CN101981212A - Cu-Ni-Si Alloys for Conductive Elastic Materials - Google Patents

Abstract

A Cu-Ni-Si base alloy containing Ni in an amount of 1.0 to 4.0 mass% and Si in a concentration of 1/6 to 1/4 of that of Ni, wherein the density of twin boundaries (Sigma3 boundaries) is 15 to 60% of all the grain boundaries. The alloy may further contain Mg: 0.2% or less, Sn: 0.2 to 1%, Zn: 0.2 to 1%, Co: 1 to 1.5%, and/or Cr: 0.05 to 0.2%.

Description

Cu-Ni-Si Alloys for Conductive Elastic Materials

technical field

The present invention relates to a Cu-Ni-Si alloy used as a conductive elastic material for electronic parts, especially for electronic parts such as connectors, terminals, relays, switches, etc., and its strength, bending workability and conductivity Cu-Ni-Si alloy with excellent balance.

Background technique

In recent years, with the thinner and lighter electronic equipment, terminals, connectors, etc. have also been miniaturized and thinned, requiring strength and bending workability, replacing existing solid-solution-strengthened copper alloys such as phosphor bronze and brass, The demand for precipitation strengthened copper alloys such as Corson (Cu-Ni-Si system) alloys, beryllium copper and titanium copper is increasing. Among them, Corson alloys are excellent in balance between strength and electrical conductivity, and are frequently used in electronic components such as connectors.

In general, strength and bendability are opposite properties. For Corson alloys, improving bendability while maintaining high strength has also been studied in the past, and the following measures have been widely carried out: adjustment of the manufacturing process, individual or mutual control of crystal grain size, and precipitation. The number, shape, and texture of objects can be improved, thereby improving bending workability.

In Patent Document 1, for a Corson alloy to which Co, Zn, Mn, Cr, and Al are further added, grain growth during solid solution is suppressed, and bending workability is improved. In Patent Document 2, by making the Corson alloy contain an appropriate amount of Ti, Zr, Hf, or Th, it is preferable to refine the crystal grain size, thereby improving blanking workability and bending workability. In Patent Document 3, the contents of S and O in the Corson alloy are limited to less than 0.005%, the contents of Sn and Mg, optionally Zn are optimized, and the crystal grain size is further controlled, thereby improving bending workability.

In Patent Documents 4 and 5, the S content in the Corson alloy is limited, the content of Mg, Sn, and Zn is optimized, and the grain size and aspect ratio of the grain are controlled, thereby improving bending workability and stress relaxation properties . In Patent Document 6, the texture of the Corson alloy is controlled, and the pole density in the {123}<412> orientation is controlled within a predetermined range, thereby improving the bending workability.

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

Patent Document 1: Japanese Patent Application Laid-Open No. 5-179377

Patent Document 2: Japanese Patent Application Laid-Open No. 6-184681

Patent Document 3: Japanese Patent Application Laid-Open No. 11-222641

Patent Document 4: Japanese Patent Laid-Open No. 2002-38228

Patent Document 5: Japanese Patent Laid-Open No. 2002-180161

Patent Document 6: Japanese Patent Laid-Open No. 2007-92135

Patent Document 7: Japanese Patent Laid-Open No. 2006-16629

Patent Document 8: Japanese Patent Laid-Open No. 2007-169781

Contents of the invention

In recent years, along with the miniaturization of electronic components, in addition to the presence or absence of cracks, the size of wrinkles generated in bent portions has also become a problem in the evaluation of bending workability. This is because when the bent portion is used as an electrical contact, if the wrinkle is 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 resistance to bending cracks (cracks), and almost no consideration is given to bending wrinkling, and Cu—Ni—Si alloys excellent in bending wrinkling resistance have not been obtained. In Patent Document 3, wrinkle is described in bending workability evaluation, but the size of bending wrinkle is not quantitatively evaluated, and no invention example without wrinkle is obtained. In Patent Document 6, bending wrinkles were evaluated, but in order to obtain a Cu-Ni-Si-based alloy excellent in strength and bendability, attention was paid to the {123}<412> orientation on the {111} positive electrode diagram (Patent Document 6 [0016] paragraph), adjust the conditions of cold rolling and solution treatment before solution treatment (patent document 6 [0019]). Also in Patent Document 8, bending wrinkling was evaluated, but in order to obtain a Cu-Ni-Si-based alloy excellent in strength and bendability, focusing on remaining Ni-Si grains (Patent Document 8 [0009]), Ni, Si amount, hot rolling, and solution treatment conditions (Patent Document 8 [0019]).

In order to achieve the above object, the present inventors have repeatedly studied the bending workability from the perspective of grain boundary control of polycrystalline metals differently from the prior art. As a result, it was found that by controlling The occurrence frequency of annealing twins is high, and a Cu-Ni-Si alloy with high strength and good bending workability in the evaluation of bending wrinkles can be obtained.

The Cu—Ni—Si alloy of the present invention is suitable for applications such as terminals and connectors as a copper alloy having good bending workability and reduced bending wrinkles while maintaining high strength.

Detailed ways

Next, the elements of the present invention and their effects will be described.

[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 increases significantly, while the electrical conductivity also increases.

Ni is added in a 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 will occur during hot rolling.

The addition concentration (mass %) of Si is 1/6 to 1/4 of the addition concentration (mass %) of Ni. If the added concentration of Si is less than 1/6 of the added concentration of Ni, the strength will decrease, and if it is more than 1/4 of the added concentration of Ni, not only will it not contribute to the strength, but the excess Si will cause a decrease in electrical conductivity.

[Mg, Sn, Zn, Co, Cr]

Mg has the effect of improving stress relaxation properties and hot workability, but if it exceeds 0.2% by mass, castability (decreases the surface quality of castings), hot workability, and plating heat peeling resistance will decrease. Therefore, the concentration of Mg is specified to be 0.2% or less.

Sn and Zn have effects of improving strength and heat resistance, and Sn has an effect of improving stress relaxation resistance, and Zn has an effect of improving heat resistance of solder joints. Sn is added in a range of 0.2 to 1% by mass, and Zn is added in a 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 will decrease.

Co and Cr form compounds with Si to improve strength by precipitation. Furthermore, Co has an effect of preventing crystal grains from coarsening during heat treatment, and Cr has an effect of improving heat resistance.

Co is added in a range of 1 to 1.5% by mass, and Cr is added in a 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 will decrease.

[twin boundary]

Metal materials are usually aggregates of crystal grains with various crystal orientations, that is, polycrystals, and the arrangement of atoms in metal materials is different, resulting in the existence of boundaries, namely grain boundaries. Grain boundaries are divided into high-angle grain boundaries, small-angle grain boundaries, and sub-grain boundaries according to the orientation difference between adjacent grains. Generally, grain boundaries refer to high-angle grain boundaries where the orientation difference between adjacent grains is more than 15°. On the other hand, grain boundaries are classified into random grain boundaries and double-positioned grain boundaries according to the integration between adjacent grains. The annealing twins produced by Cu-Ni-Si alloy through processing and heat treatment are Σ3 heavy-site grain boundaries, and the integration between grains is high.

The Σ value is an indicator of the integrity of the grain boundary. When the left and right crystal lattices sandwiching the grain boundary overlap, when the density ratio of the overlapped lattice and the lattice is 1/n, there is a corresponding relationship of Σ=n . Due to the good integration of atoms at the twin boundary, uneven deformation is not easy to occur near the boundary, and cracks and wrinkles based on the vicinity of the boundary are not easy to occur during bending deformation. Thus, bending workability can be improved by controlling the proportion of twin boundaries in all boundaries including grain boundaries and twin boundaries (wherein low-angle grain boundaries and subgrain boundaries are excluded).

In the Cu-Ni-Si alloy of the present invention, the bending process is improved by controlling the frequency (ratio) of twin boundaries (Σ3 boundaries) in all boundaries to 15% to 60%, preferably 30% to 60%. sex. If it is less than 15%, desired bending workability cannot be obtained, and if it exceeds 60%, the crystal grains become coarse during solid solution and the strength decreases.

As a method of obtaining the ratio of the twin boundary, there is, for example, the EBSP (Electron Back Scattering Pattern) method using FESEM (Field Emission Scanning Electron Microscope). This method is a method of analyzing crystal orientation based on a backscattered electron diffraction pattern (Kikuchi pattern) generated when an electron beam is irradiated obliquely to a sample surface. After the crystal orientation is analyzed by this method, the orientation difference between adjacent crystal orientations can be obtained, and the ratio of random grain boundaries and grain boundaries of each heavy position (characteristic distribution of grain boundaries) can be determined. Since the twin boundary is equivalent to the Σ3 gravity boundary, the ratio of the twin boundary is calculated by (the sum of the length of the gravity boundary Σ3)/(the sum of the length of the grain boundary)×100. It should be noted that the grain boundary refers to a boundary where the misorientation between adjacent crystal grains is 15° or more, and does not include small-angle grain boundaries and sub-grain boundaries.

The twins in the present invention are annealing twins, and are twins formed with recrystallization by annealing after rolling. The frequency of twinning is related to the stacking fault energy of the material. If the stacking fault energy is low, the frequency of twinning during annealing increases, and if it is high, the frequency decreases. On the other hand, the stacking fault energy can be reduced by increasing the amount of solid solution Ni and Si (actually increasing the amount of solid solution Si). Therefore, in order to increase the twin boundary frequency, it is sufficient to increase the amount of solid solution Ni and Si to reduce the stacking fault energy before final recrystallization annealing (corresponding to solution treatment in the present invention).

However, in the conventional manufacturing method of Corson alloy, the solid solution of Ni and Si is carried out during the solution treatment is a common method, because the cost is increased due to hot rolling at an unnecessary high temperature, and cracks occur during hot rolling. The possibility of increasing, so do not proceed. In addition, there is also a manufacturing method that uses hot rolling as a solution treatment, but after annealing equivalent to solution treatment, even if hot rolling is performed, the Ni-Si crystallization produced during casting cannot be completely dissolved, and cannot be used. Stacking faults can be substantially reduced. As a result, the frequency of twin boundaries obtained by the conventional method was about 12%. On the other hand, in the present invention, by increasing the cooling rate during casting, the number and particle size of Ni-Si crystallization products are reduced, and within the limit of not generating cracks in the hot rolling process, high temperature and long The annealing condition of the time is to cool the material, so that the amount of solid solution Ni and Si is higher than that of the existing method, and the expected twin boundary frequency is obtained.

[Manufacturing method]

The Corson alloy of the present invention is produced by a general production method of combining solution treatment, cold rolling and aging treatment after "melting, casting→hot rolling→face cutting", and stress relief annealing after final cold rolling. The case, or the case of using hot rolling as a solution treatment. Since annealing twins are produced along with recrystallization during solution treatment, in order to make the frequency of twin boundaries 15% to 60%, the conditions from the above-mentioned casting to hot rolling are carried out in the following ranges, and in the final recrystallization Crystallization annealing means that Ni and Si are fully dissolved in advance before solution treatment.

The ingot cooling rate during casting is set at 300 to 500° C./min, and the crystallization of coarse Ni—Si particles is suppressed during casting cooling. An ingot cooling rate exceeding 500°C/min is not practical from the viewpoint of cost. Next, annealing is performed at a heating temperature of 940 to 1000° C., preferably 950 to 980° C., for a heating time of 3 to 6 hours to dissolve the Ni—Si particles remaining in the ingot, 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 is insufficient. On the other hand, hot-rolling cracks may increase during annealing at a high temperature exceeding 1000° C. during hot rolling. The annealing for more than 6 hours in the above-mentioned temperature range is not preferable from the viewpoint of cost due to excessive annealing for the desired effect. The temperature of the material at the completion of the hot rolling is set at 650° C. or higher. If the temperature is lower than 650°C, the amount of Ni ₂ Si precipitated during hot rolling increases, and sufficient solid-solution Ni and Si amounts cannot be secured, so the twin boundary frequency decreases.

After face cutting, cold rolling with a working degree of 85% or more is performed, solution treatment is performed at 700-820°C for 5 seconds to 30 minutes (at this time, final recrystallization annealing), and then at 350-550°C 2 to 30 hours of aging treatment. Further, cold rolling is performed at a working degree of 5% to 50%.

Example 1

(production of sample)

Melt the electrolytic copper, put a specified amount of additive elements in the atmosphere melting furnace, and stir the molten soup. Thereafter, it was poured into a mold at a casting temperature of 1250° C. to obtain an ingot. By changing the water cooling conditions of the mold, the ingot cooling rate during casting was adjusted to the conditions in the table. The ingot cooling rate during casting refers to the average cooling rate (°C/min) of the ingot temperature from 1100°C to 500°C after the molten soup solidifies. Next, the ingot was processed and heat-treated according to the following procedures to obtain a sample with a plate thickness of 0.25 mm.

(1) The cast ingots were annealed and hot-rolled under the conditions shown in the table, and the plate thickness was treated to a predetermined thickness, followed by water cooling.

(2) Remove the scale on the surface by plane cutting.

(3) Cold rolling treatment was performed until the plate thickness became 0.3 mm.

(4) Solution treatment was performed for 1 minute at the solution temperature in the table.

(5) Aging treatment was performed under the condition of 450° C.×10 hours.

(6) The aging material is cold-rolled to 0.25mm.

For the above-mentioned materials, EBSP measurement, tensile test, and W bending test related to the twin boundary were carried out according to the following standards.

[twin boundary]

As a method of obtaining the ratio of the twin boundary, the EBSP (Electron Back Scattering Pattern) method using FESEM (Field Emission Scanning Electron Microscope) is used. After the crystal orientation is analyzed by this method, the orientation difference between adjacent crystal orientations is obtained, and the grain boundary characteristic distribution is determined. The observation magnification was 1000 times, and the observation field of view was 2 mm ² in total. The heavy position grain boundary is represented by Σ value, and the twin boundary is equivalent to Σ3 heavy position grain boundary. The ratio (%) of the twin boundary was calculated by (sum of the lengths of the grain boundaries Σ3)/(sum of the lengths of the grain boundaries)×100. It should be noted that the grain boundary in the formula refers to the boundary where the misorientation between adjacent crystal grains is 15° or more, excluding small grain boundaries and sub-grain boundaries.

[Tensile Strength]

For each copper alloy sheet, a tensile test was performed in a direction parallel to the rolling direction, and it was obtained in accordance with JIS Z2241. In the following examples, high strength refers to alloy A having a tensile strength of 700 MPa or more, alloy B being 650 MPa or more, and alloy C being 600 MPa or more.

[curved crack]

Make the bending axis parallel to the rolling direction, and take a thin rectangular test piece with a width of 10 mm x a length of 30 mm. The W bending test (JIS H3130) was performed on the test piece, and the minimum bending radius without cracking was MBR (Minimum Bend Radius), and the ratio MBR/t to the plate thickness t (mm) was evaluated. For alloy A, when the MBR/t in the Bad way (B.W.) direction is 1 or less, the cracking of the bending workability was evaluated as good (◯), and otherwise it was judged as bad (×).

For the alloys B and C, when the MBR/t is 0.5 or less, it is judged that the bending workability is good.

[curved folds]

In the above-mentioned W bending test, SEM photographs were taken of wrinkles observed on the surface of the curved convex portion of the test piece bent by MBR. On the photograph, the width of bending wrinkles was measured, and the width of the largest bending wrinkles in the test piece was obtained. Three test pieces were measured for each test material, and the average value was defined as the width of the bending wrinkles. When the width of the bending wrinkles in the B.W. direction is 30 μm or less, the wrinkle evaluation of bending workability is good (◯), and if it exceeds 30 μm, it is judged as bad (×). It should be noted that "-" in the table means that evaluation cannot be performed.

Table 1 shows examples of the Ni-Si-based copper alloy A (Cu-2%Ni-0.5%Si-0.1%Mg) of the present invention.

Table 2 shows 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.

Table 3 shows examples of the Ni-Si-based copper alloy C (Cu-1.6%Ni-0.4%Si) of the present invention.

In Comparative Examples 1, 8, and 15, since the cooling rate during casting was less than 300°C/min, coarse Ni-Si crystal grain precipitates were generated in the ingot, and the solid solution amount of Ni and Si to the parent phase decreased, The stacking fault energy is not sufficiently reduced, so the twin boundary frequency is less than 15%.

In Comparative Examples 2 to 4, 9 to 11, and 16 to 18, since any one of the hot rolling conditions of 940°C or higher and 3 hours or higher and the completion temperature of 650°C or higher was not satisfied, Ni-Si grain inclusions The material is not fully dissolved, and the stacking fault energy is not reduced, so the twin boundary frequency is less than 15%.

In Comparative Examples 5, 12, and 19, since the cold-rolling degree was 85% or less, recrystallization during solid solution was insufficient, and the twin boundary 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 boundary frequency was less than 15%, and the strength also decreased.

In Comparative Examples 7, 14, and 21, since the solution temperature exceeds 820° C., the twin boundary frequency exceeds 60%, and the crystal grain size becomes large, so the bending wrinkle width becomes large.

Example 2

(production of sample)

Electrolytic copper was melted, and a predetermined amount of additive elements was put into an atmospheric melting furnace so that the desired composition shown in Table 4 was obtained, and the molten soup was stirred. Afterwards, it was poured into a mold at a casting temperature of 1250° C., and the cooling rate was adjusted to 400° C./min to obtain an ingot. Next, the ingot was processed and heat-treated according to the following procedures to obtain a sample with a plate thickness of 0.25 mm.

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

(2) Carry out plane cutting on the oxide skin on the surface, and process the plate thickness to 5mm.

(3) Cold rolling treatment was performed until the plate thickness became 0.3 mm.

(4) Solution treatment was performed at 750° C. for 1 minute.

(5) Aging treatment was performed under the condition of 450° C.×10 hours.

(6) The aging material is cold-rolled to 0.25mm.

For the above materials, EBSP measurements related to twin boundaries, tensile test electrical conductivity and W bending tests were carried out. Evaluations of twin boundary frequency and W bending test were carried out in the same manner as in Example 1 above, and since the tensile strength is greatly affected by the composition, it was judged that 600 MPa or more was high strength.

[Table 4]

The results are shown in Table 5. As shown in Table 5, in Invention Examples 13 to 24, the desired twin boundary frequency was obtained, the bending workability was good, and the strength was also good. In Comparative Example 22, the amount of Ni was lower than the specified amount, and the bending workability was good, but the tensile strength was lowered. In Comparative Example 23, the amount of Ni was higher than the specified amount, hot-rolling cracks occurred, and a sample could not be produced.

Claims (4)

1.Cu-Ni-Si be alloy, it contains the Ni of 1.0～4.0 quality %, the quality % concentration that contains with respect to Ni is the Si of 1/6～1/4 concentration, remainder comprises Cu and unavoidable impurities, measure the texture observations of carrying out by EBSP and find that the frequency control with the twin boundary in whole crystal boundaries (∑ 3 borders) is 15%～60%.

2. Cu-Ni-Si according to claim 1 is an alloy, and it also contains the following Mg of 0.2 quality %.

3. Cu-Ni-Si according to claim 1 and 2 is an alloy, and it also contains the Sn of 0.2～1 quality %, the Zn of 0.2～1 quality %.

4. be alloy according to each described Cu-Ni-Si in the claim 1～3, it also contains the Co of 1～1.5 quality %, the Cr of 0.05～0.2 quality %.