JPS635475B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to aluminum or aluminum alloy members for obtaining aluminum products with excellent water wettability and corrosion resistance. Aluminum and its alloys (hereinafter referred to as aluminum) have a low density, improve corrosion resistance with appropriate surface treatment, and have excellent electrical and heat transfer performance, so they are used not only as construction materials and aircraft materials, but also in heavy industrial products and general households. As is well known, it is widely used for supplies and the like. In particular, its excellent heat transfer and light weight properties lead to reduced product weight and energy savings, so its use is likely to continue to expand in the future. One field of use in this field is heat exchanger tubes and associated fins, and many of them are already in practical use. Generally, heat exchanger tubes (hereinafter also referred to as fins) used in the atmospheric environment are corroded by the action of moisture, sea salt particles, and acid gases such as NOx and SOx contained in the environment, so the surface It is common to use some method of surface treatment to improve corrosion resistance. However, the method of applying a thick layer of paint is useful for improving corrosion resistance, but is not preferable for products where heat transfer is important, and treatment with various chemical solutions containing chromic acid or dichromate is usually performed. There is. However, these methods do not exhibit sufficient performance as anticorrosive treatment for heat exchanger tubes for the following reasons. In other words, long-term corrosion resistance cannot be expected with any chemical conversion treatment unless painting is also used. In a temperature environment where moisture condenses on the heat exchanger tubes, the shape of the condensed water adhesion has a great effect on heat transfer characteristics, the composition of the corrosive environment, and the comfort of the usage environment, as shown below. When the condensed water adheres in droplets, if the flow velocity of air flowing on the surface becomes large, a phenomenon occurs that is accompanied by this, and problems occur on the downstream side due to the scattering of cold water. Although this phenomenon does not occur when condensed water adheres in the form of a film, the contact area between the water and the pipe becomes larger, which increases the supply of corrosive components in the atmosphere, which prematurely deteriorates the corrosion resistance life of the chemical conversion film. In order to compensate for this drawback, a method has been implemented in which a hydrophilic compound containing an alkali metal compound (e.g. Na ₂ SiO ₃ ) is applied to the chemically treated surface; occurs, and as the period of use increases, it gradually wears out (wears out as condensed water leaves),
There is a drawback that the effect is lost. The above-mentioned phenomena are not desirable for heat exchangers (especially for air conditioning), but there are some problems such as improving performance will degrade performance, and improving performance will inevitably lead to other phenomena. There is a cycle. Therefore, with the current technology, no method has been found to solve both problems simultaneously over a long period of time. As a method of imparting corrosion resistance other than the above-mentioned chemical conversion treatment,
A method is known in which a thin layer of zinc is diffused into the surface of aluminum, but this method causes the above-mentioned problem. In addition, for aluminum parts used in areas where heat transfer is not a problem, the surface is painted after anodizing (alumite treatment), but this method It cannot be used for exchanger tubes because of its poor heat transfer properties. Furthermore, there is a known method of improving the corrosion resistance of the oxide film by immersing it in an aqueous solution of chromate or sodium silicate and heating it after anodizing treatment. This treatment attempts to improve corrosion resistance by passivating the porous oxide film using the oxidizing power of chromic acid and filling the pores with silicate. Even if this method is used, sufficient corrosion resistance cannot be expected. In addition, after the anodized film is formed, it is immersed in boiling water or exposed to steam to form aluminum hydrate in the pores by the action of moisture, filling the pores (usually with sealing treatment). ) has also been put into practical use. Although it exhibits superior corrosion resistance compared to those without sealing treatment, this treatment alone is not sufficient. If corrosion resistance is insufficient, this type of aluminum material will develop white rust (mainly composed of hydrated aluminum), and condensed water will form droplets in such areas, causing further problems. The inventors of the present invention aim to develop a cooling (heating) unit for indoor and vehicle use that has high performance, high corrosion resistance, and excellent livability, and provides an aluminum product that has excellent corrosion resistance and water resistance. As a result of repeated research, we focused on anodic oxide coating as a corrosion-resistant treatment for aluminum, and developed a method to improve transmission by filling a hydrophilic and corrosion-resistant compound into the coating by making use of its numerous pores. The present invention was achieved by discovering that it is possible to impart excellent performance in both water wettability and corrosion resistance without impairing thermal properties. That is, the present invention provides an aluminum or alloy member thereof, which has an oxide film formed on its surface by anodic oxidation, and the pores of the film are filled with a zinc-silicon compound. It has an oxide film formed on its surface by anodic oxidation, the pores of the film are filled with a zinc-silicon compound, and the pores further hold dichromate or chromate. It relates to aluminum or its alloy members. The present invention will be explained in detail below. Aluminum is electrolyzed as an anode in an aqueous solution of oxalic acid, chromic acid, sulfuric acid, etc. to form an oxide film on its surface. This film has countless pores with a diameter of about 100 to 500 Å, so it has the disadvantage of poor corrosion resistance if left as is. In the present invention, the purpose is achieved by filling the pores with a compound that is highly corrosion resistant and hydrophilic. First, the pores are filled with a silicon compound containing zinc, and then water is evaporated. As a result, the silicon compound containing zinc present in the pores becomes gel-like and is immobilized therein. A silicon compound containing zinc fills the inside of the pores to physically prevent the intrusion of solid foreign matter, and when condensed water adheres, releases zinc ions to suppress the corrosive nature of water. On the other hand, in the known silicon treatment that does not contain zinc, the silicon compound exists in the form of a gel, so it has adsorption properties, and if water adheres to it, it has a strong tendency to retain it. A corrosion reaction occurs and corrosion resistance deteriorates. Examples of the zinc-containing silicon compound used in the present invention include metal zinc or zinc oxide powder added to a sodium silicate aqueous solution, and a combination of an organosilicon compound such as methyl silicate and a zinc-containing caustic soda or a sodium silicate aqueous solution. In this case, the aluminum is treated with an organic silicon compound and then immersed in a caustic soda or sodium silicate aqueous solution containing zinc. Babok, potassium silicate,
Lithium silicate, amine silicate, etc. can also be used. In the present invention, after filling the pores of the oxide film with a silicon compound containing zinc as described above, it is preferably dried, and then further immersed in a chemical conversion treatment solution containing chromate or dichromate. Corrosion resistance can also be further increased. In this case, the silicon compound containing zinc present in the pores becomes a gel and is fixed therein, and also acts to adsorb chromate or dichromate, and due to the coexistence of the two, each can act independently. It exhibits far greater corrosion resistance than other sealing treatments. That is, the silicon compound containing zinc fills the inside of the pores to physically prevent the intrusion of solid foreign matter, and has the effect of adsorbing dichromate. Therefore, when condensed water adheres, zinc ions are released to suppress the corrosivity of the water, and chromic acid, which exhibits hydrophilicity, is released to form a film of adhered water to improve its water-wetting performance. On the other hand, chromate or dichromate improves its wettability against moisture intrusion and prevents the corrosion caused by moisture, but it is strongly physically adsorbed by silicon compounds containing zinc. A large amount of it is contained in the pores, and its action continues for a long period of time. Examples of chromate or dichromate include sodium chromate, potassium chromate, sodium dichromate, potassium dichromate, etc., and they may also be used in a neutral state, meaning that chromium is Cr ³ It is necessary to be ionized in ^{the +} and C ⁶⁺ states. Note that Cr ⁶⁺ has a greater oxidizing power (passivity effect) than Cr ³⁺ . In the present invention, after the silicon compound containing zinc is impregnated into the oxide film, it is preferably heated to a temperature of 100°C or higher to volatilize the moisture. It is possible to prevent the phenomenon in which particles are fixed in the pores and re-eluted during subsequent dichromic acid treatment. or
It is also effective to use a steam atmosphere for heating to 100°C or higher. The present invention is effective when applied to aluminum heat exchangers and aluminum products in general. Examples The aluminum materials used were five types of alloy numbers 1050, 2014, 3003, 5005, and 7075 according to the JIS H4000 (1982) standard, and each was cut into dimensions of width 50 x length 100 x thickness 1 mm. Table 1 shows the types and conditions of surface treatments carried out to examine the effects of the present invention, as well as existing surface treatments used for comparison. Further, details of the processing method of the present invention are as follows. (1) Add 1 to 5% of finely powdered metal zinc or zinc oxide powder to a 5 to 10% sodium silicate aqueous solution and heat. The hydrogen ion concentration of the sodium silicate aqueous solution is controlled by caustic soda or sodium carbonate, but the solution exhibits clarity when the SiO ₂ /Na ₂ O molar ratio in the solution is up to the 5th position. However, when this is pulled up and dried, a silicic acid compound is precipitated. Also, as the molar ratio increases
SiO ₂ becomes a colloid and is suspended in the solution.
When the temperature rises further, it becomes sol-like or gel-like. When zinc is present in such an environment, zinc adheres to the silicic acid sol or gel as a type of hydrate, producing a sol or gel-like substance that is a mixture of the two. Naturally, the SiO ₂ /Na ₂ O molar ratio is 5.
Even in the following cases, the silicic acid compound will contain zinc when pulled out of the solution. The present invention involves filling the pores of an anodic oxide film with such a silicic acid compound containing zinc and then heating it in the presence of moisture;
Alternatively, after drying in a moisture-free environment, the material may be treated in a dichromate or a chemical solution containing chromate. Note that when heated in the presence of moisture, in addition to the impregnated silicon compound containing zinc, the aluminum itself becomes a hydrate and fills the pores, which has the effect of improving the packing density. (2) When an anodized specimen is immersed in an organic silicon compound such as methyl silicate, methyl silicate easily penetrates into the pores because of its low surface tension. When the test piece is then pulled up, the organic matter is evaporated and a fine powder of silicon oxide remains. Therefore, it is possible to achieve the objective by immersing this test piece in a caustic soda aqueous solution containing zinc or in the above-mentioned (1) sodium silicate containing zinc.

[Table] Notes: ◎: No abnormality, ○: Discoloration but no white rust, △: White rust, ×: White rust and pitting corrosion
Occurrence The effectiveness of the present invention was evaluated as follows. (1) Salt spray test: Tested continuously for 1000 hours using the method specified in JIS Z2371. (2) Observation of water wetness: Immediately after surface treatment,
This was carried out using the apparatus shown in the figure. That is, ion-exchanged water 2 is placed in a glass flask 1 and heated by a heater 3. As water vapor 2 boils, water vapor is generated, which is introduced into a test specimen mounting box 5 made of aluminum through a thin glass tube 4 kept warm. A test piece 6 is installed in close contact with the wall surface of a mounting box 5 at a position opposite to the mounting portion 4, and the wall surface of the mounting box is cooled by pouring water 7 from the outside. As a result, the water vapor generated from 4 condenses 8 on the surface of the test piece, and as this amount gradually increases, it falls downward. After 1 hour of condensation time, the test piece is removed from the mounting box and left at room temperature. After repeating the 3-hour drying cycle 20 times, the state of adhesion of water droplets to the test piece was observed. The appearance of the test pieces after the salt spray test was investigated and the corrosion resistance of each test piece was determined. The results are shown in Table 1. As a result, among the comparative products, test specimen F treated with 1050 showed relatively good corrosion resistance, but white rust and local pitting corrosion were observed in the other specimens. In contrast, no abnormalities were observed in all treatments of the present invention. Treatments such as C that is simply anodized, D that is immersed in boiling water and the pores are filled with aluminum hydrate, E that is filled with water glass, and F that is immersed in dichromic acid for materials other than 1015. All of the specimens treated with this method exhibited white rust and sometimes pitting corrosion. Next, the results of the water wetness investigation are shown in Table 2. Only 1050 material was used for this test.

[Table] As is clear from the results, it was found that the products of the present invention exhibited extremely good water wetting performance not only immediately after treatment but also after conducting a long-term dew condensation test. In comparison, although comparative products made by existing technology have relatively good corrosion resistance, they have poor water wettability and there is no product that has both of these properties. These results also revealed that the treatment of the present invention was hardly affected by the type of material tested, and good corrosion resistance and water wettability could be obtained. As an effect of the present invention, after anodizing in 5% sulfuric acid and 3% chromic acid, secondary treatment and tertiary treatment were performed according to the steps in Table 1. Performance tests were conducted. In addition, in this test, a test was also conducted in which sodium chromate was used instead of sodium dichromate. 3003 was used as the test material in this test, and the results are shown in Table 3. Good corrosion resistance and water wettability were observed in all cases. It has been found that using chromic acid instead of acid is also effective.

[Table] Furthermore, in order to determine the effect of zinc in the treatment of the present invention, a salt water spray test similar to that described above was carried out on specimens immersed in a sodium silicate solution containing no zinc. The results are shown in Table 4, and showed much better corrosion resistance than those containing no zinc.
This effect is thought to be due to the improvement of the anticorrosion effect due to the inclusion of zinc, and the effect of making the effect effective even during the passivation treatment with dichromate carried out during the tertiary treatment. In other words, a portion of the zinc in the pores forms zinc chromate, which has excellent anticorrosion properties, by treatment with dichromic acid. Furthermore, the results of a water wetting performance test for the treatment of the present invention shown in Table 4 showed good results, similar to the results of the present invention shown in Table 2.

【table】

[Table] Notes: ◎: No abnormality, ○: Discoloration but no white rust, △: White rust occurred, ×: White rust and pitting corrosion occurred.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a test apparatus used to examine the water wettability of aluminum products according to the present invention.

Claims (1)

[Scope of Claims] 1. An aluminum or aluminum alloy member having an oxide film formed on its surface by an anodic oxidation method, the pores of the film being filled with a zinc-silicon compound. 2 It has an oxide film formed on its surface by anodic oxidation, the pores of the film are filled with a zinc-silicon compound, and the pores further hold dichromate or chromate. , aluminum or its alloy members.