A hot-pressing densification process and a method for manufacturing 18K color gold composite profiles

Abstract

This invention relates to the field of jewelry processing and provides a hot-pressing densification process and a method for manufacturing 18K colored gold composite profiles. The hot-pressing densification process uses a hot-pressing sintering method to prepare the blank material, performs small deformation toughening treatment on the blank material, and performs large deformation static cavity extrusion treatment on the blank material to obtain a fully dense substrate with a multicolored texture on the surface. The material made from this has good rolling performance, is easy to weld, has material stability, is easy to roll, stretch and forge deformation processing, and has excellent oxidation resistance and corrosion resistance, thus solving the problems of difficult interface eutectic and single color of precious metals.

Description

Technical Field

[0001] This invention belongs to the field of jewelry processing, and particularly relates to a hot pressing densification process and a method for manufacturing 18K colored gold composite profiles. Background Technology

[0002] my country boasts a long history of metal craftsmanship, with a wide variety of unique styles. These crafts maintain a unity of practicality and aesthetics in both content and form, representing a brilliant treasure of the Chinese nation and a crystallization of China's excellent traditional culture. Metal crafts are widely used because they can create objects of different properties and possess artistic beauty and decorative qualities. After thousands of years of accumulation and development, machine manufacturing is gradually replacing purely handcrafted techniques, leading to an ever-expanding variety of metal crafts, and the demand for them remains consistently high.

[0003] With the enrichment of material life and the improvement of aesthetics, colorful and diverse metal handicrafts have gained market popularity. Among them, colorful non-ferrous metal handicrafts have the advantages of being dazzling and radiant. Non-ferrous metals have long been used in the field of metal jewelry due to their colorful appearance. Therefore, how to make individual metal elements colorful has always been a topic that practitioners in the jewelry processing industry have been pursuing.

[0004] Currently, the production of multicolored non-ferrous metals in China is mostly concentrated in ethnic minority areas such as Tibet, Mongolia, and Miao. Constrained by insufficient industrial technology, products are limited to small-scale workshops that use hot deformation and hammering techniques, followed by casting, fine polishing, and complex post-processing. The base materials are primarily silver and copper, used in small-scale production, hindering widespread application and preventing significant development. Existing metal densification processes typically include: closed-mold hot pressing, hot isostatic pressing, hot extrusion, hot die forging, laser zone melting, and powder sintering. Elements with similar physicochemical properties and melting points exhibit infinite intermelting characteristics. Conventional fusion of different colored metals only yields solid solutions without color separation interfaces. The aforementioned densification processes suffer from difficulties such as interface eutectic, easy oxidation during heating, unclear textures, and low yield. Summary of the Invention

[0005] This invention provides a hot-pressing densification process, which aims to solve the problems of difficult interface eutectic and limited color range of precious metals in existing metal manufacturing processes.

[0006] This invention is implemented as follows: a hot-pressing densification process includes the following steps:

[0007] The blank material is prepared by hot pressing and sintering.

[0008] The blank material is subjected to a small deformation strengthening and toughening treatment;

[0009] The blank material is subjected to large deformation static cavity extrusion treatment;

[0010] A fully dense substrate is obtained, wherein the surface of the fully dense substrate has a multicolored texture.

[0011] Optionally, the hot pressing sintering method specifically includes:

[0012] Place the preform inside a closed mold;

[0013] The preform is heated to a specified temperature, and gas is introduced for atmosphere protection to maintain a constant static pressure.

[0014] After annealing, the preform is extruded at a hot forging temperature to produce the billet material.

[0015] Optionally, heating the preform to a specified temperature specifically involves:

[0016] The preform is heated to a specified temperature at a heating rate of 10-25°C in isothermal stages, wherein the specified temperature is greater than 600°C.

[0017] Optionally, the gas introduction for atmosphere protection specifically includes:

[0018] Hydrogen gas is introduced into the preform for reduction for 4-6 minutes, then the hydrogen gas is turned off and argon gas is introduced.

[0019] Optionally, maintaining a constant hydrostatic pressure state specifically means:

[0020] The air pressure inside the sealed mold is controlled at 80-200Pa, and the temperature and pressure are maintained at a predetermined temperature for 4-6 minutes, wherein the predetermined temperature is greater than 600℃.

[0021] Optionally, the duration of extruding the preform at a hot forging temperature after annealing is 15-60 minutes, and the hot forging temperature is greater than 600°C.

[0022] Optionally, the small deformation strengthening treatment of the blank material specifically includes:

[0023] The blank is heated to 750-780℃ for 2-4 minutes to reforge the blank to a size smaller than the mold cavity.

[0024] Optionally, the large deformation static cavity extrusion treatment of the blank material specifically includes:

[0025] The preform is heated in a protective atmosphere at 830-850℃ in an ammonia decomposition furnace. After homogenization, it is quickly placed into an extrusion die cavity at 380℃ and continuously and rapidly extruded into the die cavity under a continuous pressure of 350-600MPa.

[0026] Optionally, the inlet and outlet area ratio of the extrusion die is set to 7 / 1 to 13 / 1.

[0027] The present invention also provides a method for manufacturing an 18K gold-plated composite profile, comprising:

[0028] A fully dense substrate is produced using the hot-pressing densification process described above;

[0029] A pattern is drawn on the surface of the substrate;

[0030] 18K gold composite profiles are obtained through non-directional precision rolling.

[0031] This invention uses hot pressing sintering to prepare the blank material, performs small deformation toughening treatment on the blank material, and performs large deformation static cavity extrusion treatment on the blank material to obtain a fully dense substrate with colorful textures on the surface. The material made from this has good rolling performance, is easy to weld, has material stability, and has excellent oxidation resistance and corrosion resistance, thus solving the problems of difficult interface eutectic and single color of precious metals. Attached Figure Description

[0032] Figure 1 This is a flowchart of a hot-pressing densification process provided in an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Example 1

[0034] like Figure 1 As shown, an embodiment of the present invention provides a hot-pressing densification process, including the following steps:

[0035] The blank material is prepared by hot pressing and sintering.

[0036] The blank material is subjected to a small deformation strengthening and toughening treatment;

[0037] The preform is subjected to large deformation static cavity extrusion to obtain a fully dense substrate with a multicolored texture on its surface.

[0038] This invention is based on the concepts of hypoeutectic supersolid diffusion sintering and large deformation twin metastable instantaneous fusion. Supersolid sintering involves heating fully pre-alloyed powder to a temperature between the solidus and liquidus lines on the alloy phase diagram, causing liquid phases to form within the grains, grain boundaries, and on the surface of each pre-alloyed powder grain. This allows the sintered body to rapidly achieve densification. The hot-pressing densification process, without significant liquid-to-liquid melting, rapidly completes the high-speed twin metastable fusion process of the grains under surface supersolid diffusion conditions. The interfaces of different colored metals are tightly bonded, resulting in a clear color separation interface and multi-colored texture in the fully dense substrate, achieving the effect of clear demarcation of multi-colored gold and full densification.

[0039] In another optional embodiment of the present invention, gold, silver and copper are used as main elements, and are combined with different elements (nickel, palladium, cobalt, zinc, aluminum and iron) to form copper alloys with different colors and melting points. The similarity and compatibility of the elements meet the conditions for short-range diffusion and small-area welding.

[0040] In addition, since gold and silver are high-quality welding materials that play a decisive role in fusion, the hot pressing sintering method can strictly control the arrangement of adjacent elements and avoid the formation of excessive molten alloy.

[0041] The hot pressing sintering method can easily obtain sintered bodies with near-theoretical density and near-zero porosity, easily achieve fine-grained structures, and easily obtain custom crystal orientations. Furthermore, since the material is in a thermoplastic state during hot pressing, the deformation resistance is small, making it easy to plastically flow and densify. The required forming pressure is only a fraction of that of the cold pressing method. Therefore, the resulting material has good calendering properties, material stability, and is easy to roll, stretch, and forge deformation processing. It also has excellent oxidation and corrosion resistance, and the forming pressure is low, thereby improving densification efficiency. Example 2

[0042] In an optional embodiment of the present invention, the hot pressing sintering method specifically comprises:

[0043] Place the preform inside a closed mold;

[0044] The preform is heated to a specified temperature, and gas is introduced for atmosphere protection to maintain a constant static pressure.

[0045] After annealing, the preform is extruded at a hot forging temperature to produce the billet material.

[0046] The process of extruding the preform at a hot forging temperature involves using the preform's excellent plasticity and rheological properties at the hot forging temperature to perform various extrusion moldings on the preform. The hot pressing densification process can not only form non-ferrous metals and their alloys with good plasticity and low strength, but also materials such as low and medium carbon steel with high strength.

[0047] Since the preform must be heated to the hot forging temperature for extrusion, it is often accompanied by severe oxidation heating defects, which will affect the dimensional accuracy and surface roughness of the substrate. High gold content precious metals also have the need for anti-oxidation treatment due to the presence of easily oxidized copper. The hot pressing sintering method is completed in a closed controlled atmosphere medium frequency induction furnace, and inert gas is introduced for atmosphere protection. Inert gas or vacuum environment is not easy to oxidize. Vacuuming or using inert gas protection throughout the process can slow down the oxidation process.

[0048] High temperature and pressure pose a severe test to the strength of the mold. The mold material can be graphene ceramic, which has the characteristics of explosion-proof and safety, long service life, and exhibits reliability and working stability during hot pressing and sintering.

[0049] Annealing involves heating the workpiece to a suitable temperature, holding it at that temperature for different times depending on the material and workpiece size, and then slowly cooling it. The purpose is to bring the internal structure of the metal to or near equilibrium, thereby obtaining good processing and performance properties. Annealing can reduce the distortion or hardening of the blank and increase its toughness and ductility. Example 3

[0050] Temperature is a crucial parameter affecting density, and the densification result is largely determined by temperature. In this invention, the hot-pressing temperature of the hot-pressing sintering method is selected to be 15-20°C below the melting point. Temperature and time have an inverse relationship with the densification result; to achieve the same density, higher temperatures require shorter densification times, while lower temperatures require longer holding times.

[0051] In an optional embodiment of the present invention, heating the preform to a specified temperature specifically involves:

[0052] The preform is heated to a specified temperature at a heating rate of 10-25°C in isothermal stages, wherein the specified temperature is greater than 600°C.

[0053] The following experiments used 18K gold preforms with a melting point of 940℃-950℃, heated to the specified temperature using isothermal stepped heating at a rate of 10-25℃. The temperatures and times in the table refer to the time spent holding the temperature after reaching it at a heating rate of 10-25℃.

[0054] Experiment 1:

[0055]

[0056] Experiment 2:

[0057]

[0058] Experiment 3:

[0059]

[0060] Experiment 4:

[0061]

[0062] Experimental test results:

[0063]

[0064] Since increasing the copper content raises the melting point of the material, the specified temperature of the hot pressing sintering method can also be evaluated based on the copper content to ensure temperature reliability. Example 4

[0065] In an optional embodiment of the present invention, the gas introduction for atmosphere protection specifically refers to:

[0066] Hydrogen gas is introduced into the preform for reduction for 4-6 minutes, then the hydrogen gas is turned off and argon gas is introduced. Hydrogen gas has reducing properties; after a certain period of time, the trace amount of copper oxide on the surface of the preform is decomposed and reduced by hydrogen in ammonia. Argon gas, as a colorless and odorless inert gas, has stability. Introducing argon gas as a protective gas prevents the preform from re-oxidizing. This not only solves the problem of oxidation resistance during the heating process, but also results in a smooth surface of the preform and improved processing performance. Example 5

[0067] In an optional embodiment of the present invention, maintaining a constant static pressure state specifically means:

[0068] The air pressure inside the closed mold is controlled at 80-200 Pa, and maintained at a predetermined temperature and pressure for 4-6 minutes. The predetermined temperature is greater than 600℃. High temperature and pressure help shorten the densification time. As the temperature increases, the resistance of the preform to plastic deformation decreases, which is beneficial to the plastic welding of pores. However, at the same time, the extrusion pressure decreases, and the hydrostatic pressure experienced by the preform during deformation decreases, which weakens the pores. The hydrostatic pressure is a force that is uniformly applied to the surface of the preform in all directions.

[0069] The mold has a self-feeding function with a radial displacement of not less than 1 / 20 of the height, ensuring the propulsion speed and supporting continuous propulsion. The constant temperature control accuracy is not greater than 0.2%, and the pressure is tracked throughout the process with a pressure control accuracy of not greater than 0.5%. The hot pressing sintering method completes the high-speed twinning metastable fusion process of the grains under continuous pressure and rapid propulsion in the suitable solid solution temperature range. The fusion is completed instantly, avoiding remote alloying and ensuring that the interfaces of different colored copper alloys are tightly bonded. The thickness of the metallurgical fusion solid solution layer is not greater than 0.05-0.10 mm, forming a uniform solid phase. Example 6

[0070] In an optional embodiment of the present invention, the duration of extruding the preform at the hot forging temperature after annealing is 15-60 minutes. The hot forging temperature is greater than 600°C. Rapid water vapor heat exchange cooling improves the cooling rate and obtains good process performance. The preform is continuously extruded at the hot forging temperature, and the plastic flow characteristics are utilized to make the preform form quickly. Example 7

[0071] In an optional embodiment of the present invention, the small deformation strengthening treatment of the blank material specifically involves:

[0072] The blank is heated to 750-780℃ for 2-4 minutes to reforge the blank to a size smaller than the mold cavity.

[0073] The blank material is generally rectangular in structure. For example, if the pre-made blank weighs 2700-3200 grams and the blank material size is (30-50)×(30-50)×(100-130) mm, it is difficult to enter the extruder cavity and needs to be shaped. The blank material is heated at 750-780°C in the ammonia decomposition heating furnace for 2-4 minutes to reforge the blank material to a size smaller than the cavity size. Example 8

[0074] In an optional embodiment of the present invention, the large deformation static cavity extrusion treatment of the blank material specifically includes:

[0075] The billet is heated in a protective atmosphere at 830-850℃ in an ammonia decomposition furnace. Trace amounts of copper oxide on the surface are reduced by ammonia gas from the decomposed ammonia. After homogenization, it is rapidly placed into a 380℃ extrusion die cavity. Under continuous pressure of 350-600MPa, the billet is extruded rapidly and continuously with varying diameters, achieving further densification and secondary twinning interface fusion. The fusion process is instantaneous, preventing remote alloying of grain boundaries and ensuring clear color separation. This embodiment can use a 450-550 ton hot extrusion press. The effective and close combination of pressure processing deformation and heat treatment gives the billet a good balance of strength and toughness, resulting in excellent ductility. Example 9

[0076] In an optional embodiment of the present invention, the inlet-outlet area ratio of the extrusion die is set to 7 / 1 to 13 / 1, depending on the finished product specifications, to meet the needs of various finished product specifications. Increasing the inlet-outlet area ratio of the extrusion die will increase the degree of deformation of the substrate and improve its density. Example 10

[0077] This invention also provides a method for manufacturing an 18K gold-plated composite profile, comprising:

[0078] A fully dense substrate is produced using the hot-pressing densification process described above;

[0079] A pattern is drawn on the surface of the substrate;

[0080] 18K gold composite profiles are obtained through non-directional precision rolling.

[0081] The fully dense substrate produced by the hot pressing densification process has a colorful texture on its surface. Patterns are etched and drawn on the surface of the substrate to meet the personalized needs of the jewelry processing industry. The change in the extrusion ratio of the extrusion die causes the profile pattern to extend excessively along the central axis. Appropriate non-directional rolling along the XY axis can obtain 18K colored gold composite profiles with the desired pattern texture effect.

[0082] This invention integrates multiple densification processes, and the optimized process route is simple and practical. It maintains the basic physical properties of gold, silver and copper alloys, is rich in multi-colored elements, can be cold-deformed, has good ductility, stabilizes process parameters, solves the basic problem of oxidation resistance during heating, and enables the multi-colored monomers to be produced. It successfully produces multi-colored 18K gold composite materials. It is a combination of technologically advanced metalworking methods and creativity, which will create a more brilliant future for metalworking.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hot-pressing densification process, characterized in that, Includes the following steps: The preparation of blanks using hot pressing sintering includes: Place the preform inside a closed mold; The preform is heated to a specified temperature, hydrogen is introduced into the preform for reduction for 4-6 minutes, the hydrogen is turned off and argon is introduced for atmosphere protection, and a constant static pressure is maintained. After annealing, the preform is extruded at a hot forging temperature greater than 600°C for 15-60 minutes to produce the billet material. The billet is subjected to a small deformation strengthening and toughening treatment, including: heating the billet at 750-780°C for 2-4 minutes, and forging the billet to a size smaller than the mold cavity size; The large deformation static cavity extrusion process of the preform includes: heating the preform in a decomposed ammonia heating furnace at 830-850°C in a protective atmosphere, and after homogenization, quickly placing it into a 380°C extrusion die cavity, and continuously and rapidly extruding the preform into the die cavity under a continuous pressure of 350-600MPa. A fully dense substrate is obtained, wherein the surface of the fully dense substrate has a multicolored texture.

2. The hot-pressing densification process as described in claim 1, characterized in that, The specific meaning of maintaining a constant static pressure state is as follows: The air pressure inside the sealed mold is controlled at 80-200Pa, and the temperature and pressure are maintained at a predetermined temperature for 4-6 minutes, wherein the predetermined temperature is greater than 600℃.

3. The hot-pressing densification process as described in claim 1, characterized in that, The ratio of the inlet and outlet area of ​​the extrusion die is set between 7 / 1 and 13 / 1.

4. The hot-pressing densification process as described in claim 1, characterized in that, Gold, silver, and copper were used as the main elements in the preform.

5. A method for manufacturing an 18K gold-plated composite profile, characterized in that, include: A fully dense substrate is prepared using the hot-pressing densification process as described in any one of claims 1-4; A pattern is drawn on the surface of the substrate; 18K gold composite profiles are obtained through non-directional precision rolling.

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