CN107974573B - Manganese-containing free-cutting silicon brass alloy and preparation method and application thereof - Google Patents

Abstract

The invention discloses a manganese-containing free-cutting silicon brass alloy, which consists of the following components: 60.2-64.0 wt% of Cu, 1.0-2.0 wt% of Si, 0.2-1.0 wt% of Al, 0.2-0.48 wt% of Mn, 0.1-0.25 wt% of Pb, one or more elements selected from P, Mg and Sn, wherein the content of the elements is 0.01-0.25 wt% of P, 0.01-0.25 wt% of Mg, 0.01-0.1 wt% of Sn, and the balance of Zn and impurities with the total amount not more than 0.5 wt%. The invention also discloses a method for preparing the alloy. The manganese-containing free-cutting silicon brass alloy has excellent dezincification corrosion resistance, good casting performance and cutting performance and relatively low cost, and is suitable for casting and molding parts of drinking water systems, such as taps, valves, quick opening and the like.

Description

Manganese-containing free-cutting silicon brass alloy and preparation method and application thereof

Technical Field

The invention relates to a brass alloy, in particular to a manganese-containing free-cutting silicon brass alloy and a preparation method and application thereof.

Background

The lead brass has good cold and hot forming performance, cutting processing performance and corrosion resistance, so the lead brass is widely applied to the industries of electronics, daily hardware and the like, but the lead brass has high lead content, is easy to separate out to pollute the environment, and causes serious harm to human body when being particularly applied to a drinking water system. Corresponding regulations continuously issued in various countries in the world strictly limit the content of lead in the copper alloy, and GB/T18145-.

In recent years, a large number of patents have been published or granted in the united states, europe, japan and china for lead-free, low-lead brass alloys, mainly bismuth brass, antimony brass and manganese brass. For example, the "Low-lead bismuth-containing brass" filed in Chinese patent No. 94192613.3 by Kohler corporation of America has a composition of 55 to 70 wt% of Cu, 30 to 45 wt% of Zn, 0.2 to 1.5 wt% of Bi, 0.2 to 1.5 wt% of Al, and 0.1 to 1.0 wt% of Pb; the alloy has high Bi content, is easy to generate heat crack and has poor welding performance, so the practical application is difficult. An easy-cutting copper alloy containing a very small amount of lead, which is published by Sanbao in Japan and has a Chinese patent application No. 200580046460.7, relates to a Cu-Zn-Si brass alloy, which comprises 71.5 to 78.5 wt% of Cu, 2.0 to 4.5 wt% of Si, 0.005 to 0.02 wt% of Pb and the balance of zinc; the alloy has high Cu content and high cost, so the market competitiveness is not strong. The lead-free-cutting antimony brass alloy invented by Ningbo Bowei group, wherein the national patent application number is 200410015836.5, and the alloy comprises 55-65 wt% of Cu, 0.3-2.0 wt% of Sb, 0.4-1.6 wt% of Mn and 0.1-1.0 wt% of other elements; the content of the antimony alloy is high, and the precipitation amount of the antimony alloy exceeds the limit of 0.6 mu g/L specified by NSF61 and GB/T18145, so the antimony alloy cannot be popularized and applied in the field of drinking water systems. "an environmental protection type manganese brass alloy and its manufacturing method" of xiamen luda application, patent number 201010117783.3, discloses a Cu-Zn-Mn series brass alloy, because of the higher manganese content, the alloy hardness is higher, the abrasion to the cutting tool is serious, the cutting processing performance is worse, so it is not suitable for batch production.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the environment-friendly manganese-containing free-cutting silicon brass alloy which has excellent dezincification resistance and stress corrosion resistance, good casting performance and cutting performance and relatively low cost, and the preparation method and the application thereof.

The technical scheme of the invention is as follows:

the manganese-containing free-cutting silicon brass alloy consists of the following components: 60.2-64.0 wt% of Cu, 1.0-2.0 wt% of Si, 0.2-1.0 wt% of Al, 0.2-0.48 wt% of Mn and 0.1-0.25 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.01-0.25 wt% of P, 0.01-0.25 wt% of Mg, and 0.01-0.1 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

Optionally, the alloy consists of the following components: 60.2-62.0 wt% of Cu, 1.0-1.5 wt% of Si, 0.2-0.7 wt% of Al, 0.2-0.45 wt% of Mn and 0.1-0.15 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.05-0.1 wt% of P, 0.01-0.15 wt% of Mg, and 0.01-0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

Optionally, the alloy consists of the following components: 60.2-61.0 wt% of Cu, 1.2-1.4 wt% of Si, 0.5-0.7 wt% of Al, 0.2-0.35 wt% of Mn and 0.1-0.15 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.05-0.1 wt% of P, 0.01-0.1 wt% of Mg, and 0.01-0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

Optionally, the alloy consists of the following components: 62.0 to 64.0 wt% of Cu, 1.4 to 2.0 wt% of Si, 0.4 to 1.0 wt% of Al, 0.2 to 0.48 wt% of Mn, 0.1 to 0.15 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.01-0.1 wt% of P, 0.01-0.15 wt% of Mg, and 0.01-0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

Optionally, the alloy consists of the following components: 62.0 to 63.0 wt% of Cu, 1.5 to 1.7 wt% of Si, 0.6 to 0.9 wt% of Al, 0.3 to 0.48 wt% of Mn, 0.1 to 0.15 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.05-0.1 wt% of P, 0.01-0.10 wt% of Mg, and 0.01-0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

Optionally, the alloy consists of the following components: 60.5 to 63.3 wt% of Cu, 1.1 to 1.73 wt% of Si, 0.25 to 0.46 wt% of Al, 0.2 to 0.35 wt% of Mn, 0.1 to 0.15 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.01-0.1 wt% of P, 0.01-0.15 wt% of Mg, and 0.01-0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

Optionally, the area fraction of β phase in the brass alloy is more than or equal to 80%, the area fraction of gamma phase is 1-10%, and the sum of the area fractions of Mn-Si compound, Cu-P compound and Cu-Mg compound is 1-10%.

Optionally, the cutting efficiency of the brass alloy is more than 80%, the average dezincification layer depth is less than 300 μm, and the casting relative volume shrinkage rate is less than 2%.

The manganese-containing free-cutting silicon brass alloy is used for casting and forming parts of drinking water systems, including gravity casting and low-pressure casting.

The preparation method of the manganese-containing free-cutting silicon brass alloy comprises the following steps:

1) according to the proportion, placing the raw materials of silicon metal and copper in the bottom layer of an induction furnace, adding a slag-cleaning refining agent, covering with charcoal, heating to 1050-1150 ℃ until the materials are completely melted, and filtering out floating slag and impurities;

2) adjusting the temperature to 1000-1050 ℃, adding 0# zinc, quickly pressing into the furnace bottom, and fully stirring after melting;

3) adding aluminum ingots, tin ingots and lead ingots, and fully stirring to ensure that the components of the alloy liquid are uniform;

4) adding a Cu-P intermediate alloy, an Al-Mg intermediate alloy and a Cu-Mn intermediate alloy, wherein the mass percent of phosphorus in the Cu-P intermediate alloy is 10-15%, the mass percent of magnesium in the Al-Mg intermediate alloy is 25-50%, and the mass percent of Mn in the Cu-Mn intermediate alloy is 25-30%;

5) adding modifier boron, titanium, zirconium or rare earth elements, heating to 1050-1150 ℃, flaming, stirring and preserving heat for 2-3 minutes;

6) standing at 1000-1050 ℃ for 10-20 minutes to ensure that the alloy is uniform and impurities float, and filtering out floating slag and impurities;

7) heating to 1050-1100 ℃, discharging and pouring.

Preferably, the copper raw material is electrolytic copper, copper pipe or copper wire.

Preferably, the Cu-P master alloy, the Al-Mg master alloy and the Cu-Mn master alloy are added by pressing a graphite bell jar.

In the manganese-containing free-cutting silicon brass alloy of the invention:

the main function of Cu is to form β phase and gamma phase of a matrix with Zn, wherein the β phase is a solid solution based on a CuZn compound, the strength and hardness are high, and the plasticity is low, the crystal structure of the gamma phase is complex cube, and has the characteristics of hardness and brittleness, in order to obtain a microstructure based on the β phase and on which a small amount of the gamma phase is dispersed, the addition ratio of Cu and other main elements (such as Si, Al and Mn) needs to be coordinated, the Cu content in the alloy is controlled to be 60.2-64.0 wt%, when the Cu content is more than 64%, a small amount of α phase appears and the gamma phase is reduced, the cutting processing performance and the dezincification resistance of the material are reduced, when the Cu content is less than 60.2%, the gamma phase is obviously improved, and when the gamma phase is too high, the aggregation effect is generated, the room-temperature plasticity of the material is reduced, and the cold processing performance of the alloy.

The alloy has the main functions of improving the casting performance and the welding performance of the alloy, improving the corrosion resistance of the alloy, simultaneously increasing the content of β phase and forming a small amount of gamma phase to improve the cutting performance of the alloy, and the silicon can also improve the strength and the elongation of the alloy and is beneficial to improving the corrosion resistance of the alloy.

The main function of Al is to improve the flow property of the alloy and facilitate casting forming, and Al can form Al on the surface of a casting₂O₃And the film improves the corrosion resistance of the casting. The content of Al in the alloy is controlled to be 0.2-1.0 wt%, the content of Al is lower than 0.2 wt%, the flowing property and the casting shrinkage property of the alloy are poor, the content of Al is higher than 1.0 wt%, the solid solution strengthening of the alloy is serious, and the materialThe hardness is too high to facilitate cutting.

Pb is mainly distributed at crystal grains and grain boundaries in a granular manner, phase transformation β' → β is generated in the two-phase brass during heating, part of granular lead distributed at the crystal grains and the grain boundaries can be transferred into the crystal grains, the lead dispersed in the crystal grains is beneficial to cutting, when the content of the Pb is higher than 0.25%, the metal precipitation amount of the Pb exceeds the statistical limit of 5 mu g/L specified in GB 18145-2014, when the content of the Pb is lower than 0.1%, the cutting processing performance and the casting shrinkage performance of the alloy are obviously reduced, and the reduction of the casting performance of the alloy is mainly reflected in the increase of shrinkage cavities and shrinkage defects in the casting production process of a product.

The Mn content in the alloy is controlled to be 0.2-0.48 wt%, when the Mn content is lower than 0.2 wt%, the improvement effect on the alloy cutting processing performance and the casting shrinkage performance is obviously weakened, when the Mn content is higher than 0.48 wt%, the Mn-Si compound is easy to aggregate at a grain boundary, the room-temperature plasticity and the dezincification corrosion resistance of the alloy are reduced, and the loosening risk of the alloy is increased rapidly.

The existence form of P in brass is divided into two types, one is solid solution in Cu (α -Cu), and the other is Cu formed with Cu₃The solubility of phosphorus in α -copper is reduced rapidly with the temperature reduction, and when the P content exceeds 0.05-0.06% at room temperature, brittle Cu appears₃P phase, Cu₃The P secondary phase is precipitated from solid solution, and therefore preferentially appears on grain boundaries. During the cutting process, the compound is easy to cut and break, so that the alloy has good cutting performance. Meanwhile, the addition of P increases the cooling rate of the alloy, and a greater cooling rate results in a large undercooling, which increases the nucleation rate to produce a finer grain structure. In the alloy of the invention, the phosphorus content is controlled within the range of 0.01-0.25 wt%In the enclosure, when the phosphorus content is more than 0.25%, the brittle Cu₃The P content is sharply increased and is segregated at the grain boundary, the room temperature plasticity and the dezincification corrosion resistance of the alloy are reduced, the cold processing performance is influenced, and the loosening risk of the alloy is sharply increased.

Mg has the functions of deoxidizing, refining crystal grains, improving the dezincification corrosion resistance of the alloy and can also form an intermetallic compound Cu with copper₂Mg is beneficial to improving the cutting performance of the alloy. At the same time, magnesium may also form intermetallic compounds Mg with silicon₂The Mg content in the alloy is controlled to be 0.01-0.25 wt%, and when the Mg content is higher than 0.25 wt%, and the Mg content is increased, the dezincification resistance and the casting performance of the alloy are reduced.

The Sn has the functions of inhibiting the dezincification of the brass and improving the corrosion resistance of the brass. The value range of Sn in the alloy is controlled to be 0.01-0.1 wt%, and when the content of Sn exceeds 0.1 wt%, the risk of casting porosity of a brass product is aggravated, so that water leakage and failure of the product are caused.

Fe and Ni are taken as high-melting point metals, which are beneficial to the generation of the nucleation process of the alloy, thereby playing the effect of refining grains, however, the addition of Fe and Ni easily generates hard particles, and seriously influences the appearance quality of the product. Because the alloy of the invention is mainly suitable for parts of drinking water systems and has strict requirements on the appearance of products, the alloy of the invention does not add Fe and Ni.

The modifier B, Ti, Zr and Re are mainly used for refining grains and modifying the alloy, the gamma phase is generated by peritectic transformation L + β → gamma when the temperature of the alloy is reduced to 835 ℃, the gamma phase in an as-cast state mainly exists on a β phase crystal boundary in a net shape, and is in coarse star-shaped distribution in a β phase crystal, and the distribution form has adverse effect on the comprehensive performance of the brass.

The alloy of the invention is prepared by multi-element alloying, in particular by adjusting the contents of copper, silicon, aluminum and manganese, the phase composition of the alloy is β phase + a small amount of gamma phase + a small amount of dispersed intermetallic compounds such as Mn-Si compound, Cu-P compound and Mg-Si compound, wherein a small amount of gamma phase and the dispersed intermetallic compounds such as Mn-Si phase, Cu-P phase and Mg-Si are used for replacing the traditional Pb particles to play the role of cutting chip breaking, meanwhile, the selected favorable elements are on the one hand dissolved in Cu to improve the high-temperature feeding capability of β phase and form intermetallic compounds with lower melting point, which is helpful for feeding of a pouring channel, thereby reducing the defect of casting shrinkage, and by adding a proper amount of alterant, refining β phase grains and improving the distribution form of gamma phase, the alloy strength and the cutting processing efficiency can be improved, the occurrence of loose defect is reduced, better casting performance can be obtained, the casting performance of the alloy is equivalent to that wide range of lead ZCuZn40Pb2 is used on the market, the cutting processing efficiency is about ZCu40 Pb, and the low-pressure zinc removal corrosion resistance of a zinc casting system is superior to production of a low-opening drinking water tap 2 and a zero-opening water tap.

Detailed Description

The manganese-containing free-cutting silicon brass alloy consists of the following components: 60.2-64.0 wt% of Cu, 1.0-2.0 wt% of Si, 0.2-1.0 wt% of Al, 0.2-0.48 wt% of Mn and 0.1-0.25 wt% of Pb; one or more elements selected from P, Mg and Sn, and the content is 0.01-0.25 wt% of P, 0.01-0.25 wt% of Mg, and 0.01-0.1 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

The method for preparing the manganese-containing free-cutting silicon brass alloy comprises the following steps: according to the proportion, the raw materials of the metal silicon and the metal copper are placed at the bottom layer of an induction furnace, a slag cleaning refining agent is added, charcoal is used for covering the raw materials, the temperature is raised to 1050-1150 ℃, the raw materials are heated until the raw materials are completely melted, and scum and impurities are filtered; adjusting the temperature to 1000-1050 ℃, adding 0# zinc, quickly pressing into the furnace bottom, and fully stirring after melting; adding aluminum ingots, tin ingots and lead ingots, and fully stirring to ensure that the components of the alloy liquid are uniform; adding a Cu-P intermediate alloy, an Al-Mg intermediate alloy and a Cu-Mn intermediate alloy, wherein the mass percent of phosphorus in the Cu-P intermediate alloy is 10-15%, the mass percent of magnesium in the Al-Mg intermediate alloy is 25-50%, and the mass percent of Mn in the Cu-Mn intermediate alloy is 25-30%; adding modifier boron, titanium, zirconium or rare earth elements, heating to 1050-1150 ℃, flaming, stirring and preserving heat for 2-3 minutes; standing at 1000-1050 ℃ for 10-20 minutes to ensure that the alloy is uniform and impurities float, and filtering out floating slag and impurities; heating to 1050-1100 ℃, discharging and pouring. Specifically, the copper raw material can be electrolytic copper, a copper pipe or a copper wire. The Cu-P intermediate alloy, the Al-Mg intermediate alloy and the Cu-Mn intermediate alloy are added in a graphite bell jar pressing mode.

Manganese-containing free-cutting silicon brass alloys of examples 1 to 8 were prepared in the above-described manner in various proportions, and the composition thereof is shown in Table 1, and commercially available silicon brass and lead brass ZCuZn40Pb2 were used as comparative samples.

Table 1: manganese-containing free-cutting silicon brass alloy composition

Serial number	Cu	Si	Al	Mn	Pb	P	Mg	Sn	B+Ti+Zr+RE	Zn	Impurities
												Example 1	63.0	1.66	0.82	0.48	0.15	-	0.15	-	0.065	Balance of	＜0.5
Example 2	60.2	1.25	0.62	0.28	0.13	0.03	-	-	0.0016	Balance of	＜0.5
												Example 3	61.0	1.44	0.65	0.45	0.15	-	-	0.03	0.0020	Balance of	＜0.5
Example 4	60.5	1.10	0.25	0.35	0.10	0.06	0.23	-	0.012	Balance of	＜0.5
												Example 5	62.6	1.52	0.70	0.44	0.12	0.10	-	0.06	0.033	Balance of	＜0.5
Example 6	64.0	1.92	0.95	0.33	0.17	-	0.05	0.1	0.096	Balance of	＜0.5
												Example 7	63.3	1.73	0.46	0.20	0.22	0.24	0.12	0.05	0.072	Balance of	＜0.5
Example 8	61.4	1.35	0.57	0.40	0.25	-	-	0.08	0.0010	Balance of	＜0.5
												Comparative silicon Brass	62.0	0.62	0.60	-	0.13	-	-	-	-	Balance of	＜0.5
ZCuZn40Pb2	60.0	-	0.62	1.40	-	-	-	-	-	Balance of	＜0.5

The performance test structures for the manganese containing free-cutting silicon brass alloys of examples 1-8 and the comparative samples are shown in table 2, wherein:

1. brinell hardness

The test alloy is in an as-cast state, and the Brinell hardness detection is carried out according to the Brinell hardness test part 1 of the metal material of the national standard GB/T231.1-2009: test methods were performed;

2. cutting performance

The cutting performance test sample is in an as-cast state, is uniformly processed into round bars with the diameter of 20mm, the excircle is cut by adopting the same cutter, cutting speed and feed amount, the cutting resistance of the alloy in the table 1 is respectively measured by adopting a KISTLER 5070 dynamometer, the cutting rate of the ZCuZn40Pb2 alloy is 100 percent, and the relative cutting rate is calculated according to the following formula.

Relative cutting rate (. omega.) F (cutting resistance of ZCuZn40Pb 2)/F (cutting resistance of test alloy) × 100%

In the test, the cutter model: VCGT160404-AK H01, speed: 800r/min, feed per revolution: 0.2mm/r, and 1mm of unilateral cutting depth.

3. Dezincification corrosion resistance

The test alloy is in an as-cast state, a dezincification corrosion test is executed according to the national standard GB/T10119-;

4. precipitation of metal contaminants

The metal pollutant precipitation detection is carried out according to the national standard GB/T18145-.

5. Shrinkage property in casting

The casting performance is judged by the relative volume shrinkage rate (psi) measured by a volume shrinkage mold, and the original volume of a volume shrinkage sample is V₀Volume of the shrinkage cavity of the body shrinkage sample is V_S(test by the dripping method), the calculation formula of the relative volume shrinkage ratio (. psi.) is:

relative volume shrinkage ratio (psi) (volume shrinkage-like shrinkage volume V)_SVolume shrinkage sample original volume V₀)*100％.

Table 2: performance of the test alloy and the comparative alloy

The manganese-containing free-cutting silicon brass alloy has good casting processability which is close to common lead brass, can meet the requirements of practical production and application, has dezincification corrosion resistance which is obviously superior to that of the lead brass, is qualified in metal pollutant precipitation inspection, and can be widely applied to water heating, valves and other various industries with limits on metal pollutant precipitation. The manganese-containing free-cutting silicon brass alloy has the advantages of simple manufacturing process, low requirements on raw materials, low manufacturing cost and suitability for popularization, and is a novel material with better comprehensive performance and capable of replacing the traditional lead brass.

The above examples are only intended to further illustrate the manganese-containing free-cutting silicon brass alloy of the present invention, the preparation method and the application thereof, but the present invention is not limited to the examples, and any simple modification, equivalent change and modification made to the above examples according to the technical essence of the present invention fall within the scope of the technical solution of the present invention.

Claims (7)

1. The manganese-containing free-cutting silicon brass alloy is characterized in that: the alloy consists of the following components: 60.2-64.0 wt% of Cu, 1.52-2.0 wt% of Si, 0.2-0.7 wt% of Al, 0.33-0.48 wt% of Mn, 0.1-0.25 wt% of Pb, 0.01-0.25 wt% of P, 0.01-0.25 wt% of Mg and 0.01-0.1 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5 wt%;

wherein the area fraction of β phase in the brass alloy is more than or equal to 80%, the area fraction of gamma phase is 1-10%, and the sum of the area fractions of Mn-Si compound, Cu-P compound and Cu-Mg compound is 1-10%.

2. A manganese-containing free-cutting silicon brass alloy in accordance with claim 1, consisting of: 62.0 to 64.0 wt% of Cu, 1.52 to 2.0 wt% of Si, 0.4 to 0.7 wt% of Al, 0.33 to 0.48 wt% of Mn, 0.1 to 0.15 wt% of Pb, 0.01 to 0.1 wt% of P, 0.01 to 0.15 wt% of Mg, 0.01 to 0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

3. A manganese-containing free-cutting silicon brass alloy according to claim 2, consisting of: 62.0 to 63.0 wt% of Cu, 1.52 to 1.7 wt% of Si, 0.6 to 0.7 wt% of Al, 0.33 to 0.48 wt% of Mn, 0.1 to 0.15 wt% of Pb, 0.05 to 0.1 wt% of P, 0.01 to 0.10 wt% of Mg, 0.01 to 0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

4. A manganese-containing free-cutting silicon brass alloy in accordance with claim 1, consisting of: 60.5 to 63.3 wt% of Cu, 1.52 to 1.73 wt% of Si, 0.25 to 0.46 wt% of Al, 0.33 to 0.35 wt% of Mn, 0.1 to 0.15 wt% of Pb, 0.01 to 0.1 wt% of P, 0.01 to 0.15 wt% of Mg, 0.01 to 0.05 wt% of Sn; at least one modifier is selected from B, Ti, Zr or RE, and the total content of the modifier is 0.001-0.1 wt%; the balance of Zn and impurities with the total amount not more than 0.5wt percent.

5. The manganese-containing free-cutting silicon brass alloy according to any one of claims 1 to 4, wherein the brass alloy has a cutting efficiency of greater than 80%, an average dezincification layer depth of less than 300 μm, and a casting relative volume shrinkage of less than 2%.

6. Use of a manganese-containing free-cutting silicon brass alloy according to any one of claims 1 to 5, wherein the brass alloy is used for casting of drinking water system components, including gravity casting and low pressure casting.

7. A method for preparing the manganese-containing free-cutting silicon brass alloy according to any one of claims 1 to 5, wherein: the method comprises the following steps:

1) according to the proportion, placing the raw materials of silicon metal and copper in the bottom layer of an induction furnace, adding a slag-cleaning refining agent, covering with charcoal, heating to 1050-1150 ℃ until the materials are completely melted, and filtering out floating slag and impurities;

2) adjusting the temperature to 1000-1050 ℃, adding 0# zinc, quickly pressing into the furnace bottom, and fully stirring after melting;

3) adding aluminum ingots, tin ingots and lead ingots, and fully stirring to ensure that the components of the alloy liquid are uniform;

4) adding a Cu-P intermediate alloy, an Al-Mg intermediate alloy and a Cu-Mn intermediate alloy, wherein the mass percent of phosphorus in the Cu-P intermediate alloy is 10-15%, the mass percent of magnesium in the Al-Mg intermediate alloy is 25-50%, and the mass percent of Mn in the Cu-Mn intermediate alloy is 25-30%;

5) adding modifier boron, titanium, zirconium or rare earth elements, heating to 1050-1150 ℃, flaming, stirring and preserving heat for 2-3 minutes;

6) standing at 1000-1050 ℃ for 10-20 minutes to ensure that the alloy is uniform and impurities float, and filtering out floating slag and impurities;

7) heating to 1050-1100 ℃, discharging and pouring.