Copper-titanium-magnesium alloy and its manufacturing method

Abstract

To provide a copper-titanium-magnesium alloy that has improved mechanical strength and electrical conductivity, and a method for manufacturing the same.SOLUTION: Provided are a copper-titanium-magnesium alloy, which is a Cu, Ti and Mg-containing copper-titanium-magnesium alloy, and in which the atomic percent of Ti is 1.7 atom% to 4.1 atom%, the atomic percent of Mg is 0.7 atom% to 2.0 atom%, the balance is Cu and unavoidable impurities, and the total of the atomic percent is 100 atom%, and a method for manufacturing the same.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to copper-titanium-magnesium alloys and methods for making the same. [Background technology]

[0002] Modern automotive and computer technologies are driven by the miniaturization of electronic and electromechanical components, necessitating the development of high-performance conductive materials. Furthermore, there is a need for non-toxic, environmentally friendly alternatives to the widely used copper-beryllium alloys. Among these, copper-based alloys have attracted attention because they offer a balance of mechanical strength and electrical conductivity, as well as excellent bending workability and stress relaxation properties, depending on the application.

[0003] For example, Patent Document 1 discloses a copper-titanium-hydrogen alloy that exhibits higher strength than copper and higher electrical conductivity than conventional titanium-copper alloys by incorporating hydrogen into the titanium-copper alloy through aging treatment in a hydrogen atmosphere at a temperature below 500°C. Also, Non-Patent Document 1 reports that aging a titanium-copper alloy in hydrogen significantly suppresses the formation of discontinuous precipitates, and also reduces the amount of titanium dissolved in the matrix due to the activation of titanium hydride precipitation, which contributes to a significant improvement in electrical conductivity.

[0004] Patent Document 2 discloses a copper-titanium-magnesium alloy in which the mass percentages of copper (Cu), titanium (Ti), and magnesium (Mg) are 93% to 97%, 2% to 4%, and 1% to 3%, respectively, in order to improve mechanical strength and electrical conductivity, and a method for producing the alloy. Non-Patent Document 2 also reports on the effects of cold rolling and aging treatment on the microstructure and properties of copper-titanium-magnesium alloys.

[0005] Furthermore, the present inventors have presented a paper on the aging behavior and aging precipitate structure of copper-titanium-magnesium alloys at the 59th Annual Meeting of the Japan Copper and Copper Society. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-222623 [Patent Document 2] Chinese Patent No. 108642317 [Non-patent literature]

[0007] [Non-Patent Document 1] Satoshi Chiboshi and four others, "Suppression of discontinuous precipitate formation in Cu-Ti alloys by hydrogen aging", Journal of the Japan Copper and Copper Association, Copper and Copper Alloys, Japan Copper and Brass Association, 2018, Vol. 57, No. 1, pp. 249-253 [Non-patent document 2] Cong Li, et.al., “Effect of cold rolling and aging treatment on the microstructure and properties of Cu-3Ti-2Mg alloy”, Journal of Alloys and Compounds, 2020, Vol. 818, Article 152915 Summary of the Invention [Problem to be solved by the invention]

[0008] Figure 1 is a schematic diagram of discontinuous precipitates in a titanium-copper alloy. Typical age-hardenable titanium-copper alloys contain approximately 3 at% to 5 at% Ti and are manufactured by solution treatment followed by aging. At the beginning of aging, fine metastable β'-CuTi (tetragonal crystals) continuously precipitates at high density within the Cu matrix (supersaturated solid solution phase). However, with the aging time, discontinuous precipitation of coarse plate-like stable β-CuTi (orthorhombic crystals) and α-Cu solid solution phases occurs at grain boundaries in competition with the continuous precipitation of fine β'-CuTi. Furthermore, overaging is known to develop a lamellar structure containing plate-like β-CuTi, which reduces the average amount of solute Ti in the Cu matrix, improving electrical conductivity, but reducing the fine β'-CuTi, thereby reducing strength.

[0009] In view of the above circumstances, the present invention aims to provide a copper-titanium-magnesium alloy that has a high level of balance between mechanical strength and electrical conductivity, as well as high strength (tensile strength) and high ductility (elongation at break), and a method for producing the same. [Means for solving the problem]

[0010] The first invention is a copper-titanium-magnesium alloy containing Cu, Ti, and Mg, in which the atomic percentage of Ti is 1.7 at% to 4.1 at%, the atomic percentage of Mg is 0.7 at% to 2.0 at%, and the remainder is Cu and unavoidable impurities, with the total atomic percentage being 100 at%.

[0011] The copper-titanium-magnesium alloy of the first aspect of the present invention preferably has a tensile strength of 550 MPa or more and a breaking elongation of 15% or more.

[0012] The second present invention is a method for producing a copper-titanium-magnesium alloy having an atomic percentage of Ti of 1.7 at% to 4.1 at%, an atomic percentage of Mg of 0.7 at% to 2.0 at%, and the remainder being Cu and unavoidable impurities, with the total atomic percentage being 100 at%, the method comprising a casting step, a homogenization treatment step, a cold rolling treatment step, a solution treatment step, and an aging treatment step.

[0013] In the method for producing a copper-titanium-magnesium alloy according to the second aspect of the present invention, the aging treatment step is preferably carried out at an aging temperature of 350° C. to 550° C. for a holding time at the aging temperature of 1 hour to 100 hours. [Effects of the Invention]

[0014] The copper-titanium-magnesium alloy and its manufacturing method disclosed herein can provide a balance between high levels of mechanical strength and electrical conductivity, as well as high strength (tensile strength) and high ductility (elongation at break). [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing discontinuous precipitates in a titanium-copper alloy. [Figure 2] FIG. 2 is a diagram showing steps S1 of a method for producing a copper-titanium-magnesium alloy according to an embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing the thermomechanical treatment of a copper-titanium-magnesium alloy in a method for producing the alloy according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing the hardening curves and electrical conductivity changes resulting from isothermal aging of various alloys. [Figure 5] FIG. 1 is a diagram showing an example of stress-strain curves of aging peak materials of various alloys. [Figure 6] The following are SEM images of overaged alloys and enlarged images of discontinuous precipitates, which are the cause of overaging softening. [Figure 7]This is an HAADF-STEM image capturing a localized region containing a different phase interface in discontinuous precipitates of overaged Cu-4Ti. [Figure 8] FIG. 1 is a diagram showing an example of extraction of discontinuous precipitates by FIB processing. [Figure 9] FIG. 1 shows the results of STEM / EDS analysis of discontinuous precipitates in an overaged Cu-4Ti-2Mg material. [Figure 10] FIG. 10 shows the results of STEM / EDS analysis of a partial region of FIG. 9 obtained under a high-magnification microscope. [Figure 11] These are electron diffraction patterns obtained from localized regions inside and outside discontinuous precipitates in an overaged Cu-4Ti-2Mg alloy. [Figure 12] This is a high-resolution ABF-STEM image capturing a localized region including the interphase interface of discontinuous precipitates in an overaged Cu-4Ti-2Mg alloy. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Copper-titanium-magnesium alloy] The copper-titanium-magnesium alloy of the present disclosure is a copper-titanium-magnesium alloy having an atomic percentage of Ti of 1.7 at% to 4.1 at%, an atomic percentage of Mg of 0.7 at% to 2.0 at%, and the remainder being Cu and unavoidable impurities, with the total atomic percentage being 100 at%.

[0017] Furthermore, according to the copper-titanium-magnesium alloy of the above composition, the yield strength is 400 Pa or more, more preferably 450 Pa or more, and even more preferably 610 Pa or more, the tensile strength is 550 MPa or more, more preferably 600 MPa or more, and even more preferably 780 MPa or more, and the breaking elongation is 15% or more, more preferably 19% or more, and even more preferably 20% or more.

[0018] From the viewpoint of improving strength, stress relaxation resistance, bending workability, etc., the atomic percentage of Ti in the copper-titanium-magnesium alloy is preferably 1.7 at% to 4.1 at%, with the lower limit being more preferably 1.9 at% or more, even more preferably 3.8 at% or more, and even more preferably a value close to 4.0 at%.

[0019] From the viewpoint of suppressing the formation of discontinuous precipitates during aging treatment, the atomic percentage of Mg in the copper-titanium-magnesium alloy is preferably 0.7 at% to 2.0 at%, more preferably 0.9 at% to 2.0 at%, even more preferably 1.6 at% to 2.0 at%, and even more preferably a value close to 2.0 at%. Suppressing discontinuous precipitates reduces the number of interphase interfaces and the number of locations where stress concentration occurs, leading to improved ductility.

[0020] From the viewpoint of improving electrical conductivity after aging treatment, the total atomic percentage of Ti and Mg may be reduced, and the total atomic percentage of Ti and Mg in the copper-titanium-magnesium alloy may be 2.4 at% to 5.7 at%.

[0021] [Method of manufacturing copper-titanium-magnesium alloy] Fig. 2 is a diagram showing the steps of a manufacturing method S1 of a copper-titanium-magnesium alloy according to one embodiment. As shown in Fig. 2, the manufacturing method S1 of a copper-titanium-magnesium alloy includes a melting step S10, a homogenization treatment step S20, a cold rolling treatment step S30, a solution treatment step S40, and an aging treatment step S50. Fig. 3 is a diagram showing the thermomechanical treatment of the copper-titanium-magnesium alloy in the manufacturing method of the alloy.

[0022] Step S10 is a melting step in which a mixture of Cu, Ti, and Mg is melted. Cu, Ti, and Mg can be melted without restriction from known raw metals as long as the atomic percentages described above are satisfied. Examples of raw metals include Cu, Ti, magnesium copper, etc.

[0023] In step S10, any known melting process can be used without limitation, and for example, the melting method may be arc melting, high-frequency induction melting, etc., the melting atmosphere may be high vacuum, inert gas (Ar, He), etc., and the crucible may be made of alumina ceramic, etc. After melting, the molten metal is tapped into a copper mold or the like to produce an alloy ingot.

[0024] The purity of each of Cu, Ti, and Mg used in step S10 is 99.9% (3N) or more, preferably 99.99% (4N) or more.

[0025] Step S20 is a homogenization treatment step for the alloy ingot melted in step S10. Any known homogenization treatment step can be used for step S20 without any restrictions. In step S20, the optimal homogenization temperature varies depending on the alloy composition, from the viewpoint of eliminating the inhomogeneity of the internal structure that appears after melting and casting. However, it is preferable to set the homogenization temperature at a constant temperature that does not exceed the liquidus temperature, for example, within the range of 730°C to 950°C, or alternatively, 800°C to 950°C. The holding time at the homogenization temperature may be 0.1 to 2 hours, 0.3 to 1 hour, or approximately 0.5 hours.

[0026] Step S30 is a cold rolling treatment step for the alloy ingot homogenized in step S20. Any known cold rolling treatment step can be used for step S30 without any restrictions, and examples include a cold rolling treatment step in which the reduction is controlled at room temperature and rolling is performed in multiple passes. From the viewpoint of grain refinement by recrystallization, the reduction rate in step S30 may be 80% to 90%, and preferably 90% or more. The reduction rate per cold rolling pass may be, for example, 0.1 mm to 0.4 mm, or 0.2 mm to 0.3 mm.

[0027] Step S40 is a solution treatment step for the alloy ingot cold-rolled in step S30. Any known solution treatment step can be used for step S40 without any restrictions. In step S40, from the viewpoint of forming a supersaturated solid solution of Mg and Ti in Cu, the solution treatment temperature is preferably 800°C to 900°C, more preferably 830°C to 870°C, and even more preferably around 850°C. The holding time at the solution treatment temperature may be 0.1 hours to 2 hours, 0.3 hours to 1 hour, or even around 0.5 hours. The solution-treated alloy ingot is hereinafter referred to as SS material. The SS material is water-quenched at a water-quenching temperature of, for example, about 20°C to 30°C.

[0028] Step S50 is an aging treatment step for the SS material in step S40. Any known aging treatment step can be used for step S50 without any restrictions. The aging treatment temperature in step S50 is preferably 350°C to 550°C, more preferably 400°C to 500°C, even more preferably 430°C to 470°C, and most preferably about 450°C, from the viewpoint of setting a temperature that simultaneously activates precipitation hardening of the Cu-Ti solid solution and stabilizes the Cu-Mg solid solution. The holding time at the aging temperature is preferably 1 hour to 100 hours, more preferably 2 hours to 20 hours, even more preferably about 5 hours to 15 hours, and most preferably about 10 hours. The aging treatment step is carried out, for example, in the atmosphere. Hereinafter, the aging peak material that has reached the peak of age hardening will be referred to as PA material. [Example]

[0029] The present disclosure will be further described below based on examples, although the present disclosure is not limited to the examples.

[0030] [Production of Cu-Ti-Mg alloy] Four types of copper-titanium-magnesium alloys were produced as Examples 1 to 4, and a Mg-free titanium-copper alloy was produced as Comparative Example 1. Table 1 shows the nominal compositions and analyzed compositions of the alloy ingots of Examples 1 to 4 and Comparative Example 1.

[0031] [Table 1]

[0032] Example 1 Cu (4N purity), Ti (3N purity), and Mg (3N purity) were melted by high-frequency induction heating in an argon gas atmosphere to produce an alloy ingot with nominal compositions of Cu, Ti, and Mg of 97 at%, 2 at%, and 1 at%, respectively. The actual composition of the melted alloy ingot was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and the analyzed compositions of Cu, Ti, and Mg were 97.6 at%, 1.7 at%, and 0.7 at%, respectively. Hereinafter, the copper-titanium-magnesium alloy with the composition of Example 1 will be referred to as Cu-2Ti-1Mg. In the homogenization process, the homogenization temperature was 730°C and the holding time was 2 hours. The material was then cold rolled to a thickness of 1 mm at a reduction rate of 90% (0.25 mm per cold rolling pass). In the solution treatment process, the solution treatment temperature was 850°C and the holding time was 0.5 hours, followed by water quenching. In the aging process, the homogenization temperature was 450°C and the holding time was 10 hours.

[0033] <Example 2> This alloy was prepared in the same manner as in Example 1, except that the nominal compositions of Cu, Ti, and Mg were 95 at%, 2 at%, and 3 at%, respectively. The analyzed compositions of Cu, Ti, and Mg were 96.1 at%, 1.9 at%, and 2.0 at%, respectively. Hereinafter, the copper-titanium-magnesium alloy with the composition of Example 2 will be referred to as Cu-2Ti-2Mg.

[0034] Example 3 This alloy was prepared in the same manner as in Example 1, except that the nominal compositions of Cu, Ti, and Mg were 95 at%, 4 at%, and 1 at%, respectively. The analyzed compositions of Cu, Ti, and Mg were 95.3 at%, 3.8 at%, and 0.9 at%, respectively. Hereinafter, the copper-titanium-magnesium alloy with the composition of Example 3 will be referred to as Cu-4Ti-1Mg.

[0035] Example 4 This alloy was prepared in the same manner as in Example 1, except that the nominal compositions of Cu, Ti, and Mg were 93 at%, 4 at%, and 3 at%, respectively, and the homogenization treatment was performed at a temperature of 950°C for 0.5 hours. The analyzed compositions of Cu, Ti, and Mg were 94.3 at%, 4.1 at%, and 1.6 at%, respectively. Hereinafter, the copper-titanium-magnesium alloy with the composition of Example 4 will be referred to as Cu-4Ti-2Mg.

[0036] <Comparative Example 1> This alloy was produced in the same manner as in Example 1, except that no Mg was added and the nominal compositions of Cu and Ti were 96 at% and 4 at%, respectively. The analyzed compositions of Cu and Ti were 95.8 at% and 4.2 at%, respectively. Hereinafter, the titanium-copper alloy with the composition of Comparative Example 1 will be referred to as Cu-4Ti.

[0037] As a result of ICP-MS, the analyzed compositions of Mg in the alloy ingots of Examples 1 to 4 were lower than the corresponding nominal compositions. This difference between the analyzed compositions and the nominal compositions is thought to be due to excessive vaporization of Mg during induction heating, etc.

[0038] [Vickers hardness test and electrical resistance measurement] Vickers hardness tests and electrical resistivity measurements were performed on Cu-2Ti-1Mg, Cu-2Ti-2Mg, Cu-4Ti-1Mg, Cu-4Ti-2Mg, and Cu-4Ti SS specimens after aging in air at 450°C for up to 100 hours. Vickers hardness tests were performed at room temperature using a micro-Vickers hardness tester (Matsuzawa Seisakusho) under a load of 0.1 kgf. The average Vickers hardness was calculated from 10 or more indentations. Electrical conductivity was calculated by measuring electrical resistivity at room temperature using a DC constant-current four-terminal method.

[0039] The hardening curves and electrical conductivity changes with isothermal aging for Cu-2Ti-1Mg, Cu-2Ti-2Mg, Cu-4Ti-1Mg, Cu-4Ti-2Mg, and Cu-4Ti are shown in Figure 4. In Figure 4, the vertical axis represents Vickers hardness (Hv) (right) and electrical conductivity (%IACS) (left), and the horizontal axis represents the aging time common to both physical properties.

[0040] As shown in Figure 4, the Hv values ​​of Cu-4Ti, Cu-4Ti-1Mg, and Cu-4Ti-2Mg were larger than those of Cu-2Ti-1Mg and Cu-2Ti-2Mg, suggesting that the effect of aging on hardening was greater due to the Ti content than to the Mg content. Furthermore, for Cu-4Ti, Cu-4Ti-1Mg, and Cu-4Ti-2Mg, which have the same atomic percent Ti, increasing the Mg content increased the Hv values. The Hv values ​​increased with aging time, then reached a broad peak at approximately 10 hours, and finally decreased with further aging time, indicating overaging softening.

[0041] Furthermore, the electrical conductivity decreased as the Ti and Mg contents in the alloy decreased, and this tendency was more pronounced for Ti than for Mg. Each %IACS continued to increase in the range of approximately 5%IACS to 22%IACS with the aging time, and these values ​​roughly agreed with the values ​​estimated based on Nordheim's law, assuming that Ti and Mg are not mutually dissolved in solid solution and independently affect the electrical conductivity of Cu.

[0042] As shown in FIG. 4, the copper-titanium-magnesium alloy of the present disclosure had a slightly lower %IACS than a titanium-copper alloy with the same atomic percentage of Ti to which no Mg was added, but still achieved a high level of Hv value.

[0043] [Tensile test] Tensile tests were performed at room temperature until fracture using SS and PA specimens of Cu-2Ti-1Mg, Cu-2Ti-2Mg, Cu-4Ti, and Cu-4Ti-2Mg with a cross section of 5 mm × 1 mm and a gauge length of 10 mm. A load testing machine (Shimadzu AG-IS) equipped with a video camera was used, with the load axis of the load testing machine set parallel to the rolling direction of the specimen, and the strain rate was 1 × 10 -3 [s -1 ].

[0044] Table 2 shows the mechanical properties of each SS material and each PA material obtained from the results of the tensile test.

[0045] [Table 2]

[0046] As shown in Table 2, aging treatment improves yield strength and tensile strength and reduces elongation at break. The Cu-2Ti-1Mg, Cu-2Ti-2Mg, and Cu-4Ti-2Mg PA alloys achieve yield strengths of over 400 Pa, tensile strengths of over 550 MPa, and elongation at break of over 15%. The Cu-4Ti-2Mg PA alloy, in particular, achieved a yield strength of 645.0 MPa, a tensile strength of 811.1 MPa, and an elongation at break of 25.0%. Compared to titanium-copper alloys with the same atomic percentage of Ti but without Mg, these alloys exhibit superior mechanical performance, with higher Vickers hardness, tensile strength, and elongation at break.

[0047] Figure 5 shows stress-strain curves generated from tensile tests performed on the Cu-2Ti-1Mg, Cu-2Ti-2Mg, Cu-4Ti, and Cu-4Ti-2Mg PA materials. Figure 5 shows that the addition of Ti has a more significant effect on improving tensile strength than the addition of Mg, and that the addition of Mg tends to have a more significant effect on improving fracture elongation than the addition of Ti. In other words, adding an appropriate amount of Mg (e.g., 1 at% to 2 at% in Figure 5) to a titanium-copper alloy increases deformation resistance and improves ductility.

[0048] [Electron microscope observation] The microstructure of the overaged material is observed using a scanning electron microscope (SEM), a transmission electron microscope (TEM) / scanning transmission electron microscope (STEM), an energy dispersive X-ray spectrometer (EDS), a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), and an annular bright-field scanning transmission electron microscope (ABF-STEM). The specimen material used for observation was extracted using focused ion beam (FIB) processing. Figure 8 shows secondary electron images illustrating the extraction process of discontinuous precipitates using FIB processing. Figures 8(a) and 8(b) show the deposition of a carbon protective film on a portion of the discontinuous precipitate (the target) to protect against radiation damage prior to subsequent gallium ion irradiation. Figures 8(c) and 8(d) show the excavation of the area surrounding the target region by irradiating gallium ions. Figures 8(e) and 8(f) show the process of using a micromanipulator to move the plate-shaped target, which has been separated from the parent phase, and finally placing it on a grid for TEM observation.

[0049] SEM images were taken using a field-emission scanning electron microscope (JEOL JSM-7800F) using backscattered electron imaging. Figure 6 shows SEM images of three types of overaged materials after aging at 450°C for 100 hours. Figures 6(a) and 6(b) show Cu-4Ti, Figure 6(c) shows Cu-4Ti-1Mg, and Figure 6(d) shows Cu-4Ti-2Mg. Figure 6(b) is an enlarged view of region A in Figure 6(a). As shown in Figure 6, the amount of discontinuous precipitates (shown as dark areas) decreases with increasing Mg content. Computer image analysis revealed that the area fractions of the dark areas in the overall specimens were 34.4%, 13.6%, and 8.1% for Cu-4Ti, Cu-4Ti-1Mg, and Cu-4Ti-2Mg, respectively. In the copper-titanium-magnesium alloy of the present disclosure, the amount of discontinuous precipitates formed is suppressed to approximately 50% or less compared to a titanium-copper alloy with the same atomic percentage of Ti to which no Mg is added, although this amount varies depending on the amount of Mg added.

[0050] A 200kV electron microscope (JEOL JEM-2100F) and a 300kV electron microscope (FEI Titan) equipped with a Super-X EDS system were used. 3 Selected area electron diffraction (SAD) and high-angle anti-reflection (HAADF)-STEM images were taken using a G2 60-300 Probe Corrector.

[0051] Figure 7 shows a HAADF-STEM image of discontinuous precipitates in a Cu-4Ti alloy overaged for 100 hours at 450°C, along with electron diffraction patterns obtained from local regions of both phases on either side of the interface. It is well known that overaging in typical age-hardenable titanium-copper alloys results in discontinuous precipitation of lamellar structures consisting of coarse, plate-like, stable β-Cu4Ti (orthorhombic) and α-Cu solid solution phases, originating from grain boundaries. Figure 7 shows that the electron diffraction pattern in the Ti-rich phase region is a β-Cu4Ti tetragonal Au4Zr-type crystal structure, while the electron diffraction pattern in the Ti-poor phase region is a face-centered cubic (FCC) crystalline structure of the α-Cu solid solution phase, confirming the reproducibility of known phenomena. This is the first case in which these results have been verified by direct observation using an electron microscope.

[0052] Figures 9 and 10 show the results of STEM / EDS analysis of discontinuous precipitates in an overaged Cu-4Ti-2Mg alloy, and Figure 10 shows the results of STEM / EDS analysis of region B in Figure 9, obtained under a high-magnification microscope. Figure 9(a) is an HAADF-STEM image, and Figures 9(b) to 9(d) are EDS mapping images of the constituent elements Cu, Ti, and Mg, respectively. Figure 10(a) is an ABF-STEM image, Figure 10(b) is an HAADF-STEM image, and Figures 10(c) to 10(f) are EDS mapping images of the constituent elements Cu, Ti, and Mg, respectively. In FIG. 10(c), Area#1, Area#2, and Area#3 are Ti-deficient phase, Ti-enriched phase, and Cu matrix phase, respectively. The compositions of Cu, Ti, and Mg in Area#1, Area#2, and Area#3 are Cu, Ti, and Mg, respectively, expressed in at%. 98.9 Ti 0.375 Mg 0.714 , Cu 83.6 Ti 15.9 Mg 0.492 , and Cu 98.9 Ti 0.327 Mg 0.79 It was.

[0053] Figure 11 shows electron diffraction images obtained from local regions inside and around discontinuous precipitates in an overaged Cu-4Ti-2Mg alloy. Figure 11(a) is an HAADF-STEM image, and Figures 11(b) to 11(e) show electron diffraction images for each of the local regions SAD1 to SAD5 in Figure 11(a), respectively. The crystal structure in each of the local regions SAD1 to SAD5 is represented by the lattice-like dots in the electron diffraction image. As shown in Figures 11(b) to 11(e), a crystal structure based on the FCC structure of the α-Cu solid solution phase was observed in local regions SAD1 to SAD3, while a crystal structure based on the Cu matrix was observed in local regions SAD4 and SAD5.

[0054] Figure 12 is a high-resolution ABF-STEM image capturing a local region including the interphase boundary of discontinuous precipitates in an overaged Cu-4Ti-2Mg specimen. Magnified photographs of the Ti-enriched and Ti-poor phases on either side of the interphase boundary are shown in the inset. As shown in Figure 12, both the Ti-enriched and Ti-poor phase regions are determined to consist of the FCC structure of the α-Cu solid solution phase, which differs from the crystal structure of the constituent phases of the discontinuous precipitates in the overaged Cu-4Ti specimen shown in Figure 7.

[0055] The Cu-4Ti-2Mg overaged material had fewer interphase boundaries than the Cu-4Ti overaged material of Comparative Example 1. This is because the addition of an appropriate amount of Mg to the titanium-copper alloy suppressed the formation of discontinuous precipitates that develop from grain boundaries, even during overaging, and the formation of the stable phase β-Cu4Ti (orthorhombic crystals) within the discontinuous precipitates. It is believed that the above-mentioned structural effects reduced the number of interphase boundaries, reduced the number of stress concentration sites, and led to improved ductility.

[0056] The copper-titanium-magnesium alloy of the present disclosure exhibits high levels of Vickers hardness, tensile strength, and elongation at break, compared to titanium-copper alloys with the same atomic percentage of Ti but without added Mg, and exhibits excellent mechanical performance. By subjecting the copper-titanium-magnesium alloy of the present disclosure to appropriate thermomechanical treatment and aging treatment, it is possible to achieve both high strength (tensile strength) and high ductility (elongation at break), that is, high elongation and toughness. [Industrial Applicability]

[0057] The technology disclosed herein can be an important technology in the field of copper alloys that combine high electrical conductivity with high strength and high ductility, and is applicable to a wide range of industries, including the automotive industry, electronics industry, electrical and electronic equipment industry, and information equipment industry.

Claims

1. A copper-titanium-magnesium alloy containing Cu, Ti, and Mg, wherein the atomic percentage of Ti is 1.7 at% to 4.1 at%, the atomic percentage of Mg is 0.7 at% to 2.0 at%, and the balance is Cu and unavoidable impurities, the total atomic percentages being 100 at%; the sum of the atomic percentage of Ti and the atomic percentage of Mg is 2.4 at% to 5.7 at%; The tensile strength is 550 MPa or more and the elongation at break is 15% or more. Copper-titanium-magnesium alloy.

2. 2. The method for producing a copper-titanium-magnesium alloy according to claim 1, comprising the steps of casting, homogenizing, cold rolling, solution treatment, and aging.

3. 3. The method for producing a copper-titanium-magnesium alloy according to claim 2, wherein the aging treatment step is carried out at an aging temperature of 350°C to 550°C, and the aging treatment temperature is maintained for 1 hour to 100 hours.

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