JP4810704B2 - Method for producing Cu-Ni-Si-Zn-based copper alloy having excellent resistance to stress corrosion cracking - Google Patents

Description

The present invention relates to a method for producing a Cu—Ni—Si—Zn based copper alloy suitable for electrical / electronic components such as connectors, relays, switches, sockets, lead frames and the like.

  With the recent development of electronics, the electrical wiring of various machines has become more complex and highly integrated, and further reduction in weight and improvement in reliability have been desired for electrical / electronic components such as connectors, relays and switches. Especially for connectors and sockets used in personal computers and mobile phones, space saving and high functionality are progressing at the same time. The copper alloys that make up these current-carrying parts have been reduced in thickness. Therefore, there is a demand for excellent characteristics that can exhibit spring characteristics and reliability equivalent to or better than these materials. Specifically, improvement of “strength” and “spring characteristics” to cope with downsizing and thinning, improvement of “press workability” and “bending workability” to cope with complicated parts shapes, There is a demand for an increase in the amount of energization per unit cross-sectional area and an improvement in “conductivity” to cope with the increase in the speed of electrical signals. Furthermore, in order to improve contact reliability, electrical and electronic parts are often plated with Sn, Ag, Au, etc. depending on the application, and often involve a soldering process. For this reason, it is also important that “plating adhesion” and “solder adhesion” are good. When used as a connector material for automobiles, it is also required to have excellent “stress relaxation resistance” so as to withstand the environment in the engine room.

  In this way, demands for materials are becoming more and more demanding in recent years. However, in order to spread the materials, it is also an important condition that they are inexpensive and can contribute to recycling. In view of cost and recyclability, it is extremely advantageous to adopt an alloy system that can use various types of copper alloy scrap. For example, Ni plating is often applied to connectors used in personal computers and mobile phones, and Sn plating is often applied to small terminals for automobiles. In addition, brass-plated Sn plating materials are often used for automotive applications. If a material excellent in the above characteristics can be developed by an alloy system containing Zn, which is a component of these plated metals and brass, as a component element, it can contribute to cost reduction and recycling promotion through the use of scrap.

  Examples of copper alloys having excellent strength characteristics include phosphor bronze and beryllium copper. Further, Cu—Ni—Si based alloys can be cited as copper alloys whose conductivity, strength, and spring characteristics are improved by precipitating Ni—Si based intermetallic compounds. As materials for springs used for switches, connectors, etc., inexpensive brass, foreign white having excellent spring characteristics and corrosion resistance, or phosphor bronze having excellent spring characteristics are used.

  Patent Document 1 describes that Mg is added based on a Cu—Ni—Si based alloy to improve strength and stress relaxation resistance. Patent Document 2 describes that solderability, plating adhesion, and the like are improved by controlling the size of a Ni—Si intermetallic compound in a Cu—Ni—Si based alloy.

  On the other hand, Patent Documents 3, 4, 5, and 6 describe Cu—Ni—Si—Zn based copper alloys in which Zn is added to Cu—Ni—Si based. Zn is a relatively inexpensive element, and when added to a copper alloy, the solderability is improved and the corrosion resistance is also improved.

JP-A-61-250134 Japanese Patent Laid-Open No. 58-123846 JP 56-90942 A JP-A-2-205645 JP-A-2-205642 JP-A-4-224645

However, phosphor bronze having excellent strength has a low electrical conductivity of, for example, about 12% IAS according to JIS C5210, and improvement in stress relaxation resistance is also desired. Beryllium copper is expensive and difficult to supply stably. The Cu—Ni—Si copper alloy has a relatively good balance of conductivity, strength, and spring characteristics, but it cannot sufficiently meet the strict demands required of current-carrying parts as a thin material. Even with the improved Cu-Ni-Si-based copper alloys added with the third element as in Patent Documents 1 and 2, the bending workability is not always sufficient, and the weakness that brass scrap cannot be effectively used as a raw material There is. In the case of the Cu—Ni—Si—Zn-based copper alloys of Patent Documents 3, 4, 5, and 6, brass scrap can be used. However, since it was originally developed for lead frames, there is a drawback that bending workability is not sufficient. In addition, since the conductivity is reduced by adding Zn and the stress corrosion cracking susceptibility is also increased, it is necessary to keep the additive amount of Zn low in order to apply these disclosed alloys to current-carrying parts such as connectors, The material cost reduction effect due to the addition of Zn cannot be fully enjoyed. In Patent Document 6, the stress corrosion cracking resistance, which is a drawback of conventional brass, is improved by setting the crystal grain size to 15 μm or less, but the tensile strength is 620 N / mm ² or less and sufficient strength is obtained. It is not done.

  The present invention is a copper alloy that basically has the above-mentioned characteristics required for current-carrying parts, and has strength, conductivity, bending workability, and solder wettability in order to meet the recent severe requirements accompanying the thinning of materials. In addition, the aim is to develop and provide a copper alloy that simultaneously improves the stress corrosion cracking resistance and is advantageous in terms of cost reduction and recycling.

  As a result of detailed studies by the inventors, the above object is to appropriately control the amount of Si dissolved in the matrix and to form a finely precipitated Ni—Si based precipitate. Could be achieved.

That is, in the present invention, by mass, Ni: 0.4 to 4.5%, Si: 0.15 to 0.9%, Zn: 5 to 15% are contained, and Sn: 2. Contains at least one of 0% or less, P: 0.2% or less, Fe: 1.0% or less, Mg: 0.5% or less, Co: 4.0% or less, Cr: 4.0% or less And the balance is substantially Cu, the Si solid solution index Z of the following formula (1) is 0.55 to 0.9, and the tensile strength is 650 N / mm ² or more, Preferably, a method for producing a copper alloy having an electrical conductivity of 25% IACS or more is provided.
Z = (ab) / (cb) (1)

However,
a: Measured conductivity (% IACS) of measured material,
b: Calculated conductivity (% IACS) when all of Si is solid-solved. By substituting the content of each alloy element converted to atomic% into the following formula (3), the following formula (2) P value determined by
c: Calculated conductivity (% IACS) when all of Si is deposited, Ni content (mass%) is changed to Ni _A (mass%) of the following formula (4), Si content (mass%) the after having corrected each of the following (5) Si _a (mass%) of the equation defined by the following equation (2) by substituting the content of each alloying element is converted to atomic% in the following equation (3) p-value,
It is.
p = 17.24 / ρ _S × 100 (2)
ρ _S = 17.24 + (12.2 × Ni (at%) + 39.5 × Si (at%) + 3 × Zn (at%) + 28.8 × Sn (at%) + 67 × P (at%) + 96. 6 × Fe (at%) + 6 × Mg (at%) + 63 × Co (at%) + 40 × Cr (at%)) − (0.3 × 12.2 × Ni (at%) ² + 4.9 × 39 0.5 × Si (at%) ² + 2.7 × 3 × Zn (at%) ² + 3.2 × 28.8 × Sn (at%) ² + 20 × 96.6 × Fe (at%) ² ) / 100 ...... (3)
Ni _A = Ni (mass%)-2 × (58.69 / 28.09) × Si (mass%) However, when Ni _A <0 in the above formula, Ni _A = 0 (4) )
Si _A = Si (mass%) − (1/2) × (28.09 / 58.69) × Ni (mass%) However, when Si _A <0 in the above formula, Si _A = 0 is set. ...... (5)
Here, Ni (mass%) and Si (mass%) are the Ni content and Si content in the alloy expressed by mass%, respectively.

Here, among the additive elements Sn, P, Fe, Mg, Co, and Cr, 0 (zero) is substituted for the element in the above formula (3) for the additive element.
The following values are used as the atomic weight of each element for conversion between mass% and atomic%.
Cu; 63.55, Ni; 58.69, Si; 28.09, Zn; 65.39, Sn; 118.71, P; 30.97, Fe; 55.85, Mg; 24.31, Co; 58.93, Cr; 52.00
The constant 17.24 in the equations (2) and (3) corresponds to the specific resistance value of pure copper at a temperature of 273K. The constant applied to the content of each element in the formula (3) represents a contribution to the electrical resistance per unit concentration of each solute element at a temperature of 273 K (JO Linde: Helvetica physia acta. 41 ( 1968), 1013).

The method for producing a copper alloy of the present invention can be produced by a copper alloy production process combining solution treatment and aging treatment, and in particular, an intermediate material in which the Si solid solution index Z in the formula (1) is 0.3 or less. the make, then, is due to the method of adjusting the same Z by the aging treatment for the intermediate material to from 0.55 to 0.9.

More specifically, the solution-treated material is subjected to cold rolling of 60% or less so that the Si solid solution index Z in the formula (1) is 0.3 or less, and then a temperature of 380 to 550 ° C. it adjusts the Z to from 0.55 to 0.9 by performing aging treatment to slow cooling is below average cooling rate 5 ° C. / min up to a temperature range of the heating retention after 0.99 ° C. or less in range. As said solution treatment conditions, the conditions of cooling so that the average cooling rate from 650 degreeC to 250 degreeC may be 200 degreeC / min or more after heat-maintaining within the range of 650-850 degreeC can be employ | adopted. After the aging treatment, cold rolling can be performed, and further strain relief annealing can be performed at 250 to 500 ° C. for 20 seconds to 10 minutes.

  According to the present invention, in a copper alloy having basic characteristics necessary for electrical and electronic parts such as connectors, relays, switches, etc., strength, conductivity, bending workability, and stress corrosion cracking resistance are simultaneously simultaneously at a high level. It became possible to improve. This copper alloy can meet the recent severe requirements accompanying the thinning of the material. Moreover, the effect of reducing the raw material cost by containing a relatively large amount of Zn is high, and furthermore, copper alloy scrap having Ni plating or Sn plating, or brass scrap containing Zn can be used as a raw material, so that recyclability is also excellent. Therefore, the present invention contributes to reducing the size and weight of electric / electronic devices, improving performance and reliability, and reducing costs.

[Si solid solution index Z]
In the present invention, a Cu—Ni—Si—Zn based copper alloy is employed. In the alloy system, the strength is usually increased by generating Ni-Si-based precipitates. In addition, the conductivity and thermal conductivity are improved by the formation of precipitates. Precipitates formed by Ni and Si are considered to be mainly Ni ₂ Si intermetallic compounds. In the present invention, basically, the strength and conductivity are improved. However, the added Ni and Si are not necessarily all precipitated by the aging treatment, and to some extent, they are present in a solid solution state in the Cu matrix. According to detailed studies by the inventors, it has been found that this solute Si is extremely effective in improving the stress corrosion cracking resistance. Therefore, in order to improve the strength, conductivity, and stress corrosion cracking resistance at the same time in a well-balanced manner, it is important to disperse fine Ni—Si-based precipitates that are effective in improving the strength while securing the amount of dissolved Si. .

  The Si solid solution index Z defined by the formula (1) is an index for evaluating the amount of Si dissolved in the matrix of the Cu—Ni—Si—Zn based copper alloy from the value of conductivity. It is not always easy to directly and accurately measure the amount of solute Si in the matrix in a structure state in which Ni-Si based precipitates are finely dispersed. In addition, it is difficult to calculate the amount of dissolved Si in the matrix by measuring the amount of precipitates. On the other hand, the amount of dissolved Si is greatly reflected in the electrical conductivity. However, since the conductivity value itself varies depending on the alloy composition, it is necessary to take into account the influence of the alloy composition in order to evaluate the amount of dissolved Si based on the conductivity. The Si solid solution index Z takes this point into consideration.

Assuming that the Si contained in the alloy is completely dissolved in the matrix, then the conductivity affected by Si is the lowest. On the other hand, if it is assumed that the entire amount of Si (but the maximum amount capable of forming Ni ₂ Si) is deposited, then the conductivity affected by Si is the highest. In the equation (1), the denominator corresponds to the maximum fluctuation range of the conductivity affected by the Si content, so this can be considered as the fluctuation range of the Si solid solution amount. Since the molecule is the difference in conductivity between the actual material (material to be measured) and the material (the material with the lowest conductivity) that is assumed to have dissolved all of Si, this is the actual amount of Si dissolved in the material. It is a value that reflects the degree. In other words, the Si solid solution index Z expressed by the equation (1) indicates the position of the Si solid solution amount in the matrix on the scale representing the fluctuation range of the Si solid solution amount in an alloy having a certain Si content. It is an index showing. Therefore, it is possible to know the degree of the amount of Si solid solution in the actual material (material to be measured) from Z. The smaller Z is, the more Si is dissolved, and the larger Z is, the more Si is precipitated. However, the evaluation of the Si solid solution amount based on the Z value can be applied to an alloy having a Ni content of 0.4% by mass or more and a Si content of 0.15% by mass or more.

  As described above, in the alloy system, the stress corrosion cracking resistance is improved by securing a solid solution Si amount. That is, the smaller the Si solid solution index Z, the better the stress corrosion cracking resistance. On the other hand, if Z is too small, the conductivity is lowered, and the amount of Ni—Si precipitates is insufficient, so that the strength level is also lowered. For this reason, Z being in an appropriate range after the aging treatment is a necessary condition for simultaneously improving strength, conductivity, and stress corrosion cracking resistance. However, the strength level does not improve if only the amount of precipitates is secured. This is because the size and dispersion form of the precipitates have a great influence. Therefore, as a result of further investigation, the inventors have sufficiently dissolved Si in a state after the solution treatment, that is, before the aging treatment, and then applied the aging treatment, thereby finely forming the Ni-Si-based precipitates. It has been found that dispersion is ensured and that strength can be stably improved.

  Specifically, a structure state in which the Si solid solution index Z is 0.3 or less is formed after the solution treatment. Thereafter, an aging treatment is performed to realize a precipitation state in which Z is in the range of 0.55 to 0.9, preferably in the range of 0.6 to 0.9. In the structure obtained through such a process, the strength, conductivity, and stress corrosion cracking resistance are simultaneously and stably improved.

[Alloy composition]
Ni and Si form precipitates and contribute to an increase in strength and an improvement in conductivity and thermal conductivity. In order to obtain the effect sufficiently, it is necessary to contain at least 0.4% by mass of Ni and 0.15% by mass of Si. However, if the content of these elements is too large, precipitates are likely to be coarsened particularly at the grain boundaries, leading to a decrease in bending workability. As a result of various studies, it is desirable to contain Ni in a range of 4.5% by mass or less and Si in a range of 0.9% by mass or less. Therefore, the Ni content is preferably in the range of 0.4 to 4.5 mass%, more preferably 1.5 to 3.5 mass%. The Si content is desirably 0.15 to 0.9 mass%, and more preferably 0.3 to 0.6 mass%.

It is desirable that the content ratio of Ni and Si is as close as possible to the composition ratio of the precipitate Ni ₂ Si. Therefore, in the present invention, it is preferable to adjust the Ni / Si ratio expressed in mass% to a range of 3.5 to 5.5.

  Zn has an effect of improving strength and solderability. When Zn is added, the color of the material changes from copper (reddish brown) to brass (golden), so that a decorative effect is exhibited and scrap separation is facilitated. Further, by containing a relatively large amount of Zn as an alloy element, there is an advantage that inexpensive brass scrap can be used as a raw material. If the Zn content is less than 5% by mass, the use of brass scrap is greatly restricted, and it is difficult to distinguish it from copper in terms of color. As a result of various studies, the inventors have found that even when a relatively large amount of Zn of 5% by mass or more is contained, sufficient conductivity can be ensured by the manufacturing method described later. On the other hand, if the Zn content exceeds 15% by mass, it will be difficult to ensure sufficient conductivity even if the production conditions are optimized, and bending workability and stress corrosion cracking resistance will be reduced. Use is limited. As for Zn content, it is desirable to set it as the range of 5-15 mass%, and 6-9 mass% is more preferable.

  Sn is an element effective for improving strength and stress relaxation resistance. In order to sufficiently bring out these effects, it is desirable to secure an Sn content of 0.001% by mass or more, and more preferably 0.03% by mass or more. Further, by using Sn as an alloy component, Sn plating scrap can be used, which is advantageous for cost reduction. In particular, by using both Zn and Sn as alloy components, it is possible to use brass Sn-plated scrap, and the raw material cost reduction effect and the recyclability improvement effect are further enhanced. On the other hand, Sn content exceeding 2.0% by mass is not preferable because it causes deterioration of conductivity, bending workability and hot rolling property. When it contains Sn, it is desirable to set it as the range of 0.01-2.0 mass%, It is more preferable to set it as 0.03-2.0 mass%, It is 0.05-0.5 mass%. More preferably.

  P has an effect as a deoxidizer and improves castability. In order to sufficiently obtain the effect, it is desirable to secure a P content of 0.005% by mass or more. However, when the P content exceeds 0.2% by mass, the conductivity is significantly lowered. Therefore, when P is contained, the content is preferably 0.005 to 0.2% by mass.

  Fe is an element exhibiting solid solution strengthening, and it is desirable to secure a content of 0.005% by mass or more in order to fully exert its action. However, if the Fe content exceeds 1.0% by mass, the electrical conductivity and bending workability may be significantly reduced, which is not preferable. Therefore, when it contains Fe, it is desirable to set it as 0.005 to 1.0 mass%. Note that Fe is an element that is easily mixed from scrap of Cu—Ni—Si alloy, and the Fe content can be adjusted to the above range by using the scrap.

  Mg is effective in improving the hot workability, strength, and stress relaxation resistance, and it is desirable to ensure a content of 0.005% by mass or more in order to fully exert its effects. However, if the Mg content exceeds 0.5% by mass, the electrical conductivity and bending workability may be significantly reduced, which is not preferable. Therefore, when it contains Mg, it is desirable to set it as the range of 0.005-0.5 mass%. In addition, Mg is an element which is easily mixed from the scrap of Cu—Ni—Si alloy like Fe, and the Mg content can be adjusted to the above range by using the scrap.

Co and Cr are both substituted with Ni to form an intermetallic compound with Si and improve the strength of the material. In order to fully exhibit its action, it is desirable to set the content to 0.005% by mass or more in both cases of Co and Cr, and more preferable to set the content to 0.03% by mass or more. However, if any of them is contained in a large amount exceeding 4.0% by mass, bending workability and conductivity are reduced. Therefore, in the case where Co or Cr is contained, in any case, the range is preferably 0.005 to 4.0% by mass, more preferably 0.03 to 4.0% by mass, and more preferably 0.0 to 4.0% by mass. More preferably, it is 05-0.5 mass%.
The optional additive elements Sn, P, Fe, Mg, Cr, and Co may be contained alone or in combination.

〔Characteristic〕
For reliable application to electrical and electronic parts such as connectors, relays, switches, sockets, and lead frames, the tensile strength when a tensile test is performed on the plate material in the rolling direction is 650 N / mm ² or more. It is desirable to exhibit an intensity level. Considering in particular the future stronger increasingly demand for thinner, a tensile strength of 670N / mm ² or more, or 700 N / mm ² or more, or even to exhibit 720N / mm ² or more intensity levels extremely advantageous Become. At the same time, it is desirable that the conductivity be 25% IACS or higher. According to the manufacturing method described later, such excellent characteristics can be realized in the copper alloy composition defined in the present invention.

  Further, considering the processing of various electrical / electronic components, it is desirable that the material has excellent bending workability. Specifically, in a bending process (BW) in which the direction parallel to the rolling direction is the bending axis, the bending processability is such that the minimum bending radius (MBR / t, where t is the plate thickness) is 2.0 or less. It is desirable that it exhibits 1.5 or less, or even 1.0 or less. Alloys with high strength generally have a tendency to decrease bending workability, but in the present invention, an excellent balance of strength-conductivity-bending workability is realized by a combination of solution treatment and aging treatment described later. obtain.

  As other characteristics, the elongation when the tensile test is performed in the rolling direction is preferably 5% or more, more preferably 7% or more, or even more preferably 9% or more. It is also important to have excellent solder wettability and excellent hot workability.

[Production method]
The inventors have conducted a detailed study on a technique for imparting the above excellent characteristics to a Cu—Ni—Si—Zn based copper alloy. As a result, the combination of the “solution treatment” and the “aging treatment” in which the cooling rate after the solution treatment is sufficiently increased and the cooling after the aging treatment is gradually cooled can provide the above characteristics. I found it. A copper alloy material is generally manufactured in a process of applying heat treatment and cold rolling a plurality of times after hot rolling. In the case of a copper alloy using aging precipitation, solution treatment is usually performed in any heat treatment step in the middle, and aging treatment is performed in any heat treatment step performed thereafter. Such a process can also be employed in the production of the copper alloy of the present invention. However, it is important to set the following conditions.

It is desirable that the solution treatment be performed under conditions that ensure a sufficient solid solution amount of Si so that the Si solid solution index Z is 0.3 or less after cooling. For this purpose, the heating temperature and the cooling rate are important. The heating temperature is in the range of 650 to 850 ° C. Although the optimum temperature varies somewhat depending on the alloy composition, the purpose can be achieved by heating to the above temperature range. If a material that has been subjected to approximately 80% or more hot rolling and then approximately 60% or more cold rolling is the target, the holding time in the above temperature range may be 30 min or less. In many cases, good results can be obtained by heating and holding for 10 min or less, for example, 30 sec to 10 min. And when cooling from the said temperature range, the average cooling rate from 650 degreeC to 250 degreeC shall be 200 degrees C / min or more. When this cooling rate is less than 200 ° C./min, a coarse Ni—Si-based precipitated phase is likely to be generated during the cooling process, and the Si solid solution index Z is stably reduced to 0.3 or less after the solution treatment. It becomes difficult. Moreover, bending workability is lowered.
When Z exceeds 0.3 in the state after the solution treatment (that is, the amount of solid solution Si is insufficient), sufficient precipitation strengthening cannot be obtained by the aging treatment in the subsequent step, and Z is finally 0. Even if it is within the proper range of .55 to 0.9, the improvement in strength is insufficient.

  In the aging treatment, a material that has been sufficiently solutionized by the above-described method (that is, Z is 0.3 or less) is maintained in a temperature range of 380 to 550 ° C, preferably 400 to 550 ° C. Although the optimum temperature varies somewhat depending on the alloy composition, appropriate conditions can be found in the above temperature range. The holding time (aging treatment time) may be 20 min to 8 hr, preferably 1 to 5 hr. In the present invention, in the aging treatment, it is important that the cooling after the heating and holding is “slow cooling”. That is, the average cooling rate until the temperature reaches 150 ° C. (from at least 380 ° C.) from the above temperature range is gradually cooled at 5 ° C./min or less. Such a slow cooling process yields more uniform and fine precipitates than in the case of rapid cooling, which leads to a marked improvement in strength and conductivity in the alloy system containing a relatively large amount of Zn. . However, in the alloy of the present invention, solute Si needs to remain in the matrix so that the Si solid solution index Z is in the range of 0.55 to 0.9 after the aging treatment. When Z is less than 0.55, the amount of precipitates is insufficient, resulting in insufficient strength. At the same time, the amount of dissolved Si is too large, resulting in a decrease in conductivity. On the other hand, when Z exceeds 0.9, the amount of dissolved Si in the matrix is insufficient and the stress corrosion cracking resistance is remarkably lowered. Z can be controlled mainly by optimizing the aging temperature and time.

As for the general process, for example, the following manufacturing process can be adopted.
Casting can be performed by semi-continuous casting or continuous casting after melting at 1100 to 1300 ° C. according to a general method for melting a copper alloy containing Zn.

When hot rolling is performed after casting, it is desirable to make the segregation of Sn, Mg, Ni ₂ Si phase, etc. occurring in the cast structure as uniform as possible by heating before hot rolling. Specifically, heating that is maintained for 1 hr or more in a temperature range of 800 ° C. or more that is in a homogeneous solid solution state in an equilibrium state is effective. The heating temperature is preferably 800 to 950 ° C. Hot rolling ends the final pass at a temperature of 650 ° C. or higher, and rapidly cools the temperature range of 650 ° C. or lower by water cooling or the like. After hot rolling, chamfering with an appropriate thickness is performed to remove Ni-Si based coarse precipitates and oxides generated on the surface.
When hot rolling is not performed, it is desirable to perform heat treatment for 2 hours or more at a temperature of 800 ° C. or higher after casting in order to homogenize the structure. The heating temperature is preferably 850 to 900 ° C.

  Next, for example, cold rolling is performed at a processing rate of 60% or more, and then solution treatment is performed at a temperature of 650 to 850 ° C. for 30 minutes or less. At that time, it is important that the average cooling rate until reaching at least 250 ° C. is 200 ° C./min or more as described above. Although it is possible to use the aging treatment directly after the solution treatment, it is more preferable that the aging treatment is performed after cold rolling in the range of 60% or less, preferably 50% or less. In this case, it is particularly effective to secure a cold rolling rate of 15% or more. In addition, if it is the range of said cold rolling rate, the electrical conductivity (namely, Si solid solution parameter | index Z) after solution treatment will be substantially maintained.

  In general, a copper alloy is manufactured by repeating heat treatment and cold rolling. In the present invention, an aging treatment is performed in the first heat treatment performed after the solution treatment. As described above, the aging treatment needs to be performed under conditions involving slow cooling. After the aging treatment, heating above the aging treatment temperature should be avoided so that the resulting precipitate does not change in shape. After the aging treatment, it is desirable to perform final cold rolling as necessary, and then to perform strain relief annealing that is maintained at a temperature of, for example, 250 to less than 500 ° C., preferably 250 to 350 ° C. for 20 seconds to 10 minutes. Thereby, intensity | strength, electroconductivity, bending workability, etc. can be improved further.

A copper alloy having the composition shown in Table 1 was melted using a high-frequency melting furnace, and cast in the air and under a charcoal coating by a semi-continuous casting method to obtain a slab having a thickness of 20 mm. This slab was heated and held at 910 ° C. for 2 hours, extracted, hot-rolled to a thickness of 3 mm, and water-cooled from 700 ° C. after the final pass. The obtained hot-rolled sheet was chamfered to a thickness of 2 mm, and then cold-rolled to 0.5 mm. Thereafter, solution treatment was performed under heating conditions of 650 to 800 ° C. × 20 sec to 5 minutes. For cooling in the solution treatment, the average cooling rate from 650 ° C. to 250 ° C. was controlled to 200 ° C./min or higher by forced air cooling or water cooling. However, in some samples (No. 26), the average cooling rate from 650 ° C. to 250 ° C. was slowed down to about 170 ° C./min by cooling outside the furnace. The cooling rate was measured with a thermocouple attached to the sample surface.
About the material after solution treatment, electrical conductivity was measured based on JISH0505, and Si solid solution index Z after solution treatment was calculated using the above-mentioned formulas (1) to (4).

  Then, after cold rolling to a thickness of 0.35 mm, an aging treatment of 380 to 550 ° C. × 2 to 8 hours was performed. Cooling in the aging treatment was furnace cooling, and the cooling rate in the temperature range from 380 ° C. to 150 ° C. was controlled to 5 ° C./min or less. In Sample No. 12, the aging treatment temperature was 380 ° C., and the others were in the range of 400 to 550 ° C. In No. 24, the cooling rate in the temperature range from 380 ° C. to 150 ° C. was controlled to 10 ° C./min. The cooling rate was measured with a thermocouple. Next, after cold rolling to a thickness of 0.3 mm, strain relief annealing was performed in the range of 400 to 500 ° C. × 20 sec to 5 min.

About each obtained copper alloy board | plate material, tensile strength, elongation, hardness, electrical conductivity, bending workability, solder wettability, and stress corrosion cracking resistance were investigated.
Tensile strength and elongation were measured based on JIS Z2241 using a JIS No. 5 test piece parallel to the rolling direction.
Hardness was measured with a micro Vickers hardness tester on the surface of the plate.
The conductivity was measured based on JIS H0505. Further, from the electrical conductivity, the Si solid solution index Z after the aging treatment was obtained using the above-mentioned formulas (1) to (4).

The bending workability is determined by performing a bending test in which the bending axis is perpendicular to the rolling direction (GW) and parallel direction (BW) by the W bending test method according to JCBA T307 (Japan Copper and Brass Association Standard). Evaluation was performed by MBR / t (t is the plate thickness).
The solder wettability was investigated by a method according to JIS C0053, immersed in an inactive rosin flux for 5 seconds, and then immersed in a 215 ° C. solder (60% Sn-40% Pb) bath for 3 seconds. % (Good) and less than 90% were evaluated as x (bad).

The stress corrosion cracking resistance was examined by a method according to ASTM G37-85, and after performing a bending beam test for 72 hours with a test piece parallel to the rolling direction, the surface of the test piece was washed with acid and water, and an optical microscope was used. The surface of the test piece was observed at a magnification of 50 times, and the case where no cracks were observed was evaluated as ◯ (good), and the case where cracks were observed was evaluated as x (defective).
The results are shown in Table 2.

As can be seen from Table 2, all of the examples of the present invention exhibited high strength with a tensile strength of 650 N / mm ² or more and conductivity of 25% IACS or more. Moreover, the bending workability cleared 2.0 or less in MBR / t value in BW. Furthermore, solder wettability and stress corrosion cracking resistance were also good. Although No. 3 and No. 12 are alloys having the same composition, No. 3 with an aging treatment temperature of 400 ° C. or higher had a greater strength improvement effect than No. 12 with an aging treatment temperature of 380 ° C. .

  On the other hand, Comparative Example No. 21 had a low conductivity because of a large Zn content, and was inferior in bending workability, solder wettability, and stress corrosion cracking resistance. No. 22 and No. 23 had insufficient Si content and Ni content, respectively, so that the strength improvement by Ni—Si based precipitates was insufficient. Since the content of Ni or Si is small, the characteristics cannot be evaluated by the Z value. No. 24 was inferior in conductivity because the cooling rate after the aging treatment was too fast, and the Si solid solution index Z exceeded 0.9. For this reason, strength and stress corrosion cracking resistance were poor. No. 25 is an alloy having the same composition, but the cooling rate in the solution treatment was too slow, so the Si solid solution index Z after the solution treatment (before the aging treatment) exceeded 0.3, and Z was 0 after the aging treatment. The strength level was low despite being in the range of .55 to 0.9. No. 26 was inferior in solder wettability because of low Zn content.

[Calculation example of Si solid solution index Z]
The example of said invention example No. 3 is given and the method of calculating | requiring the Si solid solution parameter | index Z is demonstrated.
[1] Si solid solution index Z after solution treatment
(I) Calculation of electrical conductivity b (% IACS) when Si is completely dissolved In No. 3 of Table 1, the content of each element represented by mass% is Ni (mass%) = 1.99, Si (mass%) = 0.41, Zn (mass%) = 5.13, Sn (mass%) = 0.31 and the balance is Cu, so Cu (mass%) = 100− (Ni (mass%) + Si (mass%) + Zn (mass%) + Sn (mass%)) = 92.16.
This composition is converted from mass% to atomic% without correction. For example, in the case of Ni (at%), the _X atomic weight M X of each element is obtained as follows.
Ni (at%) = 100 × (Ni (mass%) / M _Ni ) / (Cu (mass%) / M _Cu + Ni (mass%) / M _Ni + Si (mass%) / M _Si + Zn (mass%) / M _Zn + Sn (mass%) / M _Sn )
= 100 × (1.99 / 58.69) / (92.16 / 63.55 + 1.99 / 58.69 + 0.41 / 28.09 + 5.13 / 65.39) = 2.15
Similarly for other elements, Si (at%) = 0.92, Zn (at%) = 4.97, and Sn (at%) = 0.17. Since the balance is Cu, the atomic% of other elements (Fe (at%), etc.) are all 0 (zero).

Substituting these atomic% values into the equation (3),
ρ _S = 17.24 + (12.2 × Ni (at%) + 39.5 × Si (at%) + 3 × Zn (at%) + 28.8 × Sn (at%) + 67 × P (at%) + 96. 6 × Fe (at%) + 6 × Mg (at%) + 63 × Co (at%) + 40 × Cr (at%)) − (0.3 × 12.2 × Ni (at%) ² + 4.9 × 39 0.5 × Si (at%) ² + 2.7 × 3 × Zn (at%) ² + 3.2 × 28.8 × Sn (at%) ² + 20 × 96.6 × Fe (at%) ² ) / 100
= 17.24+ (12.2 × 2.15 + 39.5 × 0.92 + 3 × 4.97 + 28.8 × 0.17 + 67 × 0 + 96.6 × 0 + 6 × 0 + 63 × 0 + 40 × 0) − (0.3 × 12.2 × 2.15 ² + 4.9 × 39.5 × 0.92 ² + 2.7 × 3 × 4.97 ² + 3.2 × 28.8 × 0.17 ² + 20 × 96.6 × 0 ² ) / 100
= 95.78
Substituting this into the equation (2),
p = 17.24 / ρ _S × 100
= 17.24 / 95.78 × 100
= 18.00
Therefore, b = 18.00.

(Ii) Calculation of electrical conductivity c (% IACS) in the case where all Si is precipitated (in the case where the amount of solid solution is zero) As described above, in No. 3 of Table 1, each represented by mass% Element content is Ni (mass%) = 1.99, Si (mass%) = 0.41, Zn (mass%) = 5.13, Sn (mass%) = 0.31, Cu (mass% ) = 92.16. However, here, the Ni content (mass%) is corrected to Ni _{A according} to the equation (4), and the Si content (mass%) is corrected to Si _{A according} to the equation (5).
From equation (4)
Ni _A = Ni (mass%)-2 × (58.69 / 28.09) × Si (mass%)
= 1.99-2 × (58.69 / 28.09) × 0.41
= 0.28
From equation (5)
Si _A = Si (mass%)-(1/2) × (28.09 / 58.69) × Ni (mass%)
= 0.41-(1/2) x (28.09 / 58.69) x 1.9.
= -0.07
Since this calculated value is negative, from the proviso in equation (5),
Si _A = 0
It becomes. Therefore, in the procedure of (i) described above, when p in equation (2) is obtained by the same method except that Ni (mass%) is changed to 0.28 and Si (mass%) is changed to 0, the p becomes It becomes the value of c.

Specifically, first, when mass% is converted to atomic%, Ni (at%) = 0.30, Si (at%) = 0, Zn (at%) = 5.00, Sn (at%) = It is obtained as 0.17. Since the balance is Cu, the atomic% (Fe (at%), etc.) of other elements are all 0 (zero).
Substituting these atomic% values into the equation (3),
ρ _S = 17.24 + (12.2 × Ni (at%) + 39.5 × Si (at%) + 3 × Zn (at%) + 28.8 × Sn (at%) + 67 × P (at%) + 96. 6 × Fe (at%) + 6 × Mg (at%) + 63 × Co (at%) + 40 × Cr (at%)) − (0.3 × 12.2 × Ni (at%) ² + 4.9 × 39 0.5 × Si (at%) ² + 2.7 × 3 × Zn (at%) ² + 3.2 × 28.8 × Sn (at%) ² + 20 × 96.6 × Fe (at%) ² ) / 100
= 17.24 + (12.2 × 0.30 + 39.5 × 0 + 3 × 5.00 + 28.8 × 0.17 + 67 × 0 + 96.6 × 0 + 6 × 0 + 63 × 0 + 40 × 0) − (0.3 × 12.2 × 0) .30 ² + 4.9 × 39.5 × 0 ² + 2.7 × 3 × 5.00 ² + 3.2 × 28.8 × 0.17 ² + 20 × 96.6 × 0 ² ) / 100
= 38.74
Substituting this into the equation (2),
p = 17.24 / ρ _S × 100
= 17.24 / 38.74 × 100
= 44.50
Therefore, c = 44.50.

(Iii) Calculation of Z From Table 2, the conductivity a after the solution treatment of No. 3 is 23.4 (% IACS).
Substituting a = 23.4, b = 18.00, and c = 44.50 into the equation (1),
Z = (a−b) / (c−b)
= (23.4-18.00) / (44.50-18.00)
= 0.20
Therefore, the Si solid solution index Z after the solution treatment of No. 3 was calculated to be 0.20.

[2] Si solid solution index Z after aging treatment
B and c for substituting into the equation (1) are the same as those in the above [1].
Moreover, from Table 2, the electrical conductivity a after the aging treatment of No. 3 is 35.1 (% IACS).
Substituting a = 35.1, b = 18.00, and c = 44.50 into the equation (1),
Z = (a−b) / (c−b)
= (35.1-18.00) / (44.50-18.00)
= 0.65
Therefore, the Si solid solution index Z after the aging treatment of No. 3 was calculated as 0.65.

Claims (6)

The composition is composed of Ni: 0.4 to 4.5%, Si: 0.15 to 0.9%, Zn: 5 to 15%, the balance Cu and unavoidable impurities, and the following (1) A method for producing a copper alloy having a Si solid solution index Z of 0.5 to 0.9 and a tensile strength of 650 N / mm ² or more, wherein the Si solid solution index Z of the following formula (1) Is subjected to cold rolling of 60% or less, and then heated and maintained in a temperature range of 380 to 550 ° C. and then an average cooling rate of 5 to 150 ° C. or less. The manufacturing method of the said copper alloy which adjusts the said Z to 0.55-0.9 by giving the aging treatment which anneals slowly at degrees C / min or less.
Z = (ab) / (cb) (1)
However,
a: Measured conductivity (% IACS) of measured material,
b: Calculated conductivity (% IACS) when all of Si is solid-solved. By substituting the content of each alloy element converted to atomic% into the following formula (3), the following formula (2) P value determined by
c: Calculated conductivity (% IACS) when all of Si is deposited, Ni content (mass%) is changed to Ni _A (mass%) of the following formula (4), Si content (mass%) the after having corrected each of the following (5) Si _a (mass%) of the equation defined by the following equation (2) by substituting the content of each alloying element is converted to atomic% in the following equation (3) p-value,
It is.
p = 17.24 / ρ _S × 100 (2)
ρ _S = 17.24 + (12.2 × Ni (at%) + 39.5 × Si (at%) + 3 × Zn (at%) + 28.8 × Sn (at%) + 67 × P (at%) + 96. 6 × Fe (at%) + 6 × Mg (at%) + 63 × Co (at%) + 40 × Cr (at%)) − (0.3 × 12.2 × Ni (at%) ² + 4.9 × 39 0.5 × Si (at%) ² + 2.7 × 3 × Zn (at%) ² + 3.2 × 28.8 × Sn (at%) ² + 20 × 96.6 × Fe (at%) ² ) / 100 ...... (3)
Ni _A = Ni (mass%)-2 × (58.69 / 28.09) × Si (mass%) However, when Ni _A <0 in the above formula, Ni _A = 0 (4) )
Si _A = Si (mass%) − (1/2) × (28.09 / 58.69) × Ni (mass%) However, when Si _A <0 in the above formula, Si _A = 0 is set. ...... (5)
Here, Ni (mass%) and Si (mass%) are the Ni content and Si content in the alloy expressed by mass%, respectively. The copper alloy is further Sn: 2.0% or less, P: 0.2% or less, Fe: 1.0% or less, Mg: 0.5% or less, Co: 4.0% or less, Cr: 4. The method for producing a copper alloy according to claim 1, comprising one or more of 0% or less. The copper alloy is further Sn: 0.01-2.0%, P: 0.005-0.2%, Fe: 0.005-1.0%, Mg: 0.005-0.5%, 2. The method for producing a copper alloy according to claim 1, comprising at least one of Co: 0.005 to 4.0% and Cr: 0.005 to 4.0%. The method for producing a copper alloy according to claim 1, wherein the copper alloy has a conductivity of 25% IACS or more. Solution treatment, the material after holding in 650 to 850 ° C., in either 650 from claims 1 to 4 average cooling rate until 250 ° C. is made in conditions of cooling so that 200 ° C. / min or more The manufacturing method of the copper alloy of description. The method for producing a copper alloy according to any one of claims 1 to 5 , wherein cold rolling is performed after the aging treatment, and then stress relief annealing is performed at 250 to 500 ° C for 20 seconds to 10 minutes.