JPH10183275A - Copper alloy, member in contact with water, composed of copper alloy, and production of copper alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a Cu-Zn-Sn alloy for a member in contact with water, excellent in dezincification resistance and machinability, by subjecting a Cu-Zn- Sn alloy of specified composition to heating and cooling under respectively specified temp. conditions and changing its structure. SOLUTION: In producing a Cu-Zn-Sn alloy having a composition consisting of 0.9-3.0% Sn, 37-45% Zn, and the balance Cu, the alloy is heat-treated at 500-550 deg.C for 30sec and then cooled down to 350 deg.C at <=0.4 deg.C/sec cooling rate. In the structure of this alloy, γ-phases of >=3% content are precipitated at 3-20% area occupancy in the grain boundaries of α-phases having >=0.5% Sn content and 40-97% area occupancy, or the γ-phases are precipitated in the grain boundaries of the α-phases and β-phases having >=1.5% Sn content and 0-40% area occupancy. By this method, the Cu-Zn-Sn alloy, remarkably improved in dezincification resistance and machinability and having excellent properties required of a member in contact with water, such as water tap, can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Cu-Zn-Sn-based copper alloy, a water-contact member such as a faucet fitting made of a copper alloy, and a method for producing a copper alloy.

[0002]

2. Description of the Related Art As basic copper alloy materials specified in JIS, brass bars for forging (JIS O-13771), brass bars for free cutting (JIS C-3604), naval brass bars (JISC-16461), High strength brass bar (JIS O-16
782) are known.

[0003] However, with the diversification of products, the characteristics required for copper alloys also become unique to products, and various proposals have been made in response to this. For example, Tokiko Sho 61
Japanese Patent Application No. 58540 discloses a method of adding Pb, Fe, Ni, Sb and P to a Cu—Zn—Sn based copper alloy to substantially form α.
JP-A-6-108184 discloses a Cu-Zn-Sn-based copper alloy containing Pb, Fe,
It is disclosed that an alloy material to which Ni, Sb and P are added is subjected to hot extrusion or drawing and then heat-treated at 500 to 600 ° C. for 30 minutes to 13 hours to substantially form an α phase.

[0004] The crystal structure of the copper alloy is α phase,
There are β phase and γ phase. FIG. 1 shows the characteristics of these phases. α
The phase appears when the Zn equivalent is 37 wt% or less, and is excellent in corrosion resistance and ductility, but inferior in strength and machinability. β
The phase appears when the Zn equivalent is 37 wt% or more, and the workability is good but the corrosion resistance is extremely poor. The γ phase appears when Sn is added in a predetermined amount or more, and is excellent in corrosion resistance and strength but extremely weak. Here, the corrosion resistance of the copper alloy mainly refers to the dezincification corrosion resistance. Dezincification corrosion refers to a phenomenon in which zinc is easily eluted preferentially in water due to the difference in ionization tendency between Cu and Zn, and as a result, only Cu remains and the strength decreases with time. This is a problem when a Zn-based alloy is used.

[0005]

As described above, Japanese Patent Publication No. 61-58540 or Japanese Patent Application Laid-Open No. 6-10818.
In Japanese Patent Publication No. 4 (1993), a β phase and a brittle γ phase, which are extremely poor in corrosion resistance, are not precipitated, and the dezincification corrosion resistance is substantially increased as a single α phase.

However, when the α-phase is substantially used, it is inferior in workability such as machinability and is difficult to use for hot forging, so it is used as a material for casting. Yield is poor.

[0007]

Means for Solving the Problems Conventionally, the β phase, which is inferior to dezincification corrosion resistance, and the hard and brittle γ phase are prevented from precipitating as much as possible. The present invention has been made by paying attention to the fact that the hot forging property is excellent and the γ phase is hard, so that the cutting proceeds from the γ phase as a starting point.

That is, in the Cu-Zn-Sn based copper alloy according to the present invention, the area occupancy ratio of the γ phase having a Sn concentration of 3.0 wt% or more at the grain boundary of the α phase is 3% or more and 20% or less. Precipitated in proportions. This copper alloy contains substantially no β phase.
In another Cu-Zn-Sn-based copper alloy according to the present invention, a γ phase having an Sn concentration of 3.0 wt% or more is present at a grain boundary between an α phase and a β phase with an area occupancy ratio of 3% or more and 20% or more. Precipitated in the following ratio. This copper alloy has a configuration in which the γ phase surrounds the β phase.

The reason why the area occupancy ratio of the γ phase is 3% or more and 20% or less is that when the content is less than 3%, the effect of precipitation of the γ phase, that is, the effect of dezincification corrosion resistance is small, and conversely, when it exceeds 20%. It becomes brittle as a material.

If the Sn concentration in the α phase is 0.5 wt% or more and the Sn concentration in the β phase is less than 1.5 wt%, α
When the area occupancy of the phase is 97% or less and 40% or more, the area occupancy of the β phase is 0% or more and 40% or less, and Sn in the α phase
The concentration is 0.5 wt% or more, and the Sn concentration in the β phase is 1.5 w
If it is not less than t%, the area occupation ratio of the α phase is not more than 97% 2
At 0% or more, the area occupation ratio of the β phase becomes 0% or more and 60% or less.

As a method for precipitating a γ phase between the α-phase grain boundaries or the α- and β-phase grain boundaries, Cu—Zn
The Sn-based copper alloy material is subjected to a heat treatment at 500 ° C. or more and 550 ° C. or less for 30 seconds or more, and then cooled at a cooling rate of 350 ° C. or less to 0.4 ° C./second or less.

Another method for precipitating a γ phase between the grain boundaries of the α phase or at the grain boundaries of the α phase and the β phase includes Cu-
400 ° C or more and 500 for Zn-Sn based copper alloy material
A heat treatment is performed at a temperature of not more than 30 ° C. for 30 seconds or more, and then cooling is performed.

Still another method for precipitating a γ phase between grain boundaries of the α phase or at the grain boundary between the α phase and the β phase is Cu—
500 ° C or more and 550 for Zn-Sn based copper alloy material
A heat treatment is performed at 30 ° C. or less for 30 seconds or more, and then the cooling rate to 350 ° C. is set to 0.4 ° C./sec to 4 ° C./sec.

Regarding the above heat treatment and cooling rate control,
That is, as the temperature range in which the crystal structure is transformed, the first temperature range in which the γ phase is precipitated and the temperature range higher than the first temperature range are γ.
In the method for producing a copper alloy having a second temperature range in which a phase does not precipitate, heating to the second temperature range, and then controlling the cooling rate from the upper limit temperature to the lower limit temperature in the first temperature range, The method is characterized in that the area occupancy ratio is adjusted, and the cooling rate is set to 4 ° C./sec or less to precipitate the γ phase while cooling the first temperature range.
% Or more.

When this is applied to a Cu—Zn—Sn-based copper alloy, Sn in the γ phase can be controlled by controlling the cooling rate.
The concentration can be adjusted. Preferably, the Sn concentration in the γ phase is adjusted to 3.0 wt% or more.

According to the present invention, in a Cu—Zn—Sn based copper alloy, by increasing the area occupancy of the γ phase to 3% or more, the strength is improved as compared with the hard γ phase and the α is softer than the γ phase. Alternatively, the machinability is improved due to the hardness difference between the grain boundaries of the β phase and the γ phase. Here, since the γ phase is too brittle and the ductility is reduced when it is too large, the upper limit of the area occupation ratio of the γ phase is preferably 20% or less. Further, the Sn concentration is required to be 0.9 wt% or more for facilitating the precipitation of the γ phase and for improving the dezincification corrosion resistance, and desirably 3.0 wt% or less for hot ductility.

Next, in order to improve the dezincification corrosion resistance, α +
Those having a crystal structure of the γ2 phase have a Sn concentration of 3.0 wt% or more in the γ phase, and those having a crystal structure of the α + β + γ3 phase have a Sn concentration of 3.0 wt% or more in the γ phase The surroundings must be surrounded by the γ phase, or the Sn concentration in the β phase must be 1.5 wt% or more. The α + β + γ3 phase has an area occupancy ratio of the β phase of 15%.
In this case, the β phase also contributes to the improvement of the machinability.

Here, when the area occupation ratio of the β phase is 35% or more, even if the average Sn concentration in the β phase is 1.5 wt% or more, it is sometimes impossible to secure the dezincification corrosion resistance. Have confirmed.

This can be considered as follows. First, β
In the vicinity of the grain boundary with the γ phase in the phase, a portion where the Sn concentration is low is locally generated, which may cause local dezincification corrosion. Here, when the area occupation ratio of the β phase is 35% or more, the crystal grains of the β phase are not easily separated from each other, and the dezincification corrosion portion propagates through the adjacent β phase.

Therefore, in the present invention, the average Sn concentration in the β phase is set to 2.5 wt% or more to locally
The Sn concentration is ensured even near the grain boundary with the low concentration γ phase,
It reduces local dezincification corrosion.

Further, when the area occupation ratio of the β phase is 40% or more, the dezincified corrosion portion is more easily propagated.
By making the Sn concentration in the phase 3.0 wt% or more, local dezincification corrosion is further reduced.

When a part or all of the above γ phase is a β phase transformed by cooling from a high temperature range,
It is preferable to apply the present invention. This is because at the time of transformation from the β phase to the γ phase, the Sn concentration in the β phase around the γ phase tends to decrease because the surrounding Sn is taken into the γ phase.

Further, in the copper alloy according to the present invention, Z
The n equivalent is 37 wt% or more and 45 wt% or less, and the present invention includes a water contact member made of the above copper alloy. Examples of the water contacting member include fittings used for a water faucet, a water heater, a hot water flush toilet seat, and the like, and parts such as a water supply pipe, a connection pipe, a valve, and piping.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows Cu-Zn-
It shows the results of experiments on the composition (particularly, Sn) and corrosion resistance (anti-zinc corrosion resistance) of a copper alloy performed on Sn-based samples 1 to 7.

The corrosion resistance is based on the Japan Copper and Brass Association technical standard (JBMA).
T-303) was evaluated by performing a zinc removal corrosion test.
The criterion for determining the dezincification corrosion resistance is the criterion shown in JBMAT-303. That is, when the direction of the dezincing penetration search is parallel to the processing direction, the maximum dezincing penetration depth of 100 μm or less is good (○). When the zinc penetration depth direction was perpendicular to the processing direction, the maximum zinc removal depth of 70 μm or less was regarded as good (○). FIG. 2 shows that the corrosion resistance is improved when the area occupancy ratio of the γ phase is 3.0% or more and 20% or less. In addition, there was no particular problem regarding hot forgeability.

FIG. 3 shows that the area occupation ratio of the γ phase is 3.5.
% And 5.2% of the copper alloy material according to the present invention, a free-cutting brass bar (JIS C-3604), a comparative example in which the area occupancy ratio of the γ phase is 2.1%, and an α phase single phase copper alloy It shows the result of performing a cutting test on the material. This figure 3
From this, it can be seen that the cutting resistance index of the copper alloy material according to the present invention reaches 90% or more of the free-cutting brass bar which is considered to have the best machinability, and that the copper alloy material has good machinability.

On the other hand, FIG. 4 (a) is a photomicrograph showing the crystal structure of the copper alloy of Sample 7 in FIG. 2, and l (b) is (a).
FIG. 5A is a copy of a micrograph showing the crystal structure of the copper alloy of Sample 4, and FIG. 5B is a diagram prepared based on FIG. The crystal structure shown in FIG. 4 has a γ phase precipitated and grown at the grain boundary of the α phase, and the β phase has almost disappeared. The crystal structure shown in FIG.
It can be seen that the γ phase is precipitated at the grain boundary between the phase and the β phase so as to surround the β phase.

FIGS. 6A to 6C are block diagrams showing steps of a method for manufacturing a wetted member according to the present invention. In the method shown in FIG. 6A, Cu--Zn-Sn Forming is applied to the copper alloy material of the system, and 500 ° C
Heat treatment is performed at a temperature of 550 ° C. or less for 30 seconds or more, and then cooling is performed at a cooling rate of 350 ° C. or less at a rate of 0.4 ° C./sec or less.

In the method shown in FIG.
The Cu-Zn-Sn-based copper alloy material is subjected to molding, the molded body is subjected to heat treatment at 400 ° C or more and 500 ° C or less for 30 seconds or more, and then cooled, then cut, polished,
Perform the assembly. This method differs from the method shown in FIG. 3A in whether or not the cooling rate is set to 0.4 ° C./sec or less. As described above, when heat treatment is performed at a temperature of 400 ° C. or more and 500 ° C. or less, a γ phase is necessarily precipitated, and thus the cooling rate is arbitrary.

Further, in the method shown in FIG.
The Cu-Zn-Sn-based copper alloy material is subjected to molding, and the molded body is subjected to a heat treatment at a temperature of 500 ° C or more and 550 ° C or less for a holding time of 30 seconds or more. Cooling is performed at 0.4 ° C./sec or more and 4 ° C./sec or less, and thereafter, cutting and the like are performed.

FIG. 7 is a block diagram showing the steps of the conventional manufacturing method. Comparing this with the above-mentioned method of the present invention, the method of the present invention has a smaller number of steps than the conventional casting-based method. You can see that it is a little extinct.

FIG. 8 shows the area occupancy ratio (%) of the precipitated γ-phase when the Cu—Zn—Sn-based copper alloy having the composition ratio of Sample 3 was heat-treated while changing the temperature and time of the heat treatment. FIG. 8 shows that at a temperature of 500 ° C. or less, a holding time of 30 seconds or more is required to make the area occupation ratio (%) of the γ phase 3% or more. Also,
When the heat treatment temperature becomes 550 ° C., the area occupancy ratio of the γ phase does not increase even if the holding time is lengthened, but tends to decrease. Therefore, in order to make the area occupation ratio (%) of the γ phase 31% or more, the heat treatment temperature should be 550 ° C. or less.

FIG. 9 shows the composition ratio of Cu-Zn-
FIG. 9 shows the area occupation ratio (%) of the γ phase precipitated by changing the cooling conditions after the heat treatment with respect to the Sn-based copper alloy. It is difficult to obtain the area occupation ratio (%) of
It can be seen that it is preferable to set the cooling rate to 4 ° C./sec or less at a lower cooling rate to 4 ° C./sec, where the area occupation ratio (%) is larger.

Next, FIG. 10 shows that β in the α + β + γ3 phase
Phase area occupancy ratio (%), Sn concentration in β phase (%),
Shows the relationship between corrosion resistance. Here, the corrosion resistance indicates the corrosion depth (μm) perpendicular to the working direction according to the dezincification corrosion test according to the Japan Copper and Brass Association Technical Standard (JBMA T-303), and the maximum dezincification penetration depth is 70 μm or less. (O)

As can be seen from FIG. 10, when the area occupation ratio of the β phase is 35% or less, the Sn concentration in the β phase becomes 1.%.
If the content is 5 wt% or more, the corrosion resistance is good. However, if the area occupation ratio of the β phase is 35% or more and 40% or less, the Sn concentration in the β phase needs to be 2.5 wt% or more to improve the corrosion resistance. When the area occupation ratio of the β phase is 40% or more, β
The Sn concentration in the phase needs to be 3.0 wt% or more.

This can be considered as follows. First, β
In the vicinity of the grain boundary with the γ phase in the phase, a portion where the Sn concentration is low is locally generated, which may cause local dezincification corrosion. Because, in the present embodiment, the β phase is transformed by cooling from a high temperature range, the surrounding Sn is taken in at the time of transformation from the β phase to the γ phase, and the Sn in the β phase around the γ phase
This is because the concentration is reduced.

If the area occupation ratio of the β phase is 35% or more, since the β phase crystal grains are unlikely to be separated from each other by the α phase, the dezincified corrosion portion propagates through the adjacent β phase. However, if the average Sn concentration in the β phase is set to 2.5 wt% or more, the Sn concentration in the β phase near the grain boundary with the γ phase can be maintained at a relatively high level, thereby reducing local dezincification corrosion. You do it.

FIGS. 11 to 14 show examples of various water-contact members to which the copper alloy according to the present invention is applied. In the faucet fitting shown in FIG. 11, a spout which is also on the secondary pressure side is connected to a main body which is a water and pressure resistant part to which a primary pressure is applied, via a joint of a water non-pressure resistant part which is a secondary pressure side. The water contact member shown in FIG. 12 uses a forged product made of the copper alloy according to the present invention for the elbow member to which the pipe is connected. The water contact member shown in FIG. 13 uses a forged product made of the copper alloy according to the present invention as a fitting for a hose to which a shower is attached. Further, the water contact member shown in FIG. 14 uses a forged product made of the copper alloy according to the present invention as a joint member of a pipe.

[0039]

As described above, the Cu-Zn-Sn based copper alloy according to the present invention has a Sn concentration of 3.0 wt% or more at the grain boundary of the α phase or the grain boundary of the α phase and the β phase. Since the γ phase is precipitated at a ratio where the area occupation ratio is 3% or more and 20% or less, the dezincification corrosion resistance can be significantly improved. In particular, even when the β phase exists, the γ phase surrounds the periphery of the β phase, so that even if the β phase exists, the dezincification corrosion resistance does not deteriorate.

In addition, when the β phase is present, the machinability itself is improved. However, even if there is no β phase, if the γ phase is present, since the γ phase is hard, the cutting is started from the γ phase. Progresses, so that the machinability is improved.

On the other hand, according to the method for producing a copper alloy according to the method of the present invention, by controlling the cooling rate and the like, the γ phase is precipitated between the α-phase grain boundaries or the α- and β-phase grain boundaries. I can do it. Further, according to the water-contacting member made of the copper alloy according to the present invention, it is possible to provide a water-contacting member excellent in dezincification corrosion resistance and easy to manufacture.

That is, in general, the thickness of the water-contacting member such as a pipe must be not only a thickness that can withstand water pressure and the like, but also a thickness that is expected to be reduced by corrosion for a service life. When such a Cu—Zn—Sn based copper alloy is used, it is excellent in dezincification corrosion resistance and also resistant to acidic water (hypochlorous acid). Any of them can exhibit sufficient durability while being thin. Specifically, the JIS standard for hydrants requires a pressure-resistant performance of 17.5 kg / cm2 for a water-resistant metal part to which a primary pressure is applied, taking into account the decrease in wall thickness due to corrosion over time. Thus, in the past, the minimum wall thickness of the cylindrical faucet fitting part of 100 mm was 1.0 mm to 1.5 mm, but by using the copper alloy according to the present invention, the minimum wall thickness was reduced. The thickness can be reduced to 0.8 mm to 1.2 mm.

[Brief description of the drawings]

Fig. 1 Characteristics of α phase, β phase and γ phase

FIG. 2 shows the results of experiments on the composition and corrosion resistance of copper alloys performed on Cu-Zn-Sn-based samples 1 to 7

FIG. 3 shows a result of a cutting test performed on a copper alloy material according to the present invention, a free-cutting brass bar, and an α-phase single-phase copper alloy material.

4A is a copy of a micrograph showing the crystal structure of the copper alloy of Sample 7, and FIG. 4B is a diagram prepared based on FIG.

FIG. 5A is a photomicrograph showing the crystal structure of the copper alloy of Sample 4, and FIG. 5B is a diagram prepared based on FIG.

FIGS. 6A and 6B are block diagrams showing steps of a method for manufacturing a wetted member according to the present invention.

FIG. 7 is a block diagram showing steps of a conventional manufacturing method.

FIG. 8 shows the relationship between the area occupation ratio of the γ phase and the temperature and time of the heat treatment for the copper alloy of Sample 3.

FIG. 9 shows the relationship between the area occupation ratio of the γ phase and the cooling conditions after heat treatment for the copper alloy of Sample 3.

FIG. 10 shows the relationship between the area occupancy ratio (%) of the β phase, the Sn concentration (%) in the β phase, and the corrosion resistance of the copper alloy according to the present invention.

FIG. 11 is a view showing an example of various water-contact members to which the copper alloy according to the present invention is applied.

FIG. 12 is a view showing an example of various water-contacting members in which the copper alloy according to the present invention is appropriately rotated.

FIG. 13 is a view showing an example of various water-contact members to which the copper alloy according to the present invention is applied.

FIG. 14 is a view showing an example of various water-contact members to which the copper alloy according to the present invention is applied.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C22F 1/00 640 C22F 1/00 640A 681 681 682 682 692 691 691B 691C 692 692A 692B (72) Inventor Masanao Hamasaki Kokura, Kitakyushu, Fukuoka Prefecture (2-1) Toru Uchida Inventor Toru Uchida 2-1-1 Nakajima, Kitakyushu-shi, Fukuoka Prefecture

Claims (31)

[Claims] 1. A Cu—Zn—Sn based copper alloy,
This copper alloy has a Sn concentration of 0.9 wt% or more and 3.0 wt%.
In the following, a γ phase is precipitated at a grain boundary of an α phase or a grain boundary of an α phase and a β phase, the area occupation ratio of the γ phase is 3% or more and 20% or less, and the Sn concentration in the γ phase is 3. A copper alloy characterized by being at least 0 wt%. 2. The copper alloy according to claim 1, wherein said β phase is surrounded by a γ phase. 3. The copper alloy according to claim 2, wherein the Sn concentration in the α phase is 0.5 wt% or more and the Sn concentration in the β phase is less than 1.5 wt%. . 4. The copper alloy according to claim 1, wherein the Sn concentration in the α phase is 0.5 wt% or more, and the Sn concentration in the β phase is 1.5 wt% or more. . 5. The copper alloy according to claim 3, wherein the α phase has an area occupancy of 97% or less and 40% or more, and the β phase has an area occupancy of 0% or more and 40% or less. Copper alloy. 6. The copper alloy according to claim 4, wherein the area occupancy of the α phase is 97% or less and 20% or more, and the area occupancy of the β phase is 0% or more and 60% or less. Copper alloy. 7. The copper alloy according to claim 1, wherein a Zn equivalent is 37 wt% or more and 45 wt% or less. 8. A water-contact member made of the copper alloy according to claim 1. 9. The water contact member according to claim 8, wherein the water contact member is a faucet. 10. A method for producing a copper alloy according to claim 1, 3 or 5, wherein the method comprises the steps of:
500 ° C or more and 55 for 1 Zn-1 Sn based copper alloy material
Perform heat treatment at 0 ° C or less for 30 seconds or more, then 350 ° C
A method for producing a copper alloy, wherein cooling is performed at a cooling rate of 0.4 ° C./second or less. 11. A method for producing a copper alloy according to claim 1, 2 or 5, wherein the method comprises the steps of:
-400 ° C or more and 50 for Zn-Sn based copper alloy material
A method for producing a copper alloy, comprising performing a heat treatment at 0 ° C. or less for 30 seconds or more, and then cooling. 12. A method for producing a copper alloy according to claim 1, 4 or 6, wherein the method comprises the steps of:
-500 ° C or more and 55 for Zn-Sn based copper alloy material
Heat treatment at 0 ° C or less for 30 seconds or more, then 350 ° C
A method for producing a copper alloy, comprising cooling at a cooling rate of 0.4 ° C./sec to 4 ° C./sec. 13. The method for producing a copper alloy according to claim 1, wherein the temperature range in which the crystal structure is transformed is a first temperature range in which a γ phase is precipitated, and a temperature range higher than the first temperature range. And a second temperature range in which the γ phase does not precipitate, and after heating to the second temperature range, controlling the cooling rate from the upper limit temperature to the lower limit temperature of the first temperature range, thereby obtaining the area of the γ phase. A method for producing a copper alloy, comprising adjusting an occupancy ratio. 14. The temperature range in which the crystal structure is transformed is γ
In a method for producing a copper alloy having a first temperature range in which a phase precipitates and a second temperature range in which a γ phase does not precipitate in a temperature range equal to or higher than the first temperature range, heating to the second temperature range, A method for producing a copper alloy, comprising controlling a cooling rate from an upper limit temperature to a lower limit temperature of a first temperature range to adjust an area occupancy ratio of a γ phase. 15. The method for producing a copper alloy according to claim 14, wherein the cooling rate is 4 ° C./sec or less. 16. The method for producing a copper alloy according to claim 14, wherein the area occupation ratio of the γ phase is 3% or more. 17. The method for producing a copper alloy according to claim 14, wherein the Cu—Zn—Sn-based copper alloy contains Sn in the γ phase by controlling the cooling rate.
A method for producing a copper alloy, comprising adjusting the concentration. 18. The copper alloy according to claim 17, wherein
A method for producing a copper alloy, wherein the Sn concentration in the γ phase is 3.0 wt% or more. 19. A Cu—Zn—Sn based copper alloy, wherein the area occupation ratio of the γ phase is 3% or more. 20. The copper alloy according to claim 19,
A copper alloy, wherein the area occupation ratio of the γ phase is 20% or less. 21. The copper alloy according to claim 19, wherein the Sn concentration is 0.9 wt% or more and 3.0 wt% or less. 22. The copper alloy according to claim 19, wherein the copper alloy has an α + γ2 phase crystal structure and a Sn concentration in the γ phase is 3.0 wt% or more. 23. The copper alloy according to claim 19, which has an α + β + γ3 phase crystal structure,
A copper alloy, wherein the Sn concentration in the γ phase is 3.0 wt% or more, and the periphery of the β phase is surrounded by the γ phase. 24. The copper alloy according to claim 19, having a crystal structure of α + β + γ3 phase,
A copper alloy, wherein the Sn concentration in the β phase is 1.5 wt% or more. 25. The copper alloy according to claim 24,
A copper alloy, wherein the area occupation ratio of the β phase is 35% or less. 26. The copper alloy according to claim 24,
A copper alloy, wherein the area occupation ratio of the β phase is 35% or more and 40% or less, and the Sn concentration in the β phase is 2.5% by weight or more. 27. The copper alloy according to claim 24,
A copper alloy, wherein the area occupancy of the β phase is 40% or more, and the Sn concentration in the β phase is 3.0% by weight or more. 28. The copper alloy according to claim 19, wherein a part or all of the γ phase is a β phase transformed by cooling from a high temperature range. 29. The copper alloy according to claim 19, wherein the Zn equivalent is not less than 37 wt% and not more than 45 wt%. 30. A water-contact member made of the copper alloy according to claim 19. 31. The water contact member according to claim 30, wherein the water contact member is a faucet.