A method for preparing a super-fine grain LED brass

Abstract

The application discloses a kind of ultrafine grain LED brass preparation methods, comprising the following steps: S1: smelting cast H65 brass ingot, ingot is used semi-continuous casting process;S2: head and tail of brass ingot is removed;S3: after heating and heat preservation to brass ingot, hot rolling is carried out;S4: after hot rolling, rough rolling is carried out to the roll of milling face;S5: after annealing to the roll of annealing, it is washed and cut edge and is carried out medium rolling;S7: after remaining bottom material is carried out air cushion furnace annealing;S8: after the roll of air cushion furnace annealing is carried out, it is cleaned and washed, and after shearing, ultrafine grain brass strip can be obtained.The semi-continuous casting process is used, and the roll is annealed very uniformly by cooperating bell jar furnace and air cushion furnace, so that the grain size of LED brass product is very uniform, and 90% of the grain size is controlled in 1-2um.

Description

Technical Field

[0001] This invention relates to the field of materials processing technology, and in particular to a method for preparing ultrafine-grained LED brass. Background Technology

[0002] Copper strip, as an important variety of copper processed materials, possesses excellent processing and usage properties and is widely used in various sectors of the national economy. Brass strip is one of the most widely used materials. However, during the manufacturing process of brass strip, especially during cold rolling and hot rolling, phenomena such as peeling, cracking, and uncoiling are prone to occur. This not only seriously affects the edge quality of the strip, increases the amount of trimming and reduces the yield, but in severe cases, the cracks can enlarge, leading to product scrap. The annual losses of brass due to defects are enormous. To effectively control production costs and improve the economic benefits of enterprises, the analysis of the causes of defects and the improvement of brass strip production processes are urgent research topics. The most important way to improve the quality of brass strip is to refine the brass grains, thereby simultaneously improving its strength and toughness.

[0003] Currently, the grain size of most domestically produced brass strips is generally controlled at around 15-20µm, while high-end Japanese brass strips often have a grain size controlled at 1-4µm. Extensive experimental data demonstrates that reducing the grain size of brass strips results in superior mechanical properties such as plasticity, especially excellent bending resistance and etching performance. Furthermore, foreign brass from Japan and other countries has lower surface roughness and clearer texture, which is beneficial for subsequent electroplating and encapsulation processes. It is widely used in high-end LED and leadframe applications. Domestically produced brass strips have higher surface roughness and more defects, and the high-end brass strip market is still dominated by imported materials. Therefore, exploring an effective process for refining brass grain size is particularly important.

[0004] A search of Chinese patent document CN116043147A, entitled "Preparation Method of Ultrafine-Grained Bronze Material," reveals a method that uses horizontal continuous casting combined with electromagnetic casting to obtain a fine-grained bronze first billet. This billet is then homogenized and annealed, followed by rolling to obtain a second billet. This second billet is then subjected to low-rate precision rolling and annealing to obtain a first finished product. The first finished product is then cleaned, straightened, and slit to obtain an ultrafine-grained bronze strip. However, the resulting strip has grains that are not particularly uniform and range from 2-6 μm. Therefore, this application provides a method for preparing ultrafine-grained LED brass to meet this requirement. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing ultrafine LED brass, which solves the technical problems of uneven grain size and excessively large grain size in existing strip production.

[0006] To achieve the above objectives, this application provides the following technical solution: a method for preparing ultrafine crystal LED brass, characterized by comprising the following steps;

[0007] S1: Smelting and casting H65 brass ingots. The ingots are cast using a semi-continuous casting process, and the casting temperature is controlled within the range of 1200-1250 degrees Celsius.

[0008] S2: Cut off the head and tail of the brass ingot to ensure the stability of the alloy composition;

[0009] S3: After heating and holding the brass ingots at a certain temperature, hot rolling is carried out. The final rolling temperature is stably controlled above 700 degrees Celsius, and the ingots are hot rolled from 250mm to 16mm.

[0010] S4: After the hot-rolled coil is milled, it is rough rolled into a blank, and the thickness of the blank is controlled at 6 to 8 mm.

[0011] S5: After the billet is opened, the coil is annealed in a bell furnace. The annealing process is carried out at 550 degrees Celsius for 4 hours, and the coil is in a soft state.

[0012] S6: The annealed coil is cleaned, trimmed, and rolled into a bottom stock with a thickness of 0.23mm.

[0013] S7: Anneal the remaining material in an air cushion furnace at a temperature of 500°C for 3 hours at a speed of 71 to 74 m / min.

[0014] S8: The coils annealed in the air cushion furnace are then precision rolled and cleaned, and then sheared to obtain ultrafine crystalline brass strip.

[0015] In a preferred embodiment of this invention, step S1 includes the following steps:

[0016] S11: Add cathode copper with a composition of over 99.99% to the smelting furnace. The ultra-high purity ensures that the ingot composition is of very high quality with very few impurities. Add trace amounts of grain refiners, such as titanium and zirconium. Adjust the inductor power to slowly heat the smelting furnace to 1200°C. After the cathode copper has melted completely, add zinc ingots first and then evenly cover the copper liquid with charcoal.

[0017] S12: Further heat up to 1250°C, while adjusting the atmosphere inside the furnace to reduce the oxygen content and reduce the formation of oxide slag. At this time, other small amounts of metal impurities in the copper liquid will slag due to volatilization and the covering agent. Remove them and add charcoal again for heat preservation and air isolation.

[0018] S13: The molten copper is injected into the casting tank. A specific refining agent or flux is added through the injection pipe and stirred. The molten copper in the casting tank flows into the crystallizer. Then, the molten copper is solidified through the external cooling water pipe. The continuously solidified ingot is pulled down into the casting well at a uniform speed by the ingot puller until the casting is completed.

[0019] In a preferred embodiment of this invention, in step S13, the flow channel is heated by flame heating to prevent the copper liquid at the bottom of the flow channel from solidifying and to consume the air above the flow channel, thereby reducing the volatilization of zinc in the copper liquid.

[0020] As a preferred embodiment of this invention, an electromagnetic stirring device is also included, which can be installed in a smelting furnace and / or a flow channel to stir the molten copper.

[0021] In a preferred embodiment of this invention, the crystallizer is equipped with five temperature gradients, allowing the molten copper to experience different cooling rates during solidification.

[0022] First temperature gradient: temperature is 1250℃ - 1180℃, cooling rate is set to 5-15℃ / min;

[0023] Second temperature gradient: temperature is 1180℃ - 1020℃, cooling rate is set to 10-25℃ / min;

[0024] The third temperature gradient is 1020℃ - 950℃, with a cooling rate of 5-10℃ / min.

[0025] Fourth temperature gradient: temperature is 950℃ - 880℃, cooling rate is set to 3-5℃ / min;

[0026] Fifth temperature gradient: temperature is 880℃ - room temperature, cooling rate is set to 2-4℃ / min.

[0027] In summary, the technical effects and advantages of this invention are as follows:

[0028] The present invention has a reasonable structure. By adopting a semi-continuous casting process and combining it with bell furnace and air cushion furnace annealing, the annealing of the material coil is very uniform, which in turn makes the grain size of the LED brass finished product very uniform, with 90% of the grain size controlled within 1-2um. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The crystal phase structure diagram of the LED brass finished product prepared by this method is shown in the first test.

[0031] Figure 2 for Figure 1 Grain size distribution diagram;

[0032] Figure 3 This is a second crystal phase structure diagram of the LED brass finished product prepared by this method;

[0033] Figure 4 for Figure 3 Medium grain orientation diagram. Detailed Implementation

[0034] 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.

[0035] Example: A method for melting and casting H65 brass ingots, wherein the ingots are cast using a semi-continuous casting method and the casting temperature is controlled within the range of 1200-1250 degrees Celsius;

[0036] When smelting and casting H65 ingots, the cathode copper (melting point 1086℃) and zinc (melting point 420℃) are melted first. Controlling the ingot casting temperature between 1200-1250℃ primarily reduces zinc volatilization, while also ensuring complete melting of the cathode copper. Furthermore, the molten copper exhibits good fluidity within this temperature range, resulting in high-quality ingots, stable inductor heating power, and reasonable production cost control.

[0037] S2: Cut off the head and tail of the brass ingot to ensure the stability of the alloy composition;

[0038] The head and tail sections of an ingot are susceptible to oxidation and contamination during the casting process. The head of the ingot is usually in contact with the refractory material of the melting furnace, while the tail may be exposed to air, both of which can lead to oxidation and contamination of the ingot's head and tail sections. These oxidation and contaminants can affect the uniformity and integrity of the material's composition, and the head and tail sections are prone to defects such as shrinkage cavities and porosity. These defects can reduce the material's density, affecting its mechanical and electrical properties, thus requiring removal.

[0039] S3: After heating and holding the brass ingots at a certain temperature, hot rolling is carried out, and the final rolling temperature is stably controlled above 700 degrees Celsius.

[0040] After hot rolling the ingot from 250mm to approximately 16mm, the 93.6% processing rate leads to work hardening of the strip. Final rolling is stabilized above 700 degrees Celsius. At this temperature, the strip temperature is above the recrystallization temperature, allowing the strip to recrystallize and restore the elongated grains to regular recrystallized grains. This facilitates subsequent milling and roughing processes; otherwise, excessively hard strips can easily damage milling tools and roughing rolls.

[0041] S4: After the hot-rolled coil is milled, it is rough rolled into a blank, and the thickness of the blank is controlled at 6 to 8 mm.

[0042] This thickness provides sufficient machining allowance for subsequent intermediate rolling and ensures a more uniform temperature distribution inside the brass strip during gas cushion furnace annealing, which is beneficial for uniform grain refinement. A thinner billet thickness means that fewer rolling passes are needed to reach the target thickness in subsequent rolling processes, thereby reducing the chance of grain growth. However, an excessively thin billet may also lead to difficulties and instability in the rolling process.

[0043] S5: After the billet is opened, the coil is annealed in a bell furnace. The annealing process is carried out at 550 degrees Celsius for 4 hours, and the coil is in a soft state.

[0044] Currently, there are two methods for annealing heat treatment in factories: continuous annealing furnaces and bell-type furnaces. For the first blank blank with a thickness greater than 2mm, only bell-type furnaces can be used for annealing. Continuous annealing furnaces have a fast annealing speed but are only suitable for coils with a thickness of less than 2mm. The annealing temperature is set to 550 degrees Celsius and held for 4 hours. This ensures that the atoms in the brass have enough energy to migrate and rearrange, but it is not too high and will cause grain coarsening. This is to allow the rolled grains of the coil to fully recrystallize and recover, which is convenient for subsequent processing. This process has a good annealing effect, uniform annealing performance of the coil, and lower cost.

[0045] S6: The annealed coil is cleaned, trimmed, and rolled into a bottom stock with a thickness of 0.23mm.

[0046] S7: Anneal the remaining material in an air cushion furnace at a temperature of 500°C for 3 hours at a speed of 71 to 74 m / min.

[0047] Because the thickness of the base material is only 0.23mm, annealing in an air cushion furnace is fast, requiring only 40 minutes to anneal a roll (high production efficiency and high annealing temperature). If a bell furnace is used, it takes more than 20 hours to complete heating, holding, cooling, and unloading, resulting in extremely low production efficiency. Furthermore, such thin rolls are prone to sticking together in the bell furnace, affecting the strip surface quality. The annealing process temperature is 500°C for 3 hours, ensuring recrystallization of the strip without grain growth. The annealing speed is 71 to 74 m / min (preferably 72 m / min, which yields the best results). This high speed limits the energy absorption of the grains, resulting in very small nucleation sites and ultrafine grains. A faster annealing speed may cause the grains to cool rapidly before they have enough time to grow, thus promoting grain refinement. However, if the annealing speed is too fast, atoms at the grain boundaries may not have enough time to rearrange and migrate, affecting the grain refinement effect.

[0048] In step S1, the semi-continuous casting process includes the following steps:

[0049] S11: Add cathode copper with a composition of over 99.99% to the smelting furnace. The ultra-high purity ensures that the ingot composition is of very high quality with very few impurities. Add trace amounts of grain refiners, such as titanium and zirconium. Adjust the inductor power to slowly heat the smelting furnace to 1200°C. After the cathode copper has melted completely, add zinc ingots first and then evenly cover the copper liquid with charcoal.

[0050] The heat-insulating and air-isolating properties of charcoal can significantly reduce the impurity content and oxide slag formation in the melt, contributing to a purer melt environment. In a purer melt, grain growth is less restricted, leading to finer and more regular grain structures. At high temperatures, charcoal reacts with oxygen in the melt to produce gases such as carbon monoxide and carbon dioxide. This process further reduces the oxygen content in the melt, minimizing the negative impact of oxidation on the grains. Simultaneously, the reducing effect of charcoal promotes the uniform distribution and refinement of metallic elements, which is beneficial for forming finer and more uniform grain structures.

[0051] S12: Further heat up to 1250°C, while adjusting the atmosphere inside the furnace to reduce the oxygen content and reduce the formation of oxide slag. At this time, other small amounts of metal impurities in the copper liquid will slag due to volatilization and the covering agent. Remove them and add charcoal again for heat preservation and air isolation.

[0052] S13: The molten copper is injected into the casting tank. A specific refining agent or flux is added through the injection pipe and stirred. The molten copper in the casting tank flows into the crystallizer. Then, the molten copper is solidified through the external cooling water pipe. The continuously solidified ingot is pulled down into the casting well at a uniform speed by the ingot puller until the casting is completed.

[0053] In the above process, the initial heating of the melting furnace to 1200°C ensures that the added cathode copper can be fully melted. By initially heating to a temperature slightly above the melting point of copper, the solid portion inside the cathode copper block gradually transforms into a liquid state, resulting in fully molten copper. This step is beneficial for subsequent alloying, impurity removal, and the uniform distribution of refining agents. The subsequent heating to 1250°C is to meet the higher temperature requirements of the casting process. During casting, it is necessary to maintain a certain fluidity of the molten metal to facilitate its injection into the runner and crystallizer, while also ensuring that the chemical components and refining agents in the melt are fully mixed and reacted. This temperature helps accelerate these processes, promoting the homogenization and refining of the melt. Furthermore, staged heating reduces the damage to the melting equipment and furnace lining caused by thermal stress and thermal shock. Sudden changes in high temperature can lead to equipment deformation or damage, while staged heating allows the equipment and furnace lining to gradually adapt to temperature changes, thereby extending their service life.

[0054] In a preferred embodiment of this invention, in step S13, the flow channel is heated by flame heating to prevent the copper liquid at the bottom of the flow channel from solidifying and to consume the air above the flow channel, thereby reducing the volatilization of zinc in the copper liquid.

[0055] As a preferred embodiment of this invention, an electromagnetic stirring device is also included, which can be set in a smelting furnace and / or a flow tank to stir the molten copper. Stirring the molten copper by the eddy current generated by the magnetic field is beneficial to promoting the refinement and uniform distribution of grains.

[0056] In a preferred embodiment of this invention, the crystallizer is equipped with five temperature gradients, allowing the molten copper to experience different cooling rates during solidification.

[0057] First temperature zone: temperature is 1250℃ - 1180℃, cooling rate is set to 5-15℃ / min;

[0058] H65 brass melts completely within this temperature range, ensuring a uniform distribution of alloy composition while providing sufficient fluidity to fill the crystallizer. The high-temperature environment also helps reduce gases and inclusions in the alloy, minimizing their interference with grain growth and promoting grain refinement.

[0059] Second temperature zone: temperature is 1180℃ - 1020℃, cooling rate is set to 10-25℃ / min;

[0060] Rapidly decreasing the temperature promotes the rapid formation of crystal nuclei in the molten brass. H65 brass exhibits a high solidification rate within this temperature range, which is beneficial for refining the grain size.

[0061] Third temperature zone: temperature is 1020℃ - 950℃, cooling rate is set to 5-10℃ / min;

[0062] During this stage, controlling the cooling rate allows for stable nucleus growth, preventing excessive grain coarsening. This temperature range is a sensitive area for H65 brass grain growth; appropriate temperature control and cooling rate help refine the grains.

[0063] Fourth temperature zone: temperature is 950℃ - 880℃, cooling rate is set to 3-5℃ / min;

[0064] As the temperature decreases further, the brass gradually solidifies. During this stage, the slow cooling provides ample time for the grains to grow uniformly. Under these conditions, grain growth is less restricted, which is conducive to forming a fine and uniform grain structure.

[0065] Fifth temperature zone: Temperature is 880℃ - room temperature, cooling rate is set to 2-4℃ / min

[0066] At the stage close to room temperature, uniform cooling is used to prevent deformation and cracking of the ingot during the cooling process. This cooling method can maintain the grain refinement state and prevent the grains from growing in subsequent processes, thereby maintaining the overall performance of the ingot.

[0067] Figure 1 and Figure 2 This document describes the crystallographic phase diagram and grain size distribution obtained using EBSD analysis at Shanghai University. Figure 3 and Figure 4 The crystal phase diagram and grain orientation diagram of the finished product were obtained by EBSD testing at Jiangxi University of Science and Technology.

[0068] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultrafine crystal LED brass, characterized in that: Includes the following steps; S1: Smelting and casting H65 brass ingots. The ingots are cast using a semi-continuous casting process, and the casting temperature is controlled within the range of 1200-1250 degrees Celsius. The semi-continuous casting process includes the following steps: S11: Add cathode copper with a composition of over 99.99% to the smelting furnace. The ultra-high purity ensures that the ingot composition is of very high quality with very few impurities. Add trace amounts of grain refiners, such as titanium and zirconium. Adjust the inductor power to slowly heat the smelting furnace to 1200℃. After the cathode copper has melted completely, add zinc ingots first and then evenly cover the copper liquid with charcoal. S12: Further heat up to 1250℃, while adjusting the atmosphere inside the furnace to reduce the oxygen content and reduce the formation of oxide slag. At this time, other small amounts of metal impurities in the copper liquid will slag due to volatilization and the covering agent. Remove them and add charcoal again for heat preservation and air isolation. S13: The copper liquid is injected into the flow channel, and a specific refining agent or flux is added through the injection pipe and stirred. The copper liquid in the flow channel flows into the crystallizer, and then the copper liquid is solidified through the external cooling water pipe. The continuously solidified ingot is pulled down the casting well at a uniform speed by the ingot puller until the casting is completed. The crystallizer is equipped with five temperature gradients, which allow the copper liquid to experience different cooling rates during solidification. The first temperature gradient has a temperature of 1250℃ - 1180℃ and a cooling rate of 5-15℃ / min. Second temperature gradient: temperature is 1180℃ - 1020℃, cooling rate is set to 10-25℃ / min; The third temperature gradient is 1020℃ - 950℃, with a cooling rate of 5-10℃ / min. Fourth temperature gradient: temperature is 950℃ - 880℃, cooling rate is set to 3-5℃ / min; Fifth temperature gradient: Temperature from 880℃ to room temperature, cooling rate set to 2-4℃ / min S2: Cut off the head and tail of the brass ingot to ensure the stability of the alloy composition; S3: After heating and holding the brass ingots at a certain temperature, hot rolling is carried out. The final rolling temperature is stably controlled above 700 degrees Celsius, and the ingots are hot rolled from 250mm to 16mm. S4: After the hot-rolled coil is milled, it is rough rolled into a blank, and the thickness of the blank is controlled at 6 to 8 mm. S5: After the billet is opened, the coil is annealed in a bell furnace. The annealing process is carried out at 550 degrees Celsius for 4 hours, and the coil is in a soft state. S6: The annealed coil is cleaned, trimmed, and rolled into a bottom stock with a thickness of 0.23mm. S7: Anneal the remaining material in an air cushion furnace at a temperature of 500°C for 3 hours at a speed of 71 to 74 m / min. S8: The coils annealed in the air cushion furnace are then precision rolled and cleaned, and then sheared to obtain ultrafine crystalline brass strip.

2. The method for preparing ultrafine LED brass according to claim 1, characterized in that: In step S13, the flow channel is heated by flame heating to prevent the copper liquid at the bottom of the flow channel from solidifying and to consume the air above the flow channel, thereby reducing the volatilization of zinc in the copper liquid.

3. The method for preparing ultrafine LED brass according to claim 1, characterized in that: It also includes electromagnetic stirring equipment, which can be installed in a smelting furnace and / or a ladle to stir molten copper.

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