Casting method of high-conductivity free-cutting copper alloy material based on directional cooling of water-cooling steel mold

Abstract

The invention provides a casting method of a high-conductivity free-cutting copper alloy material based on directional cooling of a water-cooling steel mold, and belongs to the technical field of casting of copper alloy materials. According to the method, a high-purity pure copper block is laid at the bottom of a hollow water-cooling steel mold, independent water-cooling channels on the side wall and the bottom are combined, differential water flow parameters are set, gradient directional cooling of bottom forced cooling and side wall slow cooling is achieved, and meanwhile special smelting and annealing processes are configured for different rare earth tellurium bronze; the problems that in traditional casting, cooling directionality is poor, and a casting is prone to shrinkage cavities, air holes, cracking, coarse grains and other defects are solved. According to the copper alloy casting prepared through the method, the structure uniformity is remarkably improved, the electric conductivity is stably kept to be 92% IACS (under the condition that the temperature is 20 DEG C) or above, and the machinability is 85% or above higher than that of an HPb63-3 material under the same state. And the production requirements of high-precision and high-performance copper alloy parts in the fields of electronics, aerospace and the like can be met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of casting of copper alloy materials, and particularly relates to a casting method of high-conductivity easy-to-cut copper alloy material based on directional cooling of a water-cooled steel mold, and is particularly suitable for the precision casting field of rare earth tellurium bronze materials such as cerium tellurium bronze and lanthanum tellurium bronze. BACKGROUND

[0002] Copper and its alloys are one of the earliest metal materials used by human history, and copper alloys are important engineering materials with diverse properties and wide applications. Copper alloys are widely used in the fields of electronics, electrical appliances, aerospace, etc. due to their excellent electrical conductivity, thermal conductivity and mechanical properties. Selecting appropriate copper alloys (brass, bronze, cupronickel, etc.) and proper casting processes (sand mold, metal mold, centrifugal casting, investment casting, etc.) is the key to manufacturing high-quality castings that meet specific performance requirements (such as strength, wear resistance, corrosion resistance, electrical conductivity). With the development of technology, copper alloys will continue to play an irreplaceable role in emerging fields such as new energy vehicles, marine engineering and high-end equipment manufacturing.

[0003] Rare earth tellurium bronze such as cerium tellurium bronze and lanthanum tellurium bronze, through the synergistic effect of rare earth elements and tellurium, significantly improves the wear resistance and fatigue resistance of the material while maintaining high electrical conductivity. However, in traditional casting processes, the cooling rate of copper alloy melt is uneven and the directionality is poor, which easily leads to defects such as porosity, shrinkage, porosity, and coarse grains in the castings, seriously affecting the product quality and service life.

[0004] Although existing water-cooled steel mold casting technology can improve cooling efficiency, the cooling direction is difficult to control accurately, and the bottom of the steel mold and the melt contact area are prone to stress concentration due to rapid heat dissipation, leading to cracking at the bottom of the casting. However, this problem still cannot be solved in current industrial production.

[0005] Therefore, there is an urgent need for a copper alloy casting method that can achieve directional and uniform cooling and reduce defects, to meet the production needs of high-performance copper alloys such as rare earth tellurium bronze. SUMMARY

[0006] The present application is to solve the above technical problems, and provides a casting method of high-conductivity easy-to-cut copper alloy material based on directional cooling of a water-cooled steel mold. The technical purpose of the present application is to provide a water-cooled casting process of copper alloy, which can achieve directional and uniform cooling during casting, thereby significantly reducing defects during casting, and providing a better process for the industrial production of high-performance copper alloys with high yield.

[0007] In order to achieve the above technical purpose, the technical solution adopted by the present application is as follows: The present application provides a casting method of high-conductivity easy-to-cut copper alloy material based on directional cooling of a water-cooled steel mold, comprising the following steps: (1) Select a hollow water-cooled steel mold with independent water cooling channels, prepare pure copper blocks with copper content ≥ 99.95%, polish and clean, and then dry; (2) The pure copper blocks treated in step (1) are laid flat on the bottom of the steel mold, then a high-temperature release agent is sprayed, the steel mold is preheated to 150-200°C and kept for a certain time; (3) According to the predetermined element ratio of the copper alloy, the raw materials are put into the medium-frequency induction furnace for smelting, high-purity graphite scales are used to cover the surface, the thickness of the graphite scales is 20-30 mm, and the copper alloy liquid is prepared; (4) The copper alloy liquid is poured into the steel mold for casting, the water flow velocity of the bottom water cooling channel is maintained at 1.5-2.5 m / s, the water cooling velocity of the side wall is 1.0-1.5 m / s during the pouring process, and the casting is cooled to below 200°C after pouring is completed; (5) Take out the casting, blow, anneal, and then polish and detect.

[0008] The above pouring method provided by the application can utilize the high thermal conductivity of the pure copper block to strengthen the heat dissipation of the bottom of the steel mold, form a stable directional cooling gradient by combining the differential water cooling parameters, promote the growth of copper alloy grains along the cooling direction, and reduce the problem of coarse grains and uneven structure. In the method of the application, the pure copper block has good compatibility with the copper alloy melt, which can avoid stress cracking caused by direct contact between the bottom of the casting and the steel mold, and at the same time improve the density of the bottom of the casting.

[0009] On the other hand, according to the differential smelting and annealing parameters of cerium tellurium bronze and lanthanum tellurium bronze, the strengthening effect of rare earth elements can be fully utilized, the electrical conductivity is maintained above 92% IACS (at a temperature of 20°C), and the cutting property is higher than 85% of HPb63-3 material under the same conditions, which meets the use requirements of high-precision electronic components and wear-resistant parts.

[0010] Further, the thickness of the pure copper block in step (1) is 30-60 mm, and the error between the thickness and the size of the inner cavity of the bottom of the steel mold is ≤0.5 mm, and the surface roughness Ra of the pure copper block is ≤0.8 μm.

[0011] Further, the formula of the high-temperature release agent in step (2) is 5-8% boron nitride, 3-5% water glass, and 87-92% deionized water by weight percentage.

[0012] Further, the spraying thickness in step (2) is 0.1-0.15 mm.

[0013] Further, the holding time in step (2) is 30-40 min.

[0014] Further, the copper alloy in step (3) is cerium tellurium bronze or lanthanum tellurium bronze.

[0015] Furthermore, the elemental composition of cerium-tellurium bronze, by weight percentage, is: 99.288-99.596% electrolytic copper, 0.4-0.7% tellurium, and 0.004-0.0120% metallic cerium; the smelting temperature is 1160-1200℃.

[0016] Furthermore, the elemental composition of lanthanum-tellurium bronze, by weight percentage, is: 99.288-99.596% electrolytic copper, 0.4-0.7% tellurium, and 0.004-0.0120% metallic lanthanum; the smelting temperature is 1180-1220℃.

[0017] Furthermore, in step (4), the casting speed is 5-8 kg / min, the liquid level of the copper alloy liquid is 5-10 mm from the top of the steel mold, and the cooling time is 40-60 min.

[0018] Furthermore, the annealing parameters in step (5) are as follows: cerium tellurium bronze is annealed at 450-500℃ for 2 h, and lanthanum tellurium bronze is annealed at 480-520℃ for 1.5 h.

[0019] The beneficial effects of this invention are as follows: This invention discloses a method for casting high-conductivity, easily machinable copper alloys based on water-cooled steel mold directional cooling. This method utilizes a high-purity copper block placed at the bottom of a hollow water-cooled steel mold, combined with independent water-cooling channels on the sidewalls and bottom, and differentiated water flow parameters to achieve gradient directional cooling of "strong cooling at the bottom and slow cooling at the sidewalls." Simultaneously, specific melting and annealing processes are configured for different rare-earth tellurium bronzes, solving the problems of poor cooling directionality and defects such as shrinkage cavities, porosity, cracking, and coarse grains in traditional casting. Practice shows that copper alloy castings prepared using this method exhibit significantly improved microstructure uniformity, a stable conductivity above 92% IACS (at 20℃), and machinability exceeding that of HPb63-3 material under the same conditions by more than 85%, effectively meeting the production needs of high-precision, high-performance copper alloy components in the electronics, aerospace, and other fields. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to embodiments. It should be noted that the following embodiments are for explanation and illustration only and are not intended to limit the invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0021] Example 1

[0022] A method for casting a cerium-tellurium bronze alloy includes the following steps: (1) Equipment preparation: Select a water-cooled steel mold with an inner cavity size of φ120mm×500mm, a water flow velocity of 2.0m / s in the bottom water-cooling channel and 1.8m / s in the side wall; pure copper block with a size of φ120mm×50mm and a purity of 99.98%, which is dried after grinding and cleaning; (2) Steel mold pretreatment: lay pure copper blocks flat on the bottom of the steel mold, spray release agent (6% boron nitride, 4% water glass, 90% water) with a thickness of 0.12 mm, preheat to 180℃ and keep warm for 35 min; (3) Melt preparation: Weigh 99.492 kg of electrolytic copper, 0.5 kg of tellurium, and 8 g of metallic cerium. Heat the electrolytic copper to 1180℃ in a medium-frequency furnace, add tellurium and stir for 12 min, add cerium and stir for 10 min, and then cover with high-purity phosphorus flake graphite for smelting with a covering thickness of 15 mm. (4) Casting and cooling: The melt is allowed to stand for 10 minutes, then cast at a speed of 6 kg / min. After casting, the water flow rate at the bottom is maintained at 2.0 m / s, and the flow rate at the side wall is reduced to 1.2 m / s. Cool for 50 minutes to 180°C.

[0023] (5) Post-treatment: After purging, anneal at 480℃ for 2 hours, conductivity 94% IACS (at 20℃), machinability = 88%, no shrinkage cavities, porosity, or cracking defects.

[0024] Example 2

[0025] A method for casting a lanthanum-tellurium bronze alloy includes the following steps: (1) Equipment preparation: Same as the water-cooled steel mold in Example 1, with the same water flow velocity parameters; the same specifications for pure copper blocks; (2) Steel mold pretreatment: Same as the steps in Example 1.

[0026] (3) Melt preparation: Weigh 99.392 kg of electrolytic copper, 0.6 kg of tellurium and 8 g of metallic lanthanum, heat the medium frequency furnace to 1200℃ to melt, and stir and cover with flake graphite with the same thickness as in Example 1.

[0027] (40 Casting and Cooling: The melt is allowed to stand for 10 minutes, then cast at a rate of 7 kg / min. After casting, the water flow rate at the bottom is 2.0 m / s, and at the side wall it is 1.3 m / s. Cool for 55 minutes to 190°C.)

[0028] (5) Post-treatment: After purging, anneal at 500℃ for 1.5h, conductivity 93% IACS (at 20℃), machinability = 87%, and the uniformity of the structure is better than that of castings made by traditional process.

[0029] Performance tests were conducted on the copper alloy castings obtained in Examples 1 and 2 of this invention. The results showed that the copper alloy castings prepared by this method have significantly improved microstructure uniformity, maintained a stable conductivity of over 92% IACS (at a temperature of 20°C), and machinability that is more than 85% higher than that of HPb63-3 material under the same conditions. This can meet the production needs of high-precision, high-performance copper alloy components in the fields of electronics and aerospace.

Claims

1. A casting method of a high-conductivity free-cutting copper alloy material based on directional cooling of a water-cooled steel mold, characterized by, The method comprises the following steps: (1) selecting a hollow water-cooled steel mold with an independent water cooling channel, preparing pure copper blocks with a copper content of ≥99.95%, and drying the pure copper blocks after polishing and cleaning; (2) laying the pure copper blocks treated in step (1) on the bottom of the steel mold, then spraying a high-temperature release agent, preheating the steel mold to 150-200°C and maintaining the temperature for a certain period of time; (3) putting raw materials into a medium-frequency induction furnace according to the predetermined element ratio of the copper alloy, covering the surface with high-purity graphite flakes, and preparing a copper alloy liquid, wherein the thickness of the graphite flakes is 20-30 mm; (4) pouring the copper alloy liquid into the steel mold, maintaining the water flow speed of the bottom water cooling channel at 1.5-2.5 m / s and the water cooling speed of the side wall at 1.0-1.5 m / s during the pouring process, and cooling to below 200°C after pouring is completed; (5) taking out the casting, blowing, annealing, and then polishing and testing.

2. The method of claim 1, wherein, In step (1), the thickness of the pure copper block is 30-60 mm, the error between the pure copper block and the inner cavity size of the steel mold bottom is ≤0.5 mm, and the surface roughness Ra of the pure copper block is ≤0.8 μm.

3. The method of claim 1, wherein, In step (2), the formula of the high-temperature release agent is 5-8% boron nitride, 3-5% water glass, and 87-92% deionized water by weight percentage.

4. The method of claim 1, wherein, The spraying thickness in step (2) is 0.1-0.15 mm.

5. The method of claim 1, wherein, The holding time in step (2) is 30-40 min.

6. The method of claim 1, wherein, In step (3), the copper alloy is cerium tellurium bronze or lanthanum tellurium bronze.

7. The method of claim 6, wherein, The element ratio of cerium tellurium bronze is 99.288-99.596% electrolytic copper, 0.4-0.7% tellurium, and 0.004-0.0120% metal cerium by weight percentage, and the melting temperature is 1160-1200°C.

8. The method of claim 6, wherein, The element ratio of lanthanum tellurium bronze is 99.288-99.596% electrolytic copper, 0.4-0.7% tellurium, and 0.004-0.0120% metal lanthanum by weight percentage, and the melting temperature is 1180-1220°C.

9. The method of claim 1, wherein, In step (4), the pouring speed is 5-8 kg / min, the liquid level of the copper alloy liquid is 5-10 mm from the top of the steel mold, and the cooling time is 40-60 min.

10. The method of claim 1, wherein, In step (5), the annealing treatment parameters are as follows: cerium tellurium bronze is annealed at an annealing temperature of 450-500°C for 2 h, and lanthanum tellurium bronze is annealed at an annealing temperature of 480-520°C for 1.5 h.