A powder metallurgical copper alloy and a method for producing the same

Abstract

The application discloses a powder metallurgy copper alloy and a preparation method thereof, and relates to the field of powder metallurgy. The powder metallurgy copper alloy comprises the following components in mass fraction: powder raw material: 99.4wt%-99.7wt%; binder: 0.3wt%-0.6wt%; the powder raw material comprises copper-containing powder with a molar percentage of 98.5%-99.5% and copper phosphate powder with a molar percentage of 0.5%-1.5%, and the copper-containing powder is copper powder or copper alloy powder. The added copper phosphate powder is decomposed into copper oxide under heating in a sintering process, so that the uniformity of a sintering structure can be improved; the phosphorus element brought by the decomposition of the copper phosphate powder can form liquid-phase sintering of copper, so that the reduction sintering temperature can be reduced, the sintering performance can be improved, and finally, the sintering product has good appearance and stable size, excellent mechanical properties, and no inclusion phenomenon.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy, and more particularly to a powder metallurgy copper alloy and its preparation method. Background Technology

[0002] Currently, when sintering powder metallurgy copper and copper alloy (including brass and bronze) parts, enterprises are prone to the phenomenon of "intercalation defects" (incomplete metallurgical bonding within the metallurgical structure), leading to a decrease in overall performance. Furthermore, the presence of these defects results in significant dimensional fluctuations in sintered products and a high scrap rate. In actual production, a common approach is to first pre-oxidize and sinter the copper and copper alloy products in air after pressing and shaping, then cool and remove them from the furnace before sintering in a reducing atmosphere. This is because copper oxide diffuses more easily during sintering, resulting in a more uniform microstructure and properties in the sintered product.

[0003] Current powder metallurgy production technologies employ a pre-oxidation sintering followed by reduction sintering method, which increases the process and energy consumption, leading to higher product costs. Directly adding copper oxide powder also presents problems. Copper oxide powder, primarily prepared chemically, is fine (<10 micrometers), prone to agglomeration, and difficult to mix evenly with copper and copper alloy powders. Furthermore, its high hardness makes it susceptible to microcracks after pressing and sintering, reducing mechanical properties and impacting part lifespan. Summary of the Invention

[0004] This invention provides a powder metallurgy copper alloy and its preparation method to solve the technical problems of large dimensional changes and low mechanical properties in sintered copper alloys.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide a powder metallurgy copper alloy comprising the following components by mass fraction:

[0006] Powder raw material: 99.4wt%-99.7wt%;

[0007] Adhesive: 0.3wt%-0.6wt%;

[0008] The powder raw material includes copper-containing powder with a molar percentage of 98.5%-99.5% and copper phosphate powder with a molar percentage of 0.5%-1.5%, wherein the copper-containing powder is copper powder or copper alloy powder.

[0009] By adopting the above scheme, the copper phosphate powder added to the powder metallurgy raw materials in this application can be decomposed into copper oxide and phosphorus pentoxide during the sintering process, so as to achieve uniform precipitation and distribution of copper oxide in copper and copper alloy powders. This avoids problems such as the difficulty in thoroughly pre-oxidizing the core of large-sized products and the generation of microcracks due to uneven mixing of copper oxide powder. The final product has good appearance performance, high dimensional stability and mechanical properties, and no sintering "half-cooked" phenomenon.

[0010] As a preferred embodiment, the copper-containing powder contains more than 30 wt% copper.

[0011] As a preferred embodiment, the copper-containing powder is one of pure copper powder, bronze powder, and brass powder.

[0012] As a preferred embodiment, the bronze powder comprises 90% copper and 10% tin by mass.

[0013] As a preferred embodiment, the brass powder comprises 70% copper and 30% zinc by mass.

[0014] As a preferred embodiment, the adhesive is zinc stearate.

[0015] As a preferred embodiment, the copper-containing powder has a mesh size of 200-400 mesh.

[0016] As a preferred embodiment, the copper phosphate powder has a mesh size of 100-200 mesh.

[0017] By adopting the above scheme, the particle size of copper phosphate powder in the powder metallurgy raw material of this application is larger than that of copper-containing powder, which helps to uniformly disperse copper phosphate powder in copper-containing powder during the mixing process, effectively avoids the agglomeration of copper phosphate powder, and thus ensures the uniformity of sintering structure.

[0018] To address the aforementioned technical problems, a second objective of this invention is to provide a method for preparing powder metallurgy copper alloys, comprising the following steps:

[0019] (1) Mix the components evenly according to the proportion to obtain a premix;

[0020] (2) Press the premixed material into shape to obtain a molded green body;

[0021] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas, heat it to 750-800℃, hold it for 1-2 hours, and then continue to heat it to 930-960℃ and hold it for 0.5-1 hours to obtain the copper alloy product.

[0022] By adopting the above scheme, preheating the molded green blank to 750-800℃ can help the copper phosphate powder to thermally decompose, achieve uniform precipitation and distribution of copper oxide in copper and copper alloy powder, ensure that the copper oxide produced by decomposition diffuses fully during reduction sintering, and achieve uniform microstructure; at the same time, during the sintering process, the phosphorus element brought by the decomposition of copper phosphate powder can form the liquid phase sintering of copper, reduce the sintering temperature, and improve the sintering performance.

[0023] As a preferred option, in step (3), the reducing gas is decomposed ammonia.

[0024] As a preferred option, in step (2), the pressing pressure is 500-600 MPa.

[0025] As a preferred embodiment, in step (3), the copper-containing powder is prepared by gas atomization, water atomization or electrolysis.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This application adds copper phosphate powder to copper-containing raw materials in powder metallurgy, which decomposes into copper oxide during the sintering process, thereby achieving uniform precipitation and distribution of copper oxide in copper-containing powder, improving the uniformity of sintered structure, and the final sintered product has a good appearance and stable dimensions, excellent mechanical properties, and no sintering "half-baked" phenomenon.

[0028] 2. This application preheats the molded green blank to help the thermal decomposition of copper phosphate powder and its uniform precipitation in copper-containing powder, ensuring that the copper oxide produced by decomposition diffuses fully during reduction sintering, thereby improving the uniformity of the sintered structure. During the sintering process, the phosphorus element brought by the decomposition of copper phosphate powder can form a liquid phase of copper sintering, reducing the sintering temperature and improving the sintering performance. Attached Figure Description

[0029] Figure 1 : Digital photographs of the powder metallurgy copper alloys in Example 2 and Comparative Example 2 of the present invention (Note: Top - Example 2; Bottom - Comparative Example 2). Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] A powder metallurgy copper alloy comprises 99.5 wt% powder raw material and 0.5 wt% binder. The powder raw material comprises 99% copper-containing powder and 1% copper phosphate powder (Cu3(PO4)2) by molar percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is elemental copper powder obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0033] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0034] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 600MPa, to obtain a molded green blank;

[0035] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 780°C, hold it for 1 hour, then continue to heat it to 930°C, hold it for 1 hour, and obtain the copper alloy product after sintering.

[0036] Example 2

[0037] A powder metallurgical copper alloy comprises 99.5 wt% powder raw materials and 0.5 wt% binder. The powder raw materials include 98.5% copper-containing powder and 1.5% copper phosphate powder (Cu3(PO4)2) by molar percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is brass powder (containing 70% by mass of copper and 30% by mass of zinc) obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0038] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0039] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 500MPa, to obtain a molded green blank;

[0040] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 800°C, hold it for 2 hours, then continue to heat it to 960°C, hold it for 0.5 hours, and obtain the copper alloy product after sintering.

[0041] Example 3

[0042] A powder metallurgy copper alloy comprises 99.5 wt% powder raw materials and 0.5 wt% binder. The powder raw materials include 99.2% copper-containing powder and 0.8% copper phosphate powder (Cu3(PO4)2) by molar percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is bronze powder (containing 90% copper and 10% tin by mass) obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0043] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0044] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 550MPa, to obtain a molded green blank;

[0045] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 750°C, hold it for 1.5 hours, then continue to heat it to 940°C, hold it for 0.75 hours, and obtain the copper alloy product after sintering.

[0046] Example 4

[0047] A powder metallurgical copper alloy is prepared in the same way as Example 2, with each step and the reagents and process parameters used in each step being the same. The difference is that the powder raw materials include 99.5% copper powder and 0.5% copper phosphate powder (Cu3(PO4)2).

[0048] Example 5

[0049] A powder metallurgical copper alloy is prepared in the same way as that in Example 2, with the same steps, reagents and process parameters. The difference is that the copper powder has a mesh size of 100 mesh.

[0050] Example 6

[0051] A powder metallurgical copper alloy is prepared in the same way as that in Example 2, with the same steps, reagents and process parameters. The difference is that the copper powder has a mesh size of 400 mesh.

[0052] Example 7

[0053] A powder metallurgical copper alloy is prepared in the same way as that in Example 2, with the same steps, reagents and process parameters. The difference is that the copper phosphate powder has a mesh size of 50.

[0054] Example 8

[0055] A powder metallurgical copper alloy is prepared in the same way as that in Example 2, with each step, reagent and process parameter being the same. The difference is that the copper phosphate powder has a mesh size of 200 mesh.

[0056] Comparative Example 1

[0057] A powder metallurgy copper alloy comprises 99.5 wt% copper-containing powder and 0.5 wt% binder. The copper-containing powder has a mesh size of 200 mesh and is specifically selected from brass powder (containing 70% by mass of copper and 30% by mass of zinc) prepared by gas atomization. The binder is specifically zinc stearate. Its preparation method includes the following steps:

[0058] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0059] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 500MPa, to obtain a molded green blank;

[0060] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 800°C, hold it for 2 hours, then continue to heat it to 960°C, hold it for 0.5 hours, and obtain the copper alloy product after sintering.

[0061] Comparative Example 2

[0062] A powder metallurgical copper alloy is prepared in the same way as Example 2, except that the powder raw materials include 98% copper powder and 2% copper phosphate powder (Cu3(PO4)2).

[0063] Comparative Example 3

[0064] A powder metallurgical copper alloy comprises 99.5 wt% powder raw materials and 0.5 wt% binder. The powder raw materials include 98.5% copper-containing powder and 1.5% copper phosphate powder (Cu3(PO4)2) by molar percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is brass powder (containing 70% by mass of copper and 30% by mass of zinc) obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0065] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0066] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 500MPa, to obtain a molded green blank;

[0067] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 960°C, hold it for 2.5 hours, and obtain the copper alloy product after sintering.

[0068] Comparative Example 4

[0069] A powder metallurgical copper alloy comprises 99.5 wt% powder raw materials and 0.5 wt% binder. The powder raw materials include 98.5% copper-containing powder and 1.5% copper phosphate powder (Cu3(PO4)2) by molar percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is brass powder (containing 70% by mass of copper and 30% by mass of zinc) obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0070] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0071] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 500MPa, to obtain a molded green blank;

[0072] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 650°C, hold it for 2 hours, then continue to heat it to 960°C, hold it for 0.5 hours, and obtain the copper alloy product after sintering.

[0073] Comparative Example 5

[0074] A powder metallurgical copper alloy comprises 99.5 wt% powder raw materials and 0.5 wt% binder. The powder raw materials include 98.5% copper-containing powder and 1.5% copper phosphate powder (Cu3(PO4)2) by molar percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is brass powder (containing 70% by mass of copper and 30% by mass of zinc) obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0075] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0076] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 500MPa, to obtain a molded green blank;

[0077] (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas to decompose ammonia, heat it to 800°C, hold it for 2 hours, then continue to heat it to 1100°C, hold it for 2 hours, and obtain the copper alloy product after sintering.

[0078] Comparative Example 6

[0079] A powder metallurgy copper alloy comprises 99.5 wt% powder raw materials and 0.5 wt% binder. The powder raw materials include 98.5% copper-containing powder and 1.5% copper oxide powder by mass percentage. The copper-containing powder has a mesh size of 200 mesh, and the copper phosphate powder has a mesh size of 100 mesh. Specifically, the copper-containing powder is brass powder (containing 70% copper and 30% zinc by mass percentage) obtained by gas atomization. The binder is zinc stearate. The preparation method includes the following steps:

[0080] (1) Mix the raw materials evenly in a V-shaped mixer according to the proportion to obtain a premix;

[0081] (2) Press the premixed material into a bushing with an outer diameter of φ20 on a powder press, with a pressing pressure of 500MPa, to obtain a molded green blank;

[0082] (3) Place the molded green blank into an atmosphere furnace, introduce reducing gas to decompose ammonia, heat to 800℃, hold for 2 hours, then continue heating to 960℃, hold for 0.5 hours, and obtain the copper alloy product after sintering. Performance testing.

[0083] 1. Dimensional Variance: For each set of examples or comparative examples, the outer diameter of 30 sintered finished products was measured. The outer diameter of the sintered products was measured and the variance was calculated using the following formula: s 2 = 1 / n [(x1-x)] 2 +(x2-x) 2 +…+(x n -x) 2 The variance was calculated, and the statistical results are shown in Table 1 below.

[0084] 2. Crushing strength: Using a crushing tester, the crushing strength of 30 sintered finished products in each example or comparative example was tested, and the average crushing strength of the samples was calculated. The sintered sample was placed on the test bench, pressure was applied, the pressure when the bushing was flattened was recorded, and the corresponding crushing strength was calculated.

[0085] 3. Appearance inspection: Observe and photograph the surfaces of the samples prepared in Example 2 and Comparative Example 2. The results are as follows: Figure 1 As shown, the sample of Example 2 has a smooth and flat surface, good appearance, and no undercooked phenomenon; the sample of Comparative Example 2 has a high amount of copper phosphate powder added, which results in dense black spots on the surface of the sintered sample, which is not aesthetically pleasing and cannot be delivered.

[0086] Table 1 - Performance test results of products in the embodiments and comparative examples of this application

[0087]

[0088]

[0089] Based on the performance test results of Example 2 and Comparative Example 1 in Table 1, it can be seen that by adding copper phosphate powder to copper-containing raw materials in powder metallurgy, the copper phosphate powder is easily decomposed into copper oxide and phosphorus pentoxide when heated. After preheating, the mixed powder can achieve uniform precipitation and distribution of copper oxide in copper and copper alloy powders, avoiding problems such as difficulty in thoroughly pre-oxidizing the core of large-sized products and microcracks caused by uneven mixing of copper oxide powder. Compared with the sample without added iron phosphate powder, the final sintered product has a smooth surface, good dimensional stability, high crushing strength, and no undercut phenomenon.

[0090] Based on the performance test results of Examples 2 and 4 and Comparative Example 2 in Table 1, it can be seen that a lower content of copper phosphate powder in the powder metallurgy raw materials of this application results in a lower improvement on the undercooked phenomenon of the sintered product, while a higher content leads to greater dimensional fluctuations in the sintered product and black pits on the product surface, which is not aesthetically pleasing and makes delivery impossible.

[0091] Based on the performance test results of Example 2 and Comparative Examples 3-4 in Table 1, it can be seen that heating the molded green blank to 750-800℃ in this application is to achieve the thermal decomposition of copper phosphate powder and the uniform precipitation of copper oxide in copper or copper alloy powder, ensuring that the copper oxide produced by decomposition is fully diffused during reduction sintering, thereby achieving uniform microstructure. If the pre-firing temperature is too low, the thermal decomposition of copper phosphate will be insufficient, resulting in uneven dispersion of copper oxide in the microstructure, which will affect the size and mechanical properties of the sintered product.

[0092] Based on the performance test results of Example 2 and Comparative Example 5 in Table 1, it can be seen that copper phosphate powder is added to the powder metallurgy raw material of this application. During the reduction sintering process, the presence of phosphorus can form a liquid phase sintering of copper, reduce the sintering temperature, and improve the sintering performance. Therefore, if the sintering temperature is too high or the sintering time is too long, it will be over-burned, which will lead to a decrease in the appearance and mechanical properties of the product.

[0093] Based on the performance test results of Example 2 and Comparative Example 6 in Table 1, it can be seen that if the powder metallurgy raw material of this application is prepared by directly adding copper oxide powder, the powder is fine and easy to agglomerate due to its basic chemical preparation method, resulting in uneven dispersion. In addition, the high hardness of copper oxide powder itself makes it easy to generate microcracks after pressing and sintering, thus reducing mechanical properties.

[0094] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for preparing a powder metallurgy copper alloy, characterized in that, The powder metallurgy copper alloy comprises the following components by mass fraction: Powder raw material: 99.4wt%-99.7wt%; Adhesive: 0.3wt%-0.6wt%; The powder raw material includes copper-containing powder with a molar percentage of 98.5%-99.5% and copper phosphate powder with a molar percentage of 0.5%-1.5%, wherein the copper-containing powder is copper powder or copper alloy powder. The preparation method of the powder metallurgy copper alloy includes the following steps: (1) Mix the components evenly according to the proportions to obtain a premix; (2) Press the premixed material into shape to obtain a molded green body; (3) Place the molded green blank into an atmosphere furnace, fill it with reducing gas, heat it to 750-800℃, hold it for 1-2 hours, and then continue to heat it to 930-960℃ and hold it for 0.5-1 hours to obtain the copper alloy product.

2. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, The copper-containing powder contains more than 30 wt% copper.

3. The method for preparing a powder metallurgy copper alloy as described in claim 2, characterized in that, The copper-containing powder is one of pure copper powder, bronze powder, and brass powder.

4. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, The adhesive is zinc stearate.

5. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, The copper-containing powder has a mesh size of 200-400 mesh.

6. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, The copper phosphate powder has a mesh size of 100-200 mesh.

7. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, In step (3), the reducing gas is decomposed ammonia.

8. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, In step (2), the pressing pressure is 500-600 MPa.

9. The method for preparing a powder metallurgy copper alloy as described in claim 1, characterized in that, In step (3), the copper-containing powder is prepared by gas atomization, water atomization or electrolysis.

10. A powder metallurgy copper alloy prepared by the method for preparing powder metallurgy copper alloy as described in any one of claims 1-9.

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