COPPER ALLOY

Info

Publication number: 20110186187
Type: Application
Filed: Apr 11, 2011
Publication Date: Aug 4, 2011
Applicant: THE FURUKAWA ELECTRIC CO., LTD. (Tokyo)
Inventors: Kuniteru MIHARA (Tokyo), Nobuyuki TANAKA (Tokyo), Tatsuhiko EGUCHI (Tokyo), Kiyoshige HIROSE (Tokyo)
Application Number: 13/083,874

Abstract

A method of producing a copper alloy containing: Ni and/or Si and at least one or more of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be, the copper alloy having a precipitate X composed of Ni and Si, and a precipitate Y composed of Ni and/or Si, and at least one or more of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be, in which a grain diameter of the precipitate Y is 0.01 to 2 μm.

Description

Description

CROSS-REFERENCE TO RELATED CASES

This application is a divisional of U.S. application Ser. No. 11/846,074, filed on Aug. 28, 2007, which was a continuation application of International Application No. PCT/JP2006/303738, filed on Feb. 28, 2006, which was based on and claims priority under 35 U.S.C. §119(a) of Japanese Application Nos. 2005-055144 filed on Feb. 28, 2005 and 2005-055147 filed on Feb. 28, 2005, both of which being incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method of producing copper alloy applicable as materials for electric and electronic instruments.

BACKGROUND ART

Heretofore, generally, in addition to iron-based materials, copper-based materials, such as phosphor bronze, red brass, and brass, which are excellent in electrical conductivity and thermal conductivity, have been used widely as materials for electric and electronic instruments (electrical and electronic machinery and tools).

Recently, demands for miniaturization, weight saving, and associated high-density packaging of parts of electric and electronic instruments have increased, and various characteristics of higher levels are required for the copper-based materials applied thereto. Examples of basic characteristics required include mechanical properties, electrical conductivity, stress relaxation resistance, bending property, and spring property. Of those, improvements in stress relaxation resistance, tensile strength, and bending property are strongly required, for satisfying the recent demands for the miniaturization of parts or components for the products described above. In particular, for miniaturizing electronic parts, for example, tensile strength and bending property are necessary for lead frame materials, while stress relaxation resistance as well as tensile strength is necessary for connectors and terminal materials.

The requirements for those materials differ form each other little by little, depending on uses, kinds, shapes, or the like of the parts, and specific requirements include: a tensile strength of 700 MPa or more and a bending property of R/t≦1.0 (in which R represents a bending radius, and t represents a sheet thickness), or a tensile strength of 800 MPa or more and a bending property of R/t≦2.0; more preferably a tensile strength of 800 MPa or more and a bending property of R/t<1.5, or a tensile strength of 900 MPa or more and a bending property of R/t<2.0.

Thinning of the material is inevitable in association with miniaturization of the parts. Accordingly, conventional copper alloys are not always durable to long term uses due to increased stress loaded on the material and increased temperatures of working environments. Under these situations, more improved stress relaxation resistance is desired. Minimum stress relaxation resistance is a value defined by the Standard of the Electronic Materials Manufacturers Association of Japan (EMAS-3003), wherein the copper alloy material is desired to satisfy a stress relaxation ratio of less than 20% at a temperature condition of 150° C.

The required characteristics have reached a level that cannot be satisfied with conventional commercially available, mass-produced alloys, such as phosphor bronze, red brass, and brass. Thus, conventionally, such alloys each have an increased strength by: allowing Sn or Zn having a very different atomic radius from that of copper as a matrix phase, to be contained as a solid solution in Cu; and subjecting the resultant alloy having the solid solution to cold-working such as rolling or drawing. The method can provide high-strength materials by employing a large cold-working ratio, but employment of a large cold-working ratio (generally 50% or more) is known to conspicuously degrade bending property of the resultant alloy material. The method generally involves a combination of solid solution strengthening and working strengthening.

An alternative strengthening method is a precipitation strengthening method (a precipitation hardening method) that involves formation of a precipitate of a nanometer order in the materials. The precipitation strengthening method has merits of increasing strength and improving electrical conductivity at the same time, and is used for many alloys.

Of those, a strengthened alloy prepared by forming a precipitate composed of Ni and Si by adding Ni and Si into Cu, so-called a Corson alloy, has a remarkably high strengthening ability compared with many other precipitation-type alloys. This strengthening method is also used for some commercially available alloys (e.g. CDA70250, a registered alloy of Copper Development Association (CDA)). When the alloy generally subjected to precipitating strengthening is used for terminal/connector materials, the alloy is produced through a production process incorporating the following two important heat treatments. One is a heat treatment which involves heat treatment at a high temperature (generally 700° C. or higher) near a melting point, so-called solution treatment, to allow Ni and Si precipitated through casting or hot-rolling to be contained as a solid solution into a Cu matrix. The other is a heat treatment which involves heat treatment at a lower temperature than that of the solution treatment, so-called aging treatment, to precipitate Ni and Si, which are in the solid solution caused at the high temperature, as a precipitate. The strengthening method utilizes a difference in concentrations of Ni and Si entering Cu as a solid solution at high temperatures and low temperatures.

An example of the Corson alloy applicable for electric and electronic instruments includes an alloy having a defined grain size of precipitate (see, for example, Patent Document 1). However, the precipitation-type alloy has such problems that the crystal grain size increases to cause giant crystal grains upon the solution treatment, and that the crystal grain size upon the solution treatment remains unchanged and becomes the crystal grain size of a product since the aging treatment generally does not involve recrystallization. An increased amount of Ni or Si to be added requires a solution treatment at a higher temperature, and it results in that the crystal grain size tends to increase to cause giant crystal grains, through a heat treatment in a short period of time. The resultant giant crystal grains occurred in this way cause problems of conspicuous deterioration in bending property.

Alternatively, a method of improving the bending property of a copper alloy involves addition of Mn, Ni, and P for a mutual reaction to precipitate a compound, without use of a Ni—Si precipitate (see, for example, Patent Document 2). However, the resultant alloy has a tensile strength of about 640 MPa at most, which is not sufficient for satisfying the recent demands for high strength through miniaturization of parts. Addition of Si to the copper alloy decreases the amount of the Ni—P precipitate, to thereby reduce the mechanical strength and electrical conductivity. Further, excess Si and P cause problems of occurrence of crack upon hot working.

As is apparent from the above, the bending property is hardly maintained with increasing tensile strength. Accordingly, it is desired to develop the copper alloy allowing tensile strength, bending property, electrical conductivity, and stress relaxation resistance to be compatible at high levels to one another or keeping a good balance among them, while these properties are able to be controlled depending on the uses.

Other and further features and advantages of the present invention will appear more fully from the following description.

Patent Document 1: JP-A-11-43731 (“JP-A” means unexamined published Japanese patent application)

Patent Document 2: JP-A-2003-82425

DISCLOSURE OF INVENTION

For solving the above-mentioned problems, the present invention contemplates providing a copper alloy having high bending property and excellent tensile strength, electrical conductivity and stress relaxation resistance, wherein characteristics of the copper alloy may be readily balanced depending on uses, and the copper alloy is favorable for materials of lead frames, connectors, terminals or the like of electric and electronic instruments, particularly for materials of vehicle connectors, terminals, relays and switches or the like.

The inventors of the present invention have conducted intensive studies on a copper alloy suitably used for electrical and electronic parts, and have noticed the relations between characteristics of the alloy and grain diameters of Ni—Si precipitates and other precipitates in a copper alloy structure, and between the proportions of the distribution density of the precipitates and suppression of coarsening of crystal grains. As a result, the inventors have completed, through intensive studies, the copper alloy of the present invention that is able to form a material having excellent tensile strength and being excellent in bending property, electrical conductivity, and stress relaxation resistance.

According to the present invention, there is provided the following means:

(1) A copper alloy, having: a precipitate Y composed of Ni and/or Si, and at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be; and a precipitate X composed of Ni and Si, wherein a grain diameter of the precipitate Y is 0.01 to 2 μm;

(2) The copper alloy, wherein the grain diameter of the precipitate Y is 0.02 to 0.9 μm;

(3) A copper alloy, having: a precipitate X composed of Ni and Si; and at least one precipitate selected from the group consisting of a precipitate Y1 composed of Ni, Si, and Cr, a precipitate Y2 composed of Ni, Si, and Co, a precipitate Y3 composed of Ni, Si, and Zr, and a precipitate Z composed of Ni, Si, and B, wherein a grain diameter of the at least one precipitate selected from the group consisting of the precipitates Y1, Y2, Y3, and Z is 0.1 to 2 μm;

(4) A copper alloy, comprising: N±2.0 to 5.0 mass %, S±0.3 to 1.5 mass %, at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be each in an amount of 0.005 to 1.0 mass %, with a balance being Cu and inevitable impurities; said copper alloy having a precipitate X composed of Ni and Si; and a precipitate Y composed of Ni, Si, and at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be, wherein a grain diameter of the precipitate Y is 0.01 to 2 μm;

(5) A copper alloy, comprising: N±2.0 to 5.0 mass %, S±0.3 to 1.5 mass %, at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be each in an amount of 0.005 to 1.0 mass %, with a balance being Cu and inevitable impurities; said copper alloy having a precipitate X composed of Ni and Si; and a precipitate Y composed of Ni or Si, and at least two or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be, wherein a grain diameter of the precipitate Y is 0.01 to 2 μm;

(6) A copper alloy, comprising: N±2.0 to 5.0 mass %, S±0.3 to 1.5 mass %, at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be each in an amount of 0.005 to 1.0 mass %, with a balance being Cu and inevitable impurities; said copper alloy having a precipitate X composed of Ni and Si; and a precipitate Y composed of at least three or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be, wherein a grain diameter of the precipitate Y is 0.01 to 2 μm;

(7) The copper alloy according to any one of Claims (1) to (6), wherein the melting point of the precipitate Y is higher than a solid solution treatment temperature;

(8) The copper alloy according to any one of (1) to (7), wherein the number of precipitates X per mm²is 20 to 2,000 times the number of precipitates Y per mm²;

(9) The copper alloy according to any one of Claims (1) to (8), wherein the number of precipitates X is 10⁸to 10¹²per mm², and the number of precipitates Y is 10⁴to 10⁸per mm²;

(10) The copper alloy according to any one of Claims (1) to (9), wherein a composition of the copper alloy further comprises at least one or more selected from Sn 0.1 to 1.0 mass %, Zn 0.1 to 1.0 mass %, and Mg 0.05 to 0.5 mass %;

(11) The copper alloy according to any one of (1) to (10), which has a stress relaxation ratio of less than 20%; and

(12) The copper alloy according to any one of (1) to (11), which is for use as a material of an electric or electronic instrument.

The copper alloy of the present invention compatibly has a tensile strength and a bending property (R/t) at high levels, without impairing electrical conductivity, while stress relaxation resistance that may largely affect reliability of connectors and terminals is further improved. The copper alloy of the present invention is excellent in bending property and stress relaxation resistance, as compared with conventional copper alloys having the same level of tensile strength. The copper alloy of the present invention is a copper alloy favorable for use in electric and electronic instruments that are required for higher characteristics upon miniaturization. In addition to the above, the copper alloy of the present invention is excellent in other properties such as spring property.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferable embodiments of the copper alloy of the present invention will be described in detail.

The copper alloy of the present invention is an inexpensive, high-performance copper alloy maintaining high electrical conductivity, having excellent bending property and other favorable properties, and it is preferable for a variety of electric and electronic instruments including electronic parts, e.g. vehicle terminals/connectors, relays, and switches.

Preferable embodiments of the copper alloy of the present invention will be described in detail.

The present invention relates to controlling of a grain size of a precipitate of a copper alloy. To be specific, a method of controlling a grain size has been realized from two standpoints.

First, the method of controlling a grain size can be realized by using an element that does not allow a crystal grain size to increase to cause giant grains upon a solution treatment. Each of precipitates composed of Ni, Si and α; Ni, a and β; Si, α and β; and α, β and γ (herein α, β and γ each are an element other than Ni and Si) does not form any solid solution in a Cu matrix phase even at high temperatures of the solution treatment, and that the precipitate exists in crystal grains of the Cu matrix phase and the precipitate grains, to exhibit an action and effect of suppressing growth of the crystal grains of the matrix.

Second, the method of controlling a grain size can be realized by using an element that serves as a nucleus at initial recrystallization upon the solution treatment. An intermetallic compound which is a precipitate composed of Ni, Si and α; Ni, α and β; Si, α and β; and α, β and γ (herein α, β and γ each are an element other than Ni and Si) serves as a nucleation site for recrystallization at a solution treatment temperature, and that more crystal grains are formed (nucleation) than that in the case where the precipitate is not added. Formation of more crystal grains causes mutual interference of the crystal grains during grain growth, to thereby suppress the grain growth. Multi-component precipitates are preferable for the action and effect of the nucleation site for recrystallization.

In the present invention, the term “precipitate” means to include intermetallic compounds, carbides, oxides, sulfides, nitride, compounds (solid solutions), and element metals.

The aforementioned precipitate is not to form any solid solution in the Cu matrix even during the solution treatment. That is, the precipitate must have a melting point higher than the solution treatment temperature. The precipitate is not limited to the aforementioned precipitates as long as it has a melting point higher than the solution treatment temperature. Further, the precipitate is not limited as long as it provides an effect of preventing growth of too large crystal grains during the solution treatment or forming many crystal grains (nucleation) by serving as a nucleation site for recrystallization.

The copper alloy of the present invention is an inexpensive, high-performance copper alloy maintaining high electrical conductivity, having excellent bending property and other favorable properties, and it is preferable for a variety of electric and electronic instruments including electronic parts, e.g. vehicle terminals/connectors, relays, and switches.

Next, an alloy structure of the copper alloy of the present invention will be described.

The grain diameter of the precipitate X composed of Ni and Si is preferably 0.001 to 0.1 μm, more preferably from 0.003 to 0.05 μm, and further preferably 0.005 to 0.02 μm. The strength is not improved when the grain diameter is too small, while the bending property decreases when the grain diameter is too large.

The precipitate Y composed of Ni and/or Si and at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co and Be; the precipitate Y1 composed of Ni, Si and Cr; the precipitate Y2 composed of Ni, Si and Co; and the precipitate Y3 composed of Ni, Si and Zr each have larger effects for fining crystal grains than Ni—Si precipitate X does, during the solid solution treatment as a heat treatment at high temperatures. Those effects become particularly large by the precipitate Y1 and the precipitate Y2.

This effect acts for improving bending property. Since solid solution treatment can be applied at higher temperatures than temperatures of the conventional solid solution treatment, this effect can contribute to improvements of the tensile strength and the stress relaxation resistance by increasing the amount of the solid solution in the copper alloy as well as the amount of precipitates during aging treatments. This effect is particularly enhanced when the melting point of precipitate Y is higher than the melting point of precipitate X. The melting point of precipitate X is preferably from 650 to 1,050° C., and the melting point of precipitate Y is preferably higher than the melting point of precipitate X and 1,100° C. or less.

The grain diameter of precipitate Y is preferably 0.01 to 2.0 μm, more preferably 0.05 to 0.5 μm, and most preferably from 0.05 to 0.13 μm. This is because an effect for suppressing growth of crystal grains and an effect for increasing the number of nucleation sites are not exhibited when the grain diameter is too small, while the bending property decreases when the grain diameter is too large. In the present invention, the grain diameter of precipitate Y is preferably larger than the grain diameter of precipitate X. The ratio of the grain diameters between Y and X (Y/X) preferably exceeds 1 and 2,000 or less, more preferably 5 to 500.

Next, the action and effect of each alloy element and a range of addition amount of the alloy element will be described.

Ni and Si are elements that can be added in a controlled addition ratio of Ni to Si for forming a Ni—Si precipitate for precipitation strengthening, to thereby enhance the mechanical strength of the copper alloy. The amount of Ni to be added is generally 2.0 to 5.0 mass %, preferably 2.1 to 4.6 mass %. The Ni amount is more preferably 3.5 to 4.6 mass %, for satisfying a tensile strength of 800 MPa or more and a bending property of R/t<1.5, or a tensile strength of 900 MPa or more and a bending property of R/t<2. A too small Ni amount provides a small precipitated and hardened amount that results in insufficient mechanical strength, and a too large Ni amount results in a conspicuously low electrical conductivity.

Further, the ratio of the addition amount of Ni to Si of about 1 to 4 (i.e. the amount of Ni to be added being 4 vs. that of Si being about 1) in terms of mass ratio, is known to provide the largest strengthening effect. When the Si addition amount exceeds 1.5 mass %, it is apt to cause cracking of an ingot of the copper alloy during hot working. Thus, the Si addition amount is generally 0.3 to 1.5 mass %, preferably 0.5 to 1.1 mass %, more preferably 0.8 to 1.1 mass %. B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be form precipitate Y by themselves or in combination with Ni and/or Si. While precipitate Y serves for suppressing crystal grains from coarsening during the solid solution treatment as described above, it is not responsible for or does not largely contribute to precipitation strengthening. The content of each of the above-mentioned elements is generally 0.005 to 1.0 mass %, preferably 0.007 to 0.5 mass %, and more preferably 0.01 to 0.1 mass %. The quality of an ingot is impaired by forming large crystals during melt-casting when the amount of addition of these elements is too large, while attainment of desired effects is impossible when the amount is too small.

Further, in particularly, Cr, Co and Zr form precipitates in combination with main components, Ni and Si. While the effect is to suppress crystal grains from being coarsened during the solid solution treatment, to thereby control the crystal grain diameter as described above, it does not largely contribute to precipitation strengthening. The amount of addition of these elements is preferably 0.005 to 1.0 mass %, more preferably 0.1 to 0.3 mass % for permitting the effect to be exhibited. The quality of the ingot may be impaired by forming large crystals during melt-casting when the amount of addition of these elements is too large, while the effect of addition is not exhibited when the amount is too small.

B forms a precipitate with main constituents Ni and Si. The effect of B as the same manner as the above Cr, Co or Zr is that B is an element for suppressing increase of the crystal grain size to become too large (giant) during the solution treatment, but B takes no part in the precipitation strengthening. The B addition amount is preferably 0.005 to 0.1 mass %, more preferably 0.01 to 0.07 mass %, for exhibiting the effect. A too large B addition amount results in too large crystallized product during melt-casting to cause problems in ingot quality, and a too small B addition amount provides no addition effect.

Further, Zn, Sn, and/or Mg are preferably added to further improve the characteristics.

Zn is an element which forms a solid solution in a matrix, but Zn addition significantly alleviates solder embrittlement. Thus, Zn is added preferably in an amount of 0.1 to 1.0 mass %. The preferable primary uses of the alloy of the present invention are electric and electronic instruments and electronic part terminal materials such as vehicle terminals/connectors, relays, and switches. Most of them are joined by solder, and thus the enhancement of reliability in the joined portions is one of the important elemental techniques.

Further, Zn addition may lower the melting point of the alloy, to control the states of formation of the precipitate composed of Ni and B and the precipitate composed of Mn and P. Both the precipitates are formed during solidification. Thus, a high solidification temperature of the alloy increases the grain size, to provide a small contribution of the precipitates to the effects of suppressing increase of the crystal grain size and forming a nucleation site for the crystal grains. The lower limit of Zn addition is defined as 0.1 mass %, because it is a minimum necessary amount that provides alleviations in solder embrittlement. The upper limit of Zn addition is defined as 1.0 mass %, because a Zn addition amount more than 1.0 mass % may degrade the electrical conductivity.

Sn and Mg to be added are also preferable elements for their uses. Sn and Mg addition provides an effect of improving creep resistance, which is emphasized in electronic instrument terminals/connectors. The effect is also referred to as stress relaxing resistance, and it is an important characteristic that assumes reliability of the terminals/connectors. Solely addition of Sn or Mg may improve the creep resistance, but the use in combination of Sn and Mg can further improve the creep resistance by a synergetic effect. The lower limit of Sn addition is defined as 0.1 mass %, because it is a minimum necessary amount that provides improvements in creep resistance. The upper limit of Sn addition is defined as 1 mass %, because a Sn addition amount more than 1 mass % may degrade the electrical conductivity. The lower limit of Mg addition is defined as 0.05 mass %, because an addition amount of Mg less than 0.05 mass % provides no effect of improving the creep resistance. The upper limit of Mg addition is defined as 0.5 mass %, because an Mg addition amount of more than 0.5 mass % not only saturates the effect. Further, when an Mg addition amount is more than 0.5 mass %, it may degrade hot-workability at a particularly-high temperature, depending on the composition of the alloy.

Sn and Mg have a function of accelerating formation of a precipitate composed of Ni and Si. It is important to add preferable amounts of these Sn and Mg, serving as fine nucleation sites for the precipitate.

Next, the relationship between the number of precipitate X (the number of grains of the precipitate X) and the number of precipitate Y as another precipitate will be described below.

The number of precipitate X per mm²on an arbitrary cross section in the copper alloy is preferably 20 to 2,000 times the number of corresponding precipitate Y per mm². This is because the bending property is particularly enhanced among the characteristics, and a sufficient mechanical strength can be obtained. The number of the precipitate X is more preferably 100 to 1,500 times the number of the precipitate Y.

Specifically, the number of precipitates X is preferably 10⁸to 10¹²per mm², and the number of precipitates Y that correspond to the precipitates X is preferably 10⁴to 10⁸per mm². This is because the aforementioned ranges provide particularly excellent bending property. If the number of precipitates is too small, the resultant alloy may not have a targeted mechanical strength. On the other hand, if the number of precipitates is too large, the resultant alloy may be poor in bending property. The number of precipitates X is more preferably 5×10⁹to 6×10¹¹per mm², and the number of precipitates Y is more preferably 10⁴to 4×10⁷per mm².

The effect of precipitates becomes remarkable as the amounts of Ni and Si are increased. A tensile strength of 800 MPa or more with the bending property of R/t≦2.0, or a tensile strength of 700 MPa or more with the bending property of R/t≦1.0 may be attained, by controlling the number of precipitates Y as described above. It is also possible to attain a tensile strength of 800 MPa or more with the bending property of R/t<1.5, or a tensile strength of 900 MPa or more with the bending property of R/t<2. With respect to the stress relaxation resistance, the stress relaxation ratio of the copper alloy is preferably less than 20%, more preferably less than 18%, and further preferably 15% or less, in which an open-sided block method prescribed in the Standard of the Electronic Materials Manufacturers Association of Japan (EMAS-3003) is employed with load stress set to be a surface maximum stress of 80%-yield strength (80%-YS, 0.2%-proof stress), and the stress relaxation ratio is measured under the conditions of at 150° C. for 1,000 hours. The number of precipitates is represented by an average number per unit area.

The copper alloy of the present invention may have a crystal grain diameter (i.e. an average of a minor axis diameter and a major axis diameter) of generally 20 μm or less, preferably 10.0 μm or less. If the crystal grain diameter is longer than 10.0 μm, it may be impossible to obtain a tensile strength of 720 MPa or more and a bending property of R/t<2. More preferably, the crystal grain diameter of the copper alloy is 8.5 μm or less. The lower limit of the crystal grain diameter may be generally 0.5 μm or more. The aforementioned crystal grain diameters are measured in the following manner: The crystal grain diameters are measured in two directions parallel to or perpendicular to the finally cold-rolled direction, respectively, on cross sections parallel to the direction of thickness of the alloy sheet and parallel to the finally cold-rolled direction (the direction of the final plastic-working), thereby to determine larger lengths as major axis diameters and smaller lengths as minor axis diameters in respective directions. An average value of each four lengths of the major axis diameters and minor axis diameters is rounded up as a product of multiplying 0.005 mm times an integer, to determine the crystal grain diameter.

Next, a specific example of a preferable production method for the copper alloy according to the present invention involves: melting a copper alloy having the aforementioned preferable element composition; casting into an ingot; and hot-rolling the ingot. More specifically, the production method involves: heating the ingot at a temperature rising rate of 20 to 200° C./hr; holding the resultant ingot at 850 to 1,050° C. for 0.5 to 5 hours; hot-rolling; and, after finishing the hot-rolling at a finishing temperature of 300 to 700° C., quenching the hot-rolled product. In this way, the precipitate X, and the precipitate Y corresponding to the element composition are formed. After hot-rolling, for example, the resultant alloy is formed into a given thickness, through a combination of solution treatment, annealing, and cold-rolling.

The purpose of the solution treatment is to allow Ni and Si precipitated during casting or hot-rolling, to form a solid solution again and to recrystallize at the same time. This permits the amount of the elements in the solid solution to be increased and accumulated distortion during working to be removed, and a basic treatment for improving the strength and bending property can be provided. The temperature of the solution treatment may be adjusted according to a Ni addition amount. As preferable embodiments, the solution treatment temperature is preferably 600 to 820° C. for an Ni amount of 2.0 mass % or more but less than 2.5 mass %, 700 to 870° C. for an Ni amount of 2.5 mass % or more but less than 3.0 mass %, 750 to 920° C. for an Ni amount of 3.0 mass % or more but less than 3.5 mass %, 800 to 970° C. for an Ni amount of 3.5 mass % or more but less than 4.0 mass %, 850 to 1,020° C. for an Ni amount of 4.0 mass % or more but less than 4.5 mass %, and 920 to 1,050° C. for an Ni amount of from 4.5 mass % or more but less than 5.0 mass %. Since crystal grains are suppressed from being coarsened at high temperatures in the alloy of the present invention to which the above-mentioned elements are added, the amount of elements in the solid solution is increased by applying the solid solution treatment at higher temperatures, to thereby enable a high strength to be obtained.

For example, the heat treatment at 900° C. of an alloy material composed of N±3.0 mass % and S±0.7 mass %, allows sufficient Ni—Si precipitates that have already been precipitated, to form again the solid solution. However, the size of the crystal grain far exceeds 10 μm, and the bending property is conspicuously decreased. However, crystal grains with a size of 10 μm or less may be obtained, even by a solid solution treatment at 900° C., from an alloy material to which any one of Cr, Co, Zr, and B is further added.

Further, for example, the heat treatment at 850° C. of an alloy material whose Ni content is 3.0 mass % and Si content is 0.7 mass %, allows sufficiently precipitated Ni and Si, to form again the solid solution and thereby to give crystal grains of 10 μm or less. However, the heat treatment at the same temperature of an alloy having a too small Ni amount causes growth of crystal grains into too large grains to thereby fail in obtaining a grain size of 10 μm or less. Further, on the other hand, a too large Ni amount may not provide an ideal solution state, and the mechanical strength may not be enhanced through the subsequent aging treatment.

The size of the precipitate (e.g. precipitate Y) may be changed, by changing the conditions of the solid solution treatment, i.e. by appropriately selecting the temperature of the solid solution treatment, as described above. For example, a higher temperature of the solid solution treatment (a temperature higher by 50° C. than a standard temperature) is selected for the heat treatment when the size of precipitate Y1 is to be increased, while a lower temperature of solid solution treatment (a temperature lower by 50° C. than a standard temperature) is selected for the heat treatment when the size of precipitate Y1 is to be decreased. In addition, the change of the density is coupled with the change of the crystal grain size, and the density becomes lower as the size is larger, while the density becomes higher as the size is smaller.

The copper alloy of the present invention apparently provides improvement in, in particular, bending property, and optionally stress relaxation resistance, of a high strength copper alloy having a tensile strength of 800 MPa or more, while high electrical conductivity is maintained. Further, the copper alloy of the present invention provides similar improvement in bending property of a copper alloy having a tensile strength of less than 800 MPa. The copper alloy according to the present invention is also excellent in other properties, such as spring property and the like.

EXAMPLES

The present invention will be described in more detail based on examples given below, but the invention is not meant to be limited by these.

Example 1

An alloy component containing Ni, Si, Cr, and other elements in the amounts, as shown in Table 1, with the balance being Cu and inevitable impurities, was melted with a high frequency melting furnace, and the thus-molten alloy was cast at a cooling rate from 10 to 30° C./second, to give an ingot with a size: thickness 30 mm, width 100 mm, and length 150 mm. After holding the ingot at 900° C. for 1 hour, the resultant ingot was subjected to hot-rolling, to give a hot-rolled sheet with a sheet thickness (t) of 12 mm, each of the surfaces of the sheet was chamfered by 1 mm, to adjust the thickness (t) at 10 mm, and then the sheet was finished at a thickness (t) of 0.167 mm by cold-rolling. The sheet material was then subjected to solid solution treatment. The temperature of the solid solution treatment was selected, in accordance with the conditions described in the foregoing paragraph [0026]. For changing the size of precipitate Y1, a higher solid solution treatment temperature (a temperature higher by 50° C. than a standard temperature) was selected when the size of precipitate Y1 was to be increased, while a lower solid solution temperature (a temperature lower by 50° C. than a standard temperature) was selected when the size of precipitate Y1 was to be decreased, for conducting the heat treatment. The change of the density was coupled with the change of the crystal grain size, and the density became lower as the size was larger, while the density became higher as the size was smaller.

Immediately after the solution treatment, the sheet material was subjected to water quenching. Then, each of the resultant alloys was subjected to aging at a temperature of 450 to 500° C. for 2 hours and cold-rolling with a working ratio of 10%, to thereby obtain a sample of t=0.15 mm.

The following characteristics of the thus-obtained samples were tested and evaluated as mentioned in below, and the results are shown in Table 2.

a. Electrical Conductivity (EC):

Electrical conductivity was calculated by measuring a specific resistance of the sample through a four terminal method in a thermostatic bath maintained at 20° C. (±0.5° C.). The distance between the terminals was set to 100 mm.

b. Tensile Strength (TS):

Tensile strengths of 3 test pieces prepared according to JIS Z 2201-13B cut out from the sample in a direction parallel to the rolling direction, were measured according to JIS Z 2241, and an average value thereof was obtained.

c. Bending Property:

A test piece was cut out from the sample in a direction parallel to the rolling direction into a size of width 10 mm and length 25 mm. The resultant test piece was W-bent at 90° at a bending radius R that would be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, or 0.6 (mm), with a bending axis being perpendicular to the rolling direction. Whether cracks were occurred or not at the bent portion, was observed with the naked eye through observation with an optical microscope of 50 times magnification, and the bent sites were observed with a scanning electron microscope to examine whether cracks were observed or not. Evaluation results are designated by R/t (in which R represents a bending radius (mm), and t represents a sheet thickness (mm)), and the R/t was calculated by employing a (limit) maximum R at which cracks were occurred. If no crack is formed at R=0.15 and cracks are formed at R=0.1, since the sample had a thickness (t)=0.15 mm, R/t=0.15/0.15=1 is obtained, which is shown in the following table. As the value of R/t is smaller, the bending property is improved.

d. Grain Size of Precipitate and Distribution Density:

The sample was punched out into a shape of a disc of diameter 3 mm, and the resultant was subjected to thin-film-polishing by using a twinjet polishing method. Photographs (5,000 and 100,000 times magnification) of the resultant sample were taken at 3 arbitrary positions with a transmission electron microscope at accelerating voltage 300 kV, and the grain size of the precipitate and the density thereof were measured on the photographs. Measurement of the grain size and density of the precipitate were carried out in the following manner: setting an incident electron beam azimuth to [001], and measuring the number of fine grains of the precipitate X composed of Ni—Si in a high-power photograph (100,000 times magnification) at n=100 (n represents the number of viewing fields for observation), since the precipitate X was fine; and, on the other hand, measuring the number of grains of the precipitate Y1 in a low-power photograph (5,000 times magnification) at n=10; thereby to eliminate the localized bias on the numbers. The numbers were calculated into numbers per unit area (/mm²).

e. Crystal Grain Diameter:

The crystal grain diameter was measured according to JIS H 0501 (cutting method). The crystal grain diameters were measured in two directions parallel to and perpendicular to the finally cold-rolled direction, respectively, on cross sections parallel to the direction of thickness of the alloy sheet and parallel to the finally cold-rolled direction (the direction of the final plastic-working). The thus-measured lengths were classified into larger lengths as major axis diameters and smaller lengths as minor axis diameters in respective directions. An average value of each four lengths of the major axis diameters and minor axis diameters was rounded up as a product of multiplying 0.005 mm times an integer, to determine the crystal grain diameter.

TABLE 1 Ni Si Cr Other Classification No. [mass %] [mass %] [mass %] [mass %] Example 1 2.31 0.52 0.08 — according to 2 3.22 0.73 0.62 — this invention 3 3.82 0.86 0.19 Zn: 0.51 4 4.22 0.95 0.22 Zn: 0.49 Sn: 0.15 Mg: 0.11 5 4.81 1.09 0.41 Zn: 0.50 Sn: 0.12 Comparative 100 2.37 0.56 0.09 — example 101 3.35 0.80 0.13 — 102 3.94 0.94 0.19 Zn: 0.52 Sn: 0.15 103 4.29 1.02 0.22 —

TABLE 2 Number Crystal Grain size of Grain size of of Y1/ grain Bending precipitate X precipitate Y1 number diameter TS EC property Classification No. [μm] [μm] of X [μm] [MPa] [% IACS] [R/t] Example 1 0.02 0.21 330 5 722 44 1.0 according to 2 0.03 0.19 430 6 764 40 1.0 this invention 3 0.05 0.22 58 8 805 38 1.5 4 0.04 0.17 890 7 846 36 2.0 5 0.04 0.19 1020 5 887 33 2.0 Comparative 100 0.02 2.20 19 18 725 44 1.5 example 101 0.03 0.001 16 22 764 41 2.5 102 0.03 0.004 18 19 803 39 3.0 103 0.04 2.92 10 27 841 36 3.5

From the results shown in Tables 1 and 2, it is understood that the samples according to the present invention have excellent properties in both of the mechanical strength and the bending property. However, since the grain diameter of precipitate Y1 was outside of the range defined in the present invention, the samples in Comparative examples 100, 101, 102 and 103 each were poor in the bending property, as compared with the samples in the examples according to the present invention having the same level of mechanical strength, and the mechanical strength in the comparative examples was not compatible to the bending property. Thus, it is possible to improve the bending property (R/t) while high strength is maintained, by controlling the grain diameter of precipitate Y1 in the Cu alloy system containing Ni, Si, and Cr. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable for materials of lead frames or the like. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property.

Example 2

With respect to the copper alloys containing the elements in the amounts, as shown in Table 3, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1, except that the measurement was made on the precipitate Y2 in place of the precipitate Y1. The results are shown in Table 4. The production and measurement methods were also performed in the same manner as in Example 1.

TABLE 3 Ni Si Co Other Classification No. [mass %] [mass %] [mass %] [mass %] Example 6 2.33 0.48 0.09 — according to 7 3.20 0.67 0.55 — this invention 8 3.84 0.93 0.17 Zn: 0.51 9 4.29 1.02 0.14 Zn: 0.49 Sn: 0.15 Mg: 0.12 10 4.82 1.09 0.37 Zn: 0.50 Sn: 0.12 Comparative 105 2.40 0.52 0.04 — example 106 3.26 0.77 0.19 — 107 3.94 0.86 0.19 Zn: 0.52 Sn: 0.15 108 4.32 1.00 0.31 —

TABLE 4 Number Crystal Grain size of Grain size of of Y2/ grain Bending precipitate X precipitate Y2 number diameter TS EC property Classification No. [μm] [μm] of X [μm] [MPa] [% IACS] [R/t] Example 6 0.016 0.209 331 6 718 45 1.0 according to 7 0.021 0.189 442 6 759 40 1.0 this invention 8 0.045 0.212 60 9 805 38 1.5 9 0.034 0.170 902 7 843 37 2.0 10 0.041 0.195 1035 5 877 34 2.0 Comparative 105 0.021 2.150 34 19 723 44 1.5 example 106 0.031 0.009 19 22 763 41 2.5 107 0.029 0.005 19 20 799 39 3.0 108 0.047 2.918 17 27 830 36 3.5

From the results shown in Tables 3 and 4, it is understood that the samples according to the present invention have excellent properties in both of the mechanical strength and the bending property. However, since the grain diameter of precipitate Y2 was outside of the range defined in the present invention, the samples in Comparative examples 105, 106, 107 and 108 each were poor in the bending property, as compared with the samples in the examples according to the present invention having the same level of mechanical strength, and the mechanical strength in the comparative examples was not compatible to the bending property. Thus, it is possible to improve the bending property (R/t) while high strength is maintained, by controlling the grain diameter of precipitate Y2 in the Cu alloy system containing Ni, Si, and Co. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable for materials of lead frames or the like. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property.

Example 3

With respect to the copper alloys containing the elements in the amounts, as shown in Table 5, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1, except that the measurement was made on the precipitate Y3 in place of the precipitate Y1. The results are shown in Table 6. The production and measurement methods were also performed in the same manner as in Example 1.

TABLE 5 Ni Si Zr Other Classification No. [mass %] [mass %] [mass %] [mass %] Example 11 2.42 0.59 0.07 — according to 12 3.18 0.84 0.69 — this invention 13 3.81 0.79 0.21 Zn: 0.51 14 4.31 1.01 0.30 Zn: 0.49 Sn: 0.14 Mg: 0.10 15 4.77 1.08 0.36 Zn: 0.50 Sn: 0.13 Comparative 109 2.30 0.63 0.06 — example 110 3.28 0.83 0.15 — 111 3.90 0.78 0.20 Zn: 0.53 Sn: 0.15 112 4.37 1.08 0.18 —

TABLE 6 Number Crystal Grain size of Grain size of of Y3/ grain Bending precipitate X precipitate Y3 number diameter TS EC property Classification No. [μm] [μm] of X [μm] [MPa] [% IACS] [R/t] Example 11 0.022 0.204 361 7 709 45 1.0 according to 12 0.021 0.195 448 7 747 42 1.0 this invention 13 0.050 0.225 80 9 802 39 1.5 14 0.035 0.174 916 8 835 37 2.0 15 0.046 0.181 1048 5 875 33 2.0 Comparative 109 0.021 2.250 43 19 715 45 1.5 example 110 0.031 0.009 19 23 751 42 2.5 111 0.038 0.004 28 20 796 40 3.0 112 0.036 2.929 52 28 828 38 3.5

From the results shown in Tables 5 and 6, it is understood that the samples according to the present invention have excellent properties in both of the mechanical strength and the bending property. However, since the grain diameter of precipitate Y3 was outside of the range defined in the present invention, the samples in Comparative examples 109, 110, 111 and 112 each were poor in the bending property, as compared with the samples in the examples according to the present invention having the same level of mechanical strength, and the mechanical strength in the comparative examples was not compatible to the bending property. Thus, it is possible to improve the bending property (R/t) while high strength is maintained, by controlling the grain diameter of precipitate Y3 in the Cu alloy system containing Ni, Si, and Zr. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable for materials of lead frames or the like. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property.

Example 4

With respect to the copper alloys containing the elements in the amounts, as shown in Table 7, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1, except that the measurement was made on the precipitate Z in place of the precipitate Y1. The results are shown in Table 8. The production and measurement methods were also performed in the same manner as in Example 1.

TABLE 7 Ni Si B Other Classification No. [mass %] [mass %] [mass %] [mass %] Example 16 2.36 0.38 0.08 — according to 17 3.20 0.78 0.01 — this invention 18 3.87 0.86 0.10 Zn: 0.50 19 4.21 0.77 0.29 Zn: 0.49 Sn: 0.15 Mg: 0.11 20 4.95 1.11 0.21 Zn: 0.48 Sn: 0.13 Comparative 113 2.44 0.59 0.21 — example 114 3.43 0.86 0.02 — 115 3.91 0.92 0.18 Zn: 0.50 Sn: 0.15 116 4.31 0.89 0.08 —

TABLE 8 Number Crystal Grain size of Grain size of of Z/ grain Bending precipitate X precipitate Z number diameter TS EC property Classification No. [μm] [μm] of X [μm] [MPa] [% IACS] [R/t] Example 15 0.016 0.210 348 7 707 45 1.0 according to 16 0.023 0.187 441 8 743 41 1.0 this invention 17 0.044 0.232 106 9 802 39 1.5 18 0.036 0.170 921 9 829 36 2.0 19 0.045 0.192 1054 6 870 34 2.0 Comparative 113 0.021 2.250 59 20 712 46 1.5 example 114 0.030 0.007 42 23 750 43 2.5 115 0.042 0.003 38 20 790 40 3.0 116 0.037 2.931 61 28 820 38 3.5

From the results shown in Tables 7 and 8, it is understood that the samples according to the present invention have excellent properties in both of the mechanical strength and the bending property. However, since the grain diameter of precipitate Z was outside of the range defined in the present invention, the samples in Comparative examples 113, 114, 115 and 116 each were poor in the bending property, as compared with the samples in the examples according to the present invention having the same level of mechanical strength, and the mechanical strength in the comparative examples was not compatible to the bending property. Thus, it is possible to improve the bending property (R/t) while high strength is maintained, by controlling the grain diameter of precipitate Z in the Cu alloy containing Ni, Si, and B. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable for materials of lead frames or the like. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property.

Example 5

With respect to the copper alloys containing the elements in the amounts, as shown in Table 9, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1, except that the measurement was made on the precipitate Y2, Y3 or Z in place of a part of the precipitate Y1. The results are shown in Table 10. The production and measurement methods were also performed in the same manner as in Example 1.

TABLE 9 Cr, Co, Ni Si Zr, B Zn Sn Mg Classification No. [mass %] [mass %] [mass %] [mass %] [mass %] [mass %] Example 21 2.25 0.54 Cr: 0.08 0.2 0.10 0.20 according to 22 3.24 0.78 Co: 0.08 0.3 0.15 0.15 this invention 23 3.45 0.83 Cr: 0.2 0.5 0.10 0.10 Zr: 0.1 24 3.66 0.88 Zr: 0.1 0.5 0.12 0.12 B: 0.02 25 3.87 0.93 Cr: 0.7 0.4 0.15 0.15 26 4.02 0.97 Cr: 0.2 0.2 0.18 0.11 Co: 0.1 27 4.27 1.02 Co: 0.8 0.5 0.22 0.21 Zr: 0.1 28 4.48 1.07 Cr: 0.4 0.4 0.40 0.15 29 4.94 1.18 Cr: 0.3 0.5 0.32 0.14 Co: 0.1 Comparative 117 2.44 0.59 Cr: 0.09 0.4 0.25 0.12 example 118 3.20 0.77 Co: 0.25 0.5 0.15 0.17 119 3.77 0.91 Zr: 0.2 0.2 0.20 0.09 Cr: 0.1 120 3.94 0.95 Cr: 0.25 0.2 0.15 0.21 121 4.23 1.01 Cr: 0.3 0.3 0.12 0.14 Co: 0.1 122 4.70 1.13 Cr: 0.25 0.4 0.20 0.21

TABLE 10 Grain size of Crystal Grain size of precipitate Y1, Number of Y1, grain Bending precipitate X Y2, Y3, Z Y2, Y3, Z/ diameter TS EC property Classification No. [μm] [μm] number of X [μm] [MPa] [% IACS] [R/t] Example 21 0.023 0.204 333 6 705 44 1.0 according to 22 0.032 0.191 444 6 727 39 1.0 this invention 23 0.051 0.223 80 9 728 37 1.0 24 0.039 0.163 891 8 801 36 1.5 25 0.045 0.195 1031 5 809 34 1.5 26 0.018 0.208 365 6 811 33 2.0 27 0.031 0.197 443 8 833 31 2.0 28 0.053 0.219 94 9 854 30 2.0 29 0.036 0.166 914 8 875 28 2.0 Comparative 117 0.021 2.270 21 19 765 43 1.5 example 118 0.031 0.006 23 23 786 39 2.0 119 0.304 2.103 26 23 807 35 2.5 120 0.044 0.001 28 20 828 33 3.0 121 0.032 0.008 35 20 850 31 3.0 122 0.047 2.916 26 28 871 27 3.0

From the results shown in Tables 9 and 10, it is understood that the samples according to the present invention have excellent properties in both of the mechanical strength and the bending property. However, since the grain diameter of precipitate Y1, Y2, Y3 or Z was outside of the range defined in the present invention, the samples in Comparative examples 117, 118, 119, 120, 121 and 122 each were poor in the bending property, as compared with the samples in the examples according to the present invention having the same level of mechanical strength, and the mechanical strength in the comparative examples was not compatible to the bending property. Thus, it is possible to improve the bending property (R/t) while high strength is maintained, by controlling the grain diameter of precipitate Y1 or the like. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable for materials of lead frames or the like. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property.

In the following examples, it is shown that it is possible to control the stress relaxation resistance that has a large influence on the reliability particularly of connectors and terminal materials, by controlling the grain diameter of precipitate Y. While the copper alloys in the following examples according to the present invention are particularly favorable as connectors and terminal materials, they are also applicable to other uses, such as lead frame materials.

Example 6

With respect to the copper alloys containing Ni, Si, and elements in the given amounts as shown in Table 11, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1. The contents of Ni and Si were as follows: 3.5 mass % of Ni and 0.8 mass % of Si in the samples of Examples according to the present invention Nos. 1-4 and 1-11; 4.0 mass % of Ni and 0.95 mass % of Si in the sample of Example according to the present invention No. 1-6; and 3.8 mass % of Ni and 0.86 mass % of Si in the samples of other Examples according to the present invention and Comparative examples. The production and measurement methods for the samples were also performed in the same manner as in Example 1. Further, the stress relaxation resistance was evaluated by the following manner.

f. Stress Relaxation Resistance:

An open-sided block method prescribed in the Standard of the Electronic Materials Manufacturers Association of Japan (EMAS-3003) was employed with load stress set to be a surface maximum stress of 80%-yield strength (80%-YS, 0.2%-proof stress), and the stress relaxation ratio (S.R.R.) was measured by placing the sample in a thermostat bath at 150° C. for 1,000 hours. When the stress relaxation ratio of the copper alloy was less than 20%, it is judged that the stress relaxation resistance is “good”, while when the S.R.R. was 20% or more, it is judged that the stress relaxation resistance is “poor”.

Herein, the terms ‘GW’ and ‘BW’ in the following tables are defined as follows. GW denotes bending with a bend axis perpendicular to the direction of rolling, by using a test piece sampled in parallel to the direction of rolling; and BW denotes bending with a bend axis parallel to the direction of rolling, by using a test piece sampled perpendicular to the direction of rolling. In other words, GW means that the longitudinal direction of the test piece is parallel to the direction of rolling, and BW means that the longitudinal direction of the test piece is perpendicular to the direction of rolling.

As is apparent from the results in Table 11, the samples according to the present invention each have excellent properties with respect to the mechanical strength, electrical conductivity, bending property, and stress relaxation resistance. In particular, it is possible to control the stress relaxation resistance by the grain size of precipitate Y, to make the stress relaxation ratio be less than 20%. In the examples according to the present invention, by making the grain size of Y within the range from 0.02 to 0.9 μm, it was possible to attain a good stress relaxation ratio, which was a stress relaxation ratio of 13% or less, while maintaining excellent mechanical strength, electrical conductivity, and bending property. Based on the above, the alloys of the examples according to the present invention can be considered to be favorable, for example, for materials of terminals and connectors. Furthermore, although not shown in the examples, the similar effects can be exhibited when the grain size of Y is within the range from 0.01 to 2.0 μm. Contrary to the above, since the grain size of precipitate Y was too large due to a too large amount of B, the sample in Comparative example 1-1 was poor in the mechanical strength and the stress relaxation resistance. Since the grain size of precipitate Y was too small due to a too small amount of Fe, the sample in Comparative example 1-2 was poor in the stress relaxation resistance. Since the amount of P was too large, the sample in Comparative example 1-3 was poor in the stress relaxation resistance. Since the grain size of precipitate Y was too small, the sample in Comparative example 1-4 was poor in the bending property and the stress relaxation resistance. Since the grain size of precipitate Y was too small, the sample in Comparative example 1-5 was poor in the stress relaxation resistance. Since the grain size of precipitate Y was too small, the sample in Comparative example 1-6 was poor in the stress relaxation resistance.

TABLE 11 Number Bending Component Precipitate X Precipitate Y of X/ property α Size Density/ Composition Size Density/ number TS EC GW BW SRR mass % μm mm² Compound μm mm² of Y MPa % IACS R/t R/t % This invention Cr = 0.2 0.03 3 × 10⁹ Ni—Si—Cr 0.2 2 × 10⁷ 150 862 36 1.0 1.0 9 1-1 This invention Cr = 0.1 0.03 8 × 10⁹ Ni—Si—Cr 0.3 6 × 10¹⁰ 0.1 855 38 1.5 1.0 10 1-2 Zr = 0.1 Ni—Si—Zr Ni—Si—Cr—Zr This invention B = 0.008 0.04 1 × 10¹⁰ Ni—Si—B 0.8 2 × 10⁹ 5 833 40 1.5 1.0 12 1-3 This invention Fe = 0.15 0.08 2 × 10⁷ Ni—Si—Fe 0.2 1 × 10⁵ 200 821 40 1.5 1.0 11 1-4 P = 0.09 Ni—Si—Fe—P This invention MM = 0.008 0.09 7 × 10⁷ Ni—Si-MM 0.5 3 × 10⁶ 25 833 39 1.5 1.0 10 1-5 This invention Ti = 0.2 0.05 5 × 10⁹ Ni—Si—Ti 0.2 2 × 10³ 250000 882 33 1.5 1.0 7 1-6 This invention O = 0.006 0.04 3 × 10⁹ Ni—Si—O 0.8 7 × 10² 430000 832 37 1.5 1.0 11 1-7 This invention Be = 0.01 0.05 6 × 10⁹ Ni—Si—Be 0.5 4 × 10⁷ 150 855 39 1.0 1.0 12 1-8 This invention Cr = 0.3 0.02 7 × 10¹⁰ Ni—Si—Cr 0.7 4 × 10⁸ 175 852 37 1.0 1.0 11 1-9 Hf = 0.2 Ni—Si—Hf Ni—Si—Cr—Hf This invention C = 0.009 0.09 3 × 10⁸ Ni—Si—C 0.5 3 × 10³ 10000 830 41 1.5 1.0 12 1-10 This invention N = 0.01 0.07 2 × 10⁸ Ni—Si—N 0.9 5 × 10⁵ 400 820 38 1.0 1.0 12 1-11 This invention Mn = 0.2 0.08 4 × 10⁹ Ni—Si—Mn 0.5 5 × 10⁷ 80 842 38 1.0 1.0 13 1-12 This invention In = 0.49 0.06 5 × 10⁹ Ni—Si—In 0.3 2 × 10⁸ 25 845 36 1.0 1.0 12 1-13 Cr = 0.1 Ni—Si—Cr Ni—Si—In—Cr This invention Al = 0.3 0.08 8 × 10⁸ Ni—Si—Al 0.02 2 × 10⁶ 400 839 37 1.0 1.0 10 1-14 This invention Co = 0.2 0.04 7 × 10⁹ Ni—Si—Co 0.7 4 × 10⁷ 175 862 39 1.0 1.0 9 1-15 Comparative B = 1.1 1.25 2 × 10⁶ Ni—Si—B 2.2 2 × 10³ 1000 789 40 2.0 1.5 22 example 1-1 Comparative Fe = 0.002 0.04 3 × 10⁷ Ni—Si—Fe 0.005 3 × 10³ 10000 812 43 2.0 2.0 27 example 1-2 Comparative P = 1.2 0.06 6 × 10⁹ Ni—Si—P 2.4 2 × 10³ 3000000 812 36 2.0 2.0 23 example 1-3 Comparative C = 0.005 0.03 4 × 10⁹ Ni—Si—C 0.007 1 × 10⁸ 40 845 39 2.5 2.0 28 example 1-4 Comparative Cr = 0.5 0.04 5 × 10⁹ Ni—Ti—Cr 0.003 5 × 10⁹ 1 854 38 2.0 2.0 35 example 1-5 Comparative Be = 0.05 0.03 7 × 10¹⁰ Ni—Ti—Be 0.007 6 × 10⁷ 1200 809 37 2.0 2.0 21 example 1-6

Example 7

With respect to the copper alloys containing Ni, Si, and elements in the given amounts as shown in Table 12, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1. The contents of Ni and Si were as follows: 3.5 mass % of Ni and 0.8 mass % of Si in the samples of Examples according to the present invention Nos. 2-4 and 2-11; 4.0 mass % of Ni and 0.95 mass % of Si in the sample of Example according to the present invention No. 2-2; and 3.8 mass % of Ni and 0.86 mass % of Si in the samples of other Examples according to the present invention and Comparative examples. The production and measurement methods for the samples were also performed in the same manner as in Example 1. Further, the stress relaxation resistance was evaluated in the same manner as in Example 6.

As is apparent from the results in Table 12, the samples according to the present invention each have excellent properties with respect to the mechanical strength, electrical conductivity, bending property, and stress relaxation resistance. In particular, in the examples according to the present invention, by making the grain size of Y within the range from 0.05 to 0.9 μm, it was possible to attain a stress relaxation ratio of 14% or less, while maintaining excellent mechanical strength, electrical conductivity, and bending property. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable, for example, for materials of terminals and connectors. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property. Contrary to the above, since the values of the precipitates Y were outside of the range of from 0.01 to 2.0 μm, the samples in Comparative examples each were poor in the stress relaxation ratio of 21% or more.

TABLE 12 Number Bending Component Precipitate X Precipitate Y of X/ property α β Size Density/ Composition Size Density/ number TS EC GW BW SRR mass % mass % μm mm² Compound μm mm² of Y MPa % IACS R/t R/t % This invention Cr = 0.2 Ti = 0.01 0.04 2 × 10⁹ Ni—Cr—Ti 0.3 3 × 10⁷ 70 851 37 1.0 1.0 9 2-1 This invention Cr = 0.1 Zr = 0.2 0.02 4 × 10⁹ Ni—Cr—Zr 0.2 5 × 10¹⁰ 0.1 862 39 1.5 1.0 11 2-2 This invention B = 0.01 Mn = 0.02 0.05 2 × 10¹⁰ Ni—Mn—B 0.9 5 × 10⁹ 4 839 40 1.5 1.0 12 2-3 This invention Fe = 0.18 P = 0.09 0.07 5 × 10⁷ Ni—Fe—P 0.4 3 × 10⁵ 170 829 40 1.5 1.0 12 2-4 This invention MM = 0.008 O = 0.006 0.10 5 × 10⁷ Ni-MM-O 0.3 4 × 10⁶ 13 841 39 1.5 1.0 10 2-5 This invention Ti = 0.2 B = 0.02 0.04 6 × 10⁹ Ni—Ti—B 0.5 5 × 10³ 1200000 843 33 1.5 1.0 8 2-6 This invention O = 0.004 Cr = 0.3 0.03 2 × 10⁹ Ni—Cr—O 0.3 2 × 10² 10000000 833 38 1.5 1.0 12 2-7 This invention Be = 0.02 Al = 0.02 0.06 7 × 10⁹ Ni—Be—Al 0.6 7 × 10⁷ 100 834 39 1.0 1.0 12 2-8 This invention Cr = 0.45 Hf = 0.1 0.03 8 × 10¹⁰ Ni—Cr—Hf 0.6 7 × 10⁸ 115 857 37 1.0 1.0 11 2-9 This invention C = 0.009 Ti = 0.03 0.08 2 × 10⁸ Ni—Ti—C 0.6 3 × 10³ 67000 834 41 1.5 1.0 12 2-10 This invention N = 0.01 S = 0.006 0.08 7 × 10⁸ Ni—N—S 0.4 4 × 10⁵ 1750 825 39 1.0 1.0 12 2-11 This invention Mn = 0.2 Cr = 0.3 0.09 8 × 10⁹ Ni—Mn—Cr 0.6 7 × 10⁷ 115 846 40 1.0 1.0 14 2-12 This invention In = 0.2 Cr = 0.5 0.09 9 × 10⁹ Ni—In—Cr 0.2 2 × 10⁸ 45 848 36 1.0 1.0 13 2-13 This invention Al = 0.3 P = 0.03 0.03 6 × 10⁸ Ni—Al—P 0.05 3 × 10⁶ 200 846 38 1.0 1.0 10 2-14 This invention Co = 0.2 Cr = 0.3 0.02 7 × 10⁸ Ni—Co—Cr 0.30 7 × 10⁶ 100 859 38 1.0 1.0 11 2-15 Comparative B = 1.2 Mn = 0.19 2.25 6 × 10⁶ Ni—B—Mn 4.2 6 × 10³ 100 796 40 2.0 1.5 23 example 2-1 Comparative Fe = 0.002 P = 0.001 0.09 6 × 10⁷ Ni—Fe—P 0.005 5 × 10³ 12000 816 43 2.0 2.0 27 example 2-2 Comparative P = 0.3 Fe = 0.4 0.03 9 × 10⁹ Ni—Fe—P 3.3 3 × 10³ 3000000 815 36 2.0 2.0 23 example 2-3 Comparative C = 0.05 Ti = 0.4 0.02 8 × 10⁹ Ni—C—Ti 0.005 3 × 10⁸ 25 852 40 2.5 2.0 29 example 2-4 Comparative Cr = 0.45 P = 0.03 0.03 3 × 10⁹ Ni—Cr—P 0.002 7 × 10⁹ 0.4 854 38 2.0 2.0 35 example 2-5 Comparative Zr = 0.4 Fe = 0.2 0.07 8 × 10¹⁰ Ni—Fe—Zr 0.009 7 × 10⁷ 1150 813 36 2.0 2.0 21 example 2-6

Example 8

With respect to the copper alloys containing Ni, Si, and elements in the given amounts as shown in Table 13, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1. The contents of Ni and Si were as follows: 3.5 mass % of Ni and 0.8 mass % of Si in the samples of Examples according to the present invention Nos. 3-4 and 3-11; 4.0 mass % of Ni and 0.95 mass % of Si in the samples of Examples according to the present invention Nos. 3-8 and 3-15; and 3.8 mass % of Ni and 0.86 mass % of Si in the samples of other Examples according to the present invention and Comparative examples. The production and measurement methods for the samples were also performed in the same manner as in Example 1. Further, the stress relaxation resistance was evaluated in the same manner as in Example 6.

As is apparent from the results in Table 13, the samples according to the present invention each have excellent properties with respect to the mechanical strength, electrical conductivity, bending property, and stress relaxation resistance. In particular, in the examples according to the present invention, by making the grain size of Y within the range from 0.2 to 0.6 μm, it was possible to attain a stress relaxation ratio of 15% or less, while maintaining excellent mechanical strength, bending property, and electrical conductivity. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable, for example, for materials of terminals and connectors. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property. Contrary to the above, since the values of the precipitates Y were outside of the range of from 0.01 to 2.0 μm, the samples in Comparative examples each were poor in the stress relaxation ratio of 21% or more.

TABLE 13 Number Bending Component Precipitate X Precipitate Y of X/ property α β Size Density/ Composition Size Density/ number TS EC GW BW SRR mass % mass % μm mm² Compound μm mm² of Y MPa % IACS R/t R/t % This invention Cr = 0.45 Ti = 0.2 0.04 5 × 10⁹ Si—Cr—Ti 0.2 6 × 10⁷ 85 854 38 1.0 1.0 10 3-1 This invention Cr = 0.3 Zr = 0.15 0.01 2 × 10⁹ Si—Cr—Zr 0.3 4 × 10¹⁰ 0.05 867 40 1.5 1.0 11 3-2 This invention B = 0.008 Mn = 0.2 0.03 4 × 10¹⁰ Si—Mn—B 0.6 9 × 10⁹ 4 844 41 1.5 1.0 13 3-3 This invention Fe = 0.28 P = 0.19 0.06 3 × 10⁷ Si—Fe—P 0.5 4 × 10⁵ 75 834 41 1.5 1.0 13 3-4 This invention MM = 0.005 O = 0.005 0.10 4 × 10⁷ Si-MM-O 0.4 1 × 10⁶ 40 843 40 1.5 1.0 11 3-5 This invention Ti = 0.25 B = 0.03 0.03 3 × 10⁹ Si—Ti—B 0.2 9 × 10³ 330000 866 33 1.5 1.0 8 3-6 This invention O = 0.004 Cr = 0.45 0.02 9 × 10⁹ Si—Cr—O 0.6 8 × 10² 11250000 839 39 1.5 1.0 13 3-7 This invention Be = 0.008 Al = 0.012 0.02 5 × 10⁹ Si—Be—Al 0.4 2 × 10⁷ 250 888 41 1.0 1.0 13 3-8 This invention Cr = 0.3 Hf = 0.05 0.02 6 × 10¹⁰ Si—Cr—Hf 0.5 5 × 10⁸ 120 867 37 1.0 1.0 12 3-9 This invention C = 0.01 Ti = 0.06 0.07 5 × 10⁸ Si—Ti—C 0.2 6 × 10³ 83000 838 43 1.5 1.0 13 3-10 This invention N = 0.007 S = 0.008 0.05 9 × 10⁸ Si—N—S 0.4 5 × 10⁵ 1800 828 39 1.0 1.0 12 3-11 This invention Mn = 0.25 Cr = 0.5 0.04 8 × 10⁹ Si—Mn—Cr 0.3 2 × 10⁷ 400 848 40 1.0 1.0 15 3-12 This invention In = 0.4 Cr = 0.3 0.09 6 × 10⁹ Si—In—Cr 0.2 2 × 10⁸ 30 853 36 1.0 1.0 13 3-13 This invention Al = 0.1 P = 0.06 0.02 4 × 10⁸ Si—Al—P 0.4 3 × 10⁶ 130 848 38 1.0 1.0 11 3-14 This invention Co = 0.2 Cr = 0.15 0.03 3 × 10¹⁰ Si—Co—Cr 0.3 9 × 10⁸ 35 873 32 1.0 1.0 8 3-15 Comparative B = 0.2 Mn = 0.5 0.37 9 × 10⁶ Si—B—Mn 3.2 8 × 10³ 1100 805 41 2.0 1.5 23 example 3-1 Comparative Fe = 0.02 P = 0.008 0.07 3 × 10⁷ Si—Fe—P 0.001 3 × 10³ 10000 818 44 2.0 2.0 28 example 3-2 Comparative P = 0.04 Fe = 0.1 0.01 1 × 10⁹ Si—Fe—P 3.3 6 × 10³ 170000 823 37 2.0 2.0 24 example 3-3 Comparative C = 0.005 Ti = 0.35 0.05 2 × 10⁹ Si—C—Ti 0.005 1 × 10⁸ 20 856 41 2.5 2.0 29 example 3-4 Comparative Cr = 0.25 P = 0.3 0.01 3 × 10⁹ Si—Cr—P 0.004 4 × 10⁹ 0.8 859 39 2.0 2.0 36 example 3-5 Comparative Zr = 0.24 Fe = 0.12 0.06 4 × 10¹⁰ Si—Fe—Zr 0.005 2 × 10⁷ 2000 821 37 2.0 2.0 21 example 3-6

Example 9

With respect to the copper alloys containing Ni, Si, and elements in the given amounts as shown in Table 14, with the balance being made of Cu and inevitable impurities, the test was conducted in the same manner as in Example 1. The contents of Ni and Si were as follows: 3.5 mass % of Ni and 0.8 mass % of Si in the samples of Examples according to the present invention Nos. 4-1 and 4-4; 4.0 mass % of Ni and 0.95 mass % of Si in the samples of Examples according to the present invention Nos. 4-2 and 4-9; and 3.8 mass % of Ni and 0.86 mass % of Si in the samples of other Examples according to the present invention and Comparative examples. The production and measurement methods for the samples were also performed in the same manner as in Example 1. Further, the stress relaxation resistance was evaluated in the same manner as in Example 6.

As is apparent from the results in Table 14, the samples according to the present invention each have excellent properties with respect to the mechanical strength, electrical conductivity, bending property, and stress relaxation resistance. In particular, in the examples according to the present invention, by making the grain size of Y within the range from 0.1 to 0.6 μm, it was possible to attain a stress relaxation ratio of 15% or less, while maintaining excellent mechanical strength, bending property, and electrical conductivity. Based on the above, the copper alloys of the examples according to the present invention can be considered to be favorable, for example, for materials of terminals and connectors. Further, the copper alloys of the examples according to the present invention are also excellent in other properties, such as spring property. Contrary to the above, since the values of the precipitates Y were outside of the range of from 0.01 to 2.0 μm, the samples in Comparative examples each were poor in the stress relaxation ratio of 21% or more.

TABLE 14 Component Precipitate X Precipitate Y α β γ Size Density/ Composition mass % mass % mass % μm mm² Compound This invention Cr = 0.5 Ti = 0.1 Zr = 0.2 0.02 1 × 10⁹ Zr—Cr—Ti 4-1 This invention Cr = 0.25 Zr = 0.1 P = 0.05 0.02 5 × 10⁹ P—Cr—Zr 4-2 This invention B = 0.01 Mn = 0.15 P = 0.2 0.06 9 × 10¹⁰ P—Mn—B 4-3 This invention MM = 0.005 O = 0.005 S = 0.005 0.08 5 × 10⁷ MM-O—S 4-4 This invention Ti = 0.5 B = 0.004 Cr = 0.3 0.05 4 × 10⁹ Cr—Ti—B 4-5 This invention O = 0.003 Cr = 0.4 Zr = 0.12 0.20 3 × 10⁹ Zr—Cr—O 4-6 This invention B = 0.003 Al = 0.01 Hf = 0.2 0.05 4 × 10⁹ Hf—Be—Al 4-7 This invention Cr = 0.2 Hf = 0.15 Zr = 0.49 0.04 8 × 10¹⁰ Zr—Cr—Hf 4-8 This invention C = 0.03 Ti = 0.08 S = 0.003 0.06 2 × 10⁸ Ti—C—S 4-9 This invention N = 0.008 S = 0.008 O = 0.002 0.04 4 × 10⁸ O—N—S 4-10 This invention Mn = 0.5 Cr = 0.1 Zr = 0.3 0.01 3 × 10⁹ Zr—Mn—Cr 4-11 This invention In = 0.3 Cr = 0.3 Zr = 0.3 0.03 8 × 10⁹ Zr—In—Cr 4-12 This invention Al = 0.25 P = 0.08 Ti = 0.49 0.04 8 × 10⁸ Ti—Al—P 4-13 This invention Co = 0.1 Cr = 0.2 Zr = 0.3 0.03 3 × 10¹⁰ Co—Mn—Cr 4-14 Comparative B = 0.0002 Mn = 0.5 P = 0.6 0.55 4 × 10⁶ Mn—B—P example 4-1 Comparative C = 0.008 Ti = 0.2 Cr = 0.2 0.01 8 × 10⁹ Cr—C—Ti example 4-2 Comparative Cr = 0.25 P = 0.3 Al = 0.2 0.04 9 × 10⁹ Al—Cr—P example 4-3 Comparative Zr = 0.24 Fe = 0.12 S = 0.003 0.02 5 × 10¹⁰ Fe—Zr—S example 4-4 Number Bending Precipitate Y of X/ property Size Density/ number TS EC GW BW SRR μm mm² of Y MPa % IACS R/t R/t % This invention 0.1 1 × 10⁷ 100 822 39 1.0 1.0 10 4-1 This invention 0.2 5 × 10¹⁰ 0.1 877 40 1.5 1.0 12 4-2 This invention 0.5 2 × 10⁹ 45 846 41 1.5 1.0 13 4-3 This invention 0.4 1 × 10⁶ 50 846 40 1.5 1.0 11 4-4 This invention 0.6 4 × 10³ 1000000 844 33 1.5 1.0 9 4-5 This invention 0.5 3 × 10² 10000000 841 39 1.5 1.0 13 4-6 This invention 0.1 8 × 10⁷ 50 846 41 1.0 1.0 14 4-7 This invention 0.2 5 × 10⁸ 160 872 37 1.0 1.0 12 4-8 This invention 0.6 3 × 10³ 67000 847 43 1.5 1.0 13 4-9 This invention 0.5 4 × 10⁵ 100 838 40 1.0 1.0 13 4-10 This invention 0.3 3 × 10⁷ 400 852 40 1.0 1.0 15 4-11 This invention 0.4 4 × 10⁸ 20 862 38 1.0 1.0 13 4-12 This invention 0.4 8 × 10⁶ 100 849 39 1.0 1.0 12 4-13 This invention 0.3 1 × 10⁸ 300 852 40 1.0 1.0 15 4-14 Comparative 3.6 3 × 10³ 130 807 42 2.0 1.5 24 example 4-1 Comparative 0.009 2 × 10⁸ 40 860 41 2.5 2.0 30 example 4-2 Comparative 0.006 8 × 10⁹ 1.1 860 39 2.0 2.0 37 example 4-3 Comparative 0.004 5 × 10⁷ 1000 829 38 2.0 2.0 22 example 4-4

INDUSTRIAL APPLICABILITY

The copper alloy of the present invention can be preferably applied, for example, to lead frame, connector, or terminal materials for electric and electronic instrument materials, e.g. connector/terminal materials, relays, and switches for electric and electronic instruments, such as on-vehicle/automobile electric and electronic instruments.

Having described our invention as related to the present embodiments, it is our intention that the present invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

Claims

1. A method of producing a copper alloy, comprising the steps of:

melting a copper alloy;

casting into an ingot;

heating the ingot at a temperature rising rate of 20 to 200° C./hr after said casting step;

holding the resultant ingot at 850 to 1,050° C. for 0.5 to 5 hours;

hot-rolling the ingot; and

quenching the hot-rolled product,

wherein, after said hot-rolling step, the resultant alloy is formed into a given thickness, through a combination of solution treatment, annealing, and cold-rolling,

wherein the solution treatment temperature is 600 to 820° C. for an Ni amount of 2.0 mass % or more but less than 2.5 mass %, 700 to 870° C. for an Ni amount of 2.5 mass % or more but less than 3.0 mass %, 750 to 920° C. for an Ni amount of 3.0 mass % or more but less than 3.5 mass %, 800 to 970° C. for an Ni amount of 3.5 mass % or more but less than 4.0 mass %, 850 to 1,020° C. for an Ni amount of 4.0 mass % or more but less than 4.5 mass %, and 920 to 1,050° C. for an Ni amount of from 4.5 mass % or more but less than 5.0 mass % and

wherein the copper alloy has: a precipitate Y composed of Ni and/or Si and at least one or more selected from the group consisting of B, Al, As, Hf, Zr, Cr, Ti, C, Fe, P, In, Sb, Mn, Ta, V, S, O, N, Misch metal (MM), Co, and Be; and a precipitate X composed of Ni and Si,

wherein a grain diameter of the precipitate Y is 0.01 to 2 μm, and

wherein the number of precipitates X per mm2 is 20 to 2,000 times the number of precipitates Y per mm2.