A friction-resistant and high-toughness brass alloy and its preparation method

Abstract

This invention discloses a friction-resistant, high-toughness brass alloy and its preparation method, relating to the technical field of copper alloys for high-speed rail braking, and belonging to patent classification number C22C9 / 04. The method includes batching and melting the alloy according to a specified ratio to form an ingot. The alloy composition is Zn 30.0–32.0%, Al 1.6–2.1%, Mn 1.2–1.8%, Fe 0.60–0.90%, Cr 0.15–0.24%, Zr 0.05–0.08%, with the balance being Cu; Cr and Zr are introduced as intermediate alloys. After homogenization and hot forging, the working surface of the ingot is subjected to ultrasonic rolling to form a gradient deformation layer extending towards the center. This invention utilizes ultrasonic rolling to generate deep gradient hardening, combined with low-temperature heat treatment to eliminate residual stress in the center and improve toughness. Simultaneously, Cr and Zr synergistically stabilize the hardened layer to inhibit recovery, thus achieving a balance between the friction resistance and impact toughness of the forging.

Description

Technical Field

[0001] This invention relates to the technical field of copper alloy forgings for high-speed rail braking, belonging to patent classification number C22C9 / 04, specifically to a friction-resistant, high-toughness brass alloy and its preparation method. Background Technology

[0002] In high-speed train braking systems, guide sleeves, bushings, connecting sliders, and load-bearing components of the adjusting mechanism simultaneously endure reciprocating sliding, localized impacts, assembly eccentric loading, and temperature cycling during service. These parts are not powder metallurgy brake pad friction bodies that directly contact the brake disc, but their jamming, abnormal wear, or impact cracking can still affect the stability of the braking mechanism. Therefore, copper alloy forgings used in these components need to have low adhesive wear tendency and good scratch resistance, while retaining sufficient plasticity and impact toughness, and should be suitable for mass hot forging and machining.

[0003] Existing high-speed train braking materials mainly focus on forged steel brake discs and powder metallurgy brake pads sintered from copper powder, iron powder, graphite, and ceramic wear-resistant components. The composition, pore structure, hardness, and friction coefficient of these materials are designed for direct braking friction conditions and are not suitable for direct application to dense brass forgings. Existing high-strength wear-resistant brass is mostly used in automotive synchronizer rings, worm gears, bearing bushes, or self-lubricating bearings. Wear resistance is typically improved by increasing the content of elements such as Al, Mn, Fe, and Si to form more hard phases or a higher proportion of β phase. While this approach is beneficial for increasing hardness, coarsening or continuous distribution of the hard phase, or an excessively high proportion of β phase, can easily lead to crack initiation under impact loads. Simply increasing the α phase or using more thorough annealing to improve plasticity will reduce surface hardness and resistance to adhesive wear.

[0004] The silicon brass alloy disclosed in publication number CN118835124A uses Cu 73-79wt%, Si 2.0-4.0wt%, small amounts of P, As, B and rare earth elements, and the balance Zn as its composition base. It employs a horizontal continuous casting process followed by electromagnetic stirring, extrusion, stretching, pre-straightening, low-temperature annealing at 280-320℃, and straightening, primarily targeting fasteners. This approach relies on high-silicon dispersed phases and As, B, and rare earth elements to control the microstructure of the continuously cast bars, differing from the hot forgings used in high-speed rail braking mechanisms that withstand sliding and impact in terms of composition, forming method, microstructure gradient, and service life. Other high-strength wear-resistant aluminum brass utilizes higher contents of Al, Fe, Mn, Ni, Pb, or Si to form hard particles. There are also multi-element wear-resistant brasses that use integral quenching, tempering, or aging to improve hardness, but these methods have not yet resolved the contradiction in thermal stability arising from separately controlling the surface wear-resistant microstructure and the overall toughness of the forging. Summary of the Invention

[0005] The purpose of this invention is to provide a friction-resistant, high-toughness brass alloy and its preparation method, so as to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a friction-resistant and high-toughness brass alloy includes the following steps: The raw materials are prepared according to the alloy composition and then melted and cast in sequence to obtain alloy ingots; The alloy comprises, by mass percentage: Zn 30.0–32.0%, Al 1.6–2.1%, Mn 1.2–1.8%, Fe 0.60–0.90%, Cr 0.15–0.24%, Zr 0.05–0.08%, with the balance being Cu and unavoidable impurities, and the mass ratio of Cr to Zr being 2.5–3.2:1; wherein Cr and Zr are introduced through Cu-Cr master alloy and Cu-Zr master alloy, respectively. The alloy ingot is homogenized and hot-forged to obtain a brass alloy forging. The working surface of the brass alloy forging is subjected to ultrasonic surface rolling treatment to form a gradient deformation layer extending from the working surface into the interior of the forging; and The brass alloy forgings that have undergone ultrasonic surface rolling are held at 310–340°C for 60–120 min and then cooled to obtain the wear-resistant and high-toughness brass alloy forgings.

[0007] Preferably, the raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy and Cu-Zr40 master alloy. The Cu-Cr10 master alloy is added to the melt before the Cu-Zr40 master alloy, and the Cu-Zr40 master alloy is added below the surface of the melt under argon protection.

[0008] Preferably, the smelting includes: The cathode copper is melted, and Cu-Fe20 master alloy and Cu-Mn20 master alloy are added sequentially at 1130-1170℃, and the temperature is held for 10-15 minutes. Add Cu-Cr10 master alloy at 1130-1160℃, hold for 8-12 minutes, then reduce the melt temperature to 1060-1100℃ and add Cu-Zr40 master alloy. Stir for 2-4 minutes and hold for no more than 6 minutes. Add Cu-Al50 master alloy at 1040–1080℃ and hold for 5–8 minutes; and Reduce the melt temperature to 980-1020℃, add the zinc ingots to the melt in 2-3 batches, and add the next batch only after each batch of zinc ingots has completely melted.

[0009] As a preferred method, after the zinc ingot is completely melted, dry argon gas is introduced into the bottom of the melt for 3-5 minutes, and the melt is left to stand for 3-5 minutes to remove surface slag. After composition testing and correction, the melt is poured into a steel ingot mold preheated to 180-250°C at 1000-1020°C using a bottom-pouring method to obtain an alloy ingot with a diameter or equivalent thickness of 120-180 mm.

[0010] Preferably, the homogenization treatment includes: heating the alloy ingot to 660-690°C at a heating rate of 80-120°C / h under nitrogen protection and holding it at that temperature for 2-3 hours; the hot forging process includes: adjusting the temperature of the homogenized alloy ingot to 670-710°C and then starting forging, performing final forging at a temperature not lower than 600°C, with a cumulative cross-sectional compression rate of 50-70%, and using a forging die at a temperature of 250-320°C.

[0011] Preferably, before the ultrasonic surface rolling treatment, the hot-forged brass alloy forging is deburred and rough-machined so that the roughness Ra of the working surface to be rolled is not greater than 1.6 μm, and a dimensional correction allowance of 0.03 to 0.08 mm is reserved on the working surface.

[0012] Preferably, the ultrasonic surface rolling treatment uses a ball-head or circular arc roller type carbide tool, with an ultrasonic frequency of 18-22kHz, an amplitude of 8-14μm, a static pressure of 0.5-0.9kN, a single indentation of 0.10-0.18mm, a feed rate of 0.08-0.18mm / r, and 2-4 alternating rolling passes, with adjacent rolling passes in opposite directions.

[0013] The ultrasonic surface rolling process uses low-viscosity copper alloy rolling oil for lubrication and controls the temperature of the working surface to be no higher than 120°C; the thickness of the resulting gradient deformation layer is 0.30 to 1.00 mm.

[0014] Preferably, the heat preservation is carried out under nitrogen protection.

[0015] Preferably, after the heat preservation and cooling, the working surface is finished, and the amount of material removed from one side of the working surface does not exceed 0.02 mm.

[0016] A friction-resistant and high-toughness brass alloy is prepared by the method described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Friction resistance is achieved through a combination of matrix load-bearing strengthening, casting defect reduction, and surface gradient hardening. In the composition design, Al and Mn, after entering the brass matrix, enhance its resistance to plastic deformation and regulate the relative stability of the α and β phases. Fe tends to form a fine Fe-enriched second phase during solidification and subsequent hot working, providing dispersed load-bearing points on the contact surface. Homogenization and hot forging further reduce dendrite segregation, close casting porosity, and break up coarse second phases, resulting in a finer and more dispersed load-bearing structure. Based on this, ultrasonic surface rolling is performed. Due to repeated plastic deformation, the working surface undergoes grain refinement, dislocation proliferation, and work hardening, while simultaneously forming a gradient deformation layer that gradually transitions from the hardened surface to the tough matrix. When the forging and its mating part reciprocate, the hardened surface layer first resists contact indentation and micro-protrusion cutting. The dispersed second phase and the reinforced matrix share the local load, thus reducing plastic ploughing. The lower surface roughness after rolling reduces mechanical seizing of micro-protrusions, lowering the probability of adhesive tearing. The residual compressive stress on the surface layer inhibits the opening of frictional microcracks and delays fatigue spalling. Because the hardness decreases continuously from the surface to the interior, the contact load can be gradually transferred to the matrix and is less likely to concentrate at a single interface. Therefore, it can simultaneously resist adhesive wear, ploughing wear, and frictional fatigue spalling. The friction resistance mentioned here refers to the material's ability to resist material loss and surface damage under frictional contact conditions, and is not necessarily equivalent to a decrease in the coefficient of friction.

[0018] 2. High toughness is achieved by retaining the ductile phase, refining and breaking brittle paths, and releasing harmful residual stress. The contents of Zn, Al, Mn, and Fe are limited, allowing the alloy to retain the α phase with good plastic deformation capacity while achieving the necessary load-bearing capacity. This avoids the formation of easily penetrating brittle crack paths due to excessive and continuous distribution of β phase or hard second phase. Hot forging closes the casting pores and breaks and disperses coarse grains and second-phase agglomerates, reducing pores, inclusion clusters, and coarse phase boundaries that are prone to crack initiation. The refined grains and tortuous phase boundaries also increase the number of interfaces that need to be crossed during crack propagation. Then, an overall low-temperature treatment at 310–340℃ is performed, causing limited rearrangement of high-energy dislocations introduced by hot forging and surface rolling. This reduces residual tensile stress and local strain concentration in the core and gradient layer transition zone, but does not cause sufficient recrystallization or overall softening of the forging. When forgings are subjected to impact or eccentric loading, the α phase can absorb localized plastic deformation through slippage, while the harder β phase and finer second phases maintain load-bearing capacity. When cracks propagate to the interface between the soft and hard phases, their direction changes, and the crack tip becomes blunted due to surrounding plastic deformation, increasing the energy required for further propagation. Slow cooling after heat treatment can also reduce the thermal stress between thick and thin sections. Therefore, this approach improves the impact cracking resistance of forgings simultaneously by reducing crack initiation sites, enhancing plastic compatibility, and hindering crack propagation, rather than simply relying on reducing overall hardness to achieve toughness.

[0019] 3. While overall low-temperature treatment can release residual tensile stress and improve plasticity, heat preservation can also cause the gradient deformation layer formed by ultrasonic rolling to recover, manifested as a decrease in dislocation density, subgrain boundary migration, and a drop in surface hardness. Once the hardened layer softens significantly, its resistance to contact indentation and plastic plowing decreases, making it more prone to adhesive tearing and fatigue spalling during friction. To suppress this effect, commercially available Cu-Cr10 and Cu-Zr40 alloy raw materials were added during the smelting stage, with the Cr to Zr mass ratio controlled at 2.5–3.2:1. The Cr-related fine enriched structure hinders dislocation movement and rearrangement, while the Zr-related dispersed structure and interface segregation restrict subgrain boundary and grain boundary migration. Both delay the recovery and coarsening of the rolled layer by stabilizing the dislocation structure and refining the grains, respectively. Therefore, during heat treatment at 310–340℃, the core and gradient layer transition zone can still release harmful residual tensile stress through finite dislocation rearrangement, while the dislocation strengthening, grain refinement strengthening, and surface-to-interior hardness gradient of the working surface layer can be largely preserved. The preserved hardened surface layer continues to bear the frictional contact load, reducing the indentation depth of the micro-protrusions in the mating parts and the plastic flow of the material; the more stable gradient structure reduces the possibility of surface cracks propagating inward and forming spalling, thereby maintaining the forging's resistance to adhesive wear, ploughing wear, and frictional fatigue. Cr and Zr do not directly reduce the coefficient of friction through lubrication, but rather improve the microstructure stability of the gradient hardened layer during low-temperature treatment, avoiding a significant loss of friction resistance due to recovery softening. Attached Figure Description

[0020] Figure 1 This is a low-magnification SEM image of the surface of the friction-resistant and high-toughness brass alloy prepared in Example 5 of the present invention.

[0021] Figure 2 This is a high-magnification SEM image of the surface of the friction-resistant and high-toughness brass alloy prepared in Example 5 of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 A method for preparing a friction-resistant and high-toughness brass alloy includes the following steps: The brass alloy comprises, by mass percentage: Zn 31.5%, Al 2.0%, Mn 1.6%, Fe 0.8%, Cr 0.16%, Zr 0.05%, with unavoidable impurities totaling no more than 0.10%, and the balance being Cu, wherein the mass ratio of Cr to Zr is 3.2:1.

[0024] Step 1, Batching and Raw Material Pretreatment: Based on the target alloy composition described above, calculate and weigh each raw material according to the measured mass fraction of the target element in each raw material and the measured recovery rate of the corresponding element in the smelting equipment used. The raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy, and Cu-Zr40 master alloy; wherein, the amount of cathode copper is determined by deducting the Cu introduced by each master alloy from the target content of the remaining Cu, and the amount of zinc ingots is corrected according to the measured purity of zinc ingots and the measured recovery rate of Zn. The cathode copper, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, and Cu-Cr10 master alloy are preheated at 150℃ for 45 minutes to remove surface moisture; the Cu-Zr40 master alloy is kept sealed and dry, and is only unsealed before addition, and is not subjected to prolonged high-temperature preheating in air.

[0025] Step 2, Basic Melting: Melting is carried out in a medium-frequency induction furnace with argon protection. The crucible, sampling spoon, pressing tools, and stirring tools are thoroughly dried before use. First, the cathode copper calculated in Step 1 is added to the furnace and melted. The temperature of the copper melt is adjusted to 1160℃. The Cu-Fe20 master alloy and Cu-Mn20 master alloy are pressed below the surface of the melt in sequence. After Cu-Fe20 is completely melted, Cu-Mn20 is added. After both master alloys are completely melted, the melt is circulated at 1150℃ using induction stirring and held for 14 minutes to ensure that Fe and Mn diffuse evenly in the copper melt. During the holding period, a slight positive pressure of argon gas is maintained at the furnace opening, and slag on the surface of the melt is removed.

[0026] Step 3, Cr-Zr alloying: Maintain the melt temperature obtained in Step 2 at 1150℃, add the Cu-Cr10 master alloy calculated in Step 1, ensuring the Cu-Cr10 is completely submerged in the melt surface, and hold for 11 minutes after induction stirring. Then, lower the melt temperature to 1090℃, and under argon protection, use a dried pressing tool to press the Cu-Zr40 master alloy below the melt surface to prevent prolonged exposure of Cu-Zr40 on the surface. Stir for 3.5 minutes after addition and continue holding for 5 minutes. By adding Cu-Cr10 at a higher temperature first, and then adding Cu-Zr40 at a lower temperature and under low oxygen conditions, Cr is fully melted into the copper-based melt, while reducing Zr oxidation loss.

[0027] Step 4, Al-Zn alloying: Adjust the melt temperature obtained in Step 3 to 1070℃, add the Cu-Al50 master alloy calculated in Step 1, and hold for 7 minutes after the Cu-Al50 has completely melted; then lower the melt temperature to 1010℃, divide the zinc ingots calculated in Step 1 into three batches of approximately equal mass, and press them below the melt surface. Add the next batch only after each batch of zinc ingots has completely melted. After all the zinc has melted, maintain the melt temperature at 1010℃ to avoid unnecessary long-term high-temperature holding to promote alloying, thereby reducing the burn-off of Zn and Al and compositional fluctuations.

[0028] Step 5, Melt Purification, Composition Correction, and Casting: Dry argon gas is introduced into the bottom of the melt obtained in Step 4 at a low flow rate for 4.5 minutes. After stopping the gas flow, the melt is allowed to stand for 4.5 minutes to allow inclusions to float to the surface. Then, the slag on the melt surface is removed. Samples are taken for direct-reading spectral analysis. Based on the analysis results, the composition is corrected using appropriate metals or intermediate alloys to ensure that the contents of Zn, Al, Mn, Fe, Cr, and Zr are within the allowable control range of the target composition in this embodiment. After the composition is deemed acceptable, the melt temperature is adjusted to 1010℃. The melt is then poured into a steel ingot mold preheated to 240℃ with an inner cavity diameter of 160mm using a bottom-pouring method. After the ingot cools to below 200℃, it is demolded and cooled to room temperature in still air to obtain a brass alloy ingot.

[0029] Step 6, Homogenization and Hot Forging: Remove oxide scale, folds, and other visible defects from the surface of the brass alloy ingot. Place the treated ingot in a nitrogen-protected furnace and heat it to 680℃ at a heating rate of 110℃ / h, holding it at that temperature for 2.5h. After homogenization, adjust the ingot temperature to 700℃ and transfer it to a forging die preheated to 300℃ for hot forging. Deformation is performed using a combination of multi-pass upsetting and drawing to achieve a cumulative cross-sectional compression ratio of 60%. Deformation is stopped when the forging temperature approaches 610℃, ensuring the final forging temperature is not lower than 600℃. Forge the ingot into a guide slide blank with an equivalent cross-sectional thickness of 20mm, and cool it to room temperature in still air after forging.

[0030] Step 7, Pre-machining of the working surface: The guide slider blank obtained in Step 6 is deburred and rough-machined to remove the surface oxide layer, folds, and obvious machining marks. The surface roughness of the surface to be used as the friction working surface is machined to Ra 1.2μm, and a 0.05mm dimensional correction allowance is reserved on this working surface. Other non-working surfaces are machined according to the forging design dimensions. After machining, a chlorine-free cleaning agent is used to remove the cutting fluid and machining particles from the surface, and the surface is thoroughly dried to avoid residues affecting the subsequent rolling quality.

[0031] Step 8, ultrasonic surface rolling: A ball-head cemented carbide rolling tool is used to perform ultrasonic surface rolling on the working surface obtained in step 7. The ultrasonic frequency is set to 20 kHz, the amplitude is set to 12 μm, the static pressure is set to 0.8 kN, the single penetration depth is set to 0.16 mm, and the feed rate is set to 0.16 mm / r. A total of 3 passes of staggered rolling are performed, and the rolling directions of adjacent two passes are opposite. During the rolling process, low-viscosity copper alloy rolling oil is continuously supplied, and a non-contact temperature measuring device is used to monitor the temperature of the working surface, so as to control the temperature of the working surface below 120°C; residual oil is cleaned after rolling. Witness specimens subjected to the same smelting, hot forging and rolling treatments are set in the same batch. The gradient deformation layer is confirmed through cross-sectional metallographic observation and microhardness gradient testing. When the actually measured thickness of the gradient deformation layer is between 0.30 mm and 1.00 mm, the rolling process is judged to be qualified, and the penetration depth of the rolling tool shall not be directly used to replace the thickness of the gradient deformation layer.

[0032] Step 9, overall low-temperature treatment: Since the equivalent cross-sectional thickness of the guide slider blank in this embodiment is 20 mm, the forging obtained in step 8 is placed in a nitrogen-protected furnace and held at 330°C for 110 min, so that the residual stress generated by hot forging and ultrasonic surface rolling is limitedly released, while preventing the forging from undergoing sufficient recrystallization. After the heat preservation is completed, the forging is cooled in the furnace to 178°C at a cooling rate of 35°C / h, then taken out of the furnace and cooled to room temperature in still air. The witness specimen in the same furnace is used to compare the changes in the surface microhardness gradient and residual stress before and after the low-temperature treatment, so as to confirm that the selected low-temperature treatment system does not cause obvious recovery softening of the gradient deformation layer.

[0033] Step 10, finishing and performance inspection: Light finishing is performed on the working surface of the forging obtained in step 9, and the unilateral material removal amount is controlled to 0.02 mm to avoid cutting off the gradient deformation layer formed by ultrasonic surface rolling; after finishing, cleaning, drying and dimensional inspection are performed in sequence to obtain the friction-resistant high-toughness brass alloy forging.

[0034] Example 2 A preparation method of a friction-resistant high-toughness brass alloy, comprising the following steps: The brass alloy comprises, in mass percentage: Zn 30.5%, Al 1.7%, Mn 1.3%, Fe 0.7%, Cr 0.2%, Zr 0.08%, the total amount of unavoidable impurities does not exceed 0.10%, and the balance is Cu, wherein the mass ratio of Cr to Zr is 2.5:1.

[0035] Step 1, Batching and Raw Material Pretreatment: Based on the target alloy composition described above, calculate and weigh each raw material according to the measured mass fraction of the target element in each raw material and the measured recovery rate of the corresponding element in the smelting equipment used. The raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy, and Cu-Zr40 master alloy; wherein, the amount of cathode copper is determined by deducting the Cu introduced by each master alloy from the target content of the remaining Cu, and the amount of zinc ingots is corrected according to the measured purity of zinc ingots and the measured recovery rate of Zn. The cathode copper, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, and Cu-Cr10 master alloy are preheated at 150℃ for 45 minutes to remove surface moisture; the Cu-Zr40 master alloy is kept sealed and dry, and is only unsealed before addition, and is not subjected to prolonged high-temperature preheating in air.

[0036] Step 2, Basic Melting: Melting is carried out in a medium-frequency induction furnace with argon protection. The crucible, sampling spoon, pressing tools, and stirring tools are thoroughly dried before use. First, the cathode copper calculated in Step 1 is added to the furnace and melted. The temperature of the copper melt is adjusted to 1140℃. The Cu-Fe20 master alloy and Cu-Mn20 master alloy are pressed below the surface of the melt in sequence. After Cu-Fe20 is completely melted, Cu-Mn20 is added. After both master alloys are completely melted, the melt is circulated at 1150℃ using induction stirring and held for 12 minutes to ensure that Fe and Mn diffuse evenly in the copper melt. During the holding period, a slight positive pressure of argon is maintained at the furnace opening, and slag on the surface of the melt is removed.

[0037] Step 3, Cr-Zr alloying: Maintain the melt temperature obtained in Step 2 at 1140℃, add the Cu-Cr10 master alloy calculated in Step 1, ensuring the Cu-Cr10 is completely submerged in the melt surface, and hold at this temperature for 9 minutes after induction stirring. Then, lower the melt temperature to 1070℃, and under argon protection, use a dried pressing tool to press the Cu-Zr40 master alloy below the melt surface to prevent prolonged exposure of Cu-Zr40 on the surface. Stir for 2.5 minutes after addition and continue holding at this temperature for 5 minutes. By adding Cu-Cr10 at a higher temperature first, and then adding Cu-Zr40 at a lower temperature and under low oxygen conditions, Cr is fully melted into the copper-based melt, while reducing Zr oxidation loss.

[0038] Step 4, Al-Zn alloying: Adjust the temperature of the melt obtained in Step 3 to 1050℃, add the Cu-Al50 master alloy calculated in Step 1, and hold for 6 minutes after the Cu-Al50 has completely melted; then lower the melt temperature to 990℃, and press the zinc ingots calculated in Step 1 into three batches of roughly equal mass below the melt surface. Add the next batch only after each batch has completely melted. After all the zinc has melted, maintain the melt temperature at 990℃ to avoid unnecessary long-term high-temperature holding to promote alloying, thereby reducing the burn-off of Zn and Al and compositional fluctuations.

[0039] Step 5, Melt purification, composition correction, and casting: Dry argon gas is introduced into the bottom of the melt obtained in Step 4 at a low flow rate for 3.5 minutes. After stopping the gas flow, the melt is allowed to stand for 3.5 minutes to allow inclusions to float to the surface. Then, the slag on the surface of the melt is removed. Samples are taken for direct-reading spectral analysis. Based on the test results, the composition is corrected using the corresponding metal or intermediate alloy to ensure that the contents of Zn, Al, Mn, Fe, Cr, and Zr are within the controllable range of the target composition in this embodiment. After the composition is qualified, the melt temperature is adjusted to 1010℃, and the melt is poured into a steel ingot mold preheated to 190℃ with an inner cavity diameter of 150mm using a bottom-pouring method. After the ingot cools to below 200℃, it is demolded and cooled to room temperature in still air to obtain a brass alloy ingot.

[0040] Step 6, Homogenization and Hot Forging: Remove oxide scale, folds, and other visible defects from the surface of the brass alloy ingot. Place the treated ingot in a nitrogen-protected furnace and heat it to 670℃ at a heating rate of 90℃ / h, holding it at that temperature for 2.5h. After homogenization, adjust the ingot temperature to 680℃ and transfer it to a forging die preheated to 260℃ for hot forging. Deformation is performed using a combination of multi-pass upsetting and drawing to achieve a cumulative cross-sectional compression ratio of 60%. Deformation is stopped when the forging temperature approaches 610℃, ensuring the final forging temperature is not lower than 600℃. Forge the ingot into a guide slider blank with an equivalent cross-sectional thickness of 20mm, and cool it to room temperature in still air after forging.

[0041] Step 7, Pre-machining of the working surface: The guide slider blank obtained in Step 6 is deburred and rough-machined to remove the surface oxide layer, folds, and obvious machining marks. The surface roughness of the surface to be used as the friction working surface is machined to Ra 1.2μm, and a dimensional correction allowance of 0.04mm is reserved on this working surface. Other non-working surfaces are machined according to the forging design dimensions. After machining, a chlorine-free cleaning agent is used to remove the cutting fluid and machining particles from the surface, and the surface is thoroughly dried to avoid residues affecting the subsequent rolling quality.

[0042] Step 8, ultrasonic surface rolling: A ball-head cemented carbide rolling tool is used to perform ultrasonic surface rolling on the working surface obtained in step 7. The ultrasonic frequency is set to 19 kHz, the amplitude to 9 μm, the static pressure to 0.6 kN, the single penetration to 0.12 mm, and the feed rate to 0.1 mm / r. A total of 3 passes of staggered rolling are carried out, and the rolling directions of adjacent two passes are opposite. During the rolling process, low-viscosity copper alloy rolling oil is continuously supplied, and a non-contact temperature measuring device is used to monitor the temperature of the working surface, so as to control the temperature of the working surface below 120°C; residual oil is cleaned after the rolling is completed. Witness specimens subjected to the same smelting, hot forging and rolling treatments are set in the same batch, and the gradient deformed layer is confirmed through cross-sectional metallographic observation and microhardness gradient detection. When the actually measured thickness of the gradient deformed layer is within 0.30 to 1.00 mm, the rolling process is determined to be qualified, and the penetration of the rolling tool shall not be directly used to replace the thickness of the gradient deformed layer.

[0043] Step 9, overall low-temperature treatment: Since the equivalent cross-sectional thickness of the guide slider blank in this embodiment is 20 mm, the forging obtained in step 8 is placed in a nitrogen-protected furnace and held at 320°C for 70 min, so that the residual stress generated by hot forging and ultrasonic surface rolling is released to a limited extent, while preventing the forging from undergoing sufficient recrystallization. After the heat preservation is completed, the forging is cooled in the furnace to 178°C at a cooling rate of 25°C / h, then taken out of the furnace and cooled to room temperature in still air. The witness specimen in the same furnace is used to compare the changes of the surface microhardness gradient and residual stress before and after the low-temperature treatment, so as to confirm that the selected low-temperature treatment system does not cause obvious recovery softening of the gradient deformed layer.

[0044] Step 10, finishing and performance inspection: Light finishing is performed on the working surface of the forging obtained in step 9, and the unilateral material removal is controlled to 0.02 mm to avoid cutting off the gradient deformed layer formed by ultrasonic surface rolling; after finishing, cleaning, drying and dimension inspection are carried out in sequence to obtain a friction-resistant high-toughness brass alloy forging.

[0045] Example 3 A preparation method of a friction-resistant high-toughness brass alloy comprises the following steps: The brass alloy comprises, in mass percentage: Zn 31%, Al 1.8%, Mn 1.5%, Fe 0.8%, Cr 0.2%, Zr 0.065%, the total amount of unavoidable impurities does not exceed 0.10%, and the balance is Cu, wherein the mass ratio of Cr to Zr is 3.1:1.

[0046] Step 1, Batching and Raw Material Pretreatment: Based on the target alloy composition described above, calculate and weigh each raw material according to the measured mass fraction of the target element in each raw material and the measured recovery rate of the corresponding element in the smelting equipment used. The raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy, and Cu-Zr40 master alloy; wherein, the amount of cathode copper is determined by deducting the Cu introduced by each master alloy from the target content of the remaining Cu, and the amount of zinc ingots is corrected according to the measured purity of zinc ingots and the measured recovery rate of Zn. The cathode copper, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, and Cu-Cr10 master alloy are preheated at 150℃ for 45 minutes to remove surface moisture; the Cu-Zr40 master alloy is kept sealed and dry, and is only unsealed before addition, and is not subjected to prolonged high-temperature preheating in air.

[0047] Step 2, Basic Melting: Melting is carried out in a medium-frequency induction furnace with argon protection. The crucible, sampling spoon, pressing tools, and stirring tools are thoroughly dried before use. First, the cathode copper calculated in Step 1 is added to the furnace and melted. The temperature of the copper melt is adjusted to 1150℃. The Cu-Fe20 master alloy and Cu-Mn20 master alloy are pressed below the surface of the melt in sequence. After Cu-Fe20 is completely melted, Cu-Mn20 is added. After both master alloys are completely melted, the melt is circulated at 1150℃ using induction stirring and held for 12 minutes to ensure that Fe and Mn diffuse evenly in the copper melt. During the holding period, a slight positive pressure of argon is maintained at the furnace opening, and the slag on the surface of the melt is removed.

[0048] Step 3, Cr-Zr alloying: Maintain the melt temperature obtained in Step 2 at 1145℃, add the Cu-Cr10 master alloy calculated in Step 1, ensuring the Cu-Cr10 is completely submerged in the melt surface, and hold for 10 minutes after induction stirring. Then, lower the melt temperature to 1080℃, and under argon protection, use a dried pressing tool to press the Cu-Zr40 master alloy below the melt surface to prevent prolonged exposure of Cu-Zr40 on the surface. Stir for 3 minutes after addition and continue holding for 5 minutes. By adding Cu-Cr10 at a higher temperature first, and then adding Cu-Zr40 at a lower temperature and under low oxygen conditions, Cr is fully melted into the copper-based melt, while reducing Zr oxidation loss.

[0049] Step 4, Al-Zn alloying: Adjust the melt temperature obtained in Step 3 to 1060℃, add the Cu-Al50 master alloy calculated in Step 1, and hold for 6.5 minutes after the Cu-Al50 has completely melted; then lower the melt temperature to 1000℃, divide the zinc ingots calculated in Step 1 into three batches of approximately equal mass, and press them below the melt surface. Add the next batch only after each batch of zinc ingots has completely melted. After all the zinc has melted, maintain the melt temperature at 1000℃ to avoid unnecessary long-term high-temperature holding to promote alloying, thereby reducing the burn-off of Zn and Al and compositional fluctuations.

[0050] Step 5, Melt Purification, Composition Correction, and Casting: Dry argon gas is introduced into the bottom of the melt obtained in Step 4 at a low flow rate for 4 minutes. After stopping the gas flow, the melt is allowed to stand for 4 minutes to allow inclusions to float to the surface. Then, the slag on the melt surface is removed. Samples are taken for direct-reading spectral analysis. Based on the test results, the composition is corrected using appropriate metals or intermediate alloys to ensure that the contents of Zn, Al, Mn, Fe, Cr, and Zr are within the allowable control range of the target composition in this embodiment. After the composition is qualified, the melt temperature is adjusted to 1010℃, and the melt is poured into a steel ingot mold preheated to 220℃ with an inner cavity diameter of 150mm using a bottom-pouring method. After the ingot cools to below 200℃, it is demolded and cooled to room temperature in still air to obtain a brass alloy ingot.

[0051] Step 6, Homogenization and Hot Forging: Remove oxide scale, folds, and other visible defects from the surface of the brass alloy ingot. Place the treated ingot in a nitrogen-protected furnace and heat it to 675℃ at a heating rate of 100℃ / h, holding it at that temperature for 2.5h. After homogenization, adjust the ingot temperature to 690℃ and transfer it to a forging die preheated to 280℃ for hot forging. Deformation is performed using a combination of multi-pass upsetting and drawing to achieve a cumulative cross-sectional compression ratio of 60%. Deformation is stopped when the forging temperature approaches 610℃, ensuring the final forging temperature is not lower than 600℃. Forge the ingot into a guide slide blank with an equivalent cross-sectional thickness of 20mm, and cool it to room temperature in still air after forging.

[0052] Step 7, Pre-machining of the working surface: The guide slider blank obtained in Step 6 is deburred and rough-machined to remove the surface oxide layer, folds, and obvious machining marks. The surface roughness of the surface to be used as the friction working surface is machined to Ra 1.2μm, and a 0.05mm dimensional correction allowance is reserved on this working surface. Other non-working surfaces are machined according to the forging design dimensions. After machining, a chlorine-free cleaning agent is used to remove the cutting fluid and machining particles from the surface, and the surface is thoroughly dried to avoid residues affecting the subsequent rolling quality.

[0053] Step 8, ultrasonic surface rolling: A ball-head type cemented carbide rolling tool is used to perform ultrasonic surface rolling on the working surface obtained in step 7. The ultrasonic frequency is set to 20 kHz, the amplitude to 11 μm, the static pressure to 0.7 kN, the single penetration depth to 0.14 mm, and the feed rate to 0.13 mm / r. A total of 3 passes of staggered rolling are carried out, and the rolling directions of two adjacent passes are opposite. Low-viscosity copper alloy rolling oil is continuously supplied during the rolling process, and a non-contact temperature measuring device is used to monitor the temperature of the working surface, so as to control the temperature of the working surface below 120°C; residual oil is cleaned after rolling. Witness specimens subjected to the same smelting, hot forging and rolling treatments are set in the same batch, and the gradient deformation layer is confirmed through cross-sectional metallographic observation and microhardness gradient testing. When the actually measured thickness of the gradient deformation layer is 0.30 to 1.00 mm, the rolling process is judged to be qualified, and the penetration depth of the rolling tool shall not be directly used to replace the thickness of the gradient deformation layer.

[0054] Step 9, integral low-temperature treatment: Since the equivalent section thickness of the guide slider blank in this embodiment is 20 mm, the forging obtained in step 8 is placed in a nitrogen-protected furnace and held at 325°C for 90 min, so that the residual stress generated by hot forging and ultrasonic surface rolling is limitedly released, while preventing the forging from undergoing sufficient recrystallization. After the heat preservation is completed, the forging is cooled in the furnace to 178°C at a cooling rate of 30°C / h, then taken out of the furnace and cooled to room temperature in still air. The witness specimen from the same furnace is used to compare the changes in the surface microhardness gradient and residual stress before and after the low-temperature treatment, so as to confirm that the selected low-temperature treatment regime does not cause obvious recovery softening of the gradient deformation layer.

[0055] Step 10, finishing and performance inspection: Light finishing is performed on the working surface of the forging obtained in step 9, and the unilateral material removal amount is controlled to 0.02 mm to avoid cutting off the gradient deformation layer formed by ultrasonic surface rolling; after finishing, cleaning, drying and dimension inspection are carried out in sequence to obtain a friction-resistant high-toughness brass alloy forging.

[0056] Embodiment 4 A preparation method of a friction-resistant high-toughness brass alloy, comprising the following steps: The brass alloy comprises, in mass percentage: Zn 32%, Al 2.1%, Mn 1.8%, Fe 0.9%, Cr 0.24%, Zr 0.08%, the total amount of unavoidable impurities does not exceed 0.10%, and the balance is Cu, wherein the mass ratio of Cr to Zr is 3:1.

[0057] Step 1, Batching and Raw Material Pretreatment: Based on the target alloy composition described above, calculate and weigh each raw material according to the measured mass fraction of the target element in each raw material and the measured recovery rate of the corresponding element in the smelting equipment used. The raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy, and Cu-Zr40 master alloy; wherein, the amount of cathode copper is determined by deducting the Cu introduced by each master alloy from the target content of the remaining Cu, and the amount of zinc ingots is corrected according to the measured purity of zinc ingots and the measured recovery rate of Zn. The cathode copper, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, and Cu-Cr10 master alloy are preheated at 150℃ for 45 minutes to remove surface moisture; the Cu-Zr40 master alloy is kept sealed and dry, and is only unsealed before addition, and is not subjected to prolonged high-temperature preheating in air.

[0058] Step 2, Basic Melting: Melting is carried out in a medium-frequency induction furnace with argon protection. The crucible, sampling spoon, pressing tools, and stirring tools are thoroughly dried before use. First, the cathode copper calculated in Step 1 is added to the furnace and melted. The temperature of the copper melt is adjusted to 1170℃. The Cu-Fe20 master alloy and Cu-Mn20 master alloy are pressed below the surface of the melt in sequence. After Cu-Fe20 is completely melted, Cu-Mn20 is added. After both master alloys are completely melted, the melt is circulated at 1150℃ using induction stirring and held for 15 minutes to ensure that Fe and Mn diffuse evenly in the copper melt. During the holding period, a slight positive pressure of argon gas is maintained at the furnace opening, and the slag on the surface of the melt is removed.

[0059] Step 3, Cr-Zr alloying: Maintain the melt temperature obtained in Step 2 at 1160℃, add the Cu-Cr10 master alloy calculated in Step 1, ensuring the Cu-Cr10 is completely submerged in the melt surface, and hold for 12 minutes after induction stirring. Then, lower the melt temperature to 1100℃, and under argon protection, use a dried pressing tool to press the Cu-Zr40 master alloy below the melt surface to prevent prolonged exposure of Cu-Zr40 on the surface. Stir for 4 minutes after addition and continue holding for 5 minutes. By adding Cu-Cr10 at a higher temperature first, and then adding Cu-Zr40 at a lower temperature and under low oxygen conditions, Cr is fully melted into the copper-based melt, while reducing Zr oxidation loss.

[0060] Step 4, Al-Zn alloying: Adjust the temperature of the melt obtained in Step 3 to 1080℃, add the Cu-Al50 master alloy calculated in Step 1, and hold for 8 minutes after the Cu-Al50 has completely melted; then lower the melt temperature to 1020℃, divide the zinc ingots calculated in Step 1 into three batches of roughly equal mass, and press them below the surface of the melt. Add the next batch only after each batch of zinc ingots has completely melted. After all the zinc has melted, maintain the melt temperature at 1020℃ to avoid unnecessary long-term high-temperature holding to promote alloying, thereby reducing the burn-off of Zn and Al and compositional fluctuations.

[0061] Step 5, Melt Purification, Composition Correction, and Casting: Dry argon gas is introduced into the bottom of the melt obtained in Step 4 at a low flow rate for 5 minutes. After stopping the gas flow, the melt is allowed to stand for 5 minutes to allow inclusions to float to the surface. Then, the slag on the melt surface is removed. Samples are taken for direct-reading spectral analysis. Based on the test results, the composition is corrected using appropriate metals or intermediate alloys to ensure that the contents of Zn, Al, Mn, Fe, Cr, and Zr are within the allowable control range of the target composition in this embodiment. After the composition is qualified, the melt temperature is adjusted to 1020℃, and the melt is poured into a steel ingot mold preheated to 250℃ with an inner cavity diameter of 180mm using a bottom-pouring method. After the ingot cools to below 200℃, it is demolded and cooled to room temperature in still air to obtain a brass alloy ingot.

[0062] Step 6, Homogenization and Hot Forging: Remove oxide scale, folds, and other visible defects from the surface of the brass alloy ingot. Place the treated ingot in a nitrogen-protected furnace and heat it to 690℃ at a heating rate of 120℃ / h, holding it at that temperature for 3 hours. After homogenization, adjust the ingot temperature to 710℃ and transfer it to a forging die preheated to 250-320℃ for hot forging. Deformation is performed using a combination of multi-pass upsetting and drawing to achieve a cumulative cross-sectional compression ratio of 70%. Deformation is stopped when the forging temperature approaches 610℃, ensuring the final forging temperature is not lower than 600℃. Forge the ingot into a guide slider blank with an equivalent cross-sectional thickness of 20mm, and cool it to room temperature in still air after forging.

[0063] Step 7, Pre-machining of the working surface: The guide slider blank obtained in Step 6 is deburred and rough-machined to remove the surface oxide layer, folds, and obvious machining marks. The surface roughness of the surface to be used as the friction working surface is machined to Ra 1.2μm, and a dimensional correction allowance of 0.08mm is reserved on this working surface. Other non-working surfaces are machined according to the forging design dimensions. After machining, a chlorine-free cleaning agent is used to remove the cutting fluid and machining particles from the surface, and the surface is thoroughly dried to avoid residues affecting the subsequent rolling quality.

[0064] Step 8, ultrasonic surface rolling: A ball-head type cemented carbide rolling tool is used to perform ultrasonic surface rolling on the working surface obtained in step 7. The ultrasonic frequency is set to 22 kHz, the amplitude to 14 μm, the static pressure to 0.9 kN, the single penetration to 0.18 mm, and the feed rate to 0.18 mm / r. A total of 4 passes of staggered rolling are carried out, and the rolling directions of two adjacent passes are opposite. During the rolling process, low-viscosity copper alloy rolling oil is continuously supplied, and a non-contact temperature measuring device is used to monitor the temperature of the working surface, so as to control the temperature of the working surface below 120°C; residual oil is cleaned after the rolling is completed. Witness specimens subjected to the same smelting, hot forging and rolling treatments are set in the same batch, the gradient deformation layer is confirmed through cross-sectional metallographic observation and microhardness gradient detection. When the actually measured thickness of the gradient deformation layer is 0.30 to 1.00 mm, the rolling process is judged to be qualified, and the penetration of the rolling tool shall not be directly used to replace the thickness of the gradient deformation layer.

[0065] Step 9, overall low-temperature treatment: Since the equivalent section thickness of the guide slider blank in this embodiment is 20 mm, the forging obtained in step 8 is placed in a nitrogen protection furnace, and held at 340°C for 120 min, so that the residual stress generated by hot forging and ultrasonic surface rolling is released to a limited extent, while preventing the forging from undergoing full recrystallization. After the heat preservation is completed, the forging is cooled in the furnace to 178°C at a cooling rate of 40°C / h, then taken out of the furnace and cooled to room temperature in still air. The witness specimen in the same furnace is used to compare the changes of the surface microhardness gradient and residual stress before and after the low-temperature treatment, so as to confirm that the selected low-temperature treatment system does not cause obvious recovery and softening of the gradient deformation layer.

[0066] Step 10, finishing and performance inspection: Light finishing is performed on the working surface of the forging obtained in step 9, and the unilateral material removal amount is controlled to 0.02 mm to avoid cutting off the gradient deformation layer formed by ultrasonic surface rolling; after finishing, cleaning, drying and dimension inspection are carried out in sequence to obtain a friction-resistant and high-toughness brass alloy forging.

[0067] Embodiment 5 A method for preparing a friction-resistant and high-toughness brass alloy, comprising the following steps: The brass alloy comprises, in mass percentage: 30% Zn, 1.6% Al, 1.2% Mn, 0.6% Fe, 0.15% Cr, 0.05% Zr, the total amount of unavoidable impurities does not exceed 0.10%, and the balance is Cu, wherein the mass ratio of Cr to Zr is 3:1.

[0068] Step 1, Batching and Raw Material Pretreatment: Based on the target alloy composition described above, calculate and weigh each raw material according to the measured mass fraction of the target element in each raw material and the measured recovery rate of the corresponding element in the smelting equipment used. The raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy, and Cu-Zr40 master alloy; wherein, the amount of cathode copper is determined by deducting the Cu introduced by each master alloy from the target content of the remaining Cu, and the amount of zinc ingots is corrected according to the measured purity of zinc ingots and the measured recovery rate of Zn. The cathode copper, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, and Cu-Cr10 master alloy are preheated at 150℃ for 45 minutes to remove surface moisture; the Cu-Zr40 master alloy is kept sealed and dry, and is only unsealed before addition, and is not subjected to prolonged high-temperature preheating in air.

[0069] Step 2, Basic Melting: Melting is carried out in a medium-frequency induction furnace with argon protection. The crucible, sampling spoon, pressing tools, and stirring tools are thoroughly dried before use. First, the cathode copper calculated in Step 1 is added to the furnace and melted. The temperature of the copper melt is adjusted to 1130℃. The Cu-Fe20 master alloy and Cu-Mn20 master alloy are pressed below the surface of the melt in sequence. After Cu-Fe20 is completely melted, Cu-Mn20 is added. After both master alloys are completely melted, the melt is circulated at 1150℃ using induction stirring and held for 10 minutes to ensure that Fe and Mn diffuse evenly in the copper melt. During the holding period, a slight positive pressure of argon is maintained at the furnace opening, and slag on the surface of the melt is removed.

[0070] Step 3, Cr-Zr alloying: Maintain the melt temperature obtained in Step 2 at 1130℃, add the Cu-Cr10 master alloy calculated in Step 1, ensuring the Cu-Cr10 is completely submerged in the melt surface, and hold at this temperature for 8 minutes after induction stirring. Then, lower the melt temperature to 1060℃, and under argon protection, use a dried pressing tool to press the Cu-Zr40 master alloy below the melt surface to prevent prolonged exposure of Cu-Zr40 on the surface. Stir for 2 minutes after addition and continue holding at this temperature for 5 minutes. By adding Cu-Cr10 at a higher temperature first, and then adding Cu-Zr40 at a lower temperature and under low oxygen conditions, Cr is fully melted into the copper-based melt, while reducing Zr oxidation loss.

[0071] Step 4, Al-Zn alloying: Adjust the melt temperature obtained in Step 3 to 1040℃, add the Cu-Al50 master alloy calculated in Step 1, and hold for 5 minutes after the Cu-Al50 has completely melted; then lower the melt temperature to 980℃, and press the zinc ingots calculated in Step 1 into three batches of roughly equal mass below the melt surface. Add the next batch only after each batch has completely melted. After all the zinc has melted, maintain the melt temperature at 980℃ to avoid unnecessary long-term high-temperature holding to promote alloying, thereby reducing the burn-off of Zn and Al and compositional fluctuations.

[0072] Step 5, Melt purification, composition correction, and casting: Dry argon gas is introduced into the bottom of the melt obtained in Step 4 at a low flow rate for 3 minutes. After stopping the gas flow, the melt is allowed to stand for 3 minutes to allow inclusions to float to the surface. Then, the slag on the surface of the melt is removed. Samples are taken for direct-reading spectral analysis. Based on the test results, the composition is corrected using the corresponding metal or intermediate alloy to ensure that the contents of Zn, Al, Mn, Fe, Cr, and Zr are within the controllable range of the target composition in this embodiment. After the composition is qualified, the melt temperature is adjusted to 1000℃, and the melt is poured into a steel ingot mold preheated to 180℃ with an inner cavity diameter of 120mm using a bottom-pouring method. After the ingot cools to below 200℃, it is demolded and cooled to room temperature in still air to obtain a brass alloy ingot.

[0073] Step 6, Homogenization and Hot Forging: Remove oxide scale, folds, and other visible defects from the surface of the brass alloy ingot. Place the treated ingot in a nitrogen-protected furnace and heat it to 660℃ at a rate of 80℃ / h, holding it at that temperature for 2 hours. After homogenization, adjust the ingot temperature to 670℃ and transfer it to a forging die preheated to 250℃ for hot forging. Deformation is performed using a combination of multi-pass upsetting and drawing to achieve a cumulative cross-sectional compression ratio of 50%. Deformation is stopped when the forging temperature approaches 610℃, ensuring the final forging temperature is not lower than 600℃. Forge the ingot into a guide slider blank with an equivalent cross-sectional thickness of 20mm, and cool it to room temperature in still air after forging.

[0074] Step 7, Pre-machining of the working surface: The guide slider blank obtained in Step 6 is deburred and rough-machined to remove the surface oxide layer, folds, and obvious machining marks. The surface roughness of the surface to be used as the friction working surface is machined to Ra 1.2μm, and a 0.03mm dimensional correction allowance is reserved on this working surface. Other non-working surfaces are machined according to the forging design dimensions. After machining, a chlorine-free cleaning agent is used to remove the cutting fluid and machining particles from the surface, and the surface is thoroughly dried to avoid residues affecting the subsequent rolling quality.

[0075] Step 8, ultrasonic surface rolling: A ball-head cemented carbide rolling tool is used to perform ultrasonic surface rolling on the working surface obtained in step 7. The ultrasonic frequency is set to 18 kHz, the amplitude is set to 8 μm, the static pressure is set to 0.5 kN, the single penetration depth is set to 0.1 mm, and the feed rate is set to 0.08 mm / r. A total of 2 passes of staggered rolling are carried out, and the rolling directions of two adjacent passes are opposite. During the rolling process, low-viscosity copper alloy rolling oil is continuously supplied, and a non-contact temperature measuring device is used to monitor the temperature of the working surface, so as to control the temperature of the working surface below 120°C; residual oil is cleaned after rolling. Witness specimens subjected to the same smelting, hot forging and rolling treatments are set in the same batch, and the gradient deformed layer is confirmed through cross-sectional metallographic observation and microhardness gradient detection. When the measured thickness of the gradient deformed layer is 0.30 to 1.00 mm, the rolling process is judged to be qualified, and the penetration depth of the rolling tool shall not be directly used to replace the thickness of the gradient deformed layer.

[0076] Step 9, integral low-temperature treatment: Since the equivalent section thickness of the guide slider blank in this embodiment is 20 mm, the forging obtained in step 8 is placed in a nitrogen protection furnace and held at 310°C for 60 min, so that the residual stress generated by hot forging and ultrasonic surface rolling is limitedly released, while avoiding sufficient recrystallization of the forging. After the heat preservation is completed, the forging is cooled in the furnace to 178°C at a cooling rate of 20°C / h, then taken out of the furnace and cooled to room temperature in still air. The witness specimen from the same furnace is used to compare the changes of the surface microhardness gradient and residual stress before and after the low-temperature treatment, so as to confirm that the selected low-temperature treatment system does not cause obvious recovery and softening of the gradient deformed layer.

[0077] Step 10, finishing and performance inspection: Light finishing is performed on the working surface of the forging obtained in step 9, and the unilateral material removal amount is controlled to 0.02 mm to avoid cutting off the gradient deformed layer formed by ultrasonic surface rolling; after finishing, cleaning, drying and dimension inspection are carried out in sequence to obtain the wear-resistant and high-toughness brass alloy forging.

[0078] Comparative Example 1: Compared with Example 5, this comparative example does not add the Cu-Cr10 master alloy, so that the alloy does not contain actively added Cr, the Zr content is still 0.05%, the balance is supplemented by Cu, and other conditions are the same as those in Example 5.

[0079] Comparative Example 2: Compared with Example 5, this comparative example does not add the Cu-Zr40 master alloy, so that the alloy does not contain actively added Zr, the Cr content is still 0.15%, the balance is supplemented by Cu, and other conditions are the same as those in Example 5.

[0080] Comparative Example 3: Compared with Example 5, this comparative example adjusts the Cr content to 0.12% and the Zr content to 0.08%, keeps the total content of Cr and Zr unchanged at 0.20%, but reduces the mass ratio of Cr to Zr from 3.0:1 to 1.5:1, and other conditions are the same as those in Example 5.

[0081] Comparative Example 4: Compared with Example 5, this comparative example omits the ultrasonic surface rolling treatment in step 8, and directly performs the overall low-temperature treatment in step 9 on the brass alloy forging with the pre-processed working surface. All other conditions are the same as in Example 5.

[0082] Comparative Example 5: Compared with Example 5, this comparative example turned off ultrasonic vibration and only used the same ball-head carbide tool, 0.5kN static pressure, 0.10mm single press-in amount and 0.08mm / r feed rate to perform ordinary mechanical rolling twice. All other conditions were the same as in Example 5.

[0083] Comparative Example 6: Compared with Example 5, this comparative example omits the overall low-temperature treatment in step 9 after ultrasonic surface rolling and directly performs finishing on the working surface. All other conditions are the same as in Example 5.

[0084] Comparative Example 7: Compared with Example 5, the overall low-temperature treatment conditions in this comparative example were adjusted from 310°C for 60 min to 400°C for 180 min. The cooling method and other conditions after the heat treatment were the same as in Example 5.

[0085] Comparative Example 8: Compared with Example 5, this comparative example cancels the segmented alloying sequence of adding Cu-Cr10 first and Cu-Zr40 later, and instead adds Cu-Zr40 master alloy first and then Cu-Cr10 master alloy at 1080°C. All other conditions are the same as in Example 5.

[0086] Comparative Example 9: Compared with Example 5, this comparative example omits the homogenization and hot forging in step 6. The ingot is directly processed into a guide slider blank with the same size as that in Example 5, and then the working surface is pre-processed, ultrasonically rolled and the whole low temperature is treated. All other conditions are the same as in Example 5.

[0087] Performance testing 1. Room Temperature Tensile Properties Test: Plate-shaped tensile specimens were cut from the middle of the forgings or test specimens from the same furnace in each embodiment and comparative example, along the main forging flow line, ensuring the sampling point was at least 2 mm from the working surface to eliminate interference from the surface rolling layer on the evaluation of the forging's main performance. The gauge length of the specimen was 25 mm, the width of the parallel section was 6 mm, and the thickness was 3 mm. The specimen surface was ground to remove the wire cutting influence layer. The test was conducted at 23±2℃ according to ISO 6892-1:2019, using an extensometer to measure the strain in the gauge length section. The initial strain rate before yielding was controlled at 2.5 × 10⁻⁶. -4 s -1 After measuring the specified plastic elongation strength Rp0.2 to 0.2%, the strain rate was adjusted to 1.0 × 10⁻⁶. -3 s -1The tensile strength Rm, Rp0.2, and elongation after fracture A were recorded until the specimen broke. Three parallel specimens were tested in each group, and the results were expressed as mean ± standard deviation of the sample.

[0088] 2. Charpy V-notch Impact Performance Test: A 10mm × 10mm × 55mm standard specimen was cut from the middle of each group of forgings or test specimens from the same furnace. The length of the specimen was parallel to the main forging flow line, and the notch direction was consistent across groups. A V-shaped notch with a depth of 2mm, an included angle of 45°, and a root radius of 0.25mm was machined in the middle of the specimen. Following ISO 148-1:2016, the test was conducted at 23±2℃ using a pendulum impact testing machine with a 2mm radius impact blade. The absorbed energy KV2 of the Charpy V-notch was recorded. Three parallel specimens were tested in each group, and the results are expressed as mean ± standard deviation of the sample. If smaller specimens must be used due to limitations in actual forging size, all samples should be of the same size, and the absorbed energy should be directly recorded in the report without converting it to the standard specimen result.

[0089] 3. Near-surface microhardness and gradient deformation layer thickness testing: A cross-sectional sample of the working surface was taken along a direction perpendicular to the rolling trajectory. After progressive grinding and polishing, the sample was subjected to Vickers microhardness testing in a non-corroded state according to ASTM E384-22. The test force was 0.98 N (HV0.1), and the holding time was 15 s. The center of the first row of indentations was 100 μm from the working surface. Subsequently, a row of measuring points was set every 100 μm along the depth direction until a depth of 1.20 mm was reached. The matrix hardness was measured at a distance of not less than 2.0 mm from the surface. Five indentations were set at each depth. The spacing between adjacent indentations and the distance from the indentation to the sample edge were controlled according to ASTM E384-22. The near-surface hardness in the table is the average value at 100 μm from the surface. The gradient deformation layer thickness was defined as the depth corresponding to the point where the hardness curve drops to 1.10 times the average matrix hardness, and was determined by linear interpolation of adjacent measuring points. The average value was calculated from three independent cross-sections in each group.

[0090] 4. Surface roughness test: After the sample is cleaned and dried with anhydrous ethanol, the surface roughness Ra of the working surface is measured using a stylus profilometer in accordance with ISO 21920-2:2021. The stylus tip radius is 2μm, the measuring force is 0.75mN, the cutoff wavelength is 0.8mm, and the evaluation length is 4.0mm. The measurement direction is perpendicular to the main rolling texture or machining texture. Five measurement lines are evenly selected on each sample, avoiding edges and visible defects. The arithmetic mean of the five lines is taken as the result of the group, and the original profile curve is saved at the same time.

[0091] 5. Reciprocating Friction and Wear Performance Test: Following the ball-plane reciprocating sliding procedure of ASTM G133-22, 20mm×20mm×6mm planar specimens were prepared from the working surface of each group of forgings. A 10mm diameter GCr15 steel ball with a hardness of not less than 60HRC was used as the mating part. Before the test, the specimens and steel balls were ultrasonically cleaned with anhydrous ethanol and dried. A new steel ball was used for each test. Under unlubricated conditions of 23±2℃ and 50±5% relative humidity, a normal load of 30N was applied, with a reciprocating stroke of 10mm, a frequency of 5Hz, and a total sliding distance of 1000m. The friction coefficient was continuously recorded, and the average value within the last 80% of the sliding distance after the running-in phase was taken as the steady-state friction coefficient. After the test, a three-dimensional optical profilometer was used to integrate the volume of the complete wear track to obtain the wear volume V, and the specific wear rate was calculated according to k=V / (F×L), where F is the normal load and L is the total sliding distance. Five specimens were tested in each group, and the results are expressed as the average value ± sample standard deviation. This test is used for the relative ranking of materials under the same working conditions and is not directly equivalent to the actual service life of the high-speed rail braking mechanism.

[0092] Table 1: The tensile and impact properties of the main bodies in Examples 5, 4, and 5 are similar, but the surface properties of the working parts differ significantly, indicating that ultrasonic surface rolling mainly acts on the surface layer of the forgings. In Comparative Example 4, after omitting the rolling process, the near-surface hardness is 158 HV0.1, no gradient deformation layer was detected, the surface roughness Ra is 0.44 μm, and the specific wear rate is 2.21 × 10⁻⁶. -5 mm³ / (N·m). In Comparative Example 5, after conventional mechanical rolling, the near-surface hardness increased to 178 HV0.1, forming a 0.15 mm hardened layer, and the specific wear rate decreased to 1.76 × 10⁻⁶ mm³ / (N·m). -5 mm 3 / (N·m). In Example 5, after ultrasonic surface rolling, the near-surface hardness increased to 205HV0.1, forming a 0.38mm gradient deformation layer, Ra decreased to 0.24μm, and the specific wear rate decreased to 1.43×10⁻⁶. -5 mm 3 / (N·m). Compared with Comparative Example 4, Example 5 showed a 29.7% increase in near-surface hardness, a 45.5% decrease in surface roughness, and a 35.3% decrease in specific wear rate; compared with Comparative Example 5, the specific wear rate was further reduced by 18.8%. This demonstrates that the combined effect of ultrasonic vibration and static pressure can deepen the plastic deformation layer, improve the surface load-bearing capacity, and reduce micro-protrusion engagement, thereby reducing material loss caused by adhesive tearing and fatigue spalling.

[0093] The results of Example 5, compared with Comparative Examples 1, 2, and 3, indicate that Cr, Zr, and their mass ratio primarily affect the retention of the roll-hardened layer after low-temperature treatment. Comparative Example 1, without added Cr, had a near-surface hardness of 190 HV0.1, a gradient layer thickness of 0.29 mm, and a specific wear rate of 1.63 × 10⁻⁶. -5 mm 3 / (N·m), which is 14.0% higher than that of Example 5. Comparative Example 2 without Zr has a near-surface hardness of 188 HV0.1, a gradient layer thickness of 0.24 mm, and a specific wear rate of 1.71 × 10⁻⁶. -5 mm 3 / (N·m), which is 19.6% higher than that of Example 5. Comparative Example 3, with a Cr to Zr mass ratio of 1.5:1, has a near-surface hardness of 194 HV0.1, a gradient layer thickness of 0.28 mm, and a specific wear rate of 1.55 × 10⁻⁶. -5 mm 3 / (N·m), which is 8.4% higher than that of Example 5. Example 5 contains 0.15%Cr and 0.05%Zr, and the mass ratio of the two is controlled at 3.0:1. After low temperature treatment, it can still retain a near-surface hardness of 205HV0.1 and a gradient deformation layer of 0.38mm, indicating that this ratio is more conducive to suppressing the recovery softening of the rolling layer and maintaining wear resistance and load-bearing capacity.

[0094] The comparison between Example 5 and Comparative Examples 6 and 7 reflects the balancing effect of the cryogenic treatment on hardness and toughness. Comparative Example 6, omitting the cryogenic treatment, exhibits a near-surface hardness of 213 HV0.1, an increase of 8 HV0.1 compared to Example 5, and a gradient layer thickness increase of 0.05 mm; however, its elongation after fracture decreased from 25.6% to 21.4%, its impact absorption energy decreased from 36.8 J to 28.3 J, and its specific wear rate decreased from 1.43 × 10⁻⁶. -5 mm 3 / (N·m) increased to 1.47×10 -5 mm 3 / (N·m). This result indicates that although the high-strain surface layer without finite recovery has high hardness, the residual stress and local strain concentration are not conducive to the forging's absorption of impact energy and are also prone to local cracking during long-distance reciprocating friction. Comparative Example 7, after being held at 400℃ for 180 min, showed an increase in elongation after fracture to 28.4% and an increase in impact absorption energy to 38.6 J, but a decrease in tensile strength to 552 MPa, a decrease in near-surface hardness to 179 HV0.1, a decrease in gradient layer thickness to 0.17 mm, and an increase in specific wear rate to 1.88 × 10⁻⁶. -5 mm 3 / (N·m). Therefore, in Example 5, holding at 310℃ for 60 minutes can release some of the harmful residual stress while retaining more of the surface work hardening and gradient structure, thus balancing toughness and wear resistance.

[0095] Comparative Example 8, after changing the order of adding Cu-Cr10 and Cu-Zr40 master alloys, showed a tensile strength of 573 MPa, an elongation after fracture of 20.7%, an impact absorption energy of 25.4 J, a near-surface hardness of 189 HV0.1, and a specific wear rate of 1.68 × 10⁻⁶. - 5 mm 3 / (N·m), all results are lower than the corresponding performance of Example 5. This change is consistent with the expected effects of Zr oxidation loss and increased oxidation inclusions. Comparative Example 9, after omitting homogenization and hot forging, has a tensile strength of only 508 MPa, an elongation after fracture of 9.7%, an impact absorption energy of 12.8 J, and a specific wear rate of 2.05 × 10⁻⁶. -5 mm 3 / (N·m); Although its near-surface hardness still reaches 196HV0.1, the coarse as-cast structure, compositional segregation and casting defects weaken the support capacity under the hardened surface layer, indicating that higher surface hardness cannot replace the role of homogenization and hot forging in improving the main structure and toughness of the forging.

[0096] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a friction-resistant, high-toughness brass alloy, characterized in that, Includes the following steps: The raw materials are prepared according to the alloy composition and then melted and cast in sequence to obtain alloy ingots; The alloy comprises, by mass percentage: Zn 30.0–32.0%, Al 1.6–2.1%, Mn 1.2–1.8%, Fe 0.60–0.90%, Cr 0.15–0.24%, Zr 0.05–0.08%, with the balance being Cu and unavoidable impurities, and the mass ratio of Cr to Zr being 2.5–3.2:1; wherein Cr and Zr are introduced through Cu-Cr master alloy and Cu-Zr master alloy, respectively; The alloy ingot is homogenized and hot-forged to obtain a brass alloy forging. The working surface of the brass alloy forging is subjected to ultrasonic surface rolling treatment to form a gradient deformation layer extending from the working surface into the interior of the forging; and The brass alloy forgings that have undergone ultrasonic surface rolling are held at 310–340°C for 60–120 min and then cooled to obtain the wear-resistant and high-toughness brass alloy forgings.

2. The preparation method according to claim 1, characterized in that, The raw materials include cathode copper, zinc ingots, Cu-Al50 master alloy, Cu-Mn20 master alloy, Cu-Fe20 master alloy, Cu-Cr10 master alloy and Cu-Zr40 master alloy; The Cu-Cr10 master alloy is added to the melt before the Cu-Zr40 master alloy, and the Cu-Zr40 master alloy is added below the melt surface under argon protection.

3. The preparation method according to claim 2, characterized in that, The smelting includes: The cathode copper is melted, and Cu-Fe20 master alloy and Cu-Mn20 master alloy are added sequentially at 1130-1170℃, and the temperature is held for 10-15 minutes. Add Cu-Cr10 master alloy at 1130-1160℃, hold for 8-12 minutes, then reduce the melt temperature to 1060-1100℃ and add Cu-Zr40 master alloy. Stir for 2-4 minutes and hold for no more than 6 minutes. Add Cu-Al50 master alloy at 1040–1080℃ and hold for 5–8 minutes; and Reduce the melt temperature to 980-1020℃, add the zinc ingots to the melt in 2-3 batches, and add the next batch only after each batch of zinc ingots has completely melted.

4. The preparation method according to claim 3, characterized in that, After the zinc ingot is completely melted, dry argon gas is introduced into the bottom of the melt for 3-5 minutes, and the melt is allowed to stand for 3-5 minutes to remove surface slag. After composition testing and correction, the melt is poured into a steel ingot mold preheated to 180-250°C at 1000-1020°C using a bottom-pouring method to obtain an alloy ingot with a diameter or equivalent thickness of 120-180 mm.

5. The preparation method according to claim 1, characterized in that, The homogenization treatment includes heating the alloy ingot to 660-690°C at a heating rate of 80-120°C / h under nitrogen protection and holding it at that temperature for 2-3 hours; the hot forging process includes adjusting the temperature of the homogenized alloy ingot to 670-710°C and then starting forging, performing final forging at a temperature not lower than 600°C, with a cumulative cross-sectional compression rate of 50-70%, and using a forging die at a temperature of 250-320°C.

6. The preparation method according to claim 1, characterized in that, Before the ultrasonic surface rolling treatment, the hot-forged brass alloy forging is deburred and rough-machined so that the surface roughness Ra of the working surface to be rolled is no greater than 1.6 μm, and a dimensional correction allowance of 0.03 to 0.08 mm is reserved on the working surface.

7. The preparation method according to claim 1, characterized in that, The ultrasonic surface rolling treatment uses a ball-head or circular arc roller type carbide tool, with an ultrasonic frequency of 18-22kHz, an amplitude of 8-14μm, a static pressure of 0.5-0.9kN, a single indentation of 0.10-0.18mm, a feed rate of 0.08-0.18mm / r, and 2-4 alternating rolling passes, with adjacent rolling passes in opposite directions. The ultrasonic surface rolling process uses low-viscosity copper alloy rolling oil for lubrication and controls the temperature of the working surface to be no higher than 120°C; the thickness of the resulting gradient deformation layer is 0.30 to 1.00 mm.

8. The preparation method according to claim 1, characterized in that, The insulation is carried out under nitrogen protection.

9. The preparation method according to claim 1, characterized in that, After the heat preservation and cooling, the working surface is finished, and the amount of material removed from one side of the working surface does not exceed 0.02 mm.

10. A friction-resistant, high-toughness brass alloy, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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