Method for preparing wood grain gold through powder sintering

Abstract

The invention discloses a method for preparing wood grain gold by powder sintering, which comprises the following steps of: mixing copper-based powder and an additive to obtain copper-based mixed powder, filling the copper-based mixed powder and copper-based blocky metal into a mold in a combined manner, compacting and packaging to obtain a green body, sintering the green body to obtain a sintered blank, performing thermal deformation treatment on the sintered blank to obtain a deformed blank, and sintering the deformed blank to obtain the wood grain gold. And carrying out chemical etching on the deformed blank. The additive comprises graphite powder; according to the method, through powder-block composite lamination design, gradient sintering and controllable plastic deformation, wood grain gold with high-strength and high-precision textures is prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for preparing wood-grained gold by sintering powder. Background Art

[0002] Mokume-gane is a traditional craft that forms a wood-grain texture by stacking different metals and then diffusing and bonding them at high temperatures. Its core process relies on the lamination and plastic deformation of metals such as copper, gold, and silver.

[0003] The current mainstream technologies (such as patents such as publication numbers CN102962640A, CN108085533A and CN114871318A) all use finished block metal sheets to encapsulate through mechanical clamping or welding, followed by high-temperature sintering and forging. However, the traditional process has the following significant defects: 1. Poor interface bonding performance: The bulk metal layers are only bonded by solid-state diffusion. Due to the large difference in metal melting points and the narrow sintering temperature window, it is easy to cause the low-melting-point metal to melt and lose or the high-melting-point metal to diffuse insufficiently, resulting in low interface bonding strength (usually ≤200MPa); 2. Low material utilization: The traditional lamination process requires a large amount of processing allowance to be reserved to compensate for forging losses. The actual material utilization rate is less than 50%, and complex patterns require multiple cutting and reorganization, further increasing losses; 3. Limited pattern design: Bulk metal stacking can only achieve planar textures (such as stripes and wavy patterns), and it is difficult to embed special-shaped structures (such as tubular and grid-like) to enhance the three-dimensional level; 4. Insufficient process stability: In the existing technology, welding packaging is prone to introduce oxide inclusions (such as copper welding oxide layer), and incomplete vacuuming leads to sintering bubble defects, which seriously affects the yield rate. For example, patent CN114871318A uses stainless steel foil boxes to weld and encapsulate bulk metal layers. Although vacuum treatment is used to reduce oxidation, the bulk metal stack it relies on must strictly match thickness and melting point, and more than 20% cutting allowance is still required after sintering; CN108085533A improves bonding by adding an intermediate alloy layer, but the additional alloy elements lead to increased costs and turbid texture. Summary of the Invention

[0004] In response to the problems existing in the traditional wood grain gold preparation process, such as low interface bonding strength, insufficient material utilization and single pattern design, the purpose of the present invention is to provide a method for preparing wood grain gold by powder sintering. The present invention realizes the preparation of high-strength and high-precision wood grain gold through powder-block composite laminate design, gradient sintering and controllable plastic deformation.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for preparing wood grain gold by powder sintering, comprising mixing copper-based powder with an additive to obtain a copper-based mixed powder, combining the copper-based mixed powder with a copper-based bulk metal, filling the combined powder into a mold, and then pressing and packaging the mold to obtain a green blank, sintering the green blank to obtain a sintered blank, subjecting the sintered blank to a thermal deformation treatment to obtain a deformed blank, and chemically etching the deformed blank to obtain the finished product;

[0007] The additive includes graphite powder.

[0008] The present invention adopts a combination of powder and block to prepare wood grain gold. In the present invention, a small amount of graphite powder is first added to the copper-based powder as a diffusion activator to increase the fluidity of the powder during the sintering process. This not only reduces the sintering temperature but also obtains wood grain gold with high strength and high-precision texture after molding.

[0009] In a preferred embodiment, the copper-based powder is selected from one of red copper powder, white copper powder and brass powder.

[0010] The inventors have found that different types of copper-based powders cannot be mixed for use, because if mixed, the visual effect of the wood grain gold pattern will be reduced.

[0011] In a preferred embodiment, the particle size of the copper-based powder is 10-500 μm. Controlling the particle size of the copper-based powder within this range results in the highest density.

[0012] In a preferred embodiment, the mass fraction of graphite powder in the copper-based mixed powder is 0.3%-1wt%.

[0013] In a preferred embodiment, the process of mixing the copper-based powder and the additive is wet ball milling, the rotation speed of the wet ball milling is 200-300 r / min, and the wet ball milling time is 4-8 hours.

[0014] Further preferably, the medium for wet ball milling is anhydrous ethanol.

[0015] In the actual operation process, after the wet ball milling is completed, it is then dehydrated in a vacuum drying oven at 80°C for 4 hours.

[0016] In a preferred embodiment, the copper-based bulk metal is selected from one of tubular or sheet-shaped red copper, brass, and white copper.

[0017] In a preferred embodiment, the copper-based bulk metal has a thickness of 0.5-3 mm.

[0018] In a preferred embodiment, the surface of the copper-based bulk metal is first polished with 400# to 2000# sandpaper in stages to Ra ≤ 0.8 μm, and then ultrasonically cleaned to remove grease and oxides.

[0019] Further preferably, when the copper-based bulk metal is tubular, the combined filling method is to embed the copper-based bulk metal in the copper-based mixed powder; when the copper-based bulk metal is sheet-shaped, the combined method is to alternately layer the copper-based mixed powder and the copper-based bulk metal.

[0020] In a preferred embodiment, the mold is a stainless steel foil box with a wall thickness of 0.1-0.5 mm (dimensional error ±0.1 mm).

[0021] In a preferred embodiment, the pressure of the green compact packaging is 50-200 MPa.

[0022] In a preferred embodiment, the green compact packaging is selected from vacuum electron beam welding packaging, vacuum tube packaging, and compression molding.

[0023] Further preferably, the vacuum electron beam welding packaging process is to fill the copper-based mixed powder and the copper-based bulk metal into a mold, pre-press with a pressure of 50-200 MPa, and then seal the box body by vacuum electron beam welding, with the weld airtightness ≤1×10 - ³ Pa·m³ / s.

[0024] Further preferably, the vacuum tube packaging process is as follows: the copper-based mixed powder and the copper-based bulk metal are combined and filled into a mold, and after pre-pressing with a pressure of 50-200 MPa, a vacuum tube with a diameter of 1-3 mm is retained, and the pressure in the box is reduced to ≤1×10 - ³ Pa, clamped and laser welded to seal the tube.

[0025] By adopting the above packaging method, dense sintering can be achieved in any atmosphere.

[0026] Furthermore, preferably, during the compression molding process, the additive further includes paraffin wax, and the copper-based mixed powder has a paraffin wax mass fraction of 0.5-1%. Paraffin wax (melting point 52-68°C) is added to the powder as a temporary binder, and the paraffin wax is subsequently volatilized through sintering to form a diffusion channel.

[0027] In a preferred embodiment, the sintering temperature is 700-950° C., the sintering time is 1-2 hours, and the sintering atmosphere is selected from a protective atmosphere, a vacuum atmosphere, or an air atmosphere.

[0028] Further preferably, when the green sheet packaging is selected from vacuum electron beam welding packaging or vacuum tube packaging, the green sheet is sintered in an air environment, and during sintering, the heating rate is controlled to be 5-10° C. / min.

[0029] Further preferably, when the green sheet packaging is selected from compression molding, sintering is carried out in a protective atmosphere or a vacuum atmosphere, and the sintering process is: first heating to 350°C at a heating rate of 5-10°C / min and keeping warm for 1 hour, and then heating to 700-950°C, preferably 900°C, at a heating rate of 5-10°C / min, and keeping warm for 1-2 hours.

[0030] When the green sheet packaging is selected from compression molding, since paraffin is added to the mixed powder, the temperature is first raised to the paraffin volatilization stage, and the paraffin is formed into a diffusion channel through heat preservation, and then the temperature is continued to rise to the target temperature range to achieve co-sintering of the copper-based mixed powder and the copper-based bulk metal.

[0031] Furthermore, preferably, the protective atmosphere is argon with a purity of ≥99.99%, the flow rate of the protective atmosphere is controlled to be ≥200 ml / min during sintering, and the vacuum degree of the vacuum atmosphere is ≤1×10 - ²Pa.

[0032] In a preferred embodiment, the thermal deformation treatment is hot forging or hot rolling, and the temperature of the thermal deformation treatment is 700-800°C. When the thermal deformation treatment is hot forging, the forging rate is controlled to 10-20 times / min. When the thermal deformation treatment is hot rolling, the reduction is controlled to 50-70%. In the present invention, the thermal deformation treatment is performed at a temperature above the copper recrystallization temperature.

[0033] In a preferred embodiment, the chemical etching process comprises immersing the heat-treated part in a corrosive solution selected from HNO3 solution, FeCl3 solution, and H2SO4 solution, with the etching depth gradient ranging from 10 to 50 μm. The chemical etching enhances the three-dimensional effect of the layered / tubular texture.

[0034] Further preferably, when the wood grain gold is made of brass only, the corrosion solution is an HNO3 solution with a mass concentration of 15%-20%, and the corrosion time is 5-10s.

[0035] Further preferably, when the wood grain gold is made of only copper, the corrosion solution is a mixed solution of HNO3 and H2SO4, and the corrosion time is 10-20s.

[0036] Further preferably, when the wood grain gold is made of only white copper, the corrosion solution is HNO3 with a mass concentration of 45-50%, the corrosion time is 100-120s, and the temperature of the corrosion solution is 40-60°C.

[0037] Further preferably, when the wood grain gold is a composite of brass and copper, the chemical etching process is to first immerse the heat-treated part in a FeCl3 solution with a mass concentration of 10-15%, corrode for 30-60s, and then immerse it in a HNO3 solution with a mass concentration of 15-30%, corrode for 5-15s.

[0038] Further preferably, when the wood grain gold is a composite of brass and white copper, the chemical etching process is to first immerse the heat-treated part in a HNO3 solution with a mass concentration of 20-30% and corrode it for 10-20s, and then immerse it in a H2SO4 solution with a mass concentration of 5-10% and corrode it for 60-120s.

[0039] Further preferably, when the wood grain gold is a composite of red copper and white copper, the chemical etching process is to immerse the heat-treated part in a 30% HNO3 solution for etching for 15-30 seconds, and then immerse it in a mixed solution of HNO3 and H2SO4 in a mass ratio of 1:1 for etching for 10-20 seconds. This ratio is fixed.

[0040] Further preferably, when the wood grain gold is a composite of brass, copper, and white copper, the chemical etching process is that the heat-treated part is immersed in FeCl3 solution A, FeCl3 solution B, and FeCl3 solution C in sequence, and corroded for 30-60s respectively, and the concentration of FeCl3 solution A is 5%-10%, the concentration of FeCl3 solution B is 4~6% higher than that of FeCl3 solution A, and the concentration of FeCl3 solution C is 4~6% higher than that of FeCl3 solution B.

[0041] Beneficial effects

[0042] The present invention adopts a combination of powder and block to prepare wood grain gold. In the present invention, a small amount of graphite powder is first added to the copper-based powder as a diffusion activator to increase the fluidity of the powder during the sintering process. This can not only reduce the sintering temperature, but also, after forming, through simple deformation and etching treatment, high-strength, high-precision texture wood grain gold can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of vacuum electron beam welding packaging.

[0044] Figure 2 Schematic diagram of vacuum tube packaging.

[0045] Figure 3 Schematic diagram of compression molding.

[0046] Figure 4 The finished morphology of the wood grain gold obtained in Example 1.

[0047] Figure 5Vacuum electron beam welding packaging diagram of Example 2. DETAILED DESCRIPTION

[0048] Example 1

[0049] Brass powder and copper plates were prepared. 0.6wt% graphite powder and 0.5wt% paraffin wax were added to the brass powder. Anhydrous ethanol was then added and wet-milled in a planetary ball mill at 250 rpm for 4 hours. The brass powder was then dried in an 80°C oven for 4 hours. The resulting brass powder was then cut and welded into a stainless steel foil box measuring 40mm x 20mm x 20mm in length, width, and height, and 0.2mm thick. The brass powder and copper plates were stacked into the box, compacted using a hydraulic press at a load of 80 MPa for each layer, and the copper plates were placed on top. The assembled stainless steel box was then placed in a tube furnace and sintered with argon at 250 ml / min. The temperature was raised to 350°C at 10°C / min, held for 1 hour, and then raised to 950°C at 5°C / min, held for 1 hour. The wood-grained gold blank was removed, cooled, and hammered out. It was then reheated to 800°C and forged at a controlled forging rate of 15 times / min, ultimately producing a wood-grained gold material with layered patterns. The resulting material was then immersed in a 15% FeCl₃ solution for 20 seconds, followed by a 20% HNO₃ solution for 20 seconds, completing the wood-grained gold blank.

[0050] Example 2

[0051] Brass powder and copper plates were prepared and then cut and welded to create a stainless steel foil box measuring 40 mm x 20 mm x 20 mm, and 0.2 mm thick. The brass powder and copper plates were stacked into the box, and each layer was compacted using a hydraulic press at a load of 80 MPa. The stainless steel casing was then welded shut. The assembled box was placed in a muffle furnace and sintered in air. The temperature was raised at 5°C / min to 950°C and held for 1 hour. The wood-grained gold blank was removed, cooled, and hammered out. The blank was then reheated to 800°C and forged at a controlled forging rate of 15 strokes / min, resulting in a wood-grained gold material with a layered pattern. The resulting blank was then immersed in a 15% FeCl₃ solution for etching for 20 seconds, followed by an immersion in a 20% HNO₃ solution for etching for 20 seconds. This completed the wood-grained gold blank.

[0052] Comparative Example 1

[0053] Using existing methods, brass and copper plates measuring 40mm x 20mm x 4mm are polished, each layer brushed with boric acid solution, and then stacked in the order of brass, copper, and brass. The stacked copper plates are clamped in a small vise and placed directly in a furnace, heated to 950°C, and sintered for one hour before being removed and forged. The resulting wood-grain gold blanks do not fully bond metallurgically, with white copper oxide appearing on some surfaces. This is because the existing method for sintering wood-grain gold does not completely isolate the two copper layers from air. This accelerates the reaction between the copper surface and oxygen during sintering, forming oxides, preventing metallurgical bonding.

Claims

1. A method for preparing wood grain gold by sintering powder, characterized in that: The copper-based powder is mixed with an additive to obtain a copper-based mixed powder, the copper-based mixed powder is combined with a copper-based bulk metal and filled into a mold, and then pressed and packaged to obtain a green body, the green body is sintered to obtain a sintered body, the sintered body is subjected to thermal deformation treatment to obtain a deformed body, and the deformed body is chemically etched to obtain the product; the additive includes graphite powder.

2. The method for preparing wood grain gold by powder sintering according to claim 1, characterized in that: The copper-based powder is selected from one of red copper powder, white copper powder and brass powder; The particle size of the copper-based powder is 10-500 μm; In the copper-based mixed powder, the mass fraction of graphite powder is 0.3-1 wt %.

3. The method for preparing wood grain gold by powder sintering according to claim 1 or 2, characterized in that: The process of mixing the copper-based powder and the additive is wet ball milling, the rotation speed of the wet ball milling is 200-300 r / min, and the wet ball milling time is 4-8 hours; The medium for the wet ball milling is anhydrous ethanol.

4. The method for preparing wood grain gold by powder sintering according to claim 1 or 2, characterized in that: The copper-based bulk metal is selected from one of tubular or sheet-shaped red copper, brass, and white copper; The thickness of the copper-based bulk metal is 0.5-3 mm; The surface of the copper-based bulk metal is first polished with 400#~2000# sandpaper in stages to Ra≤0.8μm, and then ultrasonically cleaned; When the copper-based bulk metal is tubular, the combined filling method is to embed the copper-based bulk metal in the copper-based mixed powder. When the copper-based bulk metal is sheet-shaped, the combined method is to alternately layer the copper-based mixed powder and the copper-based bulk metal.

5. The method for preparing wood grain gold by powder sintering according to claim 1, characterized in that: The mold is a stainless steel foil box with a wall thickness of 0.1-0.5 mm; The pressure of the green compact packaging is 50-200 MPa; The green compact packaging is selected from vacuum electron beam welding packaging, vacuum tube packaging, and compression molding; The vacuum electron beam welding packaging process is to fill the copper-based mixed powder and copper-based bulk metal into a mold, pre-press with a pressure of 50-200 MPa, and then seal the box body by vacuum electron beam welding. The airtightness of the weld is ≤1×10 - ³ Pa·m³ / s; The vacuum tube packaging process is as follows: copper-based mixed powder and copper-based bulk metal are combined and filled into a mold, and after pre-pressing with a pressure of 50-200 MPa, a vacuum tube with a diameter of 1-3 mm is retained, and the pressure in the box is reduced to ≤1×10 - ³Pa, clamp and laser weld to seal the tube; During the compression molding, the additive further comprises paraffin, and the mass fraction of the paraffin in the copper-based mixed powder is 0.5-1%.

6. The method for preparing wood grain gold by powder sintering according to claim 1, characterized in that: The sintering temperature is 700-950° C., the sintering time is 1-2 hours, and the sintering atmosphere is selected from a protective atmosphere, a vacuum atmosphere, or an air atmosphere.

7. The method for preparing wood grain gold by powder sintering according to claim 5, characterized in that: When the green sheet packaging is selected from vacuum electron beam welding packaging or vacuum tube packaging, sintering is performed in an air environment, and during sintering, the heating rate is controlled to be 5-10°C / min; When the green compact packaging is selected from compression molding, sintering is performed in a protective atmosphere or a vacuum atmosphere, wherein the sintering process is as follows: firstly heating the temperature to 250-400°C at a heating rate of 5-10°C / min and holding the temperature for 1 hour, then heating the temperature to 700-950°C at a heating rate of 5-10°C / min and holding the temperature for 1-2 hours; The protective atmosphere is argon with a purity of ≥99.99%. During sintering, the flow rate of the protective atmosphere is controlled to be ≥200 ml / min. The vacuum degree of the vacuum atmosphere is ≤1×10 - ²Pa.

8. The method for preparing wood grain gold by powder sintering according to claim 1 or 2, characterized in that: The thermal deformation treatment is hot forging or hot rolling, the temperature of the thermal deformation treatment is 700-800°C, when the thermal deformation treatment is hot forging, the forging rate is controlled to be 10-20 times / min, when the thermal deformation treatment is hot rolling, the reduction is controlled to be 50-70%.

9. The method for preparing wood grain gold by powder sintering according to claim 1 or 2, characterized in that: The chemical etching process is to immerse the heat-treated part in a corrosion solution with a corrosion depth gradient of 10-50 μm. The corrosion solution is selected from one of HNO 3 solution, FeCl 3 solution and H 2 SO 4 solution.

10. The method for preparing wood grain gold by powder sintering according to claim 1 or 2, characterized in that: When the wood grain gold is made of brass only, the corrosion solution is a HNO3 solution with a mass concentration of 15%-20%, and the corrosion time is 5-10s; When the wood grain gold is made of only copper, the corrosion solution is a mixed solution of HNO3 and H2SO4, and the corrosion time is 10-20s; When the wood grain gold is made of only white copper, the etching solution is HNO3 with a mass concentration of 45-50%, the etching time is 100-120 seconds, and the temperature of the etching solution is 40-60°C; When the wood grain gold is a composite of brass and copper, the chemical etching process is to immerse the heat-treated part in a FeCl3 solution with a mass concentration of 10-15% for etching for 30-60 seconds, and then immerse it in a HNO3 solution with a mass concentration of 15-30% for etching for 5-15 seconds; When the wood grain gold is a composite of brass and cupronickel, the chemical etching process is to immerse the heat-treated part in a 20-30% HNO3 solution for etching for 10-20 seconds, and then immerse it in a 5-10% H2SO4 solution for etching for 60-120 seconds. When the wood grain gold is a composite of red copper and white copper, the chemical etching process is to immerse the heat-treated part in a 30% HNO3 solution for etching for 15-30 seconds, and then immerse it in a mixed solution of HNO3 and H2SO4 in a mass ratio of 1:1 for etching for 10-20 seconds; When the wood grain gold is a composite of brass, red copper, and white copper, the chemical etching process is as follows: the heat-treated part is immersed in FeCl3 solution A, FeCl3 solution B, and FeCl3 solution C in sequence, and corroded for 30-60 seconds respectively. The concentration of FeCl3 solution A is 5%-10%, the concentration of FeCl3 solution B is 4-6% higher than that of FeCl3 solution A, and the concentration of FeCl3 solution C is 4-6% higher than that of FeCl3 solution B.

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