A preparation method of a high-strength and high-toughness lead-tin bronze rod

Abstract

The preparation method of a high-strength and high-toughness lead-tin bronze rod of the present invention relates to the technical field of lead-tin bronze rod processing, and specifically relates to a preparation method of a high-strength and high-toughness lead-tin bronze rod, including the following steps: heating metal materials containing lead, tin, nickel, and the remaining component being copper to a liquid state, pouring them into a water-cooled copper mold and starting the water-cooling cycle to obtain a as-cast lead-tin bronze alloy; assembling the as-cast lead-tin bronze alloy in the blind hole on a copper sleeve to form a combined blank body; performing annealing treatment and applying a glass lubricant, and spraying a cubic boron nitride mold release agent spray on the mold; placing the combined blank body in a tapered mold for hot extrusion; and performing heat treatment to obtain a high-quality lead-tin bronze rod meeting the standards; the present invention can reduce the surface cracking problem caused by the contact friction between the lead-tin bronze and the mold, improve the hot brittleness problem in the hot working process of the alloy, inhibit the generation of cracking problems in the extrusion deformation process, and finally obtain a rod without crack defects on the surface and in the core.

Description

Technical Field

[0001] The present invention relates to the technical field of lead-tin bronze bar processing, and specifically relates to a preparation method for a high-strength and high-toughness lead-tin bronze bar. Background Art

[0002] The rotor of a high-pressure plunger pump for aviation is one of the most important components in the aircraft hydraulic system. Its performance and quality determine the transmission efficiency and service life of the high-pressure plunger pump. The inner lining of the high-pressure plunger pump rotor is wear-resistant lead-tin bronze. The presence of lead endows the alloy with excellent self-lubricity, effectively reducing friction and wear performance, while enhancing the wear resistance and fatigue resistance of the material. At the same time, the soft particles of lead can disperse stress concentration and reduce the formation of fatigue cracks. Therefore, compared with other copper alloys, lead-tin bronze has higher mechanical strength, wear resistance, self-lubricity and corrosion resistance, and is suitable for more demanding service environments. It is the core material for high-end pump bodies.

[0003] Currently, the preparation method of lead-tin bronze is the casting method. As a multi-element high-solute copper alloy, lead in lead-tin bronze is insoluble in copper, and the solid solubility of tin in copper at room temperature is only 0.5 wt.%. There are defects such as lead particle aggregation, tin-rich phase segregation and microcracks in the as-cast structure of the alloy, resulting in its mechanical properties being difficult to meet the requirements of high-speed and heavy-load service conditions. At the same time, lead-tin bronze has a significant volume shrinkage during solidification, and there are more shrinkage cavities and porosity in the casting, reducing the strength, durability and overall stability of the casting.

[0004] In summary, there are many defects such as lead particle aggregation, tin-rich phase segregation and microcracks in the as-cast lead-tin bronze, resulting in its strength and wear resistance being unable to meet the service requirements of high-speed and heavy-load, which has become a bottleneck problem restricting the improvement of the service performance of the rotor bushing of the high-pressure plunger pump for aviation.

[0005] Currently, there have been many reports on the research of improving the mechanical properties of as-cast multi-element copper alloys:

[0006] The patent "202011073090.9" describes a hot extrusion forming method for copper alloy tracks. The steps are as follows: ⑴ Blank processing: ① Saw cutting of forged bright blank round steel; ② Drilling in the center of the blank; ③ Turning, polishing the outer surface and the head; ⑵ Blank heating: The heating temperature is 900 - 950 °C; ⑶ Preparation of working dies: Using extrusion dies with the same shape; ⑷ Lubrication: Applying lubricant to the extrusion die, manipulator and extrusion cylinder; ⑸ Hot extrusion: Hot extruding the blank into shape; ⑹ Cooling: Cooling the copper alloy track to room temperature; ⑺ Solution heat treatment: The heating temperature is 930 - 950 °C; ⑻ Inspection: Inspecting the hardness and conductivity; ⑼ Straightening: Straightening the copper alloy track; ⑽ Cold drawing: Cold drawing the copper alloy track; ⑾ Aging heat treatment; ⑿ Inspecting the cross-sectional hardness, conductivity, and room temperature tensile strength; ⒀ Straightening. By optimizing the die design and the extrusion forming process, the present invention ensures that the workpiece is formed in one step, and the produced copper alloy track has good surface quality, improving the physical, chemical, and mechanical properties of the product.

[0007] The patent "202010801676.6" reports a semi-solid backward extrusion method for bushing parts, belonging to the field of semi-solid forming. The method of the present invention is as follows: Heating the semi-solid blank obtained by the SIMA method from an alloy material to a temperature above the solidus temperature and holding it, then putting it into a preheated die for backward extrusion forming and holding pressure, quenching the part after backward extrusion in water, and finally performing short-time solution + aging heat treatment. The method of the present invention adopts the semi-solid backward extrusion forming method, which has high production efficiency, low energy consumption, high product quality, high material utilization rate, and is easy to realize mechanized and automated production.

[0008] In summary, hot extrusion can improve the microstructure of copper alloys and significantly enhance their mechanical properties. However, the addition of lead particles in lead-tin bronze makes it different from other copper alloys. On the one hand, lead is a low melting point phase, with a melting point of 327.5 °C, while the hot extrusion temperature of copper alloys needs to be between 600 °C and 900 °C. The huge temperature difference makes it difficult to solve the hot brittleness of the lead-containing alloy during the hot extrusion process. The lead-tin bronze rod is extremely easy to break during the extrusion process, and the distribution of lead particles is difficult to control, resulting in limited performance improvement. On the other hand, the solid solubility of tin in copper at room temperature is extremely limited. After hot extrusion, there are a large number of tin-rich phases in the microstructure of lead-tin bronze, deteriorating the plasticity and toughness of the alloy, and it is difficult to meet the performance requirements of wear-resistant lead-tin bronze in the harsh service environment of the aviation field. Therefore, how to further post-treat to strengthen the alloy performance is particularly important. Summary of the Invention

[0009] To solve the above problems, the present invention provides a method for preparing a high-strength and high-toughness lead-tin bronze rod. This method uses the method of "preheat treatment to regulate the distribution morphology of lead particles + extrusion with a tapered die sleeve" to improve the plasticity during the hot extrusion process of lead-tin bronze, successfully realizing the hot extrusion forming of lead-tin bronze, and improving the mechanical properties of the alloy by refining the grain size and regulating the distribution morphology of lead particles. Further, current pulse heat treatment is performed on the extruded rod to regulate the content and distribution of tin-rich phases in the rod after hot extrusion, and finally a high-performance lead-tin bronze alloy rod is obtained.

[0010] A method for preparing a high-strength and high-toughness lead-tin bronze rod according to the present invention includes the following steps:

[0011] Step 1: According to the weight percentage, heat metal materials containing 2.0%-3.25% lead, 7.0%-11.0% tin, 3.0%-4.0% nickel, and the remaining component being copper to a liquid state, pour them into a water-cooled copper mold and start the water-cooling cycle. After cooling, take them out to obtain a as-cast lead-tin bronze alloy.

[0012] Step 2: Use electrolytic purple copper with a purity of 99.9% for machining to make a copper sleeve with a blind hole, assemble the as-cast lead-tin bronze obtained in the previous step into the blind hole of the copper sleeve, and seal the open end of the blind hole of the assembled copper sleeve to form an integral combined blank body.

[0013] Step 3: Anneal the assembled combined blank body at 270°C - 330°C for 25 min - 35 min and apply glass lubricant, then air-cool to 50°C - 100°C.

[0014] Step 4: Perform preheat treatment on a tapered extrusion die with a taper of 67° - 70°, a depth of 30 mm - 35 mm, and a diameter of 20 mm at 380°C - 400°C for a preheat duration of 0.5 h - 1 h. After the preheat is completed, spray cubic boron nitride release agent spray on the die.

[0015] Step 5: Put the assembled combined blank body into a muffle furnace and heat it from 350°C - 400°C to 600°C - 800°C at a heating rate of 5°C - 10°C per minute, and hold for 30 min - 45 min.

[0016] Step 6: Place the combined blank body heated in Step 5 in the tapered die for hot extrusion. The hot extrusion temperature is 650°C - 800°C, and quench the extruded combined blank body to obtain an extruded sample.

[0017] Step 7: Perform heat treatment on the extruded sample obtained in Step 6 to obtain a high-quality lead-tin bronze rod meeting the standards.

[0018] Preferably, the extrusion ratio of the hot extrusion process is 9:1, and the extrusion speed is 5 mm / s - 10 mm / s.

[0019] Preferably, the extruded samples are heat-treated, and the heat treatment is electro-pulse treatment. The voltage of the electro-pulse is set to 50 V - 100 V, the treatment time is 35 s - 40 s, the frequency range is 350 Hz - 500 Hz, and after the electro-pulse treatment is completed, it is cooled to room temperature.

[0020] Preferably, the extruded samples are heat-treated, and the heat treatment is solution treatment. The extruded samples are held at 650 °C - 750 °C for 1 h - 2 h and then air-cooled to room temperature.

[0021] The present invention proposes to place the as-cast lead-tin bronze in a blind-hole copper sleeve. The copper is in direct contact with the mold, reducing the surface cracking problem caused by the contact friction between the lead-tin bronze and the mold. At the same time, through a pre-treatment of holding at 380 °C - 400 °C for 0.5 h - 1 h, the wetting angle between α-Cu and lead particles in the lead-tin bronze is regulated, improving the hot brittleness problem during the hot working process of the alloy, suppressing the cracking problem during the extrusion deformation process, and finally obtaining a bar without crack defects on the surface and in the core.

[0022] The present invention uses electro-pulse treatment to regulate the microstructure distribution of the bar after hot extrusion. The electro-pulse treatment has both electrical and thermal effects. By the way of internal heating, it can significantly reduce the volume fraction of the tin-rich phase in the alloy, promote the recrystallization of α-Cu and the dispersion distribution of lead particles. At the same time, compared with other heat treatment methods, the electro-pulse treatment time is shorter, the grain growth effect is inhibited, and the strength and plasticity-toughness of the alloy can be further improved.

[0023] The present invention uses solution treatment to regulate the microstructure distribution of the bar after hot extrusion. During the solution treatment, the tin-rich phase dissolves back, the α-Cu matrix recrystallizes and the grains grow, and the lead particles are redispersed in the α-Cu matrix structure, which helps to further improve the strength and plasticity-toughness of the alloy. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the as-cast structure of the alloy in Example 1.

[0025] Figure 2 It is a schematic diagram of the microstructure of the extruded sample in Example 2.

[0026] Figure 3 It is a schematic diagram of the microstructure after electro-pulse treatment in Example 1.

[0027] Figure 4 It is a schematic diagram of the microstructure of the extruded sample in Example 2 after solution treatment. Detailed Embodiments

[0028] A preparation method of a high-strength and high-toughness lead-tin bronze bar according to the present invention comprises the following steps:

[0029] Step 1: According to the weight percentage, heat metal materials containing 2.0%-3.25% of lead, 7.0%-11.0% of tin, 3.0%-4.0% of nickel, and the remaining component being copper to a liquid state, pour them into a water-cooled copper mold and start the water-cooling cycle. After cooling, take them out to obtain a as-cast lead-tin bronze alloy.

[0030] Step 2: Use electrolytic purple copper with a purity of 99.9% for machining to make a copper sleeve with blind holes, assemble the as-cast lead-tin bronze alloy obtained in the previous step into the blind holes of the copper sleeve, and seal the open end of the blind holes of the assembled copper sleeve to form an integral combined blank body.

[0031] Step 3: Anneal the assembled combined blank body at 270°C - 330°C for 25 min - 35 min and apply a glass lubricant, then air-cool to 50°C - 100°C.

[0032] Step 4: Preheat a taper extrusion die with a taper of 67° - 70°, a depth of 30 mm - 35 mm, and a diameter of 20 mm at 380°C - 400°C for 0.5 h - 1 h. After the preheating is completed, spray a cubic boron nitride release agent spray on the die.

[0033] Step 5: Put the assembled combined blank body into a muffle furnace and heat it from 350°C - 400°C to 600°C - 800°C at a heating rate of 5°C - 10°C per minute, and hold for 30 min - 45 min.

[0034] Step 6: Place the combined blank body heated in Step 5 into the taper die for hot extrusion. The hot extrusion temperature is 650°C - 800°C, and quench the extruded combined blank body to obtain an extruded sample.

[0035] Step 7: Heat-treat the extruded sample obtained in Step 6 to obtain a high-quality lead-tin bronze bar meeting the standards.

[0036] In one embodiment, the extrusion ratio of the hot extrusion process is 9:1, and the extrusion speed is 5 mm / s - 10 mm / s.

[0037] In one embodiment, the extruded sample is heat-treated, and this heat treatment is an electric pulse treatment. The voltage of the electric pulse is set to 50 V - 100 V, the treatment time is 35 s - 40 s, the frequency range is 350 Hz - 500 Hz, and after the electric pulse treatment is completed, it is cooled to room temperature.

[0038] In one embodiment, the extruded sample is subjected to a heat treatment, which is a solution treatment. The extruded sample is heated at 650°C - 750°C for 1h - 2h and then air-cooled to room temperature.

[0039] Example 1: A method for preparing a high-strength and high-toughness lead-tin bronze rod according to the present invention includes the following steps:

[0040] Step 1: According to the weight percentage, an alloy of 2.3% lead, 7.79% tin, 4.0% nickel, and the remaining components being copper is heated to a liquid state, poured into a water-cooled copper mold, and the water-cooling cycle is started. After cooling, it is taken out to obtain a cast rod-shaped lead-tin bronze alloy.

[0041] Step 2: Electrolytic purple copper with a purity of 99.9% is machined to produce a copper sleeve with a blind hole having a bottom thickness of 20 mm and an inner diameter of 45 mm. The cast rod-shaped lead-tin bronze alloy obtained in the previous step is machined to a diameter of 45 mm and assembled in the blind hole of the copper sleeve. The open end of the blind hole of the assembled copper sleeve is subjected to vacuum sealing welding treatment to form an integral combined blank body.

[0042] Step 3: The combined blank body is annealed at 300°C for 25 min, coated with a glass lubricant, and then air-cooled to 50°C.

[0043] The annealing temperature can preferably be 300°C. The purpose is to regulate the tissue composition of the lead-tin bronze, ensure the extrusion quality, increase the proportion of the (α + β) / β phase by pre-treating the lead-tin bronze at 300°C, and at the same time regulate the distribution of lead particles in the lead-tin bronze to ensure that the lead particles are evenly dispersed in the matrix in a spherical shape, ensuring the quality of the subsequent processed products.

[0044] The purpose of coating the glass lubricant is to reduce the heat generated by friction, thereby preventing local overheating during extrusion and reducing the deterioration of material properties caused by overheating. It ensures the surface quality of the hot-extruded product. And in a high-temperature environment, metal materials are prone to oxidation reactions. The lubricant can act as a barrier layer to reduce the contact between the metal and air and prevent the oxidation of the material surface.

[0045] Step 4: The tapered die with a taper of 67°, a depth of 35 mm, and a diameter of 20 mm is preheated at 400°C for 1 h, and a cubic boron nitride release agent spray is applied.

[0046] Compared with flat die extrusion, tapered die extrusion can significantly reduce stress concentration and improve the processing plasticity of the alloy.

[0047] Step 5: The combined blank body is placed in a muffle furnace and heated from 400°C to 750°C at a heating rate of 7°C per minute and held for 45 min.

[0048] Step 6: Place the heated combined blank body in Step 5 into a tapered die for hot extrusion process. The hot extrusion temperature is 750 °C, and the extruded combined blank is quenched to obtain an extruded sample;

[0049] The extrusion process parameters are determined according to the following method: Conduct a hot simulation compression experiment on lead-tin bronze alloy. The experimental temperature is 600 °C - 800 °C, and the strain rate is 0.01 - 10. Based on the obtained stress-strain curves, establish the Arrhenius model and Arvaim model. Combine the geometric model and boundary conditions, namely the thermal conductivity coefficient of the environment is 50 w / m²·k and the friction ratio factor is 0.4, to establish an extrusion finite element model. Study the process of extrusion temperature range 600 °C - 800 °C, extrusion speed 0.01 - 10, and extrusion ratios of 4:1, 9:1, and 16:1 respectively, to obtain the strain distribution law, temperature distribution law, and recrystallized volume fraction distribution law. The optimal extrusion parameters are determined as follows: extrusion temperature 750 °C, extrusion ratio 9:1, and extrusion speed 10 mm / s;

[0050] Step 7: Conduct electro-pulse treatment on the extruded sample in Step 6. Specifically, the voltage of the electro-pulse is set to 65 V, the treatment time is 35 s, and the frequency is 350 Hz. After the electro-pulse treatment is completed, it is cooled to room temperature to obtain high-quality lead-tin bronze bars that meet the standards; The test results show that the tensile strength of the alloy after electro-pulse treatment reaches 450.7 MPa, and the elongation rate reaches 28.9%, fully meeting the performance standards specified in the Specification for Metal Mold Castings of Copper Alloys for Aviation HB - 2002 of the People's Republic of China's aviation industry: tensile strength greater than 238 MPa and elongation rate greater than 5%.

[0051] Example 2, A method for preparing a high-strength and high-toughness lead-tin bronze bar of the present invention includes the following steps:

[0052] Step 1: Heat an alloy containing 2.3% lead, 7.79% tin, 4.0% nickel, and the remaining component being copper to a liquid state by weight percentage, pour it into a water-cooled copper mold and start the water-cooling cycle, and take it out after cooling to obtain a cast rod-shaped lead-tin bronze alloy;

[0053] Step 2: Use electrolytic purple copper with a purity of 99.9% for machining to make a copper jacket with a blind hole having a bottom thickness of 20 mm and an inner diameter of 45 mm. Machine the cast rod-shaped lead-tin bronze alloy obtained in the previous step to a diameter of 45 mm and assemble it in the blind hole of the copper jacket. Perform vacuum sealing welding on the open end of the blind hole of the assembled copper jacket to form an integral combined blank body;

[0054] Step 3: Anneal the combined blank body at 300 °C for 25 min, apply glass lubricant, and then air-cool it to 50 °C;

[0055] The annealing temperature can preferably be 300 °C, the purpose of which is to regulate the tissue composition of lead-tin bronze, ensure the extrusion quality, increase the proportion of (α + β) / β phase by pre-treating lead-tin bronze at 300 °C, and at the same time regulate the distribution of lead particles in lead-tin bronze to ensure that the lead particles are evenly dispersed in the matrix in a spherical shape, ensuring the quality of the subsequent processed products;

[0056] The purpose of applying glass lubricant is to reduce the heat generated by friction, thereby preventing the local temperature from being too high during extrusion and reducing the deterioration of material properties caused by overheating. It ensures the surface quality of the hot-extruded products. And in a high-temperature environment, metal materials are prone to oxidation reactions. The lubricant can act as an isolation layer to reduce the contact between the metal and air and prevent the oxidation of the material surface;

[0057] Step 4: Perform a preheating treatment on the tapered die with a taper of 67°, a depth of 35 mm, and a diameter of 20 mm at 400 °C for 1 hour, and spray cubic boron nitride release agent spray;

[0058] Compared with flat die extrusion, tapered die extrusion can significantly reduce stress concentration and improve the processing plasticity of the alloy;

[0059] Step 5: Place the combined blank body into a muffle furnace and heat it from 400 °C to 750 °C at a heating rate of 7 °C per minute, and hold for 45 minutes;

[0060] Step 6: Place the combined blank body heated in Step 5 into the tapered die for hot extrusion process. The hot extrusion temperature is 750 °C, and the extruded combined blank is quenched to obtain an extruded sample;

[0061] The extrusion process parameters are determined according to the following method: Conduct a hot simulation compression experiment on lead-tin bronze alloy at an experimental temperature of 600 °C - 800 °C and a strain rate of 0.01 - 10. Based on the obtained stress-strain curve, establish the Arrhenius model and the Arvaim model. Combine the geometric model and boundary conditions, i.e., the heat transfer coefficient of the environment is 50 w / m²·k and the friction ratio factor is 0.4, to establish an extrusion finite element model. Study the processes of extrusion temperature range of 600 °C - 800 °C, extrusion speed of 0.01 - 10, and extrusion ratios of 4:1, 9:1, and 16:1 respectively, and obtain the strain distribution law, temperature distribution law, and recrystallized volume fraction distribution law. The optimal extrusion parameters are determined as: extrusion temperature of 750 °C, extrusion ratio of 9:1, and extrusion speed of 10 mm / s;

[0062] Step 7: Solution treatment is carried out on the extruded sample in Step 6. The extruded sample is heated at 650 °C for 2 h and then air-cooled to room temperature to obtain high-quality lead-tin bronze bars meeting the standards. The test results show that the tensile strength of the alloy after solution treatment reaches 446.5 MPa and the elongation reaches 29.2%, fully meeting the performance standards specified in the Specification for Metal Mold Castings of Copper Alloys for Aviation, HB-2002 of the People's Republic of China: the tensile strength is greater than 238 MPa and the elongation is greater than 5%.

[0063] Example 3. A preparation method of a high-strength and high-toughness lead-tin bronze bar of the present invention includes the following steps:

[0064] Step 1: By weight percentage, an alloy containing 2.3% lead, 7.79% tin, 4.0% nickel, and the remaining components being copper is heated to a liquid state, poured into a water-cooled copper mold, and the water-cooling cycle is started. After cooling, it is taken out to obtain a cast rod-shaped lead-tin bronze alloy;

[0065] Step 2: Electrolytic purple copper with a purity of 99.9% is machined to produce a copper jacket with a blind hole having a bottom thickness of 20 mm and an inner diameter of 45 mm. The cast rod-shaped lead-tin bronze alloy obtained in the previous step is machined to a diameter of 45 mm and assembled in the blind hole of the copper jacket. The open end of the blind hole of the assembled copper jacket is subjected to vacuum sealing welding to form an integral combined blank body;

[0066] Step 3: After annealing the combined blank body at 300 °C for 25 min and applying a glass lubricant, it is air-cooled to 50 °C;

[0067] The annealing temperature can preferably be 300 °C. The purpose is to regulate the tissue components of the lead-tin bronze, ensure the extrusion quality, increase the proportion of (α + β) / β phase by pre-treating the lead-tin bronze at 300 °C, and at the same time regulate the distribution of lead particles in the lead-tin bronze to ensure that the lead particles are evenly dispersed in the matrix in a spherical shape, ensuring the quality of the subsequent processed products;

[0068] The purpose of applying the glass lubricant is to reduce the heat generated by friction, thereby preventing local overheating during the extrusion process and reducing the deterioration of material properties caused by overheating. It ensures the surface quality of the hot-extruded product, and in a high-temperature environment, metal materials are prone to oxidation reactions. The lubricant can act as an isolation layer to reduce the contact between the metal and air and prevent the oxidation phenomenon on the material surface;

[0069] Step 4: The taper die with a taper of 67°, a depth of 35 mm, and a diameter of 20 mm is preheated at 400 °C for 1 h, and a cubic boron nitride release agent spray is applied;

[0070] Compared with flat die extrusion, taper die extrusion can significantly reduce stress concentration and improve the processing plasticity of the alloy;

[0071] Step 5: Place the combined blank body into a muffle furnace, heat it from 400 °C to 750 °C at a heating rate of 7 °C per minute, and hold for 45 min;

[0072] Step 6: Place the heated combined blank body in a tapered die for hot extrusion process. The hot extrusion temperature is 750 °C, and the extruded combined blank is quenched to obtain an extruded sample;

[0073] The extrusion process parameters are determined according to the following method: Conduct a hot simulation compression experiment on lead-tin bronze alloy at an experimental temperature of 600 °C - 800 °C and a strain rate of 0.01 - 10. Based on the obtained stress-strain curve, establish the Arrhenius model and the Arvaim model. Combine the geometric model and boundary conditions, i.e., the heat transfer coefficient of the environment is 50 w / m²·k and the friction ratio factor is 0.4, to establish an extrusion finite element model. Study the process of extrusion temperature range of 600 °C - 800 °C, extrusion speed of 0.01 - 10, and extrusion ratios of 4:1, 9:1, and 16:1 respectively, to obtain the strain distribution law, temperature distribution law, and recrystallized volume fraction distribution law. The optimal extrusion parameters are determined as: extrusion temperature of 750 °C, extrusion ratio of 9:1, and extrusion speed of 10 mm / s;

[0074] Step 7: Solution-treat the extruded sample in Step 6. Keep the extruded sample at 750 °C for 2 h and air-cool it to room temperature to obtain high-quality lead-tin bronze bars that meet the standards. The test results show that the tensile strength of the alloy after solution treatment reaches 464.4 MPa, and the elongation rate reaches 67.1%, fully meeting the performance standards specified in the Specification for Metal Mold Castings of Copper Alloys for Aviation HB - 2002 of the People's Republic of China: tensile strength greater than 238 MPa and elongation rate greater than 5%.

[0075] Example 4. A method for preparing a high-strength and high-toughness lead-tin bronze bar according to the present invention includes the following steps:

[0076] Step 1: Heat an alloy containing 2% lead, 11% tin, 4.0% nickel, and the remaining component being copper by weight percentage to a liquid state, pour it into a water-cooled copper mold, start the water-cooling cycle, and take it out after cooling to obtain a cast rod-shaped lead-tin bronze alloy;

[0077] Step 2: Use electrolytic purple copper with a purity of 99.9% for machining to make a copper jacket with a blind hole having a bottom thickness of 20 mm and an inner diameter of 45 mm. Machine the cast rod-shaped lead-tin bronze alloy obtained in the previous step to a diameter of 45 mm and assemble it in the blind hole of the copper jacket. Perform vacuum sealing welding on the open end of the blind hole of the assembled copper jacket to form an integral combined blank body;

[0078] Step 3: After annealing the combined blank body at 270 °C for 35 min and applying glass lubricant, air-cool it to 50 °C;

[0079] Step 4: Preheat a tapered die with a taper of 70°, a depth of 30 mm, and a diameter of 20 mm at 380 °C for 1 h, and spray cubic boron nitride release agent spray;

[0080] Step 5: Place the combined blank body in a muffle furnace and heat it from 350 °C to 600 °C at a heating rate of 5 °C per minute, and hold for 45 min;

[0081] Step 6: Place the heated combined blank body in the tapered die for hot extrusion process. The hot extrusion temperature is 650 °C, and quench the extruded combined blank to obtain an extruded sample;

[0082] Step 7: Perform electro-pulse treatment on the extruded sample in Step 6. Specifically, set the voltage of the electro-pulse to 50 V, the treatment time to 40 s, and the frequency to 500 Hz. After the electro-pulse treatment is completed, cool it to room temperature to obtain a high-quality lead-tin bronze rod that meets the standards. The test results show that the tensile strength of the alloy after electro-pulse treatment is increased by more than 30% compared with the as-cast alloy, and the elongation exceeds 25%, fully meeting the performance standards specified in the specification of copper alloy permanent mold castings for aviation of the Aviation Industry Standard HB-2002 of the People's Republic of China: the tensile strength is greater than 238 MPa, and the elongation is greater than 5%.

[0083] Example 5. A method for preparing a high-strength and high-toughness lead-tin bronze rod of the present invention includes the following steps:

[0084] Step 1: Heat an alloy with 3.25% lead, 7% tin, 3% nickel, and the remaining components being copper to a liquid state by weight percentage, pour it into a water-cooled copper mold, turn on the water-cooling cycle, and take it out after cooling to obtain an as-cast rod-shaped lead-tin bronze alloy;

[0085] Step 2: Use electrolytic purple copper with a purity of 99.9% for machining to make a copper sleeve with a blind hole having a bottom thickness of 20 mm and an inner diameter of 45 mm. Machine the as-cast rod-shaped lead-tin bronze alloy obtained in the previous step to a diameter of 45 mm and assemble it in the blind hole of the copper sleeve. Perform vacuum sealing welding on the open end of the blind hole of the assembled copper sleeve to form an integral combined blank body;

[0086] Step 3: After annealing the combined blank body at 330 °C for 25 min and applying glass lubricant, air-cool it to 100 °C;

[0087] Step 4: Preheat the tapered die with a taper of 67°, a depth of 35 mm, and a diameter of 20 mm at 400 °C for 0.5 h, and spray cubic boron nitride release agent spray;

[0088] Step 5: Place the combined blank body into a muffle furnace and heat it from 400 °C to 800 °C at a heating rate of 10 °C per minute, and hold for 30 min;

[0089] Step 6: Place the heated combined blank body in Step 5 into the tapered die for hot extrusion process. The hot extrusion temperature is 800 °C, and the extruded combined blank is quenched to obtain an extruded sample;

[0090] Step 7: Perform solution treatment on the extruded sample in Step 6. Keep the extruded sample at 750 °C for 1 h and air-cool it to room temperature to obtain high-quality lead-tin bronze bars that meet the standards. The test results show that the tensile strength of the alloy after solution treatment is increased by more than 35% compared with the as-cast alloy, and the elongation exceeds 30%, fully meeting the performance standards specified in the specification of copper alloy permanent mold castings for aviation, HB-2002 of the People's Republic of China: tensile strength greater than 238 MPa and elongation greater than 5%.

[0091] The results of Examples 1-5 show that the method of combining preheat treatment and tapered sleeve extrusion can inhibit the thermal brittleness during the hot extrusion of lead-tin bronze, successfully realize the extrusion forming of lead-tin bronze alloy, and the surface quality of the bars is good, without forming defects such as microcracks.

[0092] Figure 1 The figure shows the as-cast microstructure diagram of the alloy in Example 1, which is a typical dendritic morphology, with coarse grains and serious segregation between dendrites. Figure 2 The figure shows the microscopic microstructure diagram of the extruded sample in Example 2. It can be seen from the figure that after hot extrusion, the dendrites are broken, and a fine equiaxed grain morphology is obtained, with fine and uniform grains and obvious improvement in segregation. Figure 3 It is the microscopic microstructure diagram after electro-pulse treatment in Example 1. It can be seen from the figure that the microscopic microstructure distribution is fine and uniform after electro-pulse treatment, which is beneficial to the improvement of the mechanical properties of the alloy. Figure 4 It is the microscopic microstructure diagram of the extruded sample in Example 2 after solution treatment. It can be seen from the figure that the tin-rich phase dissolves back after solution treatment, and the grains tend to grow.

[0093] After being processed by electric pulse, a pulsed lead-tin bronze alloy bar is obtained. After solution treatment, a solutionized lead-tin bronze alloy bar is obtained. After hot extrusion, the dendritic crystals are transformed into fine equiaxed crystals through recrystallization. Under the action of pulse treatment or solution treatment, the tin-rich phase in the equiaxed grains dissolves back, the lead particles are redistributed, and the tissue distribution becomes more uniform, significantly improving the mechanical properties of the alloy and fully meeting the performance standards specified in the specification for metal mold castings of copper alloys for aviation, HB-2002, of the People's Republic of China.

Claims

1. A preparation method of a high-strength and high-toughness lead-tin bronze bar, characterized in that, It includes the following steps: Step 1: A metal material containing 2.0% - 3.25% lead, 7.0% - 11.0% tin, 3.0% - 4.0% nickel, and the rest being copper by weight percentage is heated to a liquid state, then poured into a water-cooled copper mold and the water-cooling cycle is started. After cooling, it is taken out to obtain as-cast lead-tin bronze alloy. Step 2: Electrolytic tough pitch copper with a purity of 99.9% is machined to make a copper sleeve with blind holes. The as-cast lead-tin bronze obtained in the previous step is assembled into the blind holes of the copper sleeve, and the open end of the blind hole of the assembled copper sleeve is sealed to form an integral combined blank body. Step 3: The assembled combined blank body is annealed at 270°C - 330°C for 25 min - 35 min and coated with glass lubricant, then air-cooled to 50°C - 100°C. Step 4: A conical extrusion die with a taper of 67° - 70°, a depth of 30 mm - 35 mm, and a diameter of 20 mm is preheated at 380°C - 400°C for 0.5 h - 1 h. After the preheating is completed, cubic boron nitride release agent spray is sprayed on the die. Step 5: The combined blank body is placed in a muffle furnace and heated from 350°C - 400°C to 600°C - 800°C at a heating rate of 5°C - 10°C per minute, and held for 30 min - 45 min. Step 6: The combined blank body heated in Step 5 is placed in the conical die for hot extrusion. The hot extrusion temperature is 650°C - 800°C, and the extruded combined blank body is quenched to obtain an extruded sample. Step 7: The extruded sample obtained in Step 6 is heat-treated to obtain high-quality lead-tin bronze bars meeting the standards.

2. The preparation method of a high-strength and high-toughness lead-tin bronze rod according to claim 1, characterized in that, The extrusion ratio of the hot extrusion process is 9:1, and the extrusion speed is 5 mm / s - 10 mm / s.

3. The preparation method of a high-strength and high-toughness lead-tin bronze rod according to claim 1, characterized in that, The extruded sample is heat-treated, and this heat treatment is an electric pulse treatment. The voltage of the electric pulse is set at 50 V - 100 V, the treatment time is 35 s - 40 s, and the frequency range is 350 Hz - 500 Hz. After the electric pulse treatment is completed, it is cooled to room temperature.

4. The preparation method of a high-strength and high-toughness lead-tin bronze rod according to claim 1, characterized in that The extruded sample is heat-treated, and this heat treatment is a solution treatment. The extruded sample is held at 650°C - 750°C for 1 h - 2 h and then air-cooled to room temperature.

Images