Corrosion-resistant lead-free brass alloy and method for manufacturing the same

Abstract

This invention belongs to the field of copper alloy technology, specifically disclosing a corrosion-resistant lead-free brass alloy and its preparation method. The elemental composition of the corrosion-resistant lead-free brass alloy provided by this invention includes: Zn 25%~40%, Si 0.8%~2.5%, Mn 0.3%~2%, Fe 0.01%~1.5%, Mg 0.01%~0.1%, Cr 0.01%~0.2%, La 0.01%~0.2%, Ce 0.01%~0.2%, Sc 0.01%~0.2%, with the balance being Cu and unavoidable impurities. This invention significantly improves the mechanical properties and corrosion resistance of the brass alloy through the synergistic effect of multiple doping elements. Furthermore, by optimizing the Si and Mn element ratio and preparation process, it promotes the formation and uniform dispersion of the Mn5Si3 phase, greatly enhancing the alloy's corrosion resistance in chloride-containing media.

Description

Technical Field

[0001] This invention relates to the field of copper alloy technology, and in particular to a corrosion-resistant lead-free brass alloy and its preparation method. Background Technology

[0002] Traditional brass alloys are widely used in various industrial fields due to their excellent comprehensive properties. However, the lead (Pb) element they commonly contain poses a threat to the environment and human health, making lead-free production an inevitable trend in industry development. In the process of achieving lead-free production, the corrosion resistance of the alloys often faces challenges, especially in corrosive media containing chloride ions, where their corrosion resistance is often insufficient to meet the requirements of harsh operating conditions such as marine environments and chemical systems. Therefore, how to systematically improve the corrosion resistance of lead-free brass through composition design and process optimization has become a key issue in current technological research and development.

[0003] Microalloying technology has proven to be an effective approach to improve the corrosion resistance of lead-free brass. Among these, the addition of silicon (Si), iron (Fe), chromium (Cr), and some rare earth elements has shown potential. The addition of Si can form a stable silicon phase, which helps refine the microstructure and strengthen the matrix; Fe exists as a fine, dispersed precipitate phase, which can effectively refine grains, inhibit grain growth, and improve the uniformity of the alloy's microstructure. However, systematic research on the synergistic effects of Si, Fe, and other elements on the corrosion resistance of lead-free brass is still relatively limited. The optimal ratio of each element and the mutual reinforcement mechanism are not yet clear, which restricts the development of corrosion-resistant lead-free brass.

[0004] Therefore, there is a need to develop a lead-free brass alloy with uniform microstructure, stable surface, and outstanding corrosion resistance by scientifically controlling the content of alloying elements and matching it with a suitable preparation process, as well as its efficient preparation method. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a corrosion-resistant lead-free brass alloy. The copper alloy of this invention possesses excellent mechanical properties and corrosion resistance without the addition of lead.

[0006] The present invention also provides a method for preparing the copper alloy.

[0007] In a first aspect, the present invention provides a corrosion-resistant lead-free brass alloy, comprising, by weight percentage: Zn 25%~40%, Si 0.8%~2.5%, Mn 0.3%~2%, Fe 0.01%~1.5%, Mg 0.01%~0.1%, Cr 0.01%~0.2%, La 0.01%~0.2%, Ce 0.01%~0.2%, Sc 0.01%~0.2%, with the balance being Cu and unavoidable impurities.

[0008] This invention significantly improves the corrosion resistance of lead-free brass by using doping and rational proportioning of Fe, Mg, Cr, La, Ce, and Sc elements. Among them, Fe can act as a heterogeneous nucleus to refine grains and improve corrosion uniformity, Mg has the effect of purifying the melt, Cr specifically enhances pitting corrosion resistance in chloride ion environment, and rare earth elements La, Ce, and Sc are used to purify grain boundaries and improve oxide film adhesion. The elements work together to form a multi-scale second-phase strengthening system, achieving comprehensive optimization of mechanical properties and corrosion resistance.

[0009] Furthermore, this invention also generates fine Mn5Si3 intermetallic compounds by doping with appropriate amounts of Si and Mn elements under specific process conditions. In addition to having high hardness, high thermal stability and excellent wear resistance, this compound phase can also achieve the effects of pinning dislocations and refining grains. Moreover, this invention also found that it can further promote the formation of a dense passivation film on the surface of brass alloys, thereby significantly improving the corrosion resistance of the alloys.

[0010] According to some embodiments of the present invention, the elemental composition of the copper alloy, by weight percentage, includes: Zn 30%~35%, Si 1%~2%, Mn 0.5%~1.5%, Fe 0.05%~1%, Mg 0.02%~0.1%, Cr 0.01%~0.1%, La 0.02%~0.1%, Ce 0.02%~0.1%, Sc 0.02%~0.1%, with the balance being Cu and unavoidable impurities.

[0011] According to some embodiments of the present invention, the total mass percentage of Mg, Cr, La, Ce and Sc is 0.1% to 0.3%.

[0012] According to some embodiments of the present invention, in addition to the α phase and β phase, the microstructure of the corrosion-resistant lead-free brass alloy contains dispersed Mn-Si intermetallic compound particles (Mn5Si3), with particle sizes in the nanometer or submicrometer range.

[0013] According to some embodiments of the present invention, the corrosion-resistant lead-free brass alloy has a hardness ≥250 HV, and after immersion in 3.5% NaCl solution for 720 h, its self-corrosion potential ≥-315 mV (vs. SCE) and self-corrosion current density ≤0.90 μA / cm². 2 The corrosion rate is ≤7.50μm / a.

[0014] A second aspect of the present invention provides a method for preparing a corrosion-resistant lead-free brass alloy as described in the first aspect of the present invention, comprising the following steps:

[0015] S1. According to the weight percentage of the elemental composition, the raw materials of copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium and scandium are mixed, heated and smelted to obtain a melt, cooled and then zinc source is added, and cast to obtain an ingot.

[0016] S2. The ingot is subjected to homogenization treatment, multi-pass hot rolling, cold rolling and recrystallization annealing treatment in sequence to obtain the corrosion-resistant lead-free brass alloy.

[0017] According to some embodiments of the present invention, the raw materials include pure or intermediate alloys of each element, wherein the intermediate alloys include copper-magnesium alloys, copper-chromium alloys, copper-lanthanum alloys, copper-cerium alloys, or copper-scandium alloys.

[0018] According to some embodiments of the present invention, in step S1, the surface of the raw material is clean, free of oil and severe oxidation, and is preheated and dried at 200~250 °C.

[0019] According to some embodiments of the present invention, in step S1, the smelting method includes any one of conventional atmospheric smelting, inert atmosphere protected smelting, and vacuum induction smelting; the heating smelting temperature is 1050~1250℃; charcoal is used as a covering agent for the melt during the heating smelting process; and the cooling is to reduce the temperature to 750~850℃.

[0020] According to some embodiments of the present invention, in step S1, after adding the zinc source, the melt is stirred and allowed to stand for 1 to 5 minutes before slag is removed. The casting temperature is 700 to 800°C, and the melt is poured into a preheated mold. After solidification, the melt is cooled by water to obtain an alloy ingot.

[0021] According to some embodiments of the present invention, in step S2, the homogenization process is as follows: the ingot is kept at 650~850℃ for 1~6 hours, followed by furnace cooling or air cooling.

[0022] The purpose of this invention is to eliminate dendritic segregation through homogenization treatment, and to promote the full diffusion and uniform distribution of elements such as Si, Mn, Fe, Mg, Cr, La, Ce, and Sc, so as to lay the microstructure foundation for subsequent hot working and the formation of a uniform and dispersed corrosion-resistant strengthening phase.

[0023] According to some embodiments of the present invention, in step S2, the method of multi-pass hot rolling is as follows: heating the ingot to 750~850°C, holding it at that temperature for 0.5~2 hours, and then performing 3~6 hot rolling passes;

[0024] The initial rolling temperature is 770~810℃, and the final rolling temperature is 650~680℃, with the rolling temperature gradually decreasing from the initial to the final pass. The deformation of the initial, intermediate, and final hot rolling passes is controlled at 5%~20%, 15%~20%, and 5%~10%, respectively, with a total hot rolling deformation of 50%~70%. During the hot rolling process, the rolled piece is reheated after every 2~3 passes at a temperature of 700~750℃. After hot rolling, the piece is immediately water-cooled to room temperature.

[0025] This invention aims to thoroughly break down the casting structure through a multi-pass hot rolling process, achieve dynamic recrystallization, significantly refine the grains, and promote the dispersed precipitation of the Mn5Si3 phase.

[0026] According to some preferred embodiments of the present invention, the initial rolling temperature of the first hot rolling (initial pass) is 770°C to 800°C, and the deformation per pass is 5% to 20%. This step aims to initially break up the as-cast structure and brittle eutectic phase, while avoiding edge cracking of the billet due to excessive deformation per pass. When the initial rolling temperature is below 770°C or the deformation per pass exceeds 20%, the material is prone to macroscopic cracking in a low plasticity state. When the deformation is less than 5%, the effect of breaking up the as-cast structure is significant, affecting the subsequent refining effect.

[0027] According to some preferred embodiments of the present invention, the initial rolling temperature of the second hot rolling treatment is 730°C to 760°C, the deformation per pass is 15% to 20%, and the cumulative total deformation reaches 35% to 45%. This pass is the main dynamic recrystallization stage. By introducing high-density dislocations at high temperatures through a large deformation, complete dynamic recrystallization is promoted, and the grains are significantly refined. At the same time, this stage is conducive to the diffusion of elements such as Si and Mn and promotes the initial precipitation of the Mn5Si3 phase. If the temperature is lower than 730°C or the deformation is insufficient, the recrystallization is insufficient, the microstructure is uneven, and the amount of Mn5Si3 phase precipitated is small and unevenly distributed. If the deformation exceeds 20%, it may lead to a surge in rolling force and loss of control over the shape of the sheet.

[0028] According to some preferred embodiments of the present invention, the initial rolling temperature of the third hot rolling process is 700°C to 730°C, the deformation per pass is 10% to 15%, and the cumulative total deformation reaches 50% to 60%. This pass aims to further homogenize the microstructure, compact the material, and control the final rolling temperature and sheet shape; through appropriate deformation, while maintaining a fine-grained structure, it promotes the dispersed distribution of the Mn5Si3 phase; if the initial rolling temperature is below 700°C, it will lead to severe work hardening, which is not conducive to subsequent cold rolling; if the deformation is not properly distributed, it is easy to cause anisotropy in the sheet properties.

[0029] According to some preferred embodiments of the present invention, the final rolling temperature of the fourth and subsequent finishing hot rolling processes is strictly controlled at 650°C to 680°C, with a single-pass deformation of 5% to 10%, ultimately achieving a total hot rolling deformation of 60% to 70%. The main purpose of this stage is to precisely control the final dimensions and surface quality of the sheet metal, and to form a fine equiaxed grain structure with preferred orientation through plastic deformation near the recrystallization temperature. Water cooling must be performed immediately after final rolling to suppress grain growth and fix the supersaturation of solute atoms.

[0030] According to some preferred embodiments of the present invention, the intermediate reheating treatment is performed after every 2 to 3 passes, with a reheating temperature of 700°C to 750°C and a holding time of 10 to 20 minutes. This treatment can effectively release accumulated work hardening, restore the high-temperature plasticity of the material, prevent cracks from occurring during multi-pass continuous rolling, and provide conditions for static recrystallization and uniform element diffusion. If the reheating temperature or time is insufficient, work hardening cannot be fully eliminated; if the reheating temperature is too high or the time is too long, it may lead to excessive grain growth and strength loss.

[0031] According to some embodiments of the present invention, the cold rolling is performed by cold rolling the hot-rolled workpiece at room temperature, with a deformation of 10% to 30%. The main function of cold rolling is to introduce high-density dislocations, achieve deformation strengthening, and provide sufficient stored energy for subsequent recrystallization annealing.

[0032] According to some embodiments of the present invention, the recrystallization annealing is performed by holding the cold-rolled workpiece at 500℃~700℃ for 0.5~1.5h, followed by air cooling or furnace cooling. The purpose of recrystallization annealing is to eliminate the work hardening caused by cold rolling, obtain a uniform and fine equiaxed crystal structure through complete recrystallization, and stabilize the dispersed Mn5Si3 phase, ultimately enabling the alloy to possess both good mechanical properties and corrosion resistance.

[0033] This invention optimizes and improves the preparation process of the brass alloy. Through multi-pass hot rolling and cold rolling, the microstructure is refined and induced, which can significantly promote the uniform and dispersed precipitation of the Mn5Si3 intermetallic compound phase. Combined with crystallization annealing, uniform fine grains are obtained and the precipitated phase is stabilized. The Mn5Si3 phase formed by this process helps to induce uniform corrosion through the microcathode effect during the corrosion process, and induces the formation of a dense and stable corrosion product film on the surface, thereby greatly improving the corrosion resistance of the alloy in chloride ion-containing media.

[0034] The beneficial effects of this invention are:

[0035] 1) This invention significantly improves the corrosion resistance of lead-free brass through synergistic microalloying of Si, Mn, and Fe, supplemented by Mg, Cr, La, Ce, and Sc elements, combined with multi-stage thermomechanical treatment. During heat treatment, Si and Mn form micron- or submicron-sized Mn5Si3 intermetallic compounds, dispersed throughout the matrix, which pin dislocations and promote the formation of a dense passivation film on the surface. Fe acts as a heterogeneous nucleation core to refine grains and improve corrosion uniformity. Mg purifies the melt; Cr enhances pitting corrosion resistance under chloride ion conditions; and rare earth elements purify grain boundaries and improve oxide film adhesion. The synergistic effect of these elements forms a multi-scale second-phase strengthening system, achieving comprehensive optimization of mechanical properties and corrosion resistance.

[0036] 2) This invention reveals the key enhancing effect of Mn5Si3 on the corrosion resistance of lead-free brass. By optimizing the process, the uniform and dispersed precipitation of the Mn5Si3 phase can be significantly promoted. This phase not only has high hardness and high thermal stability, but also induces uniform corrosion through the microcathode effect during the corrosion process, and induces the formation of a dense and stable corrosion product film on the surface, thereby greatly improving the corrosion resistance of the alloy in chloride ion-containing media.

[0037] 3) The preparation process of this invention adopts a synergistic control path of melting, homogenization heat treatment, deformation processing, and recrystallization annealing: melting ensures full alloying of elements; homogenization eliminates segregation and promotes element diffusion; multi-pass hot rolling and cold rolling refine the microstructure and induce the precipitation of Mn5Si3 phase; recrystallization annealing obtains uniform fine grains and stabilizes the precipitated phases. This process avoids expensive steps, has a stable yield, and is environmentally friendly.

[0038] 4) The corrosion-resistant lead-free brass alloy prepared by this invention exhibits excellent and stable corrosion resistance, meeting the application requirements under harsh environments: in a full immersion corrosion test simulating 3.5% NaCl solution, its average corrosion rate is lower than that of conventional lead-free brass and some leaded brasses; its hardness is not lower than 250 HV, its self-corrosion potential is not lower than -315 mV (vs. SCE), and its self-corrosion current density is not higher than 0.90 μA / cm. 2 The corrosion rate is no higher than 7.50 μm / a, and the comprehensive mechanical properties meet the requirements of structural components. This alloy is suitable for harsh corrosive environments such as marine engineering, chemical fluid transportation, coastal construction and high-performance sanitary ware, and has broad application prospects.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0041] Figure 1The image shows the metallographic microstructure of the corrosion-resistant lead-free brass alloy prepared in Example 5 of this invention.

[0042] Figure 2 The image shows the surface morphology of the corrosion-resistant lead-free brass alloy prepared in Example 5 of this invention after immersion in 3.5% NaCl solution for 720 hours.

[0043] Figure 3 This is a metallographic microstructure of the lead-free brass alloy prepared in Comparative Example 5 of the present invention. Detailed Implementation

[0044] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0045] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0046] Example 1

[0047] This embodiment provides a corrosion-resistant lead-free brass alloy and its preparation method.

[0048] The elemental composition of this brass alloy, by weight percentage, is: Zn 33%, Si 1.2%, Mn 1.0%, Fe 0.8%, Mg 0.03%, Cr 0.02%, La 0.03%, Ce 0.03%, Sc 0.02%; the remainder is Cu and unavoidable impurities, with a total impurity content of <0.1%.

[0049] The specific preparation steps are as follows:

[0050] 1) Prepare the ingredients according to the weight percentage of each element. Add copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium, and scandium to the heating furnace and melt them at a melting temperature of 1250℃. Cover the surface of the melt with charcoal to prevent oxidation. After complete melting, reduce the temperature of the melt to 850℃, add zinc source, stir until it is completely melted, let it stand for 3 minutes, remove the slag, and pour it into a mold preheated to 200℃ at a pouring temperature of 800℃. After solidification, cool it with water to obtain the alloy ingot.

[0051] The purity of each metal raw material is ≥99.9%;

[0052] 2) Place the alloy ingot in a heat treatment furnace and hold it at 750°C for 2 hours, then air cool it.

[0053] 3) Place the alloy treated in step 2) into a heat treatment furnace and hold it at 800℃ for 1 hour, followed by multiple hot rolling processes: the first hot rolling process has an initial rolling temperature of 780℃ and a deformation of 10%; the second hot rolling process has an initial rolling temperature of 750℃ and a deformation of 15%, with a cumulative deformation of 25%; the third hot rolling process has an initial rolling temperature of 730℃ and a deformation of 15%, with a cumulative deformation of 40%.

[0054] 4) Place the alloy treated in step 3) into a heat treatment furnace for reheating at 700℃ for 15 minutes; then perform the fourth hot rolling process at an initial rolling temperature of 680℃, a deformation amount of 12%, and a cumulative deformation amount of 52%, followed by immediate water cooling to room temperature.

[0055] 5) After cleaning the surface to remove the oxide scale, the hot-rolled sheet obtained in step 4) is cold-rolled at room temperature with a deformation of 20%.

[0056] 6) The alloy sample obtained after step 5) is subjected to recrystallization annealing, held at 550℃ for 1 hour, and then cooled by air cooling to obtain a corrosion-resistant lead-free brass alloy.

[0057] Example 2

[0058] This embodiment provides a corrosion-resistant lead-free brass alloy and its preparation method.

[0059] The elemental composition of this brass alloy, by weight percentage, is: Zn 32%, Si 1.8%, Mn 1.2%, Fe 0.6%, Mg 0.04%, Cr 0.03%, La 0.04%, Ce 0.03%, Sc 0.03%; the remainder is Cu and unavoidable impurities, with a total impurity content of <0.1%.

[0060] The specific preparation steps are as follows:

[0061] 1) Prepare the ingredients according to the weight percentage of each element. Add copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium, and scandium to the heating furnace and melt them at a melting temperature of 1120℃. Cover the surface of the melt with charcoal to prevent oxidation. After complete melting, reduce the temperature of the melt to 770℃, add zinc source, stir until it is completely melted, let it stand for 3 minutes, remove the slag, and pour it into a mold preheated to 200℃ at a pouring temperature of 720℃. After solidification, cool it with water to obtain the alloy ingot.

[0062] 2) Place the alloy ingot in a heat treatment furnace and hold it at 800℃ for 3 hours, then air cool it.

[0063] 3) Place the alloy treated in step 2) into a heat treatment furnace and hold it at 800℃ for 2 hours, followed by multiple hot rolling processes: the first hot rolling process has an initial rolling temperature of 770℃ and a deformation of 12%; the second hot rolling process has an initial rolling temperature of 750℃ and a deformation of 15%, with a cumulative deformation of 27%; the third hot rolling process has an initial rolling temperature of 720℃ and a deformation of 13%, with a cumulative deformation of 40%.

[0064] 4) Place the alloy treated in step 3) into a heat treatment furnace for reheating at 700℃ for 10 minutes; then perform the fourth hot rolling process with an initial rolling temperature of 680℃, a deformation amount of 12%, and a cumulative deformation amount of 52%; perform the fifth hot rolling process with an initial rolling temperature of 650℃, a deformation amount of 8%, and a cumulative deformation amount of 60%, and then immediately water cool to room temperature.

[0065] 5) After cleaning the surface to remove the oxide scale, the hot-rolled sheet obtained in step 4) is cold-rolled at room temperature, with a deformation of 15%;

[0066] 6) The alloy sample obtained after step 5) is subjected to recrystallization annealing, held at 550℃ for 1.2h, and then air-cooled to obtain a corrosion-resistant lead-free brass alloy.

[0067] Example 3

[0068] This embodiment provides a corrosion-resistant lead-free brass alloy and its preparation method.

[0069] The elemental composition of this brass alloy, by weight percentage, is: Zn 34%, Si 1.5%, Mn 1.5%, Fe 0.4%, Mg 0.02%, Cr 0.02%, La 0.02%, Ce 0.04%, Sc 0.02%; the remainder is Cu and unavoidable impurities, with a total impurity content of <0.1%.

[0070] The specific preparation steps are as follows:

[0071] 1) Prepare the ingredients according to the weight percentage of each element. Add copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium, and scandium to the heating furnace and melt them at a melting temperature of 1180℃. Cover the surface of the melt with charcoal to prevent oxidation. After complete melting, reduce the temperature of the melt to 790℃, add zinc source, stir until it is completely melted, let it stand for 2 minutes, remove the slag, and pour it into a mold preheated to 200℃ at a pouring temperature of 770℃. After solidification, cool it with water to obtain the alloy ingot.

[0072] 2) Place the alloy ingot in a heat treatment furnace and hold it at 750°C for 3 hours, then air cool it.

[0073] 3) Place the alloy treated in step 2) into a heat treatment furnace and hold it at 820℃ for 0.8 hours, followed by multiple hot rolling processes: the first hot rolling process has an initial rolling temperature of 800℃ and a deformation amount of 15%; the second hot rolling process has an initial rolling temperature of 760℃ and a deformation amount of 15%, with a cumulative deformation amount of 30%; the third hot rolling process has an initial rolling temperature of 720℃ and a deformation amount of 15%, with a cumulative deformation amount of 45%.

[0074] 4) Place the alloy treated in step 3) into a heat treatment furnace for reheating at 700℃ for 20 minutes; then perform the fourth hot rolling process with an initial rolling temperature of 670℃, a deformation amount of 15%, and a cumulative deformation amount of 60%; perform the fifth hot rolling process with an initial rolling temperature of 650℃, a deformation amount of 5%, and a cumulative deformation amount of 65%, and then immediately water cool to room temperature.

[0075] 5) After cleaning the surface to remove the oxide scale, the hot-rolled sheet obtained in step 4) is cold-rolled at room temperature with a deformation of 10%.

[0076] 6) The alloy sample obtained after step 5) is subjected to recrystallization annealing, held at 570℃ for 1 hour, and then air-cooled to obtain a corrosion-resistant lead-free brass alloy.

[0077] Example 4

[0078] This embodiment provides a corrosion-resistant lead-free brass alloy and its preparation method.

[0079] The elemental composition of this brass alloy, by weight percentage, is: Zn 31%, Si 2.0%, Mn 0.8%, Fe 1.0%, Mg 0.03%, Cr 0.03%, La 0.03%, Ce 0.02%, Sc 0.02%; the remainder is Cu and unavoidable impurities, with a total impurity content of <0.1%.

[0080] The specific preparation steps are as follows:

[0081] 1) Prepare the ingredients according to the weight percentage of each element. Add copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium, and scandium to the heating furnace and melt them at a melting temperature of 1100℃. Cover the surface of the melt with charcoal to prevent oxidation. After complete melting, reduce the temperature of the melt to 760℃, add zinc source, stir until it is completely melted, let it stand for 2 minutes, remove the slag, and pour it into a mold preheated to 200℃ at a pouring temperature of 720℃. After solidification, cool it with water to obtain the alloy ingot.

[0082] 2) Place the alloy ingot in a heat treatment furnace and hold it at 650°C for 6 hours, then air cool it.

[0083] 3) Place the alloy treated in step 2) into a heat treatment furnace and hold it at 780℃ for 1.5 hours, followed by multiple hot rolling processes: the first hot rolling process has an initial rolling temperature of 770℃ and a deformation of 12%; the second hot rolling process has an initial rolling temperature of 750℃ and a deformation of 13%, with a cumulative deformation of 25%; the third hot rolling process has an initial rolling temperature of 730℃ and a deformation of 15%, with a cumulative deformation of 40%.

[0084] 4) Place the alloy treated in step 3) into a heat treatment furnace for reheating at 700℃ for 20 minutes; then perform the fourth hot rolling process with an initial rolling temperature of 680℃, a deformation amount of 15%, and a cumulative deformation amount of 55%; perform the fifth hot rolling process with an initial rolling temperature of 660℃, a deformation amount of 10%, and a cumulative deformation amount of 65%, and then immediately water cool to room temperature;

[0085] 5) After cleaning the surface to remove the oxide scale, the hot-rolled sheet obtained in step 4) is cold-rolled at room temperature, with a deformation of 22%;

[0086] 6) The alloy sample obtained after step 5) is subjected to recrystallization annealing, held at 530℃ for 1.5h, and then air-cooled to obtain a corrosion-resistant lead-free brass alloy.

[0087] Example 5

[0088] This embodiment provides a corrosion-resistant lead-free brass alloy and its preparation method.

[0089] The elemental composition of this brass alloy, by weight percentage, is: Zn 33%, Si 1.5%, Mn 0.5%, Fe 0.05%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder is Cu and unavoidable impurities, with a total impurity content of <0.1%.

[0090] The specific preparation steps are as follows:

[0091] 1) Prepare the ingredients according to the weight percentage of each element. Add copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium, and scandium to the heating furnace and melt them at a melting temperature of 1050℃. Cover the surface of the melt with charcoal to prevent oxidation. After complete melting, reduce the temperature of the melt to 750℃, add zinc source, stir until it is completely melted, let it stand for 2 minutes, remove the slag, and pour it into a mold preheated to 200℃ at a pouring temperature of 700℃. After solidification, cool it with water to obtain the alloy ingot.

[0092] 2) Place the alloy ingot in a heat treatment furnace and hold it at 700℃ for 4 hours, then air cool it.

[0093] 3) Place the alloy treated in step 2) into a heat treatment furnace and hold it at 800℃ for 1 hour, followed by multiple hot rolling processes: the first hot rolling process has an initial rolling temperature of 780℃ and a deformation of 18%; the second hot rolling process has an initial rolling temperature of 750℃ and a deformation of 12%, with a cumulative deformation of 30%; the third hot rolling process has an initial rolling temperature of 730℃ and a deformation of 14%, with a cumulative deformation of 44%.

[0094] 4) Place the alloy treated in step 3) into a heat treatment furnace for reheating at 700℃ for 10 minutes; then perform the fourth hot rolling process with an initial rolling temperature of 680℃, a deformation amount of 10%, and a cumulative deformation amount of 54%; perform the fifth hot rolling process with an initial rolling temperature of 650℃, a deformation amount of 6%, and a cumulative deformation amount of 60%, and then immediately water cool to room temperature.

[0095] 5) After cleaning the surface to remove the oxide scale, the hot-rolled sheet obtained in step 4) is cold-rolled at room temperature, with a deformation of 15%;

[0096] 6) The alloy sample obtained after step 5) is subjected to recrystallization annealing, held at 550℃ for 1 hour, and then cooled by air cooling to obtain a corrosion-resistant lead-free brass alloy.

[0097] Comparative Example 1

[0098] The lead-free brass alloy of this comparative example has the following elemental composition by weight percentage: Zn 20%, Si 0.5%, Mn 0.5%, Fe 3.0%, Mg 1.0%, Cr 1.0%, La 1.0%, Ce 1.0%, Sc 1.0%; the remainder is Cu and unavoidable impurities.

[0099] The lead-free brass alloy in this comparative example differs from that in Example 1 only in its alloy composition; its preparation method is exactly the same as that in Example 1.

[0100] Comparative Example 2

[0101] The lead-free brass alloy in this comparative example has the following elemental composition by weight percentage: Zn 33%, Mn 0.5%, Fe 0.05%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder is Cu and unavoidable impurities.

[0102] The lead-free brass alloy in this comparative example differs from that in Example 5 only in its alloy composition; no Si element was added. However, its preparation method is exactly the same as that in Example 5.

[0103] Comparative Example 3

[0104] The lead-free brass alloy in this comparative example has the following elemental composition by weight percentage: Zn 33%, Si 1.5%, Fe 0.05%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder is Cu and unavoidable impurities.

[0105] The lead-free brass alloy in this comparative example differs from that in Example 5 only in its alloy composition; no Mn element was added, and its preparation method is exactly the same as that in Example 5.

[0106] Comparative Example 4

[0107] The lead-free brass alloy in this comparative example has the following elemental composition by weight percentage: Zn 33%, Si 1.5%, Mn 0.5%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder is Cu and unavoidable impurities.

[0108] The lead-free brass alloy in this comparative example differs from that in Example 5 in that it has a different alloy composition and does not contain Fe. However, its preparation method is exactly the same as that in Example 5.

[0109] Comparative Example 5

[0110] The lead-free brass alloy of this comparative example has the same alloy composition as that of Example 5, with the elemental composition by weight percentage as follows: Zn 33%, Si 1.5%, Mn 0.5%, Fe 0.05%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder being Cu and unavoidable impurities.

[0111] The difference between the preparation method of the lead-free brass alloy in this comparative example and that in Example 5 is that the rolling and recrystallization annealing steps 3) to 6) are omitted. That is, after the alloy ingot undergoes homogenization heat treatment in step 2), the performance of the sample is directly tested. Other process parameters are the same as in Example 5.

[0112] Comparative Example 6

[0113] The lead-free brass alloy of this comparative example has the same alloy composition as that of Example 5, with the elemental composition by weight percentage as follows: Zn 33%, Si 1.5%, Mn 0.5%, Fe 0.05%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder being Cu and unavoidable impurities.

[0114] The difference between the preparation method of the lead-free brass alloy in this comparative example and that in Example 5 is that step 6) recrystallization annealing is omitted. That is, the alloy sample is taken as the final state after completing step 5) cold rolling, and the comparative lead-free brass alloy sample is obtained. Other process parameters are the same as those in Example 5.

[0115] Comparative Example 7

[0116] The lead-free brass alloy of this comparative example has the same alloy composition as that of Example 5, with the elemental composition by weight percentage as follows: Zn 33%, Si 1.5%, Mn 0.5%, Fe 0.05%, Mg 0.05%, Cr 0.01%, La 0.03%, Ce 0.05%, Sc 0.02%; the remainder being Cu and unavoidable impurities.

[0117] The difference between the preparation method of the lead-free brass alloy in this comparative example and that in Example 5 is that the recrystallization annealing treatment in step 6) is carried out at 400 °C for 1 hour to obtain the comparative lead-free brass alloy sample. Other process parameters are the same as in Example 5.

[0118] The elemental composition of the lead-free brass alloys prepared in each embodiment and comparative example is shown in Table 1:

[0119] Performance testing:

[0120] 1. The hardness of the corrosion-resistant lead-free brass alloys obtained in each embodiment and comparative example was tested (GB / T 4340.1-2024); then they were suspended and immersed in 3.5% NaCl solution for 24, 72, 168, 240, 360 and 720 h respectively; electrochemical performance tests and weight loss tests were carried out, and the sampling positions were any positions other than the surface, bottom and top. The self-corrosion potential and self-corrosion current density obtained by Tafel fitting (GB / T 24196-2009) and the corrosion rate calculated by weight loss (GB / T16545-2025) are shown in Table 2.

[0121] 2. Observation of metallographic structure and surface morphology:

[0122] Metallographic images of the lead-free brass alloy prepared in Example 5 are shown below. Figure 1As shown, a typical α+β dual-phase brass structure was observed. The grayish-white region is the α phase (copper-rich solid solution) with good plasticity, while the dark region is the harder β phase (a solid solution based on the electron compound CuZn). The two phases are distributed alternately in a blocky and network pattern. Further observation revealed a large number of black intermetallic compound particles dispersed in the matrix. Scanning electron microscopy energy dispersive spectroscopy analysis confirmed that these particles are Mn5Si3 phase. These particles are small in size and mainly distributed at the phase boundaries, forming a uniformly dispersed reinforcing phase distribution.

[0123] The surface morphology image of the lead-free brass alloy prepared in Example 5 after immersion in 3.5% NaCl solution for 720 hours is shown below. Figure 2 As shown, the alloy surface remains largely intact, with no obvious penetrating corrosion or large-area peeling, exhibiting only uniform, slight corrosion characteristics. Small corrosion pits are visible in localized areas, but they have not developed into deep pits or cracks, indicating that the alloy has good resistance to localized corrosion. The alloy surface is covered with two types of corrosion products: one type consists of slender needle-like products, approximately 15 μm in length; the other type consists of rice-grain-like products, approximately 5 μm in size, ellipsoidal or short rod-shaped, densely distributed in the gaps between the needle-like products and on some of their surface, forming a double-layered composite structure. The synergistic coverage of these two types of products effectively prevents direct contact between the corrosive medium and the substrate.

[0124] Metallographic images of the lead-free brass alloy prepared in Comparative Example 5 are shown below. Figure 3 As shown, the α phase forms the matrix, while the β phase is coarse and unevenly distributed, accompanied by obvious dendritic segregation residues. The overall structure exhibits typical cast-state microstructure characteristics, lacking the grain refinement and microstructure homogenization effects imparted by deformation processing. Furthermore, the Mn5Si3 phase exists only in localized areas as coarse particles, failing to achieve a uniform and dispersed distribution, resulting in a comprehensive deterioration of the alloy's corrosion resistance.

[0125] Analyze the above performance test results:

[0126] The test results of Comparative Examples 2 and 3 and Example 5 show that Si and Mn are the core elements for the formation of the Mn5Si3 phase and the improvement of corrosion resistance in this invention. When Si is missing (Comparative Example 2) or Mn is missing (Comparative Example 3), fine Mn5Si3 intermetallic compound phases cannot be formed in the alloy, resulting in a significant deterioration in corrosion resistance.

[0127] A comparison between Comparative Example 4 and Example 5 shows that Fe is crucial for the dispersed precipitation of the Mn5Si3 phase. With Fe absent (Comparative Example 4), although a small amount of Mn5Si3 phase could still form in the alloy, the precipitation uniformity significantly decreased, and local aggregation occurred, leading to an increase in the corrosion rate from 7.30 μm / a to 11.45 μm / a and an increase in the self-corrosion current density to 1.42 μA / cm². This is because Fe, as a heterogeneous nucleation core, promotes the preferential and uniform precipitation of the Mn5Si3 phase at the α / β phase boundary, enhancing interfacial bonding and preventing preferential corrosion at the phase boundary. The absence of Fe renders this mechanism ineffective, resulting in a significant decrease in corrosion resistance.

[0128] The comparison between Comparative Example 5 and Example 5 shows that the multi-pass hot rolling and cold rolling deformation processing is the key to achieving a uniform and dispersed distribution of the Mn5Si3 phase. The alloy that completely omits rolling and recrystallization annealing (Comparative Example 5), although it undergoes homogenization heat treatment, still exhibits the Mn5Si3 phase only in localized areas as coarse particles, failing to achieve a uniform and dispersed distribution, resulting in a comprehensive deterioration of the alloy's corrosion resistance.

[0129] The comparison between Comparative Example 6 and Example 5 shows that recrystallization annealing is an essential step for stabilizing the Mn5Si3 phase, eliminating residual stress, and optimizing corrosion uniformity. The alloy that omitted recrystallization annealing (Comparative Example 6), although having formed the Mn5Si3 phase, retained a high density of dislocations and residual stress in the matrix, creating a micro-cell effect in the corrosive environment, leading to accelerated localized corrosion and an increased corrosion rate of 12.78 μm / a.

[0130] The comparison between Comparative Example 7 and Example 5 shows that the recrystallization annealing temperature has a decisive influence on the synergistic stability of the Mn5Si3 phase and the matrix. When the annealing temperature is too low (Comparative Example 7, 400℃), recrystallization is insufficient, the interface between the Mn5Si3 phase and the matrix does not reach the optimal matching state, the passivation film is incomplete, and the corrosion rate is still as high as 10.62 μm / a. In contrast, Example 5 uses annealing at 550℃, which enables the Mn5Si3 phase and the matrix to achieve the best electrochemical matching, and at the same time forms a dense and stable corrosion product film, achieving the best corrosion resistance performance.

[0131] Combined with the microstructure images of the lead-free brass alloy in Example 5 ( Figure 1 According to the experimental data in Table 2, after hot rolling and recrystallization annealing, the alloy of Example 5 has a large number of fine Mn5Si3 particles dispersed in the matrix. Figure 1 (As indicated by the arrows) These particles are mainly distributed in the nanometer to submicron range, preferentially precipitating at phase boundaries and within grains to form a uniformly dispersed reinforcing phase distribution. This fine Mn5Si3 phase acts as a microcathode during corrosion, inducing uniform microanodic dissolution of the substrate and promoting the formation of a dense corrosion product film on the surface (such as...). Figure 2As shown in the figure, it effectively blocks chloride ion penetration, allowing the alloy to maintain its intact surface after being immersed in 3.5% NaCl solution for 720 hours.

[0132] In contrast, the alloy in Comparative Example 2 (without Si) did not show the Mn5Si3 phase in its microstructure. Only a small amount of coarse Mn-containing phases were present. These coarse phases were unevenly distributed and poorly bonded to the matrix, which led to corrosion occurring preferentially at the phase boundaries, forming deep pit-like localized corrosion with a corrosion rate as high as 26.65 μm / a.

[0133] In the alloy of Comparative Example 3 (without Mn), although Si can form a small amount of silicide, the lack of Mn prevents the formation of the Mn5Si3 phase. Only a small amount of coarse Si-rich phase exists in the matrix. These phases have a large potential difference with the matrix and act as strong cathodes during corrosion, accelerating the anodic dissolution of the matrix and causing the corrosion rate to deteriorate further to 27.48 μm / a.

[0134] In Comparative Example 4 (Fe-free) alloy, although Mn5Si3 phase particles could be formed, the as-cast grains were significantly coarsened due to the lack of Fe element for heterogeneous nucleation, and the uniformity of the Mn5Si3 phase distribution deteriorated, with local aggregation occurring. These coarse grains and uneven precipitates resulted in uneven distribution of microcathodes during corrosion, increasing the tendency for localized corrosion and raising the corrosion rate to 11.45 μm / a.

[0135] The metallographic microstructure of the alloy in Comparative Example 5 (without rolling and recrystallization annealing) is as follows: Figure 3 As shown, the α phase forms the matrix, while the β phase is coarse and blocky with uneven distribution, accompanied by obvious dendritic segregation residues. Overall, it exhibits typical as-cast microstructure characteristics, lacking the grain refinement and microstructure homogenization effects imparted by deformation processing. The Mn5Si3 phase exists only in localized areas as coarse particles, failing to achieve a uniform and dispersed distribution, resulting in a comprehensive deterioration of the alloy's corrosion resistance, with a corrosion rate reaching 17.53 μm / a.

[0136] Although the alloy in Comparative Example 6 (without recrystallization annealing) has formed the Mn5Si3 phase, the matrix retains a high density of dislocations and residual stress, which form a micro-cell effect in the corrosive environment, leading to accelerated local corrosion.

[0137] In the alloy of Comparative Example 7 (annealing temperature too low, 400℃), due to insufficient annealing temperature and incomplete recrystallization, the Mn5Si3 phase and the matrix interface did not achieve optimal electrochemical matching, and the passivation film was not fully formed.

[0138] In summary, the lead-free brass alloy prepared using the process and parameters of this invention exhibits a uniform microstructure, excellent overall performance, and a hardness of not less than 250 HV. After immersion in 3.5% NaCl solution for 720 h, its self-corrosion potential is not less than -315 mV (vs. SCE), and its self-corrosion current density is not higher than 0.90 μA / cm. 2 The corrosion rate is no higher than 7.50 μm / a, achieving excellent corrosion resistance.

[0139] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A corrosion-resistant lead-free brass alloy, characterized in that, The elemental composition by weight percentage includes: Zn 25%~40%, Si 0.8%~2.5%, Mn 0.3%~2%, Fe 0.01%~1.5%, Mg 0.01%~0.1%, Cr 0.01%~0.2%, La 0.01%~0.2%, Ce 0.01%~0.2%, Sc 0.01%~0.2%, with the balance being Cu and unavoidable impurities.

2. The corrosion-resistant lead-free brass alloy according to claim 1, characterized in that, The elemental composition by weight percentage includes: Zn 30%~35%, Si 1%~2%, Mn 0.5%~1.5%, Fe 0.05%~1%, Mg 0.02%~0.1%, Cr 0.01%~0.1%, La 0.02%~0.1%, Ce 0.02%~0.1%, Sc 0.02%~0.1%, with the balance being Cu and unavoidable impurities.

3. The corrosion-resistant lead-free brass alloy according to claim 1, characterized in that, The total mass percentage of Mg, Cr, La, Ce and Sc is 0.1% to 0.3%.

4. The corrosion-resistant lead-free brass alloy according to claim 1, characterized in that, The microstructure of the corrosion-resistant lead-free brass alloy contains dispersed Mn-Si intermetallic compound particles (Mn5Si3), with particle sizes ranging from nanometer to submicrometer.

5. The corrosion-resistant lead-free brass alloy according to claim 1, characterized in that, The corrosion-resistant lead-free brass alloy has a hardness ≥250HV. After immersion in 3.5% NaCl solution for 720 hours, its self-corrosion potential ≥-315mV (vs. SCE) and self-corrosion current density ≤0.90μA / cm². 2 The corrosion rate is ≤7.50μm / a.

6. The method for preparing the corrosion-resistant lead-free brass alloy according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. According to the weight percentage of the elemental composition, the raw materials of copper, silicon, manganese, iron, magnesium, chromium, lanthanum, cerium and scandium are mixed, heated and smelted to obtain a melt, cooled and then zinc source is added, and cast to obtain an ingot. S2. The ingot is subjected to homogenization treatment, multi-pass hot rolling, cold rolling and recrystallization annealing treatment in sequence to obtain the corrosion-resistant lead-free brass alloy.

7. The preparation method according to claim 6, characterized in that, In step S1, the heating and melting temperature is 1050~1250℃; charcoal is used as a covering agent for the melt during the heating and melting process; and the cooling temperature is reduced to 750~850℃.

8. The preparation method according to claim 6, characterized in that, In step S2, the homogenization process involves placing the ingot at 650-850°C for 1-6 hours, followed by furnace cooling or air cooling.

9. The preparation method according to claim 6, characterized in that, In step S2, the method of multi-pass hot rolling is as follows: heating the ingot to 750~850℃, holding it at that temperature for 0.5~2h, and then performing 3~6 hot rolling passes; The initial rolling temperature is 770~810℃, and the final rolling temperature is 650~680℃, with the rolling temperature gradually decreasing from the initial to the final pass. The deformation of the initial, intermediate, and final hot rolling passes is controlled at 5%~20%, 15%~20%, and 5%~10%, respectively, with a total hot rolling deformation of 50%~70%. During the hot rolling process, the rolled piece is reheated after every 2~3 passes at a temperature of 700~750℃ for 10~20 minutes. After hot rolling, the piece is immediately water-cooled to room temperature.

10. The preparation method according to claim 6, characterized in that, In step S2, the cold rolling is performed by cold rolling the hot-rolled workpiece at room temperature with a deformation of 10% to 30%; the recrystallization annealing is performed by placing the cold-rolled workpiece at 500℃ to 700℃ for 0.5 to 1.5 hours, followed by air cooling or furnace cooling.

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