EP3128020A1

EP3128020A1 - Low-lead brass alloy for plumbing member

Info

Publication number: EP3128020A1
Application number: EP15772552.4A
Authority: EP
Inventors: Hiroshi Yamada; Masaaki Yamamoto; Takeaki Miyamoto; Syohei MATSUBA
Original assignee: Kurimoto Ltd
Current assignee: Kurimoto Ltd
Priority date: 2014-03-31
Filing date: 2015-03-06
Publication date: 2017-02-08
Anticipated expiration: 2035-03-06
Also published as: KR20160140821A; WO2015151720A1; EP3128020A4; EP3128020B1; JPWO2015151720A1; JP6482530B2; KR102314457B1; US20170121791A1; CN106103755A

Abstract

An object of the present invention is to provide a brass alloy, in which the content of Bi is reduced to secure a good recyclability while maintaining the dezincification corrosion resistance required for a member for water works, and which is capable of exhibiting an erosion-corrosion resistance and excellent mechanical properties to be used as a member for water works. This brass alloy contains: 24% by mass or more and 34% by mass or less of Zn; 0.5% by mass or more and 1.7% by mass or less of Sn; 0.4% by mass or more and 1.8% by mass or less of Al; 0.005% by mass or more and 0.2% by mass or less of P; and 0.01% by mass or more and 0.25% by mass or less of Pb; with the balance being copper and an unavoidable impurity(ies). Note, however, that in cases where the above mentioned copper alloy has a content of Sn of less than 1.0% by mass, the contents of Al and Sn in % by mass satisfy the Inequality: Al + 2 × Sn ≥ 2.8.

Description

TECHNICAL FIELD

The present invention relates to a material made of a brass alloy and having an erosion-corrosion resistance, designed for use in a member for water works.

BACKGROUND ART

JIS H5120, CAC 203, a brass casting which has been conventionally used for members related to water works, such as tap faucet parts, contains from 0.5 to 3.0% by mass of lead, and it has become difficult to comply with the lead regulations for copper alloys for use in members for water works, implemented around the world in recent years. Efforts have therefore been made to produce a copper alloy with a reduced lead content, in order to reduce the harmful effect of lead.
However, simply reducing the Pb content results in a decrease in the castability, machinability and/or pressure resistance of the copper alloy, which could potentially cause water leak when used as a valve, for example. In order to compensate for the changes in the properties of the alloy due to reduced content of lead, incorporation of Bi has been proposed to improve machinability, dezincification corrosion resistance and/or pressure resistance.
For example, the below-identified Patent Document 1 discloses a brass alloy having a reduced risk of dezincification corrosion and improved mechanical properties and castability, while having a reduced lead content, which brass alloy containing, along with Zn, from 0.4 to 3.2% by mass of Al, from 0.1 to 4.5% by mass of Bi, and from 0.001 to 0.3% by mass of P.
Further, the below-identified Patent Document 2 discloses a brass alloy (for example, No. 6 or No. 20) capable of preventing water quality deterioration and having an excellent machinability and abradability at the time of plating pretreatment, which brass alloy containing from 0.3 to 1.0% of Sn, from 0.5 to 1.0% of Ni, from 0.4 to 8% of Al, from 0.01 to 0.03% of P, from 1.0 to 2.0% of Bi, and a trace amount of Sb. Patent Document 2 also discloses a brass alloy further containing from 5 to 10 ppm by weight of B, in addition to containing the above mentioned elements within the above ranges.
However, a copper alloy which contains a large amount of Bi for the purpose of securing the machinability must be separated from other copper alloys containing no Bi, when subjected to recycling. This is because, if a copper alloy containing Pb is contaminated with Bi, for example, it causes embrittlement of the resulting alloy. Since the alloy according to the Patent Document 1 contains Bi, it has the above mentioned problem, and the same problem applies to the alloy according to Patent Document 2, specifically, the alloy No. 6 disclosed as an Example therein.
In contrast, a brass alloy is also known which contains no Bi, and which is useful as a member for water works in terms of recyclability. For example, since the alloy No. 20 disclosed as a Comparative Example in Patent Document 2 does not contain Bi, there is no need to carry out the sorting of alloys based on whether or not Bi is contained, at the time of recycling.
The below-identified Patent Document 3 discloses a copper alloy (for example, No. 803) for use in wires, which does not contain Bi or Pb, and contains from 62 to 91 mass% of Cu, from 0.01 to 4 mass% of Sn, from 0.0008 to 0.045 mass% of Zr, and from 0.01 to 0.25 mass% of P, with the balance being Zn. This copper alloy is required to have a composition in which the contents of Cu, Sn, and P, cach in percent by mass, satisfy the relation: 62 ≤ Cu -0.5 × Sn -3 × P ≤ 90, in addition to containing the above mentioned elements within the above contents. Further, the copper alloy is also required to have a phase structure in which the total content of α-phase, γ-phase, and β-phase accounts for 95 to 100% in terms of area ratio, and to have an average crystal grain size at the time of melt-solidification of 0.2 mm or less. However, when this alloy for use in wires is used as a member for water works, the alloy fails to exhibit sufficient machinability, despite having a sufficient recyclability due to containing no Bi.
In cases where a brass alloy is used as a member for water works, there are other important issues to be addressed, in addition to the recyclability. When used as a member for water works, such as a valve, any brass alloy is susceptible to corrosion induced by the rapid flow of water, referred to as an erosion-corrosion. When a brass alloy is in contact with still water, an oxide film is gradually formed on the surface of the metallic material to prevent corrosion. However, in an environment where the alloy is exposed to flowing water, the influence of the shear force or turbulent flow caused by the flowing water, in addition to ordinary corrosion, destroys the oxide film, thereby accelerating the corrosion. The alloy No. 20 disclosed as a Comparative Example in Patent Document 2 has an insufficient erosion-corrosion resistance. Examples of the brass alloy having an erosion-corrosion resistance, as described above, include alloys disclosed in the below-identified Patent Documents 4 to 6.
Patent Document 4 discloses a copper alloy containing from 10 to less than 25 wt% of Zn, from 0.005 to 0.070 wt% of P, from 0.05 to 1.0 wt% of Sn, and from 0.05 to 1.0 wt% of Al; and any one or two of from 0.005 to 1.0 wt% of Fe and from 0.005 to 0.3 wt% of Pb in a total amount of from 0.005 to 1.3 wt%; with the balance being copper and an unavoidable impurity(ies); wherein the alloy has an excellent erosion-corrosion resistance.
Patent Document 5 discloses a copper alloy containing from 25 to 40 wt% of Zn, from 0.005 to 0.070 wt% of P, from 0.05 to 1.0 wt% of Sn, and from 0.05 to 1.0 wt% of Al, as essential elements; and any one or two of from 0.005 to 1.0 wt% of Fe and from 0.005 to 0.3 wt% of Pb in a total amount of from 0.005 to 1.3 wt%; with the balance being copper and an unavoidable impurity(ies); wherein the alloy has a crystal grain size of 0.015 mm or less and an excellent dezincification corrosion resistance.
Further, Patent Document 6 discloses a copper alloy containing from 25 to 40 wt% of Zn, from 0.005 to 0.070 wt% of P, from 0.05 to 1.0 wt% of Sn, from 0.05 to 1.0 wt% of Al, and from 0.005 to 1.0 wt% of Si, as essential elements; and any one or two of from 0.005 to 1.0 wt% of Fe and from 0.005 to 0.3 wt% of Pb in a total amount of from 0.005 to 1.3 wt%; with the balance being copper and an unavoidable impurity(ies); wherein the alloy is characterized by being subjected to cold rolling at reduction of sectional area of 3 to 20%, after final annealing, and having an excellent dezincification corrosion resistance.
In addition, the below-identified Patent Document 7 discloses copper alloys containing Zr and/or Te as a trace element(s). Disclosed therein is a copper alloy containing from 8 to 40% of Zn, from 0.0005 to 0.04% of Zr, and from 0.01 to 0.25% of P; and one or more than one of from 2 to 5% of Si, from 0.05 to 6% by mass of Sn, and from 0.05 to 3.5% by mass of Al; with the balance being Cu and an unavoidable impurity(ies). Also disclosed therein, as Example 105, is a copper alloy which does not contain Si or Bi, and contains 27% of Zn, 0.8% of Sn, 0.8% of Al, 0.05% of P, 0.18% of Pb, 0.005% of Zr, and 0.12% of Te.
Moreover, the below-identified Patent Document 8 describes a finding that it is possible to obtain an alloy satisfying required physical properties by integrating the influence of each of the elements in terms of zinc equivalent (Zneq), and allowing the zinc equivalent Zneq to satisfy a certain Inequality. Note, however, that the alloy in the above mentioned description contains Bi. Specifically, the alloy contains: from 0.4 to 2.5% by mass of Al; 0.001 to 0.3% by mass of P; 0.1 to 4.5% by mass of Bi; from 0 to 5.5% by mass of Ni; from 0 to 0.5% by mass each of Mn, Fe, Pb, Sn, Si, Mg, and Cd; and Zn; with the balance being Cu and an unavoidable impurity(ies). Further, in the above mentioned alloy, it is required that the Zneq and the content of Al satisfy the following Inequalities (1) and (2): $Zneq + 1.7 \times Al \geq 35.0$
$Zneq - 0.45 \times Al \leq 37.0$

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: WO 2013/145964 A1
Patent Document 2: JP 2000-239765 A
Patent Document 3: JP 4094044 B
Patent Document 4: JP 60-138034 A
Patent Document 5: JP 61-199043 A
Patent Document 6: JP 62-30862 A
Patent Document 7: WO 2007/091690 A1
Patent Document 8: JP 5522582 B

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

However, since the alloy according to Patent Document 4 has a low Zn content, its tensile strength is insufficient, thereby causing problems in mechanical properties. In addition, although it is alleged therein that the alloy has an erosion-corrosion resistance, its Sn content is practically insufficient to provide a sufficient erosion-corrosion resistance.
Further, since the alloys disclosed in Patent Documents 5 and 6 contain a large amount of Zn, they have problems that the elongation tends to be insufficient, and that the dezincification corrosion is likely to occur. The alloys also have an insufficient erosion-corrosion resistance.
In addition, since the alloys disclosed in Patent Document 7 contain Zr and/or Te as an essential element(s), problems may occur when used as a mixture with other copper alloys. In particular, since Te is toxic, the use of this alloy as a member for water works is not desirable in the first place.
Still further, since the alloy disclosed in Patent Document 8 contains Bi, it cannot be recycled along with other common copper alloys containing Pb. This alloy also has a problem of insufficient erosion-corrosion resistance.
Accordingly, an object of the present invention is to provide a brass alloy, in which the contents of toxic elements are reduced while maintaining the dezincification corrosion resistance required for a member for water works; which is capable of exhibiting an erosion-corrosion resistance while having a reduced Bi content to secure a good recyclability; and which has excellent mechanical properties to be used as a member for water works.

MEANS FOR SOLVING THE PROBLEMS

The present invention has solved the above mentioned problems by providing a low-lead brass alloy for use in a member for water works, the brass alloy comprising: 24% by mass or more and 34% by mass or less of Zn; 0.5% by mass or more and 1.7% by mass or less of Sn; 0.4% by mass or more and 1.8% by mass or less of Al; 0.005% by mass or more and 0.2% by mass or less of P; and 0.01% by mass or more and 0.25% by mass or less of Pb; with the balance being copper and an unavoidable impurity(ies);
wherein, in cases where the brass alloy has a content of Sn of less than 1.0% by mass, the contents of Al and Sn in % by mass satisfy the following Inequality (3): $\cdot Al + 2 \times Sn \geq 2.8$
Although the content of Pb is lower the better, Pb contributes to improving the machinability of the alloy, even in a small amount within the range in which its adverse effects on health are limited. Further, Pb and Al-P compounds work in combination to serve as chip breakers, and significantly contribute to improving the machinability. This allows the alloy to have a sufficient machinability, making it suitable for a member for water works. Further, the incorporation of a specified amount of Sn allows the alloy to exhibit mechanical properties required for a brass alloy having a high content of Zn, such as tensile strength, elongation, and 0.2% proof stress, while exhibiting durability against erosion-corrosion.
In cases where the Sn content is less than 1.0% by mass, it is necessary that the alloy meet a further requirement that the relationship between the Sn content and the Al content satisfy the above mentioned Inequality (3) in order to secure the erosion-corrosion resistance. While both Al and Sn are involved in the erosion-corrosion resistance, in cases where the Sn content is less than 1.0% by mass, in particular, Sn has twice as much influence on the improvement of the erosion-corrosion resistance as Al does. Therefore, it is required that the above mentioned Inequality (3) be satisfied, in order to obtain necessary physical properties while securing a good balance of the erosion-corrosion resistance and physical properties in the alloy. On the other hand, when the Sn content is 1.0% by mass or more, a sufficient erosion-corrosion resistance and the 0.2% proof stress can both be secured, even if the above mentioned Inequality (3) is not satisfied.
As with Pb, Si is also known as an element capable of improving the machinability. However, the brass alloy according to the present invention contains Si in an amount less than the amount contained as an unavoidable impurity(ies). This is because Si tends to produce an oxide which causes problems in recyclability and mechanical properties, particularly, in elongation. In addition, Si may potentially cause a reduction in the erosion-corrosion resistance.
When 0.015% by mass or less of B is further incorporated into the brass alloy having the above mentioned composition, as a variation of the brass alloy according to the present invention, the dezincification corrosion resistance is markedly improved.
Further, when 1.8% by mass or less of Ni is further incorporated into the brass alloy having the above mentioned composition, as another variation of the brass alloy according to the present invention, the dezincification corrosion resistance is markedly improved.

EFFECT OF THE INVENTION

The present invention allows for producing a member for water works made of a brass alloy which has a good machinability and erosion-corrosion resistance while having a reduced Bi content to improve the recyclability, and in which safety, durability, and convenience are ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a tensile test evaluation method.
FIG. 2 is a schematic diagram illustrating an erosion-corrosion test apparatus.
FIG. 3 shows standards for evaluating machining chips obtained in a machinability test.
FIG. 4 is a graph obtained by plotting the maximum erosion-corrosion depth against the content of Sn, of alloys of Examples.
FIG. 5 is a graph obtained by plotting the maximum erosion-corrosion depth against the value T of Equation (4), of the alloys of Examples.
FIG. 6 shows photographs of machining chips obtained in the machinability test.

MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail.
The present invention relates to a brass alloy for use in a member for water works which contains at least Zn, Sn, Al, P, and Pb.
It is necessary that the above mentioned brass alloy contain 24% by mass or more of Zn. Preferably, the Zn content is 27% by mass or more. A Zn content of less than 24% by mass results in an insufficient tensile strength, thereby causing problems in mechanical properties. When the Zn content is 27% by mass or more, the resulting brass alloy has a sufficient 0.2% proof stress, and thus has an excellent strength. At the same time, it is necessary that the Zn content be 34% by mass or less. Preferably, the Zn content is 32% by mass or less. Too high a Zn content tends to result in an insufficient elongation. Further, a Zn content exceeding 34% by mass leads to an excessive increase in the dezincification corrosion.
It is necessary that the above mentioned brass alloy have a Sn content of 0.5% by mass or more. If the Sn content is less than 0.5% by mass, the resulting alloy has an insufficient resistance to erosion-corrosion. A Sn content of 1.0% by mass or more is preferred, because the resulting alloy has a sufficient erosion-corrosion resistance and a sufficient 0.2% proof stress. At the same time, it is necessary that the Sn content be 1.7% by mass or less. Preferably, the content is 1.3% by mass or less. This is because too high a Sn content tends to results in too low an elongation. Further, in cases where the Sn content is less than 1.0% by mass, it is necessary that the relationship between the Sn content and the Al content satisfy Inequality (3) to be described later, in order to secure the erosion-corrosion resistance.
It is necessary that the above mentioned brass alloy have an Al content of 0.4% by mass or more. Preferably, the Al content is 0.6% by mass or more. An Al content of less than 0.4% by mass results in an insufficient tensile strength and/or 0.2% proof stress, thereby causing problems in mechanical properties. Further, compounds formed between Al and P to be described later significantly contribute to the improvement in the machinability. However, if the Al content is deficient, the effect provided by the compounds will also be insufficient. At the same time, it is necessary that the Al content be 1.8% by mass or less. Preferably, the content is 1.3% by mass or less. An Al content exceeding 1.8% by mass may results in too low an elongation.
In cases where the Sn content is less than 1.0% by mass, it is necessary that the relationship between the Sn content and the Al content in the alloy satisfy the following Inequality (3). The maximum depth of the cavities caused by erosion-corrosion tends to decrease when either of the Al content and the Sn content is increased. However, in cases where the Sn content is within the range of less than 1.0% by mass, in particular, an increase in the Sn content has twice as large an effect as an increase in the Al content does in improving the erosion-corrosion resistance. $\cdot Al + 2 \times Sn \geq 2.8$
It is necessary that the above mentioned brass alloy have a P content of 0.005% by mass or more. Preferably, the P content is 0.01 % by mass or more. Too low a P content reduces the effect of improving the machinability provided by the Al-P compounds formed between P and Al, and the resulting alloy tends to produce continuous machining chips. Further, since P exhibits a deoxidizing effect, too low a P content leads to a decrease in the deoxidizing effect during casting, thereby resulting in an increased occurrence of gas defects, as well as a decreased fluidity due to oxidation of molten metal. At the same time, it is necessary that the P content be 0.2% by mass or less. Preferably, the P content is 0.15% by mass or less. Too high a P content leads to an increased formation of hard Al-P compounds and the like, thereby resulting in a decrease in the elongation. Further, P reacts with water in the mold to increase the occurrence of gas defects and shrinkage cavity defects.
It is necessary that the above mentioned brass alloy have a Pb content of 0.01 % by mass or more. Preferably, the Pb content is 0.03% by mass or more. The presence of Pb contributes to an improved machinability of the alloy, along with the Al-P compounds, but if the Pb content is less than 0.01% by mass, there is a potential risk that the machinability may be insufficient. Since the above mentioned brass alloy contains Sn, which leads to the formation of hard γ-phase, in particular, the effect of improving the machinability provided by Pb is indispensable. On the other hand, if the Pb content exceeds 0.25% by mass, it becomes difficult to comply with the leaching standards for alloys for use in members for water works, depending on the district in which it is used. Accordingly, it is necessary that the Pb content be 0.25% by mass or less, at maximum.
The above mentioned brass alloy may contain as the balance, in addition to Cu, an element(s) other than those described above as an unavoidable impurity(ies), which are inevitably included in the alloy due to the problems associated with raw materials or the production process. However, it is necessary that these elements be contained within the ranges in which the effect of the present invention is not impaired. This is because, when too large amounts of unexpected elements are incorporated into the alloy, even if the above mentioned elements are contained within the above mentioned ranges, there is a potential risk that the physical properties of the alloy may be deteriorated. The total content of the unavoidable impurities is preferably less than 1.0% by mass, and more preferably, less than 0.5% by mass.
Among the above mentioned unavoidable impurities, the content of Si is preferably less than 0.2% by mass, more preferably, less than 0.1% by mass, and still more preferably, less than the detection limit. Too high a Si content accelerates the entrainment of oxides, decrease in elongation, and occurrence of shrinkage cavities, resulting in a failure to produce a decent casting.
Among the above mentioned unavoidable impurities, it is necessary that the content of Bi be less than 0.3% by mass. The Bi content is preferably less than 0.1% by mass, and still more preferably, less than the detection limit. This is because, if the alloy contains an unignorable amount of Bi, the products made therefrom must be recycled separately, thereby complicating the recycling process. If the Bi content exceeds 0.3% by mass, the coexistence of Bi in combination with Pb contained in the brass alloy according to the present invention may cause an insufficient elongation, and there is a potential risk that problems in mechanical properties could occur.
The content of each of the elements which are considered as the unavoidable impurities, is preferably less than 0.4% by mass, more preferably, less than 0.2% by mass, and still more preferably, less than the detection limit. Examples of such impurities include Fe, Mn, Cr, Zr, Mg, Ti, Te, Se, Cd and the like. Among these, in particular, the contents of Se, Cd, and Te, which are known to be toxic, are each preferably less than 0.1% by mass, and more preferably, less than the detection limit. Further, the content of Zr, which increases the occurrence of shrinkage cavity defects, is preferably less than 0.1% by mass, and still more preferably, less than the detection limit.
On the other hand, when the above mentioned brass alloy contains 0.0005% by mass or more of B as an intentionally included element, apart from the above mentioned unavoidable impurities, the dezincification corrosion resistance is significantly improved. This is because the presence of B causes the crystal grains to be refined and to be formed into shapes less susceptible to dezincification corrosion. The content of B is preferably 0.0007% by mass or more, because the dezincification corrosion resistance is further improved. On the other hand, if the B content exceeds 0.015% by mass, a large amount of hard compounds is formed within the texture of the alloy, potentially causing adverse effects on machinability or elongation.
Further, the above mentioned brass alloy may contain Ni as an intentionally included element, apart from the unavoidable impurities. When the Ni content is 0.1% by mass or more, the surface area of α-phase, which has an excellent corrosion resistance, is increased, thereby improving the dezincification corrosion resistance of the brass alloy. It is possible to adjust the composition such that the alloy benefits from both the effect provided by containing B, and the effect provided by containing Ni. At the same time, the Ni content is preferably 1.8% by mass or less, and more preferably, 0.5% by mass or less. The addition of an excessive amount of Ni increases the amount of a phase having a high Sn content, and the resulting alloy tends to have a reduced elongation and/or machinability. A Ni content of greater than 1.8% by mass results in an unignorable decrease in elongation. In order to certainly prevent a decrease in elongation, the Ni content is preferably 0.5% by mass or less.
Further, the above mentioned brass alloy may contain both B and Ni as intentionally included elements, within the above described ranges.
Note, however, that the values of the contents of elements as used in the present invention indicate the contents thereof in the resulting alloy produced by casting or forging, not the contents in the raw materials.
The balance of the above mentioned brass alloy is Cu. The brass alloy according to the present invention can be obtained by a common method for producing a copper alloy, and when a member for water works is produced using this brass alloy, a common production method (such as casting, rolling, or forging) can be used. Examples of the production method include a method in which an alloy is melted using an oil furnace, gas furnace, high-frequency induction melting furnace, or the like, and then cast using a mold in a variety of shapes.

EXAMPLES

The brass alloy according to the present invention will now be described with reference to Examples in which the brass alloys were actually produced. First, test methods carried out for the brass alloys will be described.

A sample prepared by casting in a metal mold having a size of 28 mm diameter × 200 mm length was processed into a type 14A test specimen defined in JIS Z2241. The specific shape of the test specimen is as shown in FIG. 1. The test specimen is a proportional test piece in which the original sectional area So and the original gauge length L₀ of the parallel portion satisfy the relationship represented by the equation: L₀ = 5.65 × S₀^(1/2). The diameter do of the rod-like portion was 4 mm, the original gauge length L₀ was 20 mm, the length L_c of the parallel portion which was cylindrical was 30 mm, and the radius R of the shoulder portions was 15 mm. (L₀ = 5.65 × (2 × 2 × π)^(1/2) = 20.04)
The test specimen was subjected to a tensile test according to JIS Z2241 and the tensile strength (MPa), the 0.2% proof stress (MPa) and the elongation (%) were evaluated as follows. The tensile strength was defined as the maximum test force Fm, which was the force the test specimen withstood during the test until it exhibited discontinuous yielding. The 0.2% proof stress is the value of the stress when the plastic elongation expressed in percentage relative to the original gauge length L₀ equals to 0.2%. The elongation is the value of the permanent elongation of the test specimen after the test, obtained by continuing the test until it ruptures, expressed in percentage relative to the original gauge length L_o.

The tensile strength was evaluated according to the following standards:
- "Good" (G): 300 MPa or more; "Fair" (F): 250 MPa or more and less than 300 MPa,
- and "Insufficient" (I): less than 250 MPa.
The 0.2% proof stress was evaluated according to the following standards:
- "Good" (G): 100 MPa or more, "Fair" (F): 80 MPa or more and less than 100 MPa,
- and "Insufficient" (I): less than 80 MPa.
The elongation was evaluated according to the following standards: "Good" (G): 25% or more, "Fair" (F): 20% or more and less than 25%, and "Insufficient" (I):
- less than 20%.

<Erosion-corrosion test>

A sample prepared by casting in a metal mold having a size of 20 mm diameter × 120 mm length was cut into a cylinder having a diameter of 16 mm as shown in FIG. 2, to be used as a test specimen 12. A nozzle 11 having a bore diameter of 1.6 mm was disposed at a position 0.4 mm spaced apart from the test specimen 12, and a 1% aqueous solution of CuCl ₂ 13 was allowed to continuously flow from the nozzle 11 toward the sample at a flow rate of 0.4 L/min for 5 hours. Then the amount of the weight lost (abrasion weight loss), which is the difference in weight of the sample before and after the test, and the maximum erosion-corrosion depth in the sample were measured.
• The abrasion weight loss was evaluated according to the following standards: "Good" (G): less than 250 mg, "Fair" (F): 250 mg or more and less than 350 mg, and "Insufficient" (I): 350 mg or more.
• The maximum erosion-corrosion depth was evaluated according to the following standards: "Good" (G): 150 µm or less, "Fair" (F): 150 µm or more and 200 µm or less, and "Insufficient" (I): 200 µm or more.

Each of the alloys was subjected to a drilling test using a drilling machine. The drilling test was carried out using the samples each formed by machining to a size of 18 mm diameter × 20 mm height, and using a drilling machine, under the drilling conditions shown in Table 1. The evaluation was carried out as follows. The time required to drill a 5 mm hole in each of the samples was measured, and those with the results of 20 seconds or less were evaluated as "Good" (G), those with the results of more than 20 seconds and 25 seconds or less were evaluated as "Fair" (F), those with the results of more than 25 seconds were evaluated as "Insufficient" (I).

[Table 1]

Items		Conditions
Cutting tool (SDD0600; manufactured by Mitsubishi Corporation)	Material	High-speed steel
	Cutting diameter	Diameter: 6 mm
	Total length	102 mm
	Flute length	70 mm
	Point angle	118 degree
Load		25 kg
Rotational speed		960 rpm
Drilling depth		5 mm

For each of the alloys to be tested, a sample prepared by casting in a metal mold having a size of 28 mm diameter × 200 mm length was subjected to dry machining on a universal lathe, with a cemented carbides and/or hard metals brazed tool, at a feed of 0.15 mm/rev and a rotational speed 550 of rpm, to obtain machining chips. The machining chips were categorized based on their shapes as shown in FIG. 3. The evaluation was carried out as follows: those having favorable shapes were evaluated as "Good" (G), and those having unfavorable shapes were evaluated as "Insufficient" (I).

A sample prepared by casting in a metal mold having a size of 28 mm diameter × 200 mm length was cut out into a cubic test specimen of 10 mm x 10 mm × 10 mm, and the test was performed according to ISO 6509. Specifically, the surroundings of the test specimen was covered with an epoxy resin having a thickness of 15 mm or more such that only one surface of the test specimen was exposed from the resin. After 100 mm² of this exposed surface was polished with wet abrasive paper, the exposed surface was finished with No. 1200 abrasive paper, and washed with ethanol immediately before the test. This sample embedded in the epoxy resin with only one surface exposed was immersed in 250 mL of a 12.7 g/L aqueous solution of cupric chloride at 75 ± 5°C for 24 hours. After the completion of the test, the sample was washed with water, rinsed with ethanol, and the dezincification depth in its cross section was immediately measured using a light microscope. Specifically, an arbitrary line of 10mm on cross-section of the exposed surface was divided into 5 visual fields and the dezincification depths of the points having the minimum and the maximum depths in each of the visual fields were measured. The mean value of the total 10 points was taken as the average dezincification corrosion depth, and the depth of the deepest point of all these 10 points was taken as the maximum dezincification corrosion depth. The average and maximum dezincification corrosion depths were evaluated as follows, and those having evaluations other than "insufficient" for both the dezincification depths were defined as "pass".

The average dezincification corrosion depth was evaluated according to the following standards: "Very Good" (V): less than 50 µm, "Good" (G): 50 µm or more and less than 100 µm, "Fair" (F): 100 µm or more and less than 200 µm, and "Insufficient" (I): 200 µm or more.
The maximum dezincification corrosion depth was evaluated according to the following standards: "Very Good" (V): less than 100 µm, "Good" (G): 100 µm or more and less than 200 µm, "Fair" (F): 200 µm or more and less than 400 µm, and "Insufficient" (I): 400 µm or more.

Materials composed of each of the elements were mixed, and melted in a high frequency induction melting furnace, followed by casting to produce samples each having the composition as shown in each of the Tables. All the values of the contents of the elements are expressed in % by mass, and are values measured in the resulting castings after the production. The following tests were carried out for each of the resulting copper alloys. Note that, the content of each of Sb, Si, and Fe was less than the detection limit, in each of the alloys of Examples and Comparative Examples shown in the Tables. Elements which are not shown in the Tables, or the blanks therein, indicate that the contents of the respective elements arc less than the detection limit.
First, each of the Sn content and the Al content were varied to examine the test results of the alloy in relation to the Inequality (3). The components used in the evaluation, and the results of the mechanical properties test and erosion-corrosion (EC) test are shown in Table 2. FIG. 4 shows line graphs obtained by plotting the data of the above obtained results, categorized in 3 groups based on the concentration of Al, with the values the maximum erosion-corrosion depth on the vertical axis against the values of the Sn content on the horizontal axis. In Table 2, Test Examples 1 to 4 are alloys having an Al content of 0.6% by mass, Test Examples 5 to 8 are alloys having an Al content of 1.0% by mass, and Test Examples 9 to 12 are alloys having an Al content of 1.7% by mass. Test Examples are arranged in the order based on the content of Sn, in increasing order from top to bottom, within each of the groups based on the Al concentration.
The test results revealed that the erosion-corrosion (EC) maximum depth was markedly reduced in the alloys of Test Examples having a Sn content within the range of 1.0% by mass or more, as compared to the alloys of the Test Examples having a Sn content within the range of less than 1.0% by mass, regardless of the Al content. Further, the results also indicated that, when the Sn content is the same, the higher the Al content is, the more reduced the maximum erosion-corrosion depth is. However, the above mentioned tendency was markedly observed, particularly in cases where the Sn content is within the range of less than 1.0% by mass.

Therefore, among the alloys of Test Examples, those having a Sn content of less than 1.0% by mass were examined. Specifically, the alloys of Test Examples 1 and 2 having an Al content of 0.6% by mass, Test Examples 5 and 6 having an Al content of 1.0% by mass, and Test Examples 9 and 10 having an Al content of 1.7% by mass were selected, which are shown in Table 3. Of these, the alloys of Test Examples 1, 2, and 5 were evaluated as having an "Insufficient" in the maximum erosion-corrosion depth. The Sn content in the alloy of Test Example 2 is about 0.2% by mass higher than that of Test Example 1. Further, the Al content in the alloy of Test Example 5 is about 0.4% by mass higher than that of Test Example 1. The values of the maximum erosion-corrosion depth of Test Example 2 and Test Example 5 are almost the same. In other words, the alloy of Test Example 2 with a Sn content 0.2% higher than that of Test Example 1, and the alloy of Test Example 5 with an Al content 0.4% higher than that of Test Example 1, have the same level of reduction in the maximum erosion-corrosion depth relative to the alloy of Test Example 1. Consequently, it is assumed that, in the improvement in the erosion-corrosion resistance, which is observed as the reduction in the maximum erosion-corrosion depth associated with an increase in the Sn or Al content, an increase in the Sn content has twice as large an effect as an increase in the Al content does, when the Sn content is within the range of less than 1.0% by mass. Thus, the value T represented by the following Equation (4) can be used as an index for the erosion-corrosion resistance.

[Table 3]

	Chemical components (% by mass)						EC				Equation (4): T
Experiment No.	Zn	Al	P	Pb	Sn	Cu	Abrasion weight loss (mg)		Maximum depth (µm)		Equation (4): T
Test Example 1	28.62	0.61	0.061	0.073	0.72	Bal	266	F	257	I	2.05
Test Example 2	28.60	0.61	0.060	0.081	0.90	Bal	255	F	211	I	2.41
Test Example 5	28.52	1.02	0.061	0.070	0.71	Bal	261	F	214	I	2.44
Test Example 6	28.54	1.01	0.062	0.065	0.91	Bal	216	G	173	F	2.83
Test Example 9	27.81	1.68	0.061	0.068	0.72	Bal	216	G	171	F	3.12
Test Example 10	27.96	1.70	0.065	0.074	0.90	Bal	214	G	163	F	3.50

T = Al + 2 \times Sn

FIG. 5 shows a graph obtained by plotting the data shown in Table 2, with the values of the maximum erosion-corrosion depth on the vertical axis against the values of Equation (4) on the horizontal axis. The result revealed that, when the value T of Equation (4) is within the range of less than 2.8, the value of the maximum erosion-corrosion depth tends to decrease in an approximately linear manner, as the value T of Equation (4) increases. Further, when the value T of Equation (4) is within the range of 2.8 or more, the value of the maximum erosion-corrosion depth tends to remain approximately the same. Based on the above, it was confirmed that in cases where the alloy has a Sn content of less than 1.0% by mass, it is possible to secure a sufficient erosion-corrosion resistance by allowing the Sn content and the Al content to satisfy the above described Inequality (3).
In the above mentioned Test Examples, the alloys of Test Examples 3,4, and 6 to 12 correspond to the alloys of Examples according to the present invention. Of these, the alloys of Test Examples 6, 9, and 10 have a Sn content of less than 1.0% by mass, and meet the requirement to satisfy the above mentioned Inequality T ≥ 2.8, and thus correspond to the alloys of Examples according to the present invention. On the other hand, the alloys of Test Examples 3,4, 7, 8, 11, and 12 meet the requirement to have a Sn content of 1.0% by mass or more, and thus correspond to the alloys of Examples according to the present invention.
Next, the changes in the mechanical properties and the erosion-corrosion resistance when the contents of Zn, Al, P, Sn and Pb were varied were evaluated by the tensile test and the crosion-corrosion test. The contents of the respective components and the test results of the respective alloys are shown in Table 4.
Firstly, alloys with varying Zn content were prepared. The alloy of Comparative Example 1 having a Zn content of less than 24% by mass has a problem in tensile strength. The alloy of Example 1 having a Zn content of 24% by mass or more has a certain level of tensile strength, and the alloys of Examples 2 and 3 having a Zn content of 27% by mass or more have a sufficient tensile strength. On the other hand, the alloy of Comparative Example 2 having a Zn content of greater than 34% by mass, which is too high, has a problem in elongation.
Secondly, alloys with varying Al content were prepared. In the alloy of Comparative Example 3 having an Al content of less than the detection limit, both the tensile strength and the 0.2% proof stress were insufficient. The alloy of Example 4 having an Al content of 0.39% by mass has a certain level of tensile strength and 0.2% proof stress, and the alloys of Example 5, 3, and 6 having an Al content of 0.6% by mass or more have a sufficient tensile strength and 0.2% proof stress. On the other hand, the alloy of Comparative Example 4 having an Al content of greater than 1.8% by mass, which is too high, has a problem in elongation, while the alloy of Example 6 having an Al content of less than 1.66% by mass, which is less than 1.8% by mass, has a certain level of elongation.
Thirdly, alloys with varying P content were prepared. In the alloy of Example 8 having a slightly higher P content, the erosion-corrosion resistance was slightly reduced. Further, the alloy of Comparative Example 5 having a high P content of greater than 0.2% by mass has too low an elongation.
Fourthly, alloys with varying Sn content were prepared. In the alloy of Comparative Example 6 having a Sn content of 0.11% by mass and the alloy of Comparative Example 7 having a Sn content of 0.31% by mass, the erosion-corrosion resistance was insufficient, and both the values of the abrasion weight loss and the maximum depth were unfavorable. The alloy of Example 9, which has a Sn content of 0.91% by mass and in which the Sn content and the Al content satisfy the equation: T = Al + 2 × Sn = 2.82, has a certain level of erosion-corrosion resistance. Further, the alloys of Examples 3 and 10 having a Sn content of 1.0% by mass or more have a sufficient erosion-corrosion resistance. On the other hand, the alloys of Comparative Examples 8 and 9 having a Sn content of greater than 1.7% by mass have too low an elongation. The alloy of Example 10 having a Sn content of 1.54% by mass has a certain level of elongation.
Fifthly, alloys with varying Pb content were prepared. All of the alloys of Examples 11, 3, and 12 having a Pb content as shown in Table 4 exhibited good mechanical properties and the erosion-corrosion resistance. However, in the alloy of Example 12 whose Pb content is close to 0.25% by mass, a slight decrease in elongation was observed.

Next, alloys with varying P and Pb contents were prepared, and subjected to the drilling test and the lathe machining test to evaluate the changes in the machinability. The contents of the respective components and the test results of the respective alloys are shown in Table 5.

[Table 5]

Chemical components								Machinability test
	Zn	Al	P	Pb	Sn	Bi	Cu	Drilling time		Machining chips
	Zn	Al	P	Pb	Sn	Bi	Cu	sec
P
Comparative Example 10	29.54	1.01	0.000	0.071	1.17	0.000	Bal.	28.7	I	I (Continuous)
Example 13	29.70	1.00	0.009	0.074	1.20	0.000	Bal.	13.4	G	G (Broken)
Example 7	29.93	1.00	0.036	0.054	1.14	0.000	Bal.	19.9	G	G (Broken)
Example 3	30.17	1.06	0.057	0.063	1.21	0.000	Bal.	17.0	G	G (Broken)
Example 8	29.79	1.02	0.121	0.070	1.12	0.000	Bal.	21.9	F	G (Broken)
Comparative Example 5	29.50	1.02	0.235	0.060	1.16	0.000	Bal.	23.7	F	G (Broken)

Pb
Comparative Example 11	28.72	0.98	0.060	0.000	1.04	0.000	Bal.	42.4	I	G (Broken)
Example 11	29.40	1.04	0.056	0.025	1.05	0.000	Bal.	21.4	F	G (Broken)
Example 3	30.17	1.06	0.057	0.063	1.21	0.000	Bal.	17.0	G	G (Broken)
Example 12	30.11	1.02	0.055	0.233	1.19	0.000	Bal.	12.0	G	G (Broken)

Pb and P
Comparative Example 12	30.05	1.10	0.000	0.000	1.05	0.000	Bal.	47.3	I	I

Firstly, the changes due to varying P content are examined. The alloy of Comparative Example 10 having a P content of 0.009% by mass and the alloy of Example 13 having a P content of less than the detection limit were prepared. The thus prepared alloys and the alloys of the above mentioned Examples 7, 3, and 8, and Comparative Example 5 were subjected to the drilling test. In the alloy of Comparative Example 10 having a P content of less than the detection limit, it took too long to drill a hole, and continuous machining chips were produced. In the alloys of Example 13, 7, and 3 having a P content of 0.005% by mass or more, it was possible to drill a hole in a sufficiently short period of time. Further, in the alloys of Examples 13 and 3, the resulting machining chips were broken into pieces. This is thought to be due to the Al-P compounds, formed as a result of containing P, serving as chip breakers during the machining. On the other hand, in each of the alloys of Example 8 and Comparative Example 5 having a P content of greater than 0.1 % by mass, the time required to drill a hole was slightly increased to a level which cannot be disregarded.
In addition, the machining chips of the alloys of Comparative Example 10, Example 13, and Example 3 were evaluated based on their shapes. The photographs of the machining chips of the alloys of Comparative Example 10, Example 13, and Example 3 are shown in FIG. 6 (a), (b), and (c), respectively. The alloy of Comparative Example 10 produced helically-coiled, continuous machining chips which are unfavorable; whereas the alloy of Example 13 having a higher P content produced generally shorter machining chips, and the alloy of Example 3 having an even higher P content produced even shorter machining chips, both of which are favorable.
Next, the changes due to varying Pb content are examined. The alloy of Comparative Example 11 having a Pb content of less than the detection limit was newly prepared. The thus prepared alloy and the alloys of the above mentioned Examples 11, 3, and 12 were subjected to the drilling test. In the alloys of Comparative Example 11 having a Pb content of less than the stipulated value, the drilling time was significantly increased. In the alloys of Example 11 having a Pb content of 0.025% by mass, the drilling time was relatively reduced, and a certain level of the machinability was secured. In each of the alloys of Examples 3 and 12 having an even higher Pb content, the drilling time was reduced to a sufficiently short time. Further, the machining chips of the alloys of Comparative Example 11 and Example 11 were evaluated based on their shapes. The photographs of the machining chips of the alloys of Comparative Example 11 and Example 11 are shown in FIG. 6 (d) and (e), respectively. The machining chips produced by respective alloys had no problems.
Further, as an example containing neither P nor Pb, the alloy of Comparative Example 12 was prepared. The alloy of Comparative Example 12 was subjected to the evaluation of machining chips and the drilling test. The photograph of the machining chips of the alloy of Comparative Example 12 is shown in FIG. 6 (f). The results revealed that, the alloy of Comparative Example 12 containing neither P nor Pb produced unfavorable continuous machining chips which were even longer than those produced by the alloy of Comparative Example 10 containing Pb but not P. In the drilling test, as well, the alloy of Comparative Example 12 exhibited a drilling time which was even significantly longer than that of Comparative Example 10.
Other results will be examined individually with reference to Examples and Comparative Examples. The data thereof are shown in Table 6.

The alloys of Example 2, Example 3, and Comparative Example 2 were used to examine the changes in the dezincification corrosion depth due to varying Zn content. The alloy of Example 2 having a sufficiently low Zn content exhibited a markedly reduced dezincification corrosion depth. The alloy of Example 3 also had a low level of corrosion. In contrast, in the alloy of Comparative Example 2 having a Zn content of greater than 34% by mass, the value of the maximum depth was close to the acceptable limit, and the average depth was significantly increased.

The alloy of Comparative Example 13 having a composition close to that of Example 3 and containing 0.35% by mass of Bi was prepared and examined. The results confirmed that the alloy has a significantly reduced elongation, and thus has problems not only in recyclability but also in mechanical properties.

The alloy of Example 14 having a composition close to that of Example 3 and further containing 0.82% by mass of Ni, and the alloy of Comparative Example 14 having a composition close to that of Example 3 and further containing 1.88% by mass of Ni were prepared. While the dezincification corrosion resistance was significantly improved in both the alloys of Example 14 and Comparative Example 14, the elongation was excessively decreased in the alloy of Comparative Example 14 having a Ni content of 1.88% by mass.

The alloys of Examples 15 and 16 each having a lower Sn content and a higher Pb content as compared to that of Example 14 were prepared. In the alloy of Example 16 having a higher Ni content as compared to that of Example 15, the dezincification corrosion resistance was more improved. Further, the measurement of the erosion-corrosion resistance of the alloys of Examples 15 and 16 revealed that the both alloys have a good erosion-corrosion resistance. However, it was also shown that while the alloy of Example 16 has a certain level of elongation, but it is slightly decreased as compared to that of Examples 15.

The alloy of Example 17 having a composition close to that of Example 3 and further containing 0.006% by mass of B was prepared. In each of the alloys of Example 3 and Example 17, a marked improvement in the dezincification corrosion resistance was observed.

The alloys of Examples 18 to 20 having a composition close to that of Example 3 and further containing increasing amounts of B were prepared. The alloy of Example 18 has a B content of 0.0007% by mass, the alloy of Example 19 has B content of 0.0012% by mass, and the alloy of Example 20 has a B content of 0.011% by mass. The dezincification corrosion resistance was significantly improved with increasing B content, and thus the dezincification corrosion resistance of the alloy of Example 20 was particularly improved. It was also shown, however, that while the alloy of Example 20 has a certain level of elongation, it is somewhat decreased as compared to those of Examples 18 and 19.

The alloys of Examples 21 to 23 having a composition close to that of Example 3 and further containing both B and Ni were prepared. All the alloys exhibited a particularly excellent dezincification corrosion resistance. However, it was also shown that each of the alloys has a certain level of, but somewhat lower elongation.

[DESCRIPTION OF SYMBOLS]

11: nozzle
12: test specimen
13: aqueous solution of CuCl₂

Claims

A low-lead brass alloy for use in a member for water works, the brass alloy comprising: 24% by mass or more and 34% by mass or less of Zn; 0.5% by mass or more and 1.7% by mass or less of Sn; 0.4% by mass or more and 1.8% by mass or less of Al; 0.005% by mass or more and 0.2% by mass or less of P; and 0.01% by mass or more and 0.25% by mass or less of Pb; with the balance being copper and an unavoidable impurity(ies);
wherein, in cases where the brass alloy has a content of Sn of less than 1.0% by mass, the contents of A1 and Sn in % by mass satisfy the following Inequality (1): $Al + 2 \times Sn \geq 2.8$
The low-lead brass alloy for use in a member for water works according to claim 1, wherein the content of Sn is 1.0% by mass or more.
The low-lead brass alloy for use in a member for water works according to claim 1 or 2, further comprising 0.0005% by mass or more and 0.015% by mass or less of B.
The low-lead brass alloy for use in a member for water works according to any one of claims 1 to 3, further comprising 0.1 % by mass or more and 1.8% by mass or less of Ni.