Copper alloy with excellent stress relaxation resistance property and production method therefor

Abstract

The present invention provides a copper alloy, that includes an Sn content of 3 wt % to less than 4 wt %; a Ni content of 0.5 wt % to less than or equal to 1.0 wt %; a Zn content of 0.05 wt % to less than or equal to 5.0 wt %; and Cu and unavoidable impurities combined as the balance; wherein a total content of insolubles is less than or equal to 0.02 wt %. The present invention also relates to a method for producing the above-described copper alloy, which includes holding a copper alloy at a temperature ranging from 550 to 700° C. for a time period ranging from 5 sec to less than or equal to 5 min in the course of cold working; subsequently heat treating the copper alloy to cool the copper alloy to room temperature at a cooling speed of 5 ° C./sec or higher; subsequently cold working the copper alloy to a target dimension; and stabilizing annealing the copper alloy at a temperature ranging from 325 to 450° C. and a time period ranging from 5 sec to less than or equal to 180 min. By the present invention, a copper alloy is obtained that has excellent stress relaxation resistance, particularly at temperatures in excess of 140° C. The present invention is as good or better than phosphor bronze, and is excellent in the balance between a tensile strength and elongation, separation of the Sn plating layer, whisker generation from the Sn plating layer, ingot metal cost and stress corrosion cracking sensitivity.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to copper alloy having a stress relaxation resistance property suitable for use in applications such as electrical and electronic equipment related components, i.e., springs, switches, connectors, diaphragms, sockets, bellows, fuse-clips, sliding pieces, bearings and bushes, and automobile sheet-belt springs, washers, etc., such as those being worked from sheets or strips; bourdon tubes, flexible metal hoses, hose bellows, and sleeve bearings, etc., such as those being worked from tubes; and furthermore, coil springs and others, etc., such as those being worked from wires and rods.

[0003] 2. Discussion of the Background

[0004] Phosphor bronze in various forms such as sheets, strips, tubes, wires and rods is typically employed in applications such as springs, switches and connectors. Phosphor bronze components are often incorporated in electrical and electronic equipment for both home and industrial uses as well as bourdon tubes and coil springs.

[0005] In recent years, connectors for electrical and electronic equipment have increasingly been subject to the demands of high pin density, down-sized flat type and narrow-pitched pin arrangements, to accommodate the shrinkage in size and reduction in weight of the equipment. In addition, these components must meet the demands of increased reliability.

[0006] Although phosphor bronze has excellent strength properties, it undesirably deforms when mechanically supported at temperatures in excess of 140° C. under stress (i.e., phosphor bronze has poor stress relaxation resistance).

[0007] Generally, Ni substrate plating is carried out before tin or gold plating is applied to phosphor bronze. However, if tin plating is directly applied, without any advance Ni substrate plating, several problems arise: (1) the tin plating layer is easily and undesirably separated; (2) copper oxide is undesirably formed on the surface of the tin layer, which not only undesirably results in a dark coloration but an increase in contact resistance and a decrease in the wettability of solder; and (3) tin whiskers are easily generated on the surface. When the pitches between terminal pins of a connector are narrowed by scaling-down a connector body, the result is that electrical short-circuiting more easily occurs due to electro- or stress-migration in the presence of water. Since phosphor bronze is composed of copper and tin, thes migrations arise easily on a bare surface or a tin plating surface, which makes it difficult to obtain the goal of a narrow pitched pin arrangement in a connector.

[0008] On the other hand, J-A-86-127840 discloses a high strength, high electrical conductivity copper alloy having a composition of greater than 2 to less than or equal to 10% Sn (% means wt % based on the weight of the alloy, which applies to all cases below through the description), greater than 0.01 to less than or equal to 0.4% P, 0.05 to less than or equal to 5% Zn and 0.01 to 1% of one or more selected from the group including Ni, Co and Cr, unavoidable impurities and the balance Cu. According to an example described therein, annealing is conducted at 500° C. for 1 hour on an alloy sheet having a thickness of 1.0 mm in the course of cold rolling, and precipitates of compound(s) of Ni, Co and Cr with P are formed in the annealing, since the alloy has one or more elements selected from the group including Ni, Co and Cr. That is, in the case of the alloy according to the reference, improvements on tensile strength, heat resistance and conductivity are intentionally achieved by forming phosphides of Ni, Co and Cr. Similarly, JP-A-88-38546 discloses an alloy similar to that described above, and it is described that a compound of P and Ni is precipitated in the alloy.

[0009] J-A-91-10035 discloses a copper alloy for use in electrical, electronic parts of a composition of 2.5 to 9% Sn, 0.03 to 0.35% P, 0.1 to 1.0% Ni, 1.05 to 5.0% Zn and the balance being Cu essentially, wherein P is indispensable and a Ni phosphide is formed reacting with a constituent element Ni. In this alloy, a test temperature for a stress relaxation coefficient is only 120° C. Currently, there is a demand, however, for alloys having good stress relaxation properties at temperatures in excess of 140° C.

[0010] Accordingly, many problems remain unsolved in connectors using phosphor bronze for electrical, electronic equipment with regard to striking a balance between tensile strength and elongation, separation of the tin plating layer, whisker generation from the tin plating layer, stress relaxation at temperatures in excess of 140° C. and cost of ingot metal rich in Sn. None of the copper alloys proposed so far have solved all the problems. In addition, there has still not been proposed a copper alloy more excellent in stress corrosion cracking sensitivity than phosphor bronze.

SUMMARY OF THE INVENTION

[0011] Accordingly, one object of the present invention is to solve the above-described problems typical of the conventional alloys.

[0012] Another object of the invention is to provide a copper alloy having excellent stress relaxation resistance.

[0013] Another object of the invention is to provide a copper alloy having excellent stress relaxation resistance at temperatures in excess of 140° C.

[0014] Another object of the invention is to provide a copper alloy that is as good or better than phosphor bronze.

[0015] Another object of the present invention is to provide a copper alloy that is excellent in the balance between a tensile strength and elongation, separation of the Sn plating layer, whisker generation from the Sn plating layer, ingot metal cost and stress corrosion cracking sensitivity.

[0016] These and other objects have been attained by the present invention, which provides a copper alloy, that includes:

[0017] an Sn content of 3 wt % to less than 4 wt %;

[0018] a Ni content of 0.5 wt % to less than or equal to 1.0 wt %;

[0019] a Zn content of 0.05 wt % to less than or equal to 5.0 wt %; and

[0020] Cu and unavoidable impurities combined as the balance; wherein

[0021] a total content of insolubles is less than or equal to 0.02 wt %.

[0022] Another embodiment of the present invention relates to an article, including the above-described copper alloy according to the invention.

[0023] Another embodiment of the present invention relates to a method for producing the above-described copper alloy according to the invention, which includes:

[0024] holding a copper alloy at a temperature ranging from 550 to 700° C. for a time period ranging from 5 sec to less than or equal to 5 min in the course of cold working;

[0025] subsequently heat treating the copper alloy to cool the copper alloy to room temperature at a cooling speed of 5° C./sec or higher;

[0026] subsequently cold working the copper alloy to a target dimension; and

[0027] stabilizing annealing the copper alloy at a temperature ranging from 325 to 450° C. and a time period ranging from 5 sec to less than or equal to 180 min.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the preferred embodiments of the invention.

[0029] The copper alloy of the present invention includes:

[0030] an Sn content of 3 wt % to less than 4 wt %, more preferably 3.2 to less than or equal to 3.9, more particularly 3.4 to less than or equal to 3.8 wt %, and most preferably 3.5 to less than or equal to 3.7 wt %;

[0031] a Ni content of 0.5 wt % to less than or equal to 1.0 wt %, more preferably 0.6 wt % to less than or equal to 0.9 wt %, more particularly preferably 0.7 wt % to 0.8 wt %;

[0032] a Zn content of 0.05 wt % to less than or equal to 5.0 wt %, more preferably 0.1 wt % to less than or equal to 4 wt %, more particularly preferably 0.5 wt % to less than or equal to 3 wt %, and most preferably 1 wt % to less than or equal to 2 wt %; and

[0033] Cu and unavoidable impurities combined as the balance; wherein

[0034] a total content of insolubles is less than or equal to 0.02 wt %, more preferably less than or equal to 0.015 wt %, more particularly preferably less than or equal to 0.01 wt %, and most preferably less than or equal to 0.0015 wt %.

[0035] In a case where a copper alloy according to the present invention contains a deoxidizing agent, one or more elements selected from the group consisting of P, B, Mg and Ca are preferably controlled in a composition range of P in content of 0.001% to 0.03%, the lower limit included but the upper limit not included (more preferably 0.01% to 0.02%), B in content of 0.0001% to 0.02%, both limits included (more preferably 0.001% to 0.01%), Mg in content of 0.0001% to 0.05 both limits included (more preferably 0.001% to 0.025%), and Ca in content of 0.0001% to 0.01 both limits included (more preferably 0.001% to 0.005%), wherein a total content of one or more elements selected from the group consisting of P, B, Mg and Ca is in the range of from 0.0001% to 0.1%, both limits included (more preferably from 0.001% to 0.05%).

[0036] Some unavoidable impurities Ag, Pb, Fe, Si, Mn and S, unavoidably mixed from starting materials (Cu ingot and turning chips) and others in the gas form O and H unavoidably included during a melt preparation in an copper alloy are preferably controlled in a composition range of Ag in content equal to or less than 0.1% (more preferably 0.05%), Pb in content equal to or less than 0.01% (more preferably 0.005%), Fe in content equal to or less than 0.05% (more preferably 0.01%), Si in content equal to or less than 0.05% (more preferably 0.01%), Mn in content equal to or less than 0.1% (more preferably 0.05%), S in content equal to or less than 20 ppm (more preferably 10 ppm), O in content equal to or less than 30 ppm (more preferably 20 ppm) and H in content equal to or less than 2 ppm (more preferably 1 ppm), wherein a total content of one or more elements selected from the group consisting of Ag, Pb, Fe, Si and Mn is equal to or less than 0.3% (more preferably 0.2%).

[0037] Furthermore, the copper alloy can contain one or more elements selected from the group consisting of Be, Al, Ti, Cr, Co, Zr, Sb and In in total content equal to or less than 0.1% (more preferably 0.05%).

[0038] Typically, conventional copper alloys, such as those disclosed in the above-noted references all have precipitates of a phosphide such as that of Ni in the matrix, which limits improvement on a stress relaxation property. According to researches conducted by the present inventors, it has been found that to use a phenomenon of solid solution or spinodal decomposition is more advantageous than to strengthen by precipitation in order to meet the recent demands for high stress relaxation property.

[0039] Preferably, the copper alloy according to the present invention can contain insoluble phases such as precipitates and crystallized compounds created according to a composition and a production process. When a content of the insoluble materials is more than 0.2%, a mechanism of strengthening the copper alloy by solid solution or spinodal decomposition does not work anymore. Hence, the content is limited so as to be equal to or less than 0.02%. In addition, the average grain size is preferably controlled in the range of 1 to 15 &mgr;m from the viewpoint of bendability.

[0040] Preferably, Cu is simultaneously added with Sn in content of 3% to 4%, the lower limit included but the upper limit not included, and Ni in content of 0.5% to 1.0%, both limits included, and the work is subjected to hot and cold working processes, receives the above described heat treatment, and is then subjected to finishing cold working and stabilizing annealing, thereby entailing a copper alloy having a tensile strength equal to phosphor bronze containing 6% Sn. The copper alloy thus prepared has a stress relaxation coefficient as small as to be equal to or less than 30%, more preferably less than 20%, even when the copper alloy is supported by something under an influence of a stress at 150° C. for 1000 hr and therefore the copper alloy is hard to deform.

[0041] When Sn contained in Cu is in the range of 3% to 4%, the lower limit included but the upper limit not included, and Ni contained in Cu is less than 0.5%, a target balance between a tensile strength and elongation and a good stress relaxation property are hard to achieve, while even when Ni contained in Cu is more than 1%, contribution to improvements on a balance between a tensile strength and elongation is small and a conductivity is reduced. Further, when Ni contained in Cu is in the range of 0.5% to 1.0%, both limits included, and Sn contained in Cu is less than 3%, a target balance between a tensile strength and elongation is hard to achieve, while when Sn contained in Cu is more than 4%, a balance between a tensile strength and elongation is improved, but a conductivity is reduced.

[0042] In this copper alloy, a content of Sn+Ni is preferably less than 5%, which is a value smaller than the lower limit 5.5% of a specification from 5.5 to 7.0% of an Sn content of JIS H3110 or C5191, which are a standard for 6% phosphor bronze, and an ingot metal cost is lower than C5191, leading to increase in cost efficiency.

[0043] When Zn in content in the range of 0.05% to 5%, both limits included, is added to an copper alloy with the above described chemical composition, tin plating can be carried out directly or after being flashed with Cu as substrate plating to a thickness equal to or less than 0.1 &mgr;m without application of Ni substrate plating as in the case of phosphor bronze and further, separation of an Sn layer, darkening of the Sn surface in heating, whisker generation on an electroplating Sn layer and so on can be suppressed. Furthermore, when Zn is contained in the above described range, the migrations are suppressed. If Zn is contained to be less than 0.05%, less of the above described effect is exercised, while if in excess of 5%, stress corrosion cracking peculiar to a copper alloy arises with ease. Further, Zn also has a deoxidizing effect and a sound ingot can be attained with no addition or a small amount of a deoxidizing agent such as P, B, Mg or Ca. If a Zn content is less than 0.05%, the effect is not sufficient and therefore, a Zn content is set in the range of 0.05 to 5%.

[0044] P, B, Mg and Ca have a deoxidizing effect and a desulphurizing effect (Ca) on a melt. In a case where a copper alloy containing Sn in the range of 3.0% to 5%, the lower limit included but the upper limit not included, Ni in the range of 0.5% to 1.0%, both limits included, Zn in the range of 0.5% to 5%, both limits included, is melted in the air atmosphere, the copper alloy may preferably be deoxidized adding P in content in the range of 0.001% to 0.03%, the lower limit included but the upper limit not included, B in content in the range of 0.0001% to 0.02%, both limits included, Mg in content in the range of 0.0001% to 0.05%, both limits included and Ca in content in the range of 0.0001% to 0.01% both limits included, wherein a total content of one or more elements selected from the group consisting of P, B. Mg and Ca is in the range of 0.0001% to 0.1%, both limits included when deoxidizing of the melt is necessary to be conducted. Preferably, one or more selected from the group including 0.001% or more P, 0.001% or more B (may be added as CaB), 0.0001% or more Mg and 0.0001% or more Ca are contained in total content of 0.0001% or more in view of obtaining a preferable deoxidizing effect and to preferably reduce the chance of generating defects such as casting of oxides into an ingot. When two or more elements are added, a combination of P with another or other elements is desirable. However, if P, B, Mg and Ca are added in content of 0.03% or more, more than 0.05%, more than 0.1% and more than 0.01%, respectively, or a total content is more than 0.1%, a casting surface is of bad appearance, a conductivity of a final product is reduced and a phosphide of Ni or the like is formed in the final product with ease.

[0045] Preferably, C is mixed into the melt from charcoal for oxidation prevention of the melt and a flux used in casting and especially, when Ni, Fe and Co is included in the melt, C is mixed into the melt with ease. Since hot workability of a ingot is deteriorated if C is contained in content of more than 0.005%, a C content should preferably be controlled to be 0.005% or less.

[0046] Ag and Pb are preferably mixed into the alloy from a Cu starting material and Fe, Si and Mn come from turning chips inside or outside a factory.

[0047] Of the elements, Ag contained in the copper alloy contributes to improvement on a tensile strength without sacrificing any of conductivity, but the upper limit is preferably set to 0.1% because of a per unit-weight cost being high. Pb, as well, is inevitably contained originating from the Cu starting material and if a content is large, hot workability is reduced, thereby setting the upper limit to preferably 0.01%. When Fe, Si and/or Mn is mixed into the alloy, a conductivity is reduced while improvement on a tensile strength is achieved, and therefore, the upper limits are preferably set at 0.05%, 0.05% and 0.1%, respectively. The elements are preferably further limited in total content of one or more selected from the group including the elements to 0.3% as the upper limit, considering from angles of a tensile strength, a conductivity and a cost.

[0048] S comes from the furnace insulation, the Cu starting material, turning chips, charcoal for the oxidation prevention and the flux used when in casting. Preferably, S is not present in excess of 30 ppm to avoid cracking during hot working of an ingot.

[0049] Further, when the ingot is melted in the air atmosphere, O and H can be absorbed into the melt. However, if the melt surface is covered with charcoal, O can preferably be eliminated by charge of predetermined amounts of P, B, Mg and Ca, and H can be removed by bubbling of Ar or N, gas after the deoxidization. If either O in content of 30 ppm or H in content of 2 ppm is actually surpassed, an ingot obtained is not sound but as a content is reduced, an ingot is obtained more sound.

[0050] Even if one or more elements selected from the group including Be, Al, Ti, Co, Zr, Sb and In are totally contained in the copper alloy to be 0.1% or less, there is are no chances to deteriorate any of mechanical properties, a stress relaxation property, adhesiveness of tin, tin whisker resistance and conductivity.

[0051] Preferably, in the above described copper alloy, precipitates and crystallized compounds are not present in the bulk of final products, such as copper alloy sheets after completion of a fabrication process, strips, tubes, wires and rods, in excess of 0.02% in content in order to improve one of strengthening mechanisms utilizing a spinodal decomposition phenomenon and to maintain excellent balance between tensile strength and elongation, stress relaxation property and the like. Preferably, the average grain size after heat treatment by a continuous furnace and dipping in a salt bath which are conducted directly before final stabilization annealing should fall within the range of 1 to 15 &mgr;m. If the average grain size is less than 1 &mgr;m, bendability may be undesirably deteriorated, while if the average grain size is more than 15 &mgr;m, not only is bonding at grain boundaries weakened but bendability is poorer and surface roughening at a bent portion is aggravated. More preferably, the average grain size is in a range from 2 to 10 &mgr;m, more particularly preferably, the average grain sized is in a range of 3 to 5 &mgr;m.

[0052] In a copper alloy of the present invention, Ni and Sn can contribute to improvement on a strength and a stress relaxation resistance property by strengthening through solid solution or strengthening through a modulated structure caused by spinodal decomposition. Preferably, in order to achieve improvement on a strength intentionally though the mechanisms, the objective can be achieved by performing a fabrication process in which the alloy is put into a supersaturated solid solution state in which precipitation and spinodal decomposition are suppressed to the lowest level possible in a heat treatment in the course of cold working and further, a post heat treatment is carried out after the cold working. Most preferably, a copper alloy with a composition as described above is held at a temperature in the range of 550 to 700° C., at which Ni and Sn assume a supersaturated solid solution state, for a time period in the range of 5 sec to 5 min, both limits included, in the course of cold working; in succession, the copper alloy is cooled to room temperature at a cooling speed of 5° C./sec or higher; further the alloy is cold worked at a predetermined reduction ratio; and thereafter, stabilizing annealing on the copper alloy is conducted under conditions of a temperature in the range of 325 to 450° C. and a time period in the range of 5 sec to 180 min, both limits included.

[0053] The copper alloy thus worked preferably inheres greatly improved elongation as compared with a less proportion of reduction in tensile strength after the cold working, with the result that a balance between a tensile strength and elongation is improved and a stress relaxation property is also improved.

[0054] A preferred embodiment of the present invention relates to an article that includes or that is made from the copper alloy. Preferable articles include those that are worked from sheets or strips and/or used in applications such as electrical and electronic equipment related components, i.e., springs, switches, connectors, diaphragms, sockets, bellows, fuse-clips, sliding pieces, bearings and bushes, and automobile sheet-belt springs, washers, etc.; those that are worked from tubes such as bourdon tubes, flexible metal hoses, hose bellows, and sleeve bearings, etc.; and those that are worked from wires and rods such as coil springs, for example.

[0055] A preferred production method for a copper alloy according to the present invention includes the steps of: holding the copper alloy at a temperature in the range of 550 to 700° C. for a time period in the range of 5 sec to 5 min, both limits included, in the course of cold working; subsequently, conducting a heat treatment to cool the copper alloy to room temperature on the copper alloy at a cooling speed of 5° C./sec or higher; following the heat treatment, cold working the copper alloy to a target dimension; and thereafter, conducting stabilizing annealing on the copper alloy under conditions of a temperature in the range of 325 to 450° C. and a time period in the range of 5 sec to 180 min, both limits included.

[0056] In the method for producing the copper alloy according to the invention, the copper alloy is held at a temperature ranging from 550 to 700° C., more preferably 575 to 675° C., more particularly preferably 600 to 650° C., for a time period ranging from 5 sec to less than or equal to 5 min, more preferably from 10 sec to less than or equal to 4.5 min, more particularly preferably from 30 sec to less than or equal to 3.5 min, in the course of cold working;

[0057] the subsequent heat treating of the copper alloy to cool the copper alloy to room temperature (about 25° C.) is carried out at a cooling speed of 5° C./sec or higher, more preferably 7° C./sec or higher, more particularly preferably 9° C./sec or higher, and most preferably 10° C./sec or higher;

[0058] subsequently cold working the copper alloy to a target dimension; and

[0059] the stabilizing annealing of the copper alloy is carried out at a temperature ranging from 325 to 450° C., more preferably from 350 to 425° C., more particularly preferably from 375 to 400° C., and at a time period ranging from 5 sec to less than or equal to 180 min, more preferably ranging from 10 sec to less than or equal to 120 min, more particularly preferably ranging from 30 sec to less than or equal to 60 min, and most preferably ranging from 1 min to less than or equal to 30 min.

[0060] The preferable heat treatment conditions during cold working are described below:

[0061] (Heat Treatment Temperature)

[0062] When a heat treatment temperature exceeds 700° C., a grain size surpasses 15 &mgr;m even if a heating time is less than 5 sec and bendability suitable for a connector and others is reduced even if cold working and a second heat treatment, which follow the first heat treatment, are conducted in predetermined conditions. Further, when a heat treatment temperature decreases to lower than 550° C., a recrystallized grain size is small even if the heat treatment lasts beyond 5 min and a grain size has a chance to be smaller than 1 &mgr;m even if cold working and the second heat treatment are conducted under predetermined conditions, thereby reducing bendability.

[0063] In addition, spinodal decomposition associated with Ni and Sn occurs and further, when P and B are contained, precipitates of phosphides and/or borides of Ni are greatly produced. It should be appreciated that, in a copper alloy of the present invention, when the copper alloy is heated for a predetermined time period or longer at a temperature in the range of 325 to 450° C. after cold rolling, a modulated structure caused by spinodal decomposition, effective for improvement on strengths and on stress relaxation resistance property can be developed. On the other hand, in the spinodal decomposition occurring at a comparatively high temperature in the vicinity of 550° C. (lower than 550° C.), not only is the above described feature hard to realize but the modulated structure is not sufficiently developed either even if cold rolling and a heat treatment are conducted thereafter, which makes it impossible to attain target characteristics.

[0064] (Heat Treatment Time)

[0065] When a heat treatment time exceeds 5 min, a grain size surpasses 15 &mgr;m even at a heat treatment temperature of 700° C., thereby causing the problem of reduction in bendability. Further, a total content of materials in an insoluble phases such as precipitates excels 0.02% since a precipitation rate increases even at a heating temperature of 550° C. or higher, and thereby, not only is it impossible to achieve target characteristics but spinodal decomposition of Ni and Sn also come to occur. When a heat treatment time is less than 5 sec, a recrystallized grain size formed is small even if heating is conducted at a temperature in the range of 550 to 700° C. and bendability is reduced even if cold working and the second heat treatment following the first heat treatment are conducted under predetermined conditions. It should be appreciated that when P or/and B are contained, precipitates such as a Ni phosphide or/and a Ni boride are formed with ease.

[0066] (Cooling Speed)

[0067] When the cooling speed from the heating temperature range is lower than 5° C./sec, precipitation occurs during the cooling and therefore, a total content of insoluble materials such as precipitates exceeds 0.02% under heat treatment conditions in the course of the cold working, thereby making it impossible to attain target characteristics. Further, spinodal decomposition of Ni and Sn also come to occur.

[0068] For the above described reasons, heat treatment conditions in the course of the cold working preferably includes holding the copper alloy at a temperature in the range of 550 to 700° C. for a time period in the range of 5 sec to 5 min, both limits included, in the course of cold working; and in succession, conducting a heat treatment to cool the copper alloy to room temperature on the copper alloy at a cooling speed of 5° C./sec or higher.

[0069] After the heat treatment, cold working is preferably conducted on the copper alloy at a predetermined reduction ratio (on the order in the range of 5 to 95%) and further, the stabilizing annealing is conducted. Preferable conditions for the stabilizing annealing are described below:

[0070] (Heat Treatment Temperature)

[0071] The stabilization annealing is conducted preferably for improvement on elongation of a cold working material, restoration of a proportional limit of spring and improvement on a stress relaxation resistance property as major purposes. When a heating temperature is lower than 325° C., the objectives can not be achieved even if heating lasts for a time period in the range 5 sec to 180 min and further, when exceeds 450° C., precipitation occurs with ease and thereby a stress relaxation property is lowered contrary to the desire. Therefore, the heat temperature is set in the range of 325 to 450° C.

[0072] (Heating Time)

[0073] When a heating time is shorter than 5 sec, the objectives cannot be achieved even at a temperature in the range of 325 to 450° C. Further, when a heating time exceeds 180 min, precipitation occurs with ease and the objective cannot be attained either. Therefore, a heating time is set in the range of 5 sec to 180 min, both limits included.

[0074] For the above described reasons, the conditions for the stabilization annealing is that a temperature in the range of 325 to 450° C. and a time period in the range of 5 sec to 180 min, both limits included.

[0075] Annealing in the course of cold working is preferably conducted in a continuous heat treatment line whose atmosphere is non-oxidative or reductive in order to suppress precipitation during a heat treatment. Stabilization annealing is performed using any of continuous annealing or batch annealing. Further, acid washing, polishing or the like can be performed according to ordinary methods after the annealing. Besides, even if strain correction by a tension leveler prior to stabilization annealing may conducted, or a tension annealing treatment may conducted after stabilization annealing or instead of stabilization annealing, a copper alloy excellent in strain relaxation resistance property of the present invention can be produced.

[0076] A conventional material 6% Sn phosphor bronze C 5191 has physical properties of, at a sheet thickness in the range of 0.15 to 0.25 mm, a tensile strength of 650 N/mm2, a yield strength of 640 N/mm2, elongation of 14%, bendability of W bending R=0, the above described properties being all good, whereas a stress relaxation coefficient is maximized at 150° C. for an elapsed time of 1000 hr to 60% but still shows 30% even at 140° C., wherein a temperature of 140° C. is the maximum thereof. Further, a conductivity of 6% phosphor bronze is relatively as low as of the order of 14% IACS.

[0077] On the other hand, a copper alloy of the present invention is superior to 6% phosphor bronze in the following physical properties: a stress relaxation coefficient less than 30% at 150° C., and a conductivity higher than 17% IACS and equal to 6% phosphor bronze in the following physical property: a tensile strength and elongation (a tensile strength x elongation more than 9000 N/mm2×%) and therefore a copper alloy lower in cost than 6% phosphor bronze can be obtained. More preferably, the stress relaxation coefficient is less than 20% at 150° C. Further, in other points as well, a copper alloy of the present invention is equal to or more excellent than 6% phosphor bronze: such as adhesiveness of solder and Sn plating, stress corrosion cracking sensitivity and others.

EXAMPLES

[0078] Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

Example 1

[0079] Ingots of various compositions (Nos. 1 to 15) shown in Table 1 were casted by melting in graphite crucibles covered with charcoal in an electric furnace in the air atmosphere. A size of an ingot was typically of a thickness of 50 mm×a width of 80 mm×a length of 190 mm and the surfaces, front and back, were surface ground, thereafter, heated at 800° C. and following the heating, hot rolled to a thickness of 10 mm. The sheet of a thickness of 10 mm was heated at 800° C. for 30 min, thereafter, quenched in water and the surfaces were surface ground to a thickness of 9.8 mm. The sheet of a thickness of 9.8 mm is cold rolled to a thickness of 0.50 mm without applying annealing in the course of the cold rolling. The sheet was then held in a salt bath at 600° C. for 30 sec and thereafter, quenched in water. Thereafter, the sheet is further cold rolled to a thickness of 0.25 mm. The thus thinned sheet was held in a salt bath at 425° C. for 30 sec and thereafter, quenched in water to prepare a copper alloy sheet.

[0080] Further, 6% phosphor bronze C5191 of a comparative alloy No. 16 is produced in horizontal casting, after a homogenization treatment, cold rolling and annealing are repeated as a pair on the alloy sheet to a thickness of 0.25 mm and the thinned sheet was held in a salt bath at 350° C. for 30 sec to prepare a comparative specimen. 1 TABLE 1 alloy compositions (O, H and S in ppm and the other elements in wt %) specimen No. Cu Sn Ni Zn O H S others present invention alloys  1 residue 3.6 0.6 2.0 13 0.6  8 0.001Ag, 0.005Mg, 0.02Si, 0.001Al, 0.0002Ca  2 residue 3.6 0.7 1.0 18 0.7  6 0.01Mg, 0.02Si, 0.1Mn, 0.005Cr, 0.001Zr  3 residue 3.5 1.0 2.0 13 0.5  7 0.01Mg, 0.01B, 0.001Pb, 0.001C  4 residue 3.4 0.8 0.1 18 0.6  4 0.01Mg, 0.02P  5 residue 3.6 0.8 4.5  9 0.4  5 0.0001Ca, 0.01P, 0.005Mg, 0.001Be  6 residue 3.1 0.6 0.5 18 0.5  5 0.01Mg, 0.01P, 0.001Co, 0.002Sb  7 residue 3.1 0.9 4.8  8 0.5  6 0.01Mg, 0.01P, 0.001B, 0.001C  8 residue 3.9 0.6 0.1 20 0.8  8 0.001Fe, 0.0002Pb, 0.05Mg, 0.002In  9 residue 3.9 0.9 4.9 13 0.4  5 0.01Mg, 0.01P, 0.0002Pb, 0.002Ti comparative alloys 10 residue 3.5 0.8 0*   35* 0.6  28* 0.1Si*, 0.02Pb* 11 residue 2.8*  0.3*  6.0* 15 2.5* 17 0.05P* 12 residue 4.2*  0.4* 2.0 18 0.8  5 0.15Mg* 13 residue 3.5  0.4* 2.0 10 0.6  6 0.01Mg, 0.01P 14 residue 3.4  1.2*  6.0* 13 0.5  4 0.02Ca*, 0.2Mn*, 0.01P, 0.1Fe* 15 residue 4.1*  1.1* 2.0 15 0.6  25* 0.05P*, 0.2Be*, 0.01C* 16 residue 6.0* 0*  0*  15 2 18 0.10P* *outside a range of the present invention.

[0081] The copper alloy sheets were measured on a tensile strength, a yield strength and elongation according to the below described procedure and further on a conductivity, a stress relaxation coefficient, a stress corrosion cracking property, adhesiveness of tin and a mass of insolubles. Results of the measurements are shown in Tables 2 and 3.

[0082] Tensile strength, yield strength and elongation were measured on test pieces of JIS No. 5. A specimen whose length direction is parallel to a rolling direction is indicated with a mark ∥ while a specimen whose length direction is perpendicular to a rolling direction is indicated with a mark ⊥.

[0083] Conductivity was measured in conformity with JIS H0505.

[0084] Stress relaxation test was carried out as follows: A test piece of a size 0.25 mm t×10 mm w×80 mm l was attached to a test tool of a cantilever type and the test piece was inserted in an oven at 150° C. while a bending was given to the test piece such that a maximum bending stress is 80% of a yield strength at room temperature. Deformation of the test piece was measured at room temperature after 1000 hr elapsed in the oven and a ratio to an initial stress was computed to obtain a stress relaxation coefficient, wherein when the stress relaxation coefficient excels 30%, it is expressed with x as evaluation mark.

[0085] Stress corrosion cracking resistance was investigated in conformity with a stress corrosion cracking test method developed by D. H. Thompson, Materials Res. And Stds., I (1961)p 108 to 111. A size of a test piece was 0.25 mm t×12.7 mm w×150 mm l (n=5), a corrosive medium was 2 l of aqueous ammonia (prepared by diluting 28% aqueous ammonia with water on an equal amount basis), the test piece was held in the air above the medium in a 5 l desiccator vessel while the test piece was forcibly deformed in the form of a loop and the test piece and corrosive medium were held at 35° C. for 10 to 30 hr in the 5 l desiccator vessel. Thereafter, the test piece was released from such a restrained condition and a residual deformation of the test piece was measured over elapsed time, that is the test was conducted paying attention to an open distance between both free ends of the test piece that had been connected with each other in the constrained condition of the loop by measuring an elapsed time when the open distance was reduced to less than 50% of an initial value of the open distance. Evaluation was expressed such that when a test piece had the elapsed time shorter than that of the comparative alloy No. 16, it had a mark X, while when a test piece had the elapsed time longer, it had a mark O.

[0086] Adhesiveness of tin was measured as follows: A copper alloy was electroplated to a thickness of 1 &mgr;m using a tin sulfate bath with a brightening agent, the electroplated test piece was held in an oven at 150° C. for 1000 hr, thereafter the test piece was taken out from the oven, 180 degree bending was temporarily applied on the test piece with a tool having a head of 1 mm in radius and the bending was then canceled, and adhesiveness of tin was investigated at the bent portion. Evaluation was expressed such that when a tin film was separated from a test piece, it had a mark X, while when a film was not separated from a test piece, it had a mark O.

[0087] Insolubles weight was measured as follows: A final product was dissolved in a solution of a ratio of nitric acid:water=3:1 and precipitates as insoluble residue were captured on a filter paper (GS 25 manufactured by Toyo Roshi K.K. ). The precipitates were washed with distilled water and the precipitates and filter paper were dried in a constant temperature chamber at 105° C. for 1 hr and thereafter, a mass of the precipitates and filter paper was measured after the precipitates were further stored at room temperature for 60 min. The mass of the filter paper which was measured before the capture of the precipitates was subtracted from the total solid mass after the filtration to obtain the mass of the insolubles. Then computation was conducted to attain a ratio of the mass thus captured insolubles to the mass of the original specimen. It should be appreciated that a great part of the insolubles is precipitates, and while a size of a precipitate as primary particle is normally on the order ranging from several tens to several hundreds of Å, most of particles can be captured on the filter since the particles are agglomerated to secondary forms in the extracted state as residues after dissolution. 2 TABLE 2 Characteristics of alloys stress stress length tensile yield relaxation corrosion adhesiveness specimen direction of strength strength elongation conductivity coefficient cracking of insolubles No. specimen (N/mm2) (N/mm2) (%) (% IACS) (%) *1 property *2 tin *3 (wt %) 1 ∥ 639 597 13.7 19.1 21 ◯ ◯ 0.001 ⊥ 654 599 14.8 28 2 ∥ 642 607 13.5 20.0 16 ◯ ◯ 0.002 ⊥ 658 618 14.6 20 3 ∥ 668 614 13.3 19.3 14 ◯ ◯ 0.002 ⊥ 675 628 14.9 20 4 ∥ 636 596 13.8 19.6 13 ◯ ◯ 0.003 ⊥ 649 597 15.1 18 5 ∥ 669 616 14.0 18.2 15 ◯ ◯ 0.001 ⊥ 660 619 14.9 19 6 ∥ 634 590 14.1 21.3 20 ◯ ◯ 0.001 ⊥ 622 578 14.5 27 7 ∥ 644 599 13.8 18.3 15 ◯ ◯ 0.002 ⊥ 631 561 14.9 20 8 ∥ 643 598 13.5 20.5 22 ◯ ◯ 0.001 ⊥ 659 606 14.6 28 9 ∥ 695 646 13.4 17.5 13 ◯ ◯ 0.004 ⊥ 683 635 14.1 18 *1: 30 % in excess is expressed with X *2: Earlier than comparative alloy No. 16 is expressed with X *3: Separated within 1000 hr is expressed with X

[0088] 3 TABLE 3 Characteristics of alloys stress stress length tensile yield relaxation corrosion adhesiveness specimen direction of strength strength elongation conductivity coefficient cracking of insolubles No. specimen (N/mm2) (N/mm2) (%) (% IACS) (%) *1 property *2 tin *3 note (wt %) 10 ∥ 640 595 13.9 19.8 14 ◯ X pin holes found 0.002 ⊥ 656 604 14.5 20 in ingot 11 ∥ 595 547 13.2 18.3   32X X ◯ generation of 0.008 ⊥ 590 543 14.8   44X small cracks during hot rolling 12 ∥ 651 605 14.0 18.2   35X ◯ ◯ 0.002 ⊥ 666 619 13.5   47X 13 ∥ 627 577 13.2 20.1   33X ◯ ◯ 0.002 ⊥ 640 589 14.5   46X 14 ∥ 665 618 13.5 15.9 15 X ◯ 0.012 ⊥ 662 609 14.6 20 15 ∥ 706 648 12.8 16.1 13 X ◯ generation of 0.016 ⊥ 704 654 13.5 19 small cracks during hot rolling 16 ∥ 651 640 14.0 14.0   60X &Dgr; X 0.001 ⊥ 668 610 7.9   59X *1: 30% in excess is expressed with X *2: Earlier than comparative alloy No. 16 is expressed with X *3: Separated within 1000 hr is expressed with X

[0089] As shown in Tables 2 and 3, in regard to a tensile strength, a yield strength and elongation, the alloys Nos. 1 to 9 of the present invention all have a tensile strength of 620 N/mm2 or more, a yield strength of 570 N/mm2 or more and elongation of 13% or more, and a tensile strength x elongation of 9000 N/mm2·% or more in direction in parallel or/and perpendicular to a rolling direction. Further, the characteristics of a specimen in a direction parallel to a rolling direction are equal to those of the comparative alloy No. 16 (C5191) and the characteristics of a specimen in a direction perpendicular to a rolling direction are superior to those of the comparative alloy No. 16 (C5191).

[0090] In regard to a conductivity, the sheets of the alloys Nos. 1 to 9 of the present invention all satisfies 17% IACS and are superior to the comparative alloy No. 16.

[0091] In regard to a stress relaxation coefficient, the sheets of the alloys Nos. 1 to 9 of the present invention all show good values as small as 30% or less after 1000 hr elapsed at 150° C. as well, while the comparative alloys Nos. 11 to 13 show values in excess of 30% since an Ni content is as small as 0.3% or 0.4%.

[0092] In the evaluation of a stress corrosion cracking resistance property, while all (n=5) the sheets of the comparative alloy were cracked in a time period of 14 to 20 h, the sheets of the alloys Nos. 1 to 9 of the present invention all have a longer cracking time than the comparative alloy No. 16 and are excellent in a lifetime. Further, the comparative alloys 111 and 14 produce cracks earlier than the comparative alloy No. 16 since a Zn content exceeds 5% while the comparative alloy No. 15 has a Zn content of 2% and the alloy produces cracks earlier than No. 16 since a P content is 0.05%.

[0093] In regard to separation of tin, the sheets of the alloys Nos. 1 to 9 of the present invention show no separation of tin after 1000 hr elapses at 150° C., but the comparative alloys Nos. 10 and 16, which contain no Zn, show separation of tin.

[0094] Further, the ingot of the comparative alloy No. 10 has many of pin holes therein since the alloy has as much as 28 ppm of S and 35 ppm of 0. Nos. 11 and 15 produce small cracks in earings during hot rolling and a hot workability thereof is not good since the alloy No. 11 contains as much as 2.5 ppm of H and the alloy No. 15 contains as much as 25 ppm of S and 0.01% of C.

Example 2

[0095] Two kinds of copper alloys (both are alloys of the present invention) of compositions shown in Table 4 were obtained in the form of sheets of a thickness of 0.50 mm after being subjected to the process similar to the example 1, which includes casting an ingot, hot rolling, a solid solution treatment, and cold tolling. The sheets were further worked in processes shown in Tables 5 and 6 and specimens worked were measured on a tensile strength, a yield strength, elongation, a stress relaxation coefficient according to the procedure described above and further on a grain size, W bendability, and a weight of precipitates according to the procedure described below. Results thereof are collectively shown in Tables 5 and 6.

[0096] Grain size: Average grain sizes after the heat treatment (before the final cold rolling) were measured in conformity with a cutting method of JIS H0501.

[0097] W bendability: No. 4 test pieces of JIS Z2204 that were sampled in directions parallel or perpendicular to a rolling direction were used for a W bending test at a bending radius R=0 in conformity with JIS H3110. 4 TABLE 4 alloy compositions (O, H and S in ppm and the other elements in wt %) specimen No. Cu Sn Ni Zn O H S others present invention alloy 1 residue 3.5 0.8 2.0 15 0.6 8 0.01P, 0.01Mg 2 residue 3.5 0.8 2.0 18 0.4 7 0.02P

[0098] 5 TABLE 5 production methods and characteristics of alloys length tensile yield grain W insolubles specimen direction of strength strength elongation size bendability mass No. method working process specimen (N/mm2) (N/mm2) (%) (&mgr;m) (R = o) (wt %) 1 present 0.5 mm t → in salt bath at 600° C. for ∥ 639 597 13.9 5 good 0.003 invention 30 sec → quenching in water → acid ⊥ 651 601 14.8 good process washing → cold rolling → 0.25 mm t → annealing at 425° C. for 30 sec 1 comparative 0.5 mm t → in salt bath at 750° C. for ∥ 578 545 11.7 40 small cracks 0.002 process 30 sec → quenching in water → acid ⊥ 613 557 14.9 cracks washing → cold rolling → 0.25 mm t → annealing at 350° C. for 30 sec 1 comparative 0.5 mm t → in salt bath at 525° C. for ∥ 675 649 4.5 <1 cracks 0.025 process 60 sec → quenching in water → acid ⊥ 703 686 5.9 cracks washing → cold rolling → 0.25 mm t → annealing at 350° C. for 30 sec

[0099] 6 TABLE 6 production methods and characteristics of alloys length tensile stress specimen direction of strength elongation insolubles relaxation No. method working process specimen (N/mm2) (%) mass (wt %) coefficient (%) 2 present 0.5 mm t → in salt bath at 600° C. for 30 sec → ∥ 637 13.5 0.002 18 invention quenching in water → acid washing → cold ⊥ 650 14.6 19 process rolling → 0.25 mm t → annealing at 425° C. for 30 sec 1 comparative 0.5 mm t → annealing at 600° C. for 30 min → ∥ 645 11.2 0.03 31 process cooling in furnace (75° C./time) → acid washing → ⊥ 661 10.5 39 2 cold rolling → 0.25 mm t → annealing at 350° C. ∥ 652 9.0 0.05 35 for 30 sec ⊥ 668 6.5 42

[0100] As shown in the table 5, the sheets receiving annealing at 600° C. for 30 sec in salt bath and thereafter, quenching in water according to the present invention process have a grain size as fine as 5 &mgr;m and are good at W bendability as well, while the sheets receiving annealing at 750° C. for 30 sec in salt bath have a grain size as large as 40 &mgr;m, degraded mechanical properties and poorer bendability. Further, the sheets receiving annealing at 525° C. for 60 sec in salt bath have a small grain size, but poor elongation and poor bendability, and much of generated insolubles.

[0101] Further as shown in the table 6, the sheets produced according to the present invention process show low stress relaxation coefficients while the sheets cooled at a speed as slow as 75° C./hr after the intermediate annealing as shown in the comparative process have an amount of insolubles more than 0.03% and a stress relaxation coefficient more than 30% and further degraded mechanical properties.

[0102] A stress is hard to relax in an copper alloy according to the present invention, the copper alloy is suited for use in applications such as electrical and electronic equipment related components, i.e., springs, switches, connectors, diaphragms, sockets, bellows, fuse-clips, sliding pieces, bearings and bushes, and automobile sheet-belt springs, washers and such features are exerted in the forms of tubes, wires or rods.

[0103] A copper alloy according to the present invention has a composition of Sn in content of 3% to 4%, the lower limit included but the upper limit not included, Ni in content of 0.5% to 1.0%, both limits included, Zn in content of 0.05% to 5.0%, both limits included, and annealing in the course of production is a short duration annealing at 550 to 700° C. for 5 sec to 5 min (may be in one time) and a final annealing is conducted at 325 to 475° C. for 5 sec to 180 min, whereby the copper alloy of the present invention is lower in cost than phosphor bronze© 5191) not only in terms of composition but from the view point of a working process and further of a shorter process, whereby the copper alloy is economically very efficient.

[0104] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

[0105] This application is based on Japanese Patent Applications JP0011-140849, filed May 20, 1999, and JP2000-083099, filed Mar. 24, 2000, the entire contents of each of which are incorporated herein by reference.

Claims

1. A copper alloy, comprising:

an Sn content of 3 wt % to less than 4 wt %;

a Ni content of 0.5 wt % to less than or equal to 1.0 wt %;

a Zn content of 0.05 wt % to less than or equal to 5.0 wt %; and

Cu and unavoidable impurities combined as the balance; wherein

a total content of insolubles is less than or equal to 0.02 wt %.

2. The copper alloy according to claim 1, further comprising:

a P content of 0.001 wt % to less than 0.03 wt %;

a B content of 0.0001 wt % to less than or equal to 0.02 wt %;

an Mg content of 0.0001 wt % to less than or equal to 0.05 wt %; and

a Ca content of 0.0001 wt % to less than or equal to 0.01 wt %; wherein

a total content of one or more elements selected from the group consisting of P, B, Mg, Ca, and mixtures thereof is in the range of 0.0001 wt % to less than or equal to 0.1 wt %.

3. The copper alloy according to claim 1, wherein a total content of one or more elements selected from the group consisting of P, B, Mg, Ca, and mixtures thereof is in the range of 0.0001 wt % to less than or equal to 0.1 wt %.

4. The copper alloy according to claim 1, further comprising a P content of 0.001 wt % to less than 0.03 wt %.

5. The copper alloy according to claim 1, further comprising a B content of 0.0001 wt % to less than or equal to 0.02 wt %.

6. The copper alloy according to claim 1, further comprising an Mg content of 0.0001 wt % to less than or equal to 0.05 wt %.

7. The copper alloy according to claim 1, further comprising a Ca content of 0.0001 wt % to less than or equal to 0.01 wt %.

8. The copper alloy according to claim 1, further comprising:

an Ag content of less than or equal to 0.1 wt %;

a Pb content of less than or equal to 0.01 wt %;

an Fe content of less than or equal to 0.05 wt %;

an Si content of less than or equal to 0.05 wt %;

an Mn content of less than or equal to 0.1 wt %; wherein

a total content of one or more elements selected from the group consisting of Ag, Pb, Fe, Si, Mn and mixtures thereof is less than or equal to 0.3 wt %.

9. The copper alloy according to claim 1, wherein a total content of one or more elements selected from the group consisting of Ag, Pb, Fe, Si, Mn and mixtures thereof is less than or equal to 0.3 wt %.

10. The copper alloy according to claim 1, further comprising an Ag content of less than or equal to 0.1 wt %.

11. The copper alloy according to claim 1, further comprising a Pb content of less than or equal to 0.01 wt %.

12. The copper alloy according to claim 1, further comprising an Fe content of less than or equal to 0.05 wt %.

13. The copper alloy according to claim 1, further comprising an Si content of less 20 than or equal to 0.05 wt %.

14. The copper alloy according to claim 1, further comprising an Mn content of less than or equal to 0.1 wt %.

15. The copper alloy according to claim 1, further comprising:

an S content of less than or equal to 20 ppm;

an O content of less than or equal to 30 ppm; and

an H content of less than or equal to 2 ppm.

16. The copper alloy according to claim 1, further comprising one or more elements selected from the group consisting of Be, Al, Ti, Cr, Co, Zr, Sb, In and mixtures thereof in total content of less than or equal to 0.1 wt %.

17. The copper alloy according to claim 1, comprising an average grain size in a range of 1 to 15 &mgr;m.

18. The copper alloy according to claim 1, comprising a stress relaxation coefficient of 30% or less after the copper alloy is held at 150° C. for 1000 hr under a load of a bending stress corresponding to 80% of a 0.2% yield strength at room temperature.

19. An article, comprising the copper alloy as claimed in claim 1.

20. A method for producing the copper alloy according to claim 1, comprising:

holding a copper alloy at a temperature ranging from 550 to 700° C. for a time period ranging from 5 sec to less than or equal to 5 min in the course of cold working;

subsequently heat treating the copper alloy to cool the copper alloy to room temperature at a cooling speed of 5° C./sec or higher;

subsequently cold working the copper alloy to a target dimension; and

stabilizing annealing the copper alloy at a temperature ranging from 325 to 450° C. and a time period ranging from 5 sec to less than or equal to 180 min.