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

Abstract

Provided are a copper alloy having improved corrosion resistance against stress corrosion cracking, a copper alloy tube using the copper alloy, and a heat exchanger. The copper alloy is a copper alloy to which a base metal element (e.g., Mg, Mn, etc.) having a standard electrode potential equal to or lower than the potential of Mn is added. The copper alloy tube is formed from a copper alloy to which a base metal element having a standard electrode potential equal to or lower than the potential of Mn is added. The heat exchanger uses a copper alloy tube formed from a copper alloy to which a base metal element having a standard electrode potential equal to or lower than the potential of Mn is added.

Description

Technical Field

[0001] The present invention relates to a corrosion-resistant copper alloy having improved corrosion resistance against stress corrosion cracking, and a copper alloy tube and a heat exchanger using the copper alloy. Background Art

[0002] Phosphorus deoxidized copper pipes are widely used as refrigerant pipes and heat exchanger pipes for refrigeration and air conditioning equipment. Types of phosphorus deoxidized copper include low-phosphorus deoxidized copper C1201 and high-phosphorus deoxidized copper C1220 specified in JIS H3300:2018.

[0003] Copper is a material with excellent thermal conductivity, bending workability, brazing properties, etc. In addition, the standard electrode potential is high, so it has excellent corrosion resistance in a non-oxidizing environment. It is known that phosphorus deoxidized copper contains phosphorus but does not contain oxygen, so it is not easy to cause hydrogen embrittlement like oxygen-free copper. Phosphorus deoxidized copper has a lower manufacturing cost than oxygen-free copper, so it is often used for applications exposed to high temperatures such as brazing.

[0004] Corrosion-resistant materials such as copper materials develop stress corrosion cracking (SCC) due to the overlap of specific factors. For copper materials such as pure copper and copper alloys, SCC in ammonia environments has been reported since ancient times. SCC of copper materials is particularly significant in brass. However, in recent years, cases of phosphorus deoxidized copper tubes have also been reported.

[0005] SCC of copper materials occurs under special conditions such as an ammonia environment. It is not caused by ammonia alone, but by the coexistence of ammonia and water. When water adheres to copper materials, ammonia will dissolve in the water phase and cause corrosion. SCC occurs when residual stress and external stress are concentrated at the location where the grain boundary is corroded. SCC is a phenomenon that causes cracking due to tensile stress. As a corrosion mode of phosphorus deoxidized copper, it has the characteristics of intergranular corrosion.

[0006] In the fields of refrigerant piping, heat exchanger piping, etc., refrigerant leakage due to SCC has become a problem, and countermeasures to suppress SCC are needed. When the piping is damaged due to the progression of SCC, it will cause refrigerant leakage, and the function of the equipment cannot be maintained, or the reliability of the equipment will be damaged. In addition, there are concerns that the leakage of refrigerant will have an impact on global warming. As a countermeasure to suppress SCC, there is a method of making the grains smaller in terms of material factors. In addition, there is a method of reducing residual stress and external stress in terms of mechanical factors.

[0007] However, the method of reducing residual stress and external stress is difficult to implement in actual materials, and it is unrealistic as a countermeasure to suppress SCC. In addition, in the method of making the grains smaller, the material cannot be fully annealed, so it becomes a countermeasure that significantly impairs the processability and greatly restricts the use. Under such circumstances, countermeasures to suppress SCC have been studied from the perspective of chemical composition, etc.

[0008] Patent Document 1 describes a copper tube having excellent corrosion resistance to ant nest corrosion and excellent corrosion resistance to SCC. The copper tube is composed of a copper material containing 0.10 to 1.0 wt% of P, the remainder of which is composed of Cu and inevitable impurities, and the P concentration (P1) at the grain boundary of the copper material is less than 5.0 times the P concentration (P0) in the grains of the copper material. By adapting the final heat treatment conditions, P concentration at the grain boundary is suppressed, and the SCC sensitivity is reduced (see paragraph 0011 of Patent Document 1).

[0009] Patent Document 2 describes a copper alloy having high electrical conductivity and excellent stress relaxation resistance. In the copper alloy, the content of Mg exceeds 0.001 mass% and is 0.01 mass% or less, and the content of P is 0.001 mass% or less. In addition, the content of H is 0.001 mass% or less, the content of O is 0.01 mass% or less, and the content of C is 0.001 mass% or less.

[0010] Patent Document 3 describes a pitting-resistant copper or copper alloy tube that can prevent pitting corrosion. It describes that when lithium bromide is used as an absorbent, ammonia residue is sometimes unavoidable during the purification process; the higher the phosphorus content, the higher the stress corrosion cracking sensitivity of phosphorus-deoxidized copper (see paragraph 0002 of Patent Document 3).

[0011] Conventionally, the entire mechanism of how P added to copper promotes SCC has not been entirely clear. Generally, the following (1) to (3) are presumed to be the main causes of the mechanism of how P promotes SCC.

[0012] (1) Grain boundaries are essentially sites where impurities and added P are likely to concentrate.

[0013] (2) P is eluted from the copper phase to the aqueous phase. As P is eluted, the pH of the aqueous phase decreases and Cu is eluted. In the chemical form of the eluted Cu, copper ions are more stable than oxides and hydroxides.

[0014] (3) A distribution of pH and other factors occurs at the location where corrosion occurs.

[0015] In addition, in Copper and Copper Alloys Vol. 53 No. 1 (2014) p.128-p.133 (Electrochemical Approach for Explanation of Mechanism of the AntNest Corrosion), the cause of the following (4) is newly inferred. When ant nest corrosion proceeds, (4) a complex formation reaction occurs in which the eluted P and copper ions form complex ions. From the perspective of free energy, this reaction drives the elution of Cu from the copper phase to the aqueous phase. As for the elution reaction of copper based on the elution of P, both formic acid and ammonia can play a role in the corrosion-promoting substance. Therefore, it is believed that in SCC, the elution of P will also lead to further elution of copper ions based on the reaction of (4), which is expected to lead to the progression of more serious SCC.

[0016] Prior art literature

[0017] Patent Literature

[0018] Patent Document 1: Japanese Patent Application Publication No. 2022-056871

[0019] Patent Document 2: Japanese Patent Application Publication No. 2022-022637

[0020] Patent Document 3: Japanese Patent Application Publication No. 2007-154221 Summary of the invention

[0021] Technical problem solved by the invention

[0022] In the past, copper materials were difficult to prevent hydrogen embrittlement and suppress SCC at the same time. In order to prevent hydrogen embrittlement of copper materials, it is necessary to reduce the amount of oxygen. When copper containing oxygen is exposed to high temperature in a hydrogen atmosphere, hydrogen embrittlement occurs, which reduces strength and toughness. In applications such as furnace brazing in a hydrogen atmosphere, when the material is heated, hydrogen diffuses in a high-temperature environment, thereby reducing copper oxide and generating water vapor voids at the grain boundaries, resulting in reduced strength and toughness.

[0023] When P is added to copper materials, deoxidation is achieved, thereby suppressing such hydrogen embrittlement. However, the addition of P causes a problem in the generation and progression of SCC.

[0024] Oxygen-free copper is not only less susceptible to hydrogen embrittlement due to its low oxygen and phosphorus concentrations, but is also a material with low SCC sensitivity. However, oxygen-free copper requires special casting equipment such as vacuum melting casting, so there are problems in terms of manufacturing cost and price.

[0025] On the other hand, phosphorus deoxidized copper is less susceptible to hydrogen embrittlement, but contains P added in the melting process for deoxidation. As phosphorus deoxidized copper, there is also low-phosphorus deoxidized copper in which P is 0.004 mass % or more and less than 0.015 mass %. However, even low-phosphorus deoxidized copper cannot completely eliminate the influence of P, and its use in highly corrosive environments is limited. In addition, low-phosphorus deoxidized copper needs to reduce the proportion of recycled raw materials containing P during production, which has great constraints on manufacturing costs and prices.

[0026] In Patent Document 1, the P concentration at the grain boundary is reduced in order to reduce the SCC sensitivity of the copper material. However, in this method, the ratio of the P concentration at the grain boundary to the P concentration in the grain is adjusted, and the P in the copper material is not directly rendered harmless. In addition, in this method, a special final heat treatment is required, so it is considered that there are practical technical problems in terms of manufacturing efficiency, manufacturing equipment, etc.

[0027] Patent Document 2 gives the ratio of Mg to the total of S, P, Se, Te, Sb, Bi, and As, and the contents of H, O, and C for copper alloys. However, the amount of P in this copper alloy is a trace amount, which is equivalent to oxygen-free copper. Such an amount of P is problematic in terms of manufacturing cost and price. In addition, H may cause defects in the structure, and thus may promote SCC as a result, but it does not directly participate in SCC of copper materials.

[0028] Under such circumstances, for copper materials such as phosphorus deoxidized copper and oxygen-free copper, a technology is required that can suppress SCC while reducing costs and preventing hydrogen embrittlement. Even when P, which promotes SCC, is added, it is desired to eliminate the influence of P and directly suppress SCC of copper materials.

[0029] Therefore, an object of the present invention is to provide a copper alloy having improved corrosion resistance against stress corrosion cracking, and a copper alloy tube and a heat exchanger using the copper alloy.

[0030] Technical means of solving problems

[0031] In order to solve the above technical problems, the copper alloy of the present invention is a copper alloy to which a base metal element having a standard electrode potential lower than the potential of Mn is added. The copper alloy tube of the present invention is formed of the copper alloy. In addition, the heat exchanger of the present invention uses a copper alloy tube formed of the copper alloy.

[0032] Effects of the Invention

[0033] According to the present invention, it is possible to provide a copper alloy having improved corrosion resistance against stress corrosion cracking, and a copper alloy tube and a heat exchanger using the copper alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] [ Figure 1 ] Figure 1 This is a diagram schematically showing an example of a heat exchanger including copper alloy tubes.

[0035] [ Figure 2 ] Figure 2 It is a figure which shows the method of pre-treating the test material formed of copper alloy.

[0036] [ Figure 3 ] Figure 3 This is a diagram showing a method for measuring the crack depth due to stress corrosion cracking.

[0037] [ Figure 4 ] Figure 4 It is a magnified representation Figure 2 Figure 1 shows the main parts of the .

[0038] [ Figure 5 ] Figure 5 This is a graph showing the relationship between the crack depth due to stress corrosion cracking and the P concentration.

[0039] [ Figure 6 ] Figure 6 This is a graph showing the relationship between the Mg concentration and the P concentration and the crack depth due to stress corrosion cracking. DETAILED DESCRIPTION

[0040] Hereinafter, a copper alloy according to an embodiment of the present invention, and a copper alloy tube and a heat exchanger using the copper alloy will be described.

[0041] The copper alloy of the present embodiment is a copper alloy to which a base metal element having a standard electrode potential of less than or equal to the potential of Mn is added. As the base metal element, a phosphorus compound forming element that reacts with P to form a phosphorus compound is preferred. A preferred embodiment of the copper alloy is that P: exceeds 0% and is less than 0.040 mass %, the total of the base metal elements is more than 0.01 mass % and less than 1.5 mass %, and the balance is composed of Cu and unavoidable impurities.

[0042] The copper alloy of the present embodiment improves corrosion resistance to stress corrosion cracking (SCC) by adding base metal elements. In this copper alloy, P can be added to reduce the amount of O that is the main cause of hydrogen embrittlement. P is a factor that promotes SCC, and even if P is added for deoxidation, the generation / progress of SCC can be suppressed by the base metal elements.

[0043] It is known that when copper containing oxygen is exposed to high temperature in a hydrogen atmosphere, hydrogen embrittlement occurs. Hydrogen intrudes into the lattice of the copper phase and diffuses. When the diffused hydrogen reacts with the copper oxide in the copper phase, water vapor is generated by reducing the copper oxide. As a result, even if hydrogen itself does not directly cause embrittlement reaction, voids are formed at the grain boundaries due to the action of the generated water vapor, resulting in a decrease in strength and toughness caused by hydrogen embrittlement.

[0044] In addition, copper materials used for refrigerant piping, heat exchanger piping, etc., although rarely, may sometimes experience ant nest corrosion. Ant nest corrosion is corrosion that causes ant nest-like erosion from tiny corrosion holes generated on the surface of the material to the inside. Ant nest corrosion occurs in the presence of oxygen and moisture, using carboxylic acids such as formic acid and acetic acid, aldehydes such as formaldehyde and acetaldehyde, and alcohols as corrosive media.

[0045] These corrosive media are believed to be generated by the hydrolysis and deterioration reactions caused by water such as condensation water in lubricating oil, processing oil, organic solvents, and substances contained in the use environment used in the pipe manufacturing process and heat exchanger assembly process. Once ant nest corrosion occurs, due to its characteristic morphology, the anodic reaction is concentrated in a specific position, so the corrosion progresses faster and may progress in the wall thickness direction in a short time and penetrate.

[0046] Copper materials are often used for brazing refrigerant pipes, heat exchanger pipes, etc. in a furnace in a hydrogen atmosphere. During brazing, the pipes are exposed to high temperatures in a hydrogen atmosphere, so it is desirable to reduce the amount of O, which is the main cause of hydrogen embrittlement. However, ant nest corrosion and stress corrosion cracking are affected by P required for deoxidation in the casting process. From the perspective of improving SCC resistance and suppressing other corrosion phenomena, it is necessary to eliminate the influence of P.

[0047] In phosphorus deoxidized copper materials, the mechanism by which P added to Cu promotes SCC has not been fully elucidated. However, the corrosion mode of SCC in phosphorus deoxidized copper is always intergranular corrosion. It is believed that if an anodic reaction that causes Cu to elute occurs, a paired cathodic reaction is established. It is speculated that Cu is not easily corroded under alkaline conditions or non-oxidizing conditions, and oxygen participates in the cathodic reaction.

[0048] Copper pipes used as refrigerant pipes, heat exchanger pipes, etc. may come into contact with moisture such as condensed water. When considering the Pourbaix diagram that shows the stable state of chemical forms at each potential and pH, the reaction related to the elution of Cu in the aqueous solution can be expressed by the following equations (1) to (2).

[0049] Cu→Cu 2+ +2e - …(1)(Anode reaction)

[0050] O2+2H2O+4e - →4OH - …(2)(Cathode reaction)

[0051] When using formulas (1) to (2), the elution of Cu from the copper phase to the aqueous phase can be represented by the following formulas (3) to (4). The Cu eluted into the aqueous phase is considered to form copper (II) hydroxide by the equilibrium reaction represented by formula (4).

[0052] Cu+O2+2H2O→Cu 2+ +4OH - …(3)

[0053] Cu 2+ +4OH - ⇔Cu(OH)2+2OH - …(4)

[0054] In addition, it is said that the reaction represented by the following formula (5) occurs in an ammonia environment. It is believed that the Cu eluted into the aqueous phase forms a water complex ion and generates tetraammine copper (II) ions through the equilibrium reaction represented by formula (5).

[0055] [Cu(H2O)4] 2+ +4NH3⇔[Cu(NH3)4] 2+ +4H2O…(5)

[0056] When considering formula (3) to (4), it is believed that the elution amount of Cu from the copper phase to the water phase depends on the dissolved oxygen concentration of the water phase, the concentration of copper hydroxide (II), and the pH of the water phase. In addition, when considering formula (5), it is believed that it depends on the ammonia concentration. According to formula (5), the equilibrium of formula (4) moves, so it is worried that the elution of Cu will continue.

[0057] Based on such knowledge, the present inventors believe that it is effective to suppress the elution of Cu from the copper phase to the water phase and to suppress the formation of complex ions in which Cu participates in order to suppress the SCC of copper-based materials. As means for suppressing the elution of Cu, the suppression of the anode reaction of Cu elution, the detoxification of P in the copper phase, and the detoxification of O responsible for the cathode reaction are candidates. As means for suppressing the formation of complex ions, the removal of complex-forming components such as ammonia and the suppression of complex-forming reactions are candidates.

[0058] In addition, the inventors considered that: SCC does not occur in oxygen-free copper that does not contain P; P in the copper phase is easily eluted into the aqueous phase, and elution into the aqueous phase lowers the pH; at low pH, in the chemical form of Cu, copper ions are more stable than oxides and hydroxides, which promotes the elution of Cu from the copper phase to the aqueous phase; when P is contained in the copper phase, the electrode potential of the copper phase is reduced, which promotes the elution of Cu from the copper phase to the aqueous phase.

[0059] As a result, the inventors found a method of adding a predetermined additive element to Cu to eliminate the influence of P in order to solve the problem of SCC growth caused by P, thereby completing the present invention for suppressing SCC. As additive elements, the following characteristics (1) and (2) are considered to be effective.

[0060] (1) It is a base metal element with a lower potential than H at the standard electrode potential. Such a base metal element undergoes an anodic reaction at a potential lower than the anodic reaction that causes Cu to elute. That is, a sacrificial anodic reaction is generated relative to the cathode reaction in which oxygen participates. In addition, since the potential is lower than the hydrogen electrode potential, even if P elutes from the copper phase to the aqueous phase, it also shows an effect of suppressing the decrease in pH of the aqueous phase. Therefore, the elution of Cu from the copper phase to the aqueous phase can be suppressed by such an anodic reaction and pH suppression.

[0061] (2) It is a phosphorus compound forming element that reacts with P in the copper phase to form a phosphorus compound. The phosphorus compound forming element shows an effect of fixing P in the copper phase. When P is fixed in the copper phase, the elution of P from the copper phase to the aqueous phase is suppressed, and the pH of the aqueous phase becomes less likely to decrease. By such a pH suppression effect, the elution of Cu from the copper phase to the aqueous phase can be suppressed.

[0062] Here, the chemical composition of the copper alloy of the present embodiment will be described in more detail. In the following description, the expression "%" means mass % unless otherwise specified.

[0063] (Base Metal Elements)

[0064] As the base metal element, an element having a potential lower than H at the standard electrode potential is preferred, and an element having a potential lower than that of Mn is more preferred. In the case of such an element, even if P is eluted from the copper phase to the aqueous phase, the effect of suppressing the decrease in pH of the aqueous phase can be obtained. In addition, when the standard electrode potential is lower than the potential of Mn, the effect of phosphorus compound-forming elements such as Mn can also be obtained.

[0065] As a specific example of base metal elements, Mn, Al, first group elements, and second group elements can be cited. As first group elements, Li, Na, K, etc. can be cited. As second group elements, Mg, Ca, Ba, etc. can be cited. Through these elements, an anodic reaction occurs at a low potential lower than Cu, so the anodic reaction that makes Cu eluted can be suppressed. In addition, even if P eluted from the copper phase to the water phase, the reduction of the pH of the water phase can also be suppressed. The elution of Cu from the copper phase to the water phase can be effectively suppressed by these pH inhibitory effects.

[0066] As the base metal element, it is preferably a phosphorus compound forming element that reacts with P to form a phosphorus compound. As the phosphorus compound forming element, Mn, Mg, Ca, etc. can be cited. Through these elements, P in the copper phase can be fixed, and the elution of P from the copper phase to the aqueous phase can be suppressed. Since the reduction of the pH of the aqueous phase is suppressed, in the chemical form of Cu, compared with copper ions, oxides and hydroxides become stable, which can effectively suppress the elution of Cu from the copper phase to the aqueous phase.

[0067] As the base metal element, one element or a plurality of elements may be added to the copper matrix. As the base metal element, only phosphorus compound-forming elements may be added to the copper matrix, only non-phosphorus compound-forming elements other than phosphorus compound-forming elements may be added, or a combination of phosphorus compound-forming elements and non-phosphorus compound-forming elements may be added.

[0068] The amount of base metal elements is preferably 0.01% or more, more preferably more than 0.01%, more preferably more than 0.03%, more preferably more than 0.05%, and more preferably more than 0.10%. When it is such an amount of base metal elements, the effect of suppressing the elution of Cu from the copper phase to the water phase can be obtained. The amount of base metal elements is based on the total amount of base metal elements, and can be 0.15% or more, and can be 0.20% or more.

[0069] The amount of base metal elements is preferably less than 1.5% based on the total amount of base metal elements, more preferably less than 1.0%, further preferably less than 0.5%, further preferably less than 0.25%, further preferably less than 0.20%, and further preferably less than 0.15%. When the amount of base metal elements is too much, the cost of raw materials increases and the difficulty of casting increases. In addition, the mechanical properties and electrical properties change, making it difficult to use as a copper tube. However, when the amount of base metal elements is such, the influence on mechanical properties, brazing properties, etc. can be avoided, and the cost of raw materials and the difficulty of casting can be suppressed. The amount of base metal elements can be less than 0.10% based on the total amount of base metal elements, and can be less than 0.05%.

[0070] As the base metal element, Mg or Mn is preferably added, preferably at least one of Mg and Mn. In addition, as the base metal element, both Mg and Mn can be added. These base metal elements are phosphorus compound forming elements. When these base metal elements are added, P in the copper phase can be fixed as a phosphorus compound, and the decrease in pH of the aqueous phase caused by the elution of P can be suppressed. In addition, good processability and brazing properties can be obtained.

[0071] (Mg: 0.01% or more and 0.25% or less)

[0072] When Mg is included as a base metal element, the Mg amount is preferably 0.01% or more, more preferably 0.017% or more, further preferably 0.03% or more, further preferably 0.05% or more, and further preferably 0.10% or more. When such an Mg amount is used, the effect of suppressing the elution of Cu from the copper phase to the water phase can be obtained, and good mechanical properties such as tensile strength and wettability of the solder can be obtained. In addition, when the Mg amount is 0.017% or more, even with a P amount of 0.015%, which is the upper limit of the standard for low-phosphorus deoxidized copper, sufficient SCC resistance can be obtained. In addition, when the Mg amount is 0.10% or more, even with a P amount of 0.04%, which is the upper limit of the standard for high-phosphorus deoxidized copper, sufficient SCC resistance can be obtained.

[0073] When Mg is included as a base metal element, the Mg content is preferably 0.25% or less, more preferably less than 0.25%, more preferably 0.20% or less, and further preferably 0.15% or less. When the Mg content exceeds 0.25%, especially when it is 0.29% or more, the wettability of the solder is impaired. However, when the Mg content is 0.25% or less, good wettability of the solder can be obtained, and mechanical properties and high conductivity can be appropriately ensured.

[0074] (Mn: 0.01% or more and 1.5% or less)

[0075] When Mn is included as a base metal element, the Mn amount is preferably 0.01% or more, more preferably 0.03% or more, further preferably 0.05% or more, further preferably 0.10% or more, further preferably 0.50% or more, further preferably 1.0% or more, further preferably 1.2% or more. When such an Mn amount is used, the effect of suppressing the elution of Cu from the copper phase to the water phase can be obtained, and good mechanical properties such as tensile strength can be obtained.

[0076] When Mn is included as a base metal element, the Mn amount is preferably 1.5% or less, more preferably 1.4% or less, and further preferably 1.3% or less. When the Mn amount exceeds 1.5%, the yield strength becomes high and the bending workability decreases. However, when the Mn amount is 1.5% or less, good workability can be obtained and high conductivity can be appropriately ensured.

[0077] (P: more than 0% and less than 0.040%)

[0078] P is mainly added for deoxidation. When the amount of P is too much, toughness and processability are reduced, and SCC sensitivity and ant nest corrosion sensitivity become higher. Therefore, the amount of P is preferably 0.040% or less. The amount of P may be more than 0% and less than 0.0003%, more than 0.0003% and less than 0.001%, more than 0.001% and less than 0.004%, more than 0.004% and less than 0.015%, or more than 0.015% and less than 0.040%, depending on the acceptable amount of O, etc.

[0079] (Unavoidable impurities)

[0080] Inevitable impurities refer to substances that need to be added in the manufacture of copper alloys and copper alloy tubes, substances that are difficult to completely separate and remove, and elements that are inevitable impurities due to the mixing of raw materials and the mixing in the manufacturing process. Preferably, the copper alloy has P: more than 0% and less than 0.040 mass%, the total of base metal elements is less than 1.5 mass%, and the balance is composed of Cu and inevitable impurities.

[0081] As specific examples of inevitable impurities, O, H, S, Pb, Bi, Se, Te, As, Sb, etc., which are elements other than base metal elements, can be cited. The amount of inevitable impurities is preferably 0.1% or less, more preferably 0.05% or less, and further preferably 0.01% or less based on the total amount of each element. If the total amount of inevitable impurities is 0.1% or less, the effect of the present invention will not be inhibited.

[0082] (O: 0.01% or less)

[0083] O reacts with H to generate water vapor in a high temperature environment such as during furnace brazing in a hydrogen atmosphere, which is the main cause of hydrogen embrittlement. In addition, it forms oxides to reduce workability. Therefore, the amount of O is preferably 0.01% or less, more preferably 0.005% or less, and further preferably 0.001% or less.

[0084] (Other elements)

[0085] The amount of S is preferably 0.0018% or less. The amounts of Pb, Bi, Se, Te and C are each preferably 0.001% or less. The amounts of Zn, Cd and Hg are each preferably 0.0001% or less.

[0086] (Cu: 98.5% or more)

[0087] Cu constitutes the remainder of the copper alloy except for base metal elements and inevitable impurities. The amount of Cu is not particularly limited as long as it constitutes the remainder of the copper alloy. However, from the viewpoint of obtaining the characteristics of the copper alloy equivalent to pure copper, such as thermal conductivity, bending workability, brazing property, etc., the amount of Cu is preferably 98.5% or more, more preferably 99.0% or more, further preferably 99.5% or more, further preferably 99.80% or more, and further preferably 99.90% or more.

[0088] Next, the corrosion resistance of the copper alloy according to the present embodiment against stress corrosion cracking (SCC) will be described.

[0089] The corrosion resistance of the copper alloy of the present embodiment to stress corrosion cracking (SCC) can be evaluated based on the technical standard of the Japan Copper and Brass Association JBMA T-301-1981, which is based on the crack depth measured after exposure to a saturated environment based on an ammonia solution and applying a given stress. The crack depth based on SCC is defined as the shortest distance from the surface of the copper alloy to the deepest point of the crack.

[0090] The ammonia test based on JBMA T-301-1981 was carried out using a 14% by mass ammonia solution. The ammonia solution was prepared by diluting a 25% by mass or more ammonia solution with an equal amount of pure water. The test environment temperature was room temperature, and the container containing the ammonia solution was kept in a room controlled at room temperature of 20°C ± 5°C. The test material was arranged in a test container with a capacity of 10L to which the ammonia solution was added in a manner that it was not in direct contact with the ammonia solution. The test material was arranged at a distance of 100mm from the liquid surface of the ammonia solution. The exposure condition to the ammonia atmosphere in the test container was 72 hours at room temperature.

[0091] The test material formed of the copper alloy for the ammonia test is a plate or a tube. After the exposure test to the ammonia atmosphere, in the case of plates, Figure 2 As shown in FIG. 1 , the steel sheet is bent 180 degrees (180°) with the center line parallel to the rolling direction as the bending axis to apply external stress. In the case of a pipe, the steel sheet is squeezed from the radial direction of the pipe to less than half of the outer diameter to apply external stress. The observation point of cracking due to SCC is the surface on the peak side when bending in the case of a plate. In the case of a pipe, it is the surface on the outside of the bent portion when squeezing.

[0092] Sometimes, surface flaws are formed on the surface of copper pipes during pipe manufacturing. Usually, the maximum depth of cracks due to surface flaws is about 0.03 mm. It is difficult to distinguish between shallow cracks due to SCC and cracks caused by surface flaws. Therefore, even if the crack depth due to SCC exceeds 0.03 mm, as long as it is 0.05 mm or less, it can be judged that the corrosion resistance to SCC is good. In addition, if it is 0.03 mm or less, it can be said that SCC does not substantially occur.

[0093] The copper alloy of the present embodiment satisfies the following formula (I) when P is 0.0065 mass % or more and 0.040 mass % or less, in terms of mass %, the Mg concentration of the copper alloy is set to Y[%], and the P concentration is set to X[%]. Based on JBMA T-301-1981, after being exposed to a 14 mass % ammonia aqueous solution at a distance of 100 mm for 72 hours in a room maintained at a room temperature of 20±5°C, the copper alloy sheet is bent to 180 degrees, or the copper alloy tube is extruded to less than half of the outer diameter. The crack depth is measured, and the crack depth is preferably 0.05 mm or less.

[0094] Y≥2X-0.0130 (0.0065≤X≤0.0400)…(I)

[0095] When P is 0.0065 mass % or more and 0.040 mass % or less, and the Mg concentration satisfies the condition of formula (I), the crack depth due to SCC can be suppressed to 0.05 mm or less in the ammonia test based on JBMA T-301-1981. In an ammonia environment where SCC is promoted, the progress of SCC is suppressed to a small extent, so a copper alloy with excellent SCC resistance can be obtained.

[0096] The copper alloy of the present embodiment satisfies the following formula (II) when P is less than 0.040 mass %, in terms of mass %, the Mg concentration of the copper alloy is set to Y[%], and the P concentration is set to X[%]. Based on JBMA T-301-1981, after being exposed to a 14 mass % ammonia aqueous solution at a distance of 100 mm for 72 hours in a room maintained at a room temperature of 20±5°C, the copper alloy sheet is bent to 180 degrees, or the copper alloy tube is extruded to less than half of the outer diameter. The crack depth is more preferably less than 0.03 mm.

[0097] Y≥2X (X≤0.0400)…(II)

[0098] When P: is less than 0.040 mass %, when the Mg concentration satisfies the condition of formula (II), the crack depth based on stress corrosion cracking can be suppressed to less than 0.03 mm in the ammonia test according to JBMA T-301-1981. If P: is less than 0.0065 mass %, SCC is not easy to progress even without adding base metal elements. However, even within this range, copper alloys still show SCC sensitivity. Therefore, in the case of wanting to ensure higher SCC resistance, the condition of formula (II) is required.

[0099] As situations where higher SCC resistance is required, there are cases where copper alloys are used under conditions where the generation and progression of SCC are accelerated, such as when there is a source of ammonia in a closed environment such as a factory or a house; when the damage of copper alloys due to SCC is strictly restricted; for example, when copper alloys are used as materials for refrigerant piping, heat exchanger piping, etc., and flammable refrigerant flows inside the copper alloy pipe.

[0100] Next, the uses of the copper alloy and the copper alloy tube according to the present embodiment and the method for producing the same will be described.

[0101] The copper alloy of this embodiment can be used as a material for various copper products. Examples of copper products include pipes, plates, rods, wires, and other shaped materials. The copper alloy is particularly preferably used as a material for copper alloy pipes.

[0102] The copper alloy tube may be an inner grooved tube having grooves formed on the inner surface of the tube, or may be a smooth tube having no grooves formed on the inner surface of the tube. The inner grooved tube may be provided with spiral grooves at a given interval or linear grooves arranged in parallel to each other on the entire circumference of the inner surface of the tube. When manufacturing an inner grooved tube as a copper alloy tube, the number of grooves, the bottom width of the grooves, the wall thickness of the grooves, the height of the fins between the grooves, the top angle of the fins, the lead angle of the grooves relative to the central axis of the tube, etc. may be set as appropriate conditions.

[0103] According to the copper alloy tube, since the base metal element is added, even if P is added for deoxidation, the generation and development of SCC can be suppressed. Therefore, compared with oxygen-free copper, the cost can be suppressed, hydrogen embrittlement can be prevented by deoxidation of P, and SCC growth due to P can be suppressed. Since it is not easily affected by the amount of P, the freedom of material selection is expanded.

[0104] In particular, the inner grooved tube can increase the surface area of ​​the copper alloy tube, and the grooves can stir the fluid flowing in the copper alloy tube. Therefore, in the application of circulating the refrigerant, high energy efficiency and high energy-saving performance can be obtained. In addition, the miniaturization of the pipe for circulating the refrigerant can be achieved by expanding the surface area and improving the energy efficiency.

[0105] The copper alloy tube can be manufactured by a manufacturing method including a casting step, a soaking step, a hot extrusion step, a rolling and drawing step, and an annealing step. The internally grooved tube can be manufactured by performing a rolling process and a final annealing step after manufacturing the copper alloy tube.

[0106] (Casting process)

[0107] In the casting process, the raw material of the copper alloy is melted in a reducing atmosphere, a deoxidizing material is added to adjust the P amount, and then an ingot of a given size is cast. As the raw material, electrolytic copper, a raw metal containing a base metal element, etc. can be used. As the deoxidizing material, phosphor copper, etc. can be used. As the casting method, a semi-continuous casting method, etc. can be used to cast a billet, etc.

[0108] (Heat soaking process)

[0109] In the soaking process, the ingot such as the billet is homogenized by heat treatment. By homogenization, the segregation of P and the like is removed, and the added base metal elements are diffused. The temperature of the heat treatment is, for example, 680°C or more and 950°C or less. When it is 680°C or more, the segregation of P and the like can be fully removed. When it exceeds 950°C, the homogenization effect reaches its peak, and when it is 950°C or less, the heat treatment cost can be suppressed. The heat treatment time is, for example, 15 minutes or more and 2 hours or less.

[0110] (Hot extrusion process)

[0111] In the hot extrusion process, a heated billet or other ingot is hot extruded into a die having a mandrel inserted therein to form a tube. The temperature of the hot extrusion is, for example, 680°C or higher and 950°C or lower. The processing rate in the hot extrusion can be set to an appropriate condition as long as cracks, surface defects, etc. are not generated. The tube after extrusion is cooled, for example, by natural cooling. It should be noted that piercing and rolling using a plug and a roller die can be performed instead of hot extrusion and rolling.

[0112] (Rolling and drawing process)

[0113] In the rolling and drawing process, the formed tube blank is subjected to rolling and drawing using a mandrel to form a stretched drawn tube blank. The processing rate in the rolling and drawing processes can be set to appropriate conditions, and is preferably 95% or less from the viewpoint of reducing cracks, surface defects, etc. The drawing process can be performed with an appropriate number of passes using a continuous drawing machine using a plug, etc. From the viewpoint of reducing cracks, surface defects, etc., the processing rate in each pass is preferably 40% or less.

[0114] (Annealing process)

[0115] In the annealing process, the processed drawn tube is annealed by heat treatment. By annealing, the processing strain is removed and softened. Annealing can be performed using a roller hearth furnace, a high-frequency induction heating furnace, etc. The temperature of the heat treatment is, for example, 350°C or more and 700°C or less, preferably 350°C or more and 500°C or less. When it is 350°C or more, the processing strain can be appropriately removed. The time of the heat treatment is, for example, 5 minutes or more and 2 hours or less.

[0116] The copper alloy tube as a smooth tube can be manufactured through the above steps. The internally grooved tube can be manufactured by subjecting a drawn tube blank to groove rolling.

[0117] (Rolling process)

[0118] In the rolling process, groove rolling is performed on the drawn tube to form grooves on the inner surface of the drawn tube. The groove rolling process can be performed, for example, by roller rolling using a grooved plug. A grooved plug formed with a reverse groove for transferring the groove is inserted into the tube. Then, the tube is pulled out while being pressed by a rotating roller die, and the grooves are formed on the inner surface of the tube. The groove rolling process can be performed continuously from the diameter reduction pass of the drawing process using a grooved plug connected to a diameter reduction plug. In addition, a ball die with a bearing structure can be used instead of a roller die.

[0119] (Final annealing process)

[0120] In the final annealing step, the grooved pipe is subjected to final annealing by heat treatment. The final annealing can be performed in a roller hearth furnace, a high-frequency induction heating furnace, etc., similarly to the annealing step. The temperature of the heat treatment is, for example, 350° C. to 700° C., preferably 350° C. to 500° C. The time of the heat treatment is, for example, 5 minutes to 2 hours.

[0121] Through the above steps, a copper alloy tube as an inner grooved tube can be manufactured. The manufactured copper alloy tube can be subjected to processing such as straightening, chamfering, and cutting, and appearance inspection. In addition, the drawn tube blank can be subjected to straightening, chamfering, flaw detection, etc. after drawing and before annealing.

[0122] Copper alloy pipes can be used for various purposes. Examples of the use of copper alloy pipes include heat exchanger pipes, refrigerant pipes, hot water supply pipes, and water supply pipes. Examples of heat exchanger pipes include pipes connected to fins and the like to form heat exchangers. Examples of refrigerant pipes include pipes that circulate refrigerants. Examples of hot water supply pipes and water supply pipes include pipes that circulate hot water, warm water, and cold water.

[0123] These pipes can be installed in refrigeration and air conditioning equipment, heat exchange devices, water heaters, etc. Refrigeration and air conditioning equipment includes air conditioners, refrigerators, vapor compression refrigerators, absorption refrigerators, etc. Absorption refrigerators include ammonia type and lithium bromide type. In lithium bromide type, ammonia is sometimes inevitably left in the refrigerant purification process. Ammonia is one of the environmental factors that increase SCC. The copper alloy pipe of this embodiment is particularly effective for use in an ammonia environment.

[0124] Copper alloy tubes are preferably used as materials for heat exchangers. As heat exchangers, various heat exchangers such as finned tube type, bellows type, double tube type, etc. can be cited. Copper alloy tubes can be used for straight tube parts, and can be used for curved tube parts such as U-shaped bends and spirally wound parts relative to main pipes. Heat exchangers using copper alloy tubes can be used, for example, in air conditioners, refrigerated showcases, refrigerators, oil coolers, radiators, etc.

[0125] Figure 1 This is a diagram schematically showing an example of a heat exchanger including copper alloy tubes.

[0126] like Figure 1 As shown, the heat exchanger 30 includes a plurality of fins 10 and a heat transfer pipe 20. The plurality of fins 10 are arranged at predetermined intervals to form ventilation paths between the fins 10. The heat transfer pipe 20 is bent into a U-shape at a plurality of locations, and is inserted into the through holes on the fins 10 so as to penetrate through the plurality of fins 10 and brazed.

[0127] The heat transfer pipe 20 is formed of a copper alloy tube to which the base metal element is added. The copper alloy tube may be an inner grooved tube having grooves formed on the inner surface of the tube, or may be a smooth tube having no grooves formed on the inner surface of the tube. According to the heat exchanger using the copper alloy tube, SCC is suppressed by the base metal element, so that the heat exchange medium such as the refrigerant is unlikely to leak for a long time, and a heat exchanger with high reliability can be obtained.

[0128] Example

[0129] Hereinafter, the present invention will be described in detail by showing examples of the present invention, but the technical scope of the present invention is not limited thereto.

[0130] Copper alloy test materials with base metal elements added were prepared, and the effects of stress corrosion cracking (SCC) and other material properties were evaluated. Other material properties included ant nest corrosion resistance, tensile strength, and solder wettability. In addition, copper alloy test materials with different base metal element contents were prepared, and the crack depth based on SCC was measured for each content.

[0131] As a test material, a plate or a tube in which only a given base metal element is added to a copper alloy equivalent to phosphorus deoxidized copper is prepared. The plate is prepared by adjusting the chemical composition to cast the raw material, and then hot rolling, cold rolling, and annealing are performed in sequence. The tube is prepared by adjusting the chemical composition to cast the raw material, and then hot extrusion, cold drawing, and annealing are performed in sequence.

[0132] (Evaluation of Formicary Corrosion Resistance)

[0133] The evaluation of the ant nest corrosion resistance is carried out in the following order using a plate as a test material. First, a test material of 200 mm in length is placed in a test container filled with a corrosive solution. A plastic bottle is used as the test container, a hole is opened in the plastic bottle cover, and a silicon plug is inserted as a cover. A hole is dug in the silicon plug, and the plate is held in the form of inserting the plate in the dug hole. At this time, the plate is arranged at a height that does not directly contact the corrosive solution, so that a section of the plate with a length of 100 mm is exposed to the test environment inside the plastic bottle. At this time, in order to make the direction of the corrosion generated on the plate uniform, the plate is covered with silicone resin except for the observation surface. In addition, the test container is sealed and placed in a drying oven set with a given thermal cycle, and it is allowed to stand while repeatedly performing thermal cycles for a given test time. Then, the test material is buried in acrylic resin or epoxy resin, and the ant nest corrosion generated in the test material is observed by cross-sectional observation.

[0134] The evaluation conditions for formicary corrosion resistance are as follows.

[0135] · Dimensions of the test material: width 10~13mm×length 200mm×thickness 1.0mm (a portion of the test material is covered with rubber material, and the exposed area of ​​the inside of the test container in the corrosive environment is only one side.).

[0136] Test container: 2L plastic container

[0137] Corrosive solution: 500 mL of 0.5% by volume formic acid aqueous solution

[0138] · Test atmosphere: Based on the gas cylinder of industrial oxygen (purity 99.5vol.% or more), oxygen taken out through the indoor dedicated piping and the connected silicon tube is used as the replacement gas. Oxygen is flowed into the silicon tube inserted more than 100mm into the 2L plastic container at a flow rate of 1L / min for 5 minutes as the replacement gas, so that the inside of the container is oxygen atmosphere.

[0139] Temperature conditions (thermal cycle conditions of drying oven): Repeatedly keep at 20°C for 2 hours and then keep at 40°C for 22 hours

[0140] ·Test time: 60 days

[0141] The evaluation of the ant nest corrosion resistance is based on the following criteria. The maximum corrosion depth due to ant nest corrosion is measured as the distance from the surface of the test material to the deepest point of corrosion. Three cross sections of each test material are observed (observed with an interval of 1 mm or more between the cross sections), and the maximum distance among them is calculated as the maximum corrosion depth.

[0142] ○: Maximum corrosion depth 0.25mm or less → Good resistance to ant nest corrosion

[0143] ×: Maximum corrosion depth exceeds 0.25 mm → Poor resistance to anthill corrosion

[0144] (Evaluation of tensile strength)

[0145] The evaluation of tensile strength was carried out using a plate as a test material under the following conditions. The tensile strength was measured using a tensile testing machine.

[0146] · Dimensions of the test material: width 10mm × length 200mm × thickness 0.1mm

[0147] · Test method: Based on JIS Z2241:2011 metal material tensile test method, using a strip test piece.

[0148] The tensile strength was evaluated based on the following criteria.

[0149] ○: Tensile strength 280N / mm 2 Above → Maintaining bending and other workability

[0150] ×: Tensile strength exceeds 280 N / mm 2 →Deterioration of bending and other workability

[0151] (Evaluation of stress corrosion cracking resistance)

[0152] The stress corrosion cracking resistance is evaluated using plates or pipes as test materials, using the ammonia test based on JBMA T-301-1981, in the following order: First, the test material is placed horizontally above the middle plate in a test container filled with a corrosive liquid, at a height that does not directly contact the corrosive liquid. Figure 2 Sampling method for test materials that represent the situation of plate materials. When plate materials are used in the test materials, such as Figure 2As shown, a plate is cut from the rolled material in a manner of 10-13 mm in width × 25 mm in length × 1 mm in thickness, and is arranged above the middle plate with the front and back sides facing in the up-down direction. In the case of a pipe, a length of 20 mm is cut. A resin-covered copper wire with a diameter of 2.5 mm is placed between the two ends of the test material and the middle plate so that the test material is not in direct contact with the middle plate. Next, the test container is sealed and left to stand for a given test time. Furthermore, the test material is taken out of the test container, pickled with sulfuric acid, and then loaded with external stress as a pretreatment.

[0153] Figure 2 It is a figure which shows the method of pre-treating the test material formed of copper alloy. Figure 2 The upper left figure shows a copper alloy block before rolling used for preparation of the test material. Figure 2 The upper right figure shows the cut-out positions of the rolled material and the test material obtained by rolling the copper alloy block. Figure 2 The figure below shows the bending position of the test material used for loading stress.

[0154] like Figure 2 As shown, when the test material is a plate, it is bent 180 degrees (180°) with the center line parallel to the rolling direction as the axis in such a way that the upper surface when exposed to the test environment becomes the outer side. On the other hand, for pipes, the outer diameter is less than half, for example, in the case of Φ9.52mm, it is extruded to about 4mm in one axial direction along the radial direction as the rolling direction. From the appearance of the peak side of the extruded surface, observe the presence or absence of cracks using an optical microscope (×69 times). From the appearance, cut out the cross section of the location where the crack is severe, bury it in acrylic resin or epoxy resin, and observe the cracking of the cross section using an optical microscope (×150 times). When there are multiple points where the crack is severe, split the test material for cross-sectional observation.

[0155] Figure 3 This is a diagram showing a method for measuring the crack depth due to stress corrosion cracking. Figure 4 It is a magnified representation Figure 3 Figure 1 shows the main parts of the . Figure 4 Equivalent to Figure 3 An enlarged view of the rectangular area S in .

[0156] like Figure 3 As shown in FIG. 1 , the original outer surface of the test material does not exist at the location where stress corrosion cracking occurs. Therefore, a cross-sectional image of the test material is taken, and an imaginary line representing the outer surface of the test material is interpolated by image processing to measure the maximum crack depth due to stress corrosion cracking.

[0157] like Figure 3As shown, with point A on the valley side as the center, point B and point B' are determined on the outer surface at 45 degrees (45°) to the left and right. In addition, with point A as the center, the arc passing through point B and point B' is interpolated as an imaginary surface. Draw an imaginary straight line C passing through point A and the deepest point of the crack, and find the intersection of the imaginary straight line C and the arc-shaped imaginary curve. The shortest distance from the intersection to the deepest point of the crack is measured as the crack depth based on SCC. The maximum corrosion depth is set to the maximum crack depth in the crack confirmed between the arc B-B' set in the cross section observed for a given number of measurements.

[0158] The conditions for evaluating stress corrosion cracking resistance are as follows.

[0159] ·Sheet size: width 10~13mm×length 25mm×thickness 1.0mm

[0160] ·Pipe dimensions: outer diameter 9.52mm×thickness 0.8mm×length 20mm

[0161] Test container: 10L desiccator

[0162] Corrosive liquid: 100 mL of 14% by mass ammonia water (made by diluting a commercially available 25% by mass or higher ammonia solution with an equal amount of pure water)

[0163] Temperature conditions: The test temperature was set to room temperature, and the room temperature of the room where the test container was kept was controlled within 20°C ± 5°C by an air conditioner.

[0164] Exposure conditions: 100mm from the surface of the corrosive liquid

[0165] Test time: maximum 72 hours

[0166] The stress corrosion cracking resistance was evaluated based on the following criteria: When the maximum crack depth was 0.03 mm or less, it was difficult to distinguish from surface flaws during pipe manufacturing and therefore could not be regarded as a crack due to SCC.

[0167] ◎: Maximum crack depth is less than 0.03mm → Excellent resistance to stress corrosion cracking

[0168] ○: Maximum crack depth exceeds 0.03 mm and is 0.05 mm or less → Good stress corrosion cracking resistance

[0169] ×: Maximum crack depth exceeds 0.05 mm → poor stress corrosion cracking resistance

[0170] (Evaluation of solder wettability)

[0171] The evaluation of the wettability of the solder is carried out under the following conditions using a plate as the test material. First, the test material is bent at 90 degrees (90°) along the center line of the length direction. In addition, a rod-shaped solder is arranged in the center of the valley side of the test material. The test material with the solder is heated under given heating conditions and then cooled. Then, the length of the solder in the longitudinal direction that wets and extends on the surface of the test material is measured.

[0172] The evaluation conditions of the wettability of the brazing material are as follows.

[0173] · Dimensions of the test material: width 30mm × length 100mm × thickness 1.0mm

[0174] Type of solder: Phosphorus copper solder BCuP-2 (diameter 1.6mm x length 20mm)

[0175] Heating equipment: Infrared gold image furnace (manufactured by ULVAC Co., Ltd.)

[0176] Heating atmosphere: Nitrogen atmosphere

[0177] Heating conditions: Heating from room temperature to 850°C at a rate of 850°C / 5 minutes

[0178] Holding conditions: 850°C for 5 minutes

[0179] Cooling conditions: natural cooling

[0180] The wettability of the brazing material was evaluated based on the following criteria.

[0181] ○: The length of the brazing material in the longitudinal direction is 100 mm or more → The wettability of the brazing material is good

[0182] ×: The length of the brazing material in the longitudinal direction is less than 100 mm → The wettability of the brazing material is poor

[0183] (Analysis of chemical composition of test materials)

[0184] The chemical composition of the test material was analyzed using a light emission spectrometer PDA-7000 (manufactured by Shimadzu Corporation) under the following conditions in accordance with "5 Spark discharge light emission spectrometry" of JIS K0116:2014 Light emission spectrometry general rules.

[0185] The analysis conditions of the chemical composition are as follows.

[0186] Analysis atmosphere: high purity argon atmosphere (99.9995% by volume)

[0187] Electrode spacing: 7mm (discharge gap distance)

[0188] Quantitative method: fixed time integration based on intensity ratio method

[0189] ·Preparatory discharge: 1500 pulses

[0190] ·Formal discharge: 1200 pulses (discharge time used as integration time)

[0191] The chemical composition analysis was performed at any three points on the surface of the test material after annealing. For plates, the smooth main surface was measured. For pipes, the smooth outer surface was measured after the pipe was extruded. The average value of the measured values ​​at each position was calculated as the measurement result of each test material.

[0192] The measurement wavelength of spark emission spectrometry used for the analysis of chemical composition and the measurement sensitivity based on the wavelength are as follows.

[0193] Al: wavelength 396.1nm, measurement sensitivity 44

[0194] Cu: wavelength 296.1nm, measurement sensitivity 24

[0195] Mg: wavelength 285.2nm, measurement sensitivity 24

[0196] P: Wavelength 178.3nm, measurement sensitivity 52

[0197] Table 1 shows the chemical composition (target value of Mg content) of the test materials and the evaluation results of formicary corrosion resistance, tensile strength, stress corrosion cracking resistance, and brazing filler metal wettability. The comprehensive judgment is a comprehensive evaluation of these.

[0198] [Table 1]

[0199]

[0200] As shown in Table 1, the Mg concentrations of Examples 1 and 2 were 0.01 mass% and 0.25 mass%, and the wettability of the solder met the standard. The Mg concentration of Comparative Example 1 was 0.29 mass%, and the wettability of the solder did not meet the standard. From the perspective of the wettability of the solder, it can be said that the Mg concentration is preferably 0.25 mass% or less.

[0201] Table 2 shows the chemical composition of the test materials (analyzed values ​​of the amount of Mg, the amount of Mn, and the amount of P), the measurement results of the maximum crack depth due to stress corrosion cracking, and the evaluation results of the stress corrosion cracking resistance.

[0202] [Table 2]

[0203]

[0204] Figure 5This is a graph showing the relationship between the crack depth and P concentration due to stress corrosion cracking. Figure 5 In the graph, the vertical axis represents the crack depth [μm] measured using the test material, and the horizontal axis represents the P concentration [mass %] of the test material. The curve with ○ is the result of the test material of the embodiment with a Mg content of 0.1 mass %. The curve with ◇ is the result of the test material of the comparative example without adding the base metal element.

[0205] like Figure 5 As shown in the figure, when the P concentration of the copper alloy is low, cracks based on stress corrosion cracking are suppressed regardless of whether or not base metal elements are added. When the crack depth is 30 μm or less, it is difficult to distinguish from surface flaws during pipe making, so it can be said that cracks based on SCC do not occur. Therefore, it can be said that the addition of base metal elements is particularly effective when the P concentration is 0.0065 mass% or more.

[0206] Figure 6 This is a graph showing the relationship between Mg concentration and P concentration and crack depth due to stress corrosion cracking. Figure 6 In the graph, the vertical axis represents the Mg concentration [mass%] of the test material, and the horizontal axis represents the P concentration [mass%] of the test material. The curve of ● is the result of the test material with a maximum crack depth of 30μm or less. The curve of ▲ is the result of the test material with a maximum crack depth of more than 30μm and less than 50μm. The curve of ● is the result of the test material with a maximum crack depth of more than 50μm.

[0207] exist Figure 6 In the figure, the upper dotted line represents a straight line represented by formula (I): Y=2X-0.0130 when the Mg concentration is set to Y[%] and the P concentration is set to X[%]. The lower dotted line represents a straight line represented by formula (II): Y=2X when the Mg concentration is set to Y[%] and the P concentration is set to X[%]. These straight lines are obtained as linear boundary conditions based on the results of Examples 1-1 to 1-20 shown in Table 2.

[0208] As shown in Table 2 and Figure 6 As shown, Examples 1-1 to 1-14 satisfy the relationship shown in formula (II): Y ≥ 2X (X ≤ 0.0400), and the amount of base metal elements is appropriate relative to the amount of P, so the stress corrosion cracking resistance meets the standard of 0.03 mm or less. In Example 1-13, good stress corrosion cracking resistance is obtained by 0.041 mass% of Mg relative to 0.02 mass% of P, and the stress corrosion cracking resistance meets the standard of 0.03 mm or less.

[0209] Since Example 1-15 does not contain P, even without adding a base metal element, the stress corrosion cracking resistance satisfies the standard of 0.03 mm or less.

[0210] In Example 1-16, P is a trace amount, so the stress corrosion cracking resistance does not meet the standard of 0.03 mm or less, and even if no base metal element is added, the stress corrosion cracking resistance meets the standard of 0.05 mm or less. However, compared with Example 1-15, as P increases, the depth of the crack increases.

[0211] Example 1-17 does not satisfy the relationship shown in formula (II): Y ≥ 2X (X ≤ 0.0400), P is a trace amount, so the stress corrosion cracking resistance meets the standard of 0.05 mm or less. Examples 1-18 and 1-19 satisfy the relationship shown in formula (I): Y ≥ 2X-0.0130 (0.0065 ≤ X ≤ 0.0400), and the amount of base metal elements is appropriate relative to the amount of P, so the stress corrosion cracking resistance meets the standard of 0.05 mm or less.

[0212] In Example 1-21, the base metal element is Mn, but the amount of the base metal element is appropriate relative to the amount of P, so the stress corrosion cracking resistance satisfies the standard of 0.03 mm or less. It is found that even if the base metal element is Mn, the development of cracks due to stress corrosion cracking is suppressed.

[0213] In Comparative Examples 1-1 to 1-5, the crack depth after the stress corrosion cracking test exceeded 0.05 mm, and the relationship shown in Formula (I) and the relationship shown in Formula (II) were not satisfied. Comparative Examples 1-2 and 1-3 did not contain base metal elements, and in particular, Comparative Example 1-2 was equivalent to low phosphate copper (JIS H3300 C1201), and the stress corrosion cracking resistance did not meet the standard of 0.05 mm or less. In Comparative Examples 1-1, 1-4 and 1-5, the amount of base metal elements was insufficient relative to the amount of P, and the effect of improving the corrosion resistance to stress corrosion cracking was not confirmed.

[0214] Above, various embodiments have been described, and the present invention is certainly not limited to these examples. As long as it is a person skilled in the art, various variations or modifications can be obviously thought of within the scope described in the claims, and these certainly also belong to the technical scope of the present invention. In addition, within the scope of not departing from the gist of the invention, each constituent element in the embodiment can be arbitrarily combined.

[0215] It should be noted that the present application is based on the Japanese patent application (Japanese Patent Application No. 2022-162811) filed on October 7, 2022, and the contents thereof are incorporated herein by reference.

[0216] As described above, the following matters are disclosed in this specification.

[0217] (1) A copper alloy to which a base metal element having a standard electrode potential equal to or lower than the potential of Mn is added.

[0218] (2) The copper alloy according to (1), wherein

[0219] The base metal element is a phosphorus compound forming element that forms a compound with P.

[0220] (3) The copper alloy according to (1) or (2), wherein:

[0221] The base metal element is at least one of Mg and Mn.

[0222] (4) The copper alloy according to (3), wherein

[0223] When Mg is contained as the base metal element, Mg is 0.25 mass % or less, and when Mn is contained as the base metal element, Mn is 1.5 mass % or less.

[0224] (5) The copper alloy according to any one of (1) to (4), wherein

[0225] P: 0.0065 mass % or more,

[0226] When the Mg concentration of the copper alloy is set to Y[%] and the P concentration is set to X[%], the following formula (I) is satisfied:

[0227] Based on JBMA T-301-1981, after being exposed to a 14 mass % ammonia aqueous solution at a distance of 100 mm for 72 hours in a room maintained at a room temperature of 20±5°C, the crack depth measured when the copper alloy sheet is bent to 180 degrees or the copper alloy tube is squeezed to less than half of the outer diameter is 0.05 mm or less.

[0228] Y≥2X-0.0130…(I).

[0229] (6) The copper alloy according to any one of (1) to (5), wherein

[0230] When the Mg concentration of the copper alloy is set to Y[%] and the P concentration is set to X[%], the following formula (II) is satisfied:

[0231] Based on JBMA T-301-1981, after being exposed to a 14 mass % ammonia aqueous solution at a distance of 100 mm for 72 hours in a room maintained at a room temperature of 20±5°C, the crack depth measured when the copper alloy sheet is bent to 180 degrees or the copper alloy tube is squeezed to less than half of the outer diameter is 0.03 mm or less,

[0232] Y ≥ 2X…(II)

[0233] (7) The copper alloy according to any one of (1) to (6), wherein

[0234] containing Mn as the base metal element,

[0235] Mn: 1.2 mass % or more and 1.5 mass % or less.

[0236] (8) A copper alloy tube formed from the copper alloy according to any one of (1) to (7) above.

[0237] (9) The copper alloy tube according to (8), which is an inner grooved tube having grooves formed on the inner surface of the tube.

[0238] (10) A heat exchanger using a copper alloy tube formed of the copper alloy described in any one of (1) to (7) above.

Claims

1. A copper alloy to which a base metal element having a standard electrode potential equal to or lower than the potential of Mn is added.

2. The copper alloy according to claim 1, wherein The base metal element is a phosphorus compound forming element that forms a compound with P.

3. The copper alloy according to claim 1 or 2, wherein: The base metal element is at least one of Mg and Mn.

4. The copper alloy according to claim 3, wherein When Mg is contained as the base metal element, Mg is 0.25 mass % or less, and when Mn is contained as the base metal element, Mn is 1.5 mass % or less.

5. The copper alloy according to any one of claims 1 to 4, wherein P: 0.0065 mass % or more, When the Mg concentration of the copper alloy is set to Y[%] and the P concentration is set to X[%], the following formula (I) is satisfied: Based on JBMA T-301-1981, after being exposed to a 14 mass % ammonia aqueous solution at a distance of 100 mm for 72 hours in a room maintained at a room temperature of 20±5°C, the crack depth measured when the copper alloy sheet is bent to 180 degrees or the copper alloy tube is squeezed to less than half of the outer diameter is 0.05 mm or less. Y≥2X-0.0130…(I).

6. The copper alloy according to any one of claims 1 to 5, wherein When the Mg concentration of the copper alloy is set to Y[%] and the P concentration is set to X[%], the following formula (II) is satisfied: Based on JBMA T-301-1981, after being exposed to a 14 mass % ammonia aqueous solution at a distance of 100 mm for 72 hours in a room maintained at a room temperature of 20±5°C, the crack depth measured when the copper alloy sheet is bent to 180 degrees or the copper alloy tube is squeezed to less than half of the outer diameter is 0.03 mm or less, Y ≥ 2X…(II).

7. The copper alloy according to any one of claims 1 to 6, wherein containing Mn as the base metal element, Mn: 1.2 mass % or more and 1.5 mass % or less. 8 . A copper alloy tube, comprising the copper alloy according to claim 1 . 9 . The copper alloy tube according to claim 8 , which is an inner grooved tube having grooves formed on the inner surface of the tube. 10 . A heat exchanger using a copper alloy tube formed of the copper alloy according to claim 1 .

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