Corrosion-resistant copper alloy, copper alloy tube, and heat exchanger

Abstract

Provided are: a corrosion-resistant copper alloy which has excellent processability and excellent corrosion resistance over a long period of time against formicary corrosion in the presence of a lower carboxylic acid; a copper alloy tube which uses the corrosion-resistant copper alloy; and a heat exchanger. The present invention relates to a corrosion-resistant copper alloy comprising at least one alloy component selected from metals having a lower standard electrode potential than Al, the remainder comprising Cu and unavoidable impurities, the total content of the alloy components being 0.01 mass% or more and less than 0.5 mass%. In addition, the invention relates to a copper alloy pipe using the corrosion-resistant copper alloy. In addition, the present invention relates to a heat exchanger using the copper alloy tube.

Description

[0001] This application is a divisional application of the application filed on April 18, 2022, with application number 202280029143.8 and invention title "Corrosion-resistant copper alloy, copper alloy tube and heat exchanger". Technical Field

[0002] This invention relates to corrosion-resistant copper alloys, copper alloy tubes using such corrosion-resistant copper alloys, and heat exchangers, and particularly to corrosion-resistant copper alloys with improved resistance to anthill corrosion. Background Technology

[0003] Previously, phosphorus-deoxidized copper tubing (JIS H3300 C1220) with excellent thermal conductivity, bendability, and brazing properties was widely used in refrigerant piping and heat exchanger piping. Furthermore, copper tubing typically exhibits excellent corrosion resistance. The corrosion reaction of metals is explained through the transfer of electrons in an electrochemical reaction. The anode, which emits electrons, and the cathode, which receives electrons, are always generated in a symmetrical relationship and are also called the anode and cathode, respectively. For example, in a galvanic cell, the reaction at the anode corresponds to the dissolution reaction of the metal, and the reaction at the cathode corresponds to the deposition reaction of the metal.

[0004] As indicated by the standard electrode potential, Cu has a higher potential than H, therefore H ions cannot induce a cathodic reaction relative to Cu. In the absence of oxidizing agents such as O, there is no cathodic reaction in non-oxidizing acids, and therefore no anodic reaction is possible either. Thus, copper exhibits extremely excellent corrosion resistance in non-oxidizing environments.

[0005] However, in refrigerant piping or heat exchanger piping, a unique form of corrosion known as anthill corrosion sometimes occurs. As mentioned above, Cu has a higher potential than H, so its reaction with acids does not consume H. Once corrosion occurs in an acidic environment, it is difficult to suppress the corrosion rate with Cu alone. As a result, anthill corrosion proceeds rapidly, advancing towards the wall thickness in a short time and penetrating the copper pipe.

[0006] In copper pipes used in heat exchangers such as air conditioners, through-corrosion pits cause refrigerant leakage, rendering the equipment unusable and posing a serious problem. Furthermore, regulations related to leaks of Freon refrigerants, which have a high global warming coefficient, are becoming increasingly stringent in recent years, making strategies to address anthill-like corrosion in copper pipes even more crucial.

[0007] Regarding this issue, the market strongly demanded copper pipes with excellent resistance to ant nest corrosion, leading to the development of technologies like those in patent documents 1-3, which were subsequently commercialized.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 7-19788

[0011] Patent Document 2: International Publication No. 2014 / 148127

[0012] Patent Document 3: Japanese Patent Application Publication No. 6-122932 Summary of the Invention

[0013] The technical problem that the invention aims to solve

[0014] Patent Document 1 discloses a copper alloy containing any one of Zn, Mn, and Mg as an example of copper alloy with excellent resistance to ant nest corrosion. However, the evaluation conditions for resistance to ant nest corrosion are based on the actual cooling and air supply operation of the heat exchanger, so further research is needed to determine its effectiveness against ant nest corrosion under harsh conditions such as the presence of formic acid.

[0015] Patent document 2 discloses a copper alloy with a high phosphorus content as an example of copper alloy with excellent resistance to ant nest corrosion. However, the evaluation period for resistance to ant nest corrosion is as short as 20 days, so further research is needed to determine its effectiveness under prolonged exposure to corrosive environments. In addition, if a large amount of phosphorus is included, the pH of the dissolved portion decreases, posing a risk of increased thinning under acidic conditions.

[0016] Patent document 3 discloses a copper alloy with low phosphorus content as an excellent resistance to anthill corrosion. However, as mentioned above, Cu has a higher potential than H, making it difficult to control the pH within the corrosion pores using only Cu. Therefore, further research is needed to determine its effectiveness against anthill corrosion under more severe conditions.

[0017] Furthermore, depending on the casting method and the raw materials used, the addition or mixing of phosphorus (P) is sometimes unavoidable. Even if the P content is below a given level, if the ratio of P content to the alloy composition is above a certain value, the desired resistance to mermaid corrosion may not be obtained. In addition, a high content of alloying elements in copper alloys can sometimes reduce their machinability.

[0018] The present invention was made in view of the following situation, and its object is to provide a corrosion-resistant copper alloy with excellent processability and excellent corrosion resistance over a long period of time against anthill corrosion in the presence of lower carboxylic acids, copper alloy tubes and heat exchangers using the corrosion-resistant copper alloy.

[0019] means of solving technical problems

[0020] In the acidic environment of anthill corrosion pits, where copper dissolution occurs, Cu has a higher potential than H ions. Therefore, it does not act as a cathode in non-oxidizing acids, and Cu dissolution does not directly consume H ions. Consequently, once corrosion begins in an acidic environment, it is difficult to inhibit the rate of corrosion by Cu alone.

[0021] The inventors have discovered that by adding a base metal with a lower potential than Al at the standard electrode potential to Cu, particularly an element belonging to Group 1 or Group 2 of the long-period periodic table, such as Mg, which is easily soluble in acidic solutions and can raise the pH through dissolution, Mg and Cu can be dissolved together in the micropores. The increase in pH caused by the dissolution of Mg neutralizes the carboxylic acid inside the micropores, thus achieving harmlessness.

[0022] Furthermore, the inventors have discovered that, in order to achieve the desired resistance to ant nest corrosion, there exists an appropriate range in the ratio of the content of the alloying component (X mass%) to the content of P (p mass%) relative to the content of the alloying component (X mass%), such that the carboxylic acid neutralization effect based on the alloying component is not invalidated by P.

[0023] Specifically, such as Figure 4 As shown in the chart, if the horizontal axis is X / p (=x) and the vertical axis is the corrosion depth (y), the following relationship holds with high precision.

[0024] y = -0.0218 × ln(x - 8.87) + 0.295

[0025] This invention was made based on the following insight: that is, the invention has the following structure.

[0026] (1) The corrosion-resistant copper alloy of the present invention comprises at least one alloying element selected from metals with a standard electrode potential lower than Al, the remainder being composed of Cu and unavoidable impurities, and the total content of the alloying elements is more than 0.01% by mass and less than 0.5% by mass.

[0027] If it is such a corrosion-resistant copper alloy, the alloy components can easily dissolve into acidic solutions. The dissolution raises the pH, neutralizing the carboxylic acid inside the pores and thus achieving harmlessness.

[0028] (2) In the corrosion-resistant copper alloy of the present invention, the metal with a standard electrode potential lower than Al is preferably selected from at least one of Li, K, Ca, Na and Mg.

[0029] (3) In addition, in the corrosion-resistant copper alloy of the present invention, the metal with a standard electrode potential lower than Al is preferably selected from at least one of Ca and Mg.

[0030] (4) Furthermore, in the corrosion-resistant copper alloy of the present invention, when the corrosion-resistant copper alloy contains P, the content of P is 0.015% by mass or less, and when the content of the alloy component is set as X% by mass and the content of P is set as p% by mass, the value of X divided by p, i.e., [X / p], is 9.10 or more.

[0031] (5) Furthermore, in the corrosion-resistant copper alloy of the present invention, it is preferable that the [X / p] is 16.60 or more.

[0032] (6) The copper alloy tube of the present invention uses the corrosion-resistant copper alloy described in any one of (1) to (5).

[0033] (7) In addition, the copper alloy tube of the present invention can also be a copper alloy tube with grooves on the inner surface.

[0034] (8) The heat exchanger of the present invention uses the copper alloy tube described in (6) or (7).

[0035] Invention Effects

[0036] The corrosion-resistant copper alloy of this invention exhibits excellent machinability and superior corrosion resistance over extended periods against anthill corrosion in the presence of lower carboxylic acids. Copper alloy tubes and heat exchangers using the corrosion-resistant copper alloy of this invention also demonstrate the same advantages. Attached Figure Description

[0037] [ Figure 1 ] Figure 1 This is a schematic cross-sectional view of the test container used in the evaluation of resistance to ant nest corrosion.

[0038] [ Figure 2 ] Figure 2 The diagram shows the dimensions of the test material made of copper alloy used in the evaluation of resistance to ant nest corrosion. (a) is a top view of the test material, and (b) is a perspective view of the test material.

[0039] [ Figure 3 ] Figure 3 (a), (b), and (c) are schematic diagrams illustrating the operational steps of the solder wettability evaluation test.

[0040] [ Figure 4 ] Figure 4 This is a graph showing the relationship between the value of [X / p] and the depth of corrosion. Detailed Implementation

[0041] The embodiments of the corrosion-resistant copper alloy of the present invention will be described in detail below.

[0042] Anthill corrosion occurs as follows: For the dissolution of copper in the anode (equation (1) below), the copper surface, which undergoes a reduction reaction of dissolved oxygen in a humid environment (equation (2) below), becomes the cathode, and lower carboxylic acids such as formic acid and acetic acid act as corrosion promoters. These corrosion promoters are known to be generated from lubricating oils, processing oils, organic solvents used in pipe manufacturing and heat exchanger assembly processes, or substances present in the operating environment of air conditioning equipment.

[0043] When ant nest corrosion occurs, fine pores are formed in the copper, and the anode is concentrated at the front end of the pores. Therefore, the corrosion proceeds rapidly and spreads towards the wall thickness in a short time, penetrating the copper tube.

[0044] Referring to the pourbaix-diagram, which is known as a diagram representing the steady state of various potentials and pH values, the following are examples of reactions related to the dissolution of Cu in aqueous solutions.

[0045] Cu→Cu 2+ +2e - (1) (Anodic reaction)

[0046] O2 + 2H2O + 4e － →4OH － (2) (Cathode reaction)

[0047] (2) Cathode reaction

[0048] As mentioned above, in the dissolution of copper, the cathodic reaction is not caused solely by non-oxidizing acids such as carboxylic acids. Therefore, the dissolution of copper in anthill corrosion depends on oxygen (as stated in equation (2)) rather than on carboxylic acids, which are corrosion promoters. It is assumed that oxygen is abundant in the general environment, and the opening of the corrosion pit is in an oxygen-rich environment.

[0049] The exact role of carboxylic acids in the mechanism of ant nest corrosion is not fully understood, but it is at least different from inorganic acids such as hydrochloric acid, sulfuric acid, or nitric acid with oxidizing capabilities, indicating the occurrence of this unique form of corrosion.

[0050] It is believed that within the ant-nest-like corrosion pores, carboxylic acids exist in the form of copper complexes (as shown in formula (3) below) or remain in the corrosive environment as aldehydes, are oxidized inside the corrosion pores, and regenerate carboxylic acids (as shown in formulas (4) and (5) below), thereby undertaking the formation of specific corrosion pores.

[0051] Cu 2+ +2(HCOO) - →Cu(HCOO)2(3)

[0052] HCOOH + 2H+ →HCHO+H2O (4)

[0053] HCHO+2OH - →HCOOH + H₂O + 2e - (5)

[0054] Anthill corrosion occurs when all three elements—carboxylic acid, oxygen, and water—are present. It persists by maintaining an environment within the corrosion pit where these elements coexist. Removing any one of these elements from the pit can inhibit corrosion.

[0055] Furthermore, if a primary cause of pH reduction within the corrosion pit is also present, it will promote the corrosion reaction. For example, it is known that phosphorus (P) in phosphorus-deoxidized copper (JIS H3300 C1220) is a major cause of phosphoric acid production during dissolution, which promotes medullary corrosion.

[0056] On the other hand, at standard electrode potentials, base metals with a lower potential than H (hydrogen) generally undergo a cathodic reaction through reduction by hydrogen ions with a higher potential, consuming hydrogen ions and dissolving into the acidic solution. The lower the standard electrode potential of the metal, the more pronounced this reaction. Furthermore, when different metals come into contact in a conductive liquid, dissimilar metal contact corrosion easily occurs, where a potential difference is generated and the lower-potential (base metal) preferentially dissolves; the greater the potential difference between the metals, the more pronounced this corrosion becomes.

[0057] It is known that elements with this property are mostly from Group 1 or Group 2 in the long-period periodic table. In particular, elements from Group 1 and Group 2 are prone to dissolving in acidic solutions, causing the pH of the solution to rise along with the dissolution.

[0058] If a metal with a standard electrode potential lower than that of Al, such as Mg, is added to Cu, then Mg (metallic magnesium) or Mg oxides dispersed in the alloy have the effect of raising the pH when dissolved in an acidic solution.

[0059] Taking Mg as an example, a metal with a standard electrode potential lower than Al, the inventors investigated the addition of trace amounts of Mg to Cu substrate. The results showed that even in trace amounts, Mg or its oxides dissolved along with Cu inside the corrosion pits increased the pH inside the anthill-like corrosion pits, thus neutralizing the carboxylic acid, a corrosion promoter of anthill-like corrosion contained within the pits.

[0060] The corrosion-resistant copper alloy of the present invention comprises at least one alloying element selected from metals with a standard electrode potential lower than Al.

[0061] Adding at least one base metal with a lower standard electrode potential than Al to Cu can induce a pH increase. This effect is particularly pronounced when the metal is a Group 1 or Group 2 element from the long-period periodic table. Among metals with a standard electrode potential lower than Al, at least one of Li, K, Ca, Na, and Mg is preferred. Table 1 shows the standard electrode potential values ​​for metals with a standard electrode potential lower than Al.

[0062] [Table 1]

[0063]

[0064] In the corrosion-resistant copper alloy of the present invention, the remainder other than the added elements consists only of Cu and unavoidable impurities. Unavoidable impurities, as referred to here, are impurities that are necessary to add or difficult to completely remove during the manufacture of the alloy or alloy tube of the present invention, and which are unavoidably introduced into the mass production process under the current technological level. Specifically, they are elements other than Cu and the added elements based on the present invention, based on JIS H3300 C1220. Examples of unavoidable impurities include Zn, Pb, Fe, Sn, Ni, Si, Sb, Bi, etc. If the total content of unavoidable impurities is less than 0.1% by mass, it will not hinder the effects of the present invention.

[0065] Among metals with a standard electrode potential lower than that of Al, Ca and Mg are further preferred as metals to be added to Cu. Adding Ca or Mg can impart an inhibitory effect on corrosion caused by pH increases, while maintaining good workability and brazing properties as an alloy material. Furthermore, from the viewpoints of the effect of pH increases associated with leaching, casting, the difficulty of processing the added element itself, and the workability and brazing properties as an alloy material, Mg is particularly preferred as a metal to be added to Cu.

[0066] The inventors discovered that the inhibition of ant nest corrosion based on pH adjustment capability depends on the content of added elements in Cu.

[0067] In the corrosion-resistant copper alloy of the present invention, the total content of at least one alloying element (hereinafter, sometimes simply referred to as "alloying element") selected from metals with a standard electrode potential lower than Al is 0.01% by mass or more and less than 0.5% by mass. If the total content of the alloying element is 0.01% by mass or more, sufficient corrosion resistance is exhibited in termite corrosion. Regarding the method for evaluating resistance to termite corrosion, it can be evaluated by assessing the corrosion depth after exposure to a 0.5 vol% formic acid aqueous solution atmosphere for 60 days. If the corrosion depth is 0.25 mm or less, the resistance to termite corrosion is considered good. Details of the method for evaluating resistance to termite corrosion will be described later.

[0068] The fewer Cu elements added, the better the elongation characteristics, resulting in excellent machinability in bending and other processing. To maintain this property, the tensile strength after annealing is known to be 280 N / mm². 2 The following is sufficient. For Cu alloys, as long as the total content of the alloy components is less than 0.5% by mass, the tensile strength after annealing will meet the requirement of 280 N / mm². 2 The following conditions apply.

[0069] Regarding Cu, depending on the alloy composition, when the content of this component exceeds a certain value, stress corrosion cracking may occur when exposed to an environment containing ammonia. For Cu alloys, if the total content of the added alloying components is 0.35% by mass or less, stress corrosion cracking caused by ammonia can be further suppressed. Therefore, for Cu alloys, the total content of the added alloying components is preferably 0.35% by mass or less.

[0070] For Cu, the wettability of the solder is excellent in brazing using phosphor bronze solder, and this is more pronounced with lower levels of added elements. For Cu alloys, the wettability of the solder is even better if the total content of the added alloying elements is 0.25% by mass or less. Therefore, for Cu alloys, the total content of the added alloying elements is preferably 0.25% by mass or less.

[0071] For Cu alloys, high thermal conductivity allows for easier heat dissipation during brazing, preventing localized heating and thus improving brazability. Furthermore, high thermal conductivity facilitates heat transfer, improving heat exchanger performance. Thermal conductivity and electrical conductivity are strongly correlated. For Cu alloys, to maintain brazability comparable to conventional C1220, an electrical conductivity of 85% IACS or higher is sufficient. Therefore, for Cu alloys, the total content of added alloying components is more preferably 0.15% by mass or less.

[0072] For deoxidation purposes, phosphoric acid (P) is sometimes added to Cu. However, P in Cu dissolves to produce phosphoric acid, which lowers the surrounding pH and may hinder the effectiveness of the present invention. To avoid the adverse effects of P, the P content in Cu is preferably 0.015% by mass or less.

[0073] Regarding corrosion-resistant copper alloys, depending on the casting method and raw materials used, the addition or mixing of phosphorus (P) is sometimes unavoidable. Even if the P content is below 0.015% by mass, if the ratio of P content (p by mass%) to the alloy component content (X by mass%) is above a certain value, the pH increase effect brought about by the alloy component, i.e., the harmless effect of carboxylic acid, cannot be fully obtained. As a result, the desired resistance to mermaid corrosion may not be achieved. Therefore, the ratio of P content (p by mass%) to the alloy component content (X by mass%) should be kept at a given value.

[0074] Specifically, in corrosion-resistant copper alloys, when the content of the alloy components is set as X% by mass and the content of phosphorus (P) is set as p% by mass, the value of X divided by p, i.e., [X / p], is 9.10 or higher. By maintaining this state, the ineffectiveness of corrosion resistance caused by P can be counteracted, and the required resistance to anthill corrosion can be imparted.

[0075] Furthermore, for corrosion-resistant copper alloys, [X / p] is preferably 16.60 or higher for applications requiring durability, such as those used in slightly harsh corrosive environments, including indoor air conditioning systems.

[0076] The upper limit of [X / p] is not specifically given, for example, it is below 50.

[0077] The copper alloy tube of this invention uses the corrosion-resistant copper alloy of this invention. The heat exchanger of this invention uses the copper alloy tube of this invention.

[0078] The corrosion-resistant copper alloy of the present invention can be manufactured using known melting and casting processes.

[0079] Furthermore, the copper alloy tube of the present invention can be manufactured by known melting and casting processes, soaking processes, hot extrusion processes, rolling and stretching processes, and annealing processes.

[0080] The copper alloy tube of the present invention is preferably a tube with grooves on its inner surface. A tube with grooves on its inner surface refers to a copper alloy tube with grooves of a given shape formed on its inner surface. The number of grooves, the height of the heat sinks formed between the grooves, the wall thickness of the groove bottom, the groove lead angle, and other groove shapes can use conventionally known grooved tube shapes. By forming a grooved tube, the thermal conductivity is improved, and the performance of the heat exchanger is enhanced.

[0081] The copper alloy tubes using the corrosion-resistant copper alloy of the present invention and the tubes with grooves on the inner surface are useful as materials for heat exchangers.

[0082] Example

[0083] The present invention will be described in more detail below through embodiments that satisfy the requirements of the present invention and comparative examples that do not satisfy the requirements of the present invention.

[0084] In the following samples, those with excellent tensile strength and resistance to termite-like corrosion (Tables 3-6) are used as examples. Those with excellent resistance to termite-like corrosion (Tables 7 and 8) are used as examples.

[0085] It should be noted that, for a subset of samples, stress corrosion cracking resistance, solder wettability, and conductivity were measured as a reference. Furthermore, for Tables 3-6, a comprehensive assessment of excellent tensile strength and resistance to anthill corrosion is (○), while a comprehensive assessment of excellent tensile strength and resistance to anthill corrosion but poor performance in any one of stress corrosion cracking resistance, solder wettability, or conductivity is (△). Even with a comprehensive assessment of (△), there will be no problem depending on the usage environment and intended application, and the technical problem of this invention can be solved.

[0086] Furthermore, in Tables 3-6, the criterion for resistance to ant nest corrosion is 0.25 mm or less. However, since P is not present in the examples, the evaluation result is 0.20 mm or less, which can be considered the level of resistance to the most severe environments. For example, in air conditioning systems used in regions with developing air pollution containing large amounts of oxidizing air pollutants such as SOx and NOx, where the oxidizing gases intrude into the room, and the alcohol components present in the room oxidize and deteriorate, resulting in a significant increase in the production of lower carboxylic acids, the resistance to this increased level is envisioned. Additionally, it is also suitable for thin-walled applications to reduce material costs.

[0087] The samples in Table 7 are designed for use in environments with relatively mild corrosiveness. For example, they are designed for use in newly built, airtight houses in Japan, as well as in ordinary households where anthill-like corrosion occurs due to the effects of volatile chemical substances (VOCs) from building materials.

[0088] Table 8 envisions samples designed for use in slightly harsh corrosive environments, even within Japan. For example, it envisions a level suitable for use in newly built, airtight houses, as well as in typical households where ant nest corrosion is observed due to the presence of volatile chemicals from daily life, such as pets, frequent use of deodorizers, and frequent use of disinfectants. Furthermore, it envisions applications where the durability of equipment such as indoor air conditioners is a priority.

[0089] 1. Sample preparation method

[0090] Copper alloys were prepared by adding Mg and P as additive elements in Cu, with the amounts of additives listed in Tables 3 to 8, for testing purposes.

[0091] Copper plates are made through a series of processes including melting and casting, hot rolling, cold rolling, and annealing.

[0092] 2. Chemical composition analysis methods for samples

[0093] The analysis was performed according to Section 5 of JIS K0116:2014 General Rules for Luminescence Spectrophotometry, specifically the luminescence spectrophotometry analysis of spark discharge.

[0094] The details of the analysis conditions are as follows.

[0095] Equipment used: Shimadzu PDA-7000

[0096] Atmospheric gas: 99.9995% high-purity argon

[0097] Electrode spacing (discharge gap): 7mm

[0098] Preparatory discharge: 1500 pulses

[0099] Quantitative method: Timed integration in the intensity ratio method

[0100] Integration time: 1200 pulses

[0101] Examples of analytical lines (the wavelengths at which each element is measured) in the quantitative analysis of each element are shown in Table 2.

[0102] [Table 2]

[0103]

[0104] 3. Evaluation Methods

[0105] After annealing, the microstructure of the copper plate was observed, and its mechanical properties (tensile strength), resistance to ant nest corrosion, resistance to stress corrosion cracking, solder wettability, and conductivity were measured.

[0106] <Numbers 1-5>

[0107] [Evaluation Items] Tensile strength, resistance to termite-like corrosion

[0108] (Tensile strength)

[0109] • Dimensions of the test material: Width 30mm × Length 180mm × Thickness 0.2mm, JIS Z2241:2011 Metallic Materials, Tensile Testing, Test Piece No. 5, as reference.

[0110] • Test method: The tensile strength was determined by tensile testing machine according to JIS Z2241:2011 Metallic materials tensile test method.

[0111] • Criteria for determining tensile strength

[0112] ○: Tensile strength is 280 N / mm 2 The following maintains the processability such as bending.

[0113] ×: Tensile strength exceeds 280 N / mm 2 Reduced machinability, such as bending

[0114] (Resistant to ant nest-like corrosion)

[0115] The test material was exposed to a wet environment using formic acid, a representative corrosion promoter of ant nest corrosion, and the maximum corrosion depth after the corrosion test was determined. The test conditions are shown below. Figure 1 This is a schematic cross-sectional view of the test container used in the evaluation of resistance to termite-like corrosion. The test container 10 is a sealed container 11 that can be sealed with a silicone plug 14. A corrosion-promoting substance 12 is injected into the bottom of the sealed container 11, and the test material 13 remains hollow.

[0116] Figure 2 It is a diagram showing the dimensions of the test material, made of copper alloy, used in the evaluation of resistance to termite-like corrosion. Figure 2 (a) is a top view of the test material. Figure 2 (b) is a perspective view of the test material. Regarding the test material, in a copper alloy plate measuring 12 mm wide × 200 mm long × 1.0 mm thick, only a single side, measuring 10 mm wide × 200 mm long, is exposed to the corrosive environment inside the container. The portion outside this single side is covered with rubber material to protect it from exposure to the corrosive environment.

[0117] • Dimensions of the test material: Width 12mm × Length 200mm × Thickness 1.0mm

[0118] Corrosion promoter: 500 mL of 0.5 vol% formic acid aqueous solution

[0119] • Temperature conditions: Plastic containers are stored in a constant temperature bath and repeatedly subjected to a thermal cycle of 20°C for 2 hours followed by 40°C for 22 hours. In this method, maintaining the temperature at 20°C promotes condensation, introducing formic acid that has evaporated into the container into the condensate. Maintaining the temperature at 40°C dries the condensate, concentrating the formic acid, thus accelerating the corrosion process.

[0120] • Test container: Use a 2L hollow plastic container to hold the test material.

[0121] • Container internal atmosphere: oxygen replacement

[0122] • Trial period: 60 days

[0123] • Criteria for determining resistance to ant nest corrosion

[0124] ○: Effective, with a maximum corrosion depth of less than 0.25mm.

[0125] ×: Ineffective; maximum corrosion depth exceeds 0.25mm.

[0126] [Table 3]

[0127]

[0128] [Evaluation Results]

[0129] Table 3 shows the evaluation results of resistance to ant nest corrosion and tensile strength.

[0130] In samples 1 and 2, the Mg content was 0.01% by mass and 0.495% by mass, respectively. All tests, including resistance to ant nest corrosion and tensile strength, met the criteria, demonstrating excellent performance.

[0131] In sample number 3, the Mg content was as low as 0.005% by mass, which did not meet the criteria for resistance to ant nest corrosion.

[0132] In sample number 4, the Mg content is excessive at 0.98% by mass, and the tensile strength does not meet the judgment criteria.

[0133] In sample number 5, no Mg was added and the P content was 0.020% by mass, which did not meet the criteria for resistance to ant nest corrosion.

[0134] <Numbers 6~8>

[0135] [Evaluation Items] Resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking

[0136] The test and evaluation methods for resistance to ant nest corrosion and tensile strength are the same as those for numbers 1 to 5.

[0137] (Resistance to stress corrosion cracking)

[0138] Regarding the configuration of the test apparatus, the stress corrosion cracking test was conducted in accordance with the technical standard JBMA T-301 of the Japan Shindō Copper Industry Association. Furthermore, to investigate more detailed characteristics, the detailed test conditions are as follows.

[0139] • Dimensions of the test material: Width 12mm × Length 20mm × Thickness 1.0mm

[0140] Corrosion promoter: 14 vol% ammonia solution, 100 mL

[0141] • Test container: Desiccator

[0142] • Exposure Condition: In a desiccator containing an ammonia solution at the bottom, a middle plate is horizontally positioned approximately 100 mm above the liquid surface. The test material is then placed on top of the middle plate and sealed. It should be noted that the test material is positioned horizontally with its inside facing upwards and downwards. Furthermore, resin-coated φ2.5 mm copper wires are placed between the test material and the middle plate at both ends, without directly contacting the middle plate.

[0143] • Exposure time: 72 hours

[0144] Evaluation method: After the test, the sample is pickled (with sulfuric acid) and then bent 180° with the top surface side as the outer side. The cross-section of the bent sample is observed to evaluate the presence or absence of cracks.

[0145] • Criteria for determining resistance to stress corrosion cracking

[0146] ○: Crack depth less than 0.10 mm

[0147] ×: Crack depth is 0.10mm or more.

[0148] [Table 4]

[0149]

[0150] [Evaluation Results]

[0151] Table 4 shows the evaluation results of resistance to ant nest corrosion, tensile strength, and resistance to stress corrosion cracking.

[0152] The Mg content affects the susceptibility to stress corrosion cracking. In samples 6 and 7, the Mg content is 0.01% by mass and 0.35% by mass, respectively. They meet the criteria for resistance to ant nest corrosion, tensile strength, and resistance to stress corrosion cracking, and exhibit excellent performance.

[0153] In item number 8, the Mg content is 0.40% by mass, resulting in cracks caused by stress corrosion cracking, which does not meet the criteria for stress corrosion cracking resistance.

[0154] <Numbers 9~11>

[0155] [Evaluation Items] Resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking, and solder wettability.

[0156] The test and evaluation methods for resistance to ant nest corrosion, tensile strength, and resistance to stress corrosion cracking are the same as those for numbers 1 to 8.

[0157] (Solder filler metal wettability)

[0158] Figure 3This describes the operational steps for evaluating the wettability of solder. For example... Figure 3 As shown in (a), the test material 21 is bent 90° along its length, and brazing filler metal 20 is placed in the center of the concave portion of the test material 21. Figure 3 As shown in (b), the length of the solder 20 before heating is A. Heating is performed under the aforementioned conditions, and the overall length (length direction) B of the solder 20 after wetting and spreading is measured. Figure 3 (c)).

[0159] • Dimensions of the test material: Width 30mm × Length 100mm × Thickness 1.0mm

[0160] Brazing filler metal: BCuP-2 (φ1.6mm × length 20mm)

[0161] • Heating equipment: Gold-image plating furnace manufactured by ULVAC

[0162] Heating atmosphere: N2 replacement

[0163] • Heating conditions: (i) Temperature rise conditions: room temperature → 850℃ / 5min (temperature of the test material is measured during temperature control)

[0164] (ii) Holding conditions: 850℃, hold for 5 min

[0165] (iii) Cooling conditions: Natural cooling

[0166] Criteria for determining the wettability of solder

[0167] ○: 100mm or more

[0168] ×: Less than 100mm

[0169] [Table 5]

[0170]

[0171] [Evaluation Results]

[0172] Table 5 shows the evaluation results of resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking, and brazing filler metal wettability.

[0173] In samples 9 and 10, the Mg content is 0.01% and 0.25% by mass, respectively. They not only meet the criteria for resistance to ant nest corrosion, tensile strength, and stress corrosion cracking, but also for brazing filler metal wettability, demonstrating excellent performance.

[0174] In item number 11, the Mg content is 0.29% by mass, which does not meet the criteria for judging the wettability of the solder.

[0175] <Numbers 12~14>

[0176] [Evaluation Items] Resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking, solder wettability, conductivity

[0177] The test and evaluation methods for resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking, and brazing filler metal wettability are the same as those for numbers 1 to 11.

[0178] (Conductivity)

[0179] • Dimensions of the test material: 10mm width × 300mm length × 0.2mm thickness

[0180] • Test method: Conductivity was measured using a SIGMATEST (Ethernde portable conductivity meter SigmaCheck2).

[0181] It should be noted that the temperature during the measurement was maintained at 22℃.

[0182] Criteria for determining conductivity

[0183] ○: 85% or higher IACS (equivalent to C1220)

[0184] ×: Below 85% IACS

[0185] [Table 6]

[0186]

[0187] [Evaluation Results]

[0188] Table 6 shows the evaluation results of resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking, solder wettability, and conductivity.

[0189] In items 12 and 13, the Mg content is 0.10% by mass and 0.14% by mass, respectively. They meet the judgment criteria in terms of resistance to ant nest corrosion, tensile strength, resistance to stress corrosion cracking, solder wettability, and conductivity, and have excellent performance.

[0190] In item number 14, the Mg content is 0.18% by mass, which does not meet the criteria for determining conductivity.

[0191] <Numbers 15-20>

[0192] [Evaluation Item] Resistance to ant nest corrosion when P is added

[0193] The test methods and evaluation methods are the same as those for numbers 1 to 5.

[0194] Regarding the evaluation criteria in the evaluation method, the depth of ant nest-like corrosion produced in this test method is set as the level that is judged to be practically without problems, based on the actual use of the invention, the wall thickness of the component, and the number of years of service required by the equipment used. Specifically, as a level that can be used under relatively mild corrosive environmental conditions, the maximum corrosion depth is set to less than 0.370 mm.

[0195] ○: Effective, with a maximum corrosion depth of less than 0.370mm.

[0196] ×: No effect, maximum corrosion depth exceeds 0.370mm

[0197] [Table 7]

[0198]

[0199] [Evaluation Results]

[0200] Table 7 shows the evaluation results of resistance to ant nest corrosion.

[0201] In samples 15-18, the content of Mg (X) was 0.0440 wt%, 0.0830 wt%, 0.0470 wt%, and 0.0800 wt%, respectively, and the content of P (p) was 0.00310 wt%, 0.00680 wt%, 0.00510 wt%, and 0.00850 wt%, respectively. The ratio of X / p to the content of each element in each sample was greater than 9.10 of the baseline, thus meeting the criteria for resistance to termite-like corrosion.

[0202] In numbers 19 and 20, the X, representing the Mg content, is 0.0453% by mass and 0.0837% by mass, respectively, and the p, representing the P content, is also 0.00510% by mass and 0.00930% by mass, respectively. The X / p ratios are both lower than the benchmark of 9.10, and therefore do not meet the criteria for resistance to ant nest corrosion.

[0203] It should be noted that the Mg content in each sample is less than 0.5% by mass; therefore, the estimated tensile strength is 280 N / mm². 2 Therefore, the evaluation of tensile strength is omitted below.

[0204] <Numbers 21-26>

[0205] [Evaluation Item] Resistance to ant nest corrosion with added P (wherein, for No. 25 and No. 26, samples without added P are shown as reference examples).

[0206] The test methods and evaluation methods are the same as those for numbers 1 to 5.

[0207] Regarding the evaluation criteria in the evaluation method, 0.250 mm is used as the criterion, which is lower than the maximum corrosion depth of 0.262 mm of ant nest corrosion produced when oxygen-free copper (C1020), which has been used as a material to counteract ant nest corrosion, is tested using this test method.

[0208] The judgment criteria in this test method are also necessary and sufficient for applications that require durability, such as those used in slightly harsh corrosive environments in Japan and for applications that emphasize equipment durability, such as indoor air conditioning.

[0209] ○: Effective, with a maximum corrosion depth of less than 0.250mm.

[0210] ×: Ineffective; maximum corrosion depth exceeds 0.250mm.

[0211] [Table 8]

[0212]

[0213] [Evaluation Results]

[0214] Table 8 shows the evaluation results of resistance to ant nest corrosion.

[0215] In samples 21 and 22, the X values ​​representing the Mg content were 0.0468% and 0.0833% by mass, respectively, and the p values ​​representing the P content were 0.00270% and 0.00480% by mass, respectively. The X / p ratios representing the proportion of each element in each sample were both above 16.60 of the baseline, thus meeting the criteria for resistance to termite-like corrosion.

[0216] In numbers 23 and 24, the X, representing the Mg content, is 0.0454% by mass and 0.0840% by mass, respectively, and the p, representing the P content, is also 0.00280% by mass and 0.00530% by mass, respectively. The X / p ratios are both lower than the benchmark of 16.60, and therefore do not meet the criteria for resistance to ant nest corrosion.

[0217] It should be noted that even samples numbered 23 and 24, like those numbered 15 to 18, have no practical problems in environments with relatively mild corrosiveness.

[0218] Furthermore, the Mg content in each sample was less than 0.5% by mass, therefore the estimated tensile strength was 280 N / mm. 2 Therefore, the evaluation of tensile strength is omitted below.

[0219] The results in Tables 7 and 8 are shown below. Figure 4 . Figure 4In the table, α corresponds to Table 7, and β corresponds to Table 8. Furthermore, the circled points represent points where X for Mg content is 0.08, and the triangular points represent points where X for Mg content is 0.04.

[0220] Based on the above results, the following conclusions were drawn.

[0221] (1) When the total content of alloy components is more than 0.01% by mass and less than 0.5% by mass, a corrosion-resistant copper alloy with excellent resistance to ant nest corrosion and machinability (tensile strength) can be obtained.

[0222] (2) When the total content of alloy components is 0.01% by mass or more and 0.35% by mass or less, a corrosion-resistant copper alloy with excellent resistance to ant nest corrosion, machinability (tensile strength) and resistance to stress corrosion cracking can be obtained.

[0223] (3) When the total content of alloy components is 0.01% by mass or more and 0.25% by mass or less, a corrosion-resistant copper alloy with excellent resistance to ant nest corrosion, machinability (tensile strength), resistance to stress corrosion cracking, and brazing filler wettability can be obtained.

[0224] (4) When the total content of alloy components is 0.01% by mass or more and 0.15% by mass or less, a corrosion-resistant copper alloy with excellent resistance to ant nest corrosion, machinability (tensile strength), resistance to stress corrosion cracking, brazing filler wettability and conductivity can be obtained.

[0225] (5) When the corrosion-resistant copper alloy contains P, and the content of P is less than 0.015% by mass, and the content of the alloy component is set as X% by mass and the content of P is set as p% by mass, when the value of X divided by p, i.e. [X / p], is 9.10 or more, the ineffectiveness of P brought by the alloy component in the ant nest corrosion resistance is mitigated, and an excellent corrosion-resistant copper alloy can be made.

[0226] (6) When the [X / p] is 16.60 or higher, the ineffectiveness of P in corrosion resistance caused by alloy composition is further mitigated in the ant nest corrosion resistance, and a better corrosion-resistant copper alloy can be made.

[0227] Various embodiments have been described above with reference to the accompanying drawings, but it is self-evident that the present invention is not limited to such examples. Those skilled in the art will find various modifications or variations within the scope of the appended claims, and it should be understood that they also naturally fall within the technical scope of the present invention. Furthermore, the constituent elements in the described embodiments can be arbitrarily combined without departing from the spirit of the invention.

[0228] It should be noted that this application is based on Japanese patent applications filed on April 19, 2021 (Japanese Patent Application No. 2021-070659) and March 11, 2022 (Japanese Patent Application No. 2022-038301), the contents of which are incorporated herein by reference.

[0229] As stated above, the following matters are disclosed in this specification.

[0230] [1] A corrosion-resistant copper alloy comprising at least one alloying element selected from metals with a standard electrode potential lower than Al, the remainder consisting of Cu and unavoidable impurities, wherein the total content of the alloying elements is more than 0.01% by mass and less than 0.5% by mass.

[0231] [2] According to the corrosion-resistant copper alloy described in [1], wherein the metal with a standard electrode potential lower than Al is Li, K, Ca, Na, or Mg.

[0232] [3] According to the corrosion-resistant copper alloy described in [1] or [2], wherein the metals with a standard electrode potential lower than Al are Ca and Mg.

[0233] [4] The corrosion-resistant copper alloy according to any one of [1] to [3], wherein, when the corrosion-resistant copper alloy contains P, the content of P is 0.015% by mass or less, and when the content of the alloy component is set as X% by mass and the content of P is set as p% by mass, the value of X divided by p, i.e., [X / p], is 9.10 or more.

[0234] [5] The corrosion-resistant copper alloy according to [4], wherein the [X / p] is 16.60 or higher.

[0235] [6] A copper alloy tube that uses any one of [1] to [5] a corrosion-resistant copper alloy.

[0236] [7] The copper alloy tube according to [6] is a copper alloy tube with grooves on the inner surface.

[0237] [8] A heat exchanger that uses the copper alloy tubes described in [6] or [7].

[0238] Symbol Explanation

[0239] 10 test containers

[0240] 11 Sealed Containers

[0241] 12 Corrosion-promoting substances

[0242] 13 Test Materials

[0243] 14 Silicone Plugs

[0244] 20 Brazing filler metal

[0245] 21 Test Materials

Claims

1. A corrosion-resistant copper alloy comprising Mg as an alloying element selected from metals with a standard electrode potential lower than Al, the remainder consisting of Cu and unavoidable impurities. The content of Mg is greater than 0.01% by mass and less than 0.5% by mass. The tensile strength of the corrosion-resistant copper alloy is 280 N / mm². 2 the following, The corrosion-resistant copper alloy is used for applications requiring resistance to ant nest corrosion.

2. The corrosion-resistant copper alloy according to claim 1, wherein, When the corrosion-resistant copper alloy contains phosphorus (P), the P content is less than 0.015% by mass. When the content of Mg is set as X mass%, and the content of P is set as p mass%, the value of X divided by p, i.e., [X / p], is 9.10 or higher.

3. The corrosion-resistant copper alloy according to claim 2, wherein, The [X / p] is 16.60 or higher.

4. A copper alloy tube using the corrosion-resistant copper alloy as described in any one of claims 1 to 3.

5. The copper alloy tube according to claim 4, wherein it is a copper alloy tube with grooves on the inner surface.

6. A heat exchanger that uses the copper alloy tube as described in claim 4 or 5.

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