JPH0114989B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for manufacturing an aluminum alloy material for galvanic anodes with high current efficiency. Prior art An electrochemical technique in which a galvanic anode made of a metal with a greater ionization tendency than the metal is electrically connected to a metal structure to be protected against corrosion, and corrosion of the metal structure is inhibited by the corrosion of the galvanic anode. Corrosion prevention techniques are well known. It is well known that aluminum is suitable as a material for such galvanic anodes because it is lightweight, generates a large amount of electricity per unit weight, and has an inherently base electrode potential and can extract a large anticorrosion current. This is where I am. However, since aluminum forms a corrosion-resistant oxide film on its surface, it is unsuitable as a galvanic anode. For this purpose, elements such as zinc, tin, indium, lead, magnesium, boron, and mercury have been added singly or in combination to reduce the ability to form an oxide film and to make the corrosion potential less noble. In this regard, various aluminum alloy compositions suitable for manufacturing galvanic anodes have been developed, proposed, and put into practical use. By the way, when the various elements mentioned above are added to aluminum, the resulting alloy generally tends to increase self-corrosion. Therefore, as mentioned above, it is not possible to simply focus on improving the characteristics required for a galvanic anode based on the aluminum alloy composition.
There are limits to its improvement. In other words, in order to improve the characteristics of a galvanic anode, it is necessary to reduce the size of the crystal grains and reduce the segregation of intermetallic compounds between the crystal grains so that not only the alloy composition but also the metal structure contributes to improving the characteristics. It is necessary to consider manufacturing technology such as minimizing the Moreover, a highly productive method is desired. OBJECTS OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide a preferred method for producing an aluminum alloy material for a galvanic anode, which exhibits less self-corrosion, uniform melting, and excellent current efficiency. Structure of the Invention In the process of repeating numerous experiments in order to improve the current efficiency of galvanic anode materials, the present inventors discovered that by simply heat-treating a cast body, which had conventionally been treated exclusively as galvanic anode material, They found that the current efficiency as a galvanic anode material was even more markedly improved than that of the conventional technology by applying hot processing. As a result of various studies aimed at improving current efficiency, it was discovered that an even more significant improvement in current efficiency could be obtained by rapidly cooling after hot working.Based on these new discoveries, the present invention was developed. I was able to complete it. The manufacturing method according to the present invention is an aluminum alloy containing at least one element such as zinc, tin, indium, etc., which is dissolved in aluminum to make the anode potential more base and reduce the ability to form an oxide film. A method for producing an aluminum alloy material for a galvanic anode, in which a molten metal is cast by a semi-continuous casting method to produce a cast body, and the cast body is heat treated for homogenization, the cast body subjected to the heat treatment. The method is characterized in that it includes the steps of rapidly cooling the hot-worked product immediately after hot-working the product. More specifically, in the method according to the present invention, an alloy is used in which appropriate elements are added to aluminum from a compositional point of view in order to obtain the properties desired as a galvanic anode. In order to manufacture a current electrode that can maximize the desired properties with high efficiency, from the viewpoint of structure, semi-continuous casting is performed to obtain a cast body, and the cast body is subjected to homogeneous heat treatment and then hot working. Furthermore, it is characterized by rapidly cooling the material immediately after hot working. Embodiment To explain an embodiment of the manufacturing method according to the present invention, for example, as an aluminum alloy, AL-
Use Zn-based alloy. The amount of Zn added in this alloy is approximately 0.1 to 20% by weight. This zinc Zn
It is known that aluminum alloy has the function of increasing the dissolution rate of the oxide film formed on the surface of the aluminum alloy and shifting its natural potential in the less noble direction. If the content is less than 0.1% by weight, the self-potential will be insufficient for use as a current electrode, while if the content exceeds 20% by weight, the theoretical amount of electricity generated by zinc itself will be small compared to aluminum. Therefore, the amount of electricity generated per unit weight decreases, and manufacturing and processing of the galvanic anode becomes difficult, which is not preferable. Of course, in addition to this, for example, by adding about 0.001 to 0.1% by weight of titanium, about 0.0002 to 0.02% by weight of boron, etc., the effect of making the crystals finer can be obtained. Furthermore, other suitable elements can also be added. In the method according to the invention, such an aluminum alloy is first melted and a billet or slab is cast by a semi-continuous casting process. This semi-continuous casting method is a method in which the molten metal is solidified by passing through a water-cooled mold, and a continuous cast body, ie, a billet or slab, is produced while being cooled by a water jet. The crystal grains of billets or slabs cast in this manner are about 0.1 to 0.5 mm, which is much smaller than, for example, about 1 to 5 mm when mold casting is used, which is a conventional method. In the method according to the invention, the billet thus obtained is subjected to a homogenization heat treatment. Of course, the billet can also be cut to a suitable length in advance. In this homogenization heat treatment, for example,
Heat and hold at a temperature of about 300 to 630°C for 10 minutes to 48 hours. By this treatment, the above-mentioned additive elements are almost uniformly dispersed and homogenized. Next, the homogenized cast body is subjected to an extrusion processing machine or a rolling processing machine to produce a material for a galvanic anode or a plate material for a galvanic anode having a predetermined cross-sectional shape. In the aluminum alloy material obtained by this hot working, it is observed that the crystal grains are in the form of a fibrous structure of about 0.3 mm or less or a very fine recrystallized structure. The hot-processed aluminum alloy material is immediately quenched. This rapid cooling is performed in order to increase the amount of solid solution of the added element. Possible methods for rapid cooling include passing the aluminum alloy material immediately after hot processing into a cooling water tank placed adjacent to it, applying a shower of cooling water, and even spraying cooled gas. is not limited to this method. That is, any suitable method can be used. Here, rapid cooling means that the temperature of the aluminum alloy material is raised to approximately 150℃ within approximately 10 seconds.
Cool to below (temperature immediately after hot processing is approximately
600℃). Of course, there are no particular restrictions on this cooling as long as it is quick. It has been found that this rapid cooling is extremely effective for increasing the solid solution amount of tin and indium, for example. Effects of the Invention The aluminum alloy material obtained by the method described above has a composition selected so as to exhibit favorable characteristics as a galvanic anode, and also has an increased amount of solid solution of additive elements due to the characteristics of the manufacturing method, and has a crystalline structure. It was confirmed that because the grains are fine, it exhibits extremely high current efficiency. Moreover, if extrusion processing is used, the material for long current electrodes can be easily made.
You can get great benefits such as high productivity. Further, cooling immediately after extrusion can be achieved by simple means. Test Example Table 1 shows the measurement results of current efficiency of aluminum alloy materials manufactured by the manufacturing method of the present invention and the conventional method as described above. In addition, the manufacturing method of the present invention is to form a billet of 203 mmφ from molten aluminum alloy by a semi-continuous casting method,
This billet was heated at 480°C for 4 hours to undergo homogenization heat treatment, and then extruded into square pieces with a cross section of 20 x 20 mm, which were divided into two types: those that were rapidly cooled immediately after extrusion and those that were air-cooled without rapid cooling. . This rapid cooling was done by passing the square pieces through a cooling water tank, which cooled them down to about 150°C in about 1 second. The conventional method involves casting a molten aluminum alloy into a cast body with a cross section of 20 x 20 mm.
The samples were divided into those that were heated at 480°C for 4 hours and then rapidly cooled, and those that were air cooled without rapid cooling. The composition and current efficiency are shown in Table 1.

[Table] The current efficiency was calculated using the following formula specified in the ``Current Anode Test Method'' of the 97th Committee of the Japan Society for the Promotion of Science, Cathodic Protection Division 12. Current efficiency (%) = Quantity of electricity (A・hr)×100/Anode weight loss (g)×Theoretical amount of generated electricity (A・hr/g) From the results in Table 1, it can be seen that It is clear that the current efficiency obtained by this method is far superior to that of the conventional method.

Claims (1)

[Scope of Claims] 1. A molten aluminum alloy containing at least one element such as zinc or indium that is dissolved in aluminum and is effective in making the anode potential less noble and reducing the ability to form an oxide film. A method for producing an aluminum alloy material for a galvanic anode, which comprises casting a cast body by a semi-continuous casting method, and subjecting the cast body to heat treatment for homogenization, the heat-treated cast body being hot worked. . A method for producing an aluminum alloy material for a galvanic anode, comprising the steps of: quenching the material immediately after hot working. 2. The method for producing an aluminum alloy material for a galvanic anode according to claim 1, wherein the hot working is extrusion processing. 3. In order to rapidly cool the processed material immediately after extrusion in the extrusion process, a cooling liquid tank is disposed adjacent to the rear of the extruder, and the extruded material is passed through the cooling tank. A method for producing an aluminum alloy material for galvanic anodes.