Preparation method and use of extra-high voltage electronic aluminum foil

Abstract

The application discloses a preparation method and application of extra-high voltage electronic aluminum foil, and comprises the following steps: (1) putting pure aluminum ingot into a smelting furnace for smelting, adding aluminum-chromium intermediate alloy for continuously heating and stirring until the aluminum-chromium intermediate alloy is completely melted; refining and stirring; (2) sequentially carrying out degassing, hydrogen measurement, filtering, slag measurement and standing on the refined alloy liquid, and then casting to obtain chromium-containing aluminum ingot; (3) sequentially carrying out surface milling treatment, homogenization treatment, hot rolling treatment, cold rolling treatment and intermediate annealing treatment on the chromium-containing aluminum ingot; (4) sequentially carrying out foil rolling and finished product annealing treatment on the chromium-containing aluminum foil intermediate; (5) sequentially carrying out electrolytic polishing treatment and direct current etching treatment on the chromium-containing aluminum foil product. The prepared extra-high voltage electronic aluminum foil can be used as an anode material of an extra-high voltage aluminum electrolytic capacitor. The application can solve the technical problems of poor quality stability and small corrosion hole density of the aluminum foil produced by the existing aluminum foil production process.

Description

Technical Field

[0001] This invention relates to the field of electronic aluminum foil materials technology. Specifically, it relates to a method for preparing ultra-high voltage electronic aluminum foil and its applications. Background Technology

[0002] High-purity aluminum foil is a key material used in the anodes of ultra-high voltage electrolytic capacitors. Aluminum electrolytic capacitors have seen significant growth worldwide over the past 20 years due to their numerous advantages, including large capacitance, small size, low price, and ease of use. Currently, they account for over 30% of total capacitor production. Aluminum electrolytic capacitors are mainly used in electrical and electronic machinery, household appliances, general lighting fixtures, musical instruments, optical instruments such as flash discharge tubes, and information communication equipment including computers, among many other fields. In circuits, they primarily function as power filtering, signal coupling, noise bypassing, and energy storage. Therefore, the aluminum electrolytic capacitor market is poised for stronger growth and broader development prospects, with a faster growth rate expected.

[0003] As a core raw material for aluminum electrolytic capacitors, the performance of electronic aluminum foil directly affects many of the capacitor's characteristics. For ultra-high voltage (UHV) electrolytic capacitors, aluminum foil with a cubic texture volume fraction greater than 95% is required to increase the surface area of ​​the foil after etching, thereby improving the specific capacitance through UHV anodizing. However, under the same corrosion conditions, even with a cubic texture volume fraction greater than 95%, the specific capacitance exhibits significant instability, and the quality of the etching pits depends on the types and contents of trace elements in the aluminum foil.

[0004] Therefore, clarifying the influence of trace elements on the composition, content, and electrical properties of aluminum foil texture, effectively controlling the type and content of texture, obtaining high volume fraction cubic texture, and increasing the number of corrosion pits during the corrosion process while ensuring relatively uniform distribution, length, and size of corrosion pits are key issues that urgently need to be addressed in this research field. Currently, the biggest problem with domestically produced aluminum foil is its poor quality stability, mainly manifested in uneven specific capacitance. This is evident in the significant quality differences that sometimes occur even when aluminum foil produced under the same conditions of time, process, and raw materials. According to product requirements, the specific capacitance deviation of aluminum foil should generally not exceed 10%, but in reality, it sometimes exceeds 20%, resulting in scrap. Traditional aluminum foil, due to its limitations in conductivity, is no longer sufficient to meet the needs of high-performance electronic devices and aerospace materials. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing ultra-high voltage electronic aluminum foil and its application, so as to improve the density and uniformity of corrosion pores in electronic aluminum foil, effectively increase the surface area of ​​aluminum foil, and solve the technical problems of poor quality stability, uneven specific capacitance, and difficulty in meeting the needs of high-performance electronic devices and aerospace materials produced by existing aluminum foil production processes.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for preparing ultra-high voltage electronic aluminum foil includes the following steps:

[0008] Step (1): Place pure aluminum ingots into a melting furnace for melting. After the pure aluminum ingots are completely melted, add aluminum-chromium master alloy and continue heating and stirring until the aluminum-chromium master alloy is completely melted. Transfer the melted alloy liquid to a holding furnace for holding. After holding, transfer the alloy liquid to a refining furnace, add refining agent for refining and stirring. Holding can promote the full dissolution and uniform distribution of alloying elements such as Cr, which provides a guarantee for Cr to play a full regulatory role in the subsequent aluminum foil preparation process. In addition, the holding process itself is also conducive to the floating and escaping of bubbles (especially hydrogen) in the alloy liquid, as well as the settling of some larger inclusions, which indirectly assists the subsequent degassing, hydrogen detection and filtration processes. Refining can remove impurities and hydrogen, and purify the alloy liquid.

[0009] Step (2): The refined alloy liquid is degassed, hydrogen measured, filtered, slag measured and settled in sequence. After settling, it is semi-continuously cast by a semi-continuous casting machine to obtain chromium-containing aluminum ingots.

[0010] Step (3): The chromium-containing aluminum ingot is subjected to milling, homogenization, hot rolling, cold rolling and intermediate annealing in sequence. After the intermediate annealing is completed, the chromium-containing aluminum foil intermediate is obtained.

[0011] Step (4): The chromium-containing aluminum foil intermediate is subjected to foil rolling and finished product annealing in sequence. After the finished product annealing is completed, the chromium-containing aluminum foil finished product is obtained.

[0012] Step (5): The chromium-containing aluminum foil is subjected to electrolytic polishing and DC corrosion treatment in sequence. After the DC corrosion treatment is completed, ultra-high voltage electronic aluminum foil is obtained.

[0013] In the preparation of ultra-high voltage electronic aluminum foil, this invention incorporates a certain amount of chromium, which facilitates the production of ultra-high voltage electronic aluminum foil with high cubic texture content, small pore diameter, high pore density, and uniform pore distribution. This significantly increases the proportion of submicron-level pores on the surface of the ultra-high voltage electronic aluminum foil, particularly effectively enhancing the proportion of pores with a diameter less than 0.5 μm. Chromium plays a beneficial regulatory role throughout the entire preparation process of the ultra-high voltage electronic aluminum foil, significantly improving the quality stability and specific capacitance uniformity of the prepared aluminum foil.

[0014] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (1), the mass fraction of aluminum in the pure aluminum ingot is greater than or equal to 99.99 wt.%; in the aluminum-chromium master alloy, the mass fraction of chromium is 5 wt.%, the mass fraction of impurities is less than or equal to 0.5 wt.%, and the balance is aluminum; the amount of aluminum-chromium master alloy added is controlled so that the chromium content in the alloy liquid is 0.002 wt.%-0.008 wt.%.

[0015] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (1), the melting temperature of pure aluminum ingots is 750-760℃, the holding temperature of the alloy liquid in the holding furnace is 740-750℃, and the holding time is 3-5 min; the refining agent is sodium chloride and / or potassium chloride; the amount of refining agent is 0.1-0.3 wt.% of the total mass of the alloy liquid, the idle gas pressure in the refining furnace (the nitrogen gas pressure introduced during the refining process) is 0.1-0.5 MPa, and the nitrogen flow rate is 8-10 L / min; the refining furnace temperature is set at 720-760℃, and the refining time is 10-15 min; electromagnetic stirring is carried out during the refining process. The stirring rate is 100-150 rpm. After refining, continue stirring for 10-15 minutes, using a combination of manual and electromagnetic stirring simultaneously. The manual stirring rate is 20-25 rpm, and the electromagnetic stirring rate is 100-150 rpm. If manual stirring is used alone after refining: manual stirring relies on operator experience and is difficult to achieve forced convection across the entire molten pool depth (especially the bottom); the manual stirring speed is slow (usually <30 rpm), resulting in insufficient dispersion of the refining agent in the alloy melt; open stirring leads to rapid heat dissipation of the melt (>5℃ / min), requiring repeated heating to trigger secondary oxidation. If electromagnetic stirring is used alone: ​​the electromagnetic field attenuates at the surface of the molten pool (Lorentz force is inversely proportional to depth), failing to effectively break the oxide film; the eddy current intensity is weak near the furnace wall and corners, forming compositional segregation zones; strong electromagnetic eddy currents tear the surface oxide film and are drawn into the interior of the melt. This invention employs a simultaneous manual and electromagnetic stirring method after refining, controlling the stirring rates of both methods within specific ranges. This not only ensures the refining agent is fully dispersed in the alloy liquid but also effectively prevents the formation of component segregation zones and the entrapment of oxide films.

[0016] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (2), the degassing pressure is 0.1-0.3MPa, the nitrogen flow rate is 55-75L / min, and the rotation speed is 350-450 rpm; when measuring hydrogen, the hydrogen content is measured at least once per furnace, and the hydrogen content is less than or equal to 0.10mL / 100gAl; when filtering, a 40ppi+50ppi ceramic filter plate is used for filtration, and the filter box is uniformly coated with paint to ensure that the inner lining surface is smooth and the filter plate and the inner lining of the box are tightly bonded. The filter plate in the filter box is replaced once per furnace; when measuring slag, the slag is measured at the outlet of the ceramic filter plate, and the slag content N20≤50kJ / kg (N20 represents a size ≥20μm) The total number of non-metallic inclusions, such as Al2O3, SiO2, flux residue, etc.; k / kg represents the number of inclusion particles per kilogram of alloy liquid, counted in thousands); the settling time is 20-25 min; the casting temperature for semi-continuous casting is 710-730℃, the casting speed is 55-70 mm / min, the casting water pressure is 0.10-0.22 MPa, and the casting water temperature is less than or equal to 40℃.

[0017] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (3), a milling machine of model GMC2013 produced by Kuntai Heavy Industry is used for milling to remove surface impurities; during homogenization, the furnace is heated to a temperature of 590-610℃ and the holding time is 8-12h; homogenization can promote the full diffusion of atoms inside the chromium-containing aluminum ingot, especially to fully dissolve the impurity Fe atoms, prevent segregation to form Al3Fe and Al6Fe, thereby eliminating the segregation phenomenon; by controlling the temperature and time of homogenization, this invention can not only make the chromium element in the ingot diffuse evenly and avoid segregation, but also improve the size, morphology and distribution of secondary precipitates in the subsequent hot rolling process; if homogenization is not performed, or if the homogenization temperature or holding time exceeds the above range, it will cause serious segregation in the ingot, and the uniformity of chromium element distribution after hot rolling will be significantly poor; in addition, under the homogenization conditions of this invention, undissolved fine chromium compounds (such as high melting point intermetallic compounds Al7Cr, Al 45 Cr7 can act as a non-uniform nucleation core, promoting the precipitation of trace impurity elements such as Fe and Si as fine dispersed phases, thereby effectively reducing the risk of cracking of chromium-containing aluminum ingots during subsequent hot rolling processes.

[0018] During hot rolling, chromium-containing aluminum ingots are rolled into aluminum plates using 6-11 passes. At least three equal reduction rolling passes are performed first, and then the reduction is gradually reduced. The initial rolling temperature is 520-540℃, and the final rolling temperature is 260-280℃. The total reduction rate of hot rolling is 96.0-98.5%. If there are too few hot rolling passes, the single reduction will be too large, which will lead to the appearance of a coarse grain zone in the center of the plate. Subsequent cold rolling is prone to strip breakage; in addition, excessive reduction in a single pass can easily lead to edge cracking and uneven texture; if there are too many hot rolling passes, the total rolling time increases, the temperature drops too much, the high-temperature exposure time is prolonged, and the production efficiency is low. The present invention performs at least three equal reduction rolling passes to efficiently break up the as-cast structure, and by controlling the reduction to be the same in the first few passes, the deformation heat generated by large deformation in short intervals can be continuously compensated for and the temperature stabilized; the reduction in subsequent passes can suppress the changes in the width direction of the aluminum foil, prevent edge cracking and delamination, and significantly improve the hot rolling effect. This invention improves the hot rolling effect by controlling the number of hot rolling passes, the initial rolling temperature, the final rolling temperature, and the method of changing the reduction during rolling (first performing constant reduction rolling, then gradually reducing the reduction). This is beneficial for preparing aluminum foil with a high cubic texture content. Furthermore, under the hot rolling conditions of this invention, adding a specific amount of chromium can moderately increase the recrystallization temperature of pure aluminum, delaying the recrystallization process and increasing the nucleation rate. Chromium and the aforementioned hot rolling process can synergistically refine the aluminum alloy grain structure. Moreover, under the same hot rolling conditions, a moderate increase in chromium allows aluminum recrystallization to nucleate at more locations, resulting in a greater number of finer and more uniform newly formed grains. This invention significantly improves the hot rolling effect by controlling the amount of chromium used and the hot rolling process conditions during aluminum foil preparation.

[0019] During cold rolling, aluminum sheets are rolled into aluminum foil using 4-6 passes (if there are fewer than 4 passes, the shear band ratio will be too high, work hardening will be severe, and even sheet distortion will occur; if there are more than 6 passes, the texture will be severely randomized). The total reduction rate of cold rolling is 92-95%. Before cold rolling, the rolls and workpieces are cleaned with acetone solution and wiped with degreased cotton until there are no stains. Machine oil is added as a lubricant during rolling. In addition, due to the presence of chromium, the stacking fault energy and dislocation cross-slip ability of aluminum alloy are effectively reduced during the cold rolling process of this invention. This effectively delays the dislocation annihilation caused by cross-slip during cold rolling, increasing the dislocation density storage under higher cold rolling deformation, thereby significantly improving the strain hardening degree of aluminum alloy.

[0020] During intermediate annealing, the furnace is immersed at a temperature of 240-260℃ for 8-10 hours under vacuum. At this intermediate annealing temperature, the number of chromium atoms accumulating at grain boundaries increases, significantly enhancing the pinning effect. This pinning effect makes grain boundary migration difficult, slowing down grain growth and resulting in smaller grain size after intermediate annealing. During intermediate annealing, Cr atoms can act as nuclei for heterogeneous nucleation. When grain recrystallization occurs, Cr atoms as nuclei provide more nucleation sites. With increasing Cr content, the number of nuclei increases, the nucleation rate improves, and the grain structure is further refined.

[0021] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (4), the rolling temperature of the foil is between -50 and 70°C (preferably between room temperature and 50°C), the rolling speed is 3-5 m / s, the number of foil rolling passes is 1-2, and the total reduction rate of the foil rolling is 40-60%. When the foil rolling temperature exceeds 70°C, dynamic recrystallization occurs, forming coarse grains, which causes random orientation of the recrystallization and reduces the cubic texture content of the finished product. If the foil rolling temperature is below -50°C, the ductility of the material will drop sharply, which will easily cause brittle fracture during the foil rolling process and increase the breakage rate. If the foil rolling speed is too fast, the temperature will rise easily, causing heat accumulation of deformation, triggering the occurrence of dynamic recrystallization, and easily causing edge wavy and breakage. If the foil rolling speed is too slow, the rolling efficiency will decrease. When annealing the finished product, it is annealed in a vacuum annealing furnace. The vacuum level is (1.333-6.6)×10⁻³Pa (controlling the annealing vacuum level within this range can effectively prevent the formation of an oxide layer on the workpiece surface). The finished product annealing temperature is 350-530℃, and the holding time is 12-16h. Excessive annealing temperature will lead to abnormal grain coarsening, disrupting the continuity of the cubic texture. Coarse grains result in decreased hardness and insufficient rigidity, causing wrinkling during winding. If the finished product annealing temperature is too low, insufficient recrystallization will occur, failing to drive complete recrystallization and resulting in a mixed texture. The thickness of the chromium-containing aluminum foil finished product is 0.15-0.20mm (according to the specific capacitance formula, if the finished aluminum foil thickness is too large, the capacitance will decrease, failing to meet the usage requirements; if the finished aluminum foil thickness is too small, the strength will decrease, causing the aluminum foil to break during anodizing, posing a risk of oxide film puncture, and increasing the scrap rate during winding). During the finished product annealing process, the presence of chromium is beneficial for further reducing grain size. This invention controls the rolling temperature, rolling rate, and rolling passes of the foil rolling process within a reasonable range, and controls the vacuum degree, annealing temperature, and holding time of the finished product annealing process. Under the synergistic effect of a specific chromium element, it can effectively refine the grain size of the finished aluminum foil, ensure the continuity of the cubic texture, and improve the purity and content of the cubic texture of the aluminum foil.

[0022] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (5), during electrolytic polishing, the electrolytic polishing solution is a mixture of perchloric acid and anhydrous ethanol in a volume ratio of 1:9; the polishing voltage is 15-20V, the polishing temperature is controlled at 0℃ using liquid nitrogen, and the polishing time is 1-3min. Using these electrolytic polishing conditions, the oxide film and oil stains on the aluminum foil surface can be effectively removed, eliminating the distorted layer on the aluminum foil surface and providing an ideal surface condition for subsequent DC corrosion treatment.

[0023] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (5), during the direct current corrosion treatment, the graphite sheet is the cathode, the aluminum foil is the anode, the concentration of hydrochloric acid in the corrosion solution is 0.5-1.2 mol / L, the concentration of sulfuric acid is 3.0-4.0 mol / L, the corrosion temperature is 60-70℃, and the current density is 0.2-0.4 mA / cm². 2 The corrosion time is 1-3 minutes. During DC corrosion treatment, if the hydrochloric acid concentration is too high, the excessive chloride ions will promote explosive growth of pitting corrosion, resulting in oversized holes and deep perforations. Furthermore, high chloride ion concentrations penetrate along grain boundaries, causing excessive corrosion of the {100} cubic grain edges, thus reducing the effective surface area of ​​the aluminum foil. If the hydrochloric acid concentration is too low, the chloride ions are insufficient to dissolve the passivation film, thereby reducing the porosity. If the sulfuric acid concentration in the corrosion solution is too high, sulfate ions will promote the formation of a dense oxide film. If the sulfuric acid concentration is too low, the protective layer on the hole wall will be weak, causing corrosion to extend laterally. If the corrosion temperature is too high, the acid will easily volatilize, reducing its concentration and failing to achieve the desired corrosion effect. Furthermore, excessively high temperatures increase the acid's activity, exacerbating corrosion and producing negative effects. If the corrosion temperature is too low, the acid's activity is insufficient, requiring a longer corrosion time and affecting the corrosion effect. If the current density during corrosion treatment is too high, it can easily cause perforation and localized dissolution. If the current density is too low, the corrosion holes will be shallow, and the porosity will be poor. Excessive corrosion time can lead to localized dissolution of the aluminum foil after corrosion, while insufficient corrosion time results in shallow and few corrosion holes. This invention, by controlling the concentrations of hydrochloric acid and sulfuric acid in the etching solution, the corrosion temperature, the current density, and the corrosion time within specific ranges during the direct current corrosion process, and by controlling the chromium content, fully leverages the regulatory effect of chromium on the number, density, depth, and uniformity of corrosion holes. In particular, it effectively increases the proportion of corrosion holes with a diameter less than 0.5 μm in the etched electronic aluminum foil.

[0024] In the above-mentioned method for preparing ultra-high voltage electronic aluminum foil, in step (1), the mass fraction of aluminum in the pure aluminum ingot is 99.996 wt.%, the mass fraction of iron is 0.00032 wt.%, the mass fraction of silicon is 0.00067 wt.%, the mass fraction of copper is 0.00006 wt.%, the mass fraction of zinc is 0.00048 wt.%, the mass fraction of magnesium is 0.00014 wt.%, the mass fraction of manganese is 0.00036 wt.%, and the balance is impurities; in the aluminum-chromium master alloy, the mass fraction of chromium is 5 wt.%, and the mass fraction of impurities is 0.5 wt.%; the melting temperature of the pure aluminum ingot is 750℃, and the amount of aluminum-chromium master alloy added is controlled to make The chromium content in the alloy liquid was 0.008 wt.%; the holding temperature of the alloy liquid in the holding furnace was 750℃, and the holding time was 3 min; the refining agent was sodium chloride; the amount of refining agent was 0.2 wt.% of the total mass of the alloy liquid; the idle gas pressure in the refining furnace was 0.15 MPa, and the nitrogen flow rate was 10 L / min; the refining furnace temperature was set at 760℃, and the refining time was 15 min; during the refining process, electromagnetic stirring was carried out at a speed of 120 rpm; after the refining was completed, stirring continued for 15 min, and the stirring method was simultaneous manual stirring and electromagnetic stirring, with a manual stirring speed of 20 rpm and an electromagnetic stirring speed of 120 rpm;

[0025] In step (2), the degassing pressure is 0.2 MPa, the nitrogen flow rate is 75 L / min, and the rotation speed is 450 rpm. When measuring hydrogen, the hydrogen content is measured once per furnace, and the hydrogen content is less than or equal to 0.10 mL / 100 g Al. When filtering, a 40 ppi + 50 ppi ceramic filter plate is used for filtration. The filter box is uniformly coated with paint, and the filter plate is replaced once per furnace. When measuring slag, the slag is measured at the outlet of the ceramic filter plate, and the slag content N20 ≤ 50 kJ / kg is measured. The settling time is 25 min. The casting temperature of the semi-continuous casting is 710 ℃, the casting speed is 70 mm / min, the casting water pressure is 0.15 MPa, and the casting water temperature is 35 ℃. The dimensions of the chromium-containing ingot obtained by casting are 635 mm * 320 mm * 4930 mm.

[0026] In step (3), a GMC2013 milling machine manufactured by Kunte Heavy Industry was used for milling. After milling, the thickness of the chromium-containing ingot was 310mm. During homogenization, the temperature was 600℃ and the holding time was 8h.

[0027] During hot rolling, chromium-containing aluminum ingots are rolled into aluminum sheets using 11 passes, with an initial rolling temperature of 520℃ and a final rolling temperature of 260℃. The 11 passes of hot rolling are: 310mm-275mm-240mm-205mm-170mm-135mm-100mm-65mm-36mm-18mm-11mm-5.5mm. During cold rolling, aluminum sheets are rolled into aluminum foil using 4 passes, with a final rolling temperature below 120℃. The 4 passes of cold rolling are: 5.5mm-2.6mm-13mm-0.6mm-0.3mm. During intermediate annealing, the temperature is 250℃ and the holding time is 8 hours.

[0028] In step (4), the rolling temperature of the foil is 50℃, the rolling speed is 5m / s, and the foil rolling passes are 1; during the finished product annealing treatment, it is annealed in a vacuum annealing furnace with a vacuum degree of 1.5×10⁻³Pa, the finished product annealing temperature is 520℃, and the holding time is 12h; the thickness of the chromium-containing aluminum foil finished product is 0.161mm;

[0029] In step (5), during electrolytic polishing, the electrolytic polishing solution is a mixture of perchloric acid and anhydrous ethanol in a volume ratio of 1:9; the polishing voltage is 18V, the polishing temperature is controlled at 0℃ using liquid nitrogen, and the polishing time is 2min; during DC corrosion treatment, the graphite sheet is the cathode, the aluminum foil is the anode, the concentration of hydrochloric acid in the corrosion solution is 1.0mol / L, the concentration of sulfuric acid is 3.5mol / L, and the current density is 0.3A / cm². 2 The corrosion temperature was 70℃ and the corrosion time was 2 minutes.

[0030] The above-mentioned method for preparing ultra-high voltage electronic aluminum foil will be used as the anode material for ultra-high voltage aluminum electrolytic capacitors.

[0031] The technical solution of the present invention achieves the following beneficial technical effects:

[0032] The present invention discloses a method for preparing ultra-high voltage electronic aluminum foil. By adding a specific amount of Cr to the aluminum foil and controlling process parameters such as melting, refining, and degassing, and through milling, homogenization treatment, hot rolling, cold rolling, intermediate annealing, foil rolling, and finished product annealing, the addition of Cr can effectively improve the cubic texture content in the finished aluminum foil. Furthermore, in the subsequent electrolytic polishing and DC corrosion treatment, by adjusting the processing parameters, the principle that Cr has a higher standard electrode potential than Al and forms a galvanic cell effect under corrosion conditions after dissolving in Al is utilized to significantly increase the activity of Al, improve corrosion pitting performance, increase the density and uniformity of corrosion pits, thereby increasing the surface area of ​​the aluminum foil and improving the uniformity and quality stability of the aluminum foil's specific capacitance. Attached Figure Description

[0033] Figure 1 A schematic diagram of semi-continuous casting in an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of the DC electro-corrosion hole-generating device in this embodiment of the invention;

[0035] Figure 3a Example 1 of this invention: Texture orientation distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0036] Figure 3b Example 2 of this invention: Texture orientation distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0037] Figure 3c Example 3 of the present invention: Texture orientation distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0038] Figure 3d Example 4 of this invention: Texture orientation distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0039] Figure 4a Example 1 of this invention: Grain texture distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0040] Figure 4b Example 2 of this invention: Grain texture distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0041] Figure 4c Example 3 of this invention: Grain texture distribution diagram of ultra-high voltage electronic aluminum foil after annealing;

[0042] Figure 4d Example 4 of this invention: Grain texture distribution diagram of the finished ultra-high voltage electronic aluminum foil after annealing;

[0043] Figure 5a Surface morphology (SEM) of ultra-high voltage electronic aluminum foil after corrosion and pitting treatment in Example 1 of this invention;

[0044] Figure 5b Surface morphology (SEM) of ultra-high voltage electronic aluminum foil after corrosion and pitting treatment in Example 2 of this invention;

[0045] Figure 5c Surface morphology (SEM) of ultra-high voltage electronic aluminum foil after corrosion and pitting treatment in Example 3 of this invention;

[0046] Figure 5d Surface morphology (SEM) of ultra-high voltage electronic aluminum foil after corrosion and pitting treatment in Example 4 of this invention;

[0047] Figure 6 Distribution diagram of pore size and quantity of corrosion holes in ultra-high voltage electronic aluminum foil, Example 1 of this invention;

[0048] Figure 7 Distribution diagram of pore size and number of corrosion holes in ultra-high voltage electronic aluminum foil, Example 2 of this invention;

[0049] Figure 8 Distribution diagram of pore size and number of corrosion holes in ultra-high voltage electronic aluminum foil, Example 3 of this invention;

[0050] Figure 9 Distribution diagram of pore size and number of corrosion holes in ultra-high voltage electronic aluminum foil in Embodiment 4 of the present invention. Detailed Implementation

[0051] Example 1

[0052] The preparation method of ultra-high voltage electronic aluminum foil in this embodiment includes the following steps:

[0053] Step (1): Heat the high-purity aluminum ingot to 750℃ in a melting furnace and melt it. Add an Al-Cr master alloy containing Cr while it is in the molten state. By controlling the amount of Al-Cr master alloy added, the Cr content in the alloy liquid in the melting furnace is kept at 0.002wt.%. Transfer the melted alloy liquid to a holding furnace and hold it at 750℃ for 3 minutes. After holding, transfer the alloy liquid to a refining furnace, add refining agent, and stir. During refining, the temperature of the refining furnace is set to 760℃ (actual furnace gas temperature 735-745℃, aluminum liquid temperature 720-740℃). Disperse and evenly sprinkle 5kg (0.2wt.% of the alloy liquid mass) of refining agent (dry sodium chloride) into various parts of the melting furnace. Set the idle gas pressure to 0.15MPa and open the nitrogen valve (nitrogen flow rate is 10). (L / min) After powder is sprayed out of the refining tube outlet, insert the refining tube into the melt and move it slowly around the furnace. The melt bubbles should be less than 100 mm and there should be no dead corners. While refining, turn on the electromagnetic stirring (electromagnetic stirring speed is 120 rpm) until the refining is finished and stop. The refining time is 15 min. Insert the stirring rake into the alloy liquid to 4 / 5 of the depth and stir manually (stirring speed is 20 rpm). Manually control the stirring rake to move slowly around the furnace and push and pull it back and forth slowly. The stirring time is 15 min. Turn on the electromagnetic stirring (electromagnetic stirring speed is 120 rpm) when the manual stirring starts and stop when the manual stirring ends.

[0054] The high-purity aluminum contains: 99.996 wt.% aluminum, 0.00032 wt.% iron, 0.00067 wt.% silicon, 0.00006 wt.% copper, 0.00048 wt.% zinc, 0.00014 wt.% magnesium, and 0.00036 wt.% manganese, with the balance being impurities. The Al-Cr master alloy used contains 5 wt.% chromium and 0.5 wt.% impurities.

[0055] Step (2): Set the degassing pressure to 0.2 MPa, nitrogen flow rate to 75 L / min, and rotation speed to 450 rpm; detect the hydrogen content (1 time / furnace), the hydrogen content should be ≤0.10 ml / 100 g Al; filter through the filter box, and then perform slag testing and settling treatment; when testing the slag, test the slag at the outlet of the 40 ppi + 50 ppi ceramic filter plate, the slag content N2O ≤ 50 kJ / kg; the settling time is 25 min; after the settling treatment, open the furnace hole and release the liquid smoothly. When the liquid level in the flow channel is about 100-130 mm, slowly lift the graphite plug to allow the alloy liquid to flow smoothly into the crystallizer. When the graphite plug completely controls the molten aluminum, start the cooling water. When the molten aluminum forms a 10mm crust at the edge of the crystallizer, lift the graphite plug for secondary release. When the alloy liquid rises to 2 / 3 of the crystallizer position, set a slow descent (35-45mm / min). When the ingot shell stabilizes (i.e., the alloy liquid in the crystallizer is stable), the casting speed can be gradually adjusted from 50-70mm / min, with the final casting speed set at 70mm / min. This produces a Cr-containing aluminum ingot with a width of 635mm, a thickness of 320mm, and a length of 4930mm. The casting temperature is controlled at 710℃; the casting water pressure is 0.15MPa; and the casting water temperature is 35℃.

[0056] Step (3): Use a milling cutter to remove the impurities from the surface of the aluminum ingot; use a GMC2013 milling machine manufactured by Kunte Heavy Industry for milling treatment. After milling treatment, the thickness of the chromium-containing ingot is 310mm.

[0057] Step (4): Place the aluminum ingot into a resistance furnace with the temperature raised to 600℃ for homogenization and heat for 8 hours;

[0058] Step (5): The homogenized aluminum ingot is hot rolled using a Φ130mm two-roll mill, and a 5.5mm thick aluminum plate is obtained by hot rolling in eleven passes; the initial rolling temperature is 520℃ and the final rolling temperature is 260℃.

[0059] Table 1 Hot rolling processing parameters

[0060]

[0061] Step (6): After the hot-rolled thick aluminum plate is cooled, it is cold-rolled in four passes using a Φ130mm two-roll mill with a final rolling temperature of less than 120℃ to obtain an aluminum foil with a thickness of 0.3mm. Before cold rolling, the rolls and the rolled piece are cleaned with acetone solution and wiped with degreased cotton until there are no stains. Machine oil is added as a lubricant during rolling.

[0062] Table 2 Cold rolling processing parameters

[0063]

[0064] Step (7): Place the cold-rolled aluminum foil into an electric resistance furnace for intermediate annealing at a temperature of 250°C for 8 hours.

[0065] Step (8): After cooling the intermediate annealed aluminum foil to room temperature, use a Φ130mm two-roll mill to perform one-pass foil rolling. The rolling temperature is 50℃, the rolling speed is 5m / s, and the finished thickness is 0.161mm. Place the rolled aluminum foil into a vacuum annealing furnace for finished product annealing. The vacuum degree is 1.5×10⁻³Pa, the finished product annealing temperature is 520℃, and the holding time is 12h.

[0066] Step (9): Place the finished annealed aluminum foil into the electrolytic polishing solution for electrolytic polishing treatment. Use a constant temperature magnetic stirrer to make the solution temperature uniform. The electrolytic polishing solution is prepared by perchloric acid and anhydrous ethanol in a volume ratio of 1:9. The polishing voltage is 18V. Use liquid nitrogen to control the polishing temperature at 0℃. Polish the aluminum foil for 2 minutes to make the surface bright mirror. After polishing, repeatedly wash the aluminum foil surface with deionized water to remove the residual polishing solution.

[0067] Step (10): Using a graphite sheet as the cathode and aluminum foil as the anode, in a 1 mol / L HCl + 3.5 mol / L H2SO4 mixture, at a current density of 0.3 A / cm². 2 The aluminum foil was subjected to direct current corrosion at a temperature of 70℃ for 2 minutes.

[0068] The volume fraction of cubic texture in the UHV electronic aluminum foil after electropolishing was 96.8%. The average diameter of a single pore in the etched UHV electronic aluminum foil was 1.323 μm, the percentage of etched pores was 21.5%, and the porosity was 0.09 pores / μm. 2 .

[0069] Example 2

[0070] The only difference between this embodiment and Embodiment 1 is that in step (1), the amount of Al-Cr master alloy added is controlled so that the Cr content in the alloy liquid in the melting furnace is 0.004 wt.%. All other process steps are the same as in Embodiment 1.

[0071] The volume fraction of cubic texture in the UHV electronic aluminum foil after electropolishing was 95.9%. The average diameter of a single pore in the UHV electronic aluminum foil after etching was 1.136 μm, the percentage of etched pores was 21.1%, and the porosity was 0.06 pores / μm. 2 .

[0072] Example 3

[0073] The only difference between this embodiment and Embodiment 1 is that in step (1), the amount of Al-Cr master alloy added is controlled so that the Cr content in the alloy liquid in the melting furnace is 0.006 wt.%. All other process steps are the same as in Embodiment 1.

[0074] The volume fraction of cubic texture in the UHV electronic aluminum foil after electropolishing was 94.3%. The average diameter of a single pore in the etched UHV electronic aluminum foil was 0.868 μm, the percentage of etched pores was 22.2%, and the porosity was 0.11 pores / μm. 2 .

[0075] Example 4

[0076] The only difference between this embodiment and Embodiment 1 is that in step (1), the amount of Al-Cr master alloy added is controlled so that the Cr content in the alloy liquid in the melting furnace is 0.008 wt.%. All other process steps are the same as in Embodiment 1.

[0077] The volume fraction of cubic texture in the UHV electronic aluminum foil after electropolishing was 94.6%. The average diameter of a single pore in the etched UHV electronic aluminum foil was 0.760 μm, the percentage of etched pores was 25.3%, and the porosity was 0.20 pores / μm. 2 .

[0078] from Figures 3a to 3d It can be seen that all samples exhibit a remarkably consistent dominant color tone. This is because red in the IPF spectrum represents the normal direction (ND) parallel to the x-axis. <100> Crystal orientation; this color consistency indicates that a cubic texture (100) was formed after the finished product was annealed. <100> The dominant texture type. In addition to the predominantly red main color, there are still some trace amounts of yellow and blue grains, indicating that the grains did not completely transform into (100) crystal planes during annealing.

[0079] from Figures 4a to 4d It can be seen that pink represents cubic texture and white represents non-cubic texture. After annealing, the anode aluminum foil mainly undergoes recrystallization. The microstructure after annealing exhibits a typical equiaxed grain morphology, with clear and straightened grain boundaries, consistent with the typical characteristics of a fully recrystallized structure. For the same annealing process, observation... Figures 4a to 4d It is evident that as the Cr content increases, the size of the recrystallized grains gradually decreases (Cr mainly refines the grain size through the Zener pinning effect and by inhibiting recrystallization growth). Extending the annealing temperature and time will both lead to coarser recrystallized grains.

[0080] from Figures 5a to 5dIt can be seen that all sample surfaces exhibit a typical square corrosion pit structure. This phenomenon is closely related to the crystallographic anisotropy of the aluminum matrix during the corrosion process. On the (100) crystal plane, <100> The crystal orientation with the lowest elastic modulus and weakest atomic binding energy results in a significantly higher corrosion rate under an electric field compared to other crystal orientations. The corrosion process preferentially proceeds along... <100> The etching proceeds in the direction of the crystal plane and extends along a plane parallel to the (100) crystal plane, eventually forming a columnar square etch pit that penetrates the matrix.

[0081] from Figures 6 to 9 It can be seen that the addition of Cr significantly affects the morphology parameters of the corrosion pores: when the Cr content reaches 20 ppm, the average pore size is 1.32 μm. The average pore sizes of the 60 ppm Cr and 80 ppm Cr samples are 0.87 μm and 0.76 μm, respectively. The Cr content has a significant regulatory effect on the proportion of submicron-sized pores: when the Cr content increases to 20 ppm, the proportion of corrosion pores with a diameter less than 0.5 μm is approximately 3.19%. Further increasing the Cr content to 80 ppm results in the highest proportion of corrosion pores with a diameter less than 0.5 μm, at 19.12%. This may be because the standard electrode potential of chromium (-0.74 V) is significantly higher than that of aluminum (-1.66 V). In the corrosion solution, the two form a galvanic cell effect, accelerating the corrosion of the aluminum foil. Under the corrosion current density, corrosion temperature, and corrosion time conditions of this embodiment, the corrosion rate of the aluminum foil can be indirectly controlled by controlling the chromium content, thereby controlling the pore size of the pores formed by corrosion on the aluminum foil surface.

[0082] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing ultra-high voltage electronic aluminum foil, characterized in that, Includes the following steps: Step (1): Place the pure aluminum ingots into a melting furnace for melting. After the pure aluminum ingots are completely melted, add an aluminum-chromium master alloy and continue heating and stirring until the aluminum-chromium master alloy is completely melted. Transfer the molten alloy liquid to a holding furnace for holding. After holding, transfer the alloy liquid to a refining furnace, add a refining agent for refining and stir. Control the amount of aluminum-chromium master alloy added so that the chromium content in the alloy liquid is 0.002wt.%-0.008wt.%. Step (2): The refined alloy liquid is subjected to degassing, hydrogen testing, filtration, slag testing and settling treatment in sequence. After the settling treatment is completed, it is cast to obtain chromium-containing aluminum ingots. Step (3): The chromium-containing aluminum ingot is subjected to milling, homogenization, hot rolling, cold rolling and intermediate annealing in sequence. After the intermediate annealing is completed, the chromium-containing aluminum foil intermediate is obtained. Step (4): The chromium-containing aluminum foil intermediate is subjected to foil rolling and finished product annealing in sequence. After the finished product annealing is completed, the chromium-containing aluminum foil finished product is obtained. Step (5): The chromium-containing aluminum foil is subjected to electrolytic polishing and DC corrosion treatment in sequence. After the DC corrosion treatment is completed, ultra-high voltage electronic aluminum foil is obtained. In step (1), the melting temperature of pure aluminum ingots is 750-760℃, the holding temperature of the alloy liquid in the holding furnace is 740-750℃, and the holding time is 3-5min; the refining agent is sodium chloride and / or potassium chloride; the amount of refining agent is 0.1-0.3wt.% of the total mass of the alloy liquid, the idling pressure in the refining furnace is 0.1-0.5MPa, and the nitrogen flow rate is 8-10L / min; the refining furnace temperature is set at 720-760℃, and the refining time is 10-15min; electromagnetic stirring is carried out during the refining process, and the electromagnetic stirring speed is 100-150 rpm; after the refining is completed, stirring continues for 10-15min, and the stirring method is simultaneous manual stirring and electromagnetic stirring, with the manual stirring speed at 20-25 rpm and the electromagnetic stirring speed at 100-150 rpm; In step (2), the degassing pressure is 0.1-0.3 MPa, the nitrogen flow rate is 55-75 L / min, and the rotation speed is 350-450 rpm. When measuring hydrogen, the hydrogen content is measured at least once per furnace, and the hydrogen content is less than or equal to 0.10 mL / 100 g Al. When filtering, a 40 ppi + 50 ppi ceramic filter plate is used for filtration. The filter box is coated with paint evenly, and the filter plate is replaced once per furnace. When measuring slag, the slag is measured at the outlet of the ceramic filter plate, and the slag content N20 ≤ 50 kJ / kg is measured. The settling time is 20-25 min. A semi-continuous casting machine is used for semi-continuous casting. The casting temperature of the semi-continuous casting is 710-730℃, the casting speed is 55-70 mm / min, the casting water pressure is 0.10-0.22 MPa, and the casting water temperature is less than or equal to 40℃. In step (3), a milling machine is used for surface milling. During the homogenization process, the homogenization is carried out by entering the furnace at a temperature of 590-610℃ and holding for 8-12 hours. During hot rolling, chromium-containing aluminum ingots are rolled into aluminum plates using 6-11 passes. The initial rolling temperature is 520-540℃, and the final rolling temperature is 260-280℃. At least three passes of equal reduction rolling are performed first, and then the reduction in subsequent passes is gradually reduced. The total reduction rate of hot rolling is 96.0-98.5%. During cold rolling, aluminum sheets are rolled into aluminum foil using 4-6 passes, with a total reduction rate of 92-95%. During intermediate annealing, the temperature is 240-260℃, and the holding time in a vacuum environment is 8-10 hours. In step (4), the rolling temperature of the foil is between -50 and 70℃, the rolling speed is 3-5m / s, the number of foil rolling passes is 1-2, and the total reduction rate of the foil rolling is 40-60%. During the annealing treatment of the finished product, it is annealed in a vacuum annealing furnace with a vacuum degree of (1.333-6.6)×10⁻³Pa, the annealing temperature of the finished product is 350-530℃, and the holding time is 12-16h. The thickness of the chromium-containing aluminum foil finished product is 0.15-0.20mm.

2. The method for preparing ultra-high voltage electronic aluminum foil according to claim 1, characterized in that, In step (1), the mass fraction of aluminum in the pure aluminum ingot is greater than or equal to 99.99 wt.%; in the aluminum-chromium master alloy, the mass fraction of chromium is 5 wt.%, the mass fraction of impurities is less than or equal to 0.5 wt.%, and the balance is aluminum.

3. The method for preparing ultra-high voltage electronic aluminum foil according to claim 1, characterized in that, In step (5), during the electrolytic polishing process, the electrolytic polishing solution is a mixture of perchloric acid and anhydrous ethanol in a volume ratio of 1:9; the polishing voltage is 15-20V, the polishing temperature is controlled at 0℃ using liquid nitrogen, and the polishing time is 1-3min.

4. The method for preparing ultra-high voltage electronic aluminum foil according to claim 1, characterized in that, In step (5), during the direct current corrosion treatment, the graphite sheet is used as the cathode, the chromium-containing aluminum foil is used as the anode, the concentration of hydrochloric acid in the corrosion solution is 0.5-1.2 mol / L, the concentration of sulfuric acid is 3.0-4.0 mol / L, the corrosion temperature is 60-70℃, and the current density is 0.2-0.4 mA / cm². 2 The corrosion time is 1-3 minutes.

5. The method for preparing ultra-high voltage electronic aluminum foil according to claim 1, characterized in that, In step (1), the pure aluminum ingot contains 99.996 wt.% aluminum, 0.00032 wt.% iron, 0.00067 wt.% silicon, 0.00006 wt.% copper, 0.00048 wt.% zinc, 0.00014 wt.% magnesium, and 0.00036 wt.% manganese, with the balance being impurities; in the aluminum-chromium master alloy, the chromium content is 5 wt.% and the impurities content is 0.5 wt.%; the melting temperature of the pure aluminum ingot is 750℃, and the amount of aluminum-chromium master alloy added is controlled. The chromium content in the molten alloy was 0.008 wt.%; the holding temperature of the molten alloy in the holding furnace was 750℃, and the holding time was 3 min; the refining agent was sodium chloride; the amount of refining agent was 0.2 wt.% of the total mass of the molten alloy; the idle pressure in the refining furnace was 0.15 MPa, and the nitrogen flow rate was 10 L / min; the refining furnace temperature was set at 760℃, and the refining time was 15 min; during the refining process, electromagnetic stirring was performed at a speed of 120 rpm; after the refining was completed, stirring continued for 15 min, with manual stirring and electromagnetic stirring performed simultaneously at a speed of 120 rpm; In step (2), the degassing pressure is 0.2 MPa, the nitrogen flow rate is 75 L / min, and the rotation speed is 450 rpm. When measuring hydrogen, the hydrogen content is measured once per furnace, and the hydrogen content is less than or equal to 0.10 mL / 100 g Al. When filtering, a 40 ppi + 50 ppi ceramic filter plate is used for filtration. The filter box is uniformly coated with paint, and the filter plate is replaced once per furnace. When measuring slag, the slag is measured at the outlet of the ceramic filter plate, and the slag content N20 ≤ 50 kJ / kg is measured. The settling time is 25 min. A semi-continuous casting machine is used for semi-continuous casting. The semi-continuous casting temperature is 710℃, the casting speed is 70 mm / min, the casting water pressure is 0.15 MPa, and the casting water temperature is 35℃. The dimensions of the chromium-containing ingot obtained by casting are 635 mm * 320 mm * 4930 mm. In step (3), a milling machine is used for milling. After milling, the thickness of the chromium-containing ingot is 310 mm. During homogenization, the temperature was 600℃ and the holding time was 8 hours. During hot rolling, chromium-containing aluminum ingots are rolled into aluminum plates using 11 passes. The initial rolling temperature is 520℃, and the final rolling temperature is 260℃. The 11 passes of hot rolling are as follows: 310mm-275mm-240mm-205mm-170mm-135mm-100mm-65mm-36mm-18mm-11mm-5.5mm. During cold rolling, aluminum sheets are rolled into aluminum foil using four passes, with a final rolling temperature below 120℃. The four passes of cold rolling are: 5.5mm-2.6mm-13mm-0.6mm-0.3mm. During intermediate annealing, the temperature is 250℃ and the holding time is 8 hours; In step (4), the rolling temperature of the foil is 50℃, the rolling speed is 5m / s, and the foil rolling passes are 1; during the finished product annealing treatment, it is annealed in a vacuum annealing furnace with a vacuum degree of 1.5×10⁻³Pa, the finished product annealing temperature is 520℃, and the holding time is 12h; the thickness of the chromium-containing aluminum foil finished product is 0.161mm; In step (5), during electrolytic polishing, the electrolytic polishing solution is a mixture of perchloric acid and anhydrous ethanol in a volume ratio of 1:9; the polishing voltage is 18V, the polishing temperature is controlled at 0℃ using liquid nitrogen, and the polishing time is 2min; during DC corrosion treatment, the graphite sheet is the cathode, the aluminum foil is the anode, the concentration of hydrochloric acid in the corrosion solution is 1.0mol / L, the concentration of sulfuric acid is 3.5mol / L, and the current density is 0.3A / cm². 2 The corrosion temperature was 70℃ and the corrosion time was 2 minutes.

6. An application of an ultra-high voltage electronic aluminum foil, characterized in that, The ultra-high voltage electronic aluminum foil prepared by the method described in any one of claims 1-5 is used as the anode material for ultra-high voltage aluminum electrolytic capacitors.

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