on the strength. Therefore, if the conductivity is within the target range, it is actually appropriate that the upper limit of Si is slightly higher than the theoretical value. Therefore, the content of Si in the copper alloy according to the embodiment of the present invention is 0.02 to 1.0, preferably 0.07 to 0.85% by mass, and more preferably 0.36 to 0.83. % By mass, most preferably 0.36 to 0.71% by mass.

<Other additive elements>
When other additive elements are added to the Cu—Co—Si based alloy, there is an effect that the crystal grains are easily refined and the strength is improved even if solution treatment is performed at a high temperature at which Co is sufficiently dissolved.

  As other additive elements, Mn, Fe, Mg, Ni, Cr, V, Nb, Mo, Zr, B, Zn, Sn, Ag, Be, misch metal and P are added alone, or two or more kinds thereof are added. May be added in combination.

  When these elements contain a total of 0.05% by mass or more, the effect appears, but when the total exceeds 1.0% by mass, the solid solubility limit of Co is narrowed to precipitate coarse second-phase particles. It becomes easy and the strength is slightly improved, but the bending workability is deteriorated. At the same time, the coarse second-phase particles promote roughening of the bent portion and promote die wear during press working. Therefore, one or more selected from the group consisting of Mn, Fe, Mg, Ni, Cr, V, Nb, Mo, Zr, B, Zn, Sn, Ag, Be, Misch metal, and P as other element groups. The total content may be 0 to 1.0% by mass, preferably 0.05 to 1.0% by mass, and more preferably 0.05 to 0.5% by mass.

-Causes of bending wrinkles-
In general, when bending a material, the most distortion is applied to the outermost periphery of the bent portion. In the bending process, the surface of the material extends uniformly up to a specific strain value, but the elongation decreases locally with the specific strain value as a boundary, and bending wrinkles occur. As bending progresses, cracks start from this wrinkle. The strain limit value at which the phenomenon of locally small elongation (hereinafter referred to as non-uniform elongation) occurs largely depending on the mechanical properties of the material, but is the starting point of non-uniform elongation such as foreign matter and defects in the material. Is present, the non-uniform elongation tends to occur below the strain limit value corresponding to the original mechanical characteristics of the material, and the wrinkle of the bent portion tends to increase. Therefore, bending wrinkles can be reduced by reducing the starting points at which these non-uniform elongation occurs.
In addition, if there is a starting point where uneven elongation occurs inside the material, it is not as much as the starting point existing on the surface of the material, but this affects the surface of the material, thereby reducing the starting point where uneven stretching occurs inside the material. It is desirable.
Factors that serve as starting points for non-uniform elongation include roughness of the material surface and precipitates present on the surface layer. The surface roughness of the material can be reduced by conventional means such as surface polishing of the surface of the final rolling roll, but it alone cannot cope with the bending process required for the latest ultra-small terminals.

-Shear band in metal structure-
In general, copper alloys can be strengthened by adjusting the metal crystal grain size (crystal refinement), the amount of precipitates, grain size, distribution (precipitation strengthening), etc., but can also be strengthened by adjusting the workability of the final cold rolling. Yes (process enhancement). In rolling, a load applied by a rolling roll is applied from the vertical direction to a material in which tension is applied in the longitudinal direction, and the material is deformed (rolled). During this rolling, shear deformation locally concentrates, the crystal grain structure is deformed and broken, and a band-like structure called a shear band is formed regardless of the crystal orientation.
In this embodiment, the “shear band” is a streak-like or linear recess having a depth of 0.01 to 1 μm that is observed when a surface of a sample obtained by rolling a metal material or a rolled parallel section is etched after polishing. It means a portion continuously present inside the crystal grains (see the shear band 12 in FIG. 3).

  As a method for controlling the development of the shear band, it can be performed by changing the rolling degree, changing the viscosity of the rolling oil during cold rolling, changing the rolling load, and the like. Specifically, the frequency of occurrence of shear bands by increasing the degree of rolling work in cold rolling after aging treatment, increasing the viscosity of the rolling oil, and increasing the rolling load, etc. Can be raised.

The shear band is a structure in which deformation is locally concentrated, that is, a portion where dislocation density increases due to increased strain, and is less likely to be deformed than the surrounding structure. For this reason, in a material having a shear band, non-uniform elongation occurs starting from the shear band when bending is performed, and wrinkles and cracks occur when the non-uniform elongation reaches the surface. However, if the rolling process is not performed until the shear band is formed, the work cannot be strengthened and the required alloy strength cannot be achieved. Therefore, the product after the final cold rolling must have the shear band inherent. Yes.
The present inventors paid attention to the distribution of the shear band, and found that the smaller the shear band near the surface of the material, the less likely the non-uniform elongation to reach the surface is, so that cracks and wrinkles are reduced. That is, when the strain embodied as a shear band is less in the surface layer than the central portion of the plate thickness, cracks and wrinkles are unlikely to occur during bending. Specifically, the ratio Ss / Sc of the number Ss of shear band lines observed on the material surface layer after the final rolling and the number Sc of shear band lines at the center of the plate thickness (the portion other than the surface layer) is 1. If it is 0 or less, preferably 0.95 or less, the occurrence of bending wrinkles is reduced even during severe bending.
Further, if the number of shear band lines on the material surface layer after the final rolling is preferably 330 / 10,000 μm ² or less, more preferably 280 / 10,000 μm ² or less, the occurrence of bending wrinkles is reduced. .
In addition, if the total degree of work in the final rolling is lowered and the work strengthening is not performed sufficiently, and there are few shear bands in the surface layer of the material or the center of the plate thickness, it is possible to obtain a high strength alloy strip of the present invention. Can not. Therefore, the number Ss of shear band lines on the surface layer of the alloy strip of the present invention exceeds zero.

  In this embodiment, the presence or absence of a shear band is revealed by etching after mechanical polishing on the rolled parallel cross section of the Cu—Co—Si based alloy, and using a scanning electron microscope (SEM), Count those having a depth of 0.01 μm or more from the surface of the crystal grains (rolled surface). The reason why the lower limit of the depth is set to 0.01 μm or more is that it is difficult to count too fine shear bands.

-Particle size and number of precipitates-
Shear bands tend to occur where strains accumulate. Strain tends to accumulate locally in the vicinity of the precipitate particles in a portion where the structure becomes discontinuous, that is, in a Corson alloy. Therefore, if the density of the precipitate particles is low, the localization of strain is suppressed, and a shear band is hardly generated. Here, the “precipitate” of the present invention is a crystallized product generated during the solidification process during casting, oxides or sulfides generated by a reaction in the molten metal during melting, cooling process after ingot solidification, hot It is a general term for metal compounds such as precipitates that precipitate in the Cu matrix base material during rolling and after the solution treatment and cooling process and aging treatment. Therefore, some of the precipitate particles are made of Co and Si, and some of the particles are obtained by further adding an additive alloy element to the particles, and some of the precipitate particles do not contain any one of Co and Si, or do not contain both.
The particle size and number of the precipitates can be observed at a magnification of about 200 to 2,000 times using a FE-SEM (electrolytic emission scanning electron microscope) after polishing the rolled parallel section and etching. Components were measured using particle analysis software and EDS (energy dispersive X-ray analysis), and particles composed of components different from the base material components were determined as precipitates. The particle size of each precipitate was measured and counted. Here, the diameter of the circle circumscribing the precipitate is defined as the particle size of the precipitate.

Although the present invention is not limited by theory, in the surface layer from the surface of the material after aging treatment to 1/6 plate thickness depth, the number of precipitates having a particle diameter of 1 to 10 μm is 3.0 × 10 ⁴ / if mm ² or less, due to the low density of the precipitates as the starting point of shear bands occurrence, the occurrence of shear bands in the surface layer portion is reduced, wrinkles can also be reduced which occurs bend. On the other hand, if it exceeds 3.0 × 10 ⁴ pieces / mm ² , the generation of shear bands in the surface layer increases and wrinkles generated in the bent portion increase. The number of precipitates having a particle size of 1 to 10 μm in the surface layer is preferably 1 × 10 ⁻⁶ pieces / mm ² or more, and if it is less than that, there is little precipitation as a whole material, and the effect of increasing the strength cannot be obtained. The conductivity tends to be low.
The ratio Ns / Nc of the number Ns of precipitate particles having a particle diameter of 1 to 10 μm in the surface layer and the number Nc of precipitate particles having a particle diameter of 1 to 10 μm in the center of the plate thickness is 1.0 or less, preferably 0.8. If it is 95 or less, the generation of wrinkles is reduced even after intense bending. This is because the number of precipitate particles in the surface layer is smaller than that in the central portion of the plate thickness, so that the surface layer is not distorted, the shear band is reduced, and cracks and wrinkles are less likely to occur during bending.

In the Corson alloy, the effect of improving the strength is observed due to the uniform presence of fine precipitates. However, the precipitate having a particle size of 1 μm or more causes a decrease in the distribution density of the precipitates and the interfacial area of the precipitates, thereby improving the strength. From the point of view, it was considered unfavorable. However, in the present invention, attention is paid to precipitates having a particle diameter of 1 to 10 μm, which are likely to cause the formation of shear bands by localizing strain due to rolling, and the distribution is adjusted to achieve the desired characteristics. Yes.
Precipitate particles having a particle size of less than 1 μm contribute to precipitation strengthening but do not contribute much to the localization of strain, and have little influence on the generation of shear bands, and therefore do not affect the wrinkles of the bent portion. Furthermore, the precipitate particles having a particle size of less than 0.5 μm are too small to determine whether the component is a precipitate. On the other hand, since a precipitate having a particle size exceeding 10 μm in the entire surface layer and the center of the plate thickness causes cracking, the number is preferably 1 piece / mm ² or less, more preferably 0 piece / mm ² .

-Crystal grain size-
The crystal grain size of the Cu—Co—Si based alloy strip of the present invention is 20 μm or less, and more preferably 15 μm or less. When the particle diameter is 20 μm or more, the bendability deteriorates.

-Manufacturing method of alloy strip of the present invention-
Next, the manufacturing method for obtaining the alloy of this invention is demonstrated.
Normally, the production of an ingot of Corson alloy is carried out by a semi-continuous casting method. It is preferable to control the temperature, time, and cooling rate of the casting conditions so that coarse Co—Si based precipitates are not generated during the solidification process during casting. Co-Si-based precipitates of a certain size or less can be dissolved in the Cu matrix by strengthening the heating of hot rolling performed after casting, but to dissolve all coarse precipitates in the matrix. If the heating temperature is increased, the furnace refractory life of the heating furnace will be shortened, and if the heating time is lengthened, the lead time will become longer and the productivity will be extremely deteriorated.

  After heating at a temperature of 800 ° C. or higher for 1 hour or longer and performing hot rolling with an end temperature of 650 ° C. or higher, precipitates of a certain size or smaller that are precipitated and crystallized by casting are dissolved in the Cu matrix. . In that case, when heated at a high temperature, the precipitate precipitated and crystallized during casting can be dissolved in the Cu matrix, but when the heating temperature before hot rolling is 1,000 ° C. or more, a large amount of scale is generated, Since problems such as generation of cracks during hot rolling occur, the heating temperature before hot rolling is preferably 900 ° C. or higher and lower than 1,000 ° C. Specifically, after the ingot manufacturing process, it is preferable to perform hot rolling after heating to 900 to 1,000 ° C. and performing homogenization annealing for 3 to 24 hours.

  Corson alloy is a heat treatment at a temperature lower than the solution treatment temperature, and a solution treatment in which a Co-Si based precipitate precipitated by casting or hot rolling is heated in the Cu matrix after the hot rolling process, and at a temperature lower than the solution treatment temperature. In many cases, it is produced by a combination of aging treatment for precipitating Co and Si dissolved in the solution treatment and rolling for work hardening before and after the aging treatment. Generally, it is manufactured in the steps of solution treatment, rolling, aging treatment, rolling, and strain relief annealing. The shear band disappears by aging heat treatment and is newly generated by rolling after aging. Therefore, the rolling conditions after aging treatment are important for shear band formation. On the other hand, the strain relief annealing heat treatment has little influence on the presence of the shear band because it has a smaller heat input than aging. For rolling before and after aging treatment, conditions are set in consideration of mechanical properties such as required tensile strength and 0.2% proof stress and bending workability, but it is possible to omit either rolling before or after aging treatment. It is.

  In this case, when the solution treatment temperature is higher, the amount of Co and Si dissolved in the Cu matrix increases, and during the aging treatment, a Co—Si based intermetallic compound is precipitated from the matrix to improve the strength. The solution treatment temperature for obtaining this precipitation strength effect is such that the maximum material temperature of the test piece is the solid solution limit temperature of Co (about 370 ° C. when the Co concentration is 0.1% by mass and about 490 when the Co concentration is 0.2% by mass). C, about 560 ° C. with a Co concentration of 0.3% by mass, about 650 ° C. with a Co concentration of 0.5% by mass, about 710 ° C. with a Co concentration of 0.7% by mass, about 730 ° C. with a Co concentration of 0.8% by mass, About 750 ° C. with Co concentration of 0.9% by mass, about 770 ° C. with Co concentration of 1.0% by mass, about 840 ° C. with Co concentration of 1.5% by mass, about 865 ° C. with Co concentration of 1.7% by mass, Co concentration 1.8% by mass, about 875 ° C., Co concentration of 1.9% by mass, about 885 ° C., Co concentration of 2.0% by mass, about 890 ° C., Co concentration of 2.2% by mass, about 910 ° C., Co concentration of 2.%. 6% by mass, about 940 ° C., Co concentration of 3.0% by mass, about 960 ° C., Co concentration of 3.5% by mass, about 990 ° C.) Or so as to become higher.

  Usually, in the solution treatment step, quenching is performed in order to maintain the solid solution state of Co and Si as much as possible. In the present invention, attention is paid to the fact that a certain amount of Co-Si intermetallic compound precipitates almost uniformly in the material during the cooling process of the solution treatment, no matter how much rapid cooling is performed. By slowing down the cooling rate in the process, a temperature gradient is created in the surface layer and the center of the plate thickness in the cooling process of the solution treatment, and the number of precipitates having a particle size of 1 to 10 μm is stepped from the surface layer toward the center of the plate thickness The number of surface shear bands after the final cold rolling was reduced, and an alloy strip showing an excellent surface appearance even after bending was obtained. Although the present invention is not limited by theory, by reducing the cooling rate, the difference in cooling rate between the surface layer and the central portion of the plate thickness increases, and the vicinity of the surface layer is rapidly cooled to reduce precipitates, and the central portion of the plate thickness. Then, it is considered that the precipitate is increased by slow cooling.

The average cooling rate from the solution temperature to 400 ° C. is preferably 500 ° C./min or less, more preferably 500 to 300 ° C./min, and most preferably 500 to 400 ° C./min. If it is in the above range, the number of precipitates having a particle size of 1 μm or more is decreased because the surface layer is rapidly cooled, and precipitates having a particle size of 1 to 10 μm are generated because it is gradually cooled in the central portion. If it exceeds 500 ° C./min, it will be deposited almost uniformly inside the material, resulting in poor bendability and appearance after bending. If it is less than 300 ° C./min, the precipitate at the center of the plate thickness becomes coarse and the effect of precipitation strengthening due to aging cannot be sufficiently obtained.
The average cooling rate from 400 ° C. to 70 ° C. is preferably 300 ° C./min or less, more preferably 300 to 100 ° C./min. If it exceeds 300 ° C./min, it will be deposited almost uniformly inside the material, resulting in poor appearance after bending. On the other hand, if it is less than 100 ° C./min, the precipitate in the central part of the plate thickness becomes coarse and the effect of precipitation strengthening due to aging cannot be sufficiently obtained. In addition, since it takes time, it is not preferable industrially.
In the present invention, the average cooling temperature is used because it is actually difficult to make the cooling rate constant in cooling from the solution temperature. The average cooling rate of the present invention is the solution temperature and 400 ° C, or the difference between 400 ° C and 70 ° C divided by the time taken for cooling.

  The copper alloy material before solution treatment is heated until it reaches a temperature near the solid solution limit of the second phase particle composition. The temperature at which the solid solubility limit of Co becomes equal to the addition amount when the addition amount of Co is in the range of 0.2 to 3.5% by mass (referred to as “solid solubility limit temperature” in the present invention) is about 490 to 990 ° C. For example, when the addition amount of Co is 2.0 mass%, it is about 890 ° C. Typically, heating is performed until the temperature reaches 0 to 25 ° C., preferably 0 to 20 ° C. higher than the solid solution temperature of Co of the copper alloy material before solution treatment. However, setting the solution treatment temperature to be higher than the solid solution limit temperature of Co by exceeding 25 ° C. is not preferable because the crystal grain size increases and the bendability deteriorates. The solution treatment can be performed a plurality of times during the cold rolling.

An aging treatment is performed following the final solution treatment. In order to obtain the Cu—Co—Si based alloy according to this embodiment, it is preferable to perform an aging treatment immediately after the final solution treatment without performing cold rolling.
After the final solution treatment, aging treatment is performed to produce fine precipitates and then cold rolling (aging → cold rolling), the dislocation that is the origin of the shear band is proportional to the number of precipitates. Since it increases, high strength can be obtained with a low degree of processing. As the bendability tends to be better when the amount of strain contained in the material is smaller, the bendability of the material obtained by “aging → cold rolling” that can be rolled at a low workability is excellent. Become. On the other hand, it is difficult to achieve both bendability and strength in the “cold rolling → aging process” in which the aging treatment is performed after cold rolling in the absence of precipitates due to aging. The reason is that since there is almost no precipitate during cold rolling, a high degree of workability is required to obtain the same level of strength as aging → cold rolling, resulting in poor bendability. Although the present invention is not limited by the discussion, it is considered that the shear band disappears once by aging heat treatment and is formed again by subsequent rolling. Therefore, in order to obtain an alloy strip having an excellent balance between strength and bendability, rolling after aging is preferable, and rolling before aging can be omitted.

The aging treatment is preferably carried out under aging treatment conditions in which fine precipitates of intermetallic compounds are uniformly distributed at appropriate sizes and intervals, and peak strength is obtained while ensuring conductivity. Here, the peak intensity is, for example, when the aging treatment time is changed (for example, 15 hours) and the aging treatment temperature is changed (for example, 450, 475, 500, 525, 550, 575, 600 ° C.) Is the strength when aging treatment is performed under the condition that the strength (tensile strength) is the highest. Specifically, it is preferable to heat at a material temperature of 475 to 580 ° C. for 1 to 30 hours, more preferably to heat at a material temperature of 480 to 580 ° C. for 1.5 to 25 hours, and 5 to 5 at a material temperature of 480 to 580 ° C. It is more preferable to heat for ~ 25 hours.
The shear band is generated by localizing the strain introduced in the material. As described above, when the number of precipitates having a particle size of 1 to 10 μm is small in the surface layer part, and the material adjusted to be large in the sheet thickness center part is uniformly deformed (rolled) with respect to the surface layer and the sheet thickness center part, There are few shear bands in the surface layer, and they occur in the central part of the plate thickness to the extent sufficient for strengthening the work.

  In order to control the development of the shear band, in the embodiment of the present invention, the rolling load of the final cold rolling is preferably 115 kg / mm or less, more preferably 100 kg / mm per unit length in the width direction of the material. mm or less, for example, 100 to 85 kg / mm. This is intended to uniformly deform (roll) the surface layer and the central portion of the plate thickness, and the number of precipitates having a particle diameter of 1 to 10 μm is small in the surface layer portion and adjusted in the central portion of the plate thickness. The material has an effect that the shear band is small in the surface layer and is generated in a sufficient amount for work strengthening in the central portion of the plate thickness. Usually, the rolling load of the final cold rolling is carried out at a rolling load of 150 to 200 kg / mm or more in order to roll industrially in a short time. This is because the higher the rolling load, the stronger the force for compressing the material in the plate thickness direction, and the material can be reduced to the desired plate thickness in a shorter time. Therefore, in the prior art, the development of the shear band is not controlled, and strain concentrates on the material surface, resulting in an increase in the surface shear band.

  In the embodiment of the present invention, the viscosity of the rolling oil used in the final cold rolling is preferably less than 13 cST so that uniform deformation occurs in the surface layer and the central portion, and is preferably 10 cST or less. More preferably, it is 7 cST or less, and most preferably 6.8 to 3 cST. If it is 13 cST or more, the rolling oil is caught on the surface of the material during rolling, the surface smoothness is inferior, and the surface layer tends to be distorted, so that the number of surface shear bands tends to increase. Normally, rolling oil having a viscosity of about 7 to 25 cST or higher is generally used for industrial rolling in a short time. The higher the viscosity of the rolling oil, the more optimal lubrication oil thickness can be obtained at higher rolling speeds, so the rolling speed can be increased and the productivity can be improved by rolling in a shorter time. is there.

  In this embodiment, the presence or absence of a shear band is revealed by etching after mechanical polishing on the rolled parallel cross section of the Cu—Co—Si based alloy, and using a scanning electron microscope (SEM), Count those having a depth of 0.01 μm or more from the surface of the crystal grains (rolled surface). The reason why the lower limit of the depth is set to 0.01 μm or more is that it is difficult to count too fine shear bands.

  When the purpose is to obtain high strength, the total degree of cold rolling after aging treatment is 2% or more, preferably 5% or more, more preferably 7% or more. However, if the degree of work is too high, the proportion of crystal grains in which shear bands are present increases and the bendability deteriorates, so the degree of work is 25% or less, preferably 20% or less. The mechanical properties such as required tensile strength, 0.2% proof stress and bending workability can be arbitrarily selected.

  After the final cold rolling, strain relief annealing is performed to obtain stress relaxation characteristics necessary for application to electronic components. The conditions for strain relief annealing may be conventional conditions. Specifically, it is preferably performed under the conditions of heating at a material temperature of 200 ° C. or more and less than 550 ° C. for 0.001 to 20 hours. If the material temperature is 200 to 300 ° C. and heated for 12 to 20 hours, and if it is high temperature, it is more preferable to carry out under conditions of a short time (for example, heating at a material temperature of 300 to 400 ° C. for 0.001 to 12 hours). Depending on the required characteristics, this step can be omitted. However, the strain relief annealing conditions are set so that the number and distribution of the shear bands of the product after annealing are maintained within the scope of the present invention.

Since the copper alloy of the present invention evaluates the change in surface appearance after bending, the material surface appearance is important. The surface roughness can be adjusted, for example, by rolling or polishing. In actual operation, the surface roughness of the copper alloy can be adjusted by rolling using a rolling roll or the like whose surface roughness is adjusted. Moreover, it is also possible to adjust the surface roughness by performing buffing, for example, with different eye roughness on the material surface in the process after rolling.
The surface average roughness Ra of the alloy strip of the present invention after the following bending evaluation is 1.0 μm or less, preferably 0.8 μm or less in both the bending directions GW and BW.

  The production examples of Cu—Co—Si alloys and the results of characteristic tests according to the present invention are shown below, but these are provided for better understanding of the present invention and its advantages, and the present invention is limited. It should be noted that this is not intended.

(Production method)
In producing the copper alloy of the example, an air melting furnace was used for melting. In addition, in order to prevent unexpected side effects due to mixing of impurity elements other than the elements defined in the present invention, raw materials having a relatively high purity were carefully selected and used.

  Homogenization by adding Co and Si at the concentrations shown in Tables 1 and 2 and optionally further adding a third element and heating at 980 ° C. for 3 hours to the ingot having the composition of the remaining copper and inevitable impurities After annealing, hot rolling was performed at 900 to 950 ° C. to obtain a hot rolled sheet having a thickness of 10 mm. After descaling by chamfering, it was cold-rolled to obtain a strip thickness (2.0 mm). Next, in the intermediate cold rolling, the intermediate plate thickness was adjusted so that the final plate thickness was 0.10 mm, and cold rolling was performed. Thereafter, it was inserted into an annealing furnace capable of rapid heating and subjected to a solution treatment, and immediately after the copper alloy material reached a predetermined material temperature, it was taken out of the annealing furnace and cooled with water.

  In the examples, the solution treatment was performed such that the maximum material temperature of the test piece was 0 ° C. to 25 ° C. higher than the solid solution limit temperature of Co. It cooled, adjusting each average cooling rate in solution solution temperature -400 degreeC and 400 degreeC-70 degreeC to a predetermined | prescribed speed | rate, and adjusted the number of precipitates with a particle size of 1-10 micrometers of a surface layer and plate thickness center part.

In this example, the solution treatment holding time was unified at 10 s. “Solution treatment retention time” indicates the time from when the test piece reaches the maximum material temperature until the water cooling starts.
“Solution temperature to 400 ° C. cooling rate” in Tables 1 and 2 represents the average cooling rate until the specimen is cooled from the maximum material temperature to 400 ° C. Specifically, (cooling rate (° C./s))=((material maximum temperature (° C.) − 400 (° C.)) / (Time required from the start of water cooling until the temperature of the test piece reaches 400 ° C. (S)) The “cooling rate of 400 ° C. to 70 ° C.” in Tables 1 and 2 was also calculated in the same manner, and the time until the test piece was cooled to 70 ° C. was used as the reference for the cooling rate. This is because, in the temperature range of 70 ° C. or lower, the diffusion distance of atoms, which is the driving force for the disappearance, generation, and growth of precipitates, is negligibly small.

Thereafter, for Examples 1 to 35 and Comparative Examples 1 to 30 and 35 to 40, aging is performed under aging treatment conditions (for example, 500 ° C., 15 hours) at which peak strengths are obtained for the test pieces after the final solution treatment. After the treatment, final cold rolling was performed under the conditions shown in Table 1 (Production Method A), and test pieces of Examples and Comparative Examples were produced. Moreover, about Comparative Examples 31-34, it cold-rolls on the conditions shown in Table 1 and 2 with respect to the test piece after a solution treatment, and after that, aging treatment conditions (for example, 500 degreeC, respectively) from which peak intensity is obtained, respectively. 15 hours) was subjected to aging treatment (Production Method B). In Tables 1 and 2, “Load” indicates the rolling load per unit length in the width direction of the test piece. (Rolling load per unit length in the width direction (kg / mm)) = (Rolling load (kg)) / (Sample width (mm))
For the rolling oil, mineral oil is added to Idemitsu Kosan's trade name Daphne Stainless Oil X-60 (viscosity 9.5 cST) or Idemitsu Kosan Co., Ltd. trade name Daphne Stainless Oil X-3K (viscosity 12 cST) to adjust the viscosity. used.

Characteristic evaluation was performed on the obtained test pieces under the following conditions. The results are shown in Table 2.
<Crystal grain size>
The crystal grain size (average crystal grain size) is measured by exposing the rolled surface to a solution of phosphoric acid 67% + sulfuric acid 10% + water by electropolishing under conditions of 15 V 60 seconds, washing with water and drying for observation. did. The structure was observed using an FE-SEM (electrolytic emission scanning electron microscope), and the average crystal grain size was determined by the cross line segment method of JIS G0551.
<Number density of second phase particles>
Using the FE-SEM, the structure appears in the same way as the crystal grain size measurement, and the inclusion of multiple elements such as grain size and precipitates is determined using the FE-SEM EDS (energy dispersive X-ray analysis). It confirmed by analyzing a component with respect to all the deposits. Particle analysis software (EDS particles / phase manufactured by Phoenix Corporation) divided into second phase particles having a particle size of less than 1.0 μm, second phase particles having a particle size of 1.0 to 10 μm, and second phase particles having a particle size of more than 10 μm. Analysis software). In all Examples and Comparative Examples, precipitates having a particle size exceeding 10 μm were not present in the surface layer and the central portion of the plate thickness.

<Shear band>
The structure was revealed in the same manner as the crystal grain size measurement, and the unevenness of the structure on the sample surface was measured using a scanning electron microscope (SEM). And the thing whose depth is 0.01 micrometer or more from the surface of the crystal grain was counted as a shear zone. Specifically, a frame of 100 μm × 100 μm was prepared, and the number of shear bands present therein was counted. A shear band crossing the frame was also counted as one. The counted number was defined as the number per unit area of the shear band. The sample surface layer was revealed by electropolishing the sample surface as it was. About the center part of the sample, mechanical polishing was performed so as not to cause strain from the sample surface, and the structure of the center part of the plate thickness was revealed.
Regarding the measurement of the shear band, the unevenness of the tissue in the range where the streak or linear pattern exists is measured, and the height from a certain valley (concave portion) to the adjacent mountain (convex portion) is 0.01 μm or more. The valleys (recesses) were counted as “shear bands”. Here, the “streaky or linear pattern” was specified by visually observing an SEM photograph (magnification of 5,000 times). The crystal grain boundaries were not counted as shear bands.

<0.2% yield strength>
A JIS No. 13B specimen was prepared using a press so that the tensile direction was parallel to the rolling direction. The test piece was subjected to a tensile test according to JIS-Z2241, and the strength at 0.2% elongation in the rolling parallel direction was measured. In the present invention, high strength means 0.2% proof stress of 560 MPa or more.
<Conductivity>
In accordance with JIS H 0505, the conductivity (EC:% IACS) was measured by a four-terminal method. The Cu—Co—Si alloy strip of the present invention usually exhibits a conductivity of 60% IACS or more, preferably 65.0% IACS or more, more preferably 66.5% IACS or more.
<Elongation>
The elongation at break was measured according to JIS-Z2241 for the sample subjected to the tensile test.

<Bending surface>
In accordance with JIS Z 2248, a W-bending test was performed with a bad way (BW: bending axis is the same direction as the rolling direction) and R / t = 0, and the bending surface of this test piece was observed. As an observation method, the bending surface was photographed using a laser tech confocal microscope HD100, and the average roughness Ra was measured using the attached software, and compared. In addition, the unevenness | corrugation was not confirmed when the sample surface before a bending process was observed using the confocal microscope. The case where the average surface roughness Ra after bending exceeds 1.0 μm was evaluated as inferior in appearance after bending. The term “excellent in appearance after bending” in the present invention means that the surface average roughness Ra after BW bending is 1.0 μm or less in the above measurement. In the following example samples of the present invention, Ra after GW bending was all 1.0 μm or less.

The production conditions and characteristics of the material produced as described above are shown in Tables 1 to 4. In addition, “* 1” in the table indicates that manufacturing / evaluation was impossible because cracking occurred during hot rolling, and “* 2” indicates the ratio of the surface layer to the center of the plate thickness because there is no shear band. Indicates that it cannot be calculated.
Examples 2 and 3 are examples in which the Co content is the lower limit and the upper limit of the present invention, and Example 2 is an example in which the Si content is near the lower limit of the present invention. Examples 4 to 6 are examples in which the Co and Si contents are within the scope of the present invention, and Examples 7 to 9 are examples in which the cold rolling degree after aging treatment is changed to 3 to 18%. Examples 10 to 33 are examples in which the type and amount of additive elements were changed within the scope of the present invention, Example 34 was an example in which the Si content was the upper limit of the present invention, and Examples 36 to 41 were cooled. This is an example in which the speed is changed, but the same effect as in Example 1 was exhibited. The solution treatment temperature of Example 1 was + 15 ° C. in the solid solution limit temperature of Co, whereas it was + 15 ° C. in Example 4. However, the difference almost affected the physical properties of the manufactured test piece. There wasn't. In Example 5, since the addition amount of Co was slightly small, the solution treatment temperature was lowered, and the number of precipitates having a particle size of 1 to 10 μm was also reduced. As a result, the strength was slightly low as in Example 2.

Since the solution treatment temperature in Comparative Example 1 was 65 ° C. lower than the solid solution limit temperature, more precipitates having a particle diameter of 1 to 10 μm were deposited than in Example 1 or 4, and the strength and bendability were inferior.
In Comparative Examples 2 to 8 and 35 to 40, since the solution treatment temperature was high, the crystal grain size exceeded 20 μm and the bendability was inferior. Further, Comparative Examples 2, 3 and 35 were inferior in strength because they did not contain an additive element having an effect of improving the strength. In addition, Comparative Examples 35 to 40 were further deteriorated in bendability due to high rolling load and high rolling oil viscosity.
In Comparative Examples 9 to 12, the average cooling rate from the solution temperature to 400 ° C. or the average cooling rate from 400 ° C. to 70 ° C. was higher than that in Example 1, 4 or 9, so that the precipitate was almost contained in the material. It was deposited uniformly, and the number of lines in the central shear band was small and the bendability was poor. Further, Comparative Example 10 was inferior in strength because the crystal grain size was large. Further, Comparative Example 12 is a conventional example in which the load is large and the viscosity of the cold oil is large, the number of shear bands on the surface layer is large, and the bendability is very poor.
In Comparative Example 13, since the degree of rolling after aging treatment was zero, there was no shear band in both the surface layer and the central portion, and the strength was inferior. In Comparative Example 14, since the degree of processing was too high, there were excessive shear bands on the surface layer, but the number of shear band lines in the center was small, and the bendability was poor.
In Comparative Examples 15, 18, 19, 22, 23, 26, 27, 35 to 40, the rolling load after the aging treatment was large. And the bendability was inferior.

In Comparative Examples 16, 17, 20, 21, 24, 25, 28, and 29, since the rolling oil viscosity after aging treatment was large, the shear band in the center portion although the shear band was excessively present The number of wires was small and the bendability was poor.
In Comparative Examples 19 and 21, since the solution treatment temperature was inappropriate, the number of shear band lines in the central portion was small and the bendability was inferior even though the shear band was excessively present.
In Comparative Example 30, the Co and Si contents were too much outside the scope of the present invention, so cracking occurred during hot rolling and evaluation was impossible.
In Comparative Examples 31 to 34, cold rolling was performed before aging, and cold rolling after aging was not performed. Since Comparative Example 31 had a low workability, the bendability was good but the strength was low. Since Comparative Examples 32 and 33 were higher in workability than Comparative Example 31, the strength was high but the bendability was very poor. In Comparative Example 34, although the rolling conditions were the same as in Example 9, since cold rolling was not performed after aging, the strength was low and the bendability deteriorated.
Since Comparative Examples 35 to 40 had large loads and oil viscosities, the number of shear band lines in the central portion was smaller than that of the surface layer portion despite the presence of excessive shear bands, which was even more than Comparative Examples 2 to 8. Poor bendability.

  As described above, according to the present invention, it is possible to obtain a high-strength copper alloy exhibiting an excellent appearance of a bent portion that does not cause wrinkles or cracks in the appearance of a bent portion after BW bending as well as the GW. Suitable as a copper alloy for isoelectronic materials.

11: Precipitate 12: Shear band

Claims (4)

A Cu—Co—Si alloy strip containing 0.2 to 3.5% by mass of Co and 0.02 to 1.0% by mass of Si, the balance being copper and inevitable impurities, and a third element group 1 or more selected from the group consisting of Mn, Fe, Mg, Ni, Cr, V, Nb, Mo, Zr, B, Zn, Sn, Ag, Be, Misch metal and P in a total amount of 1. It may be contained in the range of 0% by mass or less, and the number Ss of lines of the shear band from the material surface to 1/6 depth of the plate thickness (hereinafter referred to as “surface layer”) and portions other than the material surface layer (hereinafter referred to as “surface layer”) The ratio Ss / Sc of the number Sc of the lines of the shear band of “Sheet thickness center” is 1.0 or less, the crystal grain size is 20 μm or less, and the number of precipitates having a grain size of 1 to 10 μm in the material surface layer. Is 3.0 × 10 ⁴ pieces / mm ² or less, with high strength and appearance after bending Excellent Cu-Co-Si alloy strip. ^2. The Cu—Co—Si based alloy strip according to claim 1, wherein the number of shear band lines in the material surface layer is 330 / 10,000 μm ² or less.   The ratio Ns / Nc of the number Ns of precipitates having a particle diameter of 1 to 10 μm in the surface layer of the material and the number Nc of precipitates having a particle diameter of 1 to 10 μm in the central portion of the plate thickness is 1.0 or less. Item 3. A Cu—Co—Si alloy strip according to item 1 or 2.   The Cu-Co-Si alloy strip according to any one of claims 1 to 3, which is manufactured by solution treatment at a solution temperature of within a solid solution limit temperature + 25 ° C or less.