Patent Publication Number: US-2006011275-A1

Title: Copper-titanium alloys excellent in strength, conductivity and bendability, and method for producing same

Description:
FIELD OF THE INVENTION  
      The present invention relates to copper-titanium alloys excellent in strength, electrical conductivity and bendability, and to a method for producing the same.  
     BACKGROUND OF THE INVENTION  
      In accordance with the recent trend toward miniaturization and lightening of electronic devices, miniaturization and lightening (thinner thickness and finer pitch) of electric or electronic components such as connector and the like are ongoing. Since thinner thickness and finer pitch of connector lead to a reduction in cross section area of contact part thereof, a decrease in contact-pressure and electrical conductivity caused by the decrease of cross section area needs to be compensated for. Metal materials used for the contact part are thus required to have higher strength and electrical conductivity. In addition, metal materials used need to have good bendability as they will be subjected to a severe bending work.  
      Recently, an increasing amount of age-hardening type copper alloys has been used as high strength copper alloys. In age-hardening type copper alloys, their strength is enhanced by an aging treatment of supersaturated solid solution obtained by a solution treatment to generate a uniform dispersion of fine precipitates in them.  
      Among the age-hardening type copper alloys, copper alloy containing Ti (hereinafter called “titanium copper alloy”) is widely used for a variety of terminals and connectors of electronic devices since it possesses high strength and excellent bendability. Titanium copper alloy currently available on an industrious scale is based on JIS C1990, which contains 2.9 to 3.5% by mass of Ti. This is because sufficient strength cannot be obtained when less content of Ti is used, as indicated in working examples of JP 07-258803A and JP 2002-356726A, etc.  
      High beryllium copper alloy (JIS C1720) is also known as age-hardening type high strength copper alloy as well as titanium copper alloy. Titanium copper alloy has comparable strength and bendability, and superior stress relaxation properties as compared with the high beryllium copper alloy, so the former is more appropriate than the latter for applications where higher thermal resistance is required such as burn-in-socket, etc. On the contrary, in terms of electrical conductivity, it is the current state of the art that titanium copper alloy, which has 10 to 16% IACS, is inferior to the high beryllium copper alloy, which has 20% IACS. Accordingly, the high beryllium copper alloy is used in applications where higher electrical conductivity is needed. However, the high beryllium copper alloy has such problems that it possesses toxicity and its production process is complicated and costly. Therefore, an expectation for titanium copper alloy is further increasing.  
      As dissolution of Ti in copper matrix causes a decrease in electrical conductivity, the amount of dissolved Ti may be reduced to increase electrical conductivity by precipitating Ti as Cu—Ti intermetallic compound phases. JP 2004-285408A improves the electrical conductivity of titanium copper alloy containing 2.5 to 4.5% by mass of Ti by adjusting the precipitation amount of Cu—Ti intermetallic compound phases. However, according to the inventors&#39; research, the titanium copper alloy disclosed in the specification exhibited significantly deteriorated bendability. As a reason for this deterioration in bendability, it was confirmed that coarse Cu—Ti intermetallic compound phases became starting points of crack. In particular, bendability was significantly deteriorated when there existed Cu—Ti intermetallic compound phases having a diameter of greater than 2 μm. Proper adjustment of grain size and final rolling process may enable titanium copper alloy to achieve both high strength and bendability at the same time as disclosed in JP 2002-356726A, for example. However, no technology has achieved well-balanced improvement in all of the strength, bendability and electrical conductivity of titanium copper alloy.  
     SUMMARY OF THE INVENTION  
      Therefore, it is an object of the present invention to provide a titanium copper alloy excellent in strength, conductivity and bendability.  
      The present inventors have conducted extensive research in order to provide titanium copper alloy having electrical conductivity comparable to the high beryllium copper alloy as well as excellent strength and bendability. As a result, it was found that titanium copper alloy having desired strength, bendability and electrical conductivity can be obtained by adjusting Ti concentration, Cu—Ti intermetallic compound phase size, area ratio and average grain size to optimal ranges.  
      The present inventors have discovered that the bendability deterioration in the titanium copper alloy disclosed in the aforementioned JP 2004-285408 is due to coarse Cu—Ti intermetallic compound phases precipitated in a large amount. According to the present invention, smaller amount of coarse Cu—Ti intermetallic compound phases may be precipitated by reducing Ti concentration. Moreover, titanium copper alloy has been optimized in the structure and the production process so that desired strength and bendability at the reduced Ti concentration can be achieved.  
      (1) The present invention is directed to a titanium copper alloy excellent in strength, electrical conductivity and bendability, consisting essentially of 1.5 to 2.3% by mass of Ti, balance Cu and inevitable impurities;  
      said alloy having a 0.2% yield strength of 750 MPa or greater; an electrical conductivity of 17% IACS or greater; and a relationship represented by the formula:
 
 MBR/t≦ 0.04× YS− 30,
 
 in which, 
 
 YS is a 0.2% yield strength (MPa), and 
 
 MBR/t is a ratio of a minimum bending radius (MBR; mm) for no cracking when said alloy is subjected to W bend test according to JIS H3130 standard along a transverse direction to a rolling direction, to a thickness (t; mm) of test piece. 
 
      (2) The titanium copper alloy may have an electrical conductivity of 20% IACS or greater.  
      (3) The titanium copper alloy may have a 0.2% yield strength of 800 MPa or greater.  
      (4) The titanium copper alloy may have Cu—Ti intermetallic compound phases observed in a cross section transverse to the rolling direction whose diameters are 2.0 μm or less; and an area ratio (S; %) of Cu—Ti intermetallic compound phases observed in the cross section transverse to the rolling direction whose diameters are 0.02 to 2.0 μm may have a relationship with Ti content ([Ti]; % by mass) represented by the formula: 8.1×[Ti]−11.5≦S≦7.5; and the titanium copper alloy may have an average grain size of 2 to 10 μm in the cross section transverse to the rolling direction as measured by JIS H0501 standard intercept method.  
      (5) The titanium copper alloy may be produced from an ingot by a production process comprising sequential steps of a hot rolling, a cold rolling, a solution treatment, a cold rolling, and an aging treatment;  
      a reduction ratio of said cold rolling before said solution treatment being 89% or greater,  
      a heating temperature T (° C.) for said solution treatment being in a range represented by the formula: [6580/{7.35−ln[Ti]}]−333≦T≦[6580/{7.35−ln[Ti]}]−273,  
      an average cooling rate in said solution treatment being 300° C./s or greater,  
      a reduction ratio of said cold rolling before said aging treatment being 10 to 70%,  
      a heating temperature for said aging treatment being 350 to 450° C.,  
      a heating hold time for said aging treatment being 5 to 20 hours, and  
      an average cooling rate from the heating temperature for said aging treatment being 10 to 50° C./h.  
     DETAILED DESCRIPTION OF THE INVENTION  
      (1) Electrical Conductivity  
      When materials are used for a variety of terminals and connectors, an increase in their electrical conductivity leads to a decrease in the amount of heat generated by energization. An electrical conductivity of 17% IACS or greater is needed to achieve heat generation as low as that achieved by the high beryllium copper alloy. An electrical conductivity of 20% IACS or greater is more preferable.  
      (2) 0.2% Yield Strength  
      When a 0.2% yield strength of materials used as connectors becomes less than 750 MPa, it is not possible to obtain contact resistance as low as that of the high beryllium copper alloy even when their electrical conductivity is adjusted to 17% IACS or greater. This is due to a decrease in contact pressure at an electric contact, causing an increase of the contact resistance. Consequently, a 0.2% yield strength of 750 MPa or greater is needed. A 0.2% yield strength of 800 MPa or greater is more preferable.  
      (3) Bendability  
      When materials are used for a variety of terminals and connectors, the balance between 0.2% yield strength and bendability is important. The present inventors have found a certain measure to meet the requirements for connector materials after a quantitative analysis of the relationship between 0.2% yield strength and bendability required for recent electronic components with the use of titanium copper alloys containing 1.5 to 2.3% by mass of Ti and having conductivity of 17% IACS or greater. Specifically, a titanium copper alloy having the following relationship may have well-balanced strength and bendability, meeting the recent requirements in this field. The relationship is represented by the formula: MBR/t≦0.04×YS−30,  
      in which:  
      YS is a 0.2% yield strength (MPa) and  
      MBR/t is a ratio of a minimum bending radius (MBR; mm) for no cracking when said alloy is subjected to W bend test according to JIS H3130 standard along a transverse direction to a rolling direction, to a thickness (t; mm) of test piece.  
      (4) Ti Content  
      When titanium copper alloys undergo an aging treatment, spinodal decomposition occurs to form a modulated structure of titanium concentration in base metal, thereby very high strength can be obtained. It is difficult to obtain a 0.2% yield strength of 750 MPa or greater in case where titanium copper alloys have a titanium content of less than 1.5% by mass. On the other hand, when titanium copper alloys have a titanium content of greater than 2.3% by mass, coarse Cu—Ti intermetallic compound phases having a diameter of greater than 2 μm will precipitate in case where the titanium copper alloys have been produced according to a condition mentioned below under which an electrical conductivity of 17% or greater can be obtained, thus deteriorating bendability of material. The titanium copper alloy of the present invention therefore is defined to have a titanium content of 1.5 to 2.3% by mass, preferably 1.6 to 2.0% by mass.  
      By the way, titanium copper alloys having Ti concentration in said range have never put to practical use. Though such alloys have been reported in patent literatures, none of them has achieved well-balanced improvements in all of the strength, bendability and electrical conductivity. For example, JP 2002-356726 discloses in the working example 1 an alloy containing 1.7% by mass of Ti. This alloy has an electrical conductivity of 20.3% IACS, which is comparable to that of the alloy according to the present invention. However, its 0.2% yield strength is no more than 710 MPa. Moreover JP 2002-356726 discloses in the examples 2 alloys each containing 1.5% and 2.3% by mass of Ti. Again, they failed to achieve well-balanced improvements in both strength and electrical conductivity because they have a 0.2% yield strength of 720 MPa and 1180 MPa, and an electrical conductivity of 26.4% IACS and 10.2% IACS, respectively.  
      (5) Diameter of Cu—Ti Intermetallic Compound Phase  
      The amount of dissolved Ti can be reduced by precipitating Ti as Cu—Ti intermetallic compound phase, thereby increasing electrical conductivity of titanium copper alloys. However, when the diameter of the minimum circle to surround any one piece of Cu—Ti intermetallic phases (i.e., the maximum diameter of the Cu—Ti intermetallic compound phases) observed in a cross section transverse to a rolling direction exceeds 2.0 μm, such phase may become the cause of crack during a bending process carried out on material, resulting in a decrease in bendability. Therefore Cu—Ti intermetallic compound phases are preferably 2 μm or less in diameter.  
      (6) Area Ratio of Cu—Ti Intermetallic Compound Phase  
      It is important to generate a sufficient amount of Ti precipitation and to reduce the amount of dissolved Ti as much as possible so that titanium copper alloys can have higher electrical conductivity. In other words, an increase in the precipitation amount of Cu—Ti intermetallic compound phase leads to an increase in electrical conductivity. Moreover, material may have higher strength by precipitation of finer Cu—Ti intermetallic compound phases.  
      The present inventors have found that titanium copper alloys containing Ti in an amount ranging from 1.5 to 2.3% by mass can achieve an electrical conductivity of 17% IACS or greater when it meets the following relationship represented by the formula:
 
 S≧ 8.1 ×[Ti]− 11.5:
 
 in which: 
 
 the symbol S is an area ratio (%) of the Cu—Ti intermetallic compound phases whose diameters are 0.02 to 2.0 μm observed in a cross section transverse to a rolling direction; and 
 
 [Ti] is a titanium content (% by mass). 
 
 The present inventors have also found that S exceeding 7.5% causes reduction in bendability, which makes it difficult to maintain the balance between 0.2% yield strength and bendability as defined by the present invention even if the precipitated Cu—Ti intermetallic compound phases have diameters of 2.0 μm or less. Therefore, it is preferable that the area ratio S of Cu—Ti intermetallic compound phases has a relationship represented by the formula: 8.1×[Ti]−11.5≦S≦7.5. Moreover it has been found that an electrical conductivity of 20% IACS or greater can be obtained, while maintaining the relationship between 0.2% yield strength and bendability as defined by the present invention if the relationship 8.1×[Ti]−9.5≦S≦7.5 is fulfilled with [Ti]=1.5 to 2.0% by mass. 
 
      (7) Average Grain Size  
      When an average grain size in a cross section transverse to a rolling direction exceeds 10 μm as measured by JIS H0501 standard intercept method, the strength of material cannot be sufficiently improved by the mechanism of fine grain size, making it difficult to achieve a 0.2% yield strength of 750 MPa or greater. When the average grain size is adjusted to less than 2 μm, non-recrystallized structure region may remain. The remaining of non-recrystallized structure region has an adverse effect on bendability of material. Therefore the titanium copper alloy of the present invention preferably has an average grain size of 2 to 10 μm in a cross section transverse to a rolling direction.  
      (8) Method for Production  
      The present inventors have found that titanium copper alloys that meet the characteristics of the present invention can be obtained through a production process comprising sequential steps of melting and casting of a raw material, and a hot rolling, a cold rolling, a solution treatment, a cold rolling and an aging treatment on a resulting ingot, on condition that each of the cold rolling before the solution treatment, the solution treatment, the cold rolling after the solution treatment and the aging treatment is appropriately adjusted. The specific conditions of the abovementioned steps are discussed below.  
      Cold Rolling Before Solution Treatment  
      In recrystallization of material, strain introduced by a cold rolling process can be nucleus for recrystallization. The higher reduction ratio in the cold rolling before the solution treatment can introduce more strain, which promotes formation of an increasing number of recrystallization grains and restriction of grain growth, resulting in finer grain size. An average grain size of 10 μm or less can be obtained by using a reduction ratio of 89% or greater in the cold rolling before the solution treatment.  
      Solution Treatment  
      Solution treatment on titanium copper alloy is generally carried out at a temperature equal to or greater than that where solubility of Ti in Cu corresponds to the content of Ti. However, solution treatment at this temperature range results in grain size of 10 μm or greater. The present inventors have determined by experiment a heating temperature range for solution treatment to steadily obtain grain size of 2 to 10 μm. Specifically, if the solution treatment is carried out at temperatures T (° C.) according to the formula: T&gt;[6580/{7.35−ln[Ti]}]−273, grain size would grow 10 μm or greater, thus making it difficult to obtain a 0.2% yield strength of 750 MPa or greater. On the contrary, if the solution treatment is carried out at temperatures T (° C.) according to the formula: T&lt;[6580/{7.35−ln[Ti]}]−273, grain size would grow less than 2 μm, thus deteriorating bendability of material. If the solution treatment is carried out at temperatures T (° C.) according to the formula: [6580/{7.35−ln[Ti]}]−333≦T≦[6580/{7.35−ln[Ti]}]−273, a grain size of from 2 to 10 μm can be obtained.  
      Moreover, if an average cooling rate from the heating temperature to 25° C. is less than 300° C./s, Cu—Ti intermetallic compound phases with diameters of greater than 2.0 μm would precipitate on grain boundaries during the cooling of material. This is apt to produce cracks in grain boundaries when a bending stress is applied to material. Therefore, an average cooling rate in the solution treatment is preferably 300° C./s or greater. The cooling method used here is not limited to any particular methods but water-cooling method is generally employed.  
      Reduction Ratio in Cold Rolling After Solution Treatment  
      When the reduction ratio in the cold rolling after the solution treatment becomes less than 10%, an increase of strength by work hardening cannot be expected, making it difficult to obtain a 0.2% yield strength of 750 MPa or greater. Moreover, with such a low reduction ratio, the precipitation rate of Ti—Cu intermetallic compound phase decreases in the following aging treatment step since strain introduced by the cold rolling process also decreases, thus making it difficult to obtain an electrical conductivity of 17% IACS or greater. On the contrary, the reduction ratio over 70% may decrease ductility, causing a significant deterioration in bendability. Consequently, it becomes difficult to meet the relationship between 0.2% yield strength and bendability defined in the present invention. Therefore, the reduction ratio in the cold rolling after the solution treatment is preferably 10 to 70%. In order to obtain better relationship between 0.2% yield strength and bendability, the reduction ratio of 40 to 65% is more preferable.  
      Aging Treatment  
      In order to generate precipitation of Cu—Ti intermetallic compound phase as defined in the present invention in the aging treatment, the aging condition can be adjusted as follows, for example.  
      (1) Heating Temperature  
      When the heating temperature is less than 350° C., a 0.2% yield strength of 750 MPa or greater and an electrical conductivity of 17% IACS or greater cannot be obtained due to insufficient precipitation of Cu—Ti intermetallic compound phase. When the heating temperature is over 450° C., strength and bendability decreases due to coarsening of Cu—Ti intermetallic compound phase. Therefore, the heating temperature is preferably 350 to 450° C. The term “heating temperature” herein means the temperature inside the furnace to heat material.  
      (2) Hold Time at Heating Temperature  
      When the hold time at the heating temperature is less than 5 hours, it is difficult to obtain an electrical conductivity of 17% IACS or greater due to insufficient precipitation of Cu—Ti intermetallic compound phase. When the hold time is over 20 hours, strength and bendability decreases due to coarsening of Cu—Ti intermetallic compound phase. Therefore, the hold time at the heating temperature is preferably 5 to 20 hours. The term “hold time” herein means time between when the material temperature reaches the furnace temperature and when cooling is started.  
      (3) Average Cooling Rate  
      In the ageing treatment, precipitation of Cu—Ti intermetallic compound phase does not occur in a sufficient amount to obtain an electrical conductivity of 17% IACS or greater when an average cooling rate from the heating temperature to 200° C. is faster than 50° C./h. On the contrary, when the average cooling rate is slower than 10° C./h, precipitation of Cu—Ti intermetallic compound phase significantly increases, which causes the area ratio of Cu—Ti intermetallic compound phases having diameters of 0.02 to 2.0 μm to exceed 7.5%, resulting in deterioration of bendability. Therefore, an average cooling rate from the heating temperature to 200° C. is preferably 10 to 50° C./h.  
      The present invention can provide titanium copper alloys that are excellent in strength, bendability and electrical conductivity so that they can adapt to the recent trend toward miniaturization and thinness in electronic devices 
    
    
     EXAMPLES  
      Melting and casting was carried out in a high-frequency vacuum melting furnace using electrolytic cathode copper as raw material to form various compositions of ingots (60 mm width×30 mm thickness) as listed in Table 1, followed by a hot rolling at 900° C. to obtain a thickness of 8 mm. After that, a cold rolling before a solution treatment, the solution treatment, a cold rolling after the solution treatment, and an aging treatment were conducted under the conditions listed in Table 1 to modify average grain size, Cu—Ti intermetallic compound phase size, and area ratio. In the solution treatment, cooling was initiated after holding the test piece temperature at the designated temperature given in Table 1 for one minute. Cooling process used here was air-cooling, Ar gas spray, water spray, or immersion in water, and the amount of sprayed Ar gas and water was varied to obtain different cooling rates. A thermocouple was welded to the test piece so that cooling rate to 25° C. (ambient temperature) could be measured. In the aging treatment, cooling rate was varied by controlling furnace temperature. Average cooling rate for test piece was measured from the heating temperature to 200° C.  
      0.2% yield strength, electrical conductivity, bendability (MBR/t), average grain size in a cross section transverse to a rolling direction, and size and area ratio of Cu—Ti intermetallic compound phase were evaluated for each alloy obtained through the above mentioned method.  
      0.2% yield strength was measured according to JIS Z2241 standard using a tensile test machine. Electrical conductivity was measured by four-terminal method according to JIS H0505. Bendability was evaluated as follows. A strip test piece 10 mm in width and 50 mm in length was cut out with the longitudinal direction of the specimen being a direction transverse to a rolling direction (Bad way). W bend test (JIS H3130) was conducted on the specimen at various bend radiuses to evaluate a ratio (MBR/t) of minimum bend radius for no cracking (mm) to thickness (mm) of test piece by comparing convex surface appearance of bent portion with the evaluation standard according to JBMA T307: 1999 technical standard by Japan Copper and Brass Association.  
      In the measurement of average grain size (μm), it was determined according to the intercept method (JIS H0501 standard). The cross section transverse to a rolling direction was etched using water (100 mL)/FeCl 3  (5 g)/HCl (10 mL), and observed the crystal grains by a scanning electron microscope.  
      Observation of Cu—Ti intermetallic compound phases precipitated in alloy was made by the use of FE-SEM (XL30SFEG, FEI Company Japan Ltd.). Material was subjected to abrasion on its cross section transverse to a rolling direction using #150 waterproof abrasive paper, followed by mirror-polish with a finish-polishing agent in which colloidal silica having a diameter of 40 nm was suspended. The resulting specimen was then subjected to carbon evaporating. Backscattered electron images having a field of view of 100 μm 2  at a magnification of 1000× were observed in different 5 fields of view for each alloy. The diameter of the minimum circle that can surround each Cu—Ti intermetallic compound phase present within the observation field of view and area ratio were then determined by the use of an image analysis system. In evaluation of Cu—Ti intermetallic compound phase size, alloy was evaluated as “Yes” if it contains Cu—Ti intermetallic compound phase having a diameter of greater than 2.0 μm, and evaluated as “No” if it contains no Cu—Ti intermetallic compound phase having a diameter of greater than 2.0 μm. In evaluation of area ratio, area ratio was defined as the total area of Cu—Ti intermetallic compound phases having a diameter of 0.02 to 2.0 μm divided by the total area of observation field of view.  
      Table 2 shows the evaluation result for each alloy. Any alloy of Examples 1 to 10 fulfilled Ti content, grain size, Cu—Ti intermetallic compound phase size and area ratio defined by the present invention, and exhibited an electrical conductivity of 17% IACS or greater and a 0.2% yield strength of 750 MPa or greater, the relationship between 0.2% yield strength and MBR/t also within the range defined by the present invention. In particular, alloys of Examples 2, 4, 7 and 10, which had a Ti content of 1.5 to 2.0% by mass and area ratio S of intermetallic compound phases satisfying the formula 8.1×[Ti]−11.5≦S≦7.5, exceed an electrical conductivity of 20% IACS. In addition, alloys of Examples 2 and 5, which had a Ti content of 1.6 to 2.0% by mass with the reduction ratio of the cold rolling after the solution treatment of 40 to 65%, exhibited better bendability (MBR/t) compared with that of other Examples having similar 0.2% yield strength, while exhibiting higher 0.2 yield strength compared with that of other Examples having similar bendability.  
      On the contrary, the alloy of Comparative Example 11 cannot achieve a 0.2% yield strength of 750 MPa or greater due to the too low Ti concentration.  
      In Comparative Example 12, coarse Cu—Ti intermetallic compound phases with a size of 2.0 μm or greater are precipitated due to the too high Ti concentration. The alloy cannot achieve bendability defined by the present invention since it had the area ratio of Cu—Ti intermetallic compound phases beyond the range defined by the present invention.  
      In Comparative Example 13, the average grain size after the solution treatment exceeds 10 μm with a 0.2% yield strength less than 750 MPa due to the low cold rolling reduction ratio before the solution treatment.  
      The alloy of Comparative Example 14 cannot achieve bendability defined by the present invention since the solution treatment was carried out at a lower temperature than the range defined by the present invention and thus non-recrystallized structure region remains, and moreover, both the Cu—Ti intermetallic compound phase size and the area ratio exceed the range defined by the present invention.  
      The alloy of Comparative Example 15 had the average grain size of greater than 10 μm, and cannot achieve a 0.2% yield strength of 750 MPa or greater when the aging treatment was carried out under the condition which gives an electrical conductivity of 17% IACS or greater. This is due to the solution treatment temperature, which was beyond the range defined by the present invention.  
      The alloy of Comparative Example 16 cannot achieve bendability defined by the present invention since the average cooling rate is so slow that coarse Cu—Ti intermetallic compound phases having a size of 2.0 μm or greater are precipitated.  
      In Comparative Example 17, a 0.2% yield strength of 750 MPa or greater cannot be achieved due to the too low cold rolling reduction ratio after the solution treatment. An electrical conductivity of 17% IACS or greater cannot be also achieved since the precipitation rate in the aging treatment was so slow that the area ratio of Cu—Ti intermetallic compound phases was below the range defined by the present invention.  
      The alloy of Comparative Example 18 cannot achieve bendability defined by the present invention due to the too high cold rolling reduction ratio after the solution treatment.  
      In Comparative Example 19, a 0.2% yield strength of 750 MPa or greater cannot achieved due to the insufficient aging caused by the too low heating temperature in the aging treatment. An electrical conductivity of 17% IACS or greater cannot be also achieved since the area ratio of Cu—Ti intermetallic compound phases was below the range defined by the present invention.  
      In Comparative Example 20, the relationship between 0.2% yield strength and bendability defined by the present invention is not fulfilled since the heating temperature in the aging treatment is so high that coarsening of Cu—Ti intermetallic compound phases is occurred due to overaging.  
      The alloy of Comparative Example 21 cannot achieve an electrical conductivity of 17% IACS or greater since the heating hold time in the aging treatment is so short that the area ratio of Cu—Ti intermetallic compound phases is below the range defined by the present invention.  
      In Comparative Example 22, the relationship between 0.2% yield strength and bendability defined by the present invention is not fulfilled since the heating hold time in the aging treatment is so long that coarsening of Cu—Ti intermetallic compound phases is occurred due to overaging.  
      The alloy of Comparative Example 23 cannot achieve an electrical conductivity of 17% IACS or greater since the average cooling rate in the aging treatment is so fast that the area ratio of Cu—Ti intermetallic compound phases is below the range defined by the present invention.  
      The alloy of Comparative Example 24 cannot achieve bendability defined by the present invention since the average cooling rate in the aging treatment is so slow that the area ratio of Cu—Ti intermetallic compound phases is beyond the range defined by the present invention.  
               TABLE 1                          Production conditions                             Solution treatment                                             Reduction   Possible heating       Reduction   Aging treatment                                                                     ratio before   temperature range   Actual       ratio after       Hold time at                   Ti content   solution   according to the   Heating   Average   solution   Heating   heating   Average               (% by   treatment   present invention   temperature   cooling rate   treatment   temperature   temperature   cooling rate           No.   mass)   (%)   (° C.) * 1   (° C.)   (° C./s)   (%)   (° C.)   (h)   (° C./h)                                                                     Exmples   1   2.21   90.5   671˜731   705   350   35   430   8   37           2   1.87   94.3   646˜706   689   416   40   390   10   20           3   1.50   98.1   615˜675   658   650   18   350   20   45           4   2.00   96.5   658˜718   704   704   33   450   8   33           5   1.77   89.2   638˜698   685   541   43   400   5   18           6   2.08   94.2   661˜721   700   912   67   380   12   40           7   1.52   97.3   616˜676   670   634   24   410   10   27           8   1.66   95.8   629˜689   678   419   13   370   15   36           9   2.30   91.9   677˜737   710   617   30   420   7   48           10   1.58   96.6   622˜682   650   568   52   400   5   16       Comparative   11   1.25   95.1   590˜650   629   498   44   390   12   41       examples   12   2.62   97.4   697˜757   738   749   29   420   5   34           13   2.03   86.0   658˜718   698   579   27   400   10   17           14   2.21   93.7   671˜731   650   666   48   370   20   26           15   1.72   98.0   634˜694   750   908   37   440   6   31           16   1.54   96.6   618˜678   659   150   32   380   12   22           17   1.69   94.8   631˜691   662   764   5   440   8   13           18   1.98   92.2   654˜714   707   497   80   430   10   41           19   2.17   95.9   668˜728   710   815   15   335   20   12           20   1.83   92.7   642˜702   690   394   62   460   5   48           21   1.51   97.1   615˜675   666   517   40   400   3   10           22   1.96   91.6   652˜712   692   618   27   410   35   47           23   2.28   94.6   675˜735   705   807   33   450   10   100           24   1.91   96.5   649˜709   677   555   30   380   8   5                 * 1: [6580/[7.35 − In[Ti]}] − 333 ≦ T ≦ [6580/[7.35 − In[Ti]}] − 273             
 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                   
               
               
                 Properties of produced alloys 
               
            
           
           
               
               
            
               
                   
                 Area ratio of Cu—Ti intermetallic 
               
            
           
           
               
               
               
            
               
                   
                 Existence of 
                 compound phase; S (%) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Average 
                 Cu—Ti intermetallic 
                 Possible range 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 0.2% Yield 
                 Bendability * 2 
                 Electrical 
                 Grain 
                 compound phase 
                 according to 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Strength 
                 0.04 × 
                 MBR/t of 
                 conductivity 
                 size 
                 exceeding 
                 the present 
                 Measured 
               
               
                   
                 No. 
                 (MPa) 
                 YS − 30 
                 test piece 
                 (% IACS) 
                 (μm) 
                 2.0 μm diameter 
                 invention * 3 
                 value 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Examples 
                 1 
                 852 
                 4.1 
                 3.0 
                 19.6 
                 6.2 
                 No 
                 6.4˜7.5 
                 6.8 
               
               
                   
                 2 
                 855 
                 4.2 
                 1.8 
                 20.7 
                 4.3 
                 No 
                 3.6˜7.5 
                 6.5 
               
               
                   
                 3 
                 767 
                 0.7 
                 0 
                 17.2 
                 2.1 
                 No 
                 0.6˜7.5 
                 1.3 
               
               
                   
                 4 
                 811 
                 2.4 
                 1.6 
                 22.8 
                 7.2 
                 No 
                 4.7˜7.5 
                 7.1 
               
               
                   
                 5 
                 845 
                 3.8 
                 1.7 
                 18.8 
                 5.1 
                 No 
                 2.8˜7.5 
                 3.9 
               
               
                   
                 6 
                 890 
                 5.6 
                 4.8 
                 18.7 
                 9.8 
                 No 
                 5.3˜7.5 
                 6.2 
               
               
                   
                 7 
                 773 
                 0.9 
                 0 
                 20.4 
                 3.9 
                 No 
                 0.8˜7.5 
                 4.9 
               
               
                   
                 8 
                 792 
                 1.7 
                 0.6 
                 17.9 
                 2.5 
                 No 
                 1.9˜7.5 
                 2.8 
               
               
                   
                 9 
                 875 
                 5.0 
                 3.9 
                 18.4 
                 8.4 
                 No 
                 7.1˜7.5 
                 7.3 
               
               
                   
                 10 
                 814 
                 2.6 
                 1.4 
                 20.2 
                 3.3 
                 No 
                 1.3˜7.5 
                 5.8 
               
               
                 Comparative 
                 11 
                 715 
                 0 
                 0 
                 20.5 
                 4.8 
                 No 
                   0˜7.5 
                 0.4 
               
               
                 examples 
                 12 
                 830 
                 3.2 
                 5.9 
                 18.1 
                 8.2 
                 Yes 
                 7.5 or greater 
                 9.4 
               
               
                   
                 13 
                 735 
                 0 
                 0 
                 19.4 
                 15.7 
                 No 
                 4.9˜7.5 
                 5.2 
               
               
                   
                 14 
                 853 
                 4.1 
                 8.4 
                 19.6 
                 Not recrystallized 
                 Yes 
                 s 
                 10.1 
               
               
                   
                 15 
                 729 
                 0 
                 0.5 
                 18.2 
                 24.4 
                 No 
                 2.4˜7.5 
                 2.6 
               
               
                   
                 16 
                 771 
                 0.8 
                 2.4 
                 18.6 
                 2.9 
                 Yes 
                 1.0˜7.5 
                 2.5 
               
               
                   
                 17 
                 692 
                 0 
                 0 
                 15.4 
                 5.9 
                 No 
                 2.2˜7.5 
                 1.1 
               
               
                   
                 18 
                 897 
                 5.9 
                 8.7 
                 21.4 
                 7.1 
                 No 
                 4.5˜7.5 
                 7.8 
               
               
                   
                 19 
                 730 
                 0 
                 0 
                 14.3 
                 9.7 
                 No 
                 6.1˜7.5 
                 3.4 
               
               
                   
                 20 
                 721 
                 0 
                 1.2 
                 22.6 
                 4.2 
                 Yes 
                 3.3˜7.5 
                 8.9 
               
               
                   
                 21 
                 774 
                 1.0 
                 0.6 
                 15.9 
                 2.3 
                 No 
                 0.7˜7.5 
                 0.3 
               
               
                   
                 22 
                 733 
                 0 
                 1.4 
                 21.1 
                 3.7 
                 Yes 
                 4.4˜7.5 
                 8.4 
               
               
                   
                 23 
                 825 
                 3.0 
                 2.1 
                 16.2 
                 5.2 
                 No 
                 7.0˜7.5 
                 6.4 
               
               
                   
                 24 
                 835 
                 3.4 
                 4.1 
                 21.6 
                 2.8 
                 No 
                 4.0˜7.5 
                 7.9 
               
               
                   
               
               
                   * 2: MBR/t ≦ 0.04 × YS − 30    
               
               
                   * 3: 8.1 × [Ti] − 11.5 ≦ S ≦ 7.5    
               
            
           
         
       
     
      Equivalents  
      Although the particular embodiments of the present invention are described expressly by the specification and appended claims of the present application, those embodiments are illustrative and not restrictive. As one of ordinary skill in the art can readily appreciate many variations from the disclosure of the present invention, such variations are also included in the present invention. The scope of the present invention should be defined by the appended claims and inclusive of its equivalents.