Lead-free bismuth brass and preparation method thereof

Abstract

The invention discloses lead-free bismuth brass and a preparation method thereof. The lead-free bismuth brass is prepared from the following components: 59.5 to 61.5 weight percent of Cu, 0.5 to 0.7 weight percent of Al, 0.005 to 0.1 weight percent of As, 0.02 to 0.1 weight percent of Sn, 0.05 to 0.2 weight percent of Si, 0.6 to 1.0 weight percent of Bi, 0.05 to 0.15 weight percent of Pb, 0.05 to 0.2 weight percent of Sb and 0.02 to 0.05 weight percent of rare earth elements, wherein the rare earth elements comprise La and Ce; the microstructure comprises an alpha phase, a beta phase, a LaBi phase and a CeBi phase. According to the copper ingot material for the lead-free environment-friendly bathroom, alloy components and a processing technology are improved, the area proportion of the alpha phase, the beta phase, the LaBi phase and the CeBi phase is regulated and controlled, comprehensive optimization of cutting, brittleness and corrosion resistance is achieved, and the requirement for the copper ingot material for the lead-free environment-friendly bathroom in the household bathroom field is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of copper alloy, and particularly relates to a lead-free bismuth brass and a preparation method thereof. BACKGROUND

[0002] Lead brass is generally based on copper and zinc, and a small amount of alloying element lead is added to improve the cutting performance of the alloy. As a category of copper alloying, brass itself has the electrical conductivity and corrosion resistance of copper itself, and the addition of zinc element to the copper matrix makes the brass have high strength, hardness and wear resistance. The leaded brass after alloying has excellent cold and hot working performance, excellent cutting performance and self-lubrication, etc., and can meet the casting, forging, machining, polishing and other processes of various shaped parts, so the leaded brass is widely used in electronic communication, household appliances, aerospace, automobile, hardware decoration, shipbuilding and sanitary and plumbing industries.

[0003] However, with the improvement of environmental awareness, the lead in the sanitary products made of leaded brass is extremely easy to have a certain toxic effect on organisms and human bodies, causing serious physiological diseases. In addition, dezincification corrosion also limits the use range of the structure, so the application scenarios are limited, especially in the field of household bathroom, which is gradually abandoned, and efforts are made to research lead-free copper alloy products.

[0004] At present, the lead-free brass mentioned in the bathroom market mainly includes bismuth brass and silicon brass, which improves the machining performance of the alloy by adding elements Si or Bi similar to the performance of lead. Silicon brass has advantages in corrosion resistance and hot working performance, but the cost is relatively high, the cutting performance is quite different from that of bismuth brass, only 70%-80% of that of leaded brass, the cold working efficiency is low, and the existence of hard silicon in silicon brass causes serious tool wear and low processing efficiency, which needs to be optimized by bismuth and selenium.

[0005] The cutting performance of bismuth brass is close to that of traditional leaded brass, the chip breaking effect is good, the tool wear is small, and the cutting effect is remarkable, but bismuth brass has obvious shortcomings, mainly including (1) material brittleness, due to the insolubility and film forming property of bismuth, the risk of grain boundary brittleness of the material is increased, and the cooling speed is highly sensitive, which is easy to cause cracking; and bismuth brass has a very serious hot shortness phenomenon between 300℃ and 450℃ (medium temperature), and the welded joint in this temperature range is easy to crack, and its reliability is questionable; (2) unstable corrosion resistance, in a chloride ion environment, the bismuth phase and grain boundary are serious dezincification corrosion areas, which seriously affects the stability of the application of the material.

[0006] The invention patent with the publication number CN105925837A discloses an anti-zinc-loss free-cutting brass rod and a production method thereof. The anti-zinc-loss free-cutting brass rod is composed of raw materials with the following mass percentages: Cu 60-66%, Bi 0.1-0.6%, Sn 0.1-0.5%, Fe 0.02-0.07%, Al 0.2-0.8%, modifier <0.0038%, Si 0.2-0.3%, Ni <0.15%, Pb <0.15%, arsenic copper alloy 0.08-0.18%, and the rest is Zn and impurities with a total amount of not more than 0.5%. Although the prior art has obtained the anti-zinc-loss free-cutting brass rod with excellent mechanical properties, high density and good cutting performance by regulating the adding proportion of each element, the performance of the brass alloy is limited, and the prepared brass alloy still has deficiencies in cutting performance, corrosion resistance and low brittleness when used in the household bathroom field. SUMMARY

[0007] In view of the existing problems, the present application provides a lead-free bismuth brass and a preparation method thereof. The lead-free bismuth brass has significant cutting performance, corrosion resistance and low brittleness, and meets the needs of the household bathroom field for lead-free and environmentally friendly bathroom copper ingot materials.

[0008] The lead-free bismuth brass provided by the present application comprises Zn, Cu, Al, As, Sn, Si, Bi, Pb, Sb, rare earth elements and unavoidable impurities, and the sum of the mass percentages of all elements is 100%, wherein Cu is 59.5-61.5wt%, Al is 0.5-0.7wt%, As is 0.005-0.1wt%, Sn is 0.02-0.1wt%, Si is 0.05-0.2wt%, Bi is 0.6-1.0wt%, Pb is 0.05-0.15wt%, Sb is 0.05-0.2wt%, and the rare earth elements include La and Ce. The microstructure of the cross section of the lead-free bismuth brass comprises alpha phase, beta phase, LaBi phase and CeBi phase, wherein the area ratio of the beta phase is 40%-65%, and the LaBi phase and the CeBi phase are dispersedly distributed on the alpha phase and the beta phase.

[0009] The other elements of the lead-free bismuth brass provided by the present application have the following effects: The metal elements silicon Si and antimony Sb are added, silicon belongs to high zinc equivalent element, which can be used to increase the proportion of beta phase, improve the processing performance during hot working process, reduce the risk of cracking during processing, and the addition of silicon can also reduce a certain proportion of bismuth element, which has significant improvement effect on the improvement of overall brittleness problem and corrosion resistance of the material, and the cutting performance can also be better guaranteed, the addition of antimony is mainly used to form intermetallic compound SbBi with bismuth, and weaken the influence of Bi film formation on the grain boundary causing cracking. Therefore, the content of Si in the alloy of the present application is 0.05-0.2wt%, and the content of Sb in the alloy of the present application is 0.05-0.2wt%.

[0010] The metal elements Bi, Sn and As are added, which can be used to inhibit dezincing electrochemical corrosion by improving the electrode potential of the material, thereby improving the dezincing performance, that is, As and Cu 2+ After reaction, AS is formed 3+ and Cu - are inhibited, and Cu 2+ is formed. Since the potential of alpha phase is in the middle of Cu / Cu 2+ , Cu / Cu - potential, and the potential of beta phase is lower than Cu / Cu 2+ , Cu / Cu - potential, the beta phase is preferentially corroded; and Sn can form SnO2 film with passivation effect, which can significantly improve dezincing corrosion and seawater corrosion. Therefore, the content of Bi in the alloy of the present application is 0.6-1.0wt%, the content of Sn in the alloy of the present application is 0.05-0.1wt%, and the content of As in the alloy of the present application is 0.005-0.1wt%.

[0011] The area ratio of alpha phase and beta phase is controlled by the ratio of each alloying element, the alpha phase is a stable phase at low temperature and has strong corrosion resistance; the beta phase has greater brittleness than the alpha phase, and the beta phase is controlled within a suitable range to improve the toughness of lead-free bismuth brass in cooperation with the alpha phase, eliminate residual stress generated during forging process, and avoid stress cracking during service; the addition of rare earth elements La and Ce through alloying design can induce the generation of LaBi phase and CeBi phase as strengthening particles dispersed in the matrix, eliminate the solid solution characteristics of Bi in brass matrix, form a network structure at the grain boundary, and easily cause the increase of material brittleness, the increase of stress in the later stage and the sharp increase of the risk of cracking; through the optimization of the area ratio of alpha phase, beta phase, LaBi phase and CeBi phase, the comprehensive optimization of cutting-brittleness-corrosion resistance is realized. Therefore, the content of rare earth elements in the alloy of the present application is 0.02-0.05wt%.

[0012] Further preferably, the rare earth elements include La and Ce, wherein the proportion of La element is 45%, and the proportion of Ce element is 55%.

[0013] Preferably, the mass ratio of the total mass of Sn and As elements to the mass of Bi element is greater than 0.05.

[0014] Further preferably, the mass ratio of Bi element to Sn element is less than 20.

[0015] Since the atomic radius of Sn is 1.58 Å, the atomic radius of Cu is 1.28 Å, and the atomic radius of Zn is 1.38 Å, by increasing the solid solution ratio of Sn, sufficient lattice distortion can be caused, and then the Bi atoms can obtain more channels to enter the brass matrix, reduce the grain boundary segregation, realize uniform cutting, and weaken the grain boundary brittleness.

[0016] Preferably, the particle number of Bi is greater than 5000 / mm 2 .

[0017] By adjusting the particle number of Bi, the dispersion degree of bismuth element distribution is promoted, the probability of bismuth element forming a network film is reduced, and the brittleness of the material is weakened.

[0018] Preferably, the grain size of the lead-free bismuth brass is 10 μm-40 μm.

[0019] On the other hand, the present application also provides a preparation method of the lead-free bismuth brass, and the process flow of the preparation method comprises: Step one, ingredients are prepared and smelted according to the mass percentage of each component of the lead-free bismuth brass, and copper water is obtained after heat preservation and standing; Step two, aluminum-rare earth blocks are pressed into the copper water according to the proportion, and the slag cleaning agent is uniformly scattered on the surface of the slag, and then the refining agent is pressed into the copper water, after stirring, the furnace temperature is raised and the flame treatment is carried out, then the slag is started to be removed, and the first refining is realized; Step three, after the slag removal is completed, the furnace temperature is lowered, and then the refining agent is pressed into the copper water, after stirring, the furnace temperature is raised and the heat preservation refining is carried out, and the second refining is realized; Step four, after the second refining is completed, the sample is taken for composition analysis and furnace detection, according to the composition analysis and furnace detection results, the copper water composition is adjusted and refined until the copper water meets the discharge requirements; Step five, the copper water meeting the requirements is cast into copper ingot by gravity casting and quality detection, and the copper ingot meeting the quality requirements is annealed and rapidly air-cooled to obtain the lead-free bismuth brass.

[0020] The application realizes secondary refining by designing a staged refining process, preliminarily removing oxides and low-melting-point impurities (such as Bi segregation) in primary refining, deeply deoxidizing by adding refining agents and magnesium blocks, thoroughly purifying the melt, avoiding pores and slag inclusions, and ensuring the purity of copper water; after twice refining, the composition is dynamically controlled, and the yield of finished products is improved through closed-loop quality inspection; further, the copper ingot is produced by gravity casting to prevent shrinkage, pores and cracks from the source, ensure the compactness of the ingot, eliminate the beta phase network structure of the ingot by gradient annealing and rapid cooling, inhibit the segregation of bismuth grain boundary and fix the alpha phase structure, release the casting stress, and directly solve the two major pain points of bismuth brass: grain boundary brittleness (Bi network film) and dezincification corrosion sensitivity (beta phase preferential corrosion), and improve the mechanical and corrosion resistance performance.

[0021] Preferably, in step one, the holding temperature is 1010-1050°C, and the holding time is 5-10 min.

[0022] Optionally, step one specifically comprises: according to the required alloy elements and the proportion, adding the refining agent first, then adding the pure copper raw material in the power frequency furnace, adding the brass scrap, silicon, bismuth, antimony and copper-arsenic alloy into the furnace after melting, pressing the copper foam into the furnace, and adding zinc ingot, tin block, lead block and aluminum ingot after melting, and obtaining the copper water after holding and standing.

[0023] Optionally, the refining agent comprises potassium fluoroborate KBF4 and boron iron, wherein the potassium fluoroborate KBF4 is 40-60 wt%, and the boron iron is 40-50 wt%.

[0024] The refining agent acts on the melt, forms heterogeneous core points, promotes grain refinement during melt solidification, promotes the dispersion degree of Bi element distribution, reduces the probability of Bi element forming a network film, and weakens the brittleness of the material.

[0025] Optionally, the pure copper raw material is copper rice or electrolytic plate, and the brass scrap comprises one or more of common brass block H62 and common brass block H65. The mass ratio of the pure copper raw material to the brass scrap is 0.25-0.52.

[0026] Optionally, the copper foam comprises wire drawing foam and machining foam; and the copper foam accounts for 20%-50% of the total mass of the pure copper raw material, the brass scrap and the copper foam.

[0027] The addition of the copper foam can improve the fluidity of the melt and refine the organizational grain, and uniformize the distribution of Bi and alloy elements.

[0028] Preferably, in step two, the temperature of the furnace temperature rise is 1080-1120°C, and the flame spraying time is 10-60 s.

[0029] Preferably, in step three, after the slag is removed, the temperature of the furnace is reduced to 980-1050 DEG C, the stirring time is 30-40 s, the temperature of the furnace is increased to 1080-1150 DEG C, and the holding time is 1-2 min.

[0030] By using the stage refining process, the purity of the copper liquid is ensured, and during the refining process, the temperature of the furnace is increased, then the fire is sprayed, then the temperature of the furnace is reduced, and then the temperature of the furnace is increased again, so that the impurities are floated to achieve complete slag removal and completely remove the oxides and impurities.

[0031] Further, magnesium blocks are added during the secondary refining process for deoxidation.

[0032] Optionally, in step four, after the secondary refining process is completed, sampling is performed at a position 250 mm below the surface of the copper liquid for component analysis, during the component analysis, the temperature of the copper liquid is reduced to 980-1050 DEG C, and the copper liquid is kept still for more than 30 min, after the component analysis is qualified, the temperature of the copper liquid is increased to 1080-1150 DEG C.

[0033] Preferably, in step four, the furnace front detection includes: A cup test is used to evaluate the polishing quality of the lead-free bismuth brass. A ring flow channel test is used to evaluate the flowability of the copper liquid.

[0034] A polishing test is used to evaluate the overall mirror effect of the lead-free bismuth brass by sampling polishing, and to check the hard points and pores on the surface of the lead-free bismuth brass.

[0035] Further preferably, the detection flow channel of the ring flow channel test is greater than 390 mm.

[0036] Preferably, in step five, the copper ingot is cast by gravity casting, including: the qualified copper liquid enters a distributor through a chute, the distributor uniformly casts the copper liquid into an iron mold, and the distributor rotates to realize a continuous casting process.

[0037] The present application uses a gravity casting process to cast the lead-free bismuth brass, avoids the risk of cracking in low-pressure / high-pressure casting existing in other casting processes, and the designed casting precision of the copper ingot meets the demand of medium-precision components in the bathroom copper ingot, so that the cost-effectiveness is maximized.

[0038] Further preferably, the distributor adopts a 6-hole design, the pouring hole taper is 3-8 DEG, the V-shaped opening of the iron mold is 120-140 DEG, and the taper angle of the iron mold is 5-15 DEG.

[0039] The design of the gravity casting mold directly determines the shrinkage angle of the ingot, and further affects the processing and mechanical properties of the material, so the diverter adopts a porous design and designs a pouring hole taper to make the copper water maintain laminar flow and avoid turbulent flow causing gas entrainment; the V-shaped opening of the iron mold in the above angle range is beneficial to the solidification and shrinkage of the copper water, guides directional solidification to make the lead-free bismuth brass shrinkage uniform, stress release sufficient, and the taper angle of the gradient designed iron mold matches the wall thickness difference, realizes uniform cooling, so that the mold design and cooling are coordinated to meet the standard, the shrinkage angle of the casting and solidification is optimized, and the corrosion resistance of the material is further improved.

[0040] Optionally, the copper water pouring position is 40-50 mm away from the edge.

[0041] The pouring position in the above range makes the slag float to the edge and be discharged, reduces inclusions, and makes the finished product polished without hard points.

[0042] Preferably, in step five, the quality detection standard is that the shrinkage angle is greater than 175°.

[0043] The shrinkage angle is a physical manifestation after the solidification of the ingot, which is used to evaluate the shrinkage behavior during the solidification of the ingot, prevent cracking, shrinkage and other defects caused by shrinkage stress, and the shrinkage angle in the above range can prevent liquid cavity deepening, produce pores and hard points, and also reduce the risk of cracking caused by excessive shrinkage stress.

[0044] Preferably, in step five, the lead-free bismuth brass with qualified quality is subjected to radial annealing, the annealing temperature is 450-510 DEG C, and the annealing time is 3-5 h.

[0045] By annealing treatment in the above parameter range and adopting rapid air cooling when discharging, the beta phase network structure of the ingot and the segregation of the bismuth element are eliminated, stable alpha phase structure is obtained, and the casting stress is also released, avoiding the problem of ingot cracking caused by the superposition of organizational stress and casting stress.

[0046] The application also provides the application of the lead-free bismuth brass in the household and bathroom field.

[0047] Compared with the prior art, the application has the following beneficial effects: The application has significant improvement effects on the improvement of the overall brittleness problem of the lead-free bismuth brass and the improvement of the corrosion resistance, and the cutting performance can also be better guaranteed, realizing the comprehensive optimization of cutting-brittleness-corrosion resistance, and solving the problems of cutting performance, corrosion and brittleness in the household and bathroom field.

[0048] The alloy preparation method provided by the application ensures uniform distribution of grain structures in each part of the lead-free bismuth brass alloy material, promotes consistent metal flow of the alloy material after processing, improves the yield of finished products through closed-loop quality inspection, further produces ingots in a gravity casting manner to prevent shrinkage holes, pores and cracks from the source, ensures the density of the ingots, and significantly improves the mechanical and corrosion resistance of the lead-free bismuth brass alloy material. BRIEF DESCRIPTION OF DRAWINGS Figure 1 Metallographic structure photo of the lead-free bismuth brass prepared in Example 1. DETAILED DESCRIPTION

[0049] The application will be further described in detail below in combination with examples.

[0050] The application provides three examples, and the specific components are shown in Table 1.

[0051] Example 1 The lead-free bismuth brass has the following components: copper (Cu) 60.5%, aluminum (Al) 0.65%, arsenic (As) 0.08%, tin (Sn) 0.08%, silicon (Si) 0.15%, bismuth (Bi) 0.8%, lead (Pb) 0.1%, antimony (Sb) 0.15% and zinc (Zn) balance, (Sn+As) / Bi=0.2, M Bi :M Sn =10.

[0052] Step one: 10 branches of refiner A are added into a 3 t power frequency furnace, the refiner A includes: potassium fluoroborate KBF4 and boron iron, wherein the potassium fluoroborate KBF4 is 40-60 wt%, and the boron iron is 40-50 wt%.

[0053] Then, 1150 kg of 1# copper rice or electrolytic plate is added, after the copper rice or electrolytic plate is completely melted, 450 kg of brass scrap (common brass block H62, H65, etc.), combined silicon, bismuth, antimony and copper arsenic alloy are added into the furnace, after the back material is melted, a plurality of copper powder (mixed with wire drawing powder and machining powder) 600 kg is pressed, after the raw material is melted, 0# zinc ingot, tin block, lead block and aluminum ingot are added, after the raw material in the furnace is completely melted, the temperature is set to 1020℃.

[0054] Step two: after 6 min of holding time, 500 g of aluminum rare earth (aluminum cerium rare earth) is pressed into the aluminum, 2 kg of slag cleaning agent is evenly scattered on the surface of the slag, 2 kg of refining agent is pressed into the copper water, then the furnace temperature is raised to 1080℃, and after 15 s of spraying, the slag is started to be removed, and the first refining is realized. Step three, after the completion of the furnace slag, the temperature is reduced to 1000 °C, and then 2 kg of refining agent is pressed into the copper water using a pressure spoon, stirring for 40 s, the temperature is increased to 1120 °C, and after 1 min of holding refining, magnesium blocks are added to achieve secondary refining; Step four, after the completion of the secondary refining, sampling is performed at 250 mm below the surface of the copper water for composition analysis. After sampling, the temperature is reduced to 1000 °C for 35 min of holding and standing. After the composition is qualified, the temperature is increased to 1120 °C. The polishing quality of the lead-free bismuth brass ingot is evaluated using a spinning cup. The flowability of the copper water is evaluated using a ring-shaped runner. Finally, the overall mirror effect of the lead-free bismuth brass ingot is evaluated by sampling and polishing. Each item that does not meet the requirements needs to be re-refined, the copper water composition is adjusted and refined until the copper water meets the requirements: the runner is detected to be above 390 mm, the shrinkage angle is greater than 175°, the polishing is free of particles, the inner surface of the spinning cup is smooth, there are no wrinkles, and the composition is qualified. The casting can be arranged.

[0055] Step five, lead-free bismuth brass products are produced using gravity casting. After the copper water is melted in the power frequency furnace and is qualified, the furnace is poured. The copper water passes through the chute and enters the distributor. The distributor has a 6-hole design with a hole diameter of 70 mm, a wall thickness of 50 m, and a pouring hole taper of 3°-8°. The distributor uniformly pours the copper water into the iron mold. The distributor rotates at a certain speed to achieve a continuous casting process. The iron mold is designed as 80 mm x 400 mm x 40 mm, with a V-shaped opening of 120°-140° and a taper angle of 5°-15°. The lead-free bismuth brass ingot is cast and then subjected to radial annealing and rapid air cooling. The annealing temperature is 490 °C, and the annealing time is 3 h to obtain the lead-free bismuth brass.

[0056] The spectral composition of the lead-free bismuth brass ingot is measured to verify that the finished lead-free bismuth brass meets the composition requirements. The surface quality of the lead-free bismuth brass is free of residues, has high saturation, and is free of hard points and air hole residues after polishing. The flowability test reaches 3 turns, the runner is 395 mm, and the casting flow performance is good. The grain size of the lead-free bismuth brass is 25 μm, the β phase is 60%, and the shrinkage angle is 177°. The dezincification resistance value is 180 μm / 150 μm / 120 μm / 140 μm / 120 μm, which represents the corrosion depth measured at different measurement positions or repeated samples after the lead-free bismuth brass sample is subjected to dezincification corrosion testing according to ISO 6509 or similar standards. This result shows that the maximum corrosion depth is 180 μm, which is less than the 200 μm standard for bathroom products, indicating that it is qualified. The minimum corrosion depth is 120 μm, indicating that the lead-free bismuth brass ingot has a dense core structure and excellent corrosion resistance. The corrosion depth range is 60 μm (maximum corrosion depth - minimum corrosion depth), indicating good uniformity of the structure. The lead-free bismuth brass sample is placed in a 28% ammonium chloride solution volatilized ammonia (NH3) environment for 72 hours, and the lead-free bismuth brass ingot is observed to be free of cracking, completely solving the problem of grain boundary brittleness, and exceeding the standard of the bathroom industry.

[0057] Example 2 The lead-free bismuth brass composition requires copper (Cu) 61.5%, aluminum (Al) 0.6%, arsenic (As) 0.1%, tin (Sn) 0.09%, silicon (Si) 0.2%, bismuth (Bi) 0.8%, lead (Pb) 0.15%, antimony (Sb) 0.2%, and zinc (Zn) balance, (Sn+As) / Bi=0.23, M Bi :M Sn =8.9.

[0058] Step one: add 10 refiners A in a 3 t power frequency furnace, refiner A includes: potassium fluoroborate KBF4 and boron iron, wherein potassium fluoroborate KBF4: 40-60 wt%, boron iron: 40-50 wt%.

[0059] Then add 1# copper or electrolytic plate 1200 kg, after the copper or electrolytic plate is completely melted, add 450 kg of brass scrap (common brass block H62, H65, etc.), joint silicon, bismuth, antimony and copper arsenic alloy into the furnace, after the return material is melted, then press in a certain amount of copper powder (mixed with wire drawing powder and machining powder) 600 kg, after the raw material is melted, add 0# zinc ingot, tin block, lead block and aluminum ingot, after the furnace raw material is completely melted, carry out heat preservation and standing, and the heat preservation temperature is set at 1020℃.

[0060] Step two: after 5.5 min of heat preservation time, press in 500 g of aluminum rare earth (aluminum cerium rare earth) with a press spoon, evenly sprinkle 2 kg of slag cleaning agent on the surface of the slag, press in 2 kg of refining agent into the copper water, then carry out sufficient stirring, then increase the furnace temperature to 1100℃, spray fire for 25 s, then start slagging to realize primary refining; Step three, after the completion of the furnace liquid surface slagging, reduce the temperature to 1020℃, then press in 2 kg of refining agent into the copper water with a press spoon, stir for 35 s, increase the temperature to 1100℃, after 1 min of heat preservation refining, add magnesium block to realize secondary refining; Step four, after the second refining is completed, sample at 250 mm below the copper liquid surface for composition analysis, after sampling, the temperature is reduced to 1040 °C for 40 min, after the composition is qualified, the temperature is increased to 1140 °C, the lead-free bismuth brass polishing quality is evaluated by cup throwing, the copper liquid fluidity is evaluated by ring flow channel, finally, the polishing of the sample is evaluated for the overall mirror effect of the lead-free bismuth brass, and each item that does not meet the requirements needs to be re-refined, adjust the copper liquid composition and refine until the copper liquid discharge requirements are met: the flow channel is detected before the furnace and is more than 390 mm, the water shrinkage angle is greater than 175°, the polishing is free of particles, the inner surface of the cup is smooth, there is no wrinkle, and the composition is qualified, so that the casting can be arranged.

[0061] Step five, the lead-free bismuth brass product is produced by gravity casting, after the copper liquid is melted in the power frequency furnace, the furnace is poured, the copper liquid enters the distributor through the chute, the distributor is designed with 6 holes, the hole diameter is 70 mm, the wall thickness is 50 m, the pouring hole taper is 3°-8°, the distributor uniformly pours the copper liquid into the iron mold, the distributor rotates at a certain speed to realize a continuous casting process, the iron mold is designed as 80 mm×400 mm×40 mm, the V-shaped opening is 120°-140°, and the taper angle is 5°-15°, and the lead-free bismuth brass ingot is poured to obtain the lead-free bismuth brass, which is then subjected to radial annealing and rapid air cooling treatment, the annealing temperature is 500 °C, and the annealing time is 3 h to obtain the lead-free bismuth brass.

[0062] By measuring the spectral composition of the lead-free bismuth brass, it is verified that the finished lead-free bismuth brass meets the composition requirements, the surface quality of the lead-free bismuth brass is free of residues, the saturation is high, there are no hard points and air hole residues after polishing, the flowability test reaches 3 circles, the flow channel is 415 mm, and the lead-free bismuth brass has good casting flow performance, the grain size of the lead-free bismuth brass is 30 μm, the β phase is 60%, and the water shrinkage angle is 178°. The dezincification resistance value is 150 μm / 140 μm / 170 μm / 130 μm / 150 μm, which represents the corrosion depth measured at different measurement positions or repeated samples after the lead-free bismuth brass sample is subjected to dezincification corrosion test according to ISO 6509 or similar standards. The results show that the maximum corrosion depth is 170 μm, which is less than the 200 μm of the bathroom standard, indicating that it is qualified; the minimum corrosion depth is 130 μm, indicating that the lead-free bismuth brass ingot core organization is compact and has excellent corrosion resistance; the corrosion depth range is 40 μm (maximum corrosion depth-minimum corrosion depth), indicating that the organization uniformity is good; The lead-free bismuth brass sample is placed in an ammonia (NH3) environment volatilized by a 28% ammonium chloride solution for 72 hours, and it is observed that the lead-free bismuth brass ingot does not crack, and the grain boundary brittleness is completely solved, which exceeds the bathroom industry standard.

[0063] Example 3 The composition of lead-free bismuth brass requires copper (Cu) 60.5%, aluminum (Al) 0.6%, arsenic (As) 0.08%, tin (Sn) 0.1%, silicon (Si) 0.1%, bismuth (Bi) 0.9%, lead (Pb) 0.1%, antimony (Sb) 0.1% and zinc (Zn) balance, (Sn+As) / Bi=0.2, M Bi :M Sn =9.

[0064] Step 1: Add 10 tubes of refiner A into a 3 t power frequency furnace. Refiner A includes potassium fluoroborate KBF4 and ferroboron, wherein potassium fluoroborate KBF4: 40-60 wt%, ferroboron: 40-50 wt%.

[0065] Then add 950 kg of 1# copper rice or electrolytic plate. After the copper rice or electrolytic plate is completely melted, add 450 kg of brass scraps (ordinary brass blocks H62, H65, etc.) together with silicon, bismuth, antimony and copper-arsenic alloy into the furnace. After the recycled materials are melted, 600 kg of copper powder (a mixture of wire drawing powder and machined powder) is pressed in. After the raw materials are melted, add 0# zinc ingots, tin blocks, lead blocks and aluminum ingots. After all the raw materials in the furnace are melted, they are kept warm and allowed to stand. The insulation temperature is set at 1030℃.

[0066] Step 2: After the holding time is 7 minutes, 500 g of aluminum rare earth (aluminum cerium rare earth) is pressed into the slag with a pressing spoon, a 2 kg bag of slag cleaning agent is evenly sprinkled on the slag surface, a 2 kg bag of refining agent is pressed into the copper water, and then fully stirred. Then the furnace temperature is raised to 1110 ° C, and after 40 seconds of spraying fire, the slag is started to be removed to achieve one-time refining; Step 3: After the furnace liquid surface slag is beaten, the temperature is lowered to 1010 ° C, and then 2 kg of refining agent is pressed into the copper water using a pressure spoon, stirred for 40 seconds, and the temperature is raised to 1140 ° C. After heat preservation and refining for 1.5 minutes, magnesium blocks are added to achieve secondary refining; Step 4: After the secondary refining is completed, samples are taken 250 mm below the copper liquid surface for composition analysis. After the sampling is completed, the temperature is reduced to 1010°C and kept still for 40 minutes during the composition analysis. After the composition is qualified, the temperature is raised to 1130°C, and the polishing quality of the copper ingot is evaluated by a throwing cup, and the fluidity of the copper water is evaluated by an annular flow channel. Finally, samples are taken and polished to evaluate the overall mirror effect of the copper ingot. If any of the items does not meet the requirements, secondary refining is required again, the copper water composition is adjusted and refined until the copper water meets the requirements for discharge from the furnace: the flow channel in front of the furnace is more than 390 mm, the shrinkage elevation angle is greater than 175°, there are no particles in the polishing, the inner surface of the throwing cup is smooth and wrinkle-free, and the composition is qualified, then casting can be arranged.

[0067] Step five, the copper ingot product is produced by gravity casting, after the copper water is melted in the power frequency furnace, the furnace is poured, the copper water enters the distributor through the chute, the distributor adopts 6-hole design, the hole diameter is 70 mm, the wall thickness is 50 m, the pouring hole taper is 3-8°, the distributor uniformly pours the copper water into the iron mold, the distributor rotates at a certain speed to realize the continuous pouring process, the iron mold is designed as 80 mm*400 mm*40 mm, the V-shaped opening is 120°-140°, and the taper angle is 5°-15°, and the copper ingot is poured, Then, radial annealing and rapid air cooling treatment are carried out, the annealing temperature is 500℃, the annealing time is 3 h, and the lead-free bismuth brass is obtained.

[0068] By measuring the spectral composition of the lead-free bismuth brass ingot, it is verified that the finished lead-free bismuth brass meets the composition requirements, the surface quality of the lead-free bismuth brass is free of residues, the saturation is high, there are no hard points and pores after polishing, the flowability test reaches 4 circles, the flow channel is 425 mm, and the lead-free bismuth brass has good casting flow performance, the grain size of the lead-free bismuth brass is 25 μm, the β phase is 55%, and the shrinkage angle is 178°; The anti-zinc stripping value is 120 μm / 150 μm / 140 μm / 140 μm / 120 μm, which represents that after the sample of the lead-free bismuth brass is subjected to zinc stripping corrosion test according to ISO 6509 or a similar standard, the corrosion depth measured at different measurement positions or repeated samples, the result shows that the maximum corrosion depth is 150 μm, which is less than 200 μm of the bathroom standard, which indicates that it is qualified; the minimum corrosion depth is 120 μm, which indicates that the core organization of the copper ingot is compact and has excellent corrosion resistance; the corrosion depth range is 30 μm (maximum corrosion depth-minimum corrosion depth), which indicates that the organization uniformity is good; The copper ingot sample is placed in an ammonia (NH3) environment volatilized by a 28% ammonium chloride solution for 72 hours, and it is observed that the copper ingot does not crack, and the grain boundary brittleness is completely solved, which exceeds the bathroom industry standard.

[0069] Table 1 Chemical composition of examples For the three examples prepared, the microstructure is tested respectively, and the results are recorded in Table 2. The β phase area ratio is observed under a metallographic microscope and measured by a metallographic analysis software.

[0070] As Figure 1 The metallographic microstructure of Example 1 is shown, and by the above metallographic analysis, it can be obtained that the distribution of each organization phase is uniform, the LaBi phase and the CeBi phase are dispersedly distributed on the α phase and the β phase, and the β phase area ratio is controlled in the range of 40%-65%, which meets the requirements of the present application.

[0071] Table 2 Microstructure test results of examples The organization of the material determines the performance, and according to the results in Table 2, by improving the design of alloy composition and improving the processing technology, the area ratio of the β phase formed by the examples is 40%-65%, compared with the comparative examples, LaBi phase and CeBi phase will be formed.

[0072] By adjusting the area ratio of the microstructure, the solid solution characteristics of Bi in the brass matrix can be eliminated, a network structure is formed at the grain boundary, and the material brittleness is increased, the post-organization stress is increased, and the risk of cracking is also increased. The phenomenon is eliminated, and the comprehensive optimization of cutting-brittleness-corrosion resistance is realized.

[0073] The performance of the three examples prepared was tested respectively, and the results are recorded in Table 3.

[0074] Anti-zinc loss value: tested according to ISO 6509 or similar standard.

[0075] Ammonia fumigation: place the copper ingot sample in an ammonia gas (NH3) environment volatilized from a 28% ammonium chloride solution for 72 hours, and observe whether the copper ingot cracks.

[0076] Table 3 Test results of performance of finished products of examples According to the results in Table 4, the copper water of the examples has good flowability, and the copper water quality screening can be better performed before the furnace. The length of the flow channel is ≥390 mm and there is no hard point, and after meeting the conditions, the casting greatly improves the yield. After casting, the shrinkage angle of the measured ingot is greater than 175°, ensuring that the finished product has no pores and cracks. Through the anti-zinc loss value and the EU ammonia fumigation test, the results show that: the core organization of the copper ingot is dense, the organization uniformity is good, the ammonia fumigation test lasts for 72 hours, and the copper ingot does not crack, has excellent corrosion resistance, exceeds the standard of the bathroom industry, and solves the problems of cutting performance, corrosion and brittleness in the current home bathroom field.

Claims

1. A lead-free bismuth brass, characterized in that: Comprising Zn, Cu, Al, As, Sn, Si, Bi, Pb, Sb, rare earth elements and unavoidable impurities, the sum of the mass percentages of all elements being 100%, wherein Cu: 59.5-61.5wt%, Al: 0.5-0.7wt%, As: 0.005-0.1wt%, Sn: 0.02-0.1wt%, Si: 0.05-0.2wt%, Bi: 0.6-1.0wt%, Pb: 0.05-0.15wt%, Sb: 0.05-0.2wt%, rare earth elements: 0.02-0.05wt%, wherein the rare earth elements include La and Ce; The microstructure of the cross section of the lead-free bismuth brass includes α phase, β phase, LaBi phase and CeBi phase, wherein the β phase accounts for 40%-65% of the area, and the LaBi phase and CeBi phase are dispersed on the α phase and β phase.

2. The lead-free bismuth brass according to claim 1, characterized in that: The mass ratio of the sum of the total mass of Sn and As elements to the mass of Bi element is greater than 0.05; And the mass ratio of Bi element to Sn element is less than 20.

3. The lead-free bismuth brass according to claim 1, characterized in that: The number of Bi particles is greater than 5000 / mm 2 .

4. The lead-free bismuth brass according to claim 1, characterized in that: The grain size of the lead-free bismuth brass is 10 μm-40 μm.

5. A method for preparing lead-free bismuth brass according to any one of claims 1 to 4, characterized in that: The process flow of the preparation method includes: Step 1: preparing and smelting the lead-free bismuth brass according to the mass percentage of each component, and then keeping the mixture warm and allowing it to stand to obtain molten copper; Step 2: Press the aluminum rare earth block into the copper water according to the proportion, and evenly sprinkle the slag cleaning agent on the slag surface, then press the refining agent into the copper water, stir, raise the furnace temperature and perform flame treatment, then start to remove the slag to achieve one-step refining; Step 3: After the slag is removed, the furnace temperature is lowered, and the refining agent is pressed into the copper liquid. After stirring, the furnace temperature is raised and kept warm for refining to achieve secondary refining. Step 4: After the secondary refining is completed, samples are taken for component analysis and furnace testing. According to the results of the component analysis and furnace testing, the copper liquid composition is adjusted and refined until the copper liquid meets the requirements for discharge from the furnace; Step 5: The molten copper that meets the requirements is cast into copper ingots by gravity casting and quality inspection is carried out. The copper ingots that meet the quality requirements are annealed and rapidly air-cooled to obtain lead-free bismuth brass.

6. The preparation method according to claim 5, characterized in that In step 1, the holding temperature is 1010° C.-1050° C., and the holding time is 5 min-10 min; In step 2, the furnace temperature is raised to 1080°C-1120°C, and the flame spraying time is 10 s-60 s; In step 3, after the slag is removed, the furnace temperature is lowered to 980°C-1050°C, the furnace temperature is raised to 1080°C-1150°C, and the holding time is 1 min-2 min.

7. The preparation method according to claim 5, characterized in that In step 4, the furnace front detection includes: The cup-throwing test is used to evaluate the polishing quality of lead-free bismuth brass; Annular flow channel test, used to evaluate the fluidity of molten copper, where the test flow channel of the annular flow channel test is greater than 390 mm; Polishing test is used to evaluate the overall mirror effect of lead-free bismuth brass by polishing samples and to check the hard spots and pores on the surface of lead-free bismuth brass.

8. The preparation method according to claim 5, characterized in that The copper ingots are cast by gravity casting, which includes: molten copper that meets the requirements enters the diverter through a chute, the diverter evenly casts the molten copper into the interior of the iron mold, and the diverter rotates to achieve a continuous casting process, wherein the diverter adopts a 6-hole design, the casting hole taper is 3°-8°; the iron mold has a V-shaped opening of 120°-140°, and the iron mold taper angle is 5°-15°.

9. The preparation method according to claim 5, characterized in that In step 5, the quality inspection standard is that the shrinkage elevation angle is greater than 175°.

10. The preparation method according to claim 5, characterized in that In step 5, the qualified lead-free bismuth brass is subjected to radial annealing at a temperature of 450° C. to 510° C. for a time of 3 h to 5 h.

Images