TWI443204B - Cu-Ni-Si alloy used for conductive spring material - Google Patents

Description

Cu-Ni-Si alloy for conductive spring materials

The present invention relates to a Cu-Ni-Si alloy for use in a conductive spring material for electronic parts, and more particularly to an electronic component used for connectors, terminals, relays, switches, and the like, and having strength, bending workability, and electrical conductivity. A well-balanced Cu-Ni-Si alloy.

With the lightness and thinness of electronic devices in recent years, terminals and connectors have also become smaller and thinner, and strength and bending workability are required. Carson (Cu-Ni-Si) alloy, beryllium copper and titanium copper The demand for a precipitated reinforced copper alloy in place of the former solid solution reinforced copper alloy such as phosphor bronze or brass is increasing. Among them, the balance between the strength and the conductivity of the Carson alloy is excellent, so that the frequency used in electronic parts such as connectors is becoming higher and higher.

In general, the strength and the bending processability are opposite. In the past, studies have been conducted on maintaining high strength and improving bending workability in the Carson alloy, and the following discussion is widely carried out, that is, by adjusting the manufacturing steps, The crystal grain size, the number and shape of the precipitates, and the aggregate structure are individually or mutually controlled to improve the bending workability.

In Patent Document 1, in the Carson alloy in which Co, Zn, Mn, Cr, and Al are further added, grain growth during dissolution is suppressed, and bending workability is improved. In Patent Document 2, the Carson alloy contains an appropriate amount of Ti, Zr, Hf or Th, and it is preferable to make the crystal grain size fine, thereby improving press workability and bending workability. In Patent Document 3, the S content and the O content in the Carson alloy are limited to less than 0.005%, and the Sn content and the Mg content are optimized, and the Zn content is optimized as appropriate to control the crystal grain size. This improves the bending workability.

In Patent Document 4 and Patent Document 5, the S content in the Carson alloy is restricted, and the contents of Mg, Sn, and Zn are optimized, and the crystal grain size and the aspect ratio of the crystal grains are controlled, thereby improving the bending process. Sex and stress mitigation. In Patent Document 6, the assembly structure of the Carson alloy is controlled, and the pole density of the {123}<412> orientation is controlled to a predetermined range, thereby improving the bending workability.

In Patent Document 7, the aggregate structure of the Carson alloy is controlled, and the aggregate structure is controlled so as to satisfy (I ₍₁₁₁₎ + I ₍₃₁₁₎ ) / I ₍₂₂₀₎ > 2.0, and the bending workability is improved. In Patent Document 8, the conditions of hot rolling and solution treatment in the Carson alloy are adjusted so that the yield point effect is not exhibited in the tensile strength test, thereby improving the bending workability.

[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-179377

[Patent Document 2] Japanese Patent Laid-Open No. 6-184681

[Patent Document 3] Japanese Patent Laid-Open No. Hei 11-222641

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2002-38228

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2002-180161

[Patent Document 6] Japanese Patent Laid-Open Publication No. 2007-92135

[Patent Document 7] Japanese Patent Laid-Open Publication No. 2006-16629

[Patent Document 8] Japanese Patent Laid-Open Publication No. 2007-169781

With the recent miniaturization of electronic components, in the evaluation of bending workability, in addition to the presence or absence of cracks, the size of wrinkles generated in the bent portion also becomes a problem. The reason for this is that when the bent portion is used as an electrical contact, if the wrinkles are large, the contact resistance becomes unstable and the reliability of the electrical connection is impaired.

However, the bending workability evaluated in the prior art is bending crack resistance, and the bending wrinkles are hardly considered, so that the Cu-Ni-Si alloy excellent in bending wrinkle resistance cannot be obtained. In Patent Document 3, although wrinkles are disclosed in the evaluation of bending workability, the size of the curved wrinkles is not quantitatively evaluated, and thus an invention example without wrinkles cannot be obtained. In the patent document 6, although the bending wrinkle evaluation is performed, in order to obtain a Cu-Ni-Si alloy excellent in strength and bending workability, attention is paid to the {123}<412> orientation on the {111} positive dot map (Patent Literature) 6 "0016"), and the conditions of the cold rolling and the solution treatment before the solution treatment are adjusted (Patent Document 6 "0019"). In the case of the Cu-Ni-Si alloy which is excellent in strength and bending workability, the Ni-Si grain remaining is obtained in the patent document 8 (Patent Document 8 "0009"). The amount of Ni, the amount of Si, or the hot rolling and the solution treatment conditions are adjusted (Patent Document 8 "0019").

In order to achieve the above object, the inventors of the present invention have studied the bending workability in accordance with the viewpoint of controlling the grain boundary of the polycrystalline metal, and the result is a heat treatment by processing the Cu-Ni-Si alloy. The frequency of generation of the annealed twin crystals is controlled to obtain a Cu-Ni-Si alloy having good bending workability when evaluated for high strength and bending wrinkles.

The Cu-Ni-Si alloy of the present invention can be used as a copper alloy which maintains high strength and has good bending workability and reduced bending wrinkles, and is suitable for applications such as terminals and connectors.

Next, the necessary conditions of the present invention and their effects will be described together.

[Ni, Si]

Ni and Si are appropriately heat-treated to form fine particles of an intermetallic compound mainly composed of Ni ₂ Si. As a result, the strength of the alloy is significantly increased, and the electrical conductivity is also increased.

Ni is added in the range of 1.0 to 4.0% by mass, preferably 1.5 to 3% by mass. If Ni is less than 1.0% by mass, sufficient strength cannot be obtained. If Ni exceeds 4.0% by mass, cracks may occur due to the hot pressing delay.

The addition concentration (% by mass) of Si is set to 1/6 to 1/4 of the added concentration (% by mass) of Ni. If the added concentration of Si is less than 1/6 of the added concentration of Ni, the strength is lowered. If it is more than 1/4 of the added concentration of Ni, not only does it contribute to strength, but excessive Si causes a decrease in conductivity.

[Mg, Sn, Zn, Co, Cr]

Although Mg has an effect of improving stress relaxation properties and hot workability, when it exceeds 0.2% by mass, castability (casting surface), hot workability, and plating heat-resistant peelability are deteriorated. Therefore, the concentration of Mg is made 0.2% or less.

Sn and Zn have an effect of improving strength and heat resistance, and Sn has an effect of improving stress relaxation resistance, and Zn has an effect of improving solder heat resistance. Sn is added in the range of 0.2 to 1% by mass, and Zn is added in the range of 0.2 to 1% by mass. If it is less than the above range, the desired effect cannot be obtained, and if it is higher than the above range, the conductivity is lowered.

Co and Cr have a function of forming a compound with Si and improving the strength by precipitation. Further, Co has an effect of preventing coarsening of crystal grains during heat treatment, and Cr has an effect of improving heat resistance. Co is added in the range of 1 to 1.5% by mass, and Cr is added in the range of 0.05 to 0.2% by mass. If it is less than the above range, the desired effect cannot be obtained, and if it is higher than the above range, the conductivity is lowered.

[twin boundary]

The metal material is usually an aggregate of crystal grains having various crystal orientations, that is, a polycrystal in which a boundary exists, that is, a grain boundary due to a difference in atom arrangement method. The grain boundary is divided into a high-angle grain boundary, a low-angle grain boundary, a subgrain boundary, and usually a grain boundary according to the difference in orientation between adjacent grains. It refers to a high-angle grain boundary with a difference in orientation between adjacent grains of 15° or more. On the other hand, the grain boundaries are classified into random grain boundaries and regular grain boundaries according to the consistency between adjacent crystal grains. Due to the regular grain boundary of the annealed bimorph system 产生3 produced by the processing heat treatment of the Cu-Ni-Si alloy, the uniformity between grains is high.

The Σ value is an index indicating the consistency of the grain boundaries. When the left and right crystal lattices of the grain boundary are overlapped, the density ratio of the corresponding lattice points to the lattice points is 1/n, and the relationship is Σ=n. . Since the atomic consistency of the twin crystal interface is good, uneven deformation is less likely to occur near the boundary, and cracks or wrinkles near the boundary are less likely to occur at the time of bending deformation. Therefore, the bending workability can be improved by controlling the ratio of the twin interface in the total boundary including the grain boundary and the twin interface (except for the low angle grain boundary and the subgrain boundary).

In the Cu-Ni-Si alloy of the present invention, the frequency (ratio) of the twin interface (Σ3 boundary) in the total boundary thereof is controlled to be 15% or more and 60% or less, preferably 30% or more. 60% or less, whereby the bending workability can be improved. If it is less than 15%, the desired bending workability cannot be obtained, and if it exceeds 60%, the crystal grains at the time of solution formation are coarsened, and the strength is lowered.

As a method of determining the ratio of the twin crystal interface, for example, an Electron Back Scattering Pattern (EBSP) method using a Field Emission Scanning Electron Microscope (FESEM) is used. This method is based on the method of analyzing the crystal orientation based on an electron backscatter diffraction pattern (Kikuchi pattern) generated when the surface of the sample is obliquely irradiated with an electron beam. After analyzing the crystal orientation by the method, the azimuth difference between adjacent crystal orientations is obtained, thereby determining the ratio of the random grain boundary and the regular grain boundaries (grain boundary property distribution). Since the twin crystal interface corresponds to the Σ3 regular grain boundary, the ratio of the twin crystal interface can be calculated from (the sum of the lengths of the regular grain boundaries Σ3) / (the sum of the lengths of the grain boundaries) × 100. In addition, the grain boundary refers to a boundary where the difference in orientation between adjacent crystal grains is 15° or more, and does not include a low-angle grain boundary or a subgrain boundary.

The bicrystal-annealed twin crystal in the present invention is a twin crystal formed by recrystallization due to annealing after rolling. The frequency of twin crystal generation is related to the stacking fault energy. If the stacking energy is low, the twin crystal frequency generated during annealing will rise. If the stacking energy is high, the frequency will decrease. On the other hand, the stacking energy decreases as the amount of solid solution Ni‧Si is increased (correctly, the amount of solid solution Si is increased). Therefore, in order to increase the bimorphic interface frequency, the stacking energy can be lowered before the final recrystallization annealing (corresponding to the solution treatment in the present invention), and the amount of solid solution Ni ‧ Si can be increased for this purpose.

However, in the conventional method for producing a Carson alloy, the solid solution of Ni and Si is usually carried out at the time of the solution treatment, and in addition to the increase in cost, the heat-calendering treatment is performed at a temperature higher than necessary. The risk of cracking during hot pressing will also increase, so it will not be carried out. Further, there is a production method in which the hot press delay has a solution treatment, but even if it is subjected to hot rolling after annealing corresponding to the solution treatment, the Ni-Si crystal formed at the time of casting cannot be completely dissolved. Can not fully reduce the stacking energy. As a result, the bimorphic interface frequency obtained by the prior method was about 12%. On the other hand, in the present invention, the number and particle diameter of the Ni-Si crystals are reduced by increasing the cooling rate at the time of casting, and the high temperature is used for a long time without causing cracks in the hot rolling step. The annealing conditions are used to cool the material, thereby making the amount of solid solution Ni ‧ Si higher than the previous method, thereby obtaining the desired twin interface frequency.

[Production method]

The Carson alloy of the present invention is manufactured by a general manufacturing process in which a solution treatment, a cold rolling, and an aging treatment are combined, after "melting, casting, hot rolling, plane cutting", and also after final cold rolling. The case of stress relief annealing or the case where the hot press delay is combined with the solution treatment. Since the annealing twin crystal system is formed by recrystallization during the solution treatment, in order to achieve a frequency of the twin crystal interface of 15% or more and 60% or less, the above casting to hot pressing can be carried out under the following conditions. The treatment is continued until the final recrystallization annealing, that is, the Ni and Si are sufficiently solid-solved before the solution treatment.

The ingot cooling rate at the time of casting is set to 300 to 500 ° C / min, and the crystallization of coarse Ni-Si particles is suppressed during casting cooling. The speed at which the ingot cooling rate exceeds 500 ° C / min is not practical in terms of cost. Next, annealing is performed at a heating temperature of 940 to 1000 ° C, preferably 950 to 980 ° C for 3 to 6 hours, and the Ni-Si particles remaining on the ingot are solid-solved, followed by hot rolling. If the heating temperature is less than 940 ° C or less than 3 hours, the solid solution of the remaining Ni-Si particles may be insufficient. On the other hand, annealing at a high temperature exceeding 1000 ° C of the hot pressing delay increases the risk of hot rolling cracking. Annealing in the above temperature region for more than 6 hours is an excessive annealing for the desired effect, which is not preferable in terms of cost. The material temperature at the end of the hot rolling is set to be 650 ° C or higher. If it is less than 650 ° C, the amount of Ni ₂ Si precipitated during the hot rolling process increases, and the amount of solid solution Ni amount ‧ Si cannot be ensured, so the twin interface frequency is lowered.

After planar cutting, cold rolling is performed at a working degree of 85% or more, and after 5 to 30 minutes of dissolution treatment at 700 to 820 ° C (in this case, final recrystallization annealing), the temperature is 350 to 550 ° C. Aging treatment for 2 to 30 hours. Further, cold rolling is performed at a working degree of 5% to 50%.

[Example 1]

(Manufacture of sample)

The electrolytic copper is melted, and a predetermined amount of the added element is put into an atmospheric melting furnace, and the molten metal is stirred. Thereafter, the melt was poured into the mold at a casting temperature of 1,250 ° C to obtain an ingot. By changing the water cooling conditions of the mold, the cooling rate of the ingot during casting can be adjusted to the conditions in the table. The ingot cooling rate at the time of casting is the average cooling rate (° C/min) until the ingot temperature is lowered from 1100 ° C to 500 ° C after the solid solution is solidified. Next, the ingot was processed and heat-treated in the following order to obtain a sample having a thickness of 0.25 mm.

(1) The ingot is annealed and hot rolled under the conditions in the table, and the plate thickness is processed to a predetermined thickness, and then water-cooled.

(2) The rust scale of the surface layer is removed by planar cutting.

(3) Perform cold rolling until the sheet thickness reaches 0.3 mm.

(4) The solution treatment was carried out for 1 minute at the solution temperature in the table.

(5) The aging treatment was carried out under the conditions of 450 ° C × 10 h.

(6) Perform cold rolling until the aging material reaches 0.25 mm.

For the above materials, EBSP measurement on the twin crystal interface was carried out according to the following criteria, and a tensile test and a W bending test were carried out.

[Double crystal interface]

As a method of determining the ratio of the twin crystal interface, an Electron Back Scattering Pattern (EBSP) method using a Field Emission Scanning Electron Microscope (FESEM) was used. After analyzing the crystal orientation by the method, the azimuth difference between adjacent crystal orientations is determined to determine the grain boundary characteristic distribution. The observation magnification was set to 1000 times, and the total of the observation fields was set to 2 mm ² . The regular grain boundary is represented by a Σ value, and the twin crystal interface is equivalent to the Σ3 regular grain boundary. The ratio (%) of the twin crystal interface can be calculated from (the sum of the lengths of the regular grain boundaries Σ3) / (the sum of the lengths of the grain boundaries) × 100. In addition, the grain boundary in the formula means that the difference in orientation between adjacent crystal grains is 15° or more, and does not include a low-angle grain boundary or a subgrain boundary.

[Tensile Strength]

Each copper alloy sheet was subjected to a tensile test in a direction parallel to the rolling direction, and tensile strength was determined in accordance with JIS Z2241. In the following examples, the high strength means that the tensile strength is 700 MPa or more in the case of alloy A, and the tensile strength is 650 MPa or more in the case of alloy B, and in the case of alloy C, The tensile strength is 600 MPa or more.

[bending crack]

A strip-shaped test piece having a width of 10 mm and a length of 30 mm was selected so that the bending axis was parallel to the rolling direction. The W bending test (JIS H3130) of the test piece was carried out, and the minimum bending radius at which no crack occurred was defined as MBR (Minimum Bend Radius), and evaluated based on the ratio MBR/t to the thickness t (mm). When the MBR/t in the direction of the Bad way (B.W.) was 1 or less, the crack of the bending workability was evaluated as good (○), and the other cases were judged to be defective (×). Regarding the alloys B and C, when the MBR/t is 0.5 or less, it is judged that the bending workability is good.

[bending folds]

In the W bending test described above, a scanning electron microscope (SEM) image of the wrinkles observed on the surface of the curved convex portion of the test piece subjected to bending by MBR was imaged. The width of the curved pleats was measured on the photograph to determine the width of the largest curved pleats in the test piece. Three test pieces were measured for each material to be tested, and the average value was taken as the width of the curved pleats. When the width of the curved pleats in the B.W. direction is 30 μm or less, the wrinkle of the bending workability is evaluated as good (○), and when it exceeds 30 μm, it is judged to be defective (×). In addition, the "-" in the table indicates that it cannot be evaluated.

Examples of the Ni-Si-based copper alloy A (Cu-2% Ni-0.5% Si-0.1% Mg) of the present invention are shown in Table 1.

Examples of the Ni-Si-based copper alloy B (Cu-1.6% Ni-0.4% Si-0.4% Sn-0.5% Zn) of the present invention are shown in Table 2.

Examples of the Ni-Si-based copper alloy C (Cu-1.6% Ni-0.4% Si) of the present invention are shown in Table 3.

In Comparative Examples 1, 8 and 15, since the cooling rate at the time of casting was less than 300 ° C / min, coarse Ni-Si crystals were formed in the ingot, and the solid solution amount of Ni and Si in the mother phase was decreased. The difference in energy is not sufficiently reduced, so the double crystal interface frequency is less than 15%.

In Comparative Examples 2 to 4, 9 to 11 and 16 to 18, since the hot rolling conditions did not satisfy any of 940 ° C or more and 3 h or more and the end temperature of 650 ° C or more, the Ni-Si grain inclusions were insufficient. Solid solution, the stacking energy does not decrease, so the double crystal interface frequency is less than 15%.

In Comparative Examples 5, 12 and 19, since the degree of cold working was 85% or less, recrystallization at the time of solution formation was insufficient, and the twin interface frequency was less than 15%.

In Comparative Examples 6, 13, and 20, since the solution temperature was 700 ° C or lower, recrystallization was insufficient, the twin interface frequency was less than 15%, and the strength was also lowered.

In Comparative Examples 7, 14, and 21, since the solution temperature exceeded 820 ° C, the bimorphic interface frequency exceeded 60%, and the crystal grain size increased, so that the bending wrinkle width increased.

[Embodiment 2]

(Manufacture of sample)

The electrolytic copper was melted, and a predetermined amount of the additive element was introduced into the atmospheric melting furnace to achieve the desired composition shown in Table 4, and the molten metal was stirred. Thereafter, the melt was poured into the mold at a casting temperature of 1,250 ° C, and the cooling rate was adjusted to 400 ° C / min to obtain an ingot. Next, the ingot was processed and heat-treated in the following order to obtain a sample having a thickness of 0.25 mm.

(1) After the ingot was annealed at 950 ° C for 4 hours, hot rolling was performed so that the temperature after completion of rolling was 700 ° C.

(2) Plane cutting the rust scale of the surface layer and machine the thickness to 5 mm.

(3) Perform cold rolling until the sheet thickness reaches 0.3 mm.

(4) The solution treatment was carried out at 750 ° C for 1 minute.

(5) The aging treatment was carried out under the conditions of 450 ° C × 10 h.

(6) Perform cold rolling until the aging material reaches 0.25 mm.

For the above materials, an EBSP measurement, a tensile test, a conductivity, and a W bending test were performed on the twin crystal interface. The evaluation of the twin crystal interface frequency and the W bending test was carried out in the same manner as in the above Example 1, and the tensile strength was greatly affected by the composition. Therefore, it was judged that the strength was 600 MPa or more.

The results are shown in Table 5. As shown in Table 5, in the inventive examples 13 to 23, the desired twin-crystal interface frequency was obtained, the bending workability was good, and the strength was also good. In Comparative Example 22, the amount of Ni was less than a predetermined amount, and the bending workability was good, but the tensile strength was lowered. In Comparative Example 23, the amount of Ni was higher than a predetermined amount, and hot rolling cracking occurred, and a sample could not be produced.

Claims (4)

A Cu-Ni-Si alloy containing: 1.0 to 4.0% by mass of Ni, a concentration of Si of 1/6 to 1/4 with respect to a mass percentage of Ni, and the balance being Cu and inevitable impurities As a result of the observation of the aggregate structure by EBSP measurement, the frequency of the twin crystal interface (Σ3 boundary) in the total grain boundary is controlled to be 15% or more and 60% or less. The Cu-Ni-Si alloy according to the first aspect of the invention is further contained in an amount of 0.2% by mass or less of Mg. The Cu-Ni-Si alloy according to the first aspect of the patent application further contains 0.2 to 1% by mass of Sn and 0.2 to 1% by mass of Zn. The Cu-Ni-Si alloy according to the first aspect of the patent application further contains 1 to 1.5% by mass of Co and 0.05 to 0.2% by mass of Cr.