JPH0517856A - Method for reducing impurity in pure al sheet - Google Patents

Abstract

PURPOSE:To reduce impurities in a pure Al sheet by applying heating treatment to the pure Al sheet under specific conditions and moving the impurities in the sheet to the surface part by diffusion. CONSTITUTION:A pure Al sheet containing, as impurities, one or more elements among Sn, Pb, In, and Ga by >=20ppm in total, having <=300mum sheet thickness, and also having >=99.8% purity is subjected to heating treatment under the condition where this sheet is held in a nonoxidizing atmosphere at the prescribed temp. between 300 and 580 deg.C for the prescribed time. Then, the resulting coagulated part of the impurities moved to the surface part by diffusion is removed. By this method, the total impurity content in the pure Al sheet can be reduced to <=5ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to Sn, Pb, In, and Ga contained as impurities in a normal pure Al plate material.
It is related to the method of reducing.

[0002]

2. Description of the Related Art Conventionally, it is well known that a pure Al plate material having a purity of 99.8% or more is generally used for manufacturing a cathode material of an electrolytic capacitor or a fin material of an Al heat exchanger. .. In addition, the conventional pure Al plate material generally contains Si, Fe, Cu, Ga, Sn, Pb,
It is also known to contain In and In.

[0003]

On the other hand, in recent years, there are severe demands for downsizing and weight reduction of the above-mentioned electrolytic capacitors and Al heat exchangers, and accordingly, the cathode materials and fin materials which are these structural members are demanded. Further thinning is also required for the above, but the conventional pure Al that composes this is required.
In the plate material, in particular, Ga, Sn, Pb, and In, which are contained in a total amount of 20 ppm or more as impurities, adversely affect the corrosion resistance. Therefore, when the thickness of the plate material is reduced, through holes are likely to be formed, which causes deterioration of characteristics. Therefore, satisfactory thinning cannot be expected. Therefore, it is the current situation that attempts have been made to reduce the thickness by adding a corrosion resistance improving component as an alloy component to the conventional pure Al plate material. Ga, Sn, Pb, and In contained as impurities in the above-mentioned conventional pure Al plate material are irrespective of Al purity, in other words, for example, even if the purity is 99.85%, the purity is 99.99%. But the total amount is 20pp
It contains more than m.

[0004]

Therefore, the present inventor, from the above-mentioned viewpoint, pays attention to the conventional pure Al plate material having a purity of 99.8% or more, and as a cause of deterioration of corrosion resistance. Impurities, that is, Sn, P that is contained in the above-mentioned conventional pure Al plate material as impurities in a total amount of 20 ppm or more
As a result of reducing b, In, and Ga, and conducting research to improve corrosion resistance, the above-mentioned conventional pure Al plate material was subjected to a vacuum atmosphere or a non-oxidizing atmosphere such as Ar or N ₂ atmosphere at 300 to 580 ° C. When the heat treatment is performed at a predetermined temperature within the range for a predetermined time, the S
n, Pb, In, and Ga are positively diffused and moved to the surface of the plate material to be aggregated. Therefore, if the impurity aggregated surface portion is removed by an etching means or the like, the content of the above impurities in the pure Al plate material is increased. Will be reduced,
Moreover, if the total amount of Sn, Pb, In, and Ga as impurities is reduced to 5 ppm or less, the corrosion resistance of the pure Al plate material will be remarkably improved, and the formation of through holes will be prevented even if the thickness is reduced. That is the result of the research.

The present invention has been made based on the above-mentioned research results, and Sn, Pb, and I are used as impurities.
Purity containing one or more of n and Ga in a total amount of 20 ppm or more and having a plate thickness of 300 μm or less: 9
9.8% or more of pure Al plate material, in a non-oxidizing atmosphere, 30
A heat treatment is performed at a predetermined temperature within a range of 0 to 580 ° C. for a predetermined period of time to diffuse and move the impurities to the surface portion, and then the impurity aggregation surface portion of the pure Al plate material after the heat treatment is removed. Then, the method is characterized by a method of reducing impurities in a pure Al plate material, which comprises reducing the total content of the above impurities in the pure Al plate material to 5 ppm or less.

In the method of the present invention, the pure Al plate material subjected to the impurity reduction treatment is practically used as the cathode material, the fin material, etc. as described above, and in this case, the purity is 99.8. If less than%, the above Sn, P
In addition to b, In, and Ga, the contents of Si, Fe, Zn, etc., which are contained as impurities, increase and cause deterioration of characteristics. Therefore, those having a purity of 99.8% or more are used. Yes, and with a purity of 99.8% or higher,
Regardless of purity, Sn, Pb, In, and G are all used.
The total amount of a is 20 ppm or more.

In the method of the present invention, the plate thickness of the pure Al plate material is set to 300 μm or less because the plate thickness is 300 μm.
This is because if m is exceeded, it takes a long time for the impurities to diffuse and move to the surface of the plate material, leading to a decrease in productivity. Further, the heat treatment temperature is limited to 300 to 580 ° C. The temperature was 300 ℃
If the temperature is less than, diffusion and movement of impurities to the surface of the plate are extremely slow, which is not desirable in the production process.
This is based on the reason that when the temperature exceeds the range, the plate material partially melts.

Further, as described above, the corrosion resistance of the pure Al plate material is affected by Sn, Pb, In, and Ga contained as impurities therein, and if the total content of these impurities is 5 ppm or less, excellent corrosion resistance is obtained. Therefore, the total content of the above impurities in the pure Al plate material after the impurity reduction treatment is set to 5 ppm or less.

[0009]

EXAMPLES Next, the method of the present invention will be specifically described by way of Examples. Six types of pure Al plate materials (hereinafter referred to as conventional pure Al plate materials a to
(hereinafter referred to as “f”), and each of these conventional pure Al plate materials a to f is subjected to a heat treatment under the conditions shown in Table 1, and then the same thickness is also shown in Table 1 using an ordinary etching solution. The present invention methods 1 to 6 were carried out by removing the surface portion, and the present invention pure Al plate materials A to F having the impurity contents shown in Table 2 were manufactured.

[0010]

[Table 1]

Next, various pure Al plate materials obtained as a result were subjected to a salt spray test for 168 hours, and the number of pitting corrosion per unit area and the maximum pitting depth were measured. The measurement results are shown in Table 2.

[0012]

[Table 2]

[0013]

From the results shown in Tables 1 and 2, the reduction of Si, Fe, and Cu contained as impurities in the present invention methods 1 to 6 is slight, but Sn and P are the same.
b, In, and Ga can be significantly reduced, and the total content of these four components can be reduced from 20 ppm or more to 10 ppm or less. As a result, the pure Al plate material has excellent pitting corrosion resistance. It is clear that As described above, according to the method of the present invention, in particular, Sn, Pb, In, and G contained as impurities in the pure Al plate material are contained.
It is possible to reduce the total content of a to 5 ppm or less, which significantly improves the pitting corrosion resistance of the pure Al plate material, which leads to industrially useful effects such as further thinning. Is done.

Claims (1)

Claim: What is claimed is: 1. A total amount of one or more of Sn, Pb, In, and Ga of 20 ppm or more is contained as an impurity.
And a pure Al plate material having a plate thickness of 300 μm or less and a purity of 99.8% or more is subjected to a heat treatment in a non-oxidizing atmosphere at a predetermined temperature in the range of 300 to 580 ° C. for a predetermined time, The impurities are diffused and moved to the surface, and then the aggregated surface of impurities in the pure Al plate after the heat treatment is removed to reduce the total content of the impurities in the pure Al plate to 5 ppm or less. Method for reducing impurities in pure Al plate material.