KR102348780B1 - Brass alloy with improved corrosion resistance - Google Patents

Abstract

The brass alloy for casting with improved corrosion resistance according to the present invention is copper (Cu) 61.0 to 65.0 wt%, lead (Pb) 0.10 wt% or less, iron (Fe) 0.01 to 0.10 wt%, tin (Sn) 0.3 to 0.8 wt% %, aluminum (Al) 0.3 to 0.7 wt%, nickel (Ni) 0.2 to 0.7 wt%, bismuth (Bi) 0.1 to 0.5 wt%, phosphorus (P) 0.01 to 0.2 wt%, boron (B) 0.001 to 0.005 wt% % and the rest of the alloy composition is characterized in that it consists of Zn and unavoidable impurities.

Description

Brass alloy with improved corrosion resistance

The present invention relates to a brass alloy for casting, and more particularly, to a brass alloy for casting excellent in corrosion resistance even in a state without heat treatment as a lead-free alloy.

Brass alloys are used in drinking water-related faucets, water meters, and valves. In order to improve the workability of the conventional general brass alloy, about 1.0 to 4.5 wt% of lead (Pb) was added to the brass to ensure good machinability. Among brass alloys, lead (Pb), which has a relatively low melting point due to the heat generated at the interface between the tool and the workpiece during machining, acts as a lubricant and has the effect of reducing the machining resistance and finely pulverizing the cutting chips.

However, lead (Pb) is a toxic substance that adversely affects the human body and the environment. Nevertheless, general brass alloys containing lead (Pb) components were commonly used in faucets, water meters, and valves for the reason of securing good workability. As a result, when the faucet was installed, lead (Pb) was eluted in the drinking water, causing serious health problems to the human body. Recently, the US National Public Health Service (NSF) has restricted the content of lead (Pb) in copper alloys for faucets. With respect to brass alloys, it is expected that the standards for lead (Pb) content and elution amount will be further strengthened mainly in developed countries such as the so-called G20.

In the case of South Korea, some public institutions are planning to start placing public orders to replace all water meters with water meters made of lead-free brass alloy material that does not contain lead (Pb) from March 2020. In addition, it is expected that other public institutions and organizations in the construction field will also move from general brass materials to lead-free brass materials.

Lead-free brass alloys must satisfy lead (Pb) content of 0.25 wt% or less and lead elution amount of 1 mg/L in accordance with “Copper Alloy for Castings (EL742)” stipulated in the 「Environmental Technology and Environmental Industry Support Act」, and corrosion resistance evaluation is KS D ISO 6509 (Corrosion of metals and alloys) Measure the average corrosion depth through the dezincification corrosion test of brass, and the alloy must be less than 300 µm for ingots and less than 100 µm for copper alloy castings.

Research and development activities on lead-free brass alloys that do not contain lead have been actively carried out in order to eliminate the harmfulness to the human body. As a result of these studies, an alloy was developed in which lead (Pb) was replaced with bismuth (Bi) as a lead-free brass alloy. An example of a lead-free brass alloy to which bismuth (Bi) is added is disclosed in Korean Patent Publication Nos. 2005-0096346 and 2012-0042483.

However, the bismuth (Bi)-based lead-free brass alloy for casting has a problem that cracks easily occur during mold casting and cutting. To solve this problem, a small amount of misch metal is added to make the shape of bismuth (Bi) in lead-free brass from a film form to a spherical shape, thereby reducing the occurrence of cracks during cutting. However, the addition of misimetal caused a problem in that the metal fluidity for the lead-free brass alloy was lowered, thereby reducing the formability. In addition, in order to improve the corrosion resistance of bismuth (Bi)-based lead-free brass alloys, a method of making the structure uniform through heat treatment has been used, but in the case of brass alloys for casting, the method of improving corrosion resistance through heat treatment is not realistic. For this reason, there is a demand for the development of lead-free brass alloys for casting that do not have excellent corrosion resistance and cracks without heat treatment. Of course, without heat treatment, in order to improve corrosion resistance, in Korean Patent Publication No. 10-2011-0073900, Cu:56-58%, Sn:0.5-1.5%, Fe:0.2-0.3%, Sb:0.1- 0.2%, Ni:1.5-2.0%, P:0.04-0.08%, Al:0.8-1.2%, S:1.0-1.2%, Bi:1.3-1.5%, Se:0.1-0.2% and balance Zn A study was conducted in which a small amount of antimony (Sb) was added, but in this case, the added antimony (sb) is classified as a substance harmful to the human body, such as lead (Pb), so there is a problem in that it is not practical.

An object of the present invention is to solve the crack generation problem occurring in the bismuth (Bi)-based lead-free brass alloy for casting in order to solve the above problems, and separate heat treatment and arsenic (As), antimony (Sb) in the state of the casting product It is effective in improving corrosion resistance, but it does not contain elements harmful to the human body, and provides a brass alloy for casting that can satisfy the corrosion resistance stipulated in laws and regulations.

In order to achieve the above object, the brass alloy for casting with improved corrosion resistance according to the present invention is copper (Cu) 61.0 to 65.0 wt%, lead (Pb) 0.10 wt% or less, iron (Fe) 0.01 to 0.10 wt%, tin ( Sn) 0.3 to 0.8 wt%, aluminum (Al) 0.3 to 0.7 wt%, nickel (Ni) 0.2 to 0.7 wt%, bismuth (Bi) 0.1 to 0.5 wt%, phosphorus (P) 0.01 to 0.2 wt%, boron ( B) 0.001 to 0.005 wt % and the remaining alloy components are characterized in that they consist of Zn and unavoidable impurities.

Al and P react with each other in the alloy to form Al-P inclusions,

≤ 1.5 관계식을 만족하는 것이 바람직하다.1.1 ≤

It is preferable to satisfy the relation ≤ 1.5.

≤ 2.5 관계식을 만족하는 것이 바람직하다.If the ratio of Sn and Ni sum (Sn+Ni) to Al is 1.5 ≤

It is preferable to satisfy the relation ≤ 2.5.

When the Al-P inclusions are measured at a magnification of 1,000 times or more with a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), the average particle diameter of the Al-P inclusions is 15 μm or less,

≤ 3.0 관계식을 만족하는 것이 바람직하다.The number of Al-P inclusions and the number of Bi individuals are 0.8 ≤

It is preferable to satisfy the relation ≤ 3.0.

The brass alloy for casting with improved corrosion resistance according to the present invention forms and distributes Al-P inclusions without additional heat treatment, so that the Al-P inclusions act as a chip breaker. It has excellent machinability by suppressing it, and Al-P inclusions are located within the grains and at the grain boundaries of the α-phase and β-phase to prevent the progress of corrosion, thereby providing an effect of improving corrosion resistance. In addition, the brass alloy according to the present invention provides an effect of suppressing the occurrence of cracks caused by stress between the base material and Bi due to the Al-P inclusions being incorporated into Bi and adding Bi instead of Pb. In addition, since it provides the effect of improving corrosion resistance without adding elements harmful to the human body such as arsenic (As) and antimony (Sb), it has an environmental-friendly advantage.

1 is a table summarizing the composition, corrosion resistance, and machinability test results of Example 1 and several comparative examples of the present invention.
2 is a photograph of a casting product according to Example 1 of the present invention.
3 is a photograph of the cutting chip shape of Examples 1 to 5;
4 is a 100-fold enlarged photograph of the samples of Example 1 and Comparative Example 1.
5 is a 200-fold magnified photograph of the whole corroded from the surface to the inside of Example 1, and a 1,000-fold magnified photograph of the corroded position.
6 is a 1,000-fold magnification of Example 1 and Comparative Example 1 under a scanning electron microscope.
7 is a 500-fold enlarged photograph of Comparative Example 2 and Comparative Example 3 under a metallographic microscope.
8 is a metallographic microscope photograph of Comparative Example 4 and Comparative Example 5;
FIG. 9 is a graph showing Comparative Example 4, Example 1, and Comparative Example 5 described in FIG. 1 in order of P content %.
10 is a photograph taken at 1,000 times magnification with a scanning electron microscope of Example 1.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a table summarizing the composition, corrosion resistance, and machinability test results of Example 1 and several comparative examples of the present invention. 2 is a photograph of a casting product according to Example 1 of the present invention. 3 is a photograph of the cutting chip shape of Examples 1 to 5; 4 is a 100-fold enlarged photograph of the samples of Example 1 and Comparative Example 1. 5 is a 200-fold magnified photograph of the whole corroded from the surface to the inside of Example 1, and a 1,000-fold magnified photograph of the corroded position. 6 is a 1,000-fold magnification of Example 1 and Comparative Example 1 under a scanning electron microscope. 7 is a 500-fold magnification photograph of Comparative Example 2 and Comparative Example 3 under a metallographic microscope. 8 is a metallographic microscope photograph of Comparative Example 4 and Comparative Example 5; FIG. 9 is a graph showing Comparative Example 4, Example 1, and Comparative Example 5 described in FIG. 1 in order of P content %. 10 is a photograph taken at 1,000 times the magnification of Example 1 with a scanning electron microscope.

The brass alloy for casting with improved corrosion resistance according to the present invention does not contain lead (Pb), which is a condition stipulated as a lead-free brass alloy in the 「Environmental Technology and Environmental Industry Support Act」, a Korean law, or contains 0.25% by weight at the maximum. It relates to a copper alloy that satisfies the condition not to be exceeded. Lead (Pb) is an element added to improve the processability of lathe work, but is a material subject to international environmental regulations. California Bill AB 1953 regulates the content of lead (Pb) in faucet fittings and various valves to 0.25% by weight or less. In the present invention, the component of lead (Pb) is not included at all or is included in a maximum amount of 0.25% by weight or less to meet these international standards.

In a preferred embodiment of the present invention, by limiting the Al and P content to a specific range, Al-P inclusions (compounds) are formed to improve machinability and corrosion resistance and suppress the generation of cracks. The role of the alloy composition constituting the brass alloy for casting with improved corrosion resistance according to the present invention is as follows.

First, the content of copper (Cu) was limited to 61.0 to 65.0 wt%. Copper (Cu) is the main component of a copper alloy, and it forms α-phase and β-phase structures with zinc and additional elements depending on the content of zinc (Zn) and additional elements to improve machinability, workability, and corrosion resistance. If the content of Cu is less than 61.0 wt%, the β phase is excessively generated, and corrosion resistance deteriorates, and there is a problem in that workability is deteriorated. When the content of Cu exceeds 65.0 wt%, a large amount of α-phase is generated and corrosion resistance is improved, but there is a problem in that it is difficult to sufficiently secure machinability as well as an increase in raw material price as well as poor castability.

The content of iron (Fe) was limited to 0.01 to 0.10 wt%. In the copper alloy according to the present invention, Fe reacts with B and contributes to the improvement of strength through improved fluidity and microstructure. When the content of Fe is less than 0.01% by weight, Fe does not react with B, so there is a problem in that fluidity improvement and tissue refinement effect are not obtained. When the content of Fe exceeds 0.10% by weight, a locally hardened segregation material is formed in the metal structure called a hard spot in the cast product, which increases brittleness, thereby reducing the durability of the product. There is a problem.

The content of tin (Sn) was limited to 0.3 to 0.8% by weight. In the copper alloy according to the present invention, Sn serves to improve corrosion resistance such as dezincification corrosion resistance. When the content of Sn is less than 0.3% by weight, it does not greatly help to improve corrosion resistance. When the content of Sn exceeds 0.8% by weight, there is a problem in that the raw material price increases and the flowability of the molten metal decreases.

The content of aluminum (Al) was limited to 0.3 to 0.7 wt%. In the copper alloy according to the present invention, Al generally has an effect of improving corrosion resistance and molten metal flowability. When the content of Al is less than 0.3% by weight, there is no significant effect on improving the flowability of the molten metal. When the amount of Al exceeds 0.7 wt%, the flowability of the molten metal is greatly improved, but since the zinc equivalent of Al is 6, there is a problem in that the β phase is excessively generated, causing a decrease in corrosion resistance.

The content of nickel (Ni) was limited to 0.2 to 0.7% by weight. In the copper alloy according to the present invention, Ni serves to assist the improvement of corrosion resistance. When the content of Ni is less than 0.2% by weight, the corrosion resistance is not significantly affected. When the content of Ni exceeds 0.7% by weight, the flowability of the molten metal is lowered and a hard spot is formed on the cast product, which adversely affects the durability and quality of the product.

≤ 2.5 범위를 만족하는 것이 바람직하다.

가 1.5 미만일 경우 합금의 용탕 흐름성은 향상되나 내식성 향상에 효과가 없다.

가 2.5초과될 경우, 내식성은 향상되나 용탕 흐름성 감소되고 절삭성이 하락하고, 제품에 경점(Hard spot)이 발생하여 내구성과 품질에 악영향을 준다.In the copper alloy according to the present invention, the ratio of the content of Al and Sn+Ni plays an important role. Sn and Ni work together to improve corrosion resistance. 1.5 ≤

It is preferable to satisfy the range of ≤ 2.5.

If is less than 1.5, the molten metal flowability of the alloy is improved, but there is no effect on improving the corrosion resistance.

If is over 2.5, corrosion resistance is improved, but molten metal flow is reduced and machinability is reduced, and hard spots occur in the product, which adversely affects durability and quality.

In the present invention, the content of bismuth (Bi) is limited to 0.1 to 0.5% by weight. Bi replaces Pb and is effective in improving machinability. Bi is not dissolved in the brass alloy and exists independently. In general, the higher the Bi content, the better the workability, but cracks are caused. Unlike other metals, Bi has a characteristic that expands upon cooling, so when brass, which is a base material, contracts, Bi expands, and inter-Bi stress between the base materials is generated, which may cause cracks. For that reason, it is not preferable to add Bi in a large amount. When the content of Bi is less than 0.1% by weight, machinability is not greatly affected. When the Bi content exceeds 0.5% by weight, cracks are highly likely to occur during cooling after casting the cast product.

In the present invention, the content of phosphorus (P) was limited to 0.01 to 0.2% by weight. P generally serves as a deoxidizer during casting to improve the fluidity of the molten metal. On the other hand, in the present invention, it is used as a dispersant for evenly dispersing the particles of Bi. When the content of P is less than 0.01% by weight, the dispersion of Bi particles is not affected. When the content of P exceeds 0.2% by weight, it is effective in dispersing Bi particles, but an additional effect does not occur due to an increase in the amount of P added.

In general, Al and P act as molten metal fluidity and deoxidizer. On the other hand, in the present invention, Al and P form Al-P inclusions to improve machinability, suppress cracks, and improve corrosion resistance. Al and P combine in a 1:1 molar ratio to form an Al-P inclusion (compound). When the molar ratio is converted into a weight ratio, Al and P are 1:1.15.

≤ 1.5 관계식을 만족하는 것이 바람직하다. 주사전현미경(SEM) 또는 전계 방출형 주사전자현미경(FE-SEM)으로 1,000배 이상 배율에서 Al-P 개재물의 평균 입경을 측정하는 것이 바람직하다. 상기 Al-P 개재물의 평균 입경은 15㎛ 이하인 것이 바람직하다. 만일 Al-P 개재물의 평균 입경이 15㎛ 초과할 경우 오히려 경점(Hard Spot)을 유발하여 제품 내구성 및 제품 품질에 악영향을 미친다. 상기 Al-P 개재물의 평균 입경의 하한은 물리적으로 0㎛ 보다 큰 것은 자명하며 별도의 한정을 할 필요는 없다.In the present invention, when Al and P combine to form a compound, 1.1 ≤

It is preferable to satisfy the relation ≤ 1.5. It is preferable to measure the average particle diameter of Al-P inclusions at a magnification of 1,000 times or more with a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM). It is preferable that the average particle diameter of the Al-P inclusions is 15 μm or less. If the average particle diameter of the Al-P inclusions exceeds 15 μm, hard spots are caused to adversely affect product durability and product quality. It is obvious that the lower limit of the average particle diameter of the Al-P inclusions is physically larger than 0 μm, and there is no need to separately limit it.

가 1.1 미만일 경우 주사전현미경(SEM) 또는 전계 방출형 주사전자현미경(FE-SEM)으로 1,000배 이상 배율에서 Al-P 개재물 개체수가 현격하게 적어 절삭성, 내식성, 크랙 억제 등의 특성이 발현되지 않을 수 있다.

If is less than 1.1, the number of Al-P inclusions is remarkably small at a magnification of 1,000 times or more with a scanning electron microscope (SEM) or field emission scanning electron microscope (FE-SEM), so characteristics such as machinability, corrosion resistance, and crack suppression may not be expressed. can

가 1.5 초과일 경우 주사전현미경(SEM) 또는 전계 방출형 주사전자현미경(FE-SEM)으로 1,000배 이상 배율에서 관찰 시, Al-P 개재물 개체수가 현격하게 증가하여, 기계적 강도 하락과 더불어 절삭성 하락을 초래할 수 있다.

If is greater than 1.5, when observed at a magnification of 1,000 times or more with a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), the number of Al-P inclusions increases significantly, resulting in a decrease in machinability as well as decrease in mechanical strength may cause

In the present invention, the content of boron (B) was limited to 0.001 to 0.005% by weight. B reacts with Fe in the molten metal, which is effective in molten metal flowability and tissue refinement. When the content of B is less than 0.001% by weight, there is little effect of molten metal flowability and tissue refinement. On the other hand, when the content of B exceeds 0.005% by weight, there is no effect due to additional input.

In the present invention, zinc (Zn) forms a Cu—Zn alloy together with Cu. Depending on the content of Zn added, it contributes to the formation of α-phase and β-phase structures, and affects corrosion resistance, castability, and workability. In the present invention, the balance is added. Other elements that are unavoidably added in the alloy manufacturing process include Si, Cr, Co, Ti, and the like, and when the total content is controlled to 0.5% by weight, the physical and chemical properties of the copper alloy according to the present invention are not affected.

Hereinafter, the properties of the copper alloy according to the present invention were evaluated using preferred examples and comparative examples of the present invention.

1 is a table summarizing the composition, corrosion resistance, and machinability test results of Example 1 and several comparative examples of the present invention. In the present invention, according to the composition described in FIG. 1, copper alloy casting specimens of Example 1 and Comparative Examples were prepared. The properties of the prepared copper alloy specimen were evaluated according to the test method to be described later.

<Dezincification corrosion test method>

In the present invention, the corrosion resistance of the copper alloy specimen was measured by measuring the average depth of dezincification corrosion according to KS D ISO 6509 (Corrosion of metals and alloys - Dezincification corrosion test of brass). Dezincification corrosion is a phenomenon in which zinc is selectively removed from a brass alloy by dealloying or selective leaching corrosion. The passing standards for the dezincification corrosion test of lead-free corrosion-resistant brass for domestic water pipe materials are 300㎛ or less on average based on ingots, which are copper alloys for casting (EL742), and 100㎛ or less on average based on copper alloy casting products. In the present invention, it is a casting product, and when it is 100 μm or less based on EL742, it is evaluated as excellent in corrosion resistance. If it exceeds 100㎛, it is evaluated as bad. 2 is a photograph of a casting product according to Example 1 of the present invention.

In order to measure the depth of dezincification corrosion according to KS D ISO 6509 for the specimens according to Example 1 and Comparative Examples, the surface of each specimen was cut to 10 mm X 10 mm in width and length, and then polished up to 2000 times with abrasive paper, and then the specimen _{A solution containing 12.7 g of CuCl 2} per 1000 ml of silver distilled water was divided into 250 ml, each specimen was immersed, heated to 75 ° C. ± 5 ° C. and maintained for 24 hours, and then the average depth of dezincification was measured.

<Method of machinability test>

In the present invention, the machinability of the copper alloy was evaluated by the cutting resistance torque. The resistance torque transmitted to the cutting tool during machining was measured using a machinability tester and evaluated. During cutting, the rotational speed was 580rpm, the cutting thickness was 0.5mm, the cutting speed was 0.42mm/s, and the moving direction was horizontal from right to left. If the cutting resistance torque is large, it means that the machinability is low. If the cutting resistance torque is small, the cutting force is high even if the same depth is machined, so the cutting machinability is high. Comparative Example 1 (ASTM B30 C89580) is a Bi-based lead-free brass that is typically used.

The machining machinability of Example 1 and Comparative Examples (1,2,3,4,5) was evaluated to be excellent when the conversion ratio of 1.67kgf to the cutting resistance torque of Comparative Example 1 (ASTM B30 C89580) was 90% or more. If the conversion ratio exceeds 90%, it is evaluated as bad. Comparative Example 1 is not limited to 1.67kgf because there is a change in the cutting resistance torque due to the state of the cutting tip of the machinability tester and the minute component difference of Comparative Example 1. The cutting resistance torque of Comparative Example 1 evaluated according to the situation is set as a conversion ratio of 100%, and when the conversion ratio is more than 90%, it is defined as good, and when the conversion ratio is less than 90%, it is defined as bad.

으로 산정한다.the conversion ratio

to be calculated as

<Criteria for Judgment>

In the present invention, corrosion resistance evaluation is evaluated as excellent in corrosion resistance when the average corrosion depth is 100 μm or less based on the casting products of Examples 1 to Comparative Examples. If the average corrosion depth exceeds 100㎛, it is evaluated as bad.

In the present invention, the machinability evaluation was excellent when the conversion ratio of 1.67kgf, which is the cutting resistance torque of Comparative Example 1 (ASTM B30 C89580), was greater than 90% based on the samples of Examples 1 to Comparative Examples. If the conversion ratio is less than 90%, it is evaluated as bad.

In the present invention, the overall evaluation is evaluated as ○ when both corrosion resistance and machinability are excellent. If either one of corrosion resistance and machinability is bad, it is evaluated as ⅹ.

Such test results are well summarized in FIG. 1 .

<Microstructure analysis method>

For Example 1 and Comparative Examples, the microstructure was analyzed with a metallurgical microscope (manufacturer OLYMPUS, model name BX31) and a scanning electron microscope (manufacturer JEOL, model name JSM-7100F).

<Measurement method for average particle size and number of individuals>

In order to measure the average particle diameter of Al-P inclusions, the number of Al-P inclusions, and the number of Bi individuals, using a scanning electron microscope (manufacturer JEOL, model name: JSM-7100F), the backscattered electron mode ( Backscattered Electron Mode, BSE mode) was used. When observed in the backscattered electron mode, the contrast changes in proportion to the atomic number of the element, making it possible to measure the size and number of individuals more clearly.

The effect of Al-P inclusions as a result of such microstructure analysis will be examined. 3 is a photograph of the cutting chip shape of Examples 1 to 5; Referring to FIG. 3 , the cutting chip shape of Example 1 and Comparative Example 1 is almost similar, and the cutting resistance index of Example 1 is excellent at a conversion ratio of 94.8% of Comparative Example 1. The reason why the machinability is similar in Comparative Example 1 is that Bi is 0.652 wt% and Example 1 is 0.296 wt%, which is more than twice lowered, because Al-P inclusions contribute to the machinability. When the number of Al-P inclusions in the brass alloy is appropriate, the machinability is excellent.

4 is a 100-fold enlarged photograph of the samples of Example 1 and Comparative Example 1. The average corrosion depth was 72 μm and 201 μm in Example 1 and Comparative Example 1, respectively. Example 1 is β-phase corrosion and Comparative Example 1 is front corrosion. Front corrosion of Comparative Example 1 refers to a phenomenon of corrosion at a similar rate at any location with a constant thickness from the surface. Unlike the corroded interface of Comparative Example 1, the corroded interface of Example 1 has irregularities and is converted to β-phase corrosion rather than front corrosion.

5 is a 200-fold magnified photograph of the whole corroded from the surface to the inside of Example 1, and a 1,000-fold magnified photograph of the corroded position. Observing the corroded end of the β phase, Al-P inclusions are present. By blocking the progress of corrosion initiated from the surface by Al-P inclusions, it suppresses the progress to the front corrosion and stops only the β-phase corrosion to improve the corrosion resistance.

6 is a 1,000-fold magnification of Example 1 and Comparative Example 1 under a scanning electron microscope. Brass, the base material, is gray, white is Bi, and black is Al-P inclusions. In Comparative Example 1, only Bi was present, whereas in Example 1, some Al-P inclusions were incorporated with Bi. Cracks are suppressed by Al-P inclusions suppressing Bi, which expands during cooling.

≤ 2.5 관계식을 만족할 때 내식성과 절삭성이 편중되지 않고 균형을 이루면서 양호한 특성이 발휘한다는 것을 연구결과 도출하였다.Now let's look at the relationship between Al and Sn and Ni. Comparing Comparative Example 2 and Comparative Example 3 in FIG. 1 , in Comparative Example 2, the sum of Sn wt% and Ni wt% is 0.003, and in Comparative Example 3, the sum of Sn wt% and Ni wt% is 1.667. Comparative Example 2 has poor corrosion resistance but excellent machinability, and Comparative Example 3 has excellent corrosion resistance but poor machinability. 7 is a 500-fold magnification photograph of Comparative Example 2 and Comparative Example 3 under a metallographic microscope. In Comparative Example 2, Al-P inclusions are evenly distributed without being concentrated in any one place. Comparative Example 3 is formed by segregation of Al-P inclusions at the boundary between the α phase and the β phase. It can be seen that, if the sum of Sn wt% and Ni wt% is too low, sufficient corrosion resistance cannot be secured, and if the sum of Sn wt% and Ni wt% is too large, corrosion resistance is secured, but machinability is adversely affected. According to these characteristics, the desirable properties of machinability and corrosion resistance are 1.5 ≤

When the ≤ 2.5 relational expression is satisfied, the results of the study showed that corrosion resistance and machinability are not unbalanced and good characteristics are achieved while balancing.

≤ 1.5 관계식을 만족할 때 절삭성과 내식성이 편중되지 않고 균형을 이루면서 발휘하는 것으로 연구결과 밝혀졌다.On the other hand, the relationship between Al and P can be derived through Comparative Examples 4 and 5. Al-P inclusions affect the machinability improvement, which is the role of Bi, and at the same time have an effect on corrosion resistance improvement. P weight % of Comparative Example is extremely low as 0.009, and P weight % of Comparative Example 5 is extremely high as 0.488. 8 is a metal micrograph of Comparative Example 4 and Comparative Example 5. When P weight % is too low, the number of Al-P inclusions is too small, and thus there is no effect in improving machinability and corrosion resistance. If P weight % is too high, the number of Al-P inclusions increases, improving corrosion resistance, but machinability is adversely affected. Al weight % and P weight % 1.1 ≤

When the ≤ 1.5 relational expression is satisfied, the results of the study revealed that machinability and corrosion resistance are exhibited in a balanced manner without being biased.

FIG. 9 is a graph showing Comparative Example 4, Example 1, and Comparative Example 5 described in FIG. 1 in order of P content %. The number of Al-P inclusions and the number of Bi individuals were measured at a magnification of 1,000 times or more with a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM). 10 is a photograph taken with a scanning electron microscope at 1,000 times magnification of Example 1, black numbers indicate Al-P inclusions, and white numbers indicate Bi. Al-P inclusions play a role in improving machinability like Bi, but if the number of Al-P inclusions is too small than the number of Bi, there is no machinability improvement effect. It is accompanied by a decrease in strength and a decrease in machinability.

≤ 3.0일 때 절삭성과 내식성이 편중되지 않고 균형을 이루면서 양호한 특성을 발휘하는 것으로 연구결과 도출되었다. 만약

값이 0.8 미만일 경우, Al-P 개재물 개체수가 현격히 감소하여 절삭성 및 내식성이 하락할 수 있는 문제점이 있다. 한편,

값이 3.0을 초과할 경우, Al-P 개재물 개체수가 크게 증가하여 기계적 강도 감소와 더불어 절삭성 하락을 초래하는 문제점이 있다.The relationship between the number of Al-P inclusions and the number of Bi individuals is 0.8 ≤

When ≤ 3.0, machinability and corrosion resistance were found to be balanced and exhibit good characteristics. if

If the value is less than 0.8, there is a problem in that the number of Al-P inclusions is significantly reduced, so that machinability and corrosion resistance may decrease. Meanwhile,

When the value exceeds 3.0, there is a problem that the number of Al-P inclusions increases significantly, resulting in a decrease in machinability as well as a decrease in mechanical strength.

As described above, the brass alloy for casting with improved corrosion resistance according to the present invention forms and distributes Al-P inclusions without additional heat treatment, so that the Al-P inclusions act as a chip breaker. It has excellent machinability by suppressing this curling phenomenon, and provides an effect of improving corrosion resistance by interfering with the progress of corrosion by the presence of Al-P inclusions in the grains and at the grain boundaries of the α-phase and β-phase. In addition, the brass alloy according to the present invention provides an effect of suppressing the occurrence of cracks caused by stress between the base material and Bi due to the Al-P inclusions being incorporated into Bi and adding Bi instead of Pb. In addition, since it provides the effect of improving corrosion resistance without adding elements harmful to the human body such as arsenic (As) and antimony (Sb), it has an environmental-friendly advantage.

Above, the present invention has been described with reference to preferred embodiments, but the present invention is not limited by such examples, and various types of embodiments may be embodied within the scope without departing from the technical spirit of the present invention.

Claims (4)

Copper (Cu) 61.0 to 65.0 wt%, lead (Pb) 0.10 wt% or less, iron (Fe) 0.01 to 0.10 wt%, tin (Sn) 0.3 to 0.8 wt%, aluminum (Al) 0.3 to 0.7 wt%, nickel (Ni) 0.2 to 0.7% by weight, bismuth (Bi) 0.1 to 0.5% by weight, phosphorus (P) 0.01 to 0.2% by weight, boron (B) 0.001 to 0.005% by weight, and the remaining alloy components are Zn and unavoidable impurities. ,
Al and P react with each other in the alloy to form Al-P inclusions,
1.1 ≤

≤ 1.5 the relation is satisfied,
If the ratio of Sn and Ni sum (Sn+Ni) to Al is 1.5 ≤

A brass alloy for casting with improved corrosion resistance, characterized in that it satisfies the ≤ 2.5 relation. delete delete The method of claim 1,
When the Al-P inclusions are measured at a magnification of 1,000 times or more with a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), the average particle diameter of the Al-P inclusions is 15 μm or less,
The number of Al-P inclusions and the number of Bi individuals are 0.8 ≤

Brass alloy for casting with improved corrosion resistance, characterized in that it satisfies the ≤ 3.0 relation.

Images