JPH05247571A - Aluminum alloy having fine structure - Google Patents

Abstract

PURPOSE:To remove the variance of structure in an rapidly solidified aluminum foil forming dendrite. CONSTITUTION:An aluminum alloy having a structure where an intermetallic compound between one or >=2 elements among Ti, Ta, Zr, Hf, and Nb and Al is crystallized out in fine dendritic state in Al metal and a compound having a melting point higher than that of the intermetallic compound is contained in the dendrite. The compound is one or >=2 kinds among the oxides, nitrides, and phosphides of Al, Ti, and Zr. The aluminum alloy can be produced by subjecting a molten metal to rapid solidification. In the resulting rapidly solidified foil, dispersion in the size of dendrite due to a casting method in the direction of foil thickness can be reduced. A capacitor formed by using this foil has stable characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy used as an anode for electrolytic capacitors.

[0002]

2. Description of the Related Art A so-called valve metal capable of electrochemically forming a very thin dielectric oxide film is used as an anode material of an electrolytic capacitor. Among them, aluminum and tantalum having a purity of 99.9% or 99.99% are currently used.

The electrode foil used for the anode of the aluminum electrolytic capacitor is mechanically and electrochemically etched at a considerably high magnification in order to increase the capacitance by increasing the surface area. However, at present, the etching magnification does not exceed 100 times and almost reaches the limit.

It has also been attempted to improve the electrostatic capacity by devising an anodizing method. This is due to the composite film of pseudo boehmite film by hot water treatment and anodized film by electrolytic reaction, composite synthesis of chemical conversion film by boric acid solution and chemical conversion film by phosphoric acid solution, film by special pretreatment and electrolytic reaction. For example, a composite film with an anodized film. The increase in capacitance due to such a composite oxide film is within 30% of the increase in the film due to the usual electrolytic reaction.

More recently, instead of high-purity aluminum, an alloy foil of aluminum and titanium or other valve metal is used to form an alloy oxide film having a high relative dielectric constant such as Al ₂ O ₃ + TiO ₂ by chemical conversion. Being tried.

With the above-described high-purity aluminum anode material, it is no longer possible to increase the etching magnification to the present 2-3 times. That is, even if the electrochemical or chemical etching is strongly performed, the etching hole does not grow deeply, and conversely, aluminum near the entrance of the hole melts and the etching portion is reduced, so that the thickness is simply thin. However, the etching magnification does not necessarily increase. Further, even if a deep etching hole is formed and the apparent etching ratio is increased, the oxide film is clogged during the anodization, and the etching ratio cannot be utilized. Even when an electrolytic capacitor is manufactured using such an anode material, the contact interface with the electrolytic solution is reduced, foil resistance, tan δ, impedance, etc. are deteriorated, and the characteristics are rather deteriorated.

Regarding the problems of the conventional method, the present inventors once described in JP-A-60-66806 that Ti, Ta, Zr and Hf are contained in aluminum.
A method of forming a foil having a high capacity by forming an intermetallic compound of one member or a plurality of members of the metal group consisting of Nb and Nb and aluminum is shown. According to the present invention, the capacity of the capacitor was increased by a factor of 2 to 3, and a dramatic improvement was observed.

[0008]

However, since the invention described in the above publication uses the quenching method, the structure is sensitive to the manufacturing conditions, and the structure changes greatly with a slight fluctuation in the setting items. Further, most of the structures generally have a fine crystallized structure on the cooling roll surface side, but the structure becomes coarse on the free surface side. This is due to the difference in the cooling rate on the roll surface side and the free surface side, but the nonuniformity of this structure is due to the variation in the etching and chemical conversion steps, which are post-processes,
As a result, it leads to variations in capacitors in the product. This variation requires strict control of various mechanical factors such as the casting temperature, atmosphere, and roll rotation speed, but causes problems of cost increase and workability.

The present invention is to provide a stable and large-capacity aluminum alloy which eliminates such a variation in the structure and has a uniform and fine structure.

[0010]

The present invention has a higher melting point than that of the intermetallic compound and has a solid solubility in aluminum in order to eliminate the above-mentioned variation in the structure of the quenched aluminum foil for forming dendrites. By adding a small compound, dendrite is crystallized by using it as a crystallization nucleus, and as a result, the structure is made uniform and fine, and the capacity is stabilized and increased. Specifically, as the nucleation compound, one or more of Al, Ti, or Zr oxide, nitride, or phosphide is used. The dendrite forming metal and the nucleating component are added to Al metal, and the mixture thereof is melted and quenched,
It forms a foil.

That is, the present invention is: (1) Any one of Ti, Ta, Zr, Hf or Nb
An intermetallic compound of one or more of Al and Al crystallizes in a fine dendrite state in Al metal, and a compound having a melting point higher than the melting point of the intermetallic compound is present in the dendrite. And aluminum alloy. (2) An aluminum alloy as described in the above item, wherein the compound contained therein is one or more of oxides, nitrides or phosphides of Al, Ti or Zr. (3) The aluminum alloy according to the above (1) or (2), wherein the particle size of the compound contained therein is 1 μm or less. (4) When one or more of Ti, Ta, Zr, Hf or Nb is added to Al and melted, and is rapidly cooled to crystallize fine dendrites, oxidation of Al, Ti or Zr The method for producing a foil of an aluminum alloy is characterized in that one or more kinds of metal, nitride or phosphide are added for nucleation. It is desirable to maintain the molten metal temperature higher than the quenching temperature by 50 to 100 ° C. or more and cool it to the quenching temperature before performing the quenching in the preceding paragraph. The present invention will be described in detail below.

[0012]

According to the present invention, a molten metal containing aluminum and a dendrite forming metal is rapidly cooled to produce a foil.
At that time, the crystallized dendrite structure is finely and stably formed. The present invention makes it possible to manufacture a capacitor having a higher capacity and stableness by using this quenching foil. The nucleation compound is an oxide of Al, Ti or Zr,
It is a nitride or a phosphide, and a plurality of them may be used.

A specific production method of the present invention will be described in the case where Ti is added to form Al ₃ Ti as a crystallized dendrite and Al ₂ O ₃ is used as a nucleating material. That is, a small amount of Al ₂ O ₃ powder is added to Al: 90 and Ti: 10 parts by weight. The maximum amount of Al ₂ O ₃ added can be 1% or less, but in this case 0.01% was added. The temperature of this mixture is raised to 1400 ° C. which is higher than the melting temperature of 1200 ° C. of the composition in Ar atmosphere. After heating up to 1400 ° C, cool down to 1300 ° C at 2 ° C / sec.
After reaching the temperature, this molten metal is ejected onto a roll surface that rotates at high speed to form a quenched foil. At this time, Al ₃ Ti is formed in the aluminum to form a dendrite structure. Observation of this quenched foil with a microscope revealed that Al ₂ O ₃
In the case of adding Al ₂ O _{3 according} to the method of the present invention, the size of the dendrite formed was σ = 2 μm and the average particle size was X = 5 μm. , Σ = 1 μm, and X = 3 μm. This means that the addition of Al ₂ O ₃ made the structure finer and reduced the variation. In addition, the difference in average diameter between the surface and the inside of the foil was about twice as large as in the past, but was reduced to about 1.3 times by the method of the present invention.

As the compound to be added, the above compound (Al
Similar effects were obtained by adding AlN or AlP in addition to ₂ O ₃ ). Further, a larger effect was seen when the temperature was raised once and then lowered by 50 to 100 ° C. before the rapid cooling. The reason why the crystallized dendrite is reduced by adding the nucleating compound is considered as follows.

First, the added compound is slightly dissolved in Al. Then, by decreasing the temperature before the rapid cooling, minute amounts of these additives crystallize out. The dendrite-forming compound then crystallizes into these nuclei. The crystallization of the nucleating compound is so finely dispersed that the dendrites crystallize finely and in large amounts accordingly. On the other hand, when these nucleating compounds are not added, it is considered that the dendrite formation site becomes considerably rough and the crystal grains become rough at the time when the solidification is completed. Although the same effect can be obtained by adding a large amount of the nucleating compound, it deteriorates the characteristics of the entire material and floats on the upper portion of the melt, which only causes a bad effect on workability. A small amount is desirable.

The effects of the present invention can be applied not only to the quenching foil for capacitors but also to other cooling materials. That is, if a nucleating compound that satisfies the above conditions is added in addition to the material to be crystallized, the crystallized substance can be miniaturized and stabilized. Further, the compound to be added can be considered other than the conditions specified in the present invention, but when it is used for a capacitor, it must be considered as a substance that does not adversely affect the characteristics.

[0017]

【Example】

(Example 1) A quenching alloy using a material containing 90% by weight of aluminum and 10% by weight of Ti was prepared by a single roll method using a copper roll. Also, to prevent oxidation,
Adopted N ₂ atmosphere. At this time, as a nucleation material, 0.1 g of Al ₂ O ₃ powder was added to 100 g of the mother alloy, which was then inserted into the crucible. The average particle diameter of Al ₂ O ₃ powder is 1.5
was μm.

Next, the atmosphere is set to an Ar atmosphere, and the melting temperature of this composition is higher than 1200 ° C. by 200 ° C. 140
After the temperature was raised to 0 ° C, it was cooled to 1300 ° C at 2 ° C / sec. After reaching 1300 ° C., the molten metal was jetted onto the roll surface rotating at high speed to form a quenched foil. According to the method disclosed in Japanese Patent Application No. 61-27242, the molten metal was passed through a nozzle heated with high frequency, ejected into a rotating roll, and rapidly solidified.

After that, the formed quenching foil was cut, embedded in a resin, polished, and then observed by SEM. Al ₃ Ti is formed in aluminum and has a dendrite structure. When the quenched foil was observed with a microscope, it was found that Al ₂ O
_{When 3} was not added, the size of the dendrite formed was such that the average particle size X = 7 μm and the standard deviation σ = 2.5 of the particle size, whereas Al ₂ O ₃ was added by the method of the present invention. In that case, X = 5 μm and σ = 1.5. In addition, the CV product (capacitance x film breakdown voltage) is
While it was 2800 μFV / cm ² ± 15%, with addition, it was improved to 3200 ± 7%. Further, as a result of observation with a transmission electron microscope, it was confirmed that a fine nucleus of Al ₂ O ₃ was present in a part of the dendrite of Al ₃ Ti. This was much smaller than the initially added Al ₂ O ₃ powder and was at most 0.01 μm.

(Example 2) Z in 90% by weight of aluminum
10% by weight of r was added. Preparation of the quenched alloy was performed using a single roll method with a copper roll. Further, in order to prevent the alloy from being oxidized, an N ₂ atmosphere was adopted. As a nucleation material, 0.1 g of AlN powder was added to 100 g of the mother alloy, and the molten metal inserted in the crucible was in an Ar atmosphere at a temperature of 200 ° C rather than the melting temperature of 1300 ° C of this composition.
The temperature was raised to a high temperature of 1500 ° C., and after the temperature was raised to 1500 ° C., it was cooled to 1400 ° C. at 2 ° C./sec. 1400
After the temperature reached ℃, the molten metal was jetted to the roll surface rotating at high speed to form a quenching foil.

After that, the formed quenching foil was cut, embedded in a resin, polished, and then observed by SEM. Al ₃ Zr is formed in aluminum and has a dendrite structure. When the quenched foil is observed with a microscope, the size of the dendrite formed is σ = 2, X when AlN is not added. = 7 μm, in the case of adding AlN by the method of the present invention, σ = 1, X = 3 μ
It was m. The CV product is 3000 without addition.
While it was μFV / cm ² ± 12%, it was improved to 3500 ± 5% with the addition.

(Example 3) 90% by weight of aluminum and T
10% by weight of i was added, and A was added to 100 g of the mixture.
0.02 g of each of 1P and Al ₂ O ₃ powder was added,
I inserted it in the crucible. The production of the quenched foil was performed in the same manner as in Example 1. When the quenched foil was observed with a microscope, the size of the dendrite formed was σ = 2.5 and X = 7 μm when the nucleating compound was not added. Is added, σ =
1.5 and X = 5 μm. Further, the CV product was 2800 μFV / cm ² ± 15% without addition, whereas it was improved to 3200 μFV / cm ² ± 7% with addition.

Upon further investigation, 35% by volume of Al ₃ Ti was formed in aluminum.
Fine particles of AlP and Al ₂ O ₃ are used as crystallization nuclei. That is, when observed with an electron microscope, very small AlP
And Al ₂ O ₃ nuclei were found inside the Al ₃ Ti crystal grains.

(Example 4) 95% by weight of aluminum and T
5% by weight of a was added to produce a master alloy. This mother alloy 1
0.05 g each of Al ₂ O ₃ powder and ZrO ₂ powder was added to 00 g, and the powder was inserted into a crucible. In making the alloy, it was cast into a mold to form blocks.
After the block was formed, it was rolled with a rolling roll to form a 1 mm foil.

Observation of this foil with a microscope revealed that Al ₂
When O ₃ was not added, the size of the dendrite formed was σ = 4 μm and X = 10 μm, whereas when Al ₂ O ₃ was added by the method of the present invention, σ = 3.
μm, X = 7 μm.

[0026]

As described above, according to the present invention, the conventional quenched structure can be miniaturized and stabilized, and when used as a capacitor material, the capacity of the capacitor is increased and the stability is stabilized. Became possible.

Claims (4)

[Claims] 1. An intermetallic compound of Al with one or more of Ti, Ta, Zr, Hf, and Nb, and
An aluminum alloy characterized by being crystallized in the form of fine dendrites in Al metal, and a compound having a melting point higher than that of the intermetallic compound is present in the dendrites. 2. The intrinsic compound is Al, Ti or Z.
One or two of oxides, nitrides or phosphides of r
The aluminum alloy according to claim 1, wherein the aluminum alloy is at least one kind. 3. The aluminum alloy according to claim 1, wherein the internal compound has a particle size of 1 μm or less. 4. When one or more of Ti, Ta, Zr, Hf or Nb is added to Al and melted, and when this is rapidly cooled to crystallize fine dendrites, Al,
Ti or Zr oxide, nitride or phosphide 1
A method for producing a foil of the aluminum alloy, wherein one kind or two or more kinds are added for nucleation.