RU2588942C2 - Method of producing etched cathode of aluminium foil made from high-purity aluminium alloyed with scandium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to production of etched capacitor aluminium foil. Method of producing etched cathode capacitor aluminium foil containing 0.001-0.1 wt% scandium, thickness of 20-60 mcm, includes alloying aluminium of high purity with scandium, hot rolling and cold rolling to thickness of 20-60 mcm, alloying is performed by adding to aluminium with purity of 99.99 % alloy Al-Sc2 % in ratio of 1:2000 to 1:20, and after cold rolling smooth foil is subjected to electrochemical etching in an aqueous electrolyte containing, g/l: NaCl - 150-300, Na₂SO₄ - 15-30, polyethylene glycol - 0.1-1 at a temperature of 85-95 °C and current density - 0.5-0.7 A/cm².

EFFECT: invention is aimed at improving electromechanical characteristics, particularly production of capacitors with high specific charge, and improved weldability and corrosion resistance.

1 cl, 2 ex, 1 tbl, 1 dwg

Description

The invention relates to the production of aluminum electrolytic capacitors, in particular to a method for producing etched cathode capacitor aluminum foil. A method of obtaining an etched cathode capacitor aluminum foil includes the creation of doped with scandium in an amount of 0.001-0.1 wt. % smooth aluminum foil made of high-purity aluminum (99.99%) when 2% aluminum-scandium ligature (Al-Sc2%) is added to aluminum in a ratio of 1: 2000 to 1:20 by weight, including charge melting formed by adding Al-Sc2% ligature to high-purity aluminum (99.99%) in a ratio of 1: 2000 to 1:20 by weight, followed by cylindrical castings and their refinement (or segregation) and homogenization and then hot rolling followed by cold rolling to a thickness of 20 ÷ 60 μm, electrochemical etching of the obtained initial photo with the technical results such as reducing the thickness of the cathode foil by more than two times, in relation to the typical method of producing etched cathode aluminum foil, while maintaining the values of the electromechanical characteristics, and improved indicators with respect to welding ability, providing the creation of aluminum electrolytic capacitors with high specific charge.

The capacitance of the capacitor is directly proportional to the effective surface area of the electrodes. To increase the effective surface area of aluminum foil, electrochemical etching is usually applied, in which the following principles are observed: the total thickness of the aluminum foil should not be etched, the development of the effective surface is directly proportional to the metal removal. The removal of metal reduces the cross-sectional area of the foil, which leads to a decrease in the mechanical characteristics of the etched aluminum foil, such as bending strength and tensile strength. If you increase the mechanical strength of the original aluminum foil, this will reduce the cross-sectional area of the etched foil and will increase the effective surface.

To impart certain properties to a metal or alloy, alloying with small concentrations of certain impurities is used. The most stable results in alloying with high assimilation of the alloying element are obtained with the help of alloys - auxiliary alloys used to introduce into molten metal, here high-purity aluminum, alloying elements, in this case aluminum alloys. To obtain a high-strength, high-conductivity, with good ability to weld aluminum alloy suitable aluminum-scandium ligature containing trace amounts of scandium. The introduction of scandium significantly increases the ability of the alloy to deform (ductility) and to weld (weldability) of products while reducing hot cracks and increasing the strength of the welded joint, and also increases the temperature interval of stable operation of the alloy by 100-500 ° C.

The positive effect of scandium on technical characteristics is due to the following. Scandium is prone to the formation of supersaturated solid solutions in a nonequilibrium state even at low crystallization rates. In this case, the crystal lattice of the Al ₃ Sc intermetallide formed during the interaction of scandium with aluminum almost completely corresponds to the structural lattice of aluminum in terms of size and structural parameters; which leads to its strongest influence on the structure and properties of the alloy. It should be noted that the relatively high cost of Al-Sc alloys as a result is compensated by an increase in the margin of safety of the technical characteristics of the alloy, a significant decrease in mass and size index and an improvement in the technical characteristics of the alloy product. The most critical from the point of view of achieving these improved technical characteristics is to obtain a thin scandium-containing foil (sheet, strip), in particular, a thickness of 20 μm from a thickness range of 20-60 μm acceptable for a capacitor electrode.

Known capacitor etched cathode foil K-2, made by the standard method, from a smooth aluminum foil containing aluminum with a purity of 99.4% with such impurities, wt. %, as Fe - less than 0.225; Ti - less than 0.017; Mn - less than 0.132; Cu 0.231; Zn - less than 0.005; Si - less than 0.052, thickness 45 μm, grade 2301 V, China. Smooth aluminum foil is made according to the technology of Beijing Weihao Aluminum Group Co., LTD, and the K-2 etched cathode foil is made according to the technology of Elekond OJSC.

The disadvantage is the usual value of the electromechanical characteristics of this cathode foil, which does not significantly reduce the mass and size characteristics of capacitors.

The objective of the invention is a method for producing etched cathode aluminum foil with a thickness of 20-60 μm, which allows to reduce the thickness of the foil by more than two times, in relation to a typical method for producing etched cathode aluminum foil, while maintaining the values of electromechanical characteristics, and improved performance in relation to the ability to weld and corrosion resistance.

In the present invention, the problem is solved and the above technical results are obtained due to the above factors.

Figure 1 is a graph of determining the corrosion rate on aluminum foil in ethylene glycol-based working electrolytes using a corrosion testing complex of the American company Rorhback Cosasco System (RCS). The general indicators of the corrosion behavior of aluminum in electrolytes in terms of corrosion rate were: from 0.002 mm / year for 2301 V foil and from 0.0003 mm / year for scandium-containing aluminum foil (99.99%).

The following are examples of the experimental implementation of the prototype (comparative example 1 - cathode etched aluminum foil obtained by the standard method) and invention (examples 2 - cathode etched aluminum foil obtained by the method proposed in this invention).

In examples 1-2, samples of smooth aluminum foil were subjected to test electrochemical etching with the subsequent determination of:

- specific electric capacitance, microfarads / cm ² ;

- mechanical bending strength (characterized by a limit number of bends at a load of 50 g, where a bend at a 90 ° angle there and back is taken for one bend);

- mechanical tensile strength (characterized by the maximum value of the withstand load in kgf / cm when testing a foil sample in the form of a strip 10 or 15 mm wide).

We also tested the samples for welding ability by visual assessment of the welded joint when the strip of the etched test foil is welded, here - by cold welding, with a strip of smooth foil and when the etched foil is torn off, it gets an “unsatisfactory” rating (pieces of etched foil remain less than 3 at the welding points), “satisfactory” (pieces of etched foil remain at least at 3 welding points) or “good” (pieces of etched foil remain at about 50% of the number of welding points), or “excellent” ( pieces of etched foil remain at 100% the number of welding points) and corrosion resistance based on a quantitative indicator of the corrosion rate on aluminum foil in working electrolytes, for example, based on ethylene glycol.

The test results are listed in table 1.

Example 1 (comparative). For the manufacture of the cathode electrode, a smooth foil with a thickness of 45 μm, grade 2301 V, China, manufactured by the technology of Beijing Weihao Aluminum Group Co., LTD., From aluminum with a purity of 99.4%, which contains such impurities, wt. %, as Fe - less than 0.225; Ti - less than 0.017; Mn - less than 0.132; Cu 0.231; Zn - less than 0.005; Si is less than 0.052.

Electrochemical etching of the cathode foil was carried out according to the following modes and steps (baths):

aqueous NaOH solution - 2.0-4.0 g / l, temperature - 20-40 ° C (pre-treatment step in a degreasing bath);

aqueous electrolyte in the composition: NaCl - 150-300 g / l, Na ₂ SO ₄ - 15-30 g / l, polyethylene glycol - 0.1-1 g / l, temperature - 85-95 ° C, current density - 0, 5-0.7 A / cm ² (etching bath);

aqueous HNO ₃ solution - 50-150 g / l, temperature - 20-40 ° C (cleaning bath);

an aqueous solution of H ₃ PO ₄ - 1.0-5.0 g / l, temperature - 20-30 ° C (passivation bath).

Example 2. For the manufacture of the cathode electrode applied scandium-doped smooth aluminum foil with a purity of 99.99% and a thickness of 20 μm in accordance with the invention when using Al-Sc2% ligature, added to aluminum in a ratio of 1: 2000 by weight, contains 0.001 wt. % scandium and, the rest, aluminum (99.99%) with the following inevitable impurities, wt. %: Zn - less than 0.003, Si - less than 0.003, Cu - 0.002, Fe - less than 0.001, Mg - less than 0.001, Ti - less than 0.001, Ga - 0.0006, Mn - less than 0.0001. Made according to traditional technology: first, an alloy ingot of this composition was obtained by weighing and loading Al (99.99%) and Al-Sc alloys into a furnace, where the mixture was melted by overheating to a temperature of 720-730 ° C and cast into semi-continuous cylindrical casting molds method at a temperature of 700-710 ° C, the obtained castings were subjected to refinement and homogenization at a temperature of 460-520 ° C for 12-24 hours, and then the castings were hot rolled at 380-460 ° C followed by cold rolling to obtain strips of the above thickness .

Electrochemical etching of the foil was carried out as described in example 1.

From the data presented in Table 1, it can be seen that the performance improvement for the etched cathode foil, respectively, amounted to: 32.1% for the specific electric capacity, 6% for the limiting number of bends, 8% for the ultimate tensile load, and significant for the welded joint very significant, in terms of corrosion rate - 85%, and the thickness of the cathode foil according to the invention decreased by more than 2 times relative to the usual one, which reduces (improves) the overall dimensions of products made from such foil, so that the samples of example 2 (according to the invention, with optim ized regime parameters) have values significantly better characteristics than Comparative Example 1 (the prototype samples).

Thus, the proposed method for producing an etched cathode capacitor aluminum foil containing 0.001-0.1 wt. % scandium with a thickness of 20-60 microns, including doping of high purity aluminum with scandium, hot rolling and cold rolling to a thickness of 20-60 microns, characterized in that the alloying is carried out by adding 99.99% Al-Sc2% ligature to the aluminum in a ratio by weight of from 1: 2000 to 1:20, and subjected to the electrochemical etching in an aqueous electrolyte containing in g / l: NaCl - 150-300 g / l, Na ₂ SO ₄ - 15-30 g / l, polyethylene glycol - 0, 1-1 g / l, at a temperature of 85-95 ° C and a current density of 0.5-0.7 A / cm ² , it is possible to reduce the thickness of the foil by more than two times, relative to a typical method for producing etched cathode aluminum foil, while maintaining (actual improvement) the values of electromechanical characteristics, and improved performance in relation to the ability to weld and corrosion resistance.

Thus, the etched cathode capacitor aluminum foil made of high purity aluminum doped with scandium allows:

- reduce energy consumption per unit of obtained capacity (with the same etching mode, the resulting specific capacity is up to 32.1% higher than on the original prototype foil);

- increase the specific characteristics of capacitors up to 32%;

- reduce the overall characteristics of capacitors up to 10%;

- reduce the mass of capacitors up to 10%;

- reduce the cost of manufacturing capacitors by reducing energy consumption in the production of pickled capacitor foil.

Claims (1)

A method of obtaining an etched cathode capacitor aluminum foil containing 0.001-0.1 wt.% Scandium, a thickness of 20-60 microns, including alloying high purity aluminum with scandium, hot rolling and cold rolling to a thickness of 20-60 microns, characterized in that the alloying is carried out by adding 99.99% Al-Sc2% ligature to aluminum with a mass ratio of 1: 2000 to 1:20, and after cold rolling, the smooth foil is subjected to electrochemical etching in an aqueous electrolyte containing, g / l: NaCl - 150- 300, Na ₂ SO ₄ - 15-30, polyethylene glycol - 0.1-1, with those perature 85-95 ° C and current density - 0.5-0.7 A / cm ^2.

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