A method for preparing a high-performance copper alloy

Abstract

This invention relates to a method for preparing high-performance copper alloys, belonging to the field of copper alloy preparation. Addressing the problems of poor consistency and large fluctuations in tensile strength of existing recycled leaded brass alloy continuous castings, a method for preparing high-performance copper alloys has been invented. This method includes auxiliary heating and stirring of the melt at the crystallizer front, and the addition of a grain refiner. This improves the uniformity and consistency of the composition and microstructure of the recycled leaded brass alloy, increases its tensile strength, and enhances its surface roughness during processing.

Description

Technical Field

[0001] This invention relates to a method for preparing high-performance copper alloys, belonging to the field of recycled lead-brass alloy preparation. Addressing the problems of poor product consistency, low tensile strength, and poor surface roughness of machined recycled lead-brass alloy continuous castings, this invention provides a method for preparing high-performance copper alloys. This method achieves uniform lead content and fine, uniform grain size in recycled lead-brass alloy continuous castings of the same alloy composition from both different heat numbers. Under the same machinability conditions, the recycled lead-brass alloy prepared by this method exhibits significantly improved tensile strength and corrosion resistance. Background Technology

[0002] Among copper alloys, leaded brass has significant application value in industrial products and a very wide range of uses. Recycled leaded brass has favorable conditions for development, with abundant scrap brass resources. However, a common problem in the recycled copper industry is that recycled copper resources can only produce low-end copper alloy products; moreover, recycled leaded brass, like other recycled copper alloys, suffers from serious quality problems, such as chipping during the machining of angle valve external threads, tearing fractures in leaded brass bars, inconsistent performance of leaded brass continuous castings from the same holding furnace at different times, large fluctuations in mechanical properties, and rough machined surfaces. Although my country has been researching and producing continuously cast leaded brass from scrap copper for nearly thirty years, these problems have long existed in the industrialization process, but existing technologies are insufficient to solve them.

[0003] We conducted repeated research on these problems and finally discovered the common cause of the above problems. We adopted different technical routes for experimentation. After repeated experiments and failures, we finally invented a method for preparing high-performance copper alloys. This method greatly improves the consistency of leaded brass castings continuously cast in the same holding furnace, significantly refines the grains, increases tensile strength, and improves the surface roughness of machined parts. Summary of the Invention

[0004] This invention discloses a method for preparing a high-performance copper alloy. After smelting, slag removal, degassing, and refining scrap copper, the composition of the melt before the furnace is rapidly analyzed. Based on the pre-determined chemical composition, the optimal batching scheme is calculated. The dried metal raw materials are weighed and added to the copper alloy melt for melting. The lead-brass alloy melt is then held at 1010–1029°C. An auxiliary heating device added outside the holding furnace heats this local space between the holding furnace and the continuous casting mold, controlling the temperature of the lead-brass alloy melt in this local space at 1030±5°C. Continuous casting begins 5–10 minutes after the solution temperature reaches this controlled temperature. The surface of the lead-brass alloy melt in the holding furnace is covered with a covering agent such as dried charcoal. When the liquid begins to heat, the agitator in that local space is activated to stir the lead-brass alloy melt. Throughout the continuous casting process of the copper alloy, the melt in that local space is continuously stirred, and the uniformly stirred copper alloy melt flows orderly to the crystallizer, while simultaneously forcing the copper alloy melt in other spaces of the holding furnace to move uniformly and slowly. The grain refiner for continuous casting of copper alloy is a Cu-Zr-RE alloy with a particle size of 2-5 mm. The grain refiner particles are wrapped in copper foil and then vacuum dried and wrapped in copper foil for later use. When stirring of the lead-brass alloy melt begins, the dried grain refiner is immediately wrapped in a bell jar and added from outside the holding furnace through the hollow shaft of the agitator to the copper alloy melt at the front edge of the crystallizer. The weight of the grain refiner accounts for 0.5-0.8 wt% of the weight of the copper alloy melt, and it is added evenly in multiple batches.

[0005] This invention discloses a method for preparing a high-performance copper alloy. The grain refiner Cu-Zr-RE alloy has the following composition: Zr 7.5-8.5 wt%, RE 8.0-9.0 wt%, unavoidable impurities less than 0.5 wt%, and the remainder Cu. RE is at least one rare earth single metal selected from Nd, Pr, La, and Ce, or a commercially available mixed light rare earth alloy. Cu-Zr-RE is prepared by vacuum melting and casting ingots, followed by room temperature crushing.

[0006] Compared with existing technologies for preparing leaded brass from recycled scrap copper, this invention has the following advantages:

[0007] 1) The method of the present invention reduces the amount of deposits on the bottom and walls of the holding furnace crucible after continuous casting of leaded brass by more than 50%, greatly reduces the workload of cleaning the bottom and walls of the holding furnace crucible after continuous casting, saves the time spent cleaning the holding furnace, and improves the production efficiency of continuous casting of scrap copper leaded brass.

[0008] 2) The average grain size of the leaded brass prepared by the method of the present invention is reduced from 10-30 μm to 5-8 μm, and the average diameter of the lead particles is reduced from 5-15 μm to 1.0-1.8 μm; the grain size and lead particle size of the products continuously cast from the leaded brass alloy melt in the same holding furnace have small fluctuation ranges, which are within 5-8 μm and 1.0-1.8 μm, respectively.

[0009] 3) The leaded brass produced by continuous casting of scrap copper using the method of this invention not only has good cutting performance, but also has good consistency in processing performance, and will not have phenomena such as chipping when machining the external threads of angle valves; the continuously cast leaded brass products have good hot working performance, and will not have hot cracking when hot forging continuously cast leaded brass bars; continuously cast leaded brass has higher tensile strength, and machined parts have better surface roughness. Detailed Implementation

[0010] Examples 1 to 3

[0011] The alloy compositions of Examples 1 to 3 are shown in Table 1. The crucible of the smelting furnace was cleaned, and the scrap copper smelting raw material, which had been dismantled, vibrated, air-separated, and magnetically separated, was loaded into the crucible. Electric heating was applied, and the temperature was maintained at 80–150°C for 10–20 minutes. The temperature was then rapidly increased to 1050–1080°C, and a covering agent such as dry charcoal was added. After slag removal, degassing, and refining, the alloy molten metal was transferred from the smelting furnace to a holding furnace via a submerged liquid transfer device. A covering agent of dry charcoal was then applied to the surface of the molten metal in the holding furnace. The composition of the melt in front of the holding furnace is analyzed quickly. Based on the pre-determined chemical composition, the optimal batching scheme is calculated. The dried metal raw materials are weighed and added to the copper alloy melt for melting. The lead-brass alloy melt is then held at 1010–1029℃. An auxiliary heating device installed outside the holding furnace heats the local space between the melt flowing from the holding furnace to the continuous casting mold, controlling the temperature of the lead-brass alloy melt in this space at 1030±5℃. Continuous casting begins 5–10 minutes after the melt temperature reaches this controlled temperature. The surface of the lead-brass alloy melt in the holding furnace is covered with a covering agent such as dry charcoal. When heating of the lead-brass alloy melt in this local space begins, the blades are activated. The agitator in the furnace stirs the molten lead-brass alloy. Throughout the continuous casting process, the molten alloy in this space is continuously stirred, and the uniformly stirred molten copper alloy flows orderly into the crystallizer, while simultaneously forcing the molten copper alloy in other spaces within the holding furnace to move uniformly and slowly. The grain refiner for continuous casting of copper alloy is a Cu-Zr-RE alloy with a particle size of 2-5 mm. The grain refiner particles are wrapped in copper foil, and then vacuum-dried and packaged in copper foil for later use. When stirring of the molten lead-brass alloy begins, the dried grain refiner is immediately wrapped in a bell jar and added from outside the holding furnace through the hollow shaft of the agitator to the molten copper alloy at the front edge of the crystallizer. The weight of the grain refiner accounts for 0.5-0.8 wt% of the molten copper alloy, and it is added evenly in multiple batches.

[0012] Preparation of grain refiner. The composition of the grain refiner Cu-Zr-RE alloy is 7.5-8.5 wt% Zr, 8.0-9.0 wt% RE, and unavoidable impurities less than 0.5 wt%, with the balance being Cu; wherein RE is at least one rare earth single metal selected from Nd, Pr, La, and Ce, or a commercially available mixed light rare earth alloy; Cu-Zr-RE is prepared by vacuum melting and casting ingots, followed by room temperature crushing.

[0013] Lead brass alloys were continuously cast using a secondary cooling crystallizer. The microstructure of the continuously cast lead brass was analyzed according to national or industry standards, and the tensile strength, machinability, and corrosion resistance of the lead brass test bars were tested. The composition and properties of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0014] Comparative Examples 1-3 have the same alloy composition as Examples 1-3, but they employ existing scrap copper recycling and continuous casting technology. The scrap copper raw material is the same as in the examples. It is rapidly heated to 1050-1080°C, and covered with dry charcoal and other agents. After slag removal, degassing, and refining, the alloy melt is transferred from the smelting furnace to the holding furnace via a submerged liquid transfer device. Dry charcoal is then added to the surface of the melt in the holding furnace. The composition of the melt before the holding furnace is quickly analyzed, and the optimal batching scheme is calculated based on the pre-determined chemical composition. The dried metal raw material is weighed and added to the copper alloy melt for melting. The holding temperature of the lead-brass alloy melt is controlled at 1050-1080°C, and continuous casting is performed using a secondary water-cooled crystallizer.

[0015] Table 1. Composition (wt%) and properties of recycled lead-brass alloy continuous castings.

[0016]

[0017] Cutting index determination and calculation. On a CA-6140 bedroom lathe, using Ys8 tool material, a spindle speed of 500 r / min, a feed rate of 0.2 mm / r, and a depth of cut of 0.5 mm, with the cutting performance of HPb62-3 alloy as 100% reference, the calculated cutting indices are as follows: Example 1 and Comparative Example 1 have cutting performance indices of 80 and 81, respectively; Example 2 and Comparative Example 2 have cutting performance indices of 109 and 107, respectively; Example 3 and Comparative Example 3 have cutting indices of 91 and 90, respectively. It can be seen that, under the premise of the same alloy composition, the examples and comparative examples have similar cutting performance.

[0018] However, the recycled leaded brass produced using the method of this invention, whether after cutting or grinding, exhibits a lower surface roughness and a brighter surface compared to machined leaded brass parts produced using existing recycled continuous casting technology. Under conditions of a cutting speed of 100 m / min, a feed rate of 0.05 mm / r, and a depth of cut of 0.5 mm, the surface roughness of Example 1 and Comparative Example 1 were 0.3 μm and 5.1 μm, respectively; the surface roughness of Example 2 and Comparative Example 2 were 0.2 μm and 3.4 μm, respectively; and the surface roughness of Example 3 and Comparative Example 3 were 0.4 μm and 6.7 μm, respectively. This demonstrates that the surface roughness of the recycled leaded brass castings produced using the method of this invention, using recycled copper, is significantly improved compared to the surface roughness of leaded brass castings of the same composition produced using existing continuous casting techniques, especially after cutting.

Claims

1. A method for preparing a high-performance copper alloy, characterized in that: 1) The scrap copper raw materials, after dismantling, vibration, air separation, and magnetic separation, are loaded into the crucible of the smelting furnace. Electric heating is applied, and the temperature is maintained at 80–150℃ for 10–20 minutes. The temperature is then rapidly increased to 1050–1080℃, and a covering agent such as dry charcoal is added. After smelting, slag removal, degassing, and refining, the alloy melt is transferred from the smelting furnace to the holding furnace via a submerged liquid transfer device. A covering agent of dry charcoal is added to the surface of the melt in the holding furnace. The composition of the melt before the holding furnace is quickly analyzed, and the appropriate proportions are calculated based on the pre-determined chemical composition. The optimal solution is to weigh the dried metal raw material and add it to the copper alloy melt for melting. Then, the lead-brass alloy melt is kept at 1010-1029℃. In the local space between the holding furnace and the continuous casting crystallizer, an auxiliary heating device is added outside the holding furnace to heat the local space and control the temperature of the lead-brass alloy melt in the local space at 1030±5℃. Continuous casting begins 5-10 minutes after the melt temperature reaches the controlled temperature. 2) With the surface of the lead-brass alloy melt covered with a covering agent such as dry charcoal in the holding furnace, when the lead-brass alloy melt in this local space is heated, the agitator in this local space is immediately started to stir the lead-brass alloy melt; throughout the entire copper alloy continuous casting process, the melt in this local space is continuously stirred, and the uniformly stirred copper alloy melt flows orderly to the crystallizer, while forcing the copper alloy melt in other spaces in the holding furnace to move uniformly and slowly. 3) The grain refiner for continuous casting of copper alloy is a Cu-Zr-RE alloy with a particle size of 2-5 mm. The grain refiner particles are wrapped in copper foil and then vacuum dried and wrapped in copper foil for later use. When stirring the lead-brass alloy melt begins, the dried grain refiner is immediately wrapped in a bell jar and added from outside the holding furnace through the hollow shaft of the stirrer to the copper alloy melt at the front of the crystallizer. The weight of the grain refiner accounts for 0.5-0.8 wt% of the weight of the copper alloy melt and is added evenly in multiple batches.

2. As described in claim 1, a method for preparing a high-performance copper alloy is characterized in that: the grain refiner Cu-Zr-RE alloy has the following composition: Zr 7.5-8.5 wt%, RE 8.0-9.0 wt%, unavoidable impurities less than 0.5 wt%, and the remainder Cu; wherein RE is at least one rare earth single metal selected from Nd, Pr, La, and Ce, or a commercially available mixed light rare earth alloy; Cu-Zr-RE is prepared by vacuum melting and casting ingots, followed by room temperature crushing.

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