Brass alloy with low lead precipitation amount and preparation method and application thereof

Abstract

The invention discloses a brass alloy with a low lead precipitation amount and a preparation method and application thereof, and relates to the technical field of copper alloys. The brass alloy comprises Cu, Zn, doping elements and inevitable impurities, the total mass percentage of all the elements is 100%, the Cu accounts for 57-63 wt%, and the doping elements comprise 0.1-0.8 wt% of Pb, 0.01-1.2 wt% of Sn, 0.001-0.5 wt% of Al and 0.01-1.0 wt% of Ni; the microstructure of the brass alloy comprises an alpha phase and a beta phase, the alpha phase is in a net shape or a dendritic shape, and the beta phase is partially or completely separated by the alpha phase. The Pb precipitation statistical value Q of the brass alloy is less than or equal to 5 [mu] g / L, and a specified Pb precipitation limit value is satisfied.

Description

Technical Field

[0001] The invention relates to the technical field of copper alloys, and in particular to a brass alloy with low lead precipitation amount and a preparation method and application thereof. Background Art

[0002] Drinking water valves (hereinafter referred to as water valves) include faucets and gate valves, ball valves, stop valves, check valves, etc. on drinking water pipes, with a nominal diameter range of DN15~DN100. The main material for making water valves is lead brass, because copper has good antibacterial properties and processing properties. The role of lead (Pb) in lead brass is to break chips during cutting, and Pb is a heavy metal element that is harmful to human health.

[0003] In view of the harm caused by the precipitation of heavy metals such as Pb to people's health, North America has formulated the standard NSF / ANSI 61 Pb for toxicity testing of drinking water contact materials, which stipulates the precipitation limit of heavy metals such as Pb. According to experimental data, the statistical value of Pb precipitation is considered safe within 5μg / L. Some countries and regions, including China, directly or indirectly quote this standard to evaluate the precipitation of heavy metals from faucets. my country's revised GB / T 8464-2023 (iron, copper and stainless steel threaded water valves) standard will be implemented on October 1, 2023. Article 6.18 of the new national standard stipulates that the precipitation limit of metal pollutants in valves used for drinking water pipes is: Fe≤30μg / L, Mn≤10μg / L, Cu≤100μg / L, Zn≤100μg / L, As≤5μg / L, Hg≤1μg / L, Cr 6+ ≤5μg / L, Cd≤1μg / L, Pb≤5μg / L (statistical value), Ag≤5μg / L. 6+ , Cd, Pb, these four heavy metal elements are harmful to the human body. Generally speaking, brass water valves contain Hg, Cr 6+ , Cd will not exceed the metal pollutant precipitation limit values ​​specified in NSF / ANSI 61 and GB / T 8464-2023. However, when testing the lead brass water valves currently on the market, the Pb precipitation statistical value Q calculated according to the formula will exceed 5μg / L, and even reach more than 100μg / L.

[0004] Publication No. CN106011532A discloses an environmentally friendly brass alloy specially used for drinking water distribution, the components and weight percentage of which are: Cu 57~65%; Bi 0.4~1.6%; Sn 0.09~1.0%; Ni 0.01~0.5%; Al 0.1~1.0%; Mg 0.05~1.0%; Fe<0.2%; Pb<0.01%; the remainder is Zn and impurities with a total amount not exceeding 0.3%. The material matrix of the brass alloy is an equiaxed α phase, in which an equiaxed β phase is distributed. At the same time, both phases show obvious spheroidization characteristics, which is beneficial to inhibiting the precipitation of zinc and lead metals in the alloy.

[0005] Publication No. CN114540662A discloses a brass alloy, the mass percentage composition of the brass alloy is Cu: 59-63 wt%, Si: 0.2-0.8 wt%, Sn: 0.4-1.0 wt%, Pb: 0.05-0.15 wt%, Al: 0.1-0.2 wt%, As: 0.02-0.15 wt%, and the rest is Zn and unavoidable impurities. The Pb content of the brass alloy is extremely low, which can meet the lead precipitation limit of drinking water contact products such as NSF61, BS6920, GB18145, etc.

[0006] NSF / ANSI 61 and GB / T 8464-2023 stipulate the inspection method for Pb precipitation: the number of test samples is 3. Before the results are processed, the samples need to be tested for 19 consecutive days, the immersion solution is replaced every 24 hours, and the immersion solution samples on the 3rd, 4th, 5th, 10th, 11th, 12th, 17th, 18th, and 19th days are obtained for measurement. Since the sample test immersion time is as long as 19 days, the amount of Pb precipitation will vary with the immersion time. Therefore, the standard uses statistical principles to calculate the standard concentration using the logarithmic mean and standard deviation. Finally, the Pb precipitation statistical value Q is calculated by the formula, which is more in line with the actual situation than the single Pb precipitation test value of the old standard.

[0007] The excessive Pb precipitation is mainly caused by the presence of Pb in the water valve material, and secondly by improper treatment of Pb in the manufacturing process. The present invention aims at the problem of excessive Pb precipitation in lead brass water valves, optimizes the composition and preparation process of brass water valves, so that the Pb precipitation of brass water valves meets the standards such as NSF / ANSI 61 or GB / T 8464-2023, and meets people's urgent needs for healthy drinking water. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a brass alloy with low lead precipitation, wherein the Pb precipitation statistical value Q of the brass alloy is ≤5 μg / L, meeting the Pb precipitation limit specified in NSF / ANSI 61 or GB / T 8464-2023.

[0009] The invention provides a brass alloy with low lead precipitation, comprising Cu, Zn, doping elements and inevitable impurities, wherein the total mass percentage of all elements is 100%, wherein Cu: 57-63 wt%, the doping elements include Pb: 0.1-0.8 wt%, Sn: 0.01-1.2 wt%, Al: 0.001-0.5 wt%, and Ni: 0.01-1.0 wt%; the microstructure of the brass alloy comprises an α phase and a β phase, the morphology of the α phase is a network or dendrite, and the β phase is partially or completely separated by the α phase.

[0010] The present invention limits the types and addition amounts of metals in the brass alloy, wherein: The solubility of Pb in brass alloy is very low, and it is distributed in the crystal in the form of Pb particles. The cutting performance of brass alloy increases with the increase of Pb content. The lower limit of Pb content in brass of the present invention is 0.1 wt%, and the purpose is that a small amount of Pb can improve the cutting performance of brass alloy. Considering that under other identical production process conditions, the amount of Pb precipitation is directly related to the content of Pb element in brass alloy, the higher the Pb content, the higher the amount of Pb precipitation. When the Pb content in brass alloy exceeds 0.8 wt%, it is difficult to achieve the Pb precipitation statistical value Q≤5 μg / L of brass alloy by adding trace elements or regulating the metallographic structure of brass alloy.

[0011] Al: Since Al has a more negative standard potential than Zn, it preferentially combines with oxygen in the environment and preferentially forms a fine and hard aluminum oxide film, which has the effect of blocking substrate corrosion, thereby improving the dezincification corrosion resistance of the brass alloy. In addition, Al can also improve the hot forging performance of the brass alloy. However, Al has a strong solid solution strengthening effect in the brass alloy, and too high an Al content will increase the hardness of the brass alloy, making the brass alloy difficult to cut. Therefore, in the present invention, the Al content should be controlled in the range of 0.001-0.5 wt%.

[0012] Sn: The addition of Sn expands the β phase region of the brass alloy, and Sn can be enriched at the phase boundary and the α phase grain boundary, which plays a role in inhibiting dezincification. However, adding too much Sn to the brass alloy will reduce the plasticity of the brass alloy and cause the brass alloy to become brittle. Therefore, in the present invention, the Sn content range should be controlled within 0.01~1.2 wt%.

[0013] Ni: The addition of Ni reduces the β phase region of the brass alloy, so that when the Zn equivalent is high, the addition of Ni enables the microstructure of the brass alloy to still maintain a lower proportion of β phase, thereby improving the dezincification corrosion resistance of the brass alloy.

[0014] Since the dezincification corrosion of brass alloy is more likely to proceed in the β phase, if the α phase morphology is blocky or strip-shaped, the β phases will be interconnected, and the dezincification corrosion will accelerate along the β phase channel. The concentration of Pb precipitated in the test water sample increases with the development of dezincification corrosion. Therefore, in the present invention, by controlling the morphology of the α phase and the β phase, the diffusion of the β phase dezincification corrosion can be effectively inhibited, thereby reducing the concentration of Pb precipitated in the test water sample.

[0015] According to the calculation formula of the Pb precipitation statistical value Q provided by NSF / ANSI 61 and GB / T 8464-2023 standards, the Pb precipitation statistical value Q is obtained after statistical processing of the standardized concentration X. The standardized concentration X is mainly affected by the concentration C (µg / L) of Pb precipitated in the laboratory test water sample, the volume VL (L) of the test immersion liquid, and the CMV cold water adjustment factor. The standardized concentration X is linearly positively correlated with these three factors, among which the volume VL (L) of the test immersion liquid and the CMV cold water adjustment factor are determined by the product cavity structure. The Pb precipitation statistical value Q is not only related to the detection value of the concentration C of the precipitated Pb, but also to the fluctuation between the detection values ​​obtained by daily sampling. Therefore, three situations may occur: (1) The lower the detection value of each Pb precipitation concentration C and the smaller the fluctuation between them, the lower the Pb precipitation statistical value Q will be: that is, the detection value of the Pb precipitation concentration C is ≤100μg / L, and the difference between the maximum and minimum values ​​of the Pb precipitation concentration obtained by sampling for multiple days, that is, C max -C min ≤30μg / L, then the Pb precipitation statistical value Q≤5μg / L.

[0016] (2) Although each Pb precipitation concentration C detection value is low, the fluctuation between them is large, and the Pb precipitation statistical value Q will increase: that is, the Pb precipitation concentration C detection value is ≤100μg / L, and the difference between the maximum and minimum values ​​of the Pb precipitation concentration obtained by sampling for multiple days, that is, C max -C min ≥70μg / L, the Pb precipitation statistical value Q≥5μg / L.

[0017] (3) Although the detection value of each Pb precipitation concentration C is high, the fluctuation between them is small, and the Pb precipitation statistical value Q will be low: that is, the detection value of the Pb precipitation concentration C reaches 220~360μg / L, and the difference between the maximum and minimum values ​​of the Pb precipitation concentration obtained by sampling for multiple days, that is, C max -C min≤60μg / L, the Pb precipitation statistical value Q≤5μg / L.

[0018] (4) When the Pb precipitation concentration C exceeds 360 μg / L, even if the fluctuation between them is small, the Pb precipitation statistical value Q exceeds 5 μg / L.

[0019] The present invention controls the upper limit of the Pb content to make it possible to keep the Pb precipitation of the brass alloy at 5 μg / L, and simultaneously regulates the Al, Sn and Ni elements to appropriately improve the dezincification corrosion resistance of the brass alloy, and regulates the morphology of the α phase and the β phase to minimize the diffusion of dezincification corrosion. In summary, the synergistic effect enables the brass alloy provided by the present invention to achieve the above-mentioned Pb precipitation conditions (1) and (3). It can be understood that the purpose of the present invention is to make the Pb precipitation amount meet the standard, so the regulation of the element content and morphology only needs to meet the Pb precipitation standard.

[0020] Preferably, the area proportion of the β phase in the microstructure of the brass alloy is 8% to 36%.

[0021] The microstructure of the brass alloy provided by the present invention includes a single-substance Pb phase (Pb particles) in addition to the α phase and the β phase. The solubility of Pb in the β phase is about 10 times that in the α phase. A small amount of Pb can be dissolved in the (α+β) two-phase brass alloy. Increasing the proportion of the β phase in the brass alloy can significantly increase the amount of Pb dissolved. However, since the β phase is less corrosion-resistant than the α phase, and the concentration of Pb precipitated in the test water sample gradually increases as the sample corrodes, therefore, controlling the appropriate proportion of the β phase can balance the requirements for the amount of dissolved Pb and corrosion resistance, thereby better controlling the concentration of Pb precipitated in the test water sample.

[0022] Further preferably, in the microstructure of the brass alloy, the area proportion of the β phase is 8% to 20%.

[0023] The present invention further controls the area ratio of the β phase, so that the morphology of the α phase in the brass alloy structure provided by the present invention is a network. When the β phase is completely separated by the α phase, the diffusion of the β phase dezincification corrosion can be suppressed to a large extent, the dezincification corrosion resistance of the brass alloy is improved, and the concentration of Pb precipitated in the test water sample is reduced.

[0024] Preferably, the average grain size of the brass alloy is ≤20 μm, and the average size of the Pb particles is ≤2 μm.

[0025] The amount of Pb precipitated varies with the soaking time. For example, the concentration of Pb precipitated from the soaking liquid samples on the 3rd, 4th, 5th, 10th, 11th, 12th, 17th, 18th, and 19th days in the embodiment of the present invention fluctuates, and the fluctuation is related to the uniformity of the distribution of Pb particles in the brass water valve. If Pb is segregated, the concentration of Pb precipitation will fluctuate greatly during the 9 sampling processes. The present invention controls the average size and average grain size of Pb particles to make the distribution uniformity of Pb particles higher, thereby further reducing the fluctuation of the concentration of Pb precipitation and avoiding the concentration of Pb precipitation exceeding the specified concentration in a certain period of time.

[0026] Preferably, the zinc equivalent in the brass alloy is 38-44 wt%.

[0027] The zinc equivalent provided by the present invention refers to the Zn content in the brass alloy converted from Zn and other alloying elements according to the same principle of effect on the structure, which is equivalent to the Zn content of the brass alloy simply added. Adding an element with a positive zinc equivalent coefficient to the brass alloy is equivalent to increasing the Zn content, while adding an element with a negative zinc equivalent coefficient is equivalent to reducing the Zn content. The lower the zinc equivalent of the brass alloy, the better its resistance to dezincification corrosion, and the concentration of Pb precipitated in the brass water valve is positively correlated with its resistance to dezincification corrosion. In the present invention, the zinc equivalent coefficient of Al is +6, the zinc equivalent coefficient of Sn is +4, and the zinc equivalent coefficient of Ni is -1.5, and the zinc equivalent calculation formula is: D Zn =(100-W Cu )+(W Sn ×4+W Al ×6+W Ni × (-1.5) Among them, D Zn is zinc equivalent, W Cu is the mass fraction of Cu, W Sn is the mass fraction of Sn, W Al is the mass fraction of Al, W Ni is the mass fraction of Ni.

[0028] Preferably, the brass alloy further comprises As, and the mass percentage of As is 0.01-0.2 wt%.

[0029] In the present invention, As interacts with Cu and Zn to form a Cu-As-Zn protective layer at the grain boundary of the brass alloy, thereby hindering the preferential dissolution of Zn, inhibiting the dezincification of the brass alloy, improving the dezincification corrosion resistance of the brass alloy, and reducing the concentration of precipitated Pb in the test water sample.

[0030] Preferably, the dezincification corrosion resistance of the brass with low lead precipitation provided by the present invention should reach: the average dezincification layer depth is ≤ 200 μm.- The water-passing cavity of the water valve made of brass provided by the present invention will undergo dezincification corrosion when immersed in tap water for a long time. The concentration of Pb precipitated in the test water sample gradually increases as the dezincification corrosion of the sample proceeds. Therefore, improving the dezincification corrosion resistance of brass can reduce the concentration of Pb precipitated in the test water sample.

[0031] On the other hand, the present invention also provides a method for preparing the brass alloy with low lead precipitation, comprising: the process flow of the preparation method is smelting and casting → peeling of ingot → hot forging → surface treatment → CNC machine tool processing → stress relief annealing; Wherein, the ingredients are prepared and smelted according to the percentage of each component of the brass alloy with low lead precipitation amount; The depth of the peeling of the ingot is 2% to 10% of the maximum size of the ingot.

[0032] The present invention removes the metal on the surface of the ingot by turning with a centerless lathe or by stripping with a knife-edge die to obtain a brass rod or profile, and the stripping depth is 2% to 10% of the maximum size of the ingot. This is because the casting process is a process of melting and recrystallizing the metal, the melting point of brass is about 900°C, and the melting point of Pb is only 330°C, so the casting process will change the distribution of the Pb element in the ingot. The cooling rate of the surface of the ingot is greater than that of the interior. As the temperature decreases, Pb will first precipitate and distribute to the surface with a low temperature, resulting in the Pb content on the surface of the ingot being greater than the Pb content inside. Stripping can eliminate the Pb segregation on the surface of the ingot, and avoid the extremely uneven distribution of Pb in the segregation layer being involved in the forging structure during the hot forging process, causing uneven distribution of Pb.

[0033] The invention uses a numerically controlled machine tool to perform various cutting processes so that the blank can achieve the desired size accuracy and shape position accuracy and meet the requirements of the drawing.

[0034] Preferably, the ingot is a bar or profile blank, and the depth of peeling the ingot is 2% to 10% of the thickness of the ingot.

[0035] Preferably, the initial forging temperature of the hot forging process is 620-700°C, the final forging temperature is 520-600°C, and the temperature of the mold cavity is maintained at 300-380°C during the hot forging process.

[0036] In order to obtain a suitable grain size and a uniform recrystallized structure, the present invention adopts low-temperature forging. Since the forging forming process time is extremely short, only 1-2 seconds, the grains broken by hot forging have no time to grow in the dynamic recrystallization process and are maintained in a grain form with a smaller size. At the same time, due to the short time and hot forging breakage, the size of Pb is not easy to grow. In addition, during the entire forging process of the alloy, the temperature of the forging mold cavity is maintained at 300-380°C through online temperature control, so as to avoid excessive drop of the hot forging temperature due to heat absorption by the forging die, thereby obtaining a uniform recrystallized structure.

[0037] Preferably, the smelting temperature is 900-1100°C, and when the metal is melted, 0.005-0.03 wt% of the total weight of the molten copper is added to the molten copper and stirred thoroughly, in order to inhibit the growth of cast dendrites and refine the brass casting structure.

[0038] Preferably, the casting is horizontal continuous casting, the casting temperature is 970-1080°C, and the pulling speed is 100-600 mm / min. Further, when the ingot is a bar, the specification of the ingot is φ10-100 mm.

[0039] Preferably, the surface treatment is trimming or polishing. The purpose of surface treatment is to change the tensile stress of the blank after hot forging into compressive stress, and to remove the surface oxide scale and stains during forging, so that the surface is smooth and bright, and the lines are smoother.

[0040] Preferably, the stress relief annealing temperature is 230-300°C, and the holding time is 180-480 minutes. The present invention controls the annealing temperature and the holding time to remove the internal stress of the blank after turning.

[0041] Further preferably, the heating time of the stress relief annealing is 60-180 min, and the steel is cooled to room temperature -60°C before being taken out of the furnace.

[0042] Preferably, the preparation method of the brass alloy with low lead release also includes assembly and testing inspection, and the assembly and testing inspection include: assembling the water valve components together in a certain order, performing water test and pressure test during assembly to ensure that there is no leakage on each sealing surface, and after passing the test, transferring to the assembly line to install pressure caps, handles, etc., and finally packaging and boxing.

[0043] The present invention also provides the use of the brass alloy with low lead precipitation in drinking water valves, water meters, refrigeration valve bodies and sanitary ware.

[0044] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention controls the contents of Pb, Sn, Al and Ni elements in the brass alloy, thereby ensuring the cutting performance of the alloy and improving the anti-dezincification corrosion ability of the brass alloy to reduce the precipitation of Pb. At the same time, the β phase is partially or completely separated by the α phase, which effectively inhibits the diffusion of dezincification corrosion. Through the above synergistic effect, the concentration of precipitated Pb in the test water sample is reduced, so that the Pb precipitation statistical value Q of the brass alloy is ≤5μg / L, which meets the Pb precipitation limit specified in NSF / ANSI 61 or GB / T 8464-2023.

[0045] (2) In the preparation method of the present invention, the surface layer with a high Pb content is removed by peeling the ingot to an appropriate depth, thereby eliminating the Pb segregation phenomenon on the surface of the ingot caused by the casting process, thereby improving the uniformity of Pb distribution and reducing the fluctuation of Pb precipitation concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The metallographic structure of the brass alloy obtained in Example 1.

[0047] Figure 2 The metallographic structure of the brass alloy obtained in Example 4.

[0048] Figure 3 The metallographic structure of the brass alloy obtained in Comparative Example 1. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited to the following examples.

[0050] The raw materials used in the present invention are all commercially available.

[0051] Example 1: Preparation of a DN20 water valve (1) Smelting: Prepare the ingredients according to the mass percentage of each component in Table 1, and smelt them in an electric furnace at a smelting temperature of 900-1080°C. After all the metals are melted and the components are tested to be qualified, add a grain refiner at a rate of 0.01 wt% of the total weight of the copper water and stir thoroughly; (2) Casting: The molten copper obtained in step (1) is transferred into a holding furnace for heat preservation, and a φ28.5 mm rod is cast by a horizontal continuous casting method, the casting temperature is 990-1010°C, and the pulling speed is 280 mm / min; (3) Ingot peeling: Remove the metal on the surface of the ingot by turning on a centerless lathe or by knife-edge die peeling. The peeling depth is 2.63% of the ingot diameter to obtain a φ27 mm bar ingot. (4) Hot forging: The φ27mm bar ingot is heated and forged into a DN20 water valve body blank. The initial forging temperature is 630~650℃ and the final forging temperature is 540~570℃. During the entire forging process of the alloy, the temperature of the forging mold cavity must be maintained at 310℃ through online temperature control; (5) Surface treatment: The blank of the DN20 water valve body after hot forging is subjected to surface treatment such as trimming and polishing; (6) CNC machine processing: The surface treated DN20 water valve body blank is subjected to various cutting processes through CNC machine tools to make the water valve achieve the required dimensional accuracy and shape position accuracy and meet the drawing requirements; (7) Stress relief annealing: The blank of the DN20 water valve body after cutting is subjected to low-temperature stress relief annealing. The annealing temperature is 280°C. The time from room temperature to this temperature is 60 minutes. The heat preservation time is 180 minutes. The power is turned off and the furnace is cooled to room temperature -60°C before being taken out of the furnace. (8) Assembly and test inspection: Assemble the drinking water valve components such as the valve body, valve cover, and valve stem in a certain order. During the assembly, water test and pressure test should be carried out to ensure that there is no leakage on each sealing surface. After passing the test, transfer to the assembly line to install the pressure cap, handle, etc., and finally package and box.

[0052] Example 2: Preparation of a DN15 water valve (1) Smelting: Prepare the ingredients according to the mass percentage of each component in Table 1, and smelt in an electric furnace at a smelting temperature of 900-1080°C. After all the metals are melted and the components are tested to be qualified, add a grain refiner at 0.016 wt% of the total weight of the copper water and stir thoroughly; (2) Casting: The molten copper obtained in step (1) is transferred into a holding furnace for heat preservation, and a φ25.5 mm rod is cast by a horizontal continuous casting method, the casting temperature is 1000-1020°C, and the pulling speed is 300 mm / min; (3) Ingot peeling: Remove the metal on the surface of the ingot by turning on a centerless lathe or by knife-edge die peeling. The peeling depth is 2.94% of the ingot diameter to obtain a φ24 mm bar ingot. (4) Hot forging: The φ24mm bar ingot is heated and forged into a DN15 water valve body blank. The initial forging temperature is 650~670℃ and the final forging temperature is 550~580℃. During the entire forging process of the alloy, the temperature of the forging mold cavity must be maintained at 330℃ through online temperature control; (5) Surface treatment: The blank of the DN15 water valve body after hot forging is subjected to surface treatment such as trimming and polishing; (6) CNC machine processing: The surface treated DN15 water valve blank body is processed by CNC machine tools to achieve the required size accuracy and shape position accuracy and meet the drawing requirements; (7) Stress relief annealing: The blank of the DN15 water valve body after cutting is subjected to low-temperature stress relief annealing. The annealing temperature is 300°C. The time from room temperature to this temperature is 60 minutes. The heat preservation time is 240 minutes. The power is turned off and the furnace is cooled to room temperature -60°C before being taken out of the furnace. (8) Assembly and test inspection: Assemble the drinking water valve components such as the valve body, valve cover, and valve stem in a certain order. During the assembly, water test and pressure test should be carried out to ensure that there is no leakage on each sealing surface. After passing the test, transfer to the assembly line to install the pressure cap, handle, etc., and finally package and box.

[0053] Example 3: Preparation of a DN40 water valve (1) Smelting: Prepare the ingredients according to the mass percentage of each component in Table 1, and smelt them in an electric furnace at a smelting temperature of 900-1100°C. After all the metals are melted and the components are tested to be qualified, add a grain refiner at a rate of 0.016 wt% of the total weight of the copper water and stir thoroughly; (2) Casting: The molten copper obtained in step (1) is transferred into a holding furnace for heat preservation, and a 53.8 mm × 49.6 mm × 30 mm profile is cast by a horizontal continuous casting method, the casting temperature is 1015-1035°C, and the pulling speed is 230 mm / min; (3) Ingot peeling: The metal on the surface of the ingot is removed by turning on a centerless lathe or by knife-edge die peeling. The peeling depth is 4.46% of the maximum size of the ingot (53.8 mm), and a 49 mm × 46 mm × 28 mm ingot is obtained. (4) Hot forging: The 49mm×46mm×28mm profile ingot is heated and forged into a DN40 water valve body blank. The initial forging temperature is 660~680℃ and the final forging temperature is 560~585℃. During the entire forging process of the alloy, the temperature of the forging mold cavity must be maintained at 320℃ through online temperature control; (5) Surface treatment: The blank of the DN40 water valve body after hot forging is subjected to surface treatment such as trimming and polishing; (6) CNC machine processing: The surface treated DN40 water valve body blank is subjected to various cutting processes through CNC machine tools to make the water valve achieve the required dimensional accuracy and shape position accuracy and meet the drawing requirements; (7) Stress relief annealing: The blank of the DN40 water valve body after cutting is subjected to low-temperature stress relief annealing. The annealing temperature is 250°C. The time from room temperature to this temperature is 60 minutes. The heat preservation time is 240 minutes. The power is turned off and the furnace is cooled to room temperature -60°C before being taken out of the furnace. (8) Assembly and test inspection: Assemble the drinking water valve components such as the valve body, valve cover, and valve stem in a certain order. During the assembly, water test and pressure test should be carried out to ensure that there is no leakage on each sealing surface. After passing the test, transfer to the assembly line to install the pressure cap, handle, etc., and finally package and box.

[0054] Example 4: Preparation of a DN20 water valve (1) Smelting: Prepare the ingredients according to the mass percentage of each component in Table 1, and smelt them in an electric furnace at a smelting temperature of 900-1080°C. After all the metals are melted and the components are tested to be qualified, add a grain refiner at a rate of 0.01 wt% of the total weight of the copper water and stir thoroughly; (2) Casting: The molten copper obtained in step (1) is transferred into a holding furnace for heat preservation, and a φ28.5 mm rod is cast by a horizontal continuous casting method, the casting temperature is 990-1010°C, and the pulling speed is 280 mm / min; (3) Ingot peeling: Remove the metal on the surface of the ingot by turning on a centerless lathe or by knife-edge die peeling. The peeling depth is 2.63% of the ingot diameter to obtain a φ27 mm bar ingot. (4) Hot forging: The φ27mm bar ingot is heated and forged into a DN20 water valve body blank. The initial forging temperature is 660~680℃ and the final forging temperature is 580~600℃. During the entire forging process of the alloy, the temperature of the forging mold cavity must be maintained at 340℃ through online temperature control; (5) Surface treatment: The blank of the DN20 water valve body after hot forging is subjected to surface treatment such as trimming and polishing; (6) CNC machine processing: The surface treated DN20 water valve body blank is subjected to various cutting processes through CNC machine tools to make the water valve achieve the required dimensional accuracy and shape position accuracy and meet the drawing requirements; (7) Stress relief annealing: The blank of the DN20 water valve body after cutting is subjected to low-temperature stress relief annealing. The annealing temperature is 280°C. The time from room temperature to this temperature is 60 minutes. The heat preservation time is 180 minutes. The power is turned off and the furnace is cooled to room temperature -60°C before being taken out of the furnace. (8) Assembly and test inspection: Assemble the drinking water valve components such as the valve body, valve cover, and valve stem in a certain order. During the assembly, water test and pressure test should be carried out to ensure that there is no leakage on each sealing surface. After passing the test, transfer to the assembly line to install the pressure cap, handle, etc., and finally package and box.

[0055] Comparative Example 1: DN20 water valve prepared from lead brass HPb59-1 according to the following conventional preparation method (1) Melting: Prepare the ingredients according to the mass percentage of each component in Table 1, and melt them in an electric furnace at a melting temperature of 900-1080°C until all the metals are melted and the components are tested; (2) Casting: The molten copper obtained in step (1) is transferred into a holding furnace for heat preservation, and a φ27.6 mm rod is cast by a horizontal continuous casting method, the casting temperature is 990-1010°C, and the pulling speed is 280 mm / min; (3) Ingot peeling: Remove the metal on the surface of the ingot by turning on a centerless lathe or by knife-edge die peeling. The peeling depth is 1.09% of the ingot diameter to obtain a φ27 mm bar ingot. (4) Hot forging: The φ27mm bar billet is heated and forged into a DN20 water valve body blank. The initial forging temperature is 690~720℃ and the final forging temperature is 610~640℃; (5) Surface treatment: The blank of the DN20 water valve body after hot forging is subjected to surface treatment such as trimming and polishing; (6) CNC machine processing: The surface treated DN20 water valve body blank is subjected to various cutting processes through CNC machine tools to make the water valve achieve the required dimensional accuracy and shape position accuracy and meet the drawing requirements; (7) Stress relief annealing: The blank of the DN20 water valve body after cutting is subjected to low-temperature stress relief annealing. The annealing temperature is 280°C. The time from room temperature to this temperature is 60 minutes. The heat preservation time is 180 minutes. The power is turned off and the furnace is cooled to room temperature -60°C before being taken out of the furnace. (8) Assembly and test inspection: Assemble the drinking water valve components such as the valve body, valve cover, and valve stem in a certain order. During the assembly, water test and pressure test should be carried out to ensure that there is no leakage on each sealing surface. After passing the test, transfer to the assembly line to install the pressure cap, handle, etc., and finally package and box.

[0056] Table 1: Mass weight ratio of each component of Examples 1 to 4 and Comparative Examples

[0057] Sample analysis 1. Microstructure morphology analysis The obtained grain size, β phase area ratio, α phase morphology, Pb particle size, and average dezincification layer depth of Examples 1 to 4 and the comparative example were observed under a metallographic microscope and measured and calculated using metallographic structure analysis software. The results are shown in Tables 2 and Figure 1~Figure 3 shown.

[0058] Table 2: Microstructure of Examples 1 to 4 and Comparative Examples

[0059] From Table 2, Figure 1 and Figure 2 It can be seen that the α phase morphology of Examples 1 and 2 is dendritic, the α phase morphology of Examples 3 and 4 is reticular, the grain size does not exceed 20 μm, the average size of the Pb particles is within 2 μm, and the β phase ratio is within 8-36%, among which the β phase ratio of Examples 3 and 4 is the best 8-20%; while the α phase morphology of Comparative Example 1 is blocky ( Figure 3 ), the grain size is 38.3μm, exceeding 20μm, and the β phase ratio is 48.6%, exceeding 36%.

[0060] 2. Analysis of dezincification corrosion resistance and Pb precipitation statistical value Q The dezincification corrosion resistance of the water valves prepared in Examples 1 to 4 and the comparative example was tested according to the method specified in GB / T 10119-2008, and the Pb precipitation statistical value Q was tested and calculated according to the method specified in GB / T 8464-2023. The results are recorded in Table 3.

[0061] Table 3: Dezincification corrosion resistance and Pb precipitation statistics Q of Examples 1 to 4 and Comparative Examples

[0062] As can be seen from Table 3, the average dezincification depths of Examples 1 to 4 are all lower than 200 μm, and the Pb precipitation statistical values ​​Q are all less than 5 μg / L. Among them, the Pb precipitation statistical value Q of Example 4 is the lowest, which is only 1.88 μg / L. The main reason is that its β phase area ratio and grain size are smaller than those of Examples 1 to 3.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A brass alloy with low lead precipitation, characterized in that: The brass alloy comprises Cu, Zn, doping elements and inevitable impurities, the total mass percentage of all elements is 100%, wherein Cu: 57-63 wt%, doping elements include Pb: 0.1-0.8 wt%, Sn: 0.01-1.2 wt%, Al: 0.001-0.5 wt%, Ni: 0.01-1.0 wt%; the microstructure of the brass alloy comprises α phase and β phase, the morphology of the α phase is mesh-like or dendritic, and the β phase is partially or completely separated by the α phase.

2. The brass alloy with low lead precipitation according to claim 1, characterized in that: In the microstructure of brass alloy, the area proportion of β phase is 8%~36%.

3. The brass alloy with low lead precipitation amount according to claim 1 or 2, characterized in that: In the microstructure of brass alloy, the area of ​​β phase accounts for 8%~20%.

4. The brass alloy with low lead precipitation according to claim 1, characterized in that: The average grain size of the brass alloy is ≤20 μm, and the average size of the Pb particles is ≤2 μm.

5. The brass alloy with low lead precipitation according to claim 1, characterized in that: The zinc equivalent in the brass alloy is 38-44 wt%.

6. The brass alloy with low lead precipitation according to claim 1, characterized in that: The brass alloy further comprises As, and the mass percentage of As is 0.01-0.2 wt%.

7. A method for preparing a brass alloy with low lead precipitation according to any one of claims 1 to 6, characterized in that: The process flow of the preparation method is smelting and casting → peeling of ingot → hot forging → surface treatment → CNC machine tool processing → stress relief annealing; Wherein, the ingredients are prepared and smelted according to the percentage of each component of the brass alloy with low lead precipitation as described in any one of claims 1 to 6; The depth of the peeling of the ingot is 2% to 10% of the thickness of the ingot.

8. The method for preparing a brass alloy with low lead precipitation amount according to claim 7, characterized in that: The smelting temperature is 900-1100° C. After the metal is melted, 0.005-0.03 wt % of a grain refiner based on the total weight of the molten copper is added to the molten copper and the mixture is fully stirred.

9. The method for preparing a brass alloy with low lead precipitation according to claim 7, characterized in that: The initial forging temperature of the hot forging process is 620-700°C, the final forging temperature is 520-600°C, and the temperature of the mold cavity is maintained at 300-380°C during the hot forging process.

10. Use of the brass alloy with low lead precipitate content according to any one of claims 1 to 6 in drinking water valves, water meters, refrigeration valve bodies, and sanitary ware.

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