Cu-Ti-based copper alloy sheet material, method for producing same, and vapor chamber

Abstract

The invention relates to a Cu-Ti-based copper alloy sheet material, a manufacturing method thereof, and a vapor chamber. Provided is a metal material suitable for a case of a vapor chamber, the metal material having high strength after being held at a high temperature (for example, about 800 DEG C), and obtaining very high bonding strength in a diffusion-bonded portion exceeding a pure copper material. A copper alloy sheet material having a chemical composition containing, in mass%, 2.00-5.00% of Ti, and optionally, Ag, Al, B, Be, Co, Cr, Fe, Hf, Mg, Mn, Mo, Nb, Ni, P, S, Si, Sn, Ta, V, Zn, Zr, and a rare earth element in a total of 4.00% or less, the remainder comprising Cu and unavoidable impurities, the maximum height roughness Rz of the sheet surface in the direction perpendicular to the rolling direction being 1.5 [mu] m or less, and the maximum height roughness Rz of the sheet surface in the direction perpendicular to the rolling direction being 1.5 [mu] m or less. The expansion area ratio Sdr of the plate surface measured by a laser microscope is 0.10 or less.

Description

Technical Field

[0001] This invention relates to Cu-Ti copper alloy plates with improved bonding strength after diffusion bonding, a method for manufacturing the same, and a heat exchange plate for using the copper alloy plate as a raw material. Background Technology

[0002] In electronic devices such as personal computers, tablets, and smartphones, vapor chambers have attracted attention as cooling devices used to efficiently escape heat generated from processors such as CPUs. The shell of a vapor chamber is generally constructed by diffusion bonding or brazing between the edges of an upper plate component and a lower plate component made of copper-based materials, creating internal voids. Pure copper plates and copper alloy plates are used as the copper-based material. Pure copper plates excel in the high bonding strength at the diffusion bonding joint, but suffer from the disadvantage that the material's own strength decreases significantly due to the heating during diffusion bonding.

[0003] Patent Document 1 describes the use of a Cu-Ti copper alloy with a Ti content of 2.0 to 5.0% by mass as the shell material for a heat exchanger. Cu-Ti copper alloys are among the copper-based materials that achieve high strength levels and maintain higher strength than pure copper or other common copper alloys even after being held at the diffusion bonding heating temperature (e.g., around 800°C). According to Patent Document 1, in a test where three Cu-Ti copper alloy plates were overlapped and diffusion-bonded at 800°C, a test piece was dropped 100 times from a height of 30 cm onto asphalt. No damage (peeling, gaps) occurred at the diffusion bonding joint, maintaining a healthy bond.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-50392 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In recent years, with the increasing performance of electronic devices, the cooling components they incorporate require enhanced durability. In the housing of heat spreaders, it is particularly important to balance the high strength of the material itself with improved joint strength at the junctions. According to the technology in Patent Document 1, by using a Cu-Ti based copper alloy, the material's strength is maintained at a relatively high level even after being held at a diffusion bonding temperature (e.g., around 800°C). However, the joint strength at the diffusion bonding junction is not as high as that of pure copper, and there is still room for improvement.

[0009] The object of the present invention is to provide a metal material suitable for the housing of a heat exchanger that has the same high strength as the copper alloy sheet for heat exchangers disclosed in Patent Document 1 after being maintained at high temperatures (e.g., around 800°C) and has a very high bonding strength at the diffusion joint that exceeds that of pure copper.

[0010] Methods for solving problems

[0011] To achieve the above objectives, the following invention is disclosed in this specification.

[0012] [1] Copper alloy sheet, having the following chemical composition (in mass%): Ti: 2.00–5.00%, Ag: 0–0.30%, Al: 0–3.00%, B: 0–0.30%, Be: 0–0.15%, Co: 0–1.00%, Cr: 0–1.00%, Fe: 0–1.00%, Hf: 0–1.00%, Mg: 0–1.00%, Mn: 0–1.50%, Mo: 0–1.00%, Nb: 0–0.50%, Ni: 0–1.50%, P: 0–0.20%, S: 0–0.20%, Si: 0–1.00%, Sn: 0~1.50%, Ta: 0~1.00%, V: 0~1.00%, Zn: 0~2.00%, Zr: 0~1.00%, Total rare earth elements: 0~3.00%, Ag, Al, B, Be, Co, Cr, Fe, Hf, Mg, Mn, Mo, Nb, Ni, P, S, Si, Sn, Ta, V, Zn, Zr and total rare earth elements: less than 4.00%, balance consists of Cu and unavoidable impurities, maximum height roughness Rz in the rolling right-angle direction of the plate surface is less than 1.5μm, and the unfolded area ratio Sdr of the plate surface measured by laser microscope is less than 0.10.

[0013] [2] According to the copper alloy plate described in [1] above, when the elemental concentration distribution of Cu, Ti, O and C in the depth direction measured by XPS (X-ray photoelectron spectroscopy) is defined as the surface region from the outermost surface to the SiO2 equivalent depth (nm) where the proportion of O in the four elements is less than 5.0 atomic%, the thickness of the oxygen enrichment layer is less than 100 nm.

[0014] [3] According to the copper alloy sheet described in [1] or [2] above, the 0.2% yield strength in the rolling direction after a heat treatment test in a nitrogen atmosphere at 800°C for 1 hour is 400 MPa or more.

[0015] [4] The copper alloy plate according to any one of [1] to [3] above, wherein the plate thickness is 0.01 to 0.50 mm.

[0016] [5] The copper alloy plate according to any one of [1] to [4] above, wherein the Ti content in the chemical composition is 2.80 to 5.00%, and the unfolded area ratio Sdr is 0.08 or less.

[0017] [6] The copper alloy plate according to any one of [1] to [4] above, wherein the Ti content in the chemical composition is 2.80 to 5.00%, the maximum height roughness Rz is less than 1.1 μm, and the unfolded area ratio Sdr is less than 0.06.

[0018] [7] The copper alloy sheet according to any one of [1] to [6] above is used for the heat spreader shell.

[0019] [8] The method for manufacturing copper alloy sheet according to any one of [1] to [7] above, wherein when the intermediate product sheet is subjected to solution treatment, aging treatment, fine cold rolling and fine heat treatment in sequence to manufacture copper alloy sheet, a work roll having a roll surface with a maximum height roughness Rz of 1.7 μm or less in the roll axis direction is used, the fine cold rolling is performed under the condition of setting the rolling rate to 5.0 to 20.0%, and the fine heat treatment is performed under the condition of holding at 300 to 500°C for 10 to 300 seconds.

[0020] [9] A heat spreader having a housing having a structure in which two or more components using copper alloy plates as described in any one of [1] to [7] are joined by diffusion bonding or brazing.

[0021] In this specification, the term "sheet metal" refers to a sheet of metal material. Sometimes, thin sheet metal material is also referred to as "foil," and such "foil" is also included in the term "sheet metal" as used herein. Sheet metal material wound into a coil is also included in the term "sheet metal." Furthermore, the thickness of sheet metal material is referred to as "sheet thickness" in this specification. "Sheet surface" refers to the surfaces at both ends of the sheet in the thickness direction, and is sometimes also called the "rolled surface."

[0022] In this specification, the expression "n1~n2" indicating a numerical range means "above n1 and below n2". Here, n1 and n2 are numerical values ​​that satisfy n1 < n2.

[0023] The rolling rate (%) in a certain rolling process is determined by the following formula (1).

[0024] Rolling yield (%) = 100 × (h0 - h1) / h0…(1)

[0025] h0: Plate thickness (mm) supplied before the first rolling pass in this rolling process.

[0026] h1: Plate thickness (mm) at the final rolling pass of this rolling process.

[0027] Invention Effects

[0028] According to the present invention, a copper alloy sheet can be achieved that maintains strength at high temperatures (e.g., around 800°C) to the same extent as the copper alloy sheet for heat exchangers disclosed in Patent Document 1, and achieves a very high bond strength at the diffusion joint exceeding that of pure copper. This material is extremely useful as a copper alloy sheet for constructing the shell of heat exchangers where high durability is increasingly demanding (copper alloy sheet for heat exchanger shell). Attached Figure Description

[0029] Figure 1 A figure illustrating an example of the elemental concentration distribution along the depth direction from the outermost surface, measured by XPS for a Cu-Ti copper alloy sheet according to the present invention.

[0030] Figure 2 The diagram illustrates the state in which a test piece used to determine the bonding strength of a diffusion joint is placed in a tensile testing machine.

[0031] Explanation of reference numerals in the attached figures

[0032] 1a and 1b Plate Samples

[0033] 2. Diffusion joint

[0034] 3a Upper chuck

[0035] 3b Lower chuck Detailed Implementation

[0036] [Chemical Composition]

[0037] Unless otherwise specified, the "%" in the following references to alloy composition refers to "mass %".

[0038] Titanium (Ti) is an element that contributes to the formation of a modulated structure of Ti due to the decomposition of the spindle lines and the formation of fine second-phase particles due to precipitation, thus increasing the strength of the Cu-Ti copper alloy of the present invention. Additionally, it also contributes to the improvement of stress mitigation. Besides these previously known effects, it has also been confirmed that Ti has the effect of improving the bonding strength at the diffusion joint when held at a high temperature of around 800°C.

[0039] According to the inventors' investigation, when Cu-Ti copper alloy sheets containing a specified amount of Ti are subjected to heat treatment at high temperatures (e.g., 800°C for 1 hour) in a non-oxidizing atmosphere, XPS analysis confirms the formation of a Ti-rich layer near the material surface. Furthermore, it is known that this Ti-rich layer also forms at the bonding interface during diffusion bonding. It is speculated that the formation of such a Ti-rich layer contributes to improving the bonding strength of the diffusion bonding joint. However, to achieve a bonding strength exceeding that of pure copper, further adjustments to the surface properties (maximum height roughness Rz and unfolded area ratio Sdr, described later) become important.

[0040] To fully realize these benefits, a Ti content of 2.00% or higher is ensured. Excessive Ti content is a major cause of reduced hot and cold workability; therefore, the Ti content is limited to 5.00% or less. A more preferred range for Ti content is 2.80% to 5.00% by mass, and a further preferred range is 3.00% to 4.85% by mass.

[0041] Ag (silver), Al (aluminum), B (boron), Be (beryllium), Co (cobalt), Cr (chromium), Fe (iron), Hf (hafnium), Mg (magnesium), Mn (manganese), Mo (molybdenum), Nb (niobium), Ni (nickel), P (phosphorus), S (sulfur), Si (silicon), Sn (tin), Ta (tantalum), V (vanadium), Zn (zinc), Zr (chromium), and rare earth elements are optional elements. One or more of these elements may be included as needed. For example, Al is effective in suppressing the formation of coarse precipitates in Cu-Ti copper alloys and also in reducing the density (specific gravity) of copper alloys. Ni, Co, Fe, and Nb form intermetallic compounds with Ti, contributing to increased strength. Furthermore, these intermetallic compounds suppress grain coarsening, thus allowing for solution treatment at higher temperatures in the manufacture of copper alloy sheets, which is advantageous for achieving sufficient Ti solution. Ag, Mo, Sn, and Ta have solid solution strengthening effects and improve stress mitigation properties. Be (Be) forms CuBe precipitates, which can help improve strength and electrical conductivity. Zn (Zn) not only improves weldability and strength but also enhances castability. Mg (Mg) improves stress mitigation and has a desulfurization effect. Si (Si) can form compounds with Ti, which helps with recrystallization during copper alloy sheet manufacturing, resulting in smaller grain diameters. Cr (Cr) and Zr (Zr) are effective for dispersion reinforcement and suppressing grain coarsening. Mn (Mn) and V (V) readily form high-melting-point compounds with S (S), and B (B) and P (P) have a finer casting structure effect, thus each contributing to improved hot workability. Hf (Hf) reduces the solid solution limit of Ti, thus effectively increasing the amount of precipitates formed during aging and improving electrical conductivity.

[0042] Rare earth elements (REM) are Sc (scandium), Y (yttrium), and the lanthanides (excluding Pm (promethium)) in Group 3 of the periodic table. The presence of rare earth elements is effective for grain refinement and precipitate dispersion. Cerium-lanthanum alloys (mixtures of rare earth elements) can be used as a source of rare earth elements.

[0043] Ti and the balance of any of the above elements can become Cu (copper) and unavoidable impurities.

[0044] The content of any of the above elements can be in the range of Ag: 0-0.30%, Al: 0-3.00%, B: 0-0.30%, Be: 0-0.15%, Co: 0-1.00%, Cr: 0-1.00%, Fe: 0-1.00%, Hf: 0-1.00%, Mg: 0-1.00%, Mn: 0-1.50%, Mo: 0-1.00%, Nb: 0-0.50%, Ni: 0-1.50%, P: 0-0.20%, S: 0-0.20%, Si: 0-1.00%, Sn: 0-1.50%, Ta: 0-1.00%, V: 0-1.00%, Zn: 0-2.00%, Zr: 0-1.00%, and the total of rare earth elements: 0-3.00%. These optional elements can be contained in a total of less than 4.00% by mass.

[0045] For rare earth elements, for example, it is possible to list a range containing one or more of the following: La (lanthanum): less than 2.00%, Ce (cerium): less than 1.80%, Pr (praseodymium): less than 0.30%, Nd (neodymium): less than 0.80%, Sm (samarium): less than 2.50%, and Y (yttrium): less than 2.50%, with a total content of rare earth elements of less than 3.00%.

[0046] Furthermore, more preferred content ranges for the aforementioned optional elements include Ag: 0–0.20%, Al: 0–2.50%, B: 0–0.20%, Be: 0–0.10%, Co: 0–0.80%, Cr: 0–0.80%, Fe: 0–0.80%, Hf: 0–0.80%, Mg: 0–0.80%, Mn: 0–1.00%, M O: 0–0.80%, Nb: 0–0.30%, Ni: 0–1.00%, P: 0–0.15%, S: 0–0.15%, Si: 0–0.80%, Sn: 0–1.00%, Ta: 0–0.80%, V: 0–0.80%, Zn: 0–1.50%, Zr: 0–0.80%, and the total rare earth elements are in the range of 0–2.50%. In this case, the total content of these optional elements is preferably set to 3.00% or less.

[0047] As a more preferred range of rare earth element content considering economy and manufacturability, for example, a range can be listed that includes one or more rare earth elements selected from La: 0.30% or less, Ce: 0.70% or less, Pr: 0.20% or less, Nd: 0.30% or less, Sm: 0.20% or less, and Y: 0.40% or less, with a total rare earth element content of 2.50% or less.

[0048] Furthermore, as further preferred content ranges for the aforementioned optional elements, examples include Ag: 0–0.10%, Al: 0–1.60%, B: 0–0.07%, Be: 0–0.04%, Co: 0–0.30%, Cr: 0–0.30%, Fe: 0–0.20%, Hf: 0–0.15%, Mg: 0–0.30%, and Mn: 0–0.50%. Mo: 0–0.30%, Nb: 0–0.15%, Ni: 0–0.50%, P: 0–0.07%, S: 0–0.07%, Si: 0–0.30%, Sn: 0–0.50%, Ta: 0–0.20%, V: 0–0.30%, Zn: 0–0.70%, Zr: 0–0.40%, and the total rare earth elements are in the range of 0–1.00%. In this case, the total content of these optional elements is preferably 2.00% or less.

[0049] As a more preferred range of rare earth element content that takes into account economic efficiency and manufacturability, for example, a range can be listed that includes one or more rare earth elements selected from La: 0.18% or less, Ce: 0.35% or less, Pr: 0.10% or less, Nd: 0.15% or less, Sm: 0.10% or less, and Y: 0.20% or less, with a total rare earth element content of 1.00% or less.

[0050] For elements other than those mentioned above, their presence is permitted within a range that does not hinder the objectives of the present invention (maintaining high strength after high-temperature holding and significantly improving the bonding strength at the diffusion joint). Specifically, the total content of elements other than Ti, Ag, Al, B, Be, Co, Cr, Fe, Hf, Mg, Mn, Mo, Nb, Ni, P, S, Si, Sn, Ta, V, Zn, Zr, rare earth elements, and Cu (hereinafter sometimes referred to as "non-specified elements") is preferably 0.50% or less, and can be managed to be 0.10% or less. The content of non-specified elements can be quantitatively determined, for example, by using the following analytical methods to quantify substantially all elements that may be contained in the copper alloy sheet.

[0051] (Example of quantitative method for alloy elements)

[0052] O (oxygen) and N (nitrogen) are quantified using an oxygen-nitrogen-hydrogen analyzer (e.g., LECO, ONH-836), H (hydrogen) is quantified using a hydrogen analyzer (e.g., Horiba Manufacturing Co., Ltd., EMGA-921), C (carbon) and S (sulfur) are quantified using a carbon-sulfur analyzer (e.g., LECO, CS844), elements in periods 2 to 6 (excluding C, N, O, Group 17 elements, Group 18 elements, Tc (technetium), Po (polonium), and Pm (promethium)) are quantified using ICP-MS (e.g., Agilent, 7900), and F (fluorine), Cl (chlorine), and Br (bromine) are quantified using a combustion-ion chromatography apparatus (e.g., Thermo Scientific, DIONEX ICS-1600).

[0053] Regarding the chemical composition of the copper alloy sheet according to the present invention, in addition to being determined as “Ti, the above-mentioned optional elements (including cases where the total is 0% by mass), and the balance being Cu and unavoidable impurities”, it can also be determined as “Ti, the above-mentioned optional elements (including cases where the total is 0% by mass), the above-mentioned unspecified elements (including cases where the total is 0%), and the balance being Cu”.

[0054] [Maximum surface roughness Rz]

[0055] To improve the diffusion bonding properties of metallic materials, it is generally considered effective to reduce the surface roughness of the two metal materials that form the bonding surface. Various studies have shown that, in the case of the Cu-Ti copper alloy with the composition described above, which is the subject of this invention, in order to stably maintain a high bonding strength at the diffusion joint, it is important that the maximum height roughness Rz in the rolling right-angle direction (the direction orthogonal to the rolling direction on the plate surface) is 1.5 μm or less, and even more effective to be 1.1 μm or less. Furthermore, the maximum height roughness Rz is typically 0.2 μm or more. Here, Rz refers to the maximum height roughness specified in JIS B0601:2013. The maximum height roughness Rz in the rolling right-angle direction can be controlled to a small value by strictly managing the surface roughness of the work rolls used in the final cold rolling process (finish cold rolling).

[0056] [The unfolded area of ​​the board is greater than Sdr]

[0057] In the Cu-Ti copper alloy sheet with the composition described above, which is the subject of this invention, the maximum height roughness Rz specified above is insufficient to significantly improve the bonding strength of the diffusion joint; further surface smoothness is required. According to the inventors' research, by satisfying the aforementioned Rz requirement and exhibiting a surface property with a spread area ratio Sdr of 0.10 or less as measured by a laser microscope, a very high bonding strength exceeding that of pure copper can be obtained at the diffusion joint. The spread area ratio Sdr is an indicator of the proportion to which the actual surface area, including the surface irregularities, of the material surface when observed in a field of view is large relative to the area of ​​that field of view (projected area). This spread area ratio Sdr is a surface parameter specified in ISO 25178 and can be measured using a confocal laser microscope. Specifically, the measurement method shown in the embodiments described later can be used. A spread area ratio Sdr of 0.10 or less is more preferable, and it can also be adjusted to 0.05 or less. To control the unfolded area ratio Sdr to a small value, it is effective to strictly manage the surface roughness of the work rolls used in the final cold rolling process (finish cold rolling) as described above, and to keep the rolling rate in this rolling process low. However, if the rolling rate is too low, it is difficult to make the maximum height roughness Rz mentioned above converge to the specified range. Therefore, the unfolded area ratio Sdr is usually adjusted in the range of 0.01 or higher.

[0058] [Thickness of the oxygen enrichment layer on the panel]

[0059] Near the surface of Cu-Ti copper alloy plates, there is typically a region with a higher oxygen concentration than the interior, after the final heat treatment process (fine heat treatment) has been completed in a non-oxidizing atmosphere. In this specification, the surface region from the outermost surface to the SiO2 equivalent depth (nm) where the proportion of O in the four elements is less than 5.0 atomic percent, as measured by XPS (X-ray photoelectron spectroscopy), is referred to as the "oxygen-rich layer".

[0060] exist Figure 1 The diagram shows an example of the elemental concentration distribution along the depth direction from the outermost surface of a Cu-Ti copper alloy sheet according to the present invention, obtained using XPS. The scale on the horizontal axis represents the SiO2 equivalent depth (nm) from the outermost surface. In this example, the proportion of O in a total of 100 atomic percent of Cu, Ti, O, and C ultimately results in a SiO2 equivalent depth of 3.2 nm of less than 5.0 atomic percent (i.e., not exceeding 5.0 atomic percent). Therefore, the thickness of the oxygen-enriched layer determined from this elemental concentration distribution is 3.2 nm.

[0061] According to the inventors' research, a thinner oxygen-enriched layer is advantageous for improving the bonding strength at the diffusion junction. Specifically, the thickness of the oxygen-enriched layer is preferably 100 nm or less, more preferably 50 nm or less, and a thickness of 10 nm or less is also achievable. In the final heat treatment process (fine heat treatment) performed in a non-oxidizing atmosphere, when comparing under the same atmosphere, the thickness of the oxygen-enriched layer is affected by the temperature and holding time during the heat treatment; in particular, shortening the holding time as much as possible is effective in reducing the thickness of the oxygen-enriched layer. It should be noted that the thickness of the oxygen-enriched layer is typically 1 nm or more.

[0062] [0.2% yield strength after holding at high temperature]

[0063] When assembling the housing of a vapor chamber, the upper plate component and the bottom plate component, which serve as the housing components, are generally diffuse-bonded or brazed at their edges to create a cavity for working fluid circulation inside. During bonding, the housing components are heated and maintained at a high temperature (e.g., around 800°C in the case of diffusion bonding). Therefore, the metal material used in the housing components does not experience a significant reduction in strength due to softening during high-temperature holding, which is important in constructing a vapor chamber with high durability. According to the inventors' research, to adequately address the increasing performance requirements of processors used in electronic devices, it is desirable to use copper alloy sheets with a yield strength of 400 MPa or more in the rolling direction after a heat treatment test at 800°C for 1 hour in a nitrogen atmosphere, exhibiting resistance to softening. For the Cu-Ti copper alloy sheet of the present invention containing the aforementioned specified amount of Ti, the aforementioned resistance to softening is sufficiently satisfied, and excellent resistance to softening, achieving a yield strength of 600 MPa or more, or 720 MPa or more, after high-temperature holding, is also achieved. There is no particular limit to the upper limit of the 0.2% yield strength after holding at high temperature, which is usually below 800 MPa.

[0064] [Conductivity after high temperature maintenance]

[0065] In recent years, with the miniaturization and lightweighting of mobile devices, the demand for thinner vapor chambers used in mobile devices has also increased. To achieve thinner vapor chambers, reducing the thickness of the upper and lower plates constituting the vapor chamber's casing is effective. In this case, the casing's contribution to thermal resistance decreases, thus the importance of improving the thermal conductivity (electrical conductivity) of the sheet metal used for the casing is relatively reduced compared to factors such as strength after maintaining high temperatures. According to the inventors' research, if the electrical conductivity of the copper alloy sheet metal used for the casing of a thin vapor chamber is, for example, 10.0% IACS or higher after a heat treatment test at 800°C for 1 hour in a nitrogen atmosphere, it can be determined that it has a level of electrical conductivity that is practically acceptable. It should be noted that the electrical conductivity of the copper alloy sheet metal of the present invention is typically 20.0% IACS or lower.

[0066] [Thickness of the titanium-enriched layer on the plate surface after high-temperature holding]

[0067] As described above, in Cu-Ti based copper alloy sheets, when maintained at high temperatures in a non-oxidizing atmosphere, Ti enrichment is observed near the surface of the sheet. In this specification, for Cu-Ti based copper alloy sheet products (products that have undergone the fine heat treatment described later) that have undergone heat treatment at 800°C in a nitrogen atmosphere for 1 hour, when the elemental concentration distribution of Cu, Ti, O, C, and N in the depth direction is determined by XPS (X-ray photoelectron spectroscopy), the surface region with a SiO2 equivalent depth (nm) where the proportion of Ti in the total 100 atomic% of the five elements from the outermost surface is 9.0 atomic% or less (i.e., not exceeding 9.0 atomic%) is referred to as a "titanium-enriched layer." It is speculated that the formation of such a titanium-enriched layer contributes to improving the bonding strength of the diffusion joint. Preferably, the titanium-enriched layer has a thickness of 50 nm or more, more preferably 100 nm or more. The titanium-enriched layer is typically 300 nm or less. The property of fully forming a titanium-enriched layer can be obtained by setting the Ti content in the copper alloy to 2.00–5.00% by mass.

[0068] [Joint strength of the diffusion joint]

[0069] As described above, when the Cu-Ti copper alloy sheet according to the present invention is used as a material for assembling a heat exchanger shell, for example, when diffusion bonding is performed at around 800°C, it does not cause a significant decrease in strength due to high-temperature softening. Furthermore, when diffusion bonding is performed using the Cu-Ti copper alloy sheet, a diffusion bond with very high bonding strength can be formed. Specifically, the copper alloy sheet according to the present invention has the property that the bonding strength of the diffusion bond obtained by the method described in the embodiments described later is 75 MPa or more, and bonding strengths of 90 MPa or more, or 120 MPa or more, can also be achieved. Higher bonding strength is more preferred, and it is typically 250 MPa or less. From the viewpoint of achieving exceptionally high bond strength, Cu-Ti copper alloy sheets with a Ti content of 2.80% by mass or more and an area ratio (Sdr) of 0.08 or less are preferred. Cu-Ti copper alloy sheets with a Ti content of 2.80% by mass or more, a maximum vertical roughness (Rz) of 1.1 μm or less, and an area ratio (Sdr) of 0.06 or less are even more preferred. Among these, a Ti content of 3.00% by mass or more is even more effective.

[0070] [Manufacturing Method]

[0071] The copper alloy sheet described above can be manufactured using, for example, the following manufacturing processes.

[0072] Melting and casting → Hot working → Rough cold rolling → Solution treatment → Aging treatment → Finish cold rolling → Finish heat treatment

[0073] Although not described in the above steps, surface shaving is performed as needed after heat treatment, and pickling, grinding, or further degreasing is performed as needed after each heat treatment. The following describes each of the above steps.

[0074] [Melting & Casting]

[0075] Castings with the chemical composition specified in this invention can be manufactured using crucible furnaces or similar methods. To prevent oxidation of Ti, a non-reactive gas atmosphere or a vacuum melting furnace can be used.

[0076] [Hot working, rough and cold rolling]

[0077] Heating the cast sheet before hot working can be performed, for example, by holding it at 900–1000°C for 0.5–5 hours. There are no particular limitations on the hot working method. Hot rolling and hot forging are commonly used. In the case of hot rolling, the total hot rolling ratio can be set to, for example, 60–99%. After hot working, rapid cooling, such as by water cooling, is preferred. Then, cold rolling is performed. In this specification, the cold rolling in this stage is referred to as "rough cold rolling." The rolling ratio in rough cold rolling can be set to, for example, 50–99%. This yields intermediate sheet material for solution treatment.

[0078] [Solution treatment]

[0079] For the aforementioned intermediate product sheets, a solution treatment is performed. The solution treatment method can be a conventional method. For example, it can be performed by holding the intermediate product sheets at 800–1050°C for 10–1000 seconds.

[0080] [Time-sensitive processing]

[0081] For materials that have undergone solution treatment, aging treatment is performed. Aging treatment can be carried out by holding the material at 400–600°C, preferably 400–500°C, for 1–24 hours. This causes fine precipitates to form, thereby increasing the strength of the copper alloy sheet.

[0082] [Cold Rolled Steel]

[0083] After aging treatment, a finishing cold rolling process is performed with a rolling rate of 5.0–20.0%, preferably 10.0–15.0%, for the purpose of adjusting the final plate thickness and the surface smoothness of the plate. The final plate thickness can be adjusted, for example, within the range of 0.01–0.50 mm, depending on the application. In this finishing cold rolling, it is important to use work rolls with strictly controlled surface roughness. Specifically, work rolls with a maximum height roughness Rz (JIS B0601:2013) of 1.7 μm or less, more preferably 1.2 μm or less, in the roll axis direction are used. Extreme smoothing of the work roll surface leads to increased costs, so generally the Rz of the work roll surface only needs to be adjusted within the range of 0.20 μm or more. If the Rz of the work roll surface is too large, it is difficult to stably adjust the maximum height roughness Rz of the plate surface in the rolling right-angle direction to the specified range mentioned above. Furthermore, if the rolling rate is too low, the shape of the highly smooth work roll surface cannot be adequately transferred to the material sheet surface, making it difficult to stably adjust the Rz of the sheet surface within the specified range. On the other hand, if the rolling rate is too high, the unfolded area ratio Sdr of the material sheet surface increases. Therefore, from the viewpoint of maximizing the bonding strength of the diffusion joint, the management of the surface properties of the work rolls and the management of the rolling rate are extremely important in precision cold rolling. In particular, in order to control the unfolded area ratio Sdr of the obtained sheet to a low value, for example, 0.08 or less, and improve the bonding strength of the diffusion joint, it is effective to manage the upper limit of the rolling rate to a range of 15.0% or less. In addition, if the goal is to further improve the bonding strength of the diffusion joint by controlling the unfolded area ratio Sdr of the obtained sheet to a lower value, for example, 0.06 or less, and controlling the maximum height roughness Rz to a low value, for example, 1.1 μm or less, it is more effective to use work rolls with the maximum height roughness Rz in the roll axis direction managed to be below 1.2 μm.

[0084] [Precision Heat Treatment]

[0085] For materials that have undergone precision cold rolling, a precision heat treatment is performed, holding the material at 300–500°C for 10–300 seconds, more preferably at 400–470°C for 30–200 seconds. This reduces the lattice distortion energy introduced by precision cold rolling, thereby improving processability. This precision heat treatment is performed in a non-oxidizing atmosphere, which can be carried out in continuous or intermittent annealing furnaces in the manufacture of Cu-Ti copper alloy sheets. Even when heat treatment is performed in a non-oxidizing atmosphere, it is difficult to completely avoid oxygen intrusion in the area near the outermost surface of the sheet; normally, this oxygen intrusion is not a problem in the material properties. However, according to the inventors' research, in applications for diffusion bonding, from the viewpoint of maximizing the bonding strength at the diffusion bonding joint, it is preferable to minimize oxygen intrusion to the area near the outermost surface, i.e., to control the thickness of the aforementioned oxygen-rich layer to prevent excessive thickening. Therefore, this precision heat treatment is performed with a short heating holding time of 300 seconds or less, or 200 seconds or less, which can be performed using a continuous annealing furnace.

[0086] [Heat Spreader]

[0087] For the copper alloy sheet of the present invention described above, the material strength after exposure to the high temperatures (e.g., around 800°C in diffusion bonding) during diffusion bonding and brazing is very high compared to pure copper. Furthermore, regarding the bonding strength of the diffusion bonding portion, which is desirable to improve in conventional Cu-Ti copper alloys, a very high bonding strength exceeding that of pure copper can be obtained. Therefore, a heat exchanger with a housing having a structure in which two or more components using the copper alloy sheet according to the present invention are joined by diffusion bonding or brazing exhibits superior durability compared to conventional heat exchangers using pure copper sheets or known Cu-Ti copper alloy sheets.

[0088] Example

[0089] Except for Comparative Example No. 48, copper alloys with the chemical compositions shown in Tables 1 to 4 were melted, and the resulting cast sheets were heated and hot-rolled to the thicknesses recorded in Tables 1 to 4, followed by water cooling. After hot rolling, the surface oxide layer was removed by mechanical grinding (surface grinding), and then rough cold rolling was performed under the conditions in Tables 1 to 4 to obtain intermediate product sheets for solution treatment. However, in Comparative Example No. 46, homogenization annealing was performed before rough cold rolling, and in Comparative Example No. 50, intermediate annealing and intermediate cold rolling were performed after rough cold rolling.

[0090] Furthermore, except for Comparative Example No. 48, elemental analysis was performed on the analytical samples taken from the castings using the methods described in the "Examples of Quantitative Methods for Alloy Elements" above. The results showed that, in all examples, the total content of elements other than Ti, Ag, Al, B, Be, Co, Cr, Fe, Hf, Mg, Mn, Mo, Nb, Ni, P, S, Si, Sn, Ta, V, Zn, Zr, rare earth elements, and Cu was less than 0.10%.

[0091] Except for Comparative Example No. 48, for the aforementioned intermediate product sheets, solution treatment, aging treatment, fine cold rolling, and fine heat treatment were performed in the following order under the conditions shown in Tables 1 to 4, resulting in test materials for various evaluations described later. However, in Comparative Example No. 42, the subsequent processes were halted because cracks occurred in the material during hot rolling. In Comparative Example No. 46, intermediate cold rolling and a second solution treatment were performed before aging treatment. Processes indicated by "-" (hyphen) in Tables 1 to 4 are those that were not performed. Fine heat treatment was performed under a nitrogen atmosphere. The sheet thickness of the test materials is shown in the "Final Sheet Thickness" column. Furthermore, in Comparative Example No. 48, commercially available pure copper (C1020) sheet (0.30 mm thick) was used as the test material.

[0092] For the work rolls used in cold finishing rolling, the surface roughness of the rolls in the direction parallel to the roll axis was measured using a SURFCOM1400G machine manufactured by Tokyo Seimitsu Co., Ltd. before use. The maximum height roughness Rz (JIS B0601:2013) obtained by this measurement is shown in the table.

[0093] The following investigation was conducted on each of the tested materials.

[0094] (XPS measurement)

[0095] The samples cut from each test material were heat-treated by holding them at 800°C in a nitrogen atmosphere for 1 hour and then air-cooling them. The samples after this heat treatment are referred to as "samples after high-temperature holding".

[0096] Elemental analysis was performed using XPS from the surface to depth on both the test material samples (after heat treatment) and the samples held at high temperatures. The XPS apparatus used was a ULVAC-PHI PHI5000 Versa ProbeIII. Analytical area: φ100μm, accelerating voltage: 15kV, power: 140eV, X-ray source: monochromatic AlKα, X-ray source output: 25W, analytical angle: 45°. For determining atomic concentrations, Cu, Ti, O, C, and N were analyzed using 2p orbitals, 1s orbitals, and 1s orbitals respectively. The mole fractions of Cu, Ti, O, C, and N were calculated using the built-in computer. The Shirley method was used for background processing. Surface sputtering for depth-direction analysis was performed using an argon ion gun with Ar ion species. + The process was carried out under the following conditions: accelerating voltage: 2kV, emission current: 7mA, sputtering rate: 5nm / min (SiO2 conversion).

[0097] For the test material sample (in the state after fine heat treatment), the SiO2 equivalent depth (nm) with the proportion of O in Cu, Ti, O and C being less than 5.0 atomic% is set as the thickness of the oxygen enrichment layer.

[0098] For samples held at high temperatures, the SiO2 equivalent depth (nm) with a proportion of Ti of Cu, Ti, O, C, and N of less than 9.0 atomic% is set as the thickness of the titanium enrichment layer.

[0099] It should be noted that, in the case where Ti has not diffused to the surface (sample before high-temperature holding), the proportion of Ti mentioned above is mostly less than 4.0 atoms.

[0100] (Rz in the right-angle direction of the rolling process on the sheet)

[0101] For the surface of the test material, the maximum height roughness Rz in the rolling right-angle direction (TD) was measured using a contact surface roughness tester (SURFCOM1400G, Tokyo Seimitsu Co., Ltd.) according to JIS B0601:2013. The measurement was performed with a repetition count of n=5, and the arithmetic mean was used as the Rz value of the test material.

[0102] (The unfolded area of ​​the plate is greater than Sdr)

[0103] For the surface of the test material, the unfolded area ratio (Sdr) as specified in ISO 25178 was determined using a laser microscope (KEYENCE VX-X3000 series laser microscope, manufactured by KEYENCE Co., Ltd.) according to the following method. The sample cut from the test material was set laterally with the rolling direction as the field of view of the microscope. Note that the laser microscope objective magnification was 50x, the scanning mode was focal-shift, the measurement size was 1024 × 768, the measurement quality was standard, and the spacing was 0.16 μm. Furthermore, the Sdr calculation was performed under the filter treatment and calculation conditions shown below.

[0104] S-filter: None

[0105] F-operation: Plane tilt correction

[0106] L-filter: None

[0107] Calculated object area: 270μm × 200μm

[0108] The Sdr values ​​were measured at five randomly selected, non-repeating fields of view, and the arithmetic mean of the Sdr values ​​obtained in each field of view was used as the Sdr value of the test material.

[0109] (Joint strength of the diffusion joint)

[0110] Two sheet metal samples, each approximately 25 mm wide and cut from the test material with the rolling direction along their longitudinal axis, are overlapped to form a 3.0 mm × 2.5 mm (7.5 mm²) area at the center of the overlap. 2 The carbon sheet was clamped in the area excluding the central portion of the joint and diffusion bonding was performed. For diffusion bonding, hot pressing was used in a nitrogen atmosphere, with a bonding area of ​​7.5 mm². 2 The bonding was conducted under the following conditions: a bonding load of 10 kN, a bonding temperature of 800 °C, and a bonding time of 1 h. To apply shear force to the diffusion joint, one end of a sheet metal specimen was restrained by the upper chuck of a tensile testing machine (Shimadzu AG-X), and the end of another sheet metal specimen was restrained by the lower chuck. Tensile tests were performed at room temperature at a tensile speed of 1.0 mm / min. The load at joint fracture was divided by the initial area of ​​the joint (7.5 mm²). 2 The fracture stress (MPa) per unit area determined is used as the bond strength. The test is conducted with a repetition count n=5, and the arithmetic mean of the five bond strength values ​​is used as the bond strength value of the test material. A pure copper plate specimen, considered to have good diffusion bonding properties, achieved a bond strength of 72 MPa under the same conditions (refer to Comparative Example No. 48). Therefore, bond strengths exceeding 75 MPa are considered acceptable.

[0111] exist Figure 2 The diagram schematically illustrates the state in which test specimens for determining the bond strength of diffusion joints are placed in a tensile testing machine. The left image is the front view, and the right image is the side view. A diffusion joint 2 exists at the overlapping portion of plate specimens 1a and 1b. The end of plate specimen 1a is constrained to the upper chuck 3a of the tensile testing machine, and the end of plate specimen 1b is constrained to the lower chuck 3b. A tensile load is applied in the direction of the arrow shown in the figure. It should be noted that, at the ends of plate specimens 1a and 1b not held by the chucks, to avoid interference with the chucks or other clamps, the plate specimens are bent in opposite directions relative to the bonding partner (bonding object) by a method in which no stress is applied to the diffusion joint. The thickness of plate specimens 1a and 1b is exaggerated in the figure.

[0112] (Drop test of diffusion bonding test piece)

[0113] For reference, a drop test was conducted on a diffusion bonding test piece according to the method described in paragraph 0057 of Patent Document 1, and the diffusion bonding performance was evaluated. Specifically, it is described below.

[0114] Two 15mm × 15mm plates cut from the test material were overlapped, clamped in a fixture for fixation, and placed in a tubular furnace under a stress of 0.9 MPa. After being held at 800°C in a nitrogen atmosphere for 1 hour, they were air-cooled, resulting in a test piece where the two plates were integrated through diffusion bonding. The test piece was then subjected to 100 free-fall drops from a height of 30cm onto asphalt at an unspecified angle. If peeling occurred at the joint between the plates during the drop test, the drop test was stopped at that point. The end faces of the test piece after the drop test were observed using an optical microscope to examine whether gaps were formed at the joints between adjacent plates. This test was conducted with a test number n = 3. As a result, any test piece without peeling and without gaps at the joints between the plates was rated ○ (diffusion bonding: good), and all others were rated × (diffusion bonding: poor).

[0115] (0.2% yield strength after holding at high temperature)

[0116] For samples cut from each test material, heat treatment was carried out at 800°C for 1 hour in a nitrogen atmosphere followed by air cooling to obtain "samples after high-temperature holding". Tensile test pieces (JIS No. 5) were rolled parallel to the samples after high-temperature holding and subjected to tensile tests according to JIS Z2241 with a test number n=3 to determine the 0.2% yield strength. The average value of n=3 was taken as the score value for that test material.

[0117] The results are shown in Tables 1 to 4.

[0118] (Conductivity after being kept at high temperature)

[0119] Samples cut from each test material were held at 800°C for 1 hour in a nitrogen atmosphere and then subjected to heat treatment under air cooling to obtain "samples after high-temperature holding". The conductivity of the samples after high-temperature holding was measured using an eddy current conductivity meter (manufactured by Matec Co., Ltd., Japan, SigmaCheck) with the probe frequency set to 480 kHz. Calibration before measurement was performed using standard test pieces of copper (100.62% IACS) and cupronickel (8.644% IACS). Conductivity measurements were performed with a test number n=3, and the average value of n=3 was taken as the score for the test material.

[0120] Table 1

[0121] Table 1

[0122]

[0123] Table 2

[0124] Table 2

[0125]

[0126] Table 3

[0127] Table 3

[0128]

[0129] Underlined: Outside the scope of this invention

[0130] Table 4

[0131] Table 4

[0132]

[0133] Underlined: Outside the scope of this invention

[0134] In the copper alloy sheets of the embodiments where the chemical composition and sheet manufacturing conditions were controlled within the reasonable ranges described above, a high yield strength of 0.2% above 400 MPa was maintained after high-temperature holding. Furthermore, the sheets obtained in the embodiments all had sufficiently small maximum surface roughness Rz and unfolded area ratio Sdr, resulting in very high bond strength at the diffusion joints. These sheets possess the properties of a sufficiently thin oxygen-enriched layer on the surface and the sufficient formation of a titanium-enriched layer after high-temperature holding.

[0135] In Comparative Example No. 41, the strength level (0.2% yield strength) after high-temperature holding was low due to insufficient Ti content. Furthermore, the titanium enrichment layer did not fully form after high-temperature holding, resulting in a poor performance; although the drop test was rated 0, the bonding strength of the diffusion joint was low.

[0136] In No. 42, due to excessive Ti content, cracks were generated in the material during hot rolling, making it impossible to proceed with subsequent processes.

[0137] In No. 43 and 44, due to the use of ordinary work rolls in the finishing cold rolling process that did not strictly manage the Rz in the roll axis direction to a small value, the sheet material with a sufficiently small Rz on the sheet surface was not obtained. Although the drop test was rated as ○, the bonding strength of the diffusion joint was low.

[0138] In No. 45, the rolled rate in the cold rolling process was too high, so the unfolded area ratio of the sheet was not sufficiently reduced to Sdr. Although the drop test was rated as 0, the bonding strength of the diffusion joint was low.

[0139] Example No. 46 illustrates a known manufacturing process involving multiple solution treatments. In this example, a work roll with Rz controlled as specified in this invention was used in the finishing cold rolling, but its rolling rate was too high, thus failing to sufficiently reduce the sheet's unfolded area ratio Sdr. Although the drop test yielded a zero rating, the bonding strength of the diffusion joint was low. Furthermore, in this example, the finishing heat treatment was performed under conditions of heating and holding in an intermittent annealing furnace for 3 hours, resulting in a considerably thick oxygen-enriched layer on the obtained sheet. Compared to No. 45, the bonding strength of the diffusion joint in No. 46 is further reduced; therefore, it is considered preferable to reduce the thickness of the oxygen-enriched layer to improve the bonding strength at the diffusion joint.

[0140] Examples No. 47 and 49 use Ti-free copper alloys (Cossen series copper alloys). In these cases, the strength level after high-temperature holding (0.2% yield strength) is low, and the diffusion bonding is rated as × in drop tests, with the bonding strength also being quite low.

[0141] Example No. 48 uses commercially available pure copper (C1020). The diffusion bonding properties of pure copper are considered good among copper-based materials, and a bond strength of 72 MPa was achieved in the diffusion joint of this example. However, the strength level after high-temperature holding (0.2% yield strength) is significantly lower than other examples (Cu-Ti copper alloys, Coxon copper alloys).

[0142] Example No. 49 illustrates a known manufacturing process that sandwiches intermediate annealing and intermediate cold rolling between rough cold rolling and solution treatment. In the finish cold rolling, conventional work rolls are used without strictly controlling the Rz in the roll axis direction to a small value. In this case, a sheet with a sufficiently small Rz on the sheet surface is not obtained, and although the drop test is rated as ○, the bonding strength of the diffusion joint is low.

Claims

1. Copper alloy sheet, having the following chemical composition (by mass%): Ti: 2.00–5.00%, Ag: 0–0.30%, Al: 0–3.00%, B: 0–0.30%, Be: 0–0.15%, Co: 0–1.00%, Cr: 0–1.00%, Fe: 0–1.00%, Hf: 0–1.00%, Mg: 0–1.00%, Mn: 0–1.50%, Mo: 0–1.00%, Nb: 0–0.50%, Ni: 0–1.50%, P: 0–0. 0.20%, S: 0-0.20%, Si: 0-1.00%, Sn: 0-1.50%, Ta: 0-1.00%, V: 0-1.00%, Zn: 0-2.00%, Zr: 0-1.00%, Total rare earth elements: 0-3.00%, Ag, Al, B, Be, Co, Cr, Fe, Hf, Mg, Mn, Mo, Nb, Ni, P, S, Si, Sn, Ta, V, Zn, Zr and total rare earth elements: less than 4.00%, balance composed of Cu and unavoidable impurities. The maximum height roughness Rz in the rolling right-angle direction of the plate surface is less than 1.5 μm, and the unfolded area ratio Sdr of the plate surface measured by laser microscope is less than 0.

10.

2. The copper alloy sheet according to claim 1, wherein, In the elemental concentration distribution of Cu, Ti, O, and C measured by XPS (X-ray photoelectron spectroscopy) along the depth direction, when the surface region from the outermost surface to the SiO2 equivalent depth (nm) where the proportion of O in the four elements is less than 5.0 atomic%, is called the oxygen enrichment layer, the thickness of the oxygen enrichment layer is less than 100 nm.

3. The copper alloy sheet according to claim 1, wherein, The yield strength of 0.2% in the rolling direction after a heat treatment test in a nitrogen atmosphere at 800°C for 1 hour is above 400 MPa.

4. The copper alloy sheet according to claim 1, wherein, The plate thickness is 0.01 to 0.50 mm.

5. The copper alloy sheet according to claim 1, wherein, In the chemical composition, the Ti content is 2.80-5.00%, and the unfolded area ratio Sdr is below 0.

08.

6. The copper alloy sheet according to claim 1, wherein, In the chemical composition, the Ti content is 2.80-5.00%, the maximum height roughness Rz is less than 1.1 μm, and the unfolded area ratio Sdr is less than 0.

06.

7. The copper alloy sheet according to claim 1, used in the heat spreader shell.

8. The method for manufacturing the copper alloy plate according to claim 1, wherein, When intermediate product plates are sequentially subjected to solution treatment, aging treatment, precision cold rolling, and precision heat treatment to manufacture copper alloy plates... The precision cold rolling is performed using work rolls with a maximum height roughness Rz of 1.7 μm or less in the axial direction, under conditions where the rolling rate is set to 5.0–20.0%. The fine heat treatment is performed at 300–500°C for 10–300 seconds.

9. A heat spreader having a housing having a structure in which two or more components using copper alloy sheet as described in any one of claims 1 to 7 are joined by diffusion bonding or brazing.

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