JP6573503B2 - Cu-Ni-Co-Si-based high-strength copper alloy sheet, method for producing the same, and conductive spring member - Google Patents

Description

  The present invention relates to a Cu-Ni-Co-Si-based high-strength copper alloy thin plate suitable for a conductive spring member of an electric / electronic component, having a plate shape with a plate thickness of less than 100 μm and high flatness, and a method for producing the same About. The present invention also relates to a conductive spring member using the copper alloy thin plate material.

  A material used for a conductive member constituting an electric / electronic component is required to have excellent “strength” and “conductivity” as basic characteristics. In particular, the “conductive spring member”, which is incorporated in a small machine part and plays a role of energization and leaf spring, has a high strength, for example, 0.2% proof stress of 1000 MPa or more, and is good when processed into the member. It is required to have a property capable of obtaining a simple shape (that is, high dimensional accuracy). In particular, electronic component parts have recently been miniaturized. For example, a copper alloy sheet having a thickness of less than 100 μm, more preferably less than 60 μm, and even less than 50 μm has a high strength such as 0.2% proof stress of 1000 MPa or more. Therefore, the need for economical materials having the property of maintaining high dimensional accuracy after processing is considered to increase.

  As a copper alloy having an excellent balance between strength and conductivity, there are a Cu—Ni—Si based copper alloy (so-called Corson alloy) and a Cu—Ni—Co—Si based copper alloy to which Co is added. Various techniques for manufacturing a thin plate material and techniques for increasing the strength have been studied so far using these alloy systems.

For example, Patent Documents 1 and 2 disclose a technique for reducing drooping curl (warping in the rolling direction) of a plate material by devising aging treatment conditions and the like. In both documents, the plate thickness is assumed to be 0.005 mm, but the plate thickness of the example is 0.2 mm, and their 0.2% proof stress is 670 to 952 MPa.
Patent Document 3 describes that a texture is defined to reduce the anisotropy of yield strength. The plate thickness is assumed to be 0.03 mm, but the plate thickness of the examples is 0.08 mm, and their 0.2% proof stress is 710 to 791 MPa.
Patent Document 4 describes that a texture is defined to improve bending workability and strength after notching. In the example, the characteristics are mainly examined with a plate thickness of about 0.15 mm, and only one example has a plate thickness of 0.031 mm (Example 25). Its 0.2% proof stress is 741 MPa.
Patent Document 5 describes a technique for increasing the strength and reducing the bending deflection coefficient by defining a metal structure. In the examples, a 0.2% proof stress of 951 to 970 MPa was obtained with a plate thickness of 0.15 mm.
Patent Document 6 describes a technique for increasing the strength with a 0.2% proof stress of 980 MPa or more by defining the metal structure and the Si concentration in the matrix. In the examples, a 0.2% proof stress of 983 to 1031 MPa was obtained with a plate thickness of 0.15 mm.

  On the other hand, Patent Documents 7 and 8 disclose a technique in which a high-strength material having a thickness of 100 μm or less is applied to a conductive spring material of an autofocus camera module using a Cu—Ti based copper alloy. According to the Cu-Ti copper alloy, it is possible to obtain a very high strength of 0.2% proof stress of 1200 MPa or more (Patent Document 7).

JP 2012-126934 A JP 2012-2111355 A JP 2013-163853 A JP 2013-204079 A JP 2014-88604 A JP 2014-156623 A JP 2014-102294 A JP 2014-80670 A

  As can be seen from the above prior art, in Cu—Ni— (Co) —Si based copper alloys, a technology for industrially and stably producing a plate material having a plate thickness of less than 100 μm and an extremely high strength level. Is not established. As the factor, it is very difficult to manufacture a thin high-strength plate material that can obtain high dimensional accuracy when processed into a product. On the other hand, when a Cu—Ti based copper alloy is used, it is easy to obtain a very high strength level (Patent Document 7). However, there is a problem that Cu-Ti-based copper alloys have poor solder wettability compared to Cu-Ni- (Co) -Si-based copper alloys. Considering incorporation in an electronic device component as a conductive spring member, a copper alloy system having a solder wettability better than a material specialized for a very high strength level has a strength level of 0.2% proof stress of 1000 MPa or more. In many cases, the use of a thin plate material is advantageous in terms of cost and component performance.

  The present invention provides a conductive spring member having a high 0.2% proof stress and incorporated in a small machine component, etc., in a thin plate material of a Cu—Ni—Co—Si based copper alloy having a thickness of less than 100 μm or even 60 μm or less. It is intended to provide a plate having a good shape that can be obtained with high dimensional accuracy when processed.

According to the inventors' research, in order to obtain a high strength level in a Cu—Ni—Co—Si based copper alloy, “fine second phase particles” having a particle diameter of 5 to 10 nm have a number density of 1.0 × 10 × 10. It is very effective to make the metal structure dispersed at ⁹ pieces / mm ² or more. In addition, in order to give the property that high dimensional accuracy can be obtained when processed into parts, in low temperature annealing performed after finish cold rolling, heating is performed at a relatively low temperature for a long time while applying an appropriate tension. In addition, it has been found that it is extremely effective to use a slow temperature rise and a slow cooling. The present invention has been completed based on such findings.

That is, in the present invention, in mass%, the total of Ni and Co: 2.50 to 4.00%, Co: 0.50 to 2.00%, Si: 0.50 to 1.50%, Fe: 0 to 0.50%, Mg: 0 to 0.10%, Sn: 0 to 0.50%, Zn: 0 to 0.15%, B: 0 to 0.10%, P: 0 to 0.10%, REM (rare earth element): 0 to 0.10%, the total content of Cr, Zr, Hf, Nb and S is 0 to 0.05%, and has a chemical composition consisting of the balance Cu and inevitable impurities. And the number density of “fine second phase particles” having a particle diameter of 5 to 10 nm among the second phase particles present in the matrix phase has a metal structure of 1.0 × 10 ⁹ particles / mm ² or more. , The width W _{0 in the} direction perpendicular to the rolling is 50 mm or more, the plate thickness is 15 μm or more and less than 100 μm, more preferably 15 μm or more and 60 μm or less, and the maximum cross defined in (A) below A copper alloy sheet material having a bow q _MAX of 250 μm or less is provided.
(A) a copper alloy thin sheet from the rolling direction length 50mm, perpendicular to the rolling direction length is taken off plate P rectangular a plate width W ₀ (mm), still perpendicular to the rolling direction 50mm pitch the cutting plate P in cutting, in which, when a direction perpendicular to the rolling direction length occurs in the direction perpendicular to the rolling direction end portion of the small pieces cut plate P less than 50mm except the piece, n (n is the plate width W _0/50 A square sample of 50 mm square is prepared. However, when W ₀ = 50 mm, the cut plate P is a square sample. For each n square samples, the crossbow q when placed on a horizontal board is determined according to the measuring method (however, w = 50 mm) by the three-dimensional measuring device specified in Japan Technical Standard JCBA T320: 2003. Both surfaces (plate surfaces on both sides) are measured in the direction perpendicular to the rolling direction, and the maximum value of the absolute value | q | of each surface is defined as the crossbow q _i (i is 1 to n) of the square sample. maximum value of the crossbow q ₁ to q _n of n square samples and maximum crossbow q _MAX.

Among the above alloy elements, Fe, Mg, Sn, Zn, B, P, REM (rare earth element), Cr, Zr, Hf, Nb, and S are arbitrarily added elements. REM (rare earth element) is each element of lanthanoid series, Y and Sc.
The copper alloy sheet material that satisfies the requirement of the above (A) is intended for a sheet having a sheet width W _{0 in the} direction perpendicular to the rolling of 50 mm or more. Those having W ₀ of 60 mm or more are more suitable targets. Such a plate product may be subjected to a press punching process as it is, or may be further slit to form a narrow strip and then used for part processing.

In the copper alloy sheet material, it is more preferable that the I-unit defined in the following (B) is 5.0 or less.
(B) the rolling direction length of a copper alloy thin sheet is 400 mm, perpendicular to the rolling direction length is taken off plate Q rectangle is a plate width W ₀ (mm), placed in a horizontal surface plate. The projected surface of the cut plate Q viewed in the vertical direction is defined as a rectangular region X, and the rectangular region X is further divided into strip-shaped regions at a pitch of 10 mm in the direction perpendicular to the rolling, and the length in the direction perpendicular to the rolling is less than 10 mm. when strip-shaped region of the narrow occurs perpendicular to the rolling direction end portion of the rectangular region X except a strip area of the narrow, strip of the adjacent n points (n is an integer portion of the plate width W _0/10) A region (width 10 mm) is set. For each strip-shaped region, the surface height at the center of the width is measured over the entire length in the rolling direction, and the difference between the maximum height h _MAX and the minimum height h _MIN h _MAX −h _MIN is the wave height h (mm) The elongation difference rate e obtained by the following equation (1) is defined as the elongation difference rate e _i (i is 1 to n) of the strip-shaped region. The maximum value of the elongation difference rates e _{1 to} en of the _n strip-shaped regions is defined as I-unit.
e = (π / 2 × h / L) ² (1)
However, L is a reference length of 400 mm.

  When the 0.2% proof stress in the rolling direction is measured for the copper alloy thin plate material, it becomes 1000 MPa or more. The 0.2% yield strength is a 0.2% yield strength measured by an offset method measured according to JIS Z2241: 2011 using a tensile test piece whose longitudinal direction is parallel to the rolling direction.

In addition, as a method for producing the copper alloy sheet material, at least slab heating, hot rolling, cold rolling, heat treatment before aging treatment, aging treatment, finish cold rolling on a copper alloy slab having the above chemical composition In producing a copper alloy sheet by performing each step of low temperature annealing in the above order,
In the slab heating step, the slab is held at 1000 to 1060 ° C. for 2 hours or more,
In the heat treatment step before the aging treatment, after a solution treatment at 950 to 1020 ° C., a heat history that is maintained at 600 to 800 ° C. for 10 to 300 seconds is given,
In the aging treatment step, the number density of the “fine second phase particles” having a particle diameter of 5 to 10 nm is 1.0 × 10 ⁹ particles / mm by keeping the material having the heat history at 300 to 400 ° C. ^With a metal structure that is ^two or more,
In the finish cold rolling process, using a work roll having a roll diameter of 25 to 45 mm, cold rolling to a plate thickness of 15 μm or more and less than 100 μm,
In the low-temperature annealing step, the temperature is increased at a maximum temperature increase rate of 100 ° C./sec or less, maintained at 250 to 400 ° C. for 25 to 720 seconds while applying a tension exceeding 100 N / mm ² and not more than 150 N / mm ² , and the maximum cooling rate Apply heat treatment under conditions of cooling to room temperature (5-35 ° C.) at 100 ° C./sec or less,
A method for producing a high-strength copper alloy sheet material having a good plate shape is provided.

  Moreover, in this invention, the electroconductive spring member which used said copper alloy thin plate material as a material is provided.

  According to the present invention, a Cu—Ni—Co—Si copper alloy plate material has a plate thickness of less than 100 μm, or particularly as thin as 60 μm or less, a 0.2% proof stress as high as 1000 MPa or more, and processed into a precision part. In some cases, a good plate shape having the property of obtaining high dimensional accuracy was realized. In its manufacture, it is not necessary to perform shape correction such as a tension leveler. This plate material also has good solder wettability, and is useful as a conductive spring material incorporated in various small machine parts including a spring member of an autofocus camera module.

<Alloy composition>
In the present invention, a Cu—Ni—Co—Si based copper alloy is employed. Hereinafter, “%” regarding alloy components means “% by mass” unless otherwise specified.

  Ni and Co are elements that form Ni—Si-based precipitates and Co—Si-based precipitates, respectively, and improve the strength and conductivity of the copper alloy sheet. The strength is further improved by the synergistic effect of the coexistence of these two kinds of precipitates. The total amount of Ni and Co needs to be 2.50% or more. If it is less than this, sufficient precipitation hardening ability cannot be obtained. It is more effective to set it to 3.00% or more. However, an increase in the content of Ni or Co increases the crystallization / precipitation start temperature as a Si compound, and contributes to the formation of a coarse second phase during casting. The total content of Ni and Co is limited to 4.00% or less.

  In the present invention, the strength is increased particularly by utilizing the fine dispersion of Co—Si based precipitates. Since Co has a lower solid solubility limit in Cu than Ni, the amount of precipitates formed can be increased as compared with the case where the same amount of Ni is added. As a result of various studies, it is necessary to ensure a Co content of 0.50% or more, and more preferably 0.70% or more. However, since Co is a metal having a melting point higher than that of Ni, if the Co content is too high, solid solution in the solution heat treatment to be described later becomes insufficient, and undissolved Co is effective for improving the strength. It is not used for the formation of system precipitates and is wasted. Moreover, when Co is added in a large amount, the allowable range of Ni content becomes narrow, and there is a possibility that the hardening action by the Ni—Si based precipitate cannot be fully enjoyed. For these reasons, the Co content is preferably 2.00% or less, more preferably 1.80% or less. The Ni content is not particularly specified because it is limited by the total amount of Ni and Co described above, but it is usually set within a range of 1.00 to 3.00%.

Si is an element necessary for forming Ni—Si based precipitates and Co—Si based precipitates. The Ni—Si based precipitate is considered to be a compound mainly composed of Ni ₂ Si, and the Co—Si based precipitate is considered to be a compound mainly composed of Co ₂ Si. In the present invention intended for high strength, Si plays a role of improving the work hardening ability of the matrix (matrix). It is considered that Si dissolved in the Cu matrix exhibits the effect of increasing work hardening ability by reducing the stacking fault energy and suppressing the occurrence of cross slip. Solid solution Si is also effective in improving the stress relaxation resistance. In order to fully exhibit these effects of Si, it is desired to secure a Si content of 0.50% or more, and more preferably 0.70% or more. On the other hand, excessive addition of Si causes adverse effects such as an increase in manufacturing cost due to an increase in solution temperature and a decrease in press punchability due to the formation of coarse precipitates. The Si content is preferably 1.50% or less, and may be controlled to 1.20% or less.

  As other significant elements, one or more of Fe, Mg, Sn, Zn, B, P, and REM (rare earth elements) may be included as necessary. Fe has an effect of improving the strength by forming an Fe-Si compound, Mg is effective for improving the stress relaxation resistance, Sn has an effect of improving the strength by solid solution strengthening, and Zn is a solder of a copper alloy sheet. B has the effect of improving the attachability and castability, B has the effect of refining the cast structure, and P exhibits the effect of improving hot workability by deoxidation. Further, REM (rare earth elements) including Ce, La, Dy, Nd, and Y is effective for refining crystal grains and dispersing precipitates. In order to fully exhibit these actions, it is more effective to secure a content of 0.01% or more (REM is 0.01% or more in total). However, if the content of these elements is excessive, the electrical conductivity may be lowered, and hot workability or cold workability may be lowered. When these elements are contained, Fe is 0.50% or less, Mg is 0.10% or less, Sn is 0.50% or less, Zn is 0.15% or less, B is 0.10% or less, and P is It is desirable that the content is 0.10% or less and the REM is 0.10% or less. The total content of these elements is more preferably 0.50% or less, or 0.40% or less.

  About each element of Cr, Zr, Hf, Nb, and S, it is desirable to reduce content as much as possible. When the content of these elements increases, coarse crystallized substances and precipitates are easily formed due to the formation of Si-based compounds and the occurrence of liquid-phase two-phase separation, leading to a decrease in the amount of dissolved Si. In that case, the effect of improving the work hardening ability by Si is not sufficiently exhibited, which is disadvantageous in increasing the strength. As a result of various studies, it is desired that the total content of Cr, Zr, Hf, Nb, and S is controlled to 0.05% or less, and more preferably 0.01% or less.

"Characteristic"
[Shape of plate material]
The shape of the Cu—Ni—Co—Si-based copper alloy sheet material, that is, the flatness greatly affects the shape (dimensional accuracy) of the precision energized component obtained by processing it. As a result of various studies, it is extremely important for the dimensional accuracy of the parts to be stably improved that the bending (warpage) in the direction perpendicular to the rolling, which becomes apparent when the plate material is actually cut into small pieces, is very small. Specifically, in the case of a thin plate material having a plate thickness of less than 100 μm, a Cu—Ni—Co—Si based copper alloy plate material having a maximum crossbow q _MAX defined in (A) of 250 μm or less has a plate width in the direction perpendicular to the rolling direction. It was found that any part derived from any part (50 mm or more) can be judged to have workability capable of stably maintaining high dimensional accuracy as a precision energized part. More preferably, the maximum crossbow q _MAX is 230 μm or less. Further, the I-unit defined in (B) is more preferably 5.0 or less, and even more preferably 4.0 or less.

〔Strength〕
In order to use Cu-Ni-Co-Si-based copper alloy sheet material as a material for current-carrying parts such as lead frames and connectors, a conventional strength level in which 0.2% proof stress in the rolling parallel direction (LD) is about 800 MPa or more. It was desirable to have However, as a material of a conductive spring member used by being incorporated in a small mechanical part such as a camera part, in a thin material having a plate thickness of 15 μm or more and less than 100 μm, more preferably 15 μm or more and 60 μm or less, and even less than 50 μm, It is desirable that the 0.2% proof stress of LD is 1000 MPa or more. More preferably, it is 1030 MPa or more and 1200 MPa or less.

《Metallic structure》
The Cu—Ni—Co—Si alloy exhibits a metal structure in which second phase particles are present in a matrix (matrix) made of fcc crystals. The second phase here is a crystallization phase generated during solidification in the casting process and a precipitated phase generated in the subsequent process. In the case of the alloy, the phase is mainly between the Co—Si based intermetallic compound phase and the Ni—Si based metal. Consists of a compound phase. In this specification, particles belonging to the following particle diameter range are taken up as the second phase particles observed in the Cu—Ni—Co—Si alloy.

[Fine second phase particles]
The particle size is 5 nm or more and 10 nm or less, and is produced by an aging treatment. Greatly contributes to strength improvement. In copper alloys, it is generally known that fine precipitates having a particle size of 10 nm or less greatly contribute to strength improvement, and Cu—Ni—Co—Si based alloys have a density of precipitates of about 2 to 10 nm, for example. It is said that high strength can be achieved by ensuring sufficient. However, in order to obtain a high level of strength with a 0.2% proof stress of 1000 MPa or more, a sufficient amount of particles having a particle diameter of 5 to 10 nm, which has a particularly large contribution to curing, among particles of about 2 to 10 nm. It is important to. According to detailed studies by the inventors, it is extremely effective that the amount of the fine second phase particles be 1.0 × 10 ⁹ particles / mm ² or more. It is more effective to set it to 1.5 × 10 ⁹ pieces / mm ² or more, and it may be controlled to 2.0 × 10 ⁹ pieces / mm ² or more. The upper limit of the abundance is not particularly required because it is restricted by specifying the contents of Ni, Co, and Si as described above, but is usually in the range of 5.0 × 10 ⁹ pieces / mm ² or less. It becomes. The number density of the fine second phase particles is measured by observing a sample collected from the plate to be measured with a TEM (transmission electron microscope) and counting the number of second phase particles having a particle diameter of 5 to 10 nm. Do. The particle diameter is the diameter of the smallest circle surrounding the particle.

[Coarse second phase particles]
The particle diameter exceeds 5 μm, and mainly consists of particles that remain after the second phase produced during solidification in the casting process is not completely dissolved in the subsequent process. Does not contribute to strength improvement. The smaller the number of such coarse second phase particles, the more advantageous is the press punchability and the bending workability. As a result of various studies, it is more preferable that the abundance of coarse second phase particles is suppressed to a number density of 10 particles / mm ² or less in the current-carrying parts. The number density of coarse second phase particles is measured by electropolishing the rolled surface of the plate material to be measured to dissolve only the Cu substrate, and the number of second phase particles exposed on the surface is determined by SEM (scanning electron microscope). ). The particle diameter is the diameter of the smallest circle surrounding the particle.

"Production method"
The copper alloy sheet material described above can be produced by the following manufacturing process, for example.
"Melting / Casting → Casting Heating → Hot Rolling → Cold Rolling → Heat Treatment Before Aging Treatment → Aging Treatment → Finish Cold Rolling → Low Temperature Annealing”
Although not described in the above steps, chamfering is performed as necessary after hot rolling, and pickling, polishing, or further degreasing is performed as necessary after each heat treatment. Moreover, heat processing and cold rolling can be added in the process as needed. For example, the cold rolling performed before the solution treatment may be performed in a plurality of cold rolling steps with intermediate annealing interposed therebetween. Hereinafter, each step will be described.

[Melting / Casting]
The slab may be manufactured by continuous casting, semi-continuous casting, or the like. In order to prevent oxidation of Si or the like, it is preferable to carry out in an inert gas atmosphere or a vacuum melting furnace.

[Casting heating]
After casting, the slab is heated and held at 1000 to 1060 ° C. for 2 hours or longer. Thereby, the coarse crystallized phase and the precipitated phase generated during casting are homogenized. It is more preferable to hold at 1020 to 1060 ° C. for 2 hours or more. Since it is uneconomical if the holding time becomes too long, it is usually set within 6 hours. If the set temperature of the furnace exceeds 1060 ° C., the material may be melted due to fluctuations in conditions during operation, etc., which is not preferable. This heat treatment is preferably performed using a heating step in the next hot rolling.

(Hot rolling)
Hot rolling is performed on the slab after the above heating and holding. What is necessary is just to follow the hot rolling conditions in a conventional method. Examples of the conditions include that the slab is heated to 1000 to 1060 ° C., more preferably 1020 to 1060 ° C., and then removed from the furnace, for example, hot-rolled at a rolling rate of 70 to 97%, and then water-cooled. The rolling temperature in the final pass is preferably 700 ° C. or higher.
In addition, a rolling rate is represented by following (2) Formula.
Rolling ratio R (%) = (h ₀ −h ₁ ) / h ₀ × 100 (2)
Here, h ₀ is the plate thickness (mm) before rolling, and h ₁ is the plate thickness (mm) after rolling.

(Cold rolling)
By cold rolling before the solution treatment, reduction of the plate thickness and introduction of strain energy (dislocation) are attempted. The strain energy effectively acts on the solid solution of the second phase in the solution treatment. If necessary, cold rolling can be performed a plurality of times with intermediate annealing. When adding intermediate annealing, it is desirable to perform at 350-600 degreeC from a viewpoint of preventing the coarsening of a 2nd phase particle, and it is more preferable to carry out at 550 degreeC or less. It is effective to set the cold rolling rate before the solution treatment (the cold rolling rate after the final intermediate annealing when performing cold rolling with the intermediate annealing interposed therebetween) to, for example, 70% or more. The rolling tolerance range of 99% or less is usually used in the facility tolerance range such as mill power.

[Heat treatment before aging treatment]
In general, before the aging treatment, heating and holding are performed mainly for the purpose of recrystallization of the matrix and re-solidification of the solute atoms. In the cooling process, the conventional general production method is to rapidly cool to room temperature so as not to cause inadvertent precipitation. This heating and holding and subsequent quenching process are often referred to as solution treatment. In the present specification, the above heating and holding process is referred to as “solid solution treatment”. In the production method according to the present invention, a solution treatment is also necessary, but after that, in the stage before the aging treatment, a thermal history that is maintained in a temperature range of 600 to 800 ° C. for a predetermined time is imparted. The process of holding in this temperature range is called “precursor treatment”.

  In the manufacturing method according to the present invention, the retention temperature of the solution treatment is set to a range of 950 to 1020 ° C. The holding time (the time during which the material is in the temperature range) can be set, for example, in the range of 0.5 to 10 min. If the holding temperature is too low, recrystallization or re-solidification of solute atoms does not proceed sufficiently, or it is not preferable because holding for a long time is required. If the holding temperature is too high, the crystal grains are likely to be coarsened.

Subsequent to the solution treatment, a precursor treatment is performed. The precursor treatment is a heat treatment that is maintained in the range of 600 to 800 ° C., and it is efficient to use the cooling process of the solution treatment. The holding time in the above temperature range, that is, the time during which the material temperature is in the range of 600 to 800 ° C. is in the range of 10 to 300 seconds. When the thermal history of the precursor treatment is applied using the cooling process of the solution treatment, the temperature may be maintained at a constant temperature set in the range of 600 to 800 ° C, or the temperature range from 800 ° C to 600 ° C. May be passed while gradually cooling. In any case, the time during which the material temperature is in the range of 600 to 800 ° C. is controlled to 10 to 300 seconds.
The average cooling rate from the solution treatment temperature to 800 ° C. may be, for example, 5 to 50 ° C./sec. After the precursor treatment, it is preferable that the aging treatment temperature range is quenched and passed. For example, it is preferable to cool so that the average cooling rate from 600 ° C. to 300 ° C. is 50 ° C./sec or more.

  In addition, it is also possible to perform a precursor process with another heat processing equipment, without utilizing the cooling process of a solution treatment. As a heat pattern in that case, after the solution treatment, cooling is performed so that the average cooling rate from at least 600 ° C. to 300 ° C. is 50 ° C./sec or more, and then the temperature is increased from 300 ° C. to 600 ° C. It is preferable to employ a heat pattern that raises the temperature so that the speed is 50 ° C./sec or more and performs the above-described precursor treatment.

  In a Cu-Ni-Co-Si alloy, two types of precipitates, Ni-Si and Co-Si, contribute to increasing the strength, but the optimum precipitation conditions (temperature and time) between them are as follows. Does not match (displaces). The optimum deposition temperature is around 450 ° C. for the Ni—Si system and around 520 ° C. for the Co—Si system. Therefore, it is usually difficult to make maximum use of age hardening by these two kinds of precipitates at the same time. However, according to the research by the inventors, after holding the solution in the state of solution heat treatment in the temperature range of 600 to 800 ° C. for 10 to 300 seconds, and combining the aging treatment performed in the low temperature range described below, It turned out that a Co-Si type compound tends to precipitate. In the temperature range of 600 to 800 ° C., the Ni—Si based compound hardly precipitates, and for the Co—Si based compound, although precipitation occurs, the temperature is higher than the optimum precipitation temperature. When a matrix phase in which solute atoms are sufficiently dissolved is kept in the temperature range for a predetermined time, an embryo mainly composed of Co and Si is formed, and this serves as a driving force for precipitation of a Co-Si compound in an aging treatment described later. It is guessed that. The generation of this embryo can be considered as a precursor phenomenon of Co—Si based compound precipitation.

[Aging treatment]
An aging treatment is performed on the plate material to which the heat history of the solution treatment and the precursor treatment is applied. In general, the aging treatment of a Cu—Ni—Co—Si based alloy is performed at around 520 ° C., but the aging treatment according to the present invention is performed in a low temperature range of 300 to 400 ° C. More preferably, it is performed at 310 to 380 ° C. The free energy related to the nucleation of Co—Si based compound particles is greatly reduced by the precursor treatment in the previous step, and the Co—Si based compound is very easily precipitated. It is considered possible. According to this low temperature aging treatment, it has been found that a large amount of fine second phase particles having a particle diameter of 5 to 10 nm which are most effective for improving the strength are formed. In addition, it was confirmed that precipitation of Ni-Si compounds was also caused by this low temperature aging treatment. Therefore, it is possible to effectively enjoy the precipitation hardening phenomenon caused by the two types of precipitates, which has been difficult in the past.

In setting the aging treatment conditions, a condition is adopted in which the number density of “fine second phase particles” having a particle diameter of 5 to 10 nm is 1.0 × 10 ⁹ particles / mm ² or more after the aging treatment. Since the aging treatment temperature is as low as 300 to 400 ° C., the diffusion rate of atoms is slower than the normal aging treatment. Therefore, it is advantageous to leave the solid solution Si that contributes to strengthening. The optimum aging time can be found in the range of 3 to 10 h.

The following formula (3) can be given as an index for determining the optimum aging condition.
0.60 ≦ ECage / ECmax ≦ 0.80 (3)
Here, ECmax is the maximum conductivity obtained when heat treatment is performed at 50 ° C. intervals for 10 hours in a temperature range of 400 to 600 ° C., and ECage is the conductivity after aging treatment. By setting ECage / ECmax to 0.60 or more, a sufficient amount of precipitation is secured, which is advantageous in improving strength and conductivity. Further, by setting ECage / ECmax to 0.80 or less, the Si concentration in the matrix is sufficiently secured, which is advantageous for improving work hardening ability.

[Finish cold rolling]
The plate material that has been subjected to the aging treatment is subjected to finish cold rolling using a work roll having a roll diameter of 25 to 45 mm to obtain a plate thickness of 15 μm or more and less than 100 μm. Finish cold rolling is effective in improving the strength level (particularly 0.2% yield strength). The finish cold rolling rate (total rolling rate) is effectively 50% or more, and more preferably 75% or more. Although the upper limit of the finish cold rolling rate is limited by the capability of the rolling mill, it is usually set within a range of 99.5% or less. If the diameter of the work roll is less than 25 mm, it is difficult to stably obtain a plate having a good shape so that high dimensional accuracy can be obtained when processed into a precision part such as a lead frame. When the work roll diameter exceeds 55 mm, it becomes difficult to obtain a thin plate having a thickness of 15 μm or more and less than 100 μm due to the cold rolling rate.

[Low temperature annealing]
After finish cold rolling, low temperature annealing is usually performed for the purpose of reducing the residual stress of the strip material, improving the bending workability, and improving the stress relaxation resistance by reducing the dislocations on the pores and the sliding surface. In the present invention, this low-temperature annealing is also used for the purpose of obtaining a shape correction effect. In order to obtain a thin plate material having a good shape with the property that high dimensional accuracy can be obtained when processed into precision parts, it is necessary to strictly limit the conditions for low-temperature annealing, which is the final heat treatment. Basically, using a continuous annealing facility, heat treatment is performed at a low temperature for a long time with a moderate temperature change while applying a relatively high tension.

First, the maximum material temperature for low-temperature annealing is 250 to 400 ° C., and the holding time at 250 ° C. or higher, that is, the time during which the material temperature is 250 ° C. or higher and below the maximum material temperature is 25 to 720 sec. If the maximum material temperature is lower than 250 ° C. or shorter than 250 ° C. and shorter than 25 sec, the shape correction effect cannot be obtained sufficiently. If the maximum material temperature is higher than 400 ° C. or 250 ° C. or higher and the holding time is longer than 720 sec, the material becomes soft and it is difficult to stably obtain a predetermined high strength. More preferably, the maximum material temperature is 300 to 400 ° C., and the holding time at 250 ° C. or higher is 35 to 720 sec.
Secondly, the tension applied to the plate during heating and holding at the above temperature is controlled in the range of more than 100 N / mm ² and not more than 150 N / mm ² . In continuous annealing equipment, the direction of tension is usually the rolling direction. When the tension is 100 N / mm ² or less, the shape correction effect is insufficient, and it becomes difficult to stably impart the property of obtaining high dimensional accuracy when processed into a precision part. When the tension exceeds 150 N / mm ² , the strain distribution in the direction perpendicular to the plate surface tends to be non-uniform when the temperature is raised and lowered, and it is difficult to obtain high flatness.
Third, the maximum temperature increase rate is 100 ° C./sec or less and the maximum cooling rate is 100 ° C./sec or less. That is, a temperature change at a speed exceeding 100 ° C./sec is avoided in the low temperature annealing process. In high-strength Cu-Ni-Co-Si-based copper alloy sheet materials, it is necessary to adopt a heat pattern with gentle temperature changes as described above in low-temperature annealing, which is the final heat treatment. It is extremely effective in imparting the property of obtaining high dimensional accuracy when processed.

  A copper alloy having the composition shown in Table 1 was melted and cast using a vertical semi-continuous casting machine. The obtained slab was heated under the conditions shown in Table 2, and then removed from the furnace, hot-rolled to a thickness of 14 mm, and water-cooled. In some comparative examples in which cracking occurred during hot rolling, production was stopped at that time. The total hot rolling rate is 90 to 95%. After hot rolling, the surface oxide layer was removed (faced) by mechanical polishing. Next, cold rolling was performed at a rolling rate of 90 to 99%. Thereafter, heat treatment (solution treatment and precursor treatment) before aging treatment was performed under the conditions shown in Table 2. The precursor treatment was performed using the cooling process after the solution treatment. The solution is cooled from the solution treatment temperature to the precursor treatment temperature at an average cooling rate of 5 to 50 ° C./sec, held for the time shown in Table 2 at the precursor treatment temperature, and thereafter the average cooling rate from 600 ° C. to 300 ° C. is 50 It cooled to normal temperature so that it might be set to ℃ / sec or more. In some comparative examples in which the precursor treatment was omitted, the solution was rapidly cooled from the solution treatment temperature to a temperature range lower than 300 ° C. The material subjected to the heat treatment before the aging treatment was subjected to an aging treatment under the conditions shown in Table 2. In Table 2, the ECage / ECmax value determined by the equation (3) is also shown. The material after the aging treatment was subjected to finish cold rolling under the conditions shown in Table 3. The roll diameter in Table 3 means the diameter of the work roll used. Table 4 shows the thickness after finish cold rolling. In some comparative examples that could not be rolled to a thickness of less than 50 μm, the subsequent steps were stopped.

  Next, low-temperature annealing was performed under the conditions described in Table 3. The temperature of the low temperature annealing shown in Table 3 means the maximum material temperature, and the time of the low temperature annealing means a holding time of 250 ° C. or more, that is, a time during which the material temperature is 250 ° C. or more and below the maximum material temperature. Low-temperature annealing was performed by a method of continuously feeding a catenary furnace. The atmosphere in the furnace was a nitrogen + hydrogen mixed atmosphere. A temperature curve in which the temperature on the surface of the plate from the start of temperature rise to the end of cooling is measured at various positions in the plate direction, the average temperature at each measurement position is used, time is plotted on the horizontal axis, and temperature is plotted on the vertical axis. Asked. One test material is heat-treated under the same conditions over the entire length of the plate in the pass plate, and the temperature at each measurement position is stabilized to a substantially constant value over time. The maximum gradient at the time was adopted as the maximum rate of temperature increase of the specimen, and the maximum gradient at the time of cooling was adopted as the maximum cooling rate of the specimen. The heating rate and cooling rate for each specimen were adjusted by appropriately controlling the heating output, the ambient temperature, the fan rotation speed, etc. in the heating zone and the cooling zone, respectively, according to the position in the plate direction. Further, the tension during low-temperature annealing was calculated from the catenary curve of the material in the plate passing through the furnace (the height position of the plate at both ends and the center of the plate passing through the furnace and the length in the furnace).

After low-temperature annealing, slitting was performed with a slitter to obtain a thin plate product (test material) having a sheet width W _{0 in the} direction perpendicular to the rolling of 510 mm.

The following investigation was conducted for each specimen.
[Number density of fine second phase particles]
A 3 mm diameter disk is punched out from the specimen, a TEM observation sample is prepared by a twin jet polishing method, and is randomly selected with a TEM (EM Electronics, EM-2010) at an acceleration voltage of 200 kV and a magnification of 100,000 times. A photograph is taken for the selected 10 fields of view, and the number of fine second phase particles having a particle diameter of 5 to 10 nm is counted on the photograph, and the total number is divided by the total area of the observation region to obtain fine second phase particles. The number density (pieces / mm ² ) was determined. Here, the size of one field of view is set to 770 nm × 550 nm. The particle diameter was the diameter of the smallest circle surrounding the particle.
In addition, it can be considered that the number density of the fine second phase particles measured in the test material has not changed from the stage after the aging treatment.

[Number density of coarse second phase particles]
The rolled surface of the sample collected from the test material is electropolished to dissolve only the Cu matrix (matrix), thereby producing an observation sample with the second phase particles exposed on the surface. SEM (manufactured by Hitachi High-Technologies Corporation) , Model number S-3000N), taking a picture of 20 randomly selected fields with a magnification of 3000 times, counting the number of coarse second-phase particles with a particle diameter of 5 μm or more on the photograph, and observing the total number By dividing by the total area of the region, the number density (number / mm ² ) of coarse second phase particles was determined. Here, the size of one field of view is 41 μm × 28 μm. The particle diameter was the diameter of the smallest circle surrounding the particle.
In addition, it can be considered that the number density of the coarse second phase particles measured in the test material has not changed from the stage after the aging treatment.

[0.2% proof stress in the rolling direction]
A tensile test piece (JIS No. 5) in the rolling direction (LD) was taken from each test material, and a tensile test based on JIS Z2241 was performed with the number of tests n = 3, and a 0.2% yield strength was measured. The average value of n = 3 was defined as the result value of the test material.
[I-unit]
A rectangular cut plate Q having a length in the rolling direction of 400 mm and a length in the direction perpendicular to the rolling width of W ₀ (mm) was sampled from each test material, and the I-unit defined in (B) above was obtained. .
[Maximum crossbow q _MAX ]
The maximum crossbow q _MAX defined in (A) above was determined for each test material.
These results are shown in Table 4.

As can be seen from Table 4, each of the copper alloy sheet materials of the present invention has a high strength level in which the 0.2% proof stress of LD is 1000 MPa or more, the maximum crossbow q _MAX is 250 μm or less, and the I-unit is 5. It exhibited a plate shape with extremely high flatness of 0 or less. These thin plate materials are extremely useful as materials for precision conductive spring members used in various small machine parts such as camera modules.

  On the other hand, in Comparative Example No. 31, since the slab heating temperature was low, a large amount of the coarse second phase remained before hot rolling and could not be sufficiently dissolved by the solution treatment. The amount of phase particles deposited was insufficient and the strength was low. No. 32 was not subjected to the precursor treatment before the aging treatment, so the precipitation of the fine second phase particles was insufficient and the strength was low. In No. 33, since the aging treatment temperature was too low, precipitation of fine second phase particles was insufficient, and the strength was low. In No. 34, the aging temperature was too high, so that the precipitation of fine second phase particles was insufficient and the strength was low. In No. 35, since the slab heating time was short, a large amount of coarse second phase remained before hot rolling, and the solid solution treatment did not fully dissolve, so the precipitation amount of fine second phase particles was small. Insufficient strength. In No. 36, since the slab heating temperature was too high, cracks occurred in the hot-rolled ground, and it was not possible to proceed to the subsequent steps. In No. 37, the solution treatment temperature was low, so that the solution of solute atoms was insufficient, the precipitation amount of fine second phase particles was insufficient, and the strength was low. In No. 38, since the total content of Ni + Co was too high, coarse second-phase particles increased, and the amount of fine second-phase particles was insufficient, and the strength was low. No. 39 had a low Ni + Co total content, so the amount of fine second phase particles deposited was insufficient and the strength was low. In No. 40, since the Si content was too high, the number of coarse second-phase particles increased, and the amount of fine second-phase particles was insufficient, and the strength was low. In No. 41, since the diameter of the work roll used in the finish cold rolling was too large, a thin plate material of less than 50 μm could not be obtained, and the subsequent steps were stopped. In No. 42, since the diameter of the work roll used in the finish cold rolling was too small, the maximum crossbow and I-unit became large. In No. 43, the tension at low temperature annealing was too large, so the maximum crossbow was large. No. 44 had a small maximum crossbow and I-unit because the tension at low temperature annealing was small. In No. 45, the strength decreased because the temperature of the low-temperature annealing was too high. No. 46 had a large maximum crossbow and I-unit because the low-temperature annealing temperature was low. In No. 47, the strength was lowered because the low-temperature annealing time was too long. In No. 48, the time for low-temperature annealing was short, so the maximum crossbow and I-unit were large. In No. 49, the maximum temperature rise rate during low-temperature annealing was too large, so that the maximum crossbow and I-unit became large. In No. 50, since the maximum cooling rate in the low-temperature annealing was too large, the maximum crossbow and I-unit became large.

Next, the solder wettability of the sample material of the present invention example No. 1 and the commercially available titanium copper plate material (manufactured by DOWA Metanics Co., Ltd., C1990) was investigated. The test was conducted by immersing the material in a solder bath and then pulling it up and measuring the solder wet area ratio. The test conditions are as follows.
(Solder wettability test conditions)
-Test piece size: width 10mm x length 60mm
Solder bath composition: 3.0% by mass Ag-0.5% by mass Cu-balance Sn
・ Flux: 25% rosin, 75% IPA
・ Immersion speed: 20mm / sec
・ Immersion time: 5 sec
・ Immersion depth: 40mm

  As a result, the solder wet area ratio is 99% or more for the plate material of Invention Example No. 1 and less than 95% for the plate material of commercially available titanium copper, and the plate material of the present invention has better solder wettability than the titanium copper plate material. Was confirmed.

Claims (5)

In mass%, the total of Ni and Co: 2.50 to 4.00%, Co: 0.50 to 2.00%, Si: 0.50 to 1.50%, Fe: 0 to 0.50%, Mg: 0 to 0.10%, Sn: 0 to 0.50%, Zn: 0 to 0.15%, B: 0 to 0.10%, P: 0 to 0.10%, REM (rare earth element) : 0 to 0.10%, the total content of Cr, Zr, Hf, Nb and S is 0 to 0.05%, and has a chemical composition consisting of the remainder Cu and inevitable impurities, Among the second phase particles present in the sample, the number density of “fine second phase particles” having a particle diameter of 5 to 10 nm is 1.0 × 10 ⁹ particles / mm ² or more, The sheet width W ₀ is 50 mm or more, the sheet thickness is 15 μm or more and less than 100 μm, the maximum crossbow q _MAX defined in (A) below is 250 μm or less , and the 0.2% proof stress in the rolling direction is 10 A copper alloy sheet material of 00 MPa or more .
(A) a copper alloy thin sheet from the rolling direction length 50mm, perpendicular to the rolling direction length is taken off plate P rectangular a plate width W ₀ (mm), still perpendicular to the rolling direction 50mm pitch the cutting plate P in cutting, in which, when a direction perpendicular to the rolling direction length occurs in the direction perpendicular to the rolling direction end portion of the small pieces cut plate P less than 50mm except the piece, n (n is the plate width W _0/50 A square sample of 50 mm square is prepared. However, when W ₀ = 50 mm, the cut plate P is a square sample. For each n square samples, the crossbow q when placed on a horizontal board is determined according to the measuring method (however, w = 50 mm) by the three-dimensional measuring device specified in Japan Technical Standard JCBA T320: 2003. Both surfaces (plate surfaces on both sides) are measured in the direction perpendicular to the rolling direction, and the maximum value of the absolute value | q | of each surface is defined as the crossbow q _i (i is 1 to n) of the square sample. maximum value of the crossbow q ₁ to q _n of n square samples and maximum crossbow q _MAX. The copper alloy sheet material according to claim 1, wherein the I-unit defined in the following (B) is 5.0 or less.
(B) the rolling direction length of a copper alloy thin sheet is 400 mm, perpendicular to the rolling direction length is taken off plate Q rectangle is a plate width W ₀ (mm), placed in a horizontal surface plate. The projected surface of the cut plate Q viewed in the vertical direction is defined as a rectangular region X, and the rectangular region X is further divided into strip-shaped regions at a pitch of 10 mm in the direction perpendicular to the rolling, and the length in the direction perpendicular to the rolling is less than 10 mm. when strip-shaped region of the narrow occurs perpendicular to the rolling direction end portion of the rectangular region X except a strip area of the narrow, strip of the adjacent n points (n is an integer portion of the plate width W _0/10) A region (width 10 mm) is set. For each strip-shaped region, the surface height at the center of the width is measured over the entire length in the rolling direction, and the difference between the maximum height h _MAX and the minimum height h _MIN h _MAX −h _MIN is the wave height h (mm) The elongation difference rate e obtained by the following equation (1) is defined as the elongation difference rate e _i (i is 1 to n) of the strip-shaped region. The maximum value of the elongation difference rates e _{1 to} en of the _n strip-shaped regions is defined as I-unit.
e = (π / 2 × h / L) ² (1)
However, L is the standard length 400mm The copper alloy thin plate material according to claim 1 or 2 , wherein the plate thickness is 15 µm or more and 60 µm or less. In mass%, the total of Ni and Co: 2.50 to 4.00%, Co: 0.50 to 2.00%, Si: 0.50 to 1.50%, Fe: 0 to 0.50%, Mg: 0 to 0.10%, Sn: 0 to 0.50%, Zn: 0 to 0.15%, B: 0 to 0.10%, P: 0 to 0.10%, REM (rare earth element) A slab of copper alloy having a chemical composition of 0 to 0.10%, a total content of Cr, Zr, Hf, Nb, and S of 0 to 0.05% and the balance Cu and unavoidable impurities , at least slab heating, hot rolling, cold rolling, heat treatment prior to aging treatment, aging treatment, finish cold rolling, upon the production of the copper alloy thin sheet by performing the steps of low-temperature annealing in the order of the ,
In the slab heating step, the slab is held at 1000 to 1060 ° C. for 2 hours or more,
In the heat treatment step before the aging treatment, after a solution treatment at 950 to 1020 ° C., a heat history that is maintained at 600 to 800 ° C. for 10 to 300 seconds is given,
In the aging treatment step, the number density of the “fine second phase particles” having a particle diameter of 5 to 10 nm is 1.0 × 10 ⁹ particles / mm by keeping the material having the heat history at 300 to 400 ° C. ^With a metal structure that is ^two or more,
In the finish cold rolling process, using a work roll having a roll diameter of 25 to 45 mm, cold rolling to a plate thickness of 15 μm or more and less than 100 μm,
In the low-temperature annealing step, the temperature is increased at a maximum temperature increase rate of 100 ° C./sec or less, maintained at 250 to 400 ° C. for 25 to 720 seconds while applying a tension exceeding 100 N / mm ² and not more than 150 N / mm ² , and the maximum cooling rate The manufacturing method of the copper alloy sheet material of Claim 1 which heat-processes on the conditions cooled to normal temperature at 100 degrees C / sec or less. The electroconductive spring member which used the copper alloy thin plate material of any one of Claims 1-3 for the material.