Method for producing copper-titanium based copper alloy material for automobile and electronic parts and copper alloy material produced therefrom
11162163 · 2021-11-02
Assignee
Inventors
- Cheol Min Park (Ulsan, KR)
- Jun Hyung Kim (Ulsan, KR)
- Hyo Moon Nam (Ulsan, KR)
- Tae Yang Kwon (Ulsan, KR)
Cpc classification
B21B37/74
PERFORMING OPERATIONS; TRANSPORTING
B21B3/00
PERFORMING OPERATIONS; TRANSPORTING
B21B1/46
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
The present invention relates to a production method of a copper-titanium (Cu—Ti)-based copper alloy material and a copper alloy material produced therefrom. Thus, the copper alloy material has target yield strength, electrical conductivity, and bending workability and thus is applied to automobiles and electric/electronic parts requiring high performance.
Claims
1. A method for producing a copper alloy material for automobile and electric and electronic parts, wherein the copper alloy material contains 1.5 to 4.3 wt % of titanium (Ti), 0.05 to 1.0 wt % of nickel (Ni), 0.8 wt % or smaller of incidental impurities, and the balance being copper (Cu), wherein the incidental impurities are at least one element selected from a group consisting of Sn, Co, Fe, Mn, Cr, Zn, Si, Zr, V and P, and wherein a weight ratio of titanium/nickel (Ti/Ni) is in a range of 10<Ti/Ni<18; wherein the method comprises: (a) dissolving and casting 1.5 to 4.3 wt % of titanium (Ti), 0.05 to 1.0 wt % of nickel (Ni), 0.8 wt % or smaller of incidental impurities, and the balance of copper (Cu) to obtain a slab; (b) hot working the obtained slab at 750 to 1000° C. for 1 to 5 hours; (c) first cold-working at a cold rolling reduction ratio or a cold working ratio of 50% or greater; (d) intermediate heat treating at 550 to 740° C. for 5 to 10000 seconds; (e) second cold-working at a cold rolling reduction ratio or a cold working ratio of 50% or greater; (f) solution treating at 750 to 1000° C. for 1 to 300 seconds; (g) first aging at 550 to 700° C. for 60 to 1800 seconds, continuously lowering a temperature, and then second aging at 350 to 500° C. for 1 to 20 hours; (h) final cold-working at a cold rolling reduction ratio or a cold working ratio of 5 to 70%; and stress removal treating at 300 to 700° C. for 2 to 3000 seconds.
2. The method of claim 1, wherein each of the steps (e) and (f) is optionally repeated two to five times.
3. The method of claim 1, wherein the method further comprises correcting a shape of a plate after or before the (g) step.
4. The method of claim 1, wherein the method further comprises plating tin (Sn), silver (Ag), or nickel (Ni) on a plate after the (i) step.
5. The method of claim 1, wherein the method further comprises forming the slab into a plate, rod, or tube form.
6. The method of claim 1, wherein fine precipitates at a size in a range of 300 nm or smaller are uniformly distributed in a copper matrix of the copper alloy material, wherein each of the fine precipitates includes at least one selected from a group consisting of (Cu,Ni)Ti, (Cu,Ni.sub.3)Ti.sub.2, (Cu,Ni).sub.3Ti, and (Cu,Ni).sub.4Ti.
7. The method of claim 1, wherein an areal density of the fine precipitates is greater than or equal to 2.5×10.sup.8/cm.sup.2.
8. The method of claim 6, wherein the copper alloy material has a yield strength of at least 900 MPa, an electrical conductivity of at least 15% IACS, and a bending workability R/t≤1.5 (180°) in both a rolling direction and a direction perpendicular to the rolling direction at a 180° bending test, wherein R indicates a bending radius of curvature and t indicates a thickness of the material.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1)
(2)
(3)
(4)
SUMMARY
(5) The present disclosure provides a method for producing copper alloy material with improved strength properties including yield strength, improved electrical conductivity and improved bending workability, and provides copper alloy material produced therefrom.
(6) Followings describe a method for producing the copper alloy material according to the present disclosure.
(7) Method for Producing Copper Alloy Material According to the Present Disclosure
(8) The conventional copper-titanium (Cu—Ti)-based copper alloy material is generally produced by dissolving/casting, hot rolling, (repetition of heat treating and cold rolling), solution treating, cold rolling and aging in this order.
(9) On the other hand, the method for producing he copper alloy material according to the present disclosure may produce a copper alloy material for automobile and electric and electronic parts, wherein the copper alloy material contains: 1.5 to 4.3 wt % of titanium (Ti); 0.05 to 1.0 wt % of nickel (Ni); 0.8 wt % or smaller of incidental impurities, wherein the incidental impurities are at least one element selected from a group consisting of Sn, Co, Fe, Mn, Cr, Zn, Si, Zr, V and P; and the balance being copper (Cu), wherein a weight ratio of titanium/nickel (Ti/Ni) is in a range of 10<Ti/Ni<18. In accordance with the present disclosure, the copper alloy materials with improved strength properties including yield strength, improved electrical conductivity and improved bending workability may be produced as follows.
(10) The method for producing the copper alloy material according to the present disclosure may include (a) dissolving and casting 1.5 to 4.3 wt % of titanium (Ti), 0.05 to 1.0 wt % of nickel (Ni), 0.8 wt % or smaller of incidental impurities, and the balance of copper (Cu) to obtain a slab; (b) hot-working the obtained slab at 750 to 1000° C. for 1 to 5 hours; (c) first cold-working at a cold rolling reduction ratio or a cold working ratio of 50% or greater; (d) intermediate heat treating at 550 to 740° C. for 5 to 10000 seconds; (e) second cold-working at a cold rolling reduction ratio or a cold working ratio of 50% or greater; (f) solution treating at 750 to 1000° C. for 1 to 300 seconds; (g) first aging at 550 to 700° C. for 60 to 1800 seconds, continuously lowering a temperature, and then second aging at 350 to 500° C. for 1 to 20 hours; h) final cold-working at a cold rolling reduction ratio or a cold working ratio of 5 to 70% and (i) stress removal treating 300 to 700° C. for 2 to 3000 seconds.
(11) Specific production conditions for the copper alloy material according to the present disclosure are as follows.
(12) (a) Dissolving and Casting
(13) A composition of the copper alloy material according to the present disclosure may be controlled to contain 1.5 to 4.3 wt % of titanium (Ti), 0.05 to 1.0 wt % of nickel (Ni), 0.8 wt % or smaller of incidental impurities, and the balance of copper (Cu). Thus, the method includes dissolving and casting titanium (Ti), nickel (Ni), and the balance of copper (Cu) to obtain a slab. In order to prevent the oxidation of titanium (Ti), dissolution is carried out using a vacuum dissolving furnace and the casting is performed in an inert gas atmosphere to obtain the slab. In this connection, the weight ratio of titanium/nickel (Ti/Ni) is in the range of 10<Ti/Ni<18. The above-mentioned inevitable impurities may be included in the above process, but the total amount of the incidental impurities should be controlled so as not to exceed 0.8 weight %.
(14) (b) Hot-Working
(15) The hot-working may be carried out at a temperature of 750 to 1000° C. for 1 to 5 hours, preferably 850 to 950° C. for 2 to 4 hours. When the hot-working is carried out at 750° C. or lower for 1 hour or smaller, the casted structure remains, and thus the probability of occurrence of defects such as cracks during the hot-working is high and the strength and bending workability in the finished product production are inferior. Further, when the temperature is higher than 1000° C. or the working timing is longer than 5 hours, the crystal grains become coarser and the bending workability in the production is lowered due to the final product thickness.
(16) (c) First Cold-Working
(17) The first cold-working after the hot-working is carried out at a room temperature. A first cold-rolling reduction ratio or cold-working ratio is greater than or equal to 50%. When the first cold-working ratio is lower than 50%, sufficient precipitation driving force does not occur in the copper (Cu) matrix, so recrystallization occurs late in a solution treating proceeding continuously in a short time, which is disadvantageous for the solution treating.
(18) (d) Intermediate Heat Treating
(19) The intermediate heat treating is carried out at 550 to 740° C. for 5 to 10000 seconds. In the intermediate heat treating process, copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates having a size of 0.3 to 3 μm may be partially formed. Thereafter, when at a second cold-rolling reduction ratio or cold-working ratio of 50% or greater, a second cold-working is carried out, and, then, a solution treating is carried out, the copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates as produced during the intermediate heat treating again become a solid solution state. Then, in the solution treating, aging and final cold-working, more copper, nickel-titanium ((Cu, Ni)—Ti)) fine precipitates may be produced to achieve high strength and bending workability simultaneously.
(20) (e) Second Cold-Working
(21) The second heat-treating may be followed by the second cold-working. In the second cold-working, the second cold-rolling reduction ratio or cold-working ratio is greater than or equal to 50%. The higher the cold-rolling reduction ratio or cold-working ratio is before the solution treating, more finely and uniformly, the copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates may be distributed in the solution treating. Thus, it is advantageous to carry out the second cold-working at a cold-rolling reduction ratio or cold-working ratio of 50% or greater.
(22) (f) Solution Treating
(23) The solution treating is an important process to obtain the high strength and excellent bending workability. The solution treating may be carried out at 750 to 1000° C. for 1 to 300 seconds, preferably at 800 to 900° C. for 10 to 60 seconds. When the solution treating temperature is lower than 750° C. or the treating duration is smaller than 1 second, the solution treating does not form a sufficient supersaturated state. Thus, after the aging treatment, the copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates may not be sufficiently produced. Thus, the tensile strength and yield strength may be lowered. When the solution treating is carried out at a temperature over 1000° C. or for a time duration over 300 seconds, the grain size grows to 50 μm or larger and thus the bending workability decreases. In particular, the bending workability in the rolling direction drops sharply.
(24) (g) Double Aging Treatment
(25) Aging treatment is an important step to improve the properties such as strength, electrical conductivity and bending workability via formation of fine precipitates. In the conventional aging-curing type copper alloy material production method, it is common to execute a single aging treatment. Some of the above-mentioned prior patent documents have introduced a pre-aging process. Specifically, in Korean Patent Application Publication No. 10-2015-0055055, the pre-aging process is performed at a low temperature of 150 to 250° C. for a long period of time of 10 hours or larger. Then, an aging is executed to uniformly precipitate the second phase particles. However, there occurs a disadvantage due to the long duration of the pre-aging in that the production process cost increases and the precipitate size increases, so that the bending workability is poor.
(26) On the other hand, in the method for producing a copper alloy material according to the present disclosure, nickel (Ni) is added to the copper-titanium (Cu—Ti) based on the Ti/Ni ratio to produce precipitates of copper, nickel-titanium ((Cu, Ni)—Ti)). Then, introducing continuous double aging treatment after the solution treatment may allow distribution of finer precipitates to be obtained than that in the conventional one-stage aging treatment production process. That is, after the first aging at 550 to 700° C. for 60 to 1800 seconds, the temperature is continuously lowered and the second aging is performed at 350 to 500° C. for 1 to 20 hours. Thus, the precipitates produced in the first aging act as heterogeneous nucleation sites for precipitation in the second aging. Thus, finer precipitates may be uniformly distributed in the copper (Cu) matrix in the double aging treatments than in the single aging treatment. The first aging of the double aging treatments according to the present disclosure is carried out at 550 to 700° C. for 60 to 1800 seconds, and, subsequently, the temperature is lowered continuously and the second aging is performed at 350 to 500° C. for 1 to 20 hours.
(27) It is important that the first aging is performed at 550 to 700° C. for 60 to 1800 seconds, that is, at a higher temperature in a shorter time than in the second aging. This first aging is an important process for securing the strength by forming some of Cu.sub.3Ti precipitates which is poor in coherency among the precipitates of copper, nickel-titanium ((Cu, Ni)—Ti) which are brought into the solid solution state after the solution treating. Then, the temperature is continuously lowered and the second aging is performed at 350 to 500° C. for 1 to 20 hours. Due to this second aging, in the final cold-working after the aging, the generation and growth of copper, nickel-titanium ((Cu, Ni)—Ti))-based fine precipitates in the grain boundaries and the copper (Cu) matrix occurs, and Cu.sub.3Ti precipitates with poor coherency are significantly changed to Cu.sub.4Ti precipitates with good coherency, and fine precipitates are uniformly distributed in the copper (Cu) matrix to improve strength and improve bending workability. When the temperature is lower than 350° C. and the aging time is shorter than 1 hour in the second aging, copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates may not be sufficiently created and grown in the copper (Cu) matrix due to insufficient calorific value. Thus, the yield strength and bending workability may be deteriorated. When the temperature rises above 500° C. and the aging timing is over 20 hours in the second aging, an overaged region occurs, such that the bending workability has a maximum value, but the yield strength decreases.
(28) (h) Final Cold-Working
(29) A final cold-working is executed after the double aging treatments. The cold-rolling reduction ratio or cold-working ratio at the final cold-working is in a range of 5 to 70%. When the cold-rolling reduction ratio or the cold-working ratio is smaller than 5%, the tensile strength is significantly lowered. When the cold-rolling reduction ratio or the cold-working ratio at the final cold-working exceeds 70%, the bending workability is greatly reduced.
(30) (i) Stress Removal Treating
(31) The stress removal treating is carried out at 300 to 700° C. for 2 to 3000 seconds, preferably at 500 to 600° C. for 10 to 300 seconds. The stress removal treating step acts to remove the stress generated by the plastic deformation of the obtained product by applying heat thereto. Especially, this treating plays an important role in restoring an elastic strength after plate-shape correction. When the stress removal treating is carried out at a temperature lower than 300° C. or shorter than 2 seconds, this cannot sufficiently compensate for the elastic strength loss due to the plate-shape correction. When the temperature exceeds 700° C. or the duration exceeds 3000 seconds in this stress removal treating, softening occurs beyond the maximum recovery period of the elastic strength. Thus, the mechanical properties such as tensile strength and elastic strength may be lowered.
(32) Among the above production method steps, each of (e) the second cold-working step and (f) the solution treating step may be repeatedly performed twice to five times as necessary. That is, the times of the repetition of each of (e) the second cold-working step and (f) the solution treating step may be based on a target thickness of the final product due to a thickness reduction of the copper alloy material due to miniaturization and high integration of automobile and electric and electronic parts.
(33) Further, the plate-shape correction may be performed according to a target shape of the material before and after the aging. Those skilled in the art may appropriately perform the plate-shape correction step as needed.
(34) Further, tin (Sn), silver (Ag), or nickel (Ni) plating may be performed on the plate after the stress removal step if necessary. Those skilled in the art may appropriately carry out the plating step as necessary.
(35) In one example, the method may further include a step of forming the slab into a target form of a plate, rod, or tube, depending on the application of the copper alloy material. Specifically, the slab may be formed into a plate of a thickness of 0.03 to 0.8 mm. Alternatively, the slab may be formed into a rod or tube of 0.5 to 200Φ (=mm) of an outer diameter.
(36) The present copper alloy material may be obtained using the method for producing the copper alloy material according to the present disclosure as described above.
(37) The present copper alloy material as obtained using the method for producing the copper alloy material according to the present disclosure as described above may contain 1.5 to 4.3 wt % of titanium (Ti); 0.05 to 1.0 wt % of nickel (Ni); 0.8 wt % or smaller of incidental impurities, and the balance being copper (Cu), wherein the incidental impurities are at least one element selected from a group consisting of Sn, Co, Fe, Mn, Cr, Zn, Si, Zr, V and P wherein a weight ratio of titanium/nickel (Ti/Ni) is in a range of 10<Ti/Ni<18, wherein fine precipitates at a size in a range of 300 nm or smaller are uniformly distributed in a copper matrix of the copper alloy material, wherein each of the fine precipitates includes at least one selected from a group consisting of (Cu,Ni)Ti, (Cu,Ni.sub.3)Ti.sub.2, (Cu,Ni).sub.3Ti, and (Cu,Ni).sub.4Ti, wherein an areal density of the fine precipitates is greater than or equal to 2.5×10.sup.8/cm.sup.2. The copper alloy material has a yield strength of at least 900 MPa, an electrical conductivity of at least 15% IACS, and a bending workability R/t≤1.5 in both a rolling direction and a direction perpendicular to the rolling direction at a 180° bending test, wherein R indicates a bending radius of curvature and t indicates a thickness of the material.
(38) Followings describe the constituent elements of the copper alloy material according to the present disclosure and reasons for their content limitations.
(39) (1) Titanium (Ti)
(40) Titanium (Ti) is an element contributing to the strength improvement via forming of precipitates with nickel (Ni). The content of titanium (Ti) in the copper alloy material according to the present disclosure is in the range of 1.5 to 4.3 wt %. When the titanium (Ti) content is lower than 1.5 wt %, a sufficient strength is not secured in the aging. A resulting alloy material is not suitable to be applied to automobile, electric and electronic connectors, semiconductors and lead frames. When the titanium (Ti) content exceeds 4.3 wt %, this causes side cracks in the hot-working due to crystals formed during the casting, which causes the bending workability to deteriorate.
(41) (2) Nickel (Ni)
(42) Nickel (Ni) is an element contributing to strength improvement via forming of precipitates with titanium (Ti). As the precipitates are finely and uniformly distributed, the strength can be improved and the bending workability can be improved at the same time. Thus, according to the present disclosure, the content of nickel (Ni) as added ranges from 0.05 to 1.0 wt %. The addition of nickel (Ni) to the copper-titanium (Cu—Ti)-based copper alloy may suppress the coarsening of precipitates during the solution treating. Thus, the solution treating may be realized at a higher temperature and titanium (Ti) may be sufficiently brough into a solid solution state. When the nickel content is lower than 0.05 weight %, this content is insufficient to obtain the above effect. However, when nickel (Ni) is added in excess of 1.0 weight %, the nickel-titanium (Ni—Ti) precipitates as produced increase the amount of titanium (Ti) as consumed, which lower the strength and bending workability.
(43) (3) Weight Ratio of Titanium/Nickel (Ti/Ni)
(44) In the copper alloy material according to the present disclosure, titanium and nickel are responsible forming the copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates in the copper (Cu) matrix contributing to the strength and bending workability. In this connection, the weight ratio of titanium/nickel (Ti/Ni) contained in the copper alloy material is in a range of 10<Ti/Ni<18. When the weight ratio of titanium/nickel (Ti/Ni) is smaller than 10.0, the amount of titanium (Ti) as consumed by the formation of the copper, nickel-titanium ((Cu, Ni)—Ti)) precipitates increase, thereby to lower the strength and bending workability. When the weight ratio of titanium/nickel (Ti/Ni) is over 18.0, the strength effect due to the addition of nickel (Ni) may not be achieved. Therefore, the weight ratio of titanium/nickel (Ti/Ni) in the alloy composition of the copper alloy material according to the present disclosure is in range of 10<Ti/Ni<18.
(45) (4) Impurities (Sn, Co, Fe, Mn, Cr, Zn, Si, Zr, V, P)
(46) The copper alloy material according to the present disclosure may optionally include one or more elements from the group consisting of Sn, Co, Fe, Mn, Cr, Zn, Si, Zr, V, and P as impurities. Although the impurities are not intentionally added, they are naturally added through the copper alloy material production process such as the dissolution and casting process. In the aging process, precipitates made of the copper, nickel-titanium ((Cu, Ni)—Ti)) and the impurities may occur in the matrix to increase the strength. The total amount of the impurities is not greater than 0.8 weight %. When the total amount of the impurities exceeds 0.8 weight %, titanium-nickel-X (Ti—Ni—X)-based (where X means the impurities) precipitates are produced at a large amount, resulting in a drastic decrease in the strength and bending workability.
(47) The copper alloy material for automobiles and electronic parts as obtained according to the method for producing the copper alloy material in accordance with the present disclosure forms unique fine precipitates in the copper (Cu) matrix. In general, a copper-titanium (Cu—Ti)-based copper alloy has a Cu.sub.3Ti phase with a poor coherence with an a phase as a copper (Cu) matrix phase and a Cu.sub.4Ti phase with good coherency with the α phase. These fine particles with the Cu.sub.3Ti phase and Cu.sub.4Ti phase are known to contribute to strength properties. However, Cu.sub.3Ti, which has the poor coherency with respect to the α phase is advantageous in terms of strength but adversely affects the bending workability. Recently, it has been reported that the Cu.sub.4Ti phase particles with the good coherency with respect to the α phase are finely and uniformly dispersed to achieve both strength and bending workability. Further, a technique has been reported for locally precipitating the Cu.sub.3Ti phase in the copper (Cu) matrix to achieve both strength and bending workability. However, even when the precipitation is localized, and when the Cu.sub.3Ti phase, which has the poor coherency in the copper (Cu) matrix is dispersed in a non-solid solution state in the grain boundary, the Cu.sub.3Ti as locally dispersed has adverse effect on the strength and bending workability in machining the slab.
(48) On the other hand, the method for producing the copper alloy material in accordance with the present disclosure improves the properties of the copper-titanium (Cu—Ti)-based copper alloy material in a different manner from the above prior schemes, thereby to improve the yield strength, electrical conductivity and bending workability.
(49) Specifically, the copper alloy material in accordance with the present disclosure is prepared by adding nickel (Ni) to the copper-titanium (Cu—Ti) based on the Ti/Ni ratio to precipitate copper, nickel-titanium ((Cu, Ni)—Ti)) and by performing the solution treating and then the double aging treatments such that complex precipitates including not only the Cu.sub.3Ti phase with the poor coherence and the Cu.sub.4Ti phase with the good coherency against the a phase as a copper (Cu) matrix phase but also a CuTi phase, Cu.sub.3Ti.sub.2 phase, etc. are distributed very finely and uniformly, thereby to ensure excellent yield strength and electrical conductivity as well as excellent bending workability.
(50) The copper alloy material as obtained according to the method for producing the copper alloy material according to the present disclosure had a grain size of smaller than or equal to 5 μm in observing the cross-section of the material, and fine precipitates at a size in a range of 300 nm or smaller are uniformly distributed in a copper matrix of the copper alloy material, and an areal density of the fine precipitates is greater than or equal to 2.5×10.sup.8/cm.sup.2. In general, the average grain size of the copper alloy material greatly affects the strength and bending workability of the copper alloy material. The cross-section parallel to the rolling direction of the copper alloy material according to the present disclosure has an average grain size of 5 μm or smaller. When the average grain size on the cross-section parallel to the rolling direction is larger than 5 this is disadvantageous in terms of bending workability because this size value becomes a starting point of cracking in bending. Further, in the copper alloy material according to the present disclosure, fine precipitates at a size in a range of 300 nm or smaller are uniformly distributed in a copper matrix of the copper alloy material, and an areal density of the fine precipitates is greater than or equal to 2.5×10.sup.8/cm.sup.2. Thus, the copper alloy material has a yield strength of at least 900 MPa, an electrical conductivity of at least 15% IACS, and a bending workability R/t≤1.5 in both a rolling direction and a direction perpendicular to the rolling direction at a 180° bending test, wherein R indicates a bending radius of curvature and t indicates a thickness of the material. In other words, when an areal density of the fine precipitates is lower than 2.5×10.sup.8/cm.sup.2, the yield strength of at least 900 MPa, and the electrical conductivity of at least 15% IACS may not be achieved. Further, even when an areal density of the fine precipitates is greater than or equal to 2.5×10.sup.8/cm.sup.2 but when the size of the precipitates is larger than 300 nm, the material surface is easily roughened or crack occurs during the bending, which is very disadvantageous in terms of the bending workability.
(51) The yield strength of the copper alloy material as produced according to the present disclosure is at least 900 MPa, and more preferably at least 950 MPa. When the yield strength is lower than 900 MPa, the stress generated in the copper alloy during the working of the material exceeds the yield strength of the copper alloy, such that the contact-pressure (spring-like performance) is lowered due to the plastic deformation of the copper alloy sheet and thus the sheet sags. Thus, the higher the yield strength of the copper sheet is, the higher the contacting strength (spring-like performance) is achieved. Thus, the higher yield strength of the copper sheet is required.
(52) The electrical conductivity of the copper alloy material as produced according to the present disclosure is greater than or equal to 15% IACS. Since the electrical conductivity of a conventional copper-titanium (Cu—Ti)-based copper alloy is 10 to 13% IACS, this value is insufficient to be used for information transfer and electrical contact materials. In other words, the material with at least 15% IACS may be used as the electrical contact material. In the copper alloy material according to the present disclosure, the amount of fine precipitates of 300 nm or smaller is maximally increased and the fine precipitates are uniformly distributed, thereby to obtain the electrical conductivity of 15% IACS or higher while maintaining the yield strength.
(53) In the copper alloy material according to the present disclosure, the bending workability has R/t≤1.5 (180°) in both the rolling direction and the direction perpendicular to the rolling direction, preferably, R/t≤1.0 (180°) in both the rolling direction and the direction perpendicular to the rolling direction. When the bending workability R/t (180°) exceeds 1.5 (where R indicates a bending radius of curvature and t indicates a thickness of the material), bending induced cracks occur in the bending of narrow workpieces, making it difficult to apply the copper alloy material to small-sized or complicated workpieces. Thus, preferably, the bending workability has R/t≤1.5 (180°).
(54) Therefore, the yield strength, electrical conductivity and bending workability of the copper alloy material as produced by the production method of the present disclosure may be satisfied simultaneously to be applied to the target product.
EXAMPLE
Examples 1 to 10
(55) The copper alloy material in accordance with the present example disclosure as described above was produced with the composition as disclosed in Table 1 under the process conditions as described in Table 2 below. Specifically, the constituent elements were combined based on the composition as described in Table 1, followed by dissolution and casting using a vacuum dissolution/casting machine. Thus, a copper alloy slab with a total weight of 2 kg and a thickness of 25 mm, a width of 100 mm and a length of 150 mm was produced. The copper alloy slab was hot-worked at 950° C. to 11 mm and was water-cooled to produce a plate. Then, both surfaces of the plate were ground by a 0.5 mm thickness to remove the oxide scale. After a first cold-working was performed such that the plate had a thickness of 5 mm, and an intermediate heat treating was performed under the temperature and hour conditions as described in Table 2. Thereafter, a second cold-working was carried out to a thickness of 0.4 mm at a reduction ratio of 92%. Then, as shown in Table 2, the solution treating, double aging treatments and final cold-working were performed in this order. A finished plate with a thickness in accordance with a final cold-working ratio was produced.
Comparatives Examples 1 to 12
(56) The copper alloy materials corresponding to Comparative Examples were produced according to Table 1 and Table 2. Other general processes were the same as those in the production method of the Examples as described above. As described above, Table 1 shows the constituent elements of the copper alloy material.
(57) TABLE-US-00001 TABLE 1 Chemical composition (wt %) Ti/Ni Example Cu Ti Ni Impurities ratio Examples 1 Balance 3.2 0.25 — 12.8 2 Balance 3 0.25 — 15 3 Balance 3.5 0.2 — 17.5 4 Balance 3.2 0.25 P0.01 12.8 5 Balance 4 0.25 — 16 6 Balance 2.5 0.2 — 12.5 7 Balance 3.2 0.25 Zn0.02 12.8 8 Balance 3.8 0.35 — 10.8 9 Balance 3.2 0.25 — 12.8 10 Balance 3.2 0.25 — 12.8 Comparative 1 Balance 3.2 — — to Examples 2 Balance 5 0.25 — 20 3 Balance 1 0.25 — 4 4 Balance 3.2 0.25 — 12.8 5 Balance 3.2 0.25 — 12.8 6 Balance 3.2 0.25 — 12.8 7 Balance 3.2 0.5 Co0.35, Cr0.5 — 8 Balance 3.2 0.5 Sn 0.35, Cr0.5 — 9 Balance 3.2 to Fe 0.2 — 10 Balance 3.2 0.25 — 12.8 11 Balance 3.2 0.25 P0.02 12.8 12 Balance 3.2 0.25 — 12.8
(58) As described above, Table 2 shows the production process conditions of the copper alloy material.
(59) TABLE-US-00002 TABLE 2 Process Intermediate Solution First Second Final rolling heat treating treating aging aging (reduction Example (° C. × Sec) (° C. × Sec) (° C. × Sec) (° C. × Hour) ratio, %) Examples 1 700 × 1800 830 × 50 650 × 1800 400 × 5 10 2 700 × 1800 830 × 50 650 × 1200 400 × 5 15 3 700 × 3600 830 × 50 650 × 1200 400 × 5 10 4 700 × 1200 830 × 50 650 × 1800 400 × 5 20 5 700 × 1800 830 × 50 650 × 1800 400 × 5 10 6 700 × 3600 830 × 50 650 × 1800 400 × 5 20 7 700 × 1800 830 × 50 650 × 1800 400 × 5 15 8 700 × 3600 830 × 50 650 × 1800 400 × 5 10 9 650 × 1800 830 × 50 650 × 1800 400 × 5 15 10 600 × 1800 830 × 50 650 × 1800 400 × 5 15 Comparative 1 700 × 1800 830 × 50 650 × 1800 400 × 5 10 Examples 2 700 × 1800 830 × 50 650 × 1800 400 × 5 10 3 700 × 3600 830 × 50 650 × 1800 400 × 5 20 4 850 × 1800 830 × 50 750 × 1800 400 × 5 15 5 400 × 1800 830 × 50 450 × 1800 400 × 5 15 6 700 × 1800 830 × 50 650 × 1800 400 × 5 75 7 Cracks during hot rolling 8 9 700 × 1800 830 × 50 650 × 1800 400 × 5 10 10 700 × 1800 830 × 50 650 × 1800 300 × 5 15 11 700 × 1800 830 × 50 650 × 1800 550 × 5 15 12 — 830 × 50 — 400 × 5 15
(60) The yield strength, electrical conductivity, bending workability, average grain size, fine precipitate size and areal density of each sample were evaluated by following methods.
TEST EXAMPLE
(61) (Yield Strength)
(62) The yield strength was measured in the rolling direction in accordance with JIS Z 2241 using a tensile tester. The results are shown in Table 3.
(63) (Electrical Conductivity)
(64) The electrical resistance was measured with a 4-probe manner at 240 Hz and the percentage of the electrical conductivity ratio as a ratio between the resistance value of a pure copper as the standard reference sample and that of each sample was expressed by % IACS value. The results are shown in Table 3.
(65) (Bending Workability)
(66) R=bending radius of curvature and t=thickness of material are defined. A complete close bend test was performed in a direction perpendicular to the rolling direction (Good way direction) and in a direction parallel to the rolling direction (Bad way). The complete close bend test refers to a 180° U-shaped bend test). In this connection, R/t≤1.5 condition was applied.
(67) When cracks were not confirmed by the optical microscope, this was evaluated as O, whereas when cracks were confirmed, this was evaluated as X. The results are shown in Table 3.
(68) (Average Grain Size)
(69) After mechanical-polishing of a final specimen, a polished surface was measured using FE-SEM (manufactured by FEI, USA) at a magnification of 5,000 times and then a grain size appearing in a reflection electron image of 1000 mm.sup.2 area was measured by using a grain measurement method via an intercept method (sectioning method, Heyn method). Then, the average grain size was determined. The results are shown in Table 3.
(70) (Fine Precipitate Size and Areal Density)
(71) Fine precipitates were observed at a magnification of 100,000 times or larger using a field emission transmission electron microscope (FE-TEM). Then, the size and areal density of the fine precipitates were calculated by replica analysis thereof. The results are shown in Table 3.
(72) TABLE-US-00003 TABLE 3 Mechanical property Average Fine precipitate Yield Electrical Bending Grain Average areal strength conductivity workability size size density Example (MPa) (% IACS) (180° R/t ≤ 1.5) (μm) (nm) 10.sup.8/cm.sup.2) Examples 1 920 16.8 ◯ 2 119 4.4 2 918 18 ◯ 3.2 160 3.2 3 956 15 ◯ 2.5 127 4.8 4 932 16 ◯ 5 150 4.6 5 963 18 ◯ 1.8 195 5.4 6 902 21 ◯ 2 155 2.9 7 915 16 ◯ 3 152 3.0 8 955 17.5 ◯ 3.4 192 4.8 9 924 16 ◯ 2 165 4.0 10 922 18 ◯ 4.8 162 4.1 Comparative 1 890 13 ◯ 8.2 93 1.6 Examples 2 970 9 X 3.8 315 2.4 3 695 25 ◯ 4.5 423 0.4 4 880 15 X 3 550 2.4 5 860 15 X 4.2 195 1.8 6 945 10 X 7 252 3.4 7 Cracks during hot rolling 8 9 882 13 X 6.5 1389 2.4 10 850 18 X 15 458 2.1 11 830 21 ◯ 8 152 5.4 12 890 19 X 9 389 2.0
(73) Table 3 shows that the yield strength of specimens as produced according to Examples 1 to 10 is greater than or equal to 900 MPa, the electrical conductivity thereof was at least 15% IACS, and no crack occurs at 180° U shaped bending test under R/t≤1.5 in the rolling direction and the direction perpendicular to the rolling direction. After mechanical-polishing of a final specimen, a polished surface was measured using FE-SEM (manufactured by FEI, USA) at a magnification of 5,000 times and then a grain size appearing in a reflection electron image of 1000 mm.sup.2 area was measured by using a grain measurement method via an intercept method (sectioning method, Heyn method). Thus, it was confirmed that the average grain size was 5 μm or smaller. Fine precipitates were observed at a magnification of 100,000 times or larger using a field emission transmission electron microscope (FE-TEM). Then, the size and areal density of the fine precipitates were calculated by replica analysis thereof. The fine precipitates at a size in a range of 300 nm or smaller are uniformly distributed in a copper matrix of the copper alloy material, wherein each of the fine precipitates includes at least one selected from a group consisting of (Cu,Ni)Ti, (Cu,Ni.sub.3)Ti.sub.2, (Cu,Ni).sub.3Ti, and (Cu,Ni).sub.4Ti. An areal density of the fine precipitates was greater than or equal to 2.5×10.sup.8/cm.sup.2. In accordance with the present disclosure, we found that after the double aging treatments, the characteristics of the material were changed according to the grain sizes, precipitate sizes and areal density distributions via analysis of the fine matrix thereof using the field emission type transmission electron microscope (FE-TEM).
(74) Specifically, we found that the grain sizes, fine precipitate sizes, and fine precipitate areal densities of the present material as subjected to the double aging treatment in Example 1 and the material as subjected to a single aging treatment as in Comparative Example 12 were significantly different from each other. In case of the material as not subjected to the double aging treatment as in Comparative Example 12, the grain size is 5 μm or larger, and the rolled matrix has developed, and the size of the copper, titanium-nickel ((Cu, Ni)—Ti)) precipitate became large, such that the yield strength and bending workability were adversely affected. As shown in
(75) In contrast, in Comparative Example 1, nickel (Ni) was not added. Thus, the bending workability was excellent, but the yield strength and electrical conductivity improvement by precipitate could not be expected. In Comparative Example 2, the titanium (Ti) content was 5 wt %, and cracking occurred in the bending workability test. In Comparative Example 3, the titanium (Ti) content was lower than 1.5 wt %, and thus, sufficient yield strength was not obtained. In Comparative Example 4, the first aging temperature is above 700° C., such that a large amount of precipitates was precipitated in the first aging. Then, in the second aging, the fine precipitates did not sufficiently precipitate and thus the yield strength was deteriorated and the bending crack occurred. In Comparative Example 5, the first aging temperature was lower than 550° C. and did not apply enough heat to form the second phase precipitate. As a result, both yield strength and bending workability were significantly reduced.
(76) In Comparative Example 6, the final rolling ratio was larger than 70%, and the rolled matrix developed rapidly, failing to secure the bending workability. In Comparative Examples 7 and 8, the sum of impurities was larger than 0.8 weight % due to the addition of other elements such as Co and Sn, resulting in side cracks during the hot-working, failing to obtain the finished samples. In Comparative Example 9, copper, nickel-titanium ((Cu, Ni)—Ti) did not form a precipitate due to the alloy containing Fe, resulting in failing to secure sufficient yield strength and bending workability. However, the copper, nickel-titanium ((Cu, Ni)—Ti) did form a precipitate after the double aging treatment recited in the present disclosure. In Comparative Example 10, the second aging in the double aging treatment was performed at 350° C. or lower, such that copper, nickel-titanium ((Cu, Ni)—Ti) did not fully form the precipitates, resulting in reducing the yield strength and bending workability. In Comparative Example 11, in the double aging treatment, the second aging was performed at 500° C. or higher, such that the overaged region occurred and thus the bending workability was good but the yield strength was rapidly deteriorated.
(77) According to the method for producing the copper alloy material in accordance with the present disclosure, the copper alloy material is prepared by adding nickel (Ni) to the copper-titanium (Cu—Ti) based on the Ti/Ni ratio to precipitate copper, nickel-titanium ((Cu, Ni)—Ti)) and by performing the solution treating and then the double aging treatments such that complex precipitates including not only the Cu.sub.3Ti phase with the poor coherence and the Cu.sub.4Ti phase with the good coherency against the α phase as a copper (Cu) matrix phase but also a CuTi phase, Cu.sub.3Ti.sub.2 phase, etc. are distributed very finely and uniformly. Thus, the grain size is smaller than 5 μm and thus very fine. The fine precipitates at a size in a range of 300 nm or smaller are uniformly distributed in a copper matrix of the copper alloy material wherein each of the fine precipitates includes at least one selected from a group consisting of (Cu,Ni)Ti, (Cu,Ni.sub.3)Ti.sub.2, (Cu,Ni).sub.3Ti, and (Cu,Ni).sub.4Ti. The areal density of the fine precipitates is greater than or equal to 2.5×10.sup.8/cm.sup.2. Thus, the present copper alloy material has a yield strength of at least 900 MPa, an electrical conductivity of at least 15% IACS, and a bending workability R/t≤1.5 in both a rolling direction and a direction perpendicular to the rolling direction at a 180° bending test, wherein R indicates a bending radius of curvature and t indicates a thickness of the material. In this way, the copper alloy material according to the present disclosure is a material suitable for electrical and electronic parts such as connectors, which are evolving into lightweight, compact and high density products in the future.