Preparation method of high-hardness gold substrate by magnetic confinement suspension melting

Abstract

The present invention belongs to the field of metal processing, and specifically relates to a method for preparing a high-hardness gold substrate by magnetic confinement suspension smelting. The present invention adopts a combination of magnetic suspension and magnetic stirring under vacuum conditions and a rapid solidification process to perfectly solve the internal and external defects of high-hardness gold castings. The substrate has a dense structure and a smooth surface, which provides the greatest convenience for later deep processing and has a huge market demand. The entire process of the process described in the present invention is pollution-free and does not discharge three wastes.

Description

Technical Field

[0001] The invention belongs to the field of metal processing, and in particular relates to a method for preparing a high-hardness gold substrate by magnetically constrained suspension smelting. Background Art

[0002] Gold (Au), a transition element, is not easy to oxidize within a certain temperature range. It has a unique brilliant luster and excellent ductility, stable chemical properties, excellent thermal conductivity, and can be infinitely melted and alloyed with a variety of metals, showing good castability. It is widely used in jewelry, handicrafts, aerospace chemical and electronic industries.

[0003] As the gold processing market gradually opens up, the demand enters the market at an annual rate of 30% to meet the needs. The demand for gold and silver is derived from the extended application of 99.99% purity. Since gold is soft in texture and has a Vickers hardness of only HV22-32, it has poor wear resistance and is difficult to meet the aesthetic needs of direct inlay. For a long time, it has been difficult to make breakthrough progress in the industry that needs to ensure both sufficient toughness and gold purity.

[0004] In recent years, many domestic research institutions have tried to make breakthroughs by adding trace elements to vacuum melting and casting equipment, but the results have been less than ideal: gravity segregation, element agglomeration, and chemical poisoning of the crucible material by the added elements have occurred.

[0005] Magnetic confinement suspension heating control was once a special term for nuclear technology, which is dedicated to the special smelting of high melting point, high activity, and high specific gravity elements. It has a mature development history of more than 50 years. Magnetic confinement magnetic suspension melting technology is mainly used in precision casting, automobile manufacturing, medical sports equipment manufacturing, and additive manufacturing. After long-term development, with the maturity of equipment technology, magnetic confinement magnetic suspension melting technology can improve the quality of melting, and it is becoming more and more mature in the production of high-end components, special functional alloy melting and crystal growth. With the popularization of science and technology, some civilian material processing has gradually been popularized and applied to magnetic technology.

[0006] How to obtain fully dense, high-hardness, high-purity, and internally and externally defect-free functional gold materials has always been a major research topic in the precious metal processing industry. This study is based on the theory of dispersed system control and phase change solidification, and introduces a vacuum magnetic confinement suspension melting directional solidification process. Summary of the invention

[0007] The invention provides an alkaloid compound, an extraction method and application thereof, which can achieve high benefits.

[0008] The technical solution of the present invention is achieved in this way:

[0009] A method for preparing a high-hardness gold substrate by magnetic confinement suspension smelting, comprising the following steps:

[0010] (1) quantitatively weighing gold into a water-cooled copper crucible in a vacuum magnetic confinement levitation melting machine; quantitatively weighing added elements into a feeding cavity of a secondary crucible in the vacuum magnetic confinement levitation melting machine;

[0011] (2) Pre-vacuum to 6×10 -3 Pa, heating in steps, when the temperature reaches 800-900℃, start the argon solenoid valve to fill in argon, turn on the automatic pressure tracking system, keep the pressure at 600-800Pa, and set the temperature to T1+200 degrees;

[0012] (3) Add the additive elements under balanced pressure conditions and pre-stir mechanically; continue to increase the power and control the temperature at T2+200°C, and keep warm for 1-3 minutes according to needs;

[0013] (4) Confirm that the melt is evenly distributed, quickly dump the crucible without stopping heating, and inject the molten liquid into the mold for condensation;

[0014] (5) Make sure that all transmission mechanisms have returned to their original state, open the pressure relief valve, and after the pressure relief is completed, open the furnace chamber, remove the cast mold, and take out the product.

[0015] Furthermore, in the step (1), the mass fraction of the added element is generally 0.07-0.2% based on the weight of the finished product; and the added element is in the form of nano-sized particles.

[0016] Furthermore, in step (1), the purity of gold is at least 99.99%.

[0017] Furthermore, in the step (1), the melting point of the added element is 300-600° C. higher than the melting point of gold.

[0018] Furthermore, in the step (2), T1 is the melting point of gold, which is set to 1063° C.; and T2 is not higher than the melting point of the added element.

[0019] Furthermore, in the step (3), T2 is 200-300° C. lower than the melting point of the added element.

[0020] Furthermore, in the step (4), condensation is performed using directional condensation technology. During the condensation process, a casting water flow channel is set at the bottom of the mold to accelerate solidification, and the solidification direction of the liquid material is controlled to condense from bottom to top; the temperature is controlled at 7-10°C during the condensation process.

[0021] Beneficial effects of the present invention:

[0022] The present invention adopts magnetic levitation and magnetic stirring under vacuum conditions and rapid solidification combined process to perfectly solve the internal and external defects of high-hardness gold castings. The substrate has a dense structure and a smooth surface, which provides the greatest convenience for later deep processing and has a huge market demand. The whole process of the process described in the present invention is pollution-free and no three wastes are discharged.

[0023] The vacuum magnetic confinement suspension smelting technology relies on a strong magnetic field to support the entire smelting process. The gold molten pool is in a suspended state and does not come into contact with the crucible, thus avoiding secondary material contamination. The alternating magnetic field is synthesized by dual frequencies. The sub-frequency completes the magnetic suspension pad and magnetic stirring, and the super-frequency completes the eddy current smelting. The material is stirred at high speed by the magnetic field to achieve a deep dispersion mean distribution, thus avoiding the segregation and agglomeration of elements due to the influence of gravity, and avoiding poisoning pollution in the crucible melting process. High-speed directional solidification further guides homogenization to achieve solid solution. This process uses vacuum melting to prevent gas adsorption, and the surface of the cast embryo is smooth and delicate. Under high vacuum conditions close to the melting point of the material, gold will evaporate, and added elements (such as titanium) are very active under high temperature conditions, and are easily carbonized and oxidized, so they must be suppressed by high vacuum. The method described in the present invention strictly controls the equilibrium point and realizes effective process continuous operation.

[0024] The vacuum magnetic confinement suspension smelting directional solidification technology can effectively improve and eliminate the gravity segregation phenomenon of liquid metal in a high-temperature molten state. The added trace elements are dispersed and distributed, which solves the problem that different materials with different melting points cannot be fully homogenized and fused. Then through high-speed directional solidification, the liquid phase / solid phase solidification trajectory is forcibly transformed, and the solidified ingot material is dense and reaches the theoretical density. The material is dispersed and homogenized, the hardness is stable, and the purity meets market demand. There is no oxidation and shrinkage holes on the surface, the surface is bright, the edges are rounded and without defects, and it is nearly ideal. The internal and external quality of the ingot is better than continuous casting, vacuum casting, gravity casting and centrifugal casting. The specifications of small ingots meet the requirements of sheet and wire processing. The present invention also recommends an adaptive heat treatment process.

[0025] The standard magnetic levitation homogeneous controlled solidification technology is a typical example of cutting-edge technology. The equipment investment is huge. A five-kilogram melting and casting equipment costs more than five million yuan, which is far beyond the affordability of ordinary enterprises. The present invention is based on maintaining the original mechanism and simplifying the process for precise control. The manufacturing cost has been controlled within an acceptable range of one million yuan. It is the first new process for low-cost processing of ideal precious metals. It has a reasonable design structure, low investment, and simplified operation process. It has realized the manufacture of fully dense, high-hardness, high-purity, and internally and externally defect-free functional gold substrates, and has great promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 It is a vacuum magnetic confinement suspension melting machine;

[0028] Figure 2 The gold substrate is a product obtained by the present invention that is hardened three times, and the product hardness is HV130-167;

[0029] Figure 3 The gold substrate is a product obtained by the present invention through secondary hardening and aging hardening, and the product hardness is HV150-185;

[0030] Figure 4 Hardening curves of Au-0.1%Me alloy at different aging temperatures, Au is gold, Me is an added element;

[0031] Figure 5 Comparison between a conventional melt-cast ingot (upper figure) and an ingot made by the method described in the present invention (lower figure). DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing a high-hardness gold substrate by magnetic confinement suspension smelting, comprising the following steps:

[0035] (1) Quantitatively weigh gold into a vacuum magnetic confinement suspension melting machine ( Figure 1 As shown, the input power is 150 kilowatts) in a water-cooled copper crucible; the elements are quantitatively weighed and added into the feeding cavity of the secondary crucible in the vacuum magnetic confinement suspension melting machine; the mass fraction of the added elements is generally 0.07-0.2% based on the weight of the finished product; the added elements are nano-sized particles. The melting point of the added elements is 300-600℃ higher than the melting point of gold, such as titanium or platinum. According to the difference in hardness corresponding to different gold contents, considering the purity of the materials, the raw material configuration requires that the purity of the original gold is not less than 99.99%, avoiding the adverse reaction of silver and copper impurity elements in the melting process when low-purity gold is selected.

[0036] (2) Pre-vacuum to 6×10 -3 Pa, heating in steps, when the temperature reaches 900℃, start the argon solenoid valve to fill argon, turn on the automatic pressure tracking system, keep the pressure at 800Pa, and set the temperature to T1+200 degrees; T1 is the melting point of gold, set to 1063℃; T2 is not higher than the melting point of the added element;

[0037] (3) Add the additive elements under balanced pressure conditions and pre-stir mechanically; continue to increase the power and control the temperature at T2+200°C, and keep warm for 1-3 minutes according to needs;

[0038] (4) Confirm that the melt is evenly matched and quickly dump the crucible without stopping heating, and inject the molten liquid into the high-speed condensation cavity of the mold for condensation; the condensation adopts directional condensation technology. During the condensation process, a casting water flow channel is added to the bottom of the mold to accelerate solidification, control the solidification direction of the liquid material from bottom to top, and inhibit the growth of lateral columnar crystals; the temperature is controlled at 7-10°C during the condensation process.

[0039] (5) Make sure that all transmission mechanisms have returned to their original state, open the pressure relief valve, and after the pressure relief is completed, open the furnace chamber, remove the cast mold, and take out the product.

[0040] In this embodiment, the trace elements are selected in the form of nano-sized particles. When the material reaches nano-sized particles, the melting point will drop significantly, so T2 is selected to be 200° C. lower than the melting point of the added elements.

[0041] Example 2

[0042] A method for preparing a high-hardness gold substrate by magnetic confinement suspension smelting, comprising the following steps:

[0043] (1) Quantitatively weigh gold into a water-cooled copper crucible in a vacuum magnetic confinement levitation melting machine (input power 150 kW); quantitatively weigh the added elements into the feeding cavity of the secondary crucible in the vacuum magnetic confinement levitation melting machine; the mass fraction of the added elements is generally 0.07-0.2% based on the weight of the finished product; the added elements are nano-sized particles. The melting point of the added elements is 300-600°C higher than the melting point of gold, such as titanium or platinum. The purity of the added gold is at least 99.99%.

[0044] (2) Pre-vacuum to 6×10 -3 Pa, heating in steps, when the temperature reaches 800℃, start the argon solenoid valve to fill argon, turn on the automatic pressure tracking system, keep the pressure at 600Pa, and set the temperature to T1+200 degrees; T1 is the melting point of gold, set to 1063℃; T2 is not higher than the melting point of the added element;

[0045] (3) Add the additive elements under balanced pressure conditions and pre-stir mechanically; continue to increase the power and control the temperature at T2+200°C, and keep warm for 1-3 minutes according to needs;

[0046] (4) Confirm that the melt is evenly matched and quickly dump the crucible without stopping the heating condition, and inject the molten liquid into the mold for condensation; the condensation is carried out by directional condensation technology. During the condensation process, a casting water flow channel is set at the bottom of the mold to accelerate the solidification, and the solidification direction of the liquid material is controlled from bottom to top; the temperature is controlled at 7-10°C during the condensation process.

[0047] (5) Make sure that all transmission mechanisms are restored to their original state, open the pressure relief valve, and after the pressure relief is completed, open the furnace chamber, remove the cast mold, and take out the product. The entire ingot casting process is completed.

[0048] In the above embodiment, the trace elements are selected in the form of nano-sized particles. When the material reaches nano-sized particles, the melting point will drop significantly. Therefore, T2 is selected to be 300° C. lower than the melting point of the added elements.

[0049] The finished product obtained in the above embodiment is further processed. It mainly includes:

[0050] (1) Post-ingot processing:

[0051] 1. Check the weight and record the amount of burnt;

[0052] 2. Sampling metallographic analysis and quantitative determination of component elements;

[0053] 3. Surface burr removal and recycling;

[0054] 4. The ingots are stored at one time.

[0055] (2) Heat treatment and deformation processing:

[0056] 1. Ingot hardness measurement, record the initial hardness of the ingot;

[0057] 2.450-580℃ stress relief annealing;

[0058] 3. Roll and draw according to the predetermined deformation amount of 70-75%, and perform secondary stress relief annealing if necessary;

[0059] 4. Finish rolling and finishing drawing to the predetermined profile specifications, usually set to 0.3-0.5% of the original thickness. The test hardness is solid solution + deformation.

[0060] 5. When there is a need to press products with high-precision textures, a 400-480℃ stress relief annealing can be added, and the product will be finally aged and hardened (three times hardened) after processing.

[0061] Small ingots use directional high-speed solidification technology to ensure homogeneous dispersion of solid solution. Under the condition that the purity of raw gold is at least 99.99%, a two-kilogram ingot can achieve ideal results. The hardness of the material used for compression molding should not exceed HV80. If the hardness is greater than HV90, it is easy to stretch and tear. The third hardening is naturally generated during the compression deformation process of the product.

[0062] Finished product application examples such as Figure 2-3 shown.

[0063] The basic physical properties of the finished product are as follows: Figure 4 shown. Figure 4In the figure, the red circle is the range of hardness and holding time for aging treatment. The optimal hardness point is a fixed value. Below this temperature, a wider time adaptation zone can be obtained, which is conducive to maintaining hardness in a small range of welding in the later stage.

[0064] The process of the present invention ensures that the basic hard gold matrix has a high dispersion mean distribution. By reasonably allocating the deformation amount and corresponding heat treatment regulation, the hardening process is carried out in stages without special requirements. The delivery state is a medium hard state HV70-85, which is convenient for the later processing of the products of the processing enterprise.

[0065] It is recommended that the terminal hardening process be done under vacuum conditions.

[0066] The performance of different gold contents are as follows:

[0067] Gold content / % Yield strength / MPa Hardness / HV <![CDATA[Density / g / cm 3 > Melting point / ℃ Elongation / % 90.0-95.0 800-1200 160-230 18.5-19.0 980-1020 50-150 99.1-99.5 500-800 120-160 19.25 1020-1040 150-250 99.6-99.8 400-650 100-140 19.28 1030-1100 250-300 99.9-99.92 250-400 80-120 19，3 1050-1090 250-400

[0068] Delivery status:

[0069] Specification Sheet Strip Wire Small ingot Dimensions (H x W): mm (0.15-0.20)X25 (0.2-0.3) 10x40xL

[0070] 1. Appearance inspection: no bubbles, no wrinkles, no inclusions, no scratches.

[0071] 2. Color inspection: qualified,

[0072] 3. Calibrated weight: qualified.

[0073] 1. Comparison between the method described in the present invention and conventional ingot finished products

[0074] In the conventional ingot casting process, gold and silver materials and added elements are placed in a crucible at the same time, melted and mixed by medium frequency induction under vacuum conditions, and fully stirred (if conditions permit, the added elements can be added to the molten pool through a secondary feeding mechanism). After continuous heating and insulation, it is judged that the ingot has been fully fused, and then the ingot is poured into the furnace and slowly injected into an open or closed mold to condense into a solid state of a predetermined shape.

[0075] The conventional ingot casting method and the ingot casting method of the present invention are respectively used to cast ingots of the same batch of gold materials (purity 99.99%). Titanium is selected as the additive element, and the additive amount is 0.1%. The ingot casting is carried out according to the method of Example 1. Figure 5 Comparison of the ingots made by the traditional process and the ingots made by the method described in the present invention. The upper figure is a conventional ingot, and the lower figure is an ingot produced by the present invention. By comparison, it can be seen that in the traditional method, the surface of the ingot is not smooth, the internal structure has defects, and the material density is poor. The method described in the present invention fundamentally solves the defects of the ingot structure, the ingot material is dense, overcomes the defects of the conventional ingot, and brings great convenience to the later rolling production process.

[0076] 2. Effect of different preparation methods on ingot quality

[0077] The conventional ingot casting method and the ingot casting method of the present invention are respectively used to cast the same batch of gold materials (purity 99.99%). Titanium is selected as the additive element, and the additive amount is 0.1%. The following methods are respectively used to cast the ingots.

[0078] Method 1: Refer to Example 1, except that gold and the added elements are placed in a crucible for smelting at the same time. It is found through experiments that the trace elements are agglomerated and passivated too early, making it difficult to melt into the gold matrix, resulting in the two materials inside the ingot not being fully homogenized and fused.

[0079] Method 2: Refer to Example 1, except that after adding the gold material, argon gas is first charged and then heated to melt the metal. It is found through experiments that charging argon gas first results in poor removal of vacuum oxidizing gasification, which results in the material being unable to be fully homogenized and fused.

[0080] Method 3: Referring to Example 1, the difference is that the additional element is added first and then the argon is filled in. It is found through experiments that the argon filling later will cause the gold to evaporate, which not only cannot ensure the stability of the gold content of the finished product, but also causes the loss of gold materials and cannot meet the production requirements.

[0081] Method 4: Refer to Example 1, except that after the added elements are melted, the argon gas is turned off to restore the furnace to a vacuum state. It is found through experiments that when the argon gas is turned off, both gold and trace elements will evaporate, the gold content of the finished product cannot be kept stable, and both materials are seriously lost, which cannot meet the production requirements.

[0082] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-hardness gold substrate by magnetic confinement suspension smelting, characterized in that: The following steps are involved: (1) quantitatively weighing gold into a water-cooled copper crucible in a vacuum magnetic confinement levitation melting machine; quantitatively weighing added elements into a feeding cavity of a secondary crucible in the vacuum magnetic confinement levitation melting machine; (2) Pre-vacuum to 6×10 -3 Pa, heating in steps, when the temperature reaches 800-900℃, start the argon solenoid valve to fill in argon, turn on the automatic pressure tracking system, keep the pressure at 600-800Pa, and set the temperature to T1+200 degrees; (3) Add the additive elements under balanced pressure conditions and pre-stir mechanically; continue to increase the power and control the temperature at T2+200°C, and keep warm for 1-3 minutes according to needs; (4) Confirm that the melt is evenly distributed, quickly dump the crucible without stopping heating, and inject the molten liquid into the mold for condensation; (5) Make sure that all transmission mechanisms have returned to their original state, open the pressure relief valve, and after the pressure relief is completed, open the furnace chamber, remove the cast mold, and take out the product.

2. A method for preparing a high-hardness gold substrate by magnetic confinement suspension melting as claimed in claim 1, characterized in that: In the step (1), the mass fraction of the added element is generally 0.07-0.2% based on the weight of the finished product; the added element is in the form of nano-sized particles.

3. A method for preparing a high-hardness gold substrate by magnetic confinement suspension melting as claimed in claim 1, characterized in that: In the step (1), the purity of gold is at least 99.99%.

4. The method for preparing a high-hardness gold substrate by magnetic confinement suspension melting as claimed in claim 1, characterized in that: In the step (1), the melting point of the added element is 300-600°C higher than the melting point of gold.

5. The method for preparing a high-hardness gold substrate by magnetic confinement suspension melting as claimed in claim 1, characterized in that: In the step (2), T1 is the melting point of gold, which is set to 1063° C.; and T2 is not higher than the melting point of the added element.

6. A method for preparing a high-hardness gold substrate by magnetic confinement suspension melting as claimed in claim 1, characterized in that: In the step (3), T2 is 200-300° C. lower than the melting point of the added element.

7. A method for preparing a high-hardness gold substrate by magnetic confinement suspension melting as claimed in claim 1, characterized in that: In the step (4), condensation is performed using directional condensation technology. During the condensation process, a casting water flow channel is set at the bottom of the mold to accelerate solidification, and the solidification direction of the liquid material is controlled to condense from bottom to top; the temperature is controlled at 7-10°C during the condensation process.

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