JPH0418021B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an aluminum alloy for galvanic anodes that has an appropriate electrode potential for galvanic corrosion protection of steel structures and has excellent current efficiency. (Prior Art) Steel structures, especially those used in marine environments such as ship hull structures, port structures, oil drilling jackets, pipelines, etc., are susceptible to electrochemical reactions due to contact with seawater, etc. Prone to corrosion. In order to prevent such corrosion in steel structures, it is generally necessary to electrically connect a metal that is less electrochemically base than the steel structure and use it as an anode to protect the steel structure. A so-called galvanic corrosion protection method is used. The anode metal used in this galvanic corrosion protection method is electrochemically less noble than that of steel structures, so that it has less performance deterioration over a long period of time and can reliably and stably exhibit a corrosion protection effect. It is desirable to have a material that has low self-corrosion and no reduction in current efficiency due to adhesion of self-corrosion products to the anode alloy, that is, can continuously maintain high current efficiency. Aluminum has a large electrochemical equivalent and is a less electrochemically base metal than steel, so it can be said to be suitable as a metal for this type of galvanic anode, but the oxidation that forms on the aluminum surface The film is dense and has strong internal protective power, and even if it is used as a galvanic anode alone, it is difficult to obtain a sufficiently base potential and the current efficiency is low, so it cannot be used for corrosion protection of steel structures. do not have. Therefore, various aluminum alloys for galvanic anodes have been proposed in which the anode potential and current efficiency are improved by adding elements such as zinc, indium, gallium, cadmium, and mercury to aluminum in various proportions. (Problems to be Solved by the Invention) However, among the aluminum alloys for galvanic anodes proposed so far, those containing cadmium and mercury are unfavorable from an environmental standpoint, and Al-Zn- which does not contain these elements In-based alloys, Al-Zn-Ga-based alloys, Al-Zn-In-Ga-based alloys, etc. exhibit favorable corrosion protection effects on steel structures by appropriately adjusting the content ratio of alloy additive elements. It is said that. Although it is possible to obtain an anode potential of around -1100mV, the amount of self-corrosion is large and uniform solubility is lacking, and some of the corrosion products adhere to the surface of the anode alloy, resulting in a stable current flow over a long period of time. As the current efficiency is low at less than 90%,
It could not be said that it had sufficient performance as a practical alloy. (Means for Solving the Problems) The inventors conducted various studies in order to solve the problems with the conventional aluminum alloys for galvanic anodes described above, and as a result, they discovered that one or both of indium and gaium was used. An aluminum-zinc alloy in which manganese and titanium are added at the same time not only exhibits an appropriate anode potential suitable for corrosion protection of steel structures, but also exhibits less self-corrosion and a reduced amount of corrosion products adhering to the anode alloy. A high current efficiency of 90% or more can be obtained continuously over a long period of time even if the amount of corrosion is reduced.Also, alloys in which yttrium, rare earth elements, etc. are further added to this alloy have even less adhesion of corrosion products, resulting in even higher current efficiency. The present invention was completed based on the discovery that the following could be obtained. That is, the present invention contains more than 1.0% zinc by weight and 10% zinc by weight.
Contains manganese over 0.01% up to 1.0%, titanium over 0.05% up to 0.50%, and indium over 0.005% up to 0.1%, or gallium.
more than 0.005% up to 0.1%, or within the above range,
An aluminum alloy for galvanic anodes used for corrosion protection of steel structures, containing both of them up to a total of 0.15%, and the balance consisting of aluminum and impurities, and the above alloy further containing yttrium exceeding 0.005% and up to 0.5%.
1 of rare earth elements exceeding 0.005% and up to 1.0%
This is an aluminum alloy for galvanic anodes used for corrosion protection of steel structures, containing one or more species. (Function) According to the present invention, for corrosion protection of steel structures,
In addition to obtaining the necessary and sufficient anode potential, local dissolution of the anode alloy, formation of local batteries, and partial adhesion of corrosion products to the alloy surface are prevented, resulting in high current efficiency and stable durability. An excellent aluminum alloy for galvanic anodes for steel structures can be obtained. Next, the addition of alloy components in the aluminum alloy for galvanic anodes of the present invention and the reasons for their limitations will be explained. The content of zinc in excess of 1.0% and up to 10% activates the aluminum substrate and lowers the anode potential, as well as imparts uniform solubility to the alloy and improves current efficiency. When is less than the lower limit, the effect is not sufficient, and when it exceeds the upper limit, the amount of self-corrosion increases and the current efficiency decreases. The most preferred zinc content range is 2.0
~8.0%. The content of indium or gallium in an amount exceeding 0.005% and up to 0.1% each has the effect of activating aluminum, lowering the anode potential, and improving the anticorrosion effect on steel structures, similarly to zinc. In particular, the addition of indium has the effect of preventing corrosion products from adhering to the anode alloy surface and improving the uniform solubility of the alloy. If the content is below the lower limit, the effect will not be sufficient, and if the indium content exceeds the upper limit, local corrosion will easily occur in the alloy, and if the gallium content exceeds the upper limit, pitting corrosion will occur in the alloy. This is not desirable in any case. When indium and gallium are added together, their effects are additive and often produce good results, but in this case, their total content is 0.15
If it exceeds 0.1%, indium and gallium will segregate, causing local corrosion in the alloy and reducing current efficiency, so it is desirable to keep the total content below 0.15%. The content of manganese exceeding 0.01% and up to 1.0% is
Iron contained as an impurity in the alloy reacts with the substrate aluminum to change the form of the intermetallic compound Al ₃ Fe, reducing the harmful effects of local battery formation that occurs between this Al ₃ Fe and the substrate, and titanium. Coupled with the addition of , it promotes the dispersion and precipitation of indium and gallium in the matrix, reduces self-corrosion and reduces the amount of self-corrosion products attached to the anode alloy, improving the current efficiency of the alloy. It has a contributing effect. If the content is below the lower limit, the effect will be small, and if it exceeds the upper limit, the anode potential of the alloy will shift significantly to the noble side, reducing the potential difference with the steel structure, resulting in a decrease in the generated current, and the steel structure Reduces the anti-corrosion effect on objects. The content of titanium exceeding 0.05% and up to 0.50% imparts uniform solubility to the alloy, and together with the addition of manganese, reduces self-corrosion of the alloy and reduces the amount of self-corrosion products attached to the anode alloy. , which contributes to improving current efficiency, has little effect if its content is below the lower limit, and if it exceeds the upper limit, giant crystals such as Al ₃ Ti are generated, which damage the alloy matrix and the local battery. In addition to impairing the homogeneous solubility of the alloy, it also causes the potential of the alloy to shift significantly toward the noble side, which is undesirable in terms of corrosion prevention. From this standpoint, it is desirable to suppress the total content of manganese and titanium to 1.2% or less. Note that addition of either manganese or titanium alone is not sufficient to reduce the adhesion of self-corrosion products of the alloy to the anode alloy, and it is necessary to add and contain both at the same time. Furthermore, in the first invention alloy of the present invention, yttrium is added in excess of 0.005% to 0.5%, and rare earth elements are added in an amount of 0.005% to 0.5%.
The addition of one or more of the above % to 1.0% has the effect of promoting uniform solubility and reducing self-corrosion of the first invention alloy, and further improving the current efficiency of the alloy as a galvanic anode. If the content is below the lower limit, the effect will not be sufficient, and if it exceeds the upper limit, these elements will segregate and reduce current efficiency. Therefore, when adding two or more of these elements, the total amount should be
It is desirable to keep it below 1.2%. Rare earth elements are a group of elements that belong to Group 3 of the periodic table of elements, including lanthanum, cerium, praseodymium, neodymium, etc., but these elements can be added alone or in combination with two or more of these elements. It's okay. Furthermore, the so-called Mitsushi metal, which is generally commercially available as a mixture of these elements, is easily available and inexpensive, so it is economical to use it as it is. The aluminum alloy for galvanic anodes of the present invention is used as a cast product, or after being processed into a suitable shape. Any known casting method and processing method may be used. (Example) Alloys with various compositions shown in Table 1 were melted and cast into a round bar with a diameter of 20 mm and a length of 200 mm using die casting, and the round bar was coated with 20 cm ² of the side surface exposed. The anode potential and current efficiency of each sample were measured, and the results are shown in the same table. In addition, the state of corrosion product adhesion on the sample surface was visually observed, and the results are also shown. When melting the alloy, rare earth elements were added using commercially available Mitsushi Metal (composition: 50% Ce,
La 45%, Pr, Md balance (indicated by MM in Table 1) was used. The test conditions for the anode samples were as follows. Immersion liquid: 1000 ml of artificial seawater in a static state at room temperature Cathode: Stainless steel plate with a surface area of 430 cm ² Distance between electrodes: 35 mm Anode current density: 1 mA/cm ² Electrolysis time: 240 hours

【table】

[Table] From the results in Table 1, the aluminum alloys for galvanic anodes of the present invention are the first invention alloy (sample Nos. 1 to 7),
The anode potential of the second invention alloys (sample Nos. 8 to 14) is −1100 mV, which is an appropriate value for steel structures.
Compared to comparative alloys (Samples No. 15 to 18) and conventional alloys (Samples No. 19 to 21), the amount of corrosion products adhering to the alloy surface is small, the uniform solubility is excellent, and the current efficiency is It turns out that it is also high. (Effects) As described above, the aluminum alloy for galvanic anodes of the present invention has an appropriate anode potential for steel structures, has a small amount of corrosion products adhering to the alloy surface, and has uniform solubility. In addition to this, it also has extremely high current efficiency, making it suitable as a galvanic anode material for steel structures, especially marine structures.

Claims (1)

[Claims] 1 Contains, by weight, more than 1.0% of zinc up to 10%, more than 0.01% of manganese up to 1.0%, more than 0.05% of titanium up to 0.50%, and furthermore 0.005% of indium.
or more than 0.005% and up to 0.1% gallium, or both in the above range up to a total of 0.15%, with the balance being aluminum and impurities. Aluminum for galvanic anodes used for corrosion protection of steel structures. alloy. 2 Contains zinc from 1.0% to 10%, manganese from 0.01% to 1.0%, titanium from 0.05% to 0.50%, and indium 0.005% by weight.
or more than 0.1% of gallium, or more than 0.005% of gallium up to 0.1%, or both in the above range up to a total of 0.15%, with the balance consisting of aluminum and impurities, and further 0.005% of yttrium.
exceeding 0.5% and rare earth elements exceeding 0.005% 1.0
An aluminum alloy for galvanic anodes used for corrosion protection of steel structures, containing one or more of the following.