Patent Application
20100189593
The disclosure of International Application No. PCT/JP2007/064813 filed Jul. 27, 2007 including specification, drawings and claims is incorporated herein by reference in its entirety.
The present invention relates to a copper alloy material containing no elements such as lead (Pb), cadmium (Cd), and beryllium (Be) that render harmful environmental effects.
This copper alloy material is used in electronic and electrical components, safety tools, and the like.
Electronic and electrical components using copper (Cu) alloys include connectors for personal computers, semiconductor plugs, optical pickups, coaxial connectors, IC checkers pins and the like in the electronics field; cellular phone parts (connectors, battery terminals, antenna parts), submarine relay casings, exchanger connectors and the like in the communication field; various electric parts such as relays, various switches, micro-motors, diaphragms, and various types of terminals in the automotive field; medical connectors, industrial connectors and the like in the medical and analytical instrument field; and home appliance relays such as in air conditioners, game machine optical pickups, card media connectors and the like in the electric home appliance field. Most of these parts are usually manufactured from 0.1-0.2 mm thick sheets or coils.
Besides the above thin sheets, these alloys are also often used in wire rod or bulk shapes. Electronic or electrical components containing copper or copper alloys are also utilized for example in parts such as aircraft landing gears in the aviation and aerospace fields, and in plastic injection molds.
Parts in rod shapes may typically include diverse types of electrodes for welding, such as spot welding, or laser beam welding utilized for example to assemble automobile bodies.
Typical safety tools using copper or copper alloy may include excavating rods and hand tools such as wrenches, chain blocks, hammers, drivers, cutting pliers, and nippers which are utilized in potentially hazardous locations due to explosion hazards from sparks or flames such as in an ammunition dumps, or coal mines.
Beryllium copper (Cu—Be) alloy reinforced by beryllium (Be) age precipitation is a widely known copper alloy in the conventional art. This alloy material is extensively used for example as spring material or the like, because it possesses both excellent tensile strength and electrical conductivity. However, the Cu—Be production process and the process of working this alloy material into various parts generates oxidized beryllium compounds (Be-oxide).
Be is an environmentally harmful element ranking under lead Pb and Cd. The manufacture and working of the Cu—Be alloy therefore requires providing an additional detoxifying treatment process which causes higher production costs, and problems when recycling electronic and electrical components. In welding processes using a Cu—Be alloy electrode, Be-oxides harmful to human cardiopulmonary functions are generated, leading to huge cost increases due to the extra environmental management that is needed. Therefore the Cu—Be alloy is a problem material in terms of effects on the environment. This situation therefore has created a demand for a material possessing both excellent tensile strength and conductivity without containing any environmentally harmful elements such as lead Pb, cadmium Cd, and beryllium Be.
It is essentially difficult to simultaneously enhance both tensile strength [TS (MPa)] and electrical conductivity [relative value of annealed pure copper polycrystalline material to conductivity, IACS (%)]. User demands therefore usually center upon improving one of these characteristics. The Non-Patent Literature 1 also describes various features of actual copper and brass products that have been produced.
Patent Literature 1 for example discloses a copper alloy material called Corson alloy in which Ni2Si is precipitated. Compared to other alloy materials containing no environmentally harmful elements such as Be, this alloy material has a comparatively good balance of tensile strength and electrical conductivity, with an electrical conductivity of about 40% at a tensile strength of 750-820 MPa.
This alloy however is limited as to what extent the strength and conductivity can be enhanced and the problem of product variations still remains as described below. This alloy has age hardening capability achieved by Ni2Si precipitation. Attempting to enhance the electrical conductivity by reducing the nickel (Ni) and silicon (Si) content significantly lowers the tensile strength. On the other hand, even if the Ni and Si content is boosted in order to raise the Ni2Si precipitation quantity, the rise in tensile strength is limited and electrical conductivity is seriously reduced. The balance between tensile strength and electrical conductivity in Corson alloys is disrupted in regions with high tensile strength and regions with high electrical conductivity, which consequently narrows the range of potential product variations. The reason is as follows.
The electric resistance (or electrical conductivity that is the inverse thereof) of alloy is determined by electron scattering, and fluctuates greatly depending on the type of elements dissolved in the alloy. Since dissolving Ni in the alloy noticeably raises the electric resistance (drastically reduces conductivity), the electrical conductivity in the above-mentioned Corson alloy lowers as the Ni content is increased. The tensile strength of copper alloy material on the other hand is obtained by an age hardening effect. There is a greater improvement in tensile strength when the quantity of precipitates is larger, or as the precipitates become more finely dispersed. There are limitations on the extent that Corson alloy strength can be boosted in terms of precipitation quantity and precipitate dispersion since the precipitated particles are only made from only Ni2Si.
Patent Literature 2 discloses a copper alloy with improved balance of strength and electrical conductivity. These electrical parts are usually produced by bend forming from 100 μm to 200 μm thick alloy sheets. The bending workability is therefore also a very important characteristic in addition to above balance of strength and electrical conductivity. The alloy sheets are produced by combined process of rolling/aging. In many cases, bending workability in the direction transverse to the rolling direction (bad way) is inferior to that in the rolling direction (good way). This bending workability or ductility anisotropy (directional dependence) arises from the crystallographic grain structure of the rolled sheets. The elongated grain in other words easily causes inter-granular fractures, when the sheets are bent the bad way.
In bulk materials including rods which are used for plastic injection molds, welding electrodes, or safety tools, the ductility is also important, in addition to the balance of strength and conductivity in order to avoid cracking from occurring during use or in the production process.
In Patent Literature 3, the present inventors and others invented copper alloys possessing a good balance of both strength and electrical conductivity. However, not all of these alloys were ideal for mass production, because coarse precipitates form below 900° C. in the hot rolling process.
Copper and Copper Alloy Product Data Book, Aug. 1, 1997, issued by the Japan Copper and Brass Association, pp. 328-355
A primary object of the present invention is to provide a copper alloy material having good workability, and a good balance of strength and electrical conductivity, and also containing no environmentally harmful elements such as beryllium. A particular object of the present invention is to provide copper alloy materials possessing properties equal or superior to conventional beryllium copper (Cu—Be) alloys. A further object of the present invention is to provide a copper alloy which can be subjected to hot rolling, solution treatment, or the like.
Here, “a balance of electrical conductivity and tensile strength at a high level equal to or superior to that of a Be-added copper alloy” more specifically indicates a copper alloy material having the properties of tensile strength, TS, and conductivity, IACS, in the region indicated by “good balance” in
TS≧648.06+985.48×exp(−0.0513×IACS) (2)
Wherein TS represents tensile strength (MPa) and IACS represents electrical conductivity (%).
In addition to the above described tensile strength and electrical conductivity characteristics, a certain degree of high-temperature strength is also required in the copper alloy material. High-temperature strength is required for example in material used in connectors for automobiles and computers that are often exposed to environments of 200° C. or higher. Although the room-temperature strength of pure copper drastically declines when heated to 200° C. or higher and spring characteristics can no longer be maintained, there is virtually very small change in room-temperature strength of the above-mentioned Cu—Be alloy or Corson alloy when heated to 400° C.
Accordingly, an aim of the present invention is to attain a level of high-temperature strength equal to or superior to that of Cu—Be alloy. More specifically, a heating temperature where the drop in hardness before and after a heating test is 50% is defined as the heat resistant temperature, and a heat resistant temperature of 400° C. or more is regarded as excellent high temperature strength. An even more preferable heat resistant temperature is 500° C. or higher.
Another aim of the invention is to attain a level of bending workability equal to or superior to that of conventional alloys such as Cu—Be alloy.
More specifically, the bending workability of sheets of thin copper material can be evaluated by performing a 90° bend test at various curvature radii on a test piece prepared so the long side is the direction perpendicular to the rolling direction (bad way), and then measuring the minimum curvature radius R (mm) at which no cracking occurs, and determining the ratio B90 (=R/t) of this radius to the thickness t (mm).
A satisfactory range of bending workability here satisfies formula (3) in a sheet material with a tensile strength TS of 600 MPa or less, and satisfies the following formula (4) in a sheet material with a tensile strength TS exceeding 600 MPa.
B90≦2.0 (3)
B
90≦25.093−54.82×exp[−{(TS+583.61)/1254}2]+1.25×t (4)
Where B90 denotes the bending workability in the 90° bend test in bad way, Ts denotes the tensile strength (MPa), and t denotes the thickness (mm).
Sheet material possessing a tensile strength TS exceeding 600 MPa preferably satisfies the following formula (4′).
B
90≦24.238−43.087×exp[−{(TS+383.4)/1199.4}2]+1.25×t (4′)
Moreover, sheet material possessing a tensile strength TS exceeding 600 MPa even more preferably satisfies the following formula (4″).
B
90≦−33.0949−55.0551×exp[−{(TS+1898.3)/1949.91}2]+1.25×t (4″)
In bulk material such as rods, the workability can be evaluated via the relationship between tensile strength TS (MPa) and elongation El (%). A satisfactory range for processing wire rods satisfies the following formula (5).
El≧−24.138+24.6076×exp[−{(TS−1816.36)/2213.52}2] (5)
Where, TS denotes the tensile strength (MPa), and El denotes the elongation (%).
Bulk materials (other than sheet material) preferably satisfy the following formula (5′).
El≧59.0438−61.9662×exp[−{(TS−2359.36)/4047.4}2] (5′)
Bulk materials (other than sheet material) even more preferably satisfy the following formula (5″).
El≧89.6632−168.32×exp[−{(TS−10630.2)/11614.9}2] (5″)
Copper alloy material for safety tools are also required wear resistance as well as characteristics such as tensile strength TS and conductivity IACS described above. Therefore, an aim is to attain wear resistance equivalent to that of tool steel. Specifically, a Vickers hardness of 250 or more at a room temperature is regarded as excellent wear resistance.
As can be seen from a Ti—Cr binary phase diagram in
The essential aspects of the copper alloy material of the present invention are represented by the following from (1) through (4).
1. (1) A copper alloy material characterized by the following (A) to (F);
log N≦0.4742+17.629×exp(−0.1133×X) (1)
TS≧6 48.06+985.48×exp(−0.0513×IACS) (2)
B90≦2.0 (3)
B
90≦25.093−54.82×exp[−{(TS+583.61)/1254}2]+1.25×t (4)
El≧24.138−24.6076×exp[−{(TS−1816.36)/2213.52}2] (5)
(2) The copper alloy material according to (1), further containing not less than 0.005% and not more than 1% of Ag.
(3) The copper alloy material according to (1) or (2), further containing not less than 0.01% and not more than 1.0% of one or more elements selected from Sn, Mn, Co, Al, Si, Nb, Ta, Mo, V, W, Au, Zn, Ni, Te, Se, and Ge, and the total content of these elements is not more than 1.0%.
(4) The copper alloy material according to any of one selected from (1) to (3), further containing not less than 0.001% and not more than 0.1% in total of one or more elements selected from Zr, Mg, Li, Ca, and rare earth elements.
The invention provides a copper alloy material possessing good workability, a good balance of strength and electrical conductivity, and also containing no harmful elements that pose a problem to the environment.
The embodiment of the present invention is described next. In the following description the “%” signifies the content in “mass-%” of an element.
(A) Chemical Composition of the Copper Alloys of the Present Invention
One of the copper alloy materials in the present invention consists of 0.01% to 2.5% Ti, 0.01 to 0.5% Cr, 0.01% to 1% Fe and the remainder consists of copper (Cu) and impurities.
Ti: 0.01% to 2.5%
Titanium (or Ti) is an element essential for ensuring material strength. Titanium can in other words strengthen the material by precipitation hardening that results from use of Cu4Ti precipitates in the aging treatment. When the Ti content is less than 0.01%, sufficient strength cannot be achieved. On the other hand, increasing the content more than 2.5% lowers the electrical conductivity and ductility, although the strength is enhanced. In view of this the Ti content was set 0.01% to 2.5%. The Ti content is preferably to be set a range from 0.01% to 2%. A content of 0.1% or more is preferable in order to achieve sufficient strength.
Cr: 0.01% to 0.5%
As described above, Ti is an effective element in precipitation hardening but Ti atoms in solid solution state cause a large deterioration in the electrical conductivity. The effect of chromium (Cr) in solid solution on electrical conductivity however is very small. Moreover, the content of solid solution Ti can be reduced markedly in the matrix by strong interaction between Cr and Ti atoms leading to much improved electrical conductivity. This effect is achieved when the Cr content is 0.01% or more. When the Cr content exceeds 0.5%, bending workability or ductility deteriorates. The Cr content was therefore controlled 0.01% to 0.5%.
Fe: 0.01% to 1%
Iron (or Fe) can improve the ductility such as for bending workability while causing a small drop in both strength and electrical conductivity. Also, Fe atoms are not prone to form harmful inter-metallic compounds with Ti and/or Cr in the solidification and subsequent cooling process. No improvement in ductility can be expected if the Fe content is less than 0.01%. When the Fe content exceeds 1%, the ductility improvement effect is saturated and electrical conductivity decreases. The Fe content was therefore controlled 0.01% to 1%. The preferable Fe content is 0.05% to 0.5%, and is more preferably 0.05% to 0.3%.
A copper alloy material in the present invention may contain 0.005% to 1% of silver (Ag) instead of a portion of copper (Cu).
Ag: 0.005% to 1%
Silver (or Ag) can be included as necessary. Ag is an element causing almost no reduction in electrical conductivity even in a state where dissolved into the Cu matrix. Metallic Ag enhances the strength by fine precipitation. This effect is noticeable at 0.005% or more but saturates at a content exceeding 1%, leading to increased alloy costs. The preferred Ag content is 0.1% to 1%.
To improve corrosion resistance and/or heat resistance, a copper alloy material in the present invention may contain 0.01% to 1% in total of one or more elements selected from the following elements; Sn, Mn, Co, Al, Si, Nb, Ta, Mo, V, W, Au, Zn, Ni, Te, Se, and Ge, instead of a portion of Cu.
Sn, Mn, Co, Al, Si, Nb, Ta, Mo, V, W, Au, Zn, Ni, Te, Se, and Ge: 0.01% to 1.0% of Each Element
Each of these elements may be included as needed since they render the effect of improving corrosion resistance and heat resistance while maintaining the balance between strength and electrical conductivity.
This effect is exhibited when 0.01% or more of each element is added but when their contents exceed 1%, the electrical conductivity is reduced. The upper limit is therefore set as 1.0%, when adding Sn, Mn, Co, Al, Si, Nb, Ta, Mo, V, W, Au, Zn, Ni, Te, Se, and Ge.
Even if the content of each element is within the above-described region, the electrical conductivity deteriorates when the total amount exceeds 1.0%. The total amount of Sn, Mn, Co, Al, Si, Nb, Ta, Mo, V, W, Au, Zn, Ni, Te, Se, and Ge was therefore set to 1.0% or less. The preferred total content is in a range of 0.1% to 0.5%.
To increase the high-temperature strength, the copper alloy material of the present invention may include 0.001% to 0.5% in total of one or more elements selected from Zr, Mg, Li, Ca, and rare earth elements instead of a portion of Cu.
Zr, Mg, Li, Ca, and rare earth elements: 0.001% to 0.5% of each element These elements can be added as needed since they bond easily with oxygen in the Cu matrix causing a fine dispersion of oxides that enhance the high-temperature strength. This effect is noticeable when the total content of these elements is 0.001% or more. However, the content exceeding 0.5% causes the above effect to saturate, and causes problems such as lower bending workability. Therefore, when adding one or more elements selected from Zr, Mg, Li, Ca and rare earth elements, the total content thereof is preferably set 0.001% to 0.1%. The preferred total content is 0.005% to 0.05%. The rare earth elements here denote Sc, Y, and lanthanoid, and may be added singly or in a form of misch metal.
(B) Total Number of Precipitates and Inclusions
In the copper alloy material of the present invention, the relationship between the total number N and the diameter X satisfies the following formula (1):
Log N≦0.4742+17.629×exp(−0.1133×X) (1)
wherein N denotes the total number of precipitates and inclusions whose diameter is 1 μm or more within a 1 mm2 unit area of the copper alloy material; and X denotes the diameter in μm of precipitates and the inclusions whose diameter is 1 μm or more.
The preferred relationship between the total number N and the diameter X satisfies the following formula (1′):
Log N≦0.4742+7.9749×exp(−0.1133×X) (1′)
wherein N denotes the total number of precipitates and inclusions whose diameter is 1 μm or more within a 1 mm2 unit area of the copper alloy material; and X denotes the diameter in μm of precipitates and the inclusions whose diameter is 1 μm or more.
An even more preferable relationship between the total number N and the diameter X satisfies the following formula (1″):
Log N≦0.4742+6.3579×exp(−0.1133×X) (1″)
wherein N denotes the total number of precipitates and inclusions whose diameter is 1 μm or more within a 1 mm2 unit area of the copper alloy material; and X denotes the diameter in μm of precipitates and inclusions whose diameter is 1 μm or more.
In the copper alloy material of the present invention, the Cu4Ti, metallic Cr, or metallic Ag precipitates finely so that the strength can be increased without reducing the electrical conductivity. The strengthening mechanism in other words is precipitation hardening. The strong interaction of Cr with Ti atoms functions to reduce the solid solution Ti content which causes lower electrical conductivity. The electrical conductivity of the matrix consequently approaches that of pure Cu.
However, when the Cu4Ti, metallic Cr metallic Ag, Cr—Ti compounds are roughly precipitated at a grain size of 10 μm or more, the ductility deteriorates, causing cracking or chipping for example during the bending or punching processes when forming the connector. The poor ductility might adversely affect fatigue and impact resistance characteristics during use. Cracking or chipping tends to occur in the subsequent working process particularly when a coarse Ti—Cr compound was generated during cooling after solidification. Another drawback is that fine precipitation of Cu4Ti, metallic Cr or metallic Ag is inhibited in the subsequent aging process, resulting in insufficient precipitation hardening. This problem becomes noticeable when the relationship between the total number N and the diameter X does not satisfy the above formula (1).
An essential requirement defined for the present invention is therefore a relationship between the total number N and the diameter X that satisfies the above formula (1). This relationship should preferably satisfy the above formula (1′), and more preferably should satisfy the above formula (1″).
The total number of precipitates and inclusions whose diameter is 1 μm or more within a 1 mm2 unit area of the copper alloy material are measured as follows.
A section perpendicular to the rolling plane and parallel to the transverse direction of each specimen was polish-finished, and a visual field of 1 mm×1 mm was observed by an optical microscope at 100-fold or 500-fold magnification in situ or after being etched with an ammonia/hydrogen peroxide solution whose volume ratio was controlled to be 9:1. Thereafter, the long diameter (the length of a straight line which can be drawn longest within a grain without contacting with the grain boundary halfway) of the precipitates and the inclusions was measured, and the resulting value was defined as the grain size.
The measured value of grain size (μm) of the precipitates and inclusions obtained as described above was converted to an integer by rounding off the decimal point. A total number n1 was calculated for each grain size 1 μm, 2 μm, . . . , α μm (α is an integer) by taking one item crossing the frame line of the 1 mm×1 mm visual field as ½ piece and one item located within the frame line as 1 piece per each grain size, and an average (N/10) of the number of the precipitates and the inclusions N (=n1+n2+ . . . +n10) in for 10 optionally selected visual fields as the total number of precipitates and inclusions for each grain size of the specimen.
To obtain the value of the right side member in the formula (1), (1′) and (1″) for each grain size of 1 μm, 2 μm, 3 μm . . . , α μm (α is an integer), X=1 was substituted when the measured value of the grain size of the precipitates and inclusions was 1.0 μm or more, and less than 1.5 μm, and X=α (α is an integer of 2 or more) was substituted when the measured value was (α−0.5)μm or more, and less than (α+0.5) μm.
Values for the right side member were in this way obtained for each grain size of 1 μm, 2 μm, 3 μm . . . , α μm (α is an integer). When the formulas (1), (1′), and (1″) were satisfied for each grain size, the total number of precipitates and inclusions having a size of 1 μm or larger, N, was defined to satisfy the respective formulas (1), (1′), and (1″).
(C) Method for Producing the Copper Alloy Material of the Present Invention
In the copper alloy material of the present invention, melting is preferably conducted in a vacuum or in a non-oxidation or reducing atmosphere by for example using flux. Oxygen impurities in the melting process can cause blister problems in the following processes, making coarse oxide inclusions form easily with Ti or Cr in the subsequent thermal process, leading to deterioration of various properties such as ductility or in fatigue characteristics in the final product.
The casting method after melting is preferably continuous casting from the view point of cooling rate and productivity. The cooling rate from solidification to 600° C. is preferably controlled to be equal to or greater than 0.5° C./s on average in order to suppress coarse inclusion formation. A more preferable cooling rate is equal to or greater than 5° C./s. During slow cooling after solidification, the precipitates develop into coarse particles. Completely dissolving such coarse precipitates/inclusions requires high temperature solution treatment for an extremely long time such as dozens of hours or more at high temperatures of 800 to 900° C. This type of long heat treatment at high temperatures introduces severe surface oxidation or surface roughing. If the holding time is not long enough, then non-dissolved particles will remain. These particles might grow during the subsequent thermal process, leading to lower ductility or poor bending workability in the final product. Also, the decrease in solute elements for precipitation hardening causes inadequate strengthening in the final aging process. A high cooling rate is therefore desirable, since dissolving the coarse precipitates is difficult.
Other casting methods such as the ingot method can be employed if their cooling rate is fast enough. Durvil casting is preferably utilized because open air casting will trap oxides inside, causing quality problems on the cast piece.
The ingot, billet, or slab after casting is surface ground or the hot-top part is cut off as needed. If crude processing is not required then it may be directly cold- or warm-worked at temperatures ranging from room temperature to 300° C. Hot forging and/or hot working can be combined with above process. There are no particular restrictions on the heating temperature for hot working. The preferred temperature range is 700° C. to 950° C. The final products were obtained by a combination of cold or warm working for a degree of reduction larger than 20%, after solution treatment at temperature region from 700° C. to 950° C., and then aging for 2 to 24 hours at 350° C. to 450° C. The preferred atmosphere during the heat treatment is a non-oxidized or a reducing atmosphere. These types of combined processes may be performed repeatedly.
There are no particular restrictions on the working or processing method. For example, rolling may be used if the final product is a thin sheet shape, and if not a sheet or plate shape, then extrusion or drawing may be employed in the case of wire rod; or forging or pressing may be employed if a bulk shape.
(D) Properties of Copper Alloy Material of the Present Invention
The tensile strength, TS (MPa), elongation, El (%), electrical conductivity, IACS (%), and bending workability B90 in the 90° bending test of the copper alloy material of this invention were measured. The evaluation of their test methods and properties is described below in detail.
<Tensile Strength, TS (MPa)>
A specimen 13B was prepared from Cu material as specified in JIS Z 2201 so that the tensile direction was perpendicular to the rolling direction, and the tensile strength [TS (MPa)] at room temperature (25° C.) was determined according to the method specified in JIS Z 2241.
<Electrical Conductivity, IACS (%)>
A specimen made from Cu material with a width of 10 mm×length 60 mm was prepared so that the longitudinal direction was perpendicular to the rolling direction, and the potential difference between both ends of the specimen was measured by applying electrical current in the longitudinal direction of the specimen, and the electrical resistance then determined by the 4-terminal method. The electric resistance (resistivity) per unit volume was then successively calculated from the specimen volume measured by a micrometer, and the electrical conductivity [IACS (%)] was determined from the ratio to resistivity 1.72 μΩcm of a standard specimen obtained by annealing polycrystalline pure copper.
The copper (Cu) alloy material of the present invention is required to possess a balance of strength and high electrical conductivity that is equal to or superior to that of conventional Cu—Be alloy.
Results for cases satisfying the following formula (2) are indicated by “o”, and results for cases not satisfying (2) are indicated by “x”.
TS≧648.06+985.48×exp(−0.0513×IACS) (2)
Where TS and IACS respectively denote the tensile strength (MPa) and electrical conductivity (%).
<Bend Workability, B90 (=R/t)>
The bending workability of the sheet, was evaluated per B90 in 90° bending test by the balance of tensile strength TS and electrical conductivity IACS. Bend specimens with a width of 10 mm×length 60 mm were prepared in the direction perpendicular to the rolling direction, and a 90° bending test performed while changing the curvature radius (inside diameter) of the bent part. The bent parts of the specimens after the test were observed from the outer diameter side by utilizing an optical microscope. A minimum curvature radius free of cracks was taken as R, and the ratio B (=R/t) of R to thickness t of the specimen was determined. In some cases, the bend tests using the specimens taken in the rolling direction (good way) were performed. All the results using specimens from the good way proved good enough for industrial use.
Bending workability was evaluated as “o”, when B90 for the 90° bend test in the bad way satisfied formulas (3) or (4), for specimens having tensile strength TS respectively less than or greater than 600 MPa. Evaluation results for cases where these formulas were not satisfied were shown by “x”.
B90≦2.0 (3)
B
90≦25.093−54.82×exp[−{(TS+583.61)/1254}2]+1.25×t (4)
Where B90 is the bending workability in 90° bending test, TS is the tensile strength (MPa), and t is the thickness (mm).
In
In the case of material of other shapes in the present invention such as wire rods, the workability was evaluated by the relationship between elongation El (%) and tensile strength TS (MPa), measured by the tensile test using specimens prepared in the longitudinal direction. When the relationship between El and TS satisfied the following formula (5), the results were indicated by “o” while results not satisfying formula (5) were shown by “x”.
El≧24.138−24.6076×exp[−{(TS−1816.36)/2213.52}2] (5)
Wherein, TS and El respectively denote the tensile strength (MPa) and elongation (%).
In
Copper alloys having the chemical compositions shown in Table 1 were melted by a vacuum induction furnace, and cast into a steel-made mold where ingots of 50 mm thick, 100 mm width, and 200 mm height were obtained. Each of the rare earth elements was added singly or in a form of misch metal. In some cases, temperature changes during solidification and cooling were measured by using a thermo-couple attached to the inner wall of the mold. The cooling curve obtained by both thermal analysis and above measured data, shows that the average cooling rate to 600° C. was about 2° C. per second. In the test No. 36, a sand mold was used so that the cooling rate was decreased for the comparison. The average cooling rate to 600° C. was 0.2° C. per second.
In test No. 1 to No. 35, after cutting off the deadhead part, the ingots were heated at 900° C., and forged into 20 mm thick plate. These ingots were then heated at 900° C. and rolled into 5 mm thick plates. After surface grinding to remove scale, they were warm rolled to a 1 mm thickness at temperatures around 250° C. These were solution-treated at 850° C. for 10 minutes and then cold rolled into 0.4 mm thick sheets. After aging at 450° C. for 2 hours, they were 50% cold rolled into 0.2 mm thick sheets, and final aging treatment was conducted then at 400° C. for 8 hours. In some cases, in order to adjust for the cold rolling reduction prior to final aging, heat treating was performed for 2 hours at 450° C. after cold rolled to 0.6 mm or to 0.2 mm, and each then cold roll elongated to 0.3 mm or to 0.1 mm and ageing the performed in the same way at 400° C. for 8 hours to obtain the thin sheet.
In the test No. 36, the sheet was severely cracked during second stage rolling to 0.4 mm in thickness, and further testing was impossible. Microstructure observation shows that coarse precipitates were formed in the rolled plate as well as in the ingot, showing that particles formed during casting were not dissolved by subsequent soaking at high temperatures.
The total number of precipitates and inclusions N (mm−2), the diameter in μm of the precipitates and inclusions X (μm), tensile strength TS (MPa), elongation El (%), electrical conductivity IACS (%), and bending workability B90 in the 90° bend test were measured on specimens taken from the above-described sheets. The tensile strength TS/conductivity IACS (TS/FACS) balance, tensile strength TS/elongation El (TS/El) balance and, bending workability in bad way B90 and tensile strength TS (B90/TS) balance were respectively obtained from this data as shown in Table 1. Wherein, ⊚, ∘, and Δ in the total number column respectively show results satisfying the formula (1″), (1′), and (1).
In tests No. 1 to No. 28 of the present invention, the total number of precipitates and inclusions, N(mm−2) satisfied formula (1), and both the TS/IACS balance and B90/TS balance were good.
In the tests No. 29 to No. 35 of the comparative method, however, either of TS/IACS balance or the B90/TS balance was inferior. As mentioned above, the evaluation of test No. 36 could not be performed. In a 0.2 mm thick state after 50% cold rolling, large quantities of scattered coarse precipitates and inclusions larger than 1 μm were observed in the copper (Cu) matrix, and the formula (1) was not satisfied.
Results of the bending workability B90/tensile strength TS (B90/TS) balance were summarized in
Copper alloys having chemical compositions shown in Table 2 were melted in an induction furnace followed by horizontal continuous casting using a special graphite mold, and slabs in thicknesses of 30 mm×width 100 mm were obtained.
Utilizing these slabs, thin sheets shown by test No. 41 to No. 49 were obtained through three different types of thermo-mechanical processes A, B, and C as shown in Table 3.
The total number of precipitates and inclusions N (mm−2), the diameter in μm of the precipitates and the inclusions X (μm), tensile strength TS (MPa), elongation El (%), electrical conductivity IACS (%), and bending workability in 90° bend test B90 were measured on the specimens taken from the above-described sheets. The tensile strength TS/conductivity IACS (TS/IACS) balance, the tensile strength TS/elongation El (TS/El) balance, and the bending workability B90/tensile strength TS (B90/TS) balance were obtained from this measured data as shown in Table 2. The ∘ in the total number column shows results satisfying the formula (1′).
In tests No. 41 to No. 49 of the present invention, the total number N of precipitates and inclusions in the grain size per unit area satisfied the formula (1), and both the tensile strength TS/conductivity IACS (TS/IACS) balance and the bending workability B90/tensile strength TS (B90/TS) balance were good. These results confirmed that good results were obtained when other types of thermo-mechanical treatments were employed.
Copper alloys having the chemical compositions shown in Table 4 were melted by a vacuum induction furnace, and cast into a steel-made mold, where ingots of 70 mm in diameter and 170 mm in height were obtained. Each of rare earth elements was added singly or in the form of misch metal.
After cutting off the deadhead part, the ingots were heated at 900° C. and forged into 30 mm diameter wire rods. After surface grinding, these wire rods were warm rolled after heating at around 250° C. These wire rods were then solution-treated at 850° C. for 10 minutes and then cold rolled into 15 mm diameter wire rods. These wire rods were then aged at 400° C. for 8 hours.
The total number of precipitates and inclusions, N (mm−2), the diameter in μm of the precipitates and the inclusions X (μm), tensile strength, TS (MPa), elongation, El (%) and electrical conductivity, IACS (%) were measured on the specimens taken from the above-described wire rods as shown in Table 4. The ⊚, ∘ and, Δ in the total number column show the respective results satisfying the formulas (1″), (1′), and (1).
In tests No. 61 to No. 71 of the present invention, the total number of precipitates and inclusions N (mm−2) satisfied the formula (1), and both the tensile strength TS/conductivity IACS (TS/IACS) balance and the tensile strength TS/elongation El (TS/El) balance were good.
In the tests No. 72 to No. 78 of the comparative method, however, either of tensile strength TS/conductivity IACS (TS/IACS) balance or tensile strength TS/elongation El (TS/El) balance was inferior.
Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
The copper alloy material of the present invention is capable of providing high strength, good electrical conductivity, and good workability without containing any environmentally harmful elements.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2007/064813 | Jul 2007 | US |
| Child | 12693696 | US |
