JPH10140372A - Corrosion resistant film in aluminum based substrate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a corrosion resistant film good in corrosion resistance in an alkaline using environment at a low cost, one an aluminum based substrate, by laminating and forming a boehmite film and an inorganic film in this order. SOLUTION: The surface of an aluminum bared substrate 1 is brought into contact with hot water, heated steam or the like, and boehmite forming treatment is executed to form a boehmite film 3 having about 0.2 to 100μm thickness. Next, a sol soln. of metallic alkoxide is brought into contact with the boehmite film 3, which is allowed to be gelatinized, and an inorganic film 5 having about 0.01 to 10μm thickness is formed to be laminated on the boehimite film 3. In the case an aluminum board heat exchanger is applied as the aluminum bosed substrate 1, the boehmite forming 3 and the inorganic film 5 are laminated and formed on the face of the side in contact with a coolant in the heat exchanger, by which the corrosion of the heat exchanger can effectively be prevented even if the coolant deteriorates and is made alkaline.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion-resistant coating on an aluminum base and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Laying-Open No. 52-35358 discloses an aluminum radiator in which an aluminum fin is welded to an aluminum tube, and thereafter,
A technique for performing boehmite treatment is disclosed. Aluminum radiator replaces conventional brass radiator,
In recent years, attention has been paid to reducing weight and regulating the use of lead.

[0003] Japanese Patent Application Laid-Open No. Sho 62-13581 discloses a technique for laminating a cathodic protection layer, a boehmite film, and an organic film in this order on the inner surface of the peripheral wall of an aluminum heat absorption tube in a heat exchanger for a bath pot. It has been disclosed. In this publication, a silicon-modified phenol resin, a silicon-modified epoxy resin, and an epoxy-modified silicon resin are employed as the organic coating film.

Further, the magazine "Materia" (Vol. 34, No. 10, 1995), pages 1185 to 1187, published by:
According to the Japan Institute of Metals, an aluminum anodic oxide film is formed by alumite treatment, and then a sol solution containing Zr alkoxide is used to form a thin film of Zr oxide on the aluminum anodic oxide film by a sol-gel method. There is disclosed a technique for improving the alkali corrosion resistance thereby.

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No.
According to the technique according to 35358, corrosion resistance can be expected if the pH of the solution in contact with the aluminum base is about 4 to 9. However, considering that aluminum is an amphoteric metal that dissolves in both acids and alkalis, corrosion resistance is not always required when it is used in areas where highly acidic solutions come into contact, and where areas with highly alkaline solutions come into contact. Not satisfactory.

In particular, in the case of an aluminum heat exchanger such as a radiator, a coolant which tends to be alkaline when deteriorated may be employed, and in some cases, the deteriorated coolant becomes alkaline having a pH of 9 or more. There is also. When the coolant becomes alkaline in this way, there is a limit in securing the corrosion resistance of the aluminum base constituting the heat exchanger.

Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. Sho 62-13581, although an organic coating is laminated on a boehmite coating, the organic coating is generally weak to alkali.
Therefore, when used at a site where a solution having a high alkalinity comes into contact, the corrosion resistance is not always satisfactory. Further, in the technique according to the magazine "Materia", since an aluminum anodic oxide film is formed and a Zr oxide is laminated on the aluminum anodic oxide film by a sol-gel method, corrosion resistance can be expected. However, in the case of forming an aluminum anodic oxide film by alumite treatment, it tends to be disadvantageous in terms of equipment and cost because an acid such as sulfuric acid, oxalic acid or chromic acid is used as a treatment liquid. Therefore, it is not always sufficient in terms of industrialization where cost reduction is strongly required.

The present invention has been made in view of the above circumstances, and has a good corrosion resistance in an alkaline use environment, and is advantageous in terms of equipment and cost, and a method of manufacturing the same in an aluminum base. Is to provide.

[0009]

According to a first aspect of the present invention, there is provided a corrosion-resistant coating on an aluminum-based base, wherein a boehmite-formed boehmite coating and an inorganic coating are laminated on the aluminum-based base in this order. is there.
The corrosion-resistant film in the aluminum-based base according to claim 2 is, in claim 1, wherein the aluminum-based base is constituted by an aluminum-based heat exchanger, and the boehmite film and the inorganic film are formed by a coolant in the heat exchanger. It is characterized in that it is laminated on the surface on the contact side.

According to a third aspect of the present invention, there is provided the corrosion-resistant film in the aluminum base according to the first aspect, wherein the inorganic film is made of zirconium (Zr), silicon (Si), calcium (C
a) an oxide containing at least one of the above a). The method for producing a corrosion-resistant film on an aluminum-based base according to claim 4 is a step of boehmite-treating the exposed surface of the aluminum-based base and providing a boehmite film having at least the exposed surface boehmite; zirconium (Zr) and silicon (Si). ), Calcium (C
a) contacting a sol solution of a metal alkoxide containing at least one of a) with a boehmite film to gel the sol solution to form an inorganic film.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum base includes a base made of aluminum metal and a base made of an aluminum alloy. Boehmite film is a film made of boehmite,
Or it means a film mainly composed of boehmite. Boehmite is an alumina hydrate (Al ₂ O ₃ .H ₂ O). Boehmite is generally formed by a process of bringing at least one of hot water and heated steam into contact with an aluminum base.

The aluminum-based base can be constituted by aluminum-based equipment, for example, an aluminum-based heat exchanger. A radiator and a heater core can be adopted as typical heat exchangers. The inorganic film can be composed of an oxide containing at least one of zirconium (Zr), silicon (Si), and calcium (Ca). In this case, it is advantageous for ensuring corrosion resistance to alkali.

The thickness of the boehmite film or the inorganic film is appropriately selected according to the type of the aluminum base, the material of the inorganic film, etc. For example, the thickness of the boehmite film is 0.2 to 100 μm, 0.5 to 50 μm. Can be about.
The thickness of the inorganic film is 0.01 to 10 μm, 0.05 to
It can be about 10 μm, especially about 0.5 to 2 μm. As described in claim 4, the inorganic film can be formed by a sol-gel method. In the sol-gel method, a solution containing a metal alkoxide (M (OR) n, M is a metal element, R is an alkyl group, and n is the oxidation number of the metal element) is generally used as a starting solution, and the solution is hydrolyzed. By the decomposition and polycondensation reactions, sol formation in which fine particles of the metal oxide are dispersed or dissolved proceeds, and further, gelation proceeds with the reaction, and a film or a bulk is formed. In the starting solution, in addition to the metal compound that forms the target oxide, a solvent for preparing a homogeneous solution, and water for hydrolysis,
If necessary, an acid or ammonia having a catalytic action can be contained. As the solvent, for example, at least one of alcohols such as ethanol and methanol, ethylene glycol, ethylene oxide, xylene, triethanolamine and the like can be employed as necessary. As the acid, for example, at least one of hydrochloric acid, sulfuric acid, acetic acid, hydrofluoric acid and the like can be employed.

According to the sol-gel method, it is possible to synthesize an inorganic film such as a metal oxide at a low temperature, and it is possible to mix at a molecular level or an atomic level. Advantages such as improvement, easy thinning, and easy formation of fine particles of the film-forming particles can be expected.

[0015]

An embodiment of the present invention will be described. FIG. 1 is a configuration diagram schematically showing a film structure. In this embodiment, as illustrated in FIG. 1, a boehmite boehmite film 3 and an inorganic film 5 are laminated on an aluminum base 1 in the thickness direction in this order. The aluminum base 1 is an aluminum-zinc-magnesium base, and its basic composition is Al- (0.5-1.0)% Zn- (0.5-1.0).
% Mg.

The thickness of the boehmite film 3 is about 1 μm. According to the present inventor, when the boehmite coating 3 before laminating the inorganic coating 5 was observed with an electron microscope, it was found that the boehmite coating 3 according to the present embodiment had a large number of clogged tooth-shaped protrusions. It was confirmed that there was a void between the protruding portions. The average pore size is 10
It was about 40 nm.

The inorganic film 5 is formed of Zr oxide in a thin film. The thickness of the inorganic film 5 is about 1 to 3 μm. In the present embodiment, the boehmite film 3 was formed by using an aluminum member provided with the aluminum base 1 and immersing the aluminum member in a hot water bath for a predetermined time. The conditions are as follows.

Bath composition: 0.1 to 0.5 wt% of triethanolamine is added as an additive, and PH is adjusted to 7 to 12%.
Hot water (distilled water is used as the diluting water) Bath temperature: 90 to 100 ° C. Time: 20 to 30 minutes In this example, the inorganic film 5 was formed by the sol-gel method. That is, after the aluminum member having the boehmite film 3 formed thereon is immersed in a sol solution as a starting solution for a predetermined time, the aluminum member is pulled up, dried and heated a plurality of times (5 to 1).
0) repeated dip coating method.
As a result, a Zr oxide film which is a metal oxide film functioning as the inorganic film 5 was laminated on the boehmite film 3.
The conditions are as follows.

The sol solution was adjusted at the following molar ratio: zirconium tetra-n-butoxide: diethylene glycol: water: ethanol = 1: 2: 2: 53 Drying time: 300 seconds Heating: 300 ° C. for 1800 seconds The test was performed in an oxygen atmosphere.

(Test Example) A corrosion resistance test was performed on the above-described examples. In the corrosion resistance test, an alkaline test solution adjusted to PH10 with NaOH or the like and kept at 88 to 105 ° C. by a heater was used, and the test piece was first immersed in the test solution for 8 hours. Thereafter, while the test piece was immersed in the test solution, the heater was turned off and the test solution was cooled to room temperature. The test piece was immersed in a test solution at room temperature for 16 hours. The above operation was regarded as one cycle, and was repeated continuously for 60 cycles.

In the test pieces according to the examples, the corrosion did not progress to the aluminum base 1, and the corrosion resistance was good even when the use environment was alkaline. As Comparative Example 1, a boehmite film was formed on an aluminum base by boehmite treatment, and a test piece without an inorganic film was formed. Further, as Comparative Example 2, a boehmite film was formed on an aluminum base, and an organic film (thickness: 20 μm) was formed.
m) were laminated to form a test piece. The organic film was formed by immersing a test piece in a diluted modified epoxy resin for a predetermined time and then taking out the same and baking it at 150 ° C. for 15 minutes.

The aluminum bases according to Comparative Examples 1 to 3 were of the same type as the examples. Further, the boehmite films according to Comparative Examples 1 and 2 were formed under the same conditions as in the examples.
Further, as Comparative Example 3, a test piece was formed by forming an anodized film on an aluminum base by alumite treatment, and further laminating a Zr oxide film (thickness: 3 μm) as an inorganic film similar to the example.

The conditions of the alumite treatment were as follows. Electrolyte composition: sulfuric acid solution (H ₂ SO ₄ 10~20wt
%) Current density: Direct current (DC) 0.5 to 2 [A / dm ² ] Voltage: 10 to 20 V Temperature: 15 to 25 ° C. Time: 30 to 60 minutes Regarding the test pieces according to Comparative Examples 1 to 3 described above. Also, a corrosion resistance test was performed in the same manner. In the test piece according to Comparative Example 1, corrosion progressed to the aluminum base, and the corrosion resistance to the alkali test solution was not sufficient. In particular, the corrosion penetrated the aluminum base having a target thickness of 300 μm.
Further, in the test piece according to Comparative Example 2 in which the organic coating was laminated, corrosion was observed up to the aluminum base. In the test piece according to Comparative Example 3 in which the inorganic film was laminated, the corrosion did not progress to the aluminum base.

(Other Embodiments) Si Oxidation as Inorganic Film
If the product is formed by the sol-gel method,
Metal alkoxides such as tetraethoxysila
[Si (OC_TwoH _Five)_Four], Tetramethoxysilane
[(Si (OCH_Three)_Four] Can be adopted. With inorganic coating
When the Ca oxide is formed by the sol-gel method
As genus alkoxides, for example, Ca (OCH_Three)_TwoAdopt
it can.

(Application Example) FIG. 2 shows an application example in which the above-described embodiment is applied to an aluminum radiator of a vehicle.
As shown in FIG. 2, the radiator includes tanks 80 and 81 in which a coolant is stored, a core 84 through which the coolant flows, and plates 82 and 83. The core 84 includes a tube group including a large number of tubes through which the coolant flows, and a fin group including fins projecting from each tube and having an increased heat radiation area for heat exchange. In this application example, the above-mentioned corrosion-resistant coating is laminated on the aluminum base on the cooling liquid side (inner surface) of the tube group and the plates 82 and 83. Additives are easily added to a coolant used for a radiator of a vehicle, and therefore, if the coolant is deteriorated for a long period of use, the coolant tends to become alkaline.

(Supplementary Note) The following technical ideas can be understood from the above embodiments. A heat exchanger (radiator) provided with the corrosion-resistant coating according to each claim.

[0027]

According to the corrosion-resistant film on the aluminum base according to the present invention, the corrosion resistance is good even when the use environment is alkaline. In particular, since the inorganic film covers the pores of the boehmite film, the corrosion resistance to alkali is improved. In particular, even when the aluminum base is used in an environment where the PH is 9 or more, it is easy to ensure corrosion resistance.

Moreover, since the boehmite film is obtained using hot water or heated steam, it is advantageous in terms of equipment and cost as compared with an anodic oxide film formed by alumite treatment using sulfuric acid or the like. According to the method of the present invention, it is possible to provide a corrosion-resistant film having good corrosion resistance when the use environment is alkaline. Moreover, since the boehmite treatment can be performed using hot water or heated steam, it is advantageous in terms of equipment and cost as compared with the case of alumite treatment using sulfuric acid or the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing the structure of a corrosion resistant film.

FIG. 2 is a perspective view applied to a radiator.

[Explanation of symbols]

In the figure, 1 is an aluminum base, 3 is a boehmite film,
Reference numeral 5 denotes an inorganic film.

Claims (4)

[Claims] 1. A corrosion-resistant coating on an aluminum base, wherein a boehmite boehmite coating and an inorganic coating are laminated on the aluminum base in this order. 2. The aluminum-based base according to claim 1, wherein the aluminum-based base is formed of an aluminum-based heat exchanger, and the boehmite film and the inorganic film are disposed on a side of the heat exchanger that comes into contact with a coolant. A corrosion resistant film on an aluminum base, which is laminated on a surface. 3. The corrosion resistance of an aluminum base according to claim 1, wherein said inorganic film is an oxide containing at least one of zirconium (Zr), silicon (Si) and calcium (Ca). Film. 4. A step of boehmite-treating the exposed surface of the aluminum base to provide a boehmite film having at least the exposed surface boehmite, and at least one of zirconium (Zr), silicon (Si), and calcium (Ca). A method for producing a corrosion-resistant film on an aluminum-based base, comprising: contacting a sol solution of a metal alkoxide containing: with the boehmite film and gelling the sol solution to form an inorganic film.