JP2009242881A - Titanium copper for electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide titanium copper in which the roughening of a bent part can be suppressed without refining crystal grains over the whole of the material. <P>SOLUTION: A copper alloy is disclosed for an electronic component having a composition comprising, by mass, 2 to 4% Ti, and comprising one or more selected from the group consisting of Mn, Fe, Co, Ni, Cr, V, Nb, Mo, Zr, Si, B and P as the third element group by 0.05 to 0.5% in total, and the balance copper with inevitable impurities, and in the average major axis (a) of the crystals in the rolling face of the copper alloy, the relation of 1<a/b is valid with the average major axis (b) of the crystals at the inside of ≥10 μm from the rolling face. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to titanium copper for electronic components, and more particularly to titanium copper for connectors.

  In recent years, electronic devices typified by portable terminals and the like have been increasingly miniaturized, and accordingly, connectors used therefor have a tendency of narrow pitch and low profile. The smaller the connector, the narrower the pin width and the smaller the folded shape, so the material used must have high strength to obtain the necessary spring properties and excellent bending workability that can withstand severe bending work. It is done.

  In this regard, a copper alloy containing titanium (hereinafter referred to as “titanium copper”) has a relatively high strength and the best stress relaxation characteristics among copper alloys. It has been used for a long time as a signal system terminal material. Titanium copper is an age-hardening type copper alloy. Specifically, when a supersaturated solid solution of Ti, which is a solute atom, is formed by solution treatment and heat treatment is performed at a low temperature for a relatively long time from that state, a modulation structure that is a periodic variation of Ti concentration in the matrix phase Develops and strength increases. Based on this strengthening mechanism, various methods have been studied with the aim of further improving the properties of titanium copper.

It is known that it is effective to make crystal grains fine for improving the strength and bending workability of titanium copper, and there are several patent documents relating to this. For example, a technique focusing on the composition of second phase particles precipitated by adding a small amount of a third element such as Pb or Zn (Japanese Patent Laid-Open No. 2004-176163), a technique focusing on crystal grain variation (Patent No. 3924505). No.), a technique focusing on the area ratio of the second phase particles existing in the crystal grain boundary (Japanese Patent Laid-Open No. 2005-97639), and a technique focusing on the density of the second phase particles existing in the crystal grains (specialty). No. 2005-97638) is published.
JP 2004-176163 A Japanese Patent No. 3924505 JP 2005-97639 A JP-A-2005-97638

The conventional evaluation method for bending workability was whether or not a crack would occur when bent. This is because the bent part of the connector is a part where stress is concentrated at the time of fitting, and if this part is cracked, the contact pressure as designed cannot be obtained and the reliability in relaying is impaired.
However, in the future, it is considered that even the presence or absence of rough skin, which is a stage before the occurrence of cracks, is to be evaluated. When rough skin occurs, the plate thickness becomes non-uniform, so the thinner the pin, the more the contact pressure is affected. In other words, in connectors used in electronic devices such as mobile phones that are extremely light and thin, connector pins having a plate thickness of 0.1 mm or less and a pin width of 0.2 mm or less are becoming mainstream. When manufacturing connectors, rough skin cannot be ignored.
Furthermore, the bent portion may become a contact portion for the sake of space saving. The contact portion is often subjected to gold plating from the viewpoint of reducing contact resistance and corrosion resistance. Conventionally, the gold plating thickness is generally about 0.1 to 0.2 μm. However, since gold is an expensive metal, it tends to become thinner year by year. If rough skin occurs when the gold-plated portion is bent, the concave portion is a new surface, so that a step is generated on the gold-plated surface, and the substrate is exposed, so that the corrosion resistance is deteriorated.
Therefore, it has become important as a bendability required for a material for a small connector that not only the crack does not occur but also the rough skin does not easily occur.

  In bending of copper alloy, it has been found that refinement of crystal grains is effective to reduce the rough surface of the bent portion. Therefore, it is considered that if the prior art described in the background art column is used, it is possible to refine the crystal grains even if there is a limit. However, until now, the aim has been to uniformly refine crystal grains throughout the entire titanium-copper material. However, although it is necessary to lower the heating temperature during the solution treatment in order to refine the crystal grains of the entire material, coarse second-phase particles (stable phase) are likely to be generated. Coarse precipitates are undesirable because they adversely affect the mechanical properties of the material.

  Then, the subject of this invention is providing the titanium copper which can suppress the rough skin of a bending part, without refining a crystal grain over the whole material.

  As a result of intensive studies to solve the above problems, the present inventor has found that if the crystal grains can be refined only in the vicinity of the surface, rough skin tends to hardly occur when bent. In other words, even if the crystal grains of the entire material are not miniaturized, the occurrence of rough skin can be prevented as long as even the surface portion having a large plastic flow when bent is finely refined. And in the case of titanium copper, it discovered that such a structure | tissue form was realizable by performing a solution treatment in the reducing atmosphere containing nitrogen. Further, it was also found that the titanium copper subjected to such treatment hardly causes tool wear in press working.

  This invention completed based on the above knowledge contains 2-4 mass% of Ti in one side surface, Mn, Fe, Co, Ni, Cr, V, Nb, Mo, Zr, as 3rd element group, A copper alloy for electronic parts comprising 0.05 to 0.5% by mass in total of one or more selected from the group consisting of Si, B and P, comprising the balance copper and unavoidable impurities, The average major axis (a) of the crystal on the rolled surface of the copper alloy is a copper alloy for electronic parts in which a relationship of 1 <a / b is established with the average major axis (b) of the crystal 10 μm or more inside the rolled surface.

  In one embodiment of the copper alloy for electronic parts according to the present invention, the surface is nitrided.

  In another embodiment of the copper alloy for electronic parts according to the present invention, the average crystal grain size of the crystal 10 μm or more from the rolling surface is a circle when observed from a cross section in the thickness direction parallel to the rolling direction. The equivalent diameter is 2 to 10 μm.

  In still another embodiment of the copper alloy for electronic parts according to the present invention, the average crystal grain size of the rolled surface is 1 to 5 μm in terms of an equivalent circle diameter when observed from the rolled surface.

  In still another embodiment of the copper alloy for electronic parts according to the present invention, a relationship of 0.4 ≦ a / b ≦ 0.8 is established.

  In still another embodiment of the copper alloy for electronic parts according to the present invention, the maximum value of the N concentration in the parent phase of the rolled surface is 10 to 200 ppm.

  In another aspect of the present invention, a copper product including the above-described copper alloy.

  In another aspect, the present invention is an electronic component comprising the above copper alloy.

  Another aspect of the present invention is a connector including the above copper alloy.

  As described above, according to the present invention, it is possible to suppress roughening of the bent portion of the titanium copper without refining crystal grains throughout the material.

If the Ti content Ti is less than 2% by mass, a sufficient strengthening mechanism cannot be obtained due to the formation of the original modulation structure of titanium copper. On the contrary, if the Ti content exceeds 4% by mass, coarse TiCu ₃ Tends to precipitate, and the strength and bending workability tend to deteriorate. Therefore, the content of Ti in the copper alloy according to the present invention is 2 to 4% by mass, preferably 2.7 to 3.5% by mass. Thus, by optimizing the Ti content, both strength and bending workability suitable for electronic components can be realized.

Third element The third element contributes to the refinement of crystal grains. The present invention is particularly characterized by the refinement of crystal grains on the surface layer. However, in order to obtain basic characteristics that can be used as an electronic component, it is desirable that the internal structure is also refined to a certain extent. Therefore, a predetermined third element is added.

The effect of adding the third element is that crystal grains are easily refined even when solution treatment is performed at a high temperature at which Ti is sufficiently dissolved. In addition, since the content of the element dissolved in the matrix is negligibly small because the third element is precipitated as the second phase particles, the concentration wave of titanium formed in the matrix is There will be no disturbance in wavelength and amplitude. Furthermore, there is an effect of suppressing precipitation of TiCu ₃ . Therefore, the original age hardening ability of titanium copper can be obtained.

  In titanium copper, Fe has the highest effect. And in Mn, Co, Ni, Si, Cr, V, Nb, Mo, Zr, B and P, an effect similar to Fe can be expected, and even if added alone, the effect can be seen, but two or more kinds are added in combination May be.

  When these elements contain a total of 0.05% by mass or more, the effect appears. However, when the total exceeds 0.5% by mass, the solid solubility limit of Ti is narrowed and coarse second-phase particles are precipitated. It becomes easy and the strength is slightly improved, but the bending workability is deteriorated. At the same time, the coarse second-phase particles promote roughening of the bent portion and promote die wear during press working. Therefore, in the titanium copper according to the present invention, one or two selected from the group consisting of Mn, Fe, Co, Ni, Cr, V, Nb, Mo, Zr, Si, B and P as the third element group. The total amount is 0.05 to 0.5% by mass.

  A more preferable range of these third elements is 0.17 to 0.23% by mass in Fe, and 0.15 to 0.25% by mass in Co, Ni, Cr, Si, V, Nb, Mn, and Mo, It is 0.05-0.1 mass% in Zr, B, P.

Nitrogen layer on the surface is hard to dissolve nitrogen in pure copper, but in the case of titanium copper, Ti, which has high affinity with nitrogen, is contained as a main component, so in a reducing nitrogen atmosphere, for example, a mixture of nitrogen and hydrogen If heated in a gas atmosphere, it is easily nitrided. And since fine nitride is formed on the surface by nitriding, this significantly hinders the coarsening of grains after recrystallization. Therefore, if the solution treatment is performed in such a reducing nitrogen atmosphere, the crystal grains on the surface of the material can be made finer than the crystal grains inside the material. Therefore, in the titanium copper according to the present invention, the relationship of 1 <a / b is established, where a is the average major axis of the crystal on the rolled surface and b is the average major axis of the crystal 10 μm or more from the rolled surface. The reason for evaluating the difference with the crystal in the interior of 10 μm or more from the rolling surface is that the effect of crystal grain refinement due to nitriding is hardly exerted if it is 10 μm or more away from the rolling surface.
The major axis is the grain size in the rolling direction, a can be measured by observing the material from the rolling surface, and b can be measured by observing the material from a cross section in the thickness direction parallel to the rolling direction ( (See FIG. 1). The degree of nitriding can be basically increased with an increase in the nitrogen partial pressure in the atmosphere during the solution treatment, and a / b can be lowered accordingly. However, Ti nitride is stable, and once formed, it does not dissolve in copper, so it does not contribute to the formation of the modulation structure, so it is better to avoid excessive nitridation. In addition, if the difference between the crystal grain size of the surface and the crystal grain size of the internal structure is too large, when bending is performed, a stress concentration part is generated at the boundary surface, and in some cases, a bending crack is generated. Therefore, it is not preferable. Considering this point, a / b is preferably 0.4 to 0.8, and more preferably 0.5 to 0.7.

  The degree of nitriding can also be grasped from the N concentration detected on the material surface. The effect of refining the crystal grain size by nitriding is that when the N concentration distribution is investigated from the surface of the material in the depth direction using a field emission Auger electron spectrometer (FE-AES), the maximum N concentration is 1 mass. When it becomes ppm or more, it appears gradually, and when it is 10 mass ppm or more, it appears remarkably. However, from the viewpoint of avoiding excessive nitriding, the maximum value of the N concentration should not be too high. From such a viewpoint, in the present invention, “the surface is nitrided” means a case where the maximum concentration of N detected on the surface of the material is 1 mass ppm or more. The maximum concentration of N detected on the surface of the material is preferably 10 to 200 ppm by mass, and more preferably 20 to 100 ppm by mass. Note that the maximum value of the N concentration appears generally about 2 to 10 nm from the rolling surface.

When performing grain size bending surface, what causes skin roughness on the bent surface, a non-uniformity of plastic deformation near the surface. The more severe the bending process, the more the roughness of the skin occurs because the difference in the direction of deformation occurs for each crystal grain. However, if the structure in the vicinity of the surface is made finer, grain boundaries that become discontinuous points of deformation increase, so that rough skin becomes inconspicuous. Therefore, the smaller the crystal grains on the surface, the better. Specifically, when the average value of the crystal grain size on the surface is smaller than 5 μm in terms of the equivalent circle diameter when observed from the rolling surface, when bending a connector that is currently in practical use, At a level where no problem occurs. In the near future, more severe bending may be required, and in order to cope with this, the thickness is preferably 3 μm or less. A more desirable level for safety is 2 μm or less. However, as will be described later, since the average grain size of the internal structure is limited to refinement to about 2 μm, even if the crystal grains are further reduced by nitriding the surface, it is actually difficult to make the grain size less than 1 μm. is there. Therefore, the average value of typical surface crystal grains assumed by the present invention is 1 to 5 μm.

If considering only inside of the crystal grain size bendability, there is no problem as long grain only refinement of the surface, to increase the strength, it is necessary to finer crystal grains of the whole material. In other words, the finer the crystal grains, the better the strength and bendability. However, in the solution treatment of titanium copper, even if a trace amount of added elements and solution treatment conditions are optimized, the crystal grain size is controlled to 5 μm or less while suppressing the growth of the stable phase. Is difficult. The reason is that the crystal grains are refined because of the fine precipitation of the stable phase that occurs simultaneously with the recrystallization. If the crystal grains are controlled to 5 μm or less, the precipitation of this phase must be further increased. I must. A large amount of stable phase precipitation at this point has an adverse effect on strength and bendability. If this adverse effect is greater, it will not make sense to make crystal grains finer. The adverse effect due to the large amount of precipitation of the stable phase increases when the crystal grain size is less than 2 μm. In this case, the reverse effect due to the stable phase precipitation is larger than the effect of improving the strength and bendability due to the refinement of crystal grains, and the meaning is lost. In addition, when the average crystal grain size is less than 2 μm, the stress relaxation characteristics deteriorate.

  Therefore, in one embodiment of the copper alloy according to the present invention, the average crystal grain size of the crystal grains within 10 μm or more from the rolling surface is equivalent to the circle equivalent diameter when observed from the cross section in the thickness direction parallel to the rolling direction. And 2 to 10 μm, preferably 3 to 8 μm, more preferably 5 to 7 μm.

Characteristics of the copper alloy according to the present invention The copper alloy according to the present invention can have excellent strength and bending workability. For example, the 0.2% proof stress can be 850 MPa or more, preferably 900 MPa or more, and the MBR / t value that is the ratio of the minimum radius (MBR) to the plate thickness (t) at which cracks do not occur in the W bending test. Can be 2.0 or less, preferably 1.5 or less, and more preferably 1.0 or less.

  In addition, a major feature of the copper alloy according to the present invention is that not only cracks are hardly generated at the outer peripheral portion of the bent portion but also rough skin is hardly generated at the bent portion when bending is performed. As described above, the problem of rough skin at the bending portion becomes more obvious as the connector becomes smaller, and therefore, the material used in such a field is important to bend with little rough skin.

  The rough skin condition on the surface of the bent part when bent can be observed with an optical microscope or SEM, but it is effective to use a confocal laser microscope for quantitative evaluation. With a confocal laser microscope, high-resolution images without blur can be obtained even on uneven surfaces with optically different focal lengths, and three-dimensional information can be reconstructed. Thus, the surface roughness can be analyzed. Since the surface of the bent portion is not a flat surface, the image processing performed here is an operation to process the roughness curve obtained by scanning so that the center line becomes a straight line, and then evaluate each evaluation value such as Ra and Rz. calculate. For easy understanding, FIGS. 2 and 3 are schematic views of a cross-section of a bending portion showing a state in which the rough skin is large and a state in which the rough skin is small.

  The copper alloy strip according to the present invention is obtained by performing the 90 ° W bending test of JIS H 3130 under the condition of Badway, R / t = 1, using the above confocal laser microscope, When the surface roughness is measured, in Ra and Rz defined in JIS B 0601, Ra ≦ 0.20 μm and Rz ≦ 1.00 μm can be obtained.

Furthermore, another major feature of the copper alloy according to the present invention is that the press punchability is good. Specifically, when a connector is processed by a continuous press using the product of the present invention as a raw material, the press mold is not easily worn, and the mold life from polishing to the next polishing is long. One of the causes of mold wear that occurs when pressing titanium copper is to form hard and brittle titanium carbide (TiC) by reacting with the Ti component in the mold material and forming the tool surface It is that the carbon of the carbide that has been taken is deprived, gradually collapse and wear.
However, when the surface of titanium copper is nitrided, nitride (TiN) is stable without being thermally decomposed even at a relatively high temperature, so that what exists as TiN on the surface is in contact with the tool at high temperature and high pressure. However, it is difficult to react with C. Therefore, the titanium copper according to the present invention whose surface is nitrided is hard to progress in mold wear.

  Furthermore, nitrogen has the effect of solid lubrication, and reduces the friction between the area where the shear surface is formed and the side surface of the punch during pressing.

  The copper alloy according to the present invention can be processed into copper products having various plate thicknesses, and as described above, is useful as a material for various electronic components processed by pressing. The copper alloy according to the present invention is excellent as a small spring material requiring particularly high dimensional accuracy, and can be suitably used as a material for a switch, a connector, a jack, a terminal, a relay and the like, although not limited thereto. .

Manufacturing method of copper alloy according to the present invention The copper alloy according to the present invention is known as described in, for example, JP-A-2004-176163, JP-A-2005-97639, JP-A-2005-97638. Although it can be manufactured by combining the surface nitriding process with the titanium copper manufacturing process, suitable manufacturing examples for obtaining the properties such as strength, conductivity, and bendability required for titanium copper for electronic parts Will be described in turn.

1) Ingot manufacturing process Manufacturing of an ingot by melting and casting is basically performed in a vacuum or in an inert gas atmosphere. If the additive element remains undissolved during melting, it does not effectively act on strength improvement. Therefore, in order to eliminate undissolved residue, it is necessary to hold high-melting-point additive elements such as Fe and Cr for a certain period of time after being added and sufficiently stirred. On the other hand, since Ti is relatively easily dissolved in Cu, it may be added after the third element group is dissolved. Therefore, regarding melting, at least one type of Mn, Fe, Co, Ni, Cr, V, Nb, Mo, Zr, Si, B, and P as a third element group is added to an appropriate amount of Cu in total. Add 0.05 to 0.50% by mass and hold 2 to 4% by mass of Ti.

2) Homogenization annealing and hot rolling Here, it is desirable to eliminate solidified segregation and crystallized substances generated during casting as much as possible. This is because, in the subsequent solution treatment, the precipitation of the second phase particles is finely and uniformly dispersed, which is effective in preventing mixed grains.
After the ingot manufacturing process, hot rolling is performed after performing homogenization annealing at 900 to 960 ° C., for example, 950 ° C. for 3 to 5 hours. Titanium copper has a high diffusion rate and plastic fluidity at 900 ° C. or higher, and there is no difference in deformation resistance due to a difference in Ti concentration. Therefore, the segregation layer is divided and homogenization is promoted. In addition, since the titanium is concentrated in the segregation part and has a low melting point, when heated above 960 ° C., a liquid phase appears, and when hot rolling is performed as it is, liquid metal brittleness is generated that cracks at that part. End up. Therefore, the heating temperature of the hot rolling is set to 960 ° C. or lower before hot rolling and during hot rolling, and the pass from the original thickness to the entire workability of 90% is set to 900 ° C. or higher. In order to effectively reduce the segregation of Ti by causing appropriate recrystallization for each pass, the rolling amount per pass is set to 10 mm or more up to a plate thickness of 50 mm, and from the plate thickness of 50 mm or less, 1 A pass schedule is used so that the degree of processing per pass is 20% or more. The amount of reduction per pass is 10 to 15 mm.

3) First solution treatment After that, cold rolling and annealing are repeated as appropriate, followed by solution treatment. The reason why the solution treatment is performed in advance is to reduce the burden in the final solution treatment. That is, in the final solution treatment, it is not a heat treatment for dissolving the second phase particles, but is already in solution, so it is only necessary to cause recrystallization while maintaining that state. Just heat treatment. Therefore, in the final solution treatment, coarsening of recrystallized grains can be suppressed, and uniform fine grains can be obtained. Since the second phase particles are formed when the temperature is low even during the annealing in the middle, the annealing is performed at a temperature at which the second phase particles are completely dissolved. However, it is not preferable to perform at an unnecessarily high temperature because the third element group that has been in solid solution is internally oxidized from the surface layer by oxygen that has entered and diffused from the surface. Therefore, the first solution treatment may be performed at a heating temperature of 850 to 900 ° C. for 3 to 10 minutes. At that time, the heating rate and the cooling rate are increased as much as possible so that the second phase particles do not precipitate. This is because a fine and homogeneous structure can be obtained by performing the final solution treatment after the second phase particles are completely dissolved.

4) Intermediate rolling As the degree of processing in the intermediate rolling before the final solution treatment is increased, the second phase particles in the final solution treatment are precipitated more uniformly and finely. This is because accumulated processing strain becomes a nucleation site for recrystallization. Therefore, when the strain is increased by increasing the degree of processing, a large number of recrystallization nuclei are generated, so that the crystal grains become finer. However, if the final solution treatment is performed with a too high degree of processing, a recrystallized texture develops and plastic anisotropy occurs, which may impair the press formability. Therefore, the processing degree of intermediate rolling is preferably 70 to 99%. The degree of work is defined by {(thickness before rolling−thickness after rolling) / thickness before rolling) × 100%}.

5) Final solution treatment The final solution treatment is the most important step in the present invention. First, the atmospheric gas is a reducing gas containing nitrogen. Specifically, ammonia decomposition gas (25% N ₂ + 75% H ₂ ) is used because it is industrially easy to use. When titanium copper is heated in such an atmosphere, nitriding proceeds from the stage of temperature rise before recrystallization, and very fine titanium nitride (TiN) is formed in the vicinity of the surface. Even when the temperature at which recrystallization occurs is reached, the nitride becomes a resistance to the growth of the recrystallized grains, and as a result, a structure in which the surface crystal grains are particularly fined is obtained. Such solution treatment can be industrially performed in a continuous bright annealing furnace capable of controlling the atmosphere.
Although a large amount of nitrogen is also contained in the atmosphere, when the solution treatment is performed in the atmosphere, the surface oxidation proceeds more strongly, is blocked by a stable oxide film, and nitriding does not proceed at all. Even in a pure nitrogen atmosphere, an oxide film is formed by very little residual oxygen, so that nitriding can hardly be expected. In order to prevent oxidation, it is necessary to make a reducing atmosphere containing hydrogen.
It is desirable that the heating temperature is a temperature at which the precipitate is completely dissolved, but if it is heated to a high temperature until it completely disappears, the crystal grains become coarse, so the heating temperature is around the solid solubility limit of the second phase particle composition. (The temperature at which the solid solubility limit of Ti becomes equal to the addition amount in the range of 2 to 4% by mass of Ti is 730 to 840 ° C., for example, about 800 ° C. when the addition amount of Ti is 3% by mass. ). And if it heats rapidly to this temperature and a cooling rate is also made fast, generation | occurrence | production of coarse 2nd phase particle | grains will be suppressed. Further, the shorter the heating time at the solid solution temperature, the finer the crystal grains. The heating time is illustratively 30 to 60 seconds. If the second phase particles generated at this time are finely and uniformly dispersed, they are almost harmless to strength and bending workability. But the coarse ones are harmful because they tend to grow further in the final aging.
Since it is desirable to rapidly cool after heating, it is important to have a cooling facility with a high cooling rate. The solution of titanium copper is generally water-cooled, but need not be water-cooled if a sufficient cooling rate can be obtained. Here, the sufficient cooling rate means a rate that does not give a gap in which precipitation occurs during temperature reduction, and may be 50 ° C./s or more.

  The cooling rate depends on the heat transfer of the refrigerant, the heat transfer at the interface between the material and the refrigerant, and the heat capacity per unit area of the material. The product of the present invention is targeted for a connector material that is further miniaturized, and often has a thin plate thickness, that is, a small heat capacity per unit area. Therefore, even with a jet coolant system that blows refrigerant gas, a sufficient cooling rate can be obtained by adjusting the flow rate and pressure. However, even when the plate thickness is thin, water cooling is most preferable from the viewpoint of operational stability.

6) Final cold rolling work degree / final aging treatment After the solution treatment step, final cold rolling and aging treatment are performed. The strength of titanium copper can be increased by the final cold working. At this time, if the degree of work is less than 10%, a sufficient effect cannot be obtained, so that the degree of work is preferably 10% or more. However, the higher the degree of work, the more likely grain boundary precipitation occurs in the next aging treatment, so the degree of work is 50% or less, more preferably 25% or less. About aging treatment, precipitation to a grain boundary can be suppressed, so that it is low temperature. Even under conditions where the same strength can be obtained, grain boundary precipitation can be suppressed on the low temperature long time side than on the high temperature short time side. At 420 to 450 ° C., which was an appropriate range in the prior art, the strength is improved as aging progresses, but grain boundary precipitation is likely to occur, and CuTi ₃ which is a stable phase is generated even with slight overaging, resulting in bending workability. Will be reduced. Accordingly, although the appropriate aging conditions vary depending on the additive element, it is usually 1 to 24 hours at 360 to 420 ° C., and preferably 12 to 24 hours at 380 to 400 ° C. It is more preferably 12 to 18 hours at 390 to 400 ° C and 18 to 24 hours at 380 to 390 ° C. For example, it can be set to 400 ° C. × 12 h and 380 ° C. × 24 h.

Next, examples of the present invention will be described, but the present invention is not limited thereto.
When manufacturing the copper alloy of the present invention example, Ti, which is an active metal, is added as the second component, so a vacuum melting furnace was used for melting. In addition, in order to prevent unexpected side effects due to mixing of impurity elements other than the elements defined in the present invention, raw materials having a relatively high purity were carefully selected and used.

  First, no. 1 to 14, Mn, Fe, Co, Ni, Cr, Mo, V, Nb, Zr, Si, B and P were added to Cu in the compositions shown in Table 1, respectively, and Ti having the composition shown in the same table was added. Was added respectively. After sufficient consideration was given to the retention time after the addition so that there was no undissolved residue of the added elements, these were injected into the mold in an Ar atmosphere to produce about 2 kg of ingots.

  The ingot was subjected to homogenization annealing and subsequent hot rolling to obtain a hot rolled sheet having a thickness of 10 mm. After descaling by chamfering, it is cold-rolled to obtain a strip thickness (1.5 to 2.0 mm), and a primary solution treatment with the strip is performed to obtain an intermediate thickness (0.10). To 0.50 mm). Thereafter, it is inserted into an annealing furnace capable of rapid heating to perform a final solution treatment, and after descaling by pickling, it is cold-rolled to a sheet thickness of 0.075 mm and aged in an inert gas atmosphere. It was set as the test piece of the example and the comparative example. Table 1 shows the component composition, homogenization annealing conditions, hot rolling conditions, primary solution treatment conditions with raw strips, final solution treatment conditions, final cold rolling workability, and aging conditions. As shown in ~ 3.

Internal electrolytic polishing the thickness direction of the cross section parallel to the grain size rolling direction, SEM (magnification: 2000) by observing the cross-sectional structure, and count the number of crystal grains per unit area. At this time, the observation visual field was a region separated by 10 μm or more from the surface, and the total observation visual field area was 10,000 μm ² (100 μm × 100 μm) or more. When the straight part of the frame of the observation field crosses the crystal grain, the crystal grain is counted as ½, and when the apex (four corners) of the frame is approaching the crystal grain, It was decided to count as 1/4. Then, when a plurality of locations were counted, the total observation visual field area was summed, and the total area of the observed crystal grains was divided by the sum of the counted crystal grains to calculate the area per crystal grain. From the area, the diameter of a perfect circle having the same area as that area (equivalent circle diameter) was calculated and used as the average crystal grain size. Here, the average crystal grain size was determined from the cross section in the thickness direction parallel to the rolling direction, regardless of the final cold rolling degree, the recrystallization formed in the final solution treatment This is because the area of each crystal grain of the structure is preserved geometrically.

Lightly electrolytic etching the grain size material surface surface, SEM (magnification: 2000) to observe the rolled surface tissue, in the same manner as described above, by counting the number of grains per unit area, average crystal surface The particle size was determined. At this time, the amount of surface corrosion caused by electrolytic etching was set to 1 μm or less.
As described above, in the case of a rolled parallel cross section, the area of each crystal grain formed in the final solution treatment is the same regardless of the degree of processing, but in the case of the surface, Since the film is stretched in the rolling direction in proportion to the degree of rolling, the area of each crystal grain increases accordingly. Therefore, it should be noted that the surface crystal grain size obtained here cannot be simply compared with the above-mentioned average crystal grain size.
Particle size ratio between internal structure and surface structure (a / b)
The structure in the thickness direction parallel to the rolling direction obtained by SEM was subjected to image processing using LUZEX manufactured by Nireco Co., Ltd., and the average value b of the major axis (diameter in the rolling direction) of each particle was obtained. Similarly, the surface texture of the rolling surface observed by SEM was subjected to image processing, and the average value a of the major axis (diameter in the rolling direction) of each particle was obtained. In addition, the observation visual field at this time was set to 10000 μm ² (100 μm × 100 μm) or more similarly to the case of obtaining the average crystal grain size.
Note that a / b is an appropriate evaluation method in considering the particle size ratio between the internal structure and the surface structure. Even if the degree of cold rolling performed after the final solution treatment is different, this ratio is constant. If this value is smaller than 1, the crystal grain size is smaller on the surface than on the internal structure. It means that.

Surface nitrogen concentration field emission Auger electron spectrometer (FE-AES) (JEOL Co., Ltd. model JUNP-7800F) was used to investigate the N concentration distribution in the depth direction from the surface at a sputtering rate of 10 nm / min. The maximum value (maximum concentration part) was measured. The maximum value appears in any test piece in the very vicinity of the surface, and the depth is approximately 2 to 10 nm from the surface. In addition, the measurement location was made into the mother phase and the deposit was avoided. This is because N has a very high affinity with Ti, and therefore tends to concentrate around precipitates with a high Ti concentration, and thus does not have an average value.

Mechanical properties First, a tensile test is performed to measure a 0.2% proof stress in the rolling parallel direction in accordance with JIS Z 2201, and a W-bend test in Badway (the bending axis is the same direction as the rolling direction) in accordance with JIS H 3130. The MBR / t value, which is the ratio of the minimum radius (MBR) at which no cracks occur to the plate thickness (t), was measured.

In accordance with JIS H 3130, the surface roughness of the bent part is subjected to a W-bend test (the bending axis is the same direction as the rolling direction), the surface of the bent part is analyzed with a confocal laser microscope, and Ra and Rz defined in JIS B 0601 are specified. Asked.

Press punchability The press punchability was evaluated by actually punching a large amount of material with a continuous press, and measuring the burr height and fracture surface ratio of the cut part, which varies depending on the wear condition of the mold. Here, the burr height is the height of the protrusion shown in FIG. 4, and the burr becomes higher as the mold is worn. Further, as the mold is worn, the ratio of the shear plane shown in FIG. 5 increases, that is, the fracture surface ratio (plate thickness-length in the plate thickness direction of the shear plane) / plate thickness decreases. Two types were performed, with and without the lubricant.

Other press conditions were as follows.
Mold tool material: SKD11, clearance: 10 μm, stroke: 400 spm FIG. 6 shows a mold set shape used for evaluation. The curvature of four corners is different in a square of about 5 mm on a side, and the curvature radii are 0.05 mm, 0.1 mm, 0.2 mm, and 0.3 mm, respectively. The smaller the radius of curvature, the easier it is to wear because stress concentration occurs during shearing. However, the smaller the radius of curvature is, the more difficult it is to observe because the cut surface shape varies. In addition, it is easier to observe the punched-out side and the punched-out side of the punched-out side. Considering the above, in this evaluation, the corner having a radius of curvature of 0.1 mm on the removal side was observed.

  When there is no lubricant, the difference between the materials becomes remarkable when punched 100,000 times, and when there is a lubricant, the difference between the materials becomes remarkable when punched one million times. The value was adopted as the evaluation value. As the lubricant, G6515 manufactured by Nippon Yasaku Osamu Co., Ltd., which is normally used as a press working oil for copper alloys, is used and applied using the top roll of Futaba Electronics Industry Co., Ltd. / Min. The burr height is measured with a laser displacement meter, the fracture surface ratio is observed with an optical microscope, the length of the sag portion and the shear surface is measured, and (sheet thickness-shear surface) / sheet thickness is determined as the fracture surface ratio. As sought.

  No. 1 (comparison) and No. 1 In No. 2 (Comparative), since the final solution treatment was performed in the air, no nitriding occurred, and the press punchability was at a normal level. Of these, No. In No. 1, since the heating temperature at this time was high, the crystal grains were coarsened, rough skin was generated in a large bent portion, and the strength was low. No. In No. 3 (Comparative), the final solution treatment was performed in a pure nitrogen atmosphere instead of a reducing atmosphere, and therefore surface oxidation was preceded and surface nitridation did not occur. No. In No. 4 (Comparative), the final solution treatment was performed in a reducing atmosphere, but no nitrogen was contained in the atmosphere, so no surface nitriding occurred. Therefore, no. 3 and no. In No. 4, the crystal grains on the surface were not refined, the press punchability remained at a normal level, and the rough surface of the bent portion was also at a normal level. No. In No. 5, since the final solution treatment was performed in a reducing atmosphere containing nitrogen, nitriding occurred and good press punchability was obtained. However, since the element contributing to the refinement of the crystal grains was not added, the crystal grains became larger as a whole and the strength was lowered. In addition, although the crystal grains were smaller on the surface than in the interior, they became larger as a whole, resulting in some roughness of the bent portion. No. In No. 6, the final solution treatment was performed under ideal conditions. However, since the total content of the third elements exceeded 0.5% by mass, coarse precipitates were generated and high strength was obtained. The bendability of the material was significantly reduced. No. In No. 7, the final solution treatment atmosphere was ideal for nitriding, but the heating temperature was high, so the crystal grains became coarse and the strength was low. Therefore, no. As in the case of No. 5, good press punchability was obtained, but the rough surface of the bent portion was somewhat increased. No. In No. 8, the composition and the atmosphere in the solution treatment were appropriate, but the solution treatment temperature was low, so the crystal grains were refined as a whole, but a large number of coarse precipitates were produced, so that the bendability was high. Remarkably reduced.

  On the other hand, no. 9-No. No. 14, because the composition and final solution treatment conditions are appropriate, the balance between strength and bendability is good, the skin roughness of the bent portion is small, and the press punchability is also good. In particular, no. 11-No. In No. 14, since the titanium content is in a preferable range, the balance between strength and bendability is further improved.

It is a schematic diagram which shows the observation location of the average major axis a of the crystal | crystallization in the material surface, and the average major axis b of the crystal | crystallization inside the material which is not nitrided. Example of a cross section of a bent part with a rough skin Example of a cross-section of a bent part with low skin roughness It is a figure which shows the definition of burr height. It is a figure which shows the cut surface of the board which carried out the shearing process. It is a figure which shows the cross-sectional shape of the punch and die used by the metal mold | die abrasion test.

Claims (9)

  One or two selected from the group consisting of Mn, Fe, Co, Ni, Cr, V, Nb, Mo, Zr, Si, B, and P as the third element group containing 2 to 4% by mass of Ti A copper alloy for electronic parts containing 0.05 to 0.5% by mass in total and the balance being copper and inevitable impurities, wherein the average major axis (a) of crystals on the rolled surface of the copper alloy is rolled A copper alloy for electronic parts in which a relationship of 1 <a / b is established with an average major axis (b) of crystals within 10 μm or more from the surface.   The copper alloy for electronic parts according to claim 1, wherein the surface is nitrided.   2. The electronic component according to claim 1, wherein an average crystal grain size of a crystal within 10 μm or more from the rolling surface is 2 to 10 μm in terms of an equivalent circle diameter when observed from a cross section in a thickness direction parallel to the rolling direction. Copper alloy.   3. The copper alloy for electronic parts according to claim 1, wherein the average crystal grain size of the rolled surface is 1 to 5 μm in terms of equivalent circle diameter when observed from the rolled surface.   The copper alloy for electronic parts as described in any one of Claims 1-3 in which the relationship of 0.4 <= a / b <= 0.8 is materialized.   The copper alloy for electronic parts according to any one of claims 1 to 4, wherein the maximum value of the N concentration in the matrix of the rolled surface is 10 to 200 ppm.   The copper-stretched article provided with the copper alloy as described in any one of Claims 1-5.   The electronic component provided with the copper alloy as described in any one of Claims 1-5.   The connector provided with the copper alloy as described in any one of Claims 1-5.

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