JP3946709B2 - Cu-Ni-Si-Mg copper alloy strip - Google Patents

Description

  The present invention relates to a copper alloy having high strength, stress relaxation resistance, electrical conductivity, etc., suitable as a conductive spring material for a semiconductor device, such as a lead frame material, a connector, a terminal, a relay, and a switch. It is.

  Copper alloys for electronic materials used for lead frames, terminals, connectors, and the like are required to have both high strength, high electrical conductivity, and thermal conductivity as basic characteristics of the alloy. In addition to these characteristics, bending workability, stress relaxation resistance, heat resistance, adhesion to plating, solder wettability, etching workability, press punching, corrosion resistance, etc. are required.

JP-A-61-250134 JP 05-345941 A JP 09-209062 JP-A 63-297531 JP 05-059468 A

  On the other hand, in response to the recent downsizing and higher integration of electronic components, lead frames, terminals, and connectors have increased in the number of leads and narrow pitch, and the shape of the components has become complicated. . At the same time, there is a growing demand for improved reliability during assembly and after mounting. Against this background, the required level for the characteristics of the copper alloy material described above is becoming increasingly sophisticated.

  From the viewpoint of high strength and high conductivity, in recent years, the amount of age-hardening type copper alloys has increased as a copper alloy for electronic materials, replacing the conventional solid solution strengthened copper alloys such as phosphor bronze and brass. is doing. In an age-hardening type copper alloy, by aging the solution-treated supersaturated solid solution, fine precipitates are uniformly dispersed, the strength of the alloy is increased, and at the same time, the amount of solid solution elements in copper is reduced. Electrical conductivity is improved. For this reason, a material excellent in mechanical properties such as strength and spring property and having good electrical conductivity and thermal conductivity can be obtained.

  Of the age-hardening type copper alloys, Cu—Ni—Si based copper alloys are representative copper alloys having both high strength and high conductivity, and have been put into practical use as materials for electronic devices. In this copper alloy, strength and electrical conductivity are increased by precipitation of fine Ni—Si intermetallic particles in the copper matrix.

In order to improve mechanical characteristics and the like, elements other than Ni and Si are often added to the Cu—Ni—Si based copper alloy in many cases. In particular, Mg is a typical element added to a Cu—Ni—Si based copper alloy. As an effect of Mg addition,
a) Strength and stress relaxation resistance are improved (Japanese Patent Laid-Open No. 61-250134).
b) Hot workability is improved (Japanese Patent Laid-Open No. 05-345941),
c) By forming Mg as an oxide and trapping oxygen, generation or coarsening of Si oxide during heat treatment can be prevented (Japanese Patent Laid-Open No. 09-209062),
Etc. have been reported. A typical Cu—Ni—Si—Mg based copper alloy strip produced industrially is C70250 (CDA alloy number), and this alloy is 2.2 to 4.2 mass% of Ni, and Si is 0.00. It contains 25 to 1.2% by mass and Mg in the range of 0.05 to 0.3% by mass.

  In the general manufacturing process of Cu-Ni-Si-Mg-based copper alloy strips, first, an atmospheric melting furnace is used to melt raw materials such as electrolytic copper, Ni, Si, and Mg under a charcoal coating to obtain a desired composition. Get molten metal. Then, this molten metal is cast into an ingot. Then, hot rolling, cold rolling and heat treatment are performed to finish the strip or foil having the desired thickness and characteristics.

  As described above, when Mg is added to a Cu—Ni—Si based copper alloy, the alloy characteristics are remarkably improved. However, as reported in Japanese Patent Laid-Open No. 63-297531, when Mg is added, hot water flow during casting is improved. Decreases and irregularities are likely to occur on the casting surface of the ingot. The deterioration of the casting surface becomes more prominent as the amount of added Mg increases. When irregularities occur in the casting surface, surface cracks starting from irregularities may occur in hot rolling, or irregularities may be changed into scab surface defects. Such surface defects need to be removed by cutting in the next step. For this reason, when Mg is added to a Cu—Ni—Si based copper alloy, the manufacturing yield is lowered.

  Due to the technical background as described above, obtaining the effect of improving the characteristics by adding Mg with a smaller amount of added Mg has been a problem in industrial production of Cu—Ni—Si—Mg based copper alloy strips. It was.

  According to Japanese Patent Laid-Open No. 05-59468, when adding Mg to a Cu—Ni—Si based copper alloy, the O and S concentrations must be reduced to 0.0015 mass% or less. This is because when O or S exceeds 0.0015%, Mg becomes a large amount of oxide or sulfide, and the effect of Mg addition on the stress relaxation characteristics is lost. This invention shows that management of O and S concentrations is important to enhance the effect of improving the characteristics of Mg addition.

  An object of the present invention is to provide a Cu—Ni—Si—Mg based copper alloy strip that has a high strength and good stress relaxation characteristics and is excellent in manufacturability.

  The inventor has accumulated and analyzed data on the composition and characteristics of Cu-Ni-Si-Mg-based copper alloy strips produced industrially. As a result, it became clear that even when the O and S concentrations are 0.0015% or less, there are non-negligible variations in strength and stress relaxation characteristics between materials having the same Ni, Si and Mg concentrations. From this, it was found that the O and S concentration alone is not sufficient to effectively develop the effect of adding Mg to the Cu—Ni—Si based copper alloy.

  After that, a method for stably obtaining a sufficient characteristic improvement effect with a small amount of added Mg is studied, and it is necessary to control the concentration not only for O and S but also for Se, Te, P, As, Sb and Bi. Found that there is.

O, S, Se, Te, P, As, Sb, and Bi are non-metallic elements belonging to 5B group or 6B group, and MgO, MgS, MgSe, MgTe, Mg ₃ P ₂ , Mg with Mg, respectively. Nonmetallic inclusions such as ₃ As ₂ , Mg ₃ Sb ₂ and Mg ₃ Bi ₂ are formed. Mg in which non-metallic inclusions are formed does not contribute to improving the characteristics of the Cu—Ni—Si based copper alloy, but rather reduces the bending workability and elongation, and also reduces the manufacturability of the alloy.

  S, Se, Te, As, Sb, and Bi are typical impurities contained in electrolytic copper, which is a main raw material of a Cu—Ni—Si—Mg based copper alloy strip. It is contained in a considerable concentration in crude copper before electrolysis, and a part of it remains in electrolytic copper. In order to keep the concentrations of S, Se, Te, As, Sb, and Bi low, it is important to manage the amount of impurities in electrolytic copper used as a raw material.

  P is an element often used for deoxidation of molten copper, and examples of copper alloys to which P deoxidation is applied include phosphorous deoxidized copper and phosphor bronze. As raw materials for industrially produced Cu—Ni—Si—Mg copper alloy strips, not only pure Cu—Ni—Si—Mg raw materials but also copper alloy scraps are used. In order to keep the P concentration low, it is important not to use P deoxidation on the Cu—Ni—Si—Mg-based copper alloy strips and not to use scrap containing P.

  O is not only mixed from the atmosphere when melting the Cu—Ni—Si—Mg based copper alloy strip, but is also mixed by reducing the moisture contained in the refractory, the molten metal coating, and the like. In order to keep the O concentration low, avoid contact between the molten metal and the atmosphere with charcoal coating or melting flux, etc., dry the member in contact with the molten metal and reduce its moisture sufficiently, and control the oxygen content of the raw material That is important.

  Furthermore, the present inventor has also found that there is a correlation between the C concentration and the characteristics of the Cu—Ni—Si—Mg based copper alloy strip. That is, it has been found that even when the O, S, Se, Te, P, As, Sb, and Bi concentrations are equal, the higher the C concentration, the better the strength and stress relaxation characteristics. About this reason, when C exists in a molten metal, it was estimated that the ratio of Mg which exists in a molten metal as metal Mg increases.

The present invention has been made based on the above discovery, and as described in claim 1,
Containing 1.0 to 4.5% by mass of Ni, containing Si at a concentration of 1/6 to 1/4 with respect to the mass% concentration of Ni, further containing Mg , the balance being Cu and inevitable impurities Cu alloy composed of 0.00054 to 0.0015 mass% of C, Mg concentration and O, S, Se, Te, P, As, Sb and Bi in the inevitable impurities It is a Cu-Ni-Si-Mg-based copper alloy strip excellent in stress relaxation characteristics characterized by adjusting the equivalent concentration (T) to the range of the following formula.

(1) Ni and Si
Ni and Si form fine particles of an intermetallic compound mainly composed of Ni ₂ Si by performing an aging treatment. As a result, the strength of the alloy is significantly increased and at the same time the electrical conductivity is increased. The addition concentration (mass%) of Si is in the range of 1/6 to 1/4 of the addition concentration (mass%) of Ni. If the Si addition amount is out of this range, the electrical conductivity is lowered. Ni is added in the range of 1.0 to 4.5 mass%. If Ni is less than 1.0, sufficient strength cannot be obtained. If Ni exceeds 4.5% by mass, cracking occurs during hot rolling.

ここで，[％i]は元素ｉの含有濃度（質量％）である。また，２４，１６，３２，７９，１２８，３１，７５，１２２および２０９は，それぞれＭｇ，Ｏ，Ｓ，Ｓｅ，Ｔｅ，Ｐ，Ａｓ，ＳｂおよびＢｉの原子量である。不純物と化合物を形成していないフリ−のＭｇ，すなわち特性改善に寄与するＭｇの濃度を[％Ｍｇ]₀とすると，

となる。[％Ｍｇ]₀が強度および応力緩和特性と相関をもつことは，本発明者の実験によって確かめられた。この場合，[％Ｍｇ]₀=０〜０．０１の範囲では[％Ｍｇ]₀が増加するとともに特性が急激に向上し，[％Ｍｇ]₀が０．０１を超えると，[％Ｍｇ]₀増加による特性の向上は緩やかになった。そこで，十分なＭｇ添加効果を得るための条件を，

と規定する。この関係式により，不純物等価濃度（Ｔ）が決まっている場合はＭｇの最少添加濃度が規定され，Ｍｇ濃度が決まっている場合は不純物等価濃度（Ｔ）の最大許容値が規定される。 (2) Mg, O, S, Se, Te, P, As, Sb and Bi concentrations O, S, Se, Te, P, As, Sb and Bi are MgO, MgS, MgSe, MgTe, Mg ₃ P, respectively. By forming ₂ , Mg ₃ As ₂ , Mg ₃ Sb ₂ and Mg ₃ Bi ₂ , the effect of adding Mg to the Cu—Ni—Si based copper alloy is reduced. When all of O, S, Se, Te, P, As, Sb, and Bi form the above compound with Mg, the concentration of Mg consumed for compound formation is estimated to be 24T. T is a parameter indicating the equivalent concentration of impurities, and is given by the following equation.

Here, [% i] is the content concentration (mass%) of the element i. Further, 24, 16, 32, 79, 128, 31, 75, 122 and 209 are the atomic weights of Mg, O, S, Se, Te, P, As, Sb and Bi, respectively. Assuming that the concentration of free Mg that does not form a compound with impurities, that is, Mg that contributes to property improvement, is [% Mg] ₀ ,

It becomes. It has been confirmed by experiments of the present inventors that [% Mg] ₀ has a correlation with strength and stress relaxation characteristics. In this case, [% Mg] ₀ = in the range of 0 to 0.01 is [% Mg] ₀ is characteristic with increases rapidly increase, exceeds [% Mg] ₀ is 0.01, [% Mg] The improvement in characteristics due to an increase of ₀ has become gradual. Therefore, the conditions for obtaining a sufficient Mg addition effect are as follows:

It prescribes. According to this relational expression, when the impurity equivalent concentration (T) is determined, the minimum addition concentration of Mg is defined, and when the Mg concentration is determined, the maximum allowable value of the impurity equivalent concentration (T) is defined.

  On the other hand, the Mg addition concentration [% Mg] needs to be 0.20% or less. This is because if the amount of Mg exceeds 0.20%, the casting surface of the ingot deteriorates and surface defects are generated by hot rolling. When obtaining a particularly good casting surface, it is preferable to set [% Mg] to 0.15% or less.

となる。 The impurity equivalent concentration T needs to be 0.005 or less. When T exceeds 0.005, MgO, MgS, MgSe, MgTe, Mg ₃ P ₂ , Mg ₃ As ₂ , Mg ₃ Sb ₂ are satisfied even if the amount of Mg added is adjusted and the relationship of formula (3) is satisfied. This is because non-metallic inclusions such as Mg ₃ Bi ₂ increase, the inclusions appear on the surface during cold rolling, surface defects occur, and the properties such as elongation and bending deteriorate. . The conditions for obtaining good characteristics and manufacturability are summarized as follows.

It becomes.

  In Cu-Ni-Si-Mg-based alloys, the regulation of the concentrations of S, Se, Te, As, Sb, and Bi has been proposed in Japanese Patent Laid-Open No. 63-297531. It is to improve the hot workability of a Cu—Ni—Si—Mg based alloy containing 001 to 0.01% Mg. On the other hand, the Cu—Ni—Si—Mg alloy of the present invention contains 0.01% Mg in addition to 24T (estimated value of Mg that forms a compound with impurities) as is clear from the formula (3). Of the above impurities, there is almost no solid solution. Therefore, even though the ingot casting surface is slightly inferior due to Mg, there is almost no deterioration in hot workability due to the presence of the impurities.

Further, since the amount of Mg added in JP-A-63-297531 is as small as 0.01% by mass at the maximum, the strength and stress relaxation characteristics of the Cu—Ni—Si based copper alloy cannot be sufficiently improved.
In the Cu—Ni—Si—Mg based copper alloy, attention has been paid to the relationship between the Mg concentration and the impurity concentration, and no technology for improving the characteristics has been reported in the past.

(3) C concentration Even when T and [% Mg] are equal, if containing 0.0005 mass% or more of C, strength and stress relaxation characteristics are improved. However, if the C concentration exceeds 0.0015% by mass, C segregates at the grain boundaries of the ingot, and intergranular cracking occurs in the ingot. The C concentration range for achieving both the characteristic improvement effect and manufacturability is 0.0005 to 0.0015 mass%.

  In JP-A-11-43731, a Cu—Ni—Si—Mg based copper alloy containing 0.0003 to 0.01 mass% of C is proposed. The purpose of C addition in this invention is to reduce flash, dripping, etc. during stamping (pressing), and C improves the strength and stress relaxation characteristics of Cu—Ni—Si—Mg based copper alloys. Is not mentioned. Thus, since the object of the invention is different, the alloy according to the embodiment of JP-A-11-43731 contains a high concentration of 0.0015 to 0.080 mass%. Even if 0.0015 mass% or more of C is added, the strength and stress relaxation characteristics are hardly improved, and the manufacturability of the alloy is only lowered.

(4) Sn, Fe, Co, Mo, Mn, Zn, Ag
In order to improve the strength of Cu—Ni—Si—Mg, one or more of Sn, Fe, Co, Mo, Mn, Zn, and Ag can be added.

  When the total amount of one or more types is 0.01% by mass or less, the effect of improving the strength is small, and when the total amount of one or more types exceeds 2.0% by mass, the conductivity is lowered. Therefore, the total amount of one or more types is set to 0.01 to 2.0 mass%.

  Electrolysis was performed in a copper nitrate bath using commercially available electrolytic copper as an anode, and high-purity copper was deposited on the cathode. The concentrations of S, Se, Te, P, As, Sb, and Bi in this high purity copper were all less than 0.0001% by mass. Hereinafter, this high purity copper was used as a raw material.

Using a high frequency induction furnace, 2 kg of high-purity copper was melted in a graphite crucible having an inner diameter of 60 mm and a depth of 200 mm. After covering the surface of the molten copper with charcoal pieces, predetermined amounts of Ni, Si and Mg were added to adjust the molten copper temperature to 1200 ° C. Next, O, S, Se, Te, P, As, Sb, and Bi were added to adjust the impurity concentration. Cu ₂ O was used for addition of O, and a mother alloy of each element was used for addition of impurities other than O. Thereafter, the molten metal was cast into a mold to produce an ingot having a width of 60 mm and a thickness of 30 mm.

Next, this ingot was heated at 950 ° C. for 3 hours and then hot-rolled to a thickness of 8 mm. The oxide scale on the surface of the hot rolled sheet was ground and removed by a grinder, and then cold rolled to a sheet thickness of 0.2 mm. As a solution treatment, after heating at 800 ° C. for 20 seconds and quenching in water, the surface oxide film was removed by chemical polishing. Thereafter, cold rolling was performed at a workability of 25%, and the plate thickness was 0.15 mm. Finally, it was heated at 460 ° C. for 6 hours in hydrogen as an aging treatment.
The following test was performed on the sample thus prepared.

(1) Component analysis Ni, Si and Mg concentrations are determined by ICP-emission spectroscopy, O concentrations are determined by inert gas melting-infrared absorption method, and S, Se, Te, P, As, Sb and Bi concentrations are determined by ICP-mass. In the analytical method, the C concentration was measured by the combustion-infrared absorption method.

(2) 0.2% proof stress No. 13B test piece defined in JIS-Z2201 (2003) was collected in a direction in which the tensile direction was parallel to the rolling direction. Using this test piece, a tensile test was conducted according to JIS-Z2241 (2003) to obtain 0.2% yield strength.

(3) Stress relaxation rate A strip-shaped test piece having a width of 10 mm and a length of 100 mm was collected so that the longitudinal direction of the test piece was parallel to the rolling direction. As shown in FIG. 1, with the position of l = 50 mm as the working point, a deflection of y ₀ was given to the test piece, and a stress (σ ₀ ) corresponding to 80% of the 0.2% proof stress was applied. y ₀ was determined by the following equation.
y ₀ = (2/3) · l ² · σ ₀ / (E · T)
Here, E is Young's modulus (131 GPa), and T is the thickness of the sample. Unloading after heating at 150 ° C. for 1000 hours, measuring the amount of permanent deformation (height) y as shown in FIG. 2, and the stress relaxation rate {[y (mm) / y0 (mm)] × 100 (%)} Was calculated.

Table 1 shows the component composition, 0.2% proof stress and stress relaxation rate. The C concentration of all the samples was within the range of 0.0008 to 0.0010% by mass.

が満たされおり，６００ＭＰａを超える高い耐力，および１５％を下回る低い応力緩和率が得られている。また，[％Ｍｇ]が０．１５％以下であるＮｏ.１〜１３のインゴット鋳肌は良好であり，熱間圧延後のグラインダ−研削において，表面を０．５ｍｍ除去することにより，良好な表面品質が得られた。[％Ｍｇ]が０．１５〜０．２０のＮｏ．１４については，良好な表面品質を得るために必要な熱間圧延板表面のグラインダ−研削量は１ ｍｍであった。 In Invention Examples No. 1 to 14,

Is satisfied, and a high yield strength exceeding 600 MPa and a low stress relaxation rate of less than 15% are obtained. Moreover, the ingot casting surface of No. 1-13 whose [% Mg] is 0.15% or less is good, and it is good by removing the surface by 0.5 mm in the grinder grinding after hot rolling. The surface quality was obtained. No. [% Mg] is 0.15 to 0.20. For No. 14, the amount of grinder grinding on the surface of the hot-rolled sheet necessary for obtaining good surface quality was 1 mm.

であり，０．２％耐力が６００ＭＰａを下回り，応力緩和率が２０％を超えた。 On the other hand, No. as a comparative example. 15-18 are

The 0.2% proof stress was less than 600 MPa, and the stress relaxation rate exceeded 20%.

  The comparative example No. In No. 19, [% Mg] exceeded 0.2, so even if the surface of the hot-rolled sheet was ground by 1 mm, a cracked portion remained on the surface. The specimens for tensile tests and stress relaxation properties were collected with the surface defects removed.

  Furthermore, No. with T exceeding 0.005. For No. 20, surface flaws occurred during cold rolling due to non-metallic inclusions present on the surface.

の範囲において，[％Ｍｇ]−２４Ｔが増加すると特性が急激に向上すること，
（２）

の範囲では， [％Ｍｇ]−２４Ｔが増加すると，特性が緩やかに向上すること，
（３）

の範囲では， [％Ｍｇ]−２４Ｔが増加しても特性がほとんど変化しないこと,
がわかる。 3 and 4 show the relationship between [% Mg] -24T and 0.2% proof stress and stress relaxation rate, respectively. [% Mg] -24T is a parameter indicating the concentration of free Mg that does not form a compound with impurities.
(1)

When [% Mg] -24T is increased in the range of
(2)

When [% Mg] -24T is increased, the characteristics improve gradually.
(3)

In the range of, the characteristics hardly change even when [% Mg] -24T increases,
I understand.

  Using a high frequency induction furnace, 2 kg of high purity copper was melted in a graphite crucible or alumina crucible having an inner diameter of 60 mm and a depth of 200 mm. After covering the surface of the molten copper with charcoal pieces, predetermined amounts of Ni, Si, and Mg were added, and the molten metal temperature was maintained at a temperature of 1150 to 1450 ° C. for 10 minutes. By using an alumina crucible instead of using a graphite crucible, the C concentration in Cu—Ni—Si—Mg is lowered. Moreover, since the solubility of C in Cu-Ni-Si-Mg increases as the temperature increases, the C concentration increases as the holding temperature of the molten metal increases.

  Then, after adding O, S, Se, Te, P, As, Sb, Bi and adjusting the impurity concentration, the molten metal temperature is adjusted to 1200 ° C., the molten metal is cast into a mold, and the width is 60 mm and the thickness is 30 mm. An ingot was manufactured.

  Next, this ingot was heated at 950 ° C. for 3 hours and then hot-rolled to a thickness of 8 mm. The oxide scale on the surface of the hot-rolled material was ground and removed by a grinder, and then cold-rolled to a thickness of 0.3 mm. As a solution treatment, after heating at 800 ° C. for 20 seconds and quenching in water, the surface oxide film was removed by chemical polishing. Thereafter, cold rolling with a workability of 50% was performed to a plate thickness of 0.15 mm, and an aging treatment was performed in hydrogen at 440 ° C. for 6 hours. After aging, it was cold-rolled with a workability of 20% to a sheet thickness of 0.12 mm, and finally heated in hydrogen at 300 ° C. for 30 minutes for strain relief annealing. While the process of Example 1 is a process that places importance on ductility such as bending and elongation, the process of Example 2 is a process that places importance on strength.

  The prepared sample was subjected to component analysis in the same manner as in Example 1 to evaluate 0.2% proof stress and stress relaxation characteristics.

表２に，成分組成，０．２％耐力および応力緩和率を示す。Ｔを０．０００５程度に調整し，るつぼの種類および溶湯保持温度によりＣ濃度を変化させている。図５，６に示すように，

の範囲において，Ｃ濃度の増加とともに，0.2％耐力が増加し，応力緩和率が低下している。Ｃ添加の効果は，[％Ｃ]＝０．０００５％でほぼ飽和している。０．０００１５質量％を超えるＣを含有するＮｏ．２７〜２８では，インゴットの内部において，Ｃの粒界偏析に起因する割れが発生し，この割れにより製造歩留まりが低下した。
（実施例３）

Table 2 shows the component composition, 0.2% proof stress and stress relaxation rate. T is adjusted to about 0.0005, and the C concentration is changed depending on the type of the crucible and the molten metal holding temperature. As shown in FIGS.

In the range, the 0.2% proof stress increases and the stress relaxation rate decreases as the C concentration increases. The effect of C addition is almost saturated at [% C] = 0.0005%. No. containing C exceeding 0.00015% by mass. In Nos. 27 to 28, cracks due to segregation of C grain boundaries occurred inside the ingot, and the production yield decreased due to the cracks.
(Example 3)

  The effect of the present invention was verified for Cu—Ni—Si—Mg based copper alloy strips to which elements such as Sn, Fe, Co, Mo, Mn, Zn, and Ag were added. The experimental method is the same as in Example 1. However, Sn, Fe, Co, Mo, Mn, Zn and Ag concentrations were measured by ICP-emission spectroscopy.

表３に評価結果を示す。Ｓｎ，Ｆｅ，Ｃｏ，Ｍｏ，Ｍｎ，Ｚｎ，Ａｇ等の元素を添加したＣｕ−Ｎｉ−Ｓｉ−Ｍｇ系銅合金条においても，

に調整することにより，０．２％耐力が上昇し，応力緩和率が小さくなることがわかった。

Table 3 shows the evaluation results. Even in a Cu—Ni—Si—Mg based copper alloy strip to which elements such as Sn, Fe, Co, Mo, Mn, Zn, and Ag are added,

It was found that the 0.2% proof stress increased and the stress relaxation rate decreased by adjusting to.

It is explanatory drawing of a stress relaxation test method. It is explanatory drawing regarding the amount of permanent deformation of a stress relaxation test method. It is a figure which shows the relationship between [% Mg] -24T and 0.2% yield strength. It is a figure which shows the relationship between [% Mg] -24T and a stress relaxation rate. It is a figure which shows the relationship between C density | concentration and 0.2% yield strength. It is a figure which shows the relationship between C density | concentration and a stress relaxation rate.

Claims (1)

Containing 1.0 to 4.5% by mass of Ni, containing Si at a concentration of 1/6 to 1/4 with respect to the mass% concentration of Ni, further containing Mg, the balance being Cu and inevitable impurities Cu alloy composed of 0.00054 to 0.0015 mass% of C, Mg concentration and O, S, Se, Te, P, As, Sb and Bi in the inevitable impurities By adjusting the equivalent concentration (T) to the range of the following formula and setting the free Mg content to 0.01% by mass or more, it has a proof stress exceeding 600 MPa and a stress relaxation rate of less than 15%. Cu-Ni-Si-Mg-based copper alloy strips having excellent stress relaxation properties.

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