Corrosion-resistant copper alloys, copper alloy tubes and heat exchangers

Abstract

To provide a copper alloy which improves corrosion resistance against stress corrosion cracks, and a copper alloy pipe and a heat exchanger using the same.SOLUTION: A copper alloy is a copper alloy added with a base metal element (for example, Mg and Mn) having a standard electrode potential equal to or lower than the potential of Mn. A copper alloy pipe is formed of a copper alloy added with a base metal element having a standard electrode potential equal to or lower than the potential of Mn. A heat exchanger uses a copper alloy pipe formed of a copper alloy added with a base metal element having a standard electrode potential equal to or lower than the potential of Mn.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Phosphorus-deoxidized copper pipes are widely used as refrigerant piping and heat exchanger piping in refrigeration and air conditioning equipment. There are two types of phosphorus-deoxidized copper, C1201, which is low-phosphorus deoxidized copper as specified in JIS H3300:2018, and C1220, which is high-phosphorus deoxidized copper.

[0003] Copper is a material with excellent thermal conductivity, bendability, and brazing properties. It also has a high standard electrode potential, making it highly corrosion-resistant in non-oxidizing environments. Phosphorus-deoxidized copper contains phosphorus but no oxygen, making it less susceptible to hydrogen embrittlement, just like oxygen-free copper. Because phosphorus-deoxidized copper has lower manufacturing costs than oxygen-free copper, it is widely used in applications where it is exposed to high temperatures, such as brazing.

[0004] Corrosion-resistant materials such as copper-based materials can suffer from stress corrosion cracking (SCC) due to the combination of certain factors. Cases of SCC in copper-based materials such as pure copper and copper alloys in ammonia environments have long been reported. SCC in copper-based materials has been particularly notable in brass. However, in recent years, cases have also been reported in phosphorus-deoxidized copper pipes.

[0005] SCC of copper-based materials occurs under special conditions, such as in an ammonia environment, but it does not progress with ammonia alone; it progresses in the coexistence of ammonia and moisture. When moisture adheres to a copper-based material, ammonia dissolves in the aqueous phase, causing corrosion. SCC occurs when residual stress or external stress concentrates at the site of grain boundary corrosion. SCC is a phenomenon that leads to cracking due to tensile stress, but the corrosion mode in phosphorus-deoxidized copper is characterized by intergranular corrosion.

[0006] In fields such as refrigerant piping and heat exchanger piping, refrigerant leakage due to SCC has become a problem, and measures to suppress SCC are required. When piping is damaged due to the progression of SCC, it can lead to refrigerant leakage, making it impossible to maintain the functionality of equipment and compromising the reliability of the equipment. There are also concerns about the impact of refrigerant leakage on global warming. Measures to suppress SCC include, from a material perspective, methods to refine crystal grains, and, from a mechanical perspective, methods to reduce residual stress and external stress.

[0007] However, methods to reduce residual stress and external stress are difficult to implement in actual materials and are not practical as measures to suppress SCC. Furthermore, methods to refine crystal grains do not allow the material to be annealed sufficiently, which significantly impairs workability and severely limits its applications. Under these circumstances, measures to suppress SCC from the perspective of chemical composition, etc., are being considered.

[0008] Patent Document 1 describes a copper tube that has excellent corrosion resistance against ant nest corrosion and excellent corrosion resistance against SCC. This copper tube is made of a copper material containing 0.10 to 1.0 wt.% P, with the remainder being Cu and unavoidable impurities, and the P concentration (P1) at the grain boundaries of the copper material is less than 5.0 times the P concentration (P0) within the crystal grains of the copper material. By optimizing the final heat treatment conditions, P is prevented from concentrating at the grain boundaries, thereby reducing SCC susceptibility (see paragraph 0011).

[0009] Patent Document 2 describes a copper alloy having high electrical conductivity and excellent stress relaxation resistance. This copper alloy contains more than 0.001 mass% but not more than 0.01 mass% of Mg, and not more than 0.001 mass% of P. The alloy also contains not more than 0.001 mass% of H, not more than 0.01 mass% of O, and not more than 0.001 mass% of C.

[0010] Patent Document 3 describes pitting corrosion-resistant copper and copper alloy pipes that can prevent the occurrence of pitting corrosion. It also describes that when lithium bromide is used as an absorption liquid, ammonia inevitably remains in the refining process, and that the stress corrosion cracking susceptibility of phosphorus-deoxidized copper increases with increasing phosphorus content (see paragraph 0002).

[0011] The mechanism by which P added to copper promotes SCC has not been fully elucidated. Generally, the following factors (1) to (3) are assumed to be involved in the mechanism by which P promotes SCC.

[0012] (1) Grain boundaries are essentially locations where impurities and added P tend to concentrate. (2) P dissolves from the copper phase into the aqueous phase, which lowers the pH of the aqueous phase and causes Cu to dissolve. The dissolved Cu is more stable as a copper ion than as an oxide or hydroxide. (3) Distributions of pH and other parameters occur where corrosion progresses.

[0013] Furthermore, in Copper and Copper Alloys, Vol. 53, No. 1 (2014), pp. 128-133 (Electrochemical Approach to Elucidating the Mechanism of Ant Nest Corrosion), the following factor (4) is newly postulated: As ant nest corrosion progresses, a complexation reaction (4) occurs in which eluted P and copper ions form complex ions. From the perspective of free energy, this reaction is believed to drive the dissolution of Cu from the copper phase into the aqueous phase. This copper dissolution reaction caused by the elution of P can occur regardless of whether the corrosion-accelerating substance is formic acid or ammonia. Therefore, in the case of SCC, the elution of P is thought to lead to further elution of copper ions through reaction (4), which is expected to lead to more severe SCC progression. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2022-056871 [Patent Document 2] Japanese Patent Publication No. 2022-022637 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-154221 Summary of the Invention [Problem to be solved by the invention]

[0015] With conventional copper-based materials, it is currently difficult to prevent SCC while preventing hydrogen embrittlement. To prevent hydrogen embrittlement in copper-based materials, it is necessary to reduce the oxygen content. When copper containing oxygen is exposed to high temperatures in a hydrogen atmosphere, it experiences hydrogen embrittlement, resulting in a decrease in strength and toughness. In applications such as furnace brazing in a hydrogen atmosphere, hydrogen diffuses in the high-temperature environment when the material is heated, reducing copper oxide and generating water vapor voids at the grain boundaries, resulting in a decrease in strength and toughness.

[0016] Adding P to copper-based materials can suppress this hydrogen embrittlement by deoxidizing them, but the addition of P can cause the initiation and progression of SCC, which is a problem.

[0017] Oxygen-free copper has low oxygen and phosphorus concentrations, making it less susceptible to hydrogen embrittlement and less susceptible to SCC. However, oxygen-free copper requires special casting equipment, such as a vacuum melting and casting method, which creates issues in terms of manufacturing costs and price.

[0018] On the other hand, phosphorus-deoxidized copper is less susceptible to hydrogen embrittlement, but contains P added during the melting process for deoxidation. Phosphorus-deoxidized copper also includes low-phosphorus deoxidized copper, which contains 0.004% by mass or more but less than 0.015% by mass of P. However, even with low-phosphorus deoxidized copper, the effects of P cannot be completely eliminated, limiting its use in highly corrosive environments. Furthermore, low-phosphorus deoxidized copper requires a reduced proportion of recycled raw materials containing P during production, which places significant constraints on production costs and price.

[0019] In Patent Document 1, the P concentration at the grain boundaries is reduced to reduce the SCC susceptibility of copper materials. However, this method adjusts the ratio of the P concentration at the grain boundaries to the P concentration within the grains, and does not directly neutralize the P in the copper material. In addition, this method requires a special final heat treatment, which is thought to pose practical problems in terms of production efficiency, production equipment, etc.

[0020] Patent Document 2 specifies the ratio of Mg to the sum of S, P, Se, Te, Sb, Bi, and As, as well as the contents of H, O, and C, for copper alloys. However, this copper alloy contains trace amounts of P and is considered to be equivalent to oxygen-free copper. Such a P content poses problems in terms of manufacturing cost and price. Furthermore, H can cause defects in the structure, which may ultimately promote SCC, but it is not directly involved in SCC in copper-based materials.

[0021] Under these circumstances, there is a need for a technology that can suppress SCC while preventing hydrogen embrittlement and reducing costs for copper-based materials equivalent to phosphorus-deoxidized copper or oxygen-free copper. Even when P, which promotes SCC, is added, it is desirable to directly suppress SCC in copper-based materials by eliminating the effects of P.

[0022] 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 same. [Means for solving the problem]

[0023] In order to solve the above problems, the copper alloy according to the present invention comprises: P:0.0065 mass% or more 0.040% by mass or less, Mg: 0.25% by mass or less, The balance is Cu and unavoidable impurities. A copper alloy , The copper alloy satisfies the following formula (I): Y≧2X-0.0130 (I), where Y is the Mg concentration and X is the P concentration in the copper alloy, and the copper alloy is exposed to a 14 mass % ammonia solution at a distance of 100 mm for 72 hours in a room controlled at a room temperature of 20±5°C in accordance with JBMA T-301-1981, and then when a sheet material of the copper alloy is bent 180 degrees or when a pipe material of the copper alloy is crushed to half its outer diameter or less, the crack depth measured is 0.05 mm or less; or the copper alloy contains 0.040 mass % or less P, 0.25 mass % or less Mg, and the balance consisting of Cu and unavoidable impurities, and when Y is the Mg concentration and X is the P concentration in the copper alloy, the copper alloy satisfies the following formula (II): Y≧2X (II), and the copper alloy is compliant with JBMA T-301-1981. Copper alloys that have been exposed to a 14% by mass aqueous ammonia solution at a distance of 100 mm for 72 hours in a room controlled at a room temperature of 20±5°C in accordance with T-301-1981, and then have a crack depth of 0.03 mm or less when the copper alloy plate is bent 180 degrees or when the copper alloy pipe is crushed to less than half of its outer diameter. The copper alloy tube according to the present invention is formed from the above copper alloy. The heat exchanger according to the present invention uses the copper alloy tube formed from the above copper alloy. [Effects of the Invention]

[0024] 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 pipe and a heat exchanger using the same. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of a heat exchanger equipped with copper alloy tubes. [Figure 2] FIG. 1 is a diagram showing a method of pretreatment of a test material formed of a copper alloy. [Figure 3] FIG. 1 is a diagram showing a method for measuring crack depth due to stress corrosion cracking. [Figure 4] FIG. 4 is an enlarged view of a main part of FIG. 3. [Figure 5] FIG. 1 is a graph showing the relationship between crack depth due to stress corrosion cracking and P concentration. [Figure 6] FIG. 1 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 OF THE INVENTION

[0026] Hereinafter, a copper alloy according to one embodiment of the present invention, and a copper alloy tube and a heat exchanger using the same will be described.

[0027] The copper alloy according to this embodiment is a copper alloy to which a base metal element having a standard electrode potential equal to or lower than that of Mn is added. The base metal element is preferably a phosphorus compound-forming element that reacts with P to form a phosphorus compound. In a preferred embodiment of this copper alloy, P is more than 0% and not more than 0.040% by mass, the total amount of the base metal elements is 0.01% by mass to 1.5% by mass, and the balance is Cu and unavoidable impurities.

[0028] The copper alloy according to this embodiment improves corrosion resistance against stress corrosion cracking (SCC) by adding base metal elements. P may be added to this copper alloy to reduce the amount of O, which is a cause of hydrogen embrittlement. P is a factor that promotes SCC, but even if P is added for deoxidation, the base metal elements can suppress the initiation and progression of SCC.

[0029] Copper containing oxygen is known to suffer from hydrogen embrittlement when exposed to high temperatures in a hydrogen atmosphere. Hydrogen penetrates and diffuses between the lattices of the copper phase. When the diffused hydrogen reacts with copper oxide in the copper phase, it reduces the copper oxide and generates water vapor. As a result, even though the hydrogen itself does not directly cause an embrittlement reaction, the generated water vapor forms voids at the grain boundaries, resulting in a decrease in strength and toughness due to hydrogen embrittlement.

[0030] Furthermore, copper-based materials used for refrigerant pipes, heat exchanger pipes, etc., can sometimes suffer from ant nest corrosion, although this is rare. Ant nest corrosion is a type of corrosion in which tiny corrosion holes formed on the surface of a material cause ant nest-like erosion inward. 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 agents.

[0031] These corrosive agents are thought to be produced by hydrolysis and degradation reactions caused by moisture such as condensation in lubricating oils, processing oils, and organic solvents used in pipe manufacturing processes, heat exchanger assembly processes, and other substances contained in the usage environment.Once ant nest corrosion occurs, its characteristic shape causes the anodic reaction to concentrate in specific locations, accelerating the corrosion process and posing the risk of it progressing in the thickness direction and penetrating the wall in a short period of time.

[0032] Copper-based materials are often used in applications where brazing of refrigerant pipes and heat exchanger pipes is performed in a furnace under a hydrogen atmosphere. Because the brazing process involves high temperatures in a hydrogen atmosphere, it is desirable to reduce the amount of oxygen, which can cause hydrogen embrittlement. However, ant nest corrosion and stress corrosion cracking are affected by phosphorus, which is necessary for deoxidation during the casting process. From the perspective of improving SCC resistance and suppressing other corrosion phenomena, it is necessary to eliminate the effects of phosphorus.

[0033] The mechanism by which P added to Cu promotes SCC in phosphorus-deoxidized copper-based materials has not been fully elucidated. However, the corrosion form of SCC in phosphorus-deoxidized copper is intergranular corrosion. If an anodic reaction that dissolves Cu occurs, it is thought that a corresponding cathodic reaction is also occurring. Cu is resistant to corrosion under alkaline or non-oxidizing conditions, and it is speculated that oxygen is involved in the cathodic reaction.

[0034] Copper pipes used as refrigerant pipes, heat exchanger pipes, etc. may come into contact with moisture such as condensed water. Considering the Pourbaix diagram, which shows the stable state of chemical forms for each potential and pH, the reactions related to the dissolution of Cu in aqueous solution can be expressed by the following equations (1) and (2). Cu → Cu 2+ +2e - (1) (anode reaction) O2+2H2O+4e - → 4OH - (2) (Cathode reaction)

[0035] Using equations (1) and (2), the dissolution of Cu from the copper phase into the aqueous phase can be expressed by the following equations (3) and (4). The Cu dissolved into the aqueous phase can be considered to form copper(II) hydroxide through the equilibrium reaction expressed by equation (4). Cu+O2+2H2O → Cu 2+ +4OH - ···(3) Cu 2+ +4OH - ⇔ Cu(OH)2+2OH - ···(4)

[0036] In addition, it is said that in an ammonia environment, the reaction represented by the following formula (5) occurs: Cu dissolved in the aqueous phase forms an aqua complex ion, which is thought to generate tetraamminecopper(II) ions through the equilibrium reaction represented by formula (5). [Cu(H2O)4] 2+ +4NH3⇔[Cu(NH3)4] 2+ +4H2O (5)

[0037] Considering equations (3) and (4), the amount of Cu eluted from the copper phase to the aqueous phase is thought to depend on the dissolved oxygen concentration in the aqueous phase, the concentration of copper(II) hydroxide, and the pH of the aqueous phase. Furthermore, considering equation (5), it is thought to depend on the ammonia concentration. Since equation (5) shifts the equilibrium of equation (4), there is concern that Cu elution will continue.

[0038] Based on these findings, the inventors of the present invention have proposed that SCC of copper-based materials can be effectively suppressed by suppressing the dissolution of Cu from the copper phase into the aqueous phase and by suppressing the formation of Cu-related complex ions. Possible methods for suppressing Cu dissolution include suppressing the anodic reaction that dissolves Cu, neutralizing P in the copper phase, and neutralizing O, which is involved in the cathodic reaction. Possible methods for suppressing the formation of complex ions include removing complex-forming components such as ammonia and inhibiting the complex formation reaction.

[0039] The inventors also considered the following: SCC does not occur in oxygen-free copper that does not contain P; P in the copper phase is likely to dissolve into the aqueous phase, and dissolving into the aqueous phase lowers the pH; at low pH, copper ions are more stable than the oxides and hydroxides of Cu, among other chemical forms, and this promotes the dissolution of Cu from the copper phase into the aqueous phase; and when P is contained in the copper phase, the electrode potential of the copper phase decreases, promoting the dissolution of Cu from the copper phase into the aqueous phase.

[0040] As a result, the inventors discovered a method for eliminating the effect of P by adding specific additive elements to Cu to address the problem of SCC accelerated by P, and completed the present invention, which suppresses SCC. It was considered that the following characteristics (1) and (2) of the additive elements would be effective.

[0041] (1) It is a base metal element with a lower potential than H at the standard electrode potential. Such base metal elements cause an anodic reaction at a lower potential than the anodic reaction that dissolves Cu. In other words, they sacrificially cause an anodic reaction that is the counterpart to the cathodic reaction involving oxygen. Furthermore, because their potential is lower than the hydrogen electrode potential, they suppress the decrease in the pH of the aqueous phase even if P dissolves from the copper phase into the aqueous phase. Therefore, this anodic reaction and pH suppression effect can suppress the dissolution of Cu from the copper phase into the aqueous phase.

[0042] (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 acts to immobilize P in the copper phase. When P is immobilized in the copper phase, the elution of P from the copper phase into the aqueous phase is suppressed, making it difficult for the pH of the aqueous phase to decrease. This pH-suppressing effect can suppress the elution of Cu from the copper phase into the aqueous phase.

[0043] Here, the chemical composition of the copper alloy according to this embodiment will be described in more detail. In the following description, the notation "%" means mass % unless otherwise specified.

[0044] (base metal element) As the base metal element, an element having a standard electrode potential lower than H is preferred, and an element having a potential equal to or lower than that of Mn is more preferred. Such an element can suppress a decrease in the pH of the aqueous phase even if P dissolves from the copper phase into the aqueous phase. Furthermore, if the standard electrode potential is equal to or lower than that of Mn, the effect of a phosphorus compound-forming element such as Mn can also be obtained.

[0045] Specific examples of base metal elements include Mn, Al, Group 1 elements, and Group 2 elements. Examples of Group 1 elements include Li, Na, and K. Examples of Group 2 elements include Mg, Ca, and Ba. These elements cause an anodic reaction at a lower potential than Cu, and can therefore suppress the anodic reaction that dissolves Cu. Furthermore, even if P dissolves from the copper phase into the aqueous phase, a decrease in the pH of the aqueous phase can be suppressed. These pH suppressing effects can effectively suppress the dissolution of Cu from the copper phase into the aqueous phase.

[0046] The base metal element is preferably a phosphorus compound-forming element that reacts with P to form a phosphorus compound. Examples of phosphorus compound-forming elements include Mn, Mg, and Ca. These elements immobilize P in the copper phase and can suppress the elution of P from the copper phase into the aqueous phase. Since the decrease in pH of the aqueous phase is suppressed, oxides and hydroxides of Cu are more stable than copper ions, which can effectively suppress the elution of Cu from the copper phase into the aqueous phase.

[0047] As the base metal element, one element or a plurality of elements may be added to the copper base material. As the base metal element, only phosphorus compound-forming elements may be added to the copper base material, 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 to the copper base material.

[0048] The amount of base metal elements is preferably 0.01% or more, more preferably more than 0.01%, even more preferably 0.03% or more, even more preferably 0.05% or more, and even more preferably 0.10% or more, in terms of the total amount of base metal elements. Such an amount of base metal elements can provide the effect of suppressing Cu elution from the copper phase to the aqueous phase. The amount of base metal elements may be 0.15% or more, or 0.20% or more, in terms of the total amount of base metal elements.

[0049] The total amount of base metal elements is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, even more preferably 0.25% or less, even more preferably 0.20% or less, and even more preferably 0.15% or less. If the amount of base metal elements is too high, raw material costs increase and casting becomes more difficult. Furthermore, mechanical and electrical properties change, making it difficult to use as copper pipe. However, with such an amount of base metal elements, raw material costs and casting difficulty can be reduced while avoiding effects on mechanical properties, brazeability, etc. The total amount of base metal elements may be 0.10% or less, or 0.05% or less.

[0050] As the base metal element, it is preferable to add Mg or Mn. These base metal elements are elements that form phosphorus compounds. Adding these base metal elements fixes P in the copper phase as a phosphorus compound and suppresses a decrease in the pH of the aqueous phase due to the elution of P. In addition, good workability and brazability can be obtained.

[0051] (Mg: 0.01% or more and less than 0.25%) The Mg content is preferably 0.01% or more, more preferably 0.017% or more, even more preferably 0.03% or more, even more preferably 0.05% or more, and even more preferably 0.10% or more. Such a Mg content inhibits Cu elution from the copper phase into the aqueous phase, while also providing good mechanical properties such as tensile strength and wettability of the brazing filler metal. Furthermore, when the Mg content is 0.017% or more, sufficient SCC resistance can be obtained even with a P content of 0.015%, which is the upper limit specified for low-phosphorus deoxidized copper. Furthermore, when the Mg content is 0.10% or more, sufficient SCC resistance can be obtained even with a P content of 0.04%, which is the upper limit specified for high-phosphorus deoxidized copper.

[0052] The Mg content is preferably 0.25% or less, more preferably 0.20% or less, and even more preferably 0.15% or less. If the Mg content is 0.29% or more, the wettability of the brazing filler metal is impaired. However, if the Mg content is 0.25% or less, good wettability of the brazing filler metal can be obtained, and mechanical properties and high electrical conductivity can be appropriately ensured.

[0053] (Mn: 0.01% or more and 1.5% or less) The Mn content is preferably 0.01% or more, more preferably 0.03% or more, even more preferably 0.05% or more, even more preferably 0.10% or more, even more preferably 0.50% or more, even more preferably 1.0% or more, and even more preferably 1.2% or more. Such a Mn content not only suppresses the dissolution of Cu from the copper phase into the aqueous phase, but also provides good mechanical properties such as tensile strength.

[0054] The Mn content is preferably 1.5% or less, more preferably 1.4% or less, and even more preferably 1.3% or less. If the Mn content exceeds 1.5%, the yield strength increases and bending workability decreases. However, if the Mn content is 1.5% or less, good workability can be obtained and high electrical conductivity can be appropriately ensured.

[0055] (P: over 0% and up to 0.040%) P is added mainly for deoxidation. If the P content is too high, toughness and workability decrease, and SCC susceptibility and ant nest corrosion susceptibility increase. Therefore, the P content is preferably 0.040% or less. Depending on the allowable O content, etc., the P content 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%, 0.004% or more and less than 0.015%, or 0.015% or more and less than 0.040%.

[0056] (Inevitable impurities) The inevitable impurities are derived from substances that must be added in the production of copper alloys and copper alloy pipes or substances that are difficult to completely separate and remove, and refer to elements of impurities that are unavoidably mixed in from raw materials or during the production process. The copper alloy preferably contains more than 0% but not more than 0.040% by mass of P, a total of 1.5% by mass or less of base metal elements, and the balance being Cu and inevitable impurities.

[0057] Specific examples of unavoidable impurities include elements other than base metal elements, such as O, H, S, Pb, Bi, Se, Te, As, and Sb. The total amount of unavoidable impurities is preferably 0.1% or less, more preferably 0.05% or less, and even more preferably 0.01% or less. If the total amount of unavoidable impurities is 0.1% or less, the effects of the present invention are not impaired.

[0058] (O: 0.01% or less) O reacts with H to generate water vapor in high-temperature environments such as furnace brazing in a hydrogen atmosphere, causing hydrogen embrittlement. It also forms oxides that reduce workability. Therefore, the O content is preferably 0.01% or less, more preferably 0.005% or less, and even more preferably 0.001% or less.

[0059] (Other elements) The S content is preferably 0.0018% or less. Each of the Pb content, Bi content, Se content, Te content, and C content is preferably 0.001% or less. Each of the Zn content, Cd content, and Hg content is preferably 0.0001% or less.

[0060] (Cu:98.5% or more) Cu constitutes the balance of the copper alloy, excluding base metal elements and unavoidable impurities. The amount of Cu is not particularly limited as long as it constitutes the balance of the copper alloy. However, from the viewpoint of obtaining properties of a copper alloy equivalent to pure copper, such as thermal conductivity, bending workability, brazing ability, etc., the amount of Cu is preferably 98.5% or more, more preferably 99.0% or more, even more preferably 99.5% or more, even more preferably 99.80% or more, and even more preferably 99.90% or more.

[0061] Next, the corrosion resistance of the copper alloy according to this embodiment to stress corrosion cracking (SCC) will be described.

[0062] The corrosion resistance of the copper alloy according to this embodiment to stress corrosion cracking (SCC) can be evaluated by measuring the crack depth after applying a predetermined stress after exposing the alloy to a saturated environment with an aqueous ammonia solution in accordance with the Japan Copper and Brass Association Technical Standard JBMA T-301-1981. The crack depth due to SCC is defined as the shortest distance from the surface of the copper alloy to the deepest point of the crack.

[0063] Ammonia testing in accordance with JBMA T-301-1981 is conducted using a 14% by weight aqueous ammonia solution. The aqueous ammonia solution is prepared by diluting 25% or more by weight aqueous ammonia solution with an equal amount of pure water. The test environment temperature is room temperature, and the container containing the aqueous ammonia solution is kept in a room controlled at room temperature of 20°C ± 5°C. The test material is placed in a 10L test container containing the aqueous ammonia solution, so as not to come into direct contact with the aqueous ammonia solution. The test material is placed 100mm from the surface of the aqueous ammonia solution. The exposure conditions to the ammonia atmosphere in the test container are 72 hours at room temperature.

[0064] The copper alloy test material for the ammonia test is either plate or pipe. After the exposure test in an ammonia atmosphere, in the case of plate material, as shown in Figure 2, an external stress is applied by bending the material 180 degrees around the center line parallel to the rolling direction as the bending axis. In the case of pipe material, an external stress is applied by crushing the pipe material from the radial direction to less than half of its outer diameter. The observation point for SCC cracks in the case of plate material is the surface on the crest side when bent. In the case of pipe material, it is the outer surface of the bent part when crushed.

[0065] Surface defects can form on the surface of copper pipe during pipe manufacturing. Generally, the maximum crack depth caused by surface defects is about 0.03 mm. It is difficult to distinguish between shallow cracks caused by SCC and cracks caused by surface defects. Therefore, even if the crack depth caused by SCC exceeds 0.03 mm, if it is 0.05 mm or less, it can be determined that the corrosion resistance against SCC is good. Furthermore, if it is 0.03 mm or less, it can be said that SCC has not actually occurred.

[0066] When the copper alloy according to this embodiment contains P: 0.0065% by mass or more and 0.040% by mass or less, where Y [%] is the Mg concentration in the copper alloy and X [%] is the P concentration in mass %, it satisfies the following formula (I), and after being exposed to a 14% by mass aqueous ammonia solution at a distance of 100 mm in a room controlled at room temperature of 20±5°C in accordance with JBMA T-301-1981 for 72 hours, when a copper alloy plate is bent 180 degrees or when a copper alloy pipe is crushed to half its outer diameter or less, it is preferable that the crack depth measured is 0.05 mm or less. Y≧2X-0.0130 (0.0065≦X≦0.0400)···(I)

[0067] When P is 0.0065% by mass or more and 0.040% by mass or less, if 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 an ammonia test in accordance with JBMA T-301-1981. Since the progression of SCC is suppressed in an ammonia environment that promotes SCC, a copper alloy with excellent SCC resistance can be obtained.

[0068] When the copper alloy according to this embodiment contains 0.040% by mass or less of P, it is more preferable that, when the Mg concentration in the copper alloy is Y [%] and the P concentration in mass % is X [%], the copper alloy satisfies the following formula (II), and that, after being exposed to a 14% by mass aqueous ammonia solution at a distance of 100 mm in a room controlled at room temperature of 20±5°C in accordance with JBMA T-301-1981 for 72 hours, when a copper alloy plate is bent 180 degrees or when a copper alloy pipe is crushed to half its outer diameter or less, the crack depth measured is 0.03 mm or less. Y≧2X (X≦0.0400) (II)

[0069] When P is 0.040% by mass or less and the Mg concentration satisfies the condition of formula (II), the crack depth due to stress corrosion cracking can be suppressed to 0.03 mm or less in an ammonia test in accordance with JBMA T-301-1981. When P is less than 0.0065% by mass, SCC is less likely to develop even when no base metal elements are added. However, even within this range, copper alloys still exhibit SCC susceptibility. Therefore, if higher SCC resistance is desired, the condition of formula (II) is required.

[0070] Examples of cases where a higher level of SCC resistance is required include cases where copper alloys are used under conditions that accelerate the initiation and progression of SCC, such as when an ammonia source is present in a sealed environment such as a factory or a house, and cases where damage to copper alloys due to SCC must be strictly restricted, such as when copper alloys are used as materials for refrigerant piping or heat exchanger piping, and a flammable refrigerant flows inside the copper alloy pipe.

[0071] Next, applications of the copper alloy and copper alloy pipe according to this embodiment, and methods for producing them will be described.

[0072] The copper alloy according to 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.

[0073] The copper alloy tube may be an internally grooved tube with grooves formed on the inner surface, or a smooth tube with no grooves formed on the inner surface. The internally grooved tube has, for example, spiral grooves at predetermined intervals or linear grooves arranged parallel to each other around the entire circumference of the inner surface of the tube. When manufacturing an internally 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 apex angle of the fins, the lead angle of the grooves relative to the central axis of the tube, and other appropriate conditions can be set.

[0074] Copper alloy pipes contain base metal elements, so even if P is added for deoxidation, the occurrence and progression of SCC can be suppressed. Therefore, compared to oxygen-free copper, costs can be reduced, and hydrogen embrittlement can be prevented by deoxidation with P, while SCC, which is accelerated by P, can also be suppressed. Since the amount of P is less likely to have an effect, there is greater freedom in material selection.

[0075] In particular, inner grooved pipes increase the surface area of ​​the copper alloy pipe and allow the grooves to agitate the fluid flowing through the copper alloy pipe. This allows for high energy efficiency and energy saving performance in applications where refrigerants are passed through. Furthermore, the increased surface area and improved energy efficiency allow for the miniaturization of piping through which refrigerants pass.

[0076] The copper alloy tube can be produced by a manufacturing method including a casting step, a soaking step, a hot extrusion step, a rolling / drawing step, and an annealing step. The internally grooved tube can be produced by manufacturing the copper alloy tube, followed by a rolling step and a final annealing step.

[0077] (Casting process) In the casting process, the raw material of the copper alloy is melted in a reducing atmosphere, a deoxidizer is added to adjust the P content, and then an ingot of a predetermined size is cast. As the raw material, electrolytic copper, a base metal containing base metal elements, etc. can be used. As the deoxidizer, phosphorus copper, etc. can be used. As the casting method, billets, etc. can be cast using a semi-continuous casting method, etc.

[0078] (Soaking process) In the soaking process, the ingot, such as a billet, is homogenized by heat treatment. Homogenization removes segregation of P and the like and diffuses the added base metal elements. The heat treatment temperature is, for example, 680°C or higher and 950°C or lower. At 680°C or higher, segregation of P and the like can be sufficiently removed. At temperatures above 950°C, the homogenization effect reaches a plateau, but at 950°C or lower, the heat treatment cost can be reduced. The heat treatment time is, for example, 15 minutes to 2 hours.

[0079] (Hot extrusion process) In the hot extrusion process, a heated ingot such as a billet is hot extruded into a die with a mandrel inserted therein to form a mother pipe. The hot extrusion temperature is, for example, 680°C or higher and 950°C or lower. The processing rate in the hot extrusion can be set as appropriate as long as cracks, surface defects, etc. do not occur. The mother pipe after extrusion is cooled, for example, by natural cooling. Note that piercing and rolling using a plug and roll die may be performed instead of the hot extrusion and rolling processes.

[0080] (Rolling and drawing process) In the rolling-drawing process, the formed mother pipe is subjected to rolling using a mandrel and drawing to form a drawn mother pipe. The working ratio in the rolling and drawing processes can be set to any appropriate conditions, but is preferably 95% or less from the viewpoint of reducing cracks, surface defects, etc. The drawing process can be performed using a continuous drawing machine using a plug, for example, with an appropriate number of passes. The working ratio in each pass is preferably 40% or less from the viewpoint of reducing cracks, surface defects, etc.

[0081] (Annealing process) In the annealing step, the processed drawn blank pipe is annealed by heat treatment. By annealing, processing strain is removed and the pipe is softened. Annealing can be performed using a roller hearth furnace, a high-frequency induction heating furnace, or the like. The heat treatment temperature is, for example, 350°C or higher and 700°C or lower, preferably 350°C or higher and 500°C or lower. At 350°C or higher, processing strain can be adequately removed. The heat treatment time is, for example, 5 minutes to 2 hours.

[0082] Through the above steps, a smooth copper alloy tube can be manufactured. An internally grooved tube can be manufactured by subjecting a drawn blank tube to groove rolling.

[0083] (rolling process) In the rolling process, a drawn mother tube is subjected to groove rolling to form grooves on the inner surface of the drawn mother tube. Groove rolling can be performed, for example, by roll rolling using a grooved plug. A grooved plug with a reverse groove formed therein for transferring the groove is inserted into the mother tube. The mother tube is then drawn out while being pressed by a rotating roll die, forming grooves on the inner surface of the mother tube. Groove rolling can also be performed continuously from the diameter reduction pass of the drawing process, using a grooved plug connected to a diameter reduction plug. Furthermore, a ball die with a bearing structure can be used instead of a roll die.

[0084] (Final annealing process) In the final annealing step, the grooved pipe is subjected to final annealing by heat treatment. As in the annealing step, the final annealing can be performed in a roller hearth furnace, a high-frequency induction heating furnace, or the like. The heat treatment temperature is, for example, 350°C or higher and 700°C or lower, preferably 350°C or higher and 500°C or lower. The heat treatment time is, for example, 5 minutes or higher and 2 hours or lower.

[0085] By the above steps, an internally grooved copper alloy tube can be manufactured. The manufactured copper alloy tube can be subjected to processing such as straightening, chamfering, and cutting, and can also be subjected to an appearance inspection. Furthermore, after drawing and before annealing, the drawn mother tube can also be subjected to straightening, chamfering, flaw detection, and the like.

[0086] Copper alloy pipes can be used for a variety of purposes. Examples of uses 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 that are connected to fins or the like to form heat exchangers. Examples of refrigerant pipes include pipes that allow refrigerants to flow. Examples of hot water supply pipes and water supply pipes include pipes that allow hot water, warm water, and cold water to flow.

[0087] These pipes can be installed in refrigeration and air conditioning equipment, heat exchangers, water heaters, etc. Refrigeration and air conditioning equipment includes air conditioners, refrigerators, vapor compression refrigerators, absorption refrigerators, etc. Absorption refrigerators include ammonia types and lithium bromide types. In lithium bromide types, ammonia may inevitably remain during the refrigerant purification process. Ammonia is one of the environmental factors that promote SCC. The copper alloy tube according to this embodiment is particularly effective for applications used in an ammonia environment.

[0088] Copper alloy tubes are preferably used as materials for heat exchangers. Examples of heat exchangers include finned tube, corrugated tube, and double-tube heat exchangers. Copper alloy tubes may be used in straight pipe sections, or in curved pipe sections such as U-shaped bends and spirally wound sections around a main pipe. Heat exchangers using copper alloy tubes can be used in, for example, air conditioners, refrigerated showcases, refrigerators, oil coolers, radiators, and the like.

[0089] FIG. 1 is a diagram schematically illustrating an example of a heat exchanger equipped with copper alloy tubes. 1, the heat exchanger 30 includes a plurality of fins 10 and heat transfer tubes 20. The fins 10 are arranged at predetermined intervals, and air passages are formed between the fins 10. The heat transfer tubes 20 are bent into a U-shape at multiple locations, and are inserted into through holes on the fins 10 so as to pass through the plurality of fins 10, and are then brazed.

[0090] The heat transfer tube 20 is formed of a copper alloy tube to which the above-mentioned base metal elements are added. The copper alloy tube may be an internally grooved tube with grooves formed on the inner surface of the tube, or a smooth tube with no grooves formed on the inner surface of the tube. In a heat exchanger using a copper alloy tube, the base metal elements suppress SCC, so that a heat exchange medium such as a refrigerant is unlikely to leak for a long period of time, resulting in a highly reliable heat exchanger. [Example]

[0091] The present invention will be specifically described below with reference to examples of the present invention, but the technical scope of the present invention is not limited thereto.

[0092] Copper alloy specimens containing base metal elements were prepared and their effects on stress corrosion cracking (SCC) and other material properties were evaluated. Other material properties evaluated included resistance to termite-nest corrosion, tensile strength, and wettability with brazing filler metals. Copper alloy specimens containing different amounts of base metal elements were also prepared and the crack depth due to SCC was measured for each content.

[0093] The test materials were plates or tubes made by adding only specified base metal elements to a copper alloy equivalent to phosphorus-deoxidized copper. The plates were made by adjusting the chemical composition and casting the raw material, followed by hot rolling, cold rolling, and annealing, in that order. The tubes were made by adjusting the chemical composition and casting the raw material, followed by hot extrusion, cold drawing, and annealing, in that order.

[0094] (Evaluation of ant nest corrosion resistance) The evaluation of ant nest corrosion resistance was performed using plate specimens as test materials using the following procedure. First, a 200 mm long test specimen was placed in a test container filled with a corrosive solution. A plastic bottle was used as the test container, with a hole drilled in the bottle's inner lid and a silicone stopper inserted as the lid. A hole was drilled in the silicone stopper, and the plate was inserted into the hole to hold the plate. The plate was placed at a height that did not directly contact the corrosive solution, so that a 100 mm long section of the plate was exposed to the test environment inside the bottle. To ensure uniformity of the direction of corrosion occurring on the plate, all surfaces except the observation surface were covered with silicone resin. The test container was then sealed and placed in a drying oven with a specified heat cycle. The heat cycle was repeated for the specified test time. The test specimen was then embedded in acrylic or epoxy resin, and cross-sectional observation was performed to observe the occurrence of ant nest corrosion on the specimen.

[0095] The conditions for evaluating the resistance to termite nest corrosion are as follows. - Dimensions of the test material: Width 10-13 mm x Length 200 mm x Thickness 1.0 mm (Part of the test material was covered with rubber material, so that only one side was exposed to the corrosive environment inside the test container.) Test container: 2L plastic container Etchant: 500 mL of 0.5% by volume formic acid solution Test atmosphere: Oxygen gas was extracted from a cylinder of industrial oxygen (purity 99.5 vol.% or higher) via indoor dedicated piping and connected silicon tubing as the replacement gas. Oxygen gas was introduced as replacement gas at a flow rate of 1 L / min for 5 minutes through a silicon tubing inserted 100 mm or more into a 2 L plastic container, creating an oxygen atmosphere inside the container. Temperature conditions (heat cycle conditions of the drying oven): Repeatedly hold at 20°C for 2 hours, then at 40°C for 22 hours Testing time: 60 days

[0096] The evaluation of ant nest corrosion resistance was based on the following criteria. The maximum corrosion depth due to ant nest corrosion was measured as the distance from the surface of the test material to the deepest point of corrosion. Three cross sections (with an interval of 1 mm or more between cross sections) were observed for each test material, and the longest distance among these was calculated as the maximum corrosion depth. 〇: Maximum corrosion depth 0.25mm or less → Good resistance to termite nest corrosion ×: Maximum corrosion depth exceeds 0.25 mm → Poor resistance to ant nest corrosion

[0097] (Evaluation of tensile strength) The evaluation of tensile strength was carried out using plate materials as test materials under the following conditions: The tensile strength was measured using a tensile testing machine.

[0098] Dimensions of test material: Width 10mm x Length 200mm x Thickness 0.1mm Test method: Compliant with JIS Z2241:2011 Tensile test method for metallic materials, using rectangular test pieces.

[0099] The tensile strength evaluation is based on the following criteria. ○: Tensile strength 280N / mm 2 below→ Maintains workability such as bending ×: Tensile strength 280N / mm 2 Over → Workability such as bending is reduced

[0100] (Evaluation of stress corrosion cracking resistance) The stress corrosion cracking resistance was evaluated using plate or pipe specimens using the ammonia test in accordance with JBMA T-301-1981. The specimens were placed horizontally above a center plate in a test vessel containing a corrosive solution, positioned at a height that prevented direct contact with the solution. Figure 2 shows the sampling method for plate specimens. When using plate specimens, plates were cut from rolled material to a width of 10–13 mm, a length of 25 mm, and a thickness of 1 mm, as shown in Figure 2, and placed above the center plate with the front and back facing up and down. For pipe specimens, a 20 mm length was cut. Resin-coated copper wires with a diameter of 2.5 mm were placed between both ends of the specimen and the center plate to prevent direct contact between the specimen and the center plate. The test vessel was then sealed and allowed to stand for the specified test time. The test material was then removed from the test vessel, pickled with sulfuric acid, and then subjected to external stress as a pretreatment.

[0101] Figure 2 shows a method for pre-treating test materials made of copper alloy. The upper left image in Figure 2 shows the copper alloy ingot before rolling that was used to prepare the test materials. The upper right image in Figure 2 shows the rolled material obtained by rolling the copper alloy ingot and the cutting position of the test materials. The lower image in Figure 2 shows the bending position of the test materials to apply stress. As shown in Figure 2, when the test material was plate, it was bent 180 degrees around the centerline parallel to the rolling direction so that the surface that was on the top during exposure to the test environment was facing outward. On the other hand, for pipe material, it was crushed uniaxially along the radial direction (the rolling direction) until the outer diameter was reduced to half or less—for example, approximately 4 mm for a 9.52 mm diameter pipe. The appearance of the crushed surface was observed using an optical microscope (69x magnification) for the presence or absence of cracks. Cross sections of areas with severe cracks were cut out and embedded in acrylic or epoxy resin, and the cross-sectional cracks were observed using an optical microscope (150x magnification). When there were multiple areas with severe cracks, the test material was divided and the cross sections were observed.

[0102] Fig. 3 is a diagram showing a method for measuring crack depth due to stress corrosion cracking. Fig. 4 is an enlarged view of a main part of Fig. 3. Fig. 4 corresponds to an enlarged view of a rectangular area S in Fig. 3. As shown in Figure 3, the original outer surface of the test material was not present where stress corrosion cracking occurred. Therefore, a cross-sectional image of the test material was taken, and a virtual line representing the outer surface of the test material was interpolated using image processing to measure the maximum crack depth due to stress corrosion cracking.

[0103] As shown in Figure 3, points B and B' were set on the outer surface at 45 degrees to the left and right of point A on the valley side. Then, a circular arc passing through points B and B' was interpolated as an imaginary surface, centered on point A. An imaginary line C passing through point A and the deepest point of the crack was drawn, and the intersection of imaginary line C and the arc-shaped imaginary curve was determined. The shortest distance from this intersection to the deepest point of the crack was measured as the crack depth due to SCC. The maximum corrosion depth was defined as the deepest crack depth among the cracks observed between arc B-B' in the cross section observed for the specified number of measurements.

[0104] The conditions for evaluating stress corrosion cracking resistance are as follows. Plate dimensions: Width 10-13mm x Length 25mm x Thickness 1.0mm Tube dimensions: 9.52mm outer diameter x 0.8mm thickness x 20mm length Test container: 10L desiccator Corrosive solution: 100 mL of 14% ammonia water (commercially available 25% or higher ammonia water solution diluted with an equal amount of pure water) Temperature conditions: The test temperature was room temperature, and the room temperature in which the test container was kept was controlled within 20°C ± 5°C by an air conditioner. Exposure conditions: 100mm from the surface of the corrosive liquid Test duration: up to 72 hours

[0105] The evaluation of stress corrosion cracking resistance was based on the following criteria: If the maximum crack depth was 0.03 mm or less, it was not considered to be a crack caused by SCC because it was difficult to distinguish it from surface defects that occurred during pipe manufacturing. ◎: Maximum crack depth is 0.03 mm or less → Excellent stress corrosion cracking resistance 〇: Maximum crack depth is over 0.03mm and 0.05mm or less → Good stress corrosion cracking resistance ×: Maximum crack depth exceeds 0.05 mm → Poor stress corrosion cracking resistance

[0106] (Evaluation of wettability of brazing filler metal) The wettability of the brazing filler metal was evaluated using a plate material as the test material under the following conditions. First, the test material was bent 90 degrees along the center line in the longitudinal direction. Then, a rod-shaped brazing filler metal was placed in the center of the valley side of the test material. The test material with the brazing filler metal placed was heated under specified heating conditions and then cooled. Then, the longitudinal length of the brazing filler metal that had wetted and spread over the surface of the test material was measured.

[0107] The conditions for evaluating the wettability of the brazing filler metal are as follows. Dimensions of test material: Width 30mm x Length 100mm x Thickness 1.0mm Brazing filler metal: Phosphorus copper brazing filler BCuP-2 (diameter 1.6 mm x length 20 mm) Heating equipment: Infrared gold image furnace (ULVAC) Heating atmosphere: Nitrogen gas atmosphere Heating conditions: Heat from room temperature to 850℃ at a rate of 850℃ / 5 minutes Holding conditions: 850℃ for 5 minutes ·Cooling conditions: natural cooling

[0108] The wettability of the brazing material is evaluated according to the following criteria. 〇: The length of the brazing filler metal in the longitudinal direction is 100 mm or more → The brazing filler metal has good wettability ×: The length of the brazing filler metal in the longitudinal direction is less than 100 mm → poor wettability of the brazing filler metal

[0109] (Analysis of the chemical composition of the test material) The chemical composition of the test material was analyzed using a PDA-7000 optical emission spectrometer (Shimadzu Corporation) under the following conditions in accordance with "5. Spark discharge optical emission spectroscopy" of JIS K0116:2014 General rules for optical emission spectroscopy.

[0110] The conditions for the analysis of the chemical composition are as follows: Analysis atmosphere: High-purity argon gas atmosphere (99.9995% by volume) Electrode spacing: 7mm (discharge gap distance) Quantitative method: Fixed time integration by intensity ratio method Pre-discharge: 1500 pulses Main discharge: 1200 pulses (discharge time used as integration time)

[0111] Chemical composition analysis was performed at three random points on the surface of the annealed test material. For plate materials, measurements were taken on the smooth main surface. For pipe materials, measurements were taken on the smooth outer surface after crushing the pipe material. The average of the measurements taken at each point was calculated and used as the measurement result for each test material.

[0112] The measurement wavelengths of the spark discharge optical emission spectrometry used to analyze the chemical composition and the measurement sensitivities at those wavelengths are as follows: Al: Wavelength 396.1nm, measurement sensitivity 44 Cu: wavelength 296.1nm, measurement sensitivity 24 Mg: Wavelength 285.2nm, measurement sensitivity 24 P: wavelength 178.3nm, measurement sensitivity 52

[0113] Table 1 shows the chemical composition of the test material (target Mg content) and the evaluation results for termite-nest corrosion resistance, tensile strength, stress corrosion cracking resistance, and brazing filler metal wettability. The overall evaluation is a comprehensive assessment of these properties.

[0114] [Table 1]

[0115] As shown in Table 1, Examples 1 and 2 had Mg concentrations of 0.01 mass% and 0.25 mass%, respectively, and the wettability of the brazing filler metal met the standard. Comparative Example 1 had an Mg concentration of 0.29 mass%, and the wettability of the brazing filler metal did not meet the standard. From the viewpoint of the wettability of the brazing filler metal, it can be said that a Mg concentration of 0.25 mass% or less is preferable.

[0116] Table 2 shows the chemical composition of the test material (analytical values ​​of Mg content, Mn content, and P content), the measurement results of the maximum crack depth due to stress corrosion cracking, and the evaluation results of stress corrosion cracking resistance.

[0117] [Table 2]

[0118] Fig. 5 is a diagram showing the relationship between crack depth due to stress corrosion cracking and P concentration. In Fig. 5, the vertical axis represents the crack depth [µm] measured in the test material, and the horizontal axis represents the P concentration [mass%] of the test material. The circle plots represent the results of the test material according to the example in which the Mg content was 0.1 mass%. The diamond plots represent the results of the test material according to the comparative example in which no base metal elements were added.

[0119] As shown in Figure 5, when the P concentration of the copper alloy was low, cracks due to stress corrosion cracking were suppressed regardless of whether base metal elements were added. When the crack depth was 30 μm or less, it was difficult to distinguish it from surface defects that occurred during pipe manufacturing, so it can be said that cracks due to SCC did 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.

[0120] Figure 6 shows the relationship between the Mg concentration and the P concentration and the crack depth due to stress corrosion cracking. In Figure 6, the vertical axis shows the Mg concentration [mass%] of the test material, and the horizontal axis shows the P concentration [mass%] of the test material. The plots marked with black circles represent the results for test materials whose maximum crack depth was 30 μm or less. The plots marked with a triangle represent the results for test materials whose maximum crack depth was greater than 30 μm and less than 50 μm. ◆The plot shows the results for test materials with a maximum crack depth exceeding 50 μm.

[0121] In Figure 6, lower side The dashed line indicates the straight line expressed by formula (I): Y=2X-0.0130, where Y is the Mg concentration and X is the P concentration. upper side of solid line indicates a straight line expressed by formula (II): Y=2X, where Y is the Mg concentration and X is the P concentration. These straight lines were determined as linear boundary conditions based on the results of Examples 1-1 to 1-20 shown in Table 2.

[0122] 6, Examples 1-1 to 1-14 satisfied the relationship represented by formula (II): Y≧2X (X≦0.0400), and the amount of base metal elements was appropriate relative to the amount of P, so that the stress corrosion cracking resistance met the criterion of 0.03 mm or less. Example 1-13 obtained good stress corrosion cracking resistance due to 0.041 mass% Mg relative to 0.02 mass% P, and the stress corrosion cracking resistance met the criterion of 0.03 mm or less.

[0123] In Example 1-15, since it did not contain P, the stress corrosion cracking resistance met the standard of 0.03 mm or less even though no base metal elements were added.

[0124] In Example 1-16, the stress corrosion cracking resistance did not meet the criterion of 0.03 mm or less due to the trace amount of P, but the stress corrosion cracking resistance met the criterion of 0.05 mm or less even though no base metal elements were added. However, compared to Example 1-15, the crack depth increased as the P content increased.

[0125] Example 1-17 did not satisfy the relationship represented by formula (II): Y≧2X(X≦0.0400), but met the criterion of 0.05 mm or less in stress corrosion cracking resistance due to the trace amount of P. Examples 1-18 and 1-19 satisfied the relationship represented by formula (I): Y≧2X-0.0130(0.0065≦X≦0.0400), and the amount of base metal elements was appropriate relative to the amount of P, so met the criterion of 0.05 mm or less in stress corrosion cracking resistance.

[0126] In Example 1-21, the base metal element was Mn, but the amount of the base metal element was appropriate relative to the amount of P, so the stress corrosion cracking resistance met the standard of 0.03 mm or less. It was revealed that even when the base metal element was Mn, the propagation of cracks due to stress corrosion cracking was suppressed.

[0127] In Comparative Examples 1-1 to 1-5, the crack depth after the stress corrosion cracking test exceeded 0.05 mm, and did not satisfy the relationship expressed by formula (I) or formula (II). Comparative Examples 1-2 and 1-3 did not contain base metal elements, and Comparative Example 1-2 in particular corresponds to low-phosphate copper (JIS H3300 C1201), but did not satisfy the standard of 0.05 mm or less in stress corrosion cracking resistance. In Comparative Examples 1-1 and 1-4 to 1-5, the amount of base metal elements was insufficient relative to the amount of P, and no effect of improving corrosion resistance against stress corrosion cracking was observed.

Claims

1. A copper alloy containing P: 0.0065% by mass or more and 0.040% by mass or less, Mg: 0.25% by mass or less, and the remainder consisting of Cu and unavoidable impurities, When the Mg concentration of the copper alloy is Y [%] and the P concentration is X [%], the following formula (I) is satisfied: A copper alloy in which, in accordance with JBMA T-301-1981, the copper alloy is exposed to a 14 mass % aqueous ammonia solution at a distance of 100 mm for 72 hours in a room controlled at a room temperature of 20±5°C, and then a sheet material of the copper alloy is bent at 180 degrees, or a pipe material of the copper alloy is crushed to half or less of its outer diameter, and the crack depth measured is 0.05 mm or less. Y≧2X-0.0130...(I)

2. A copper alloy containing P: 0.040 mass% or less, Mg: 0.25 mass% or less, and the remainder consisting of Cu and unavoidable impurities, When the Mg concentration of the copper alloy is Y [%] and the P concentration is X [%], the following formula (II) is satisfied: A copper alloy in which, in accordance with JBMA T-301-1981, the copper alloy is exposed to a 14 mass % aqueous ammonia solution at a distance of 100 mm for 72 hours in a room controlled at a room temperature of 20±5°C, and then a plate material of the copper alloy is bent at 180 degrees, or a pipe material of the copper alloy is crushed to half or less of its outer diameter, and the crack depth measured is 0.03 mm or less. Y≧2X (II)

3. A copper alloy tube formed from the copper alloy according to claim 1 or 2.

4. The copper alloy tube according to claim 3, A copper alloy pipe with grooves formed on the inside surface.

5. A heat exchanger using a copper alloy tube formed from the copper alloy according to claim 1 or 2.

Images