JPH08269753A - Al alloy member for heat exchanger excellent in corrosion resistance and al alloy made heat exchanger, their production, formaiton of corrosion resistant coating film to be applied on heat exchanger, and using method of heat exchanger - Google Patents

Abstract

PURPOSE: To provide a an Al alloy member for heat exchanges excellent in corrosion resistance. CONSTITUTION: The Al alloy member for heat exchanger excellent in corrosion resistance is obtained by forming a heat resistant coating film consisting essentially of an Al oxide and/or Al hydroxide and containing at least one kind of a metal more base than Al on the surface of an a Al alloy member for heat exchanger. Where, the metal element more base than Al is preferably Mg, Li or Ca.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al alloy member for a heat exchanger having excellent corrosion resistance, a method for manufacturing the same, an Al alloy heat exchanger having excellent corrosion resistance, and a method for manufacturing the same. The present invention also includes a method for forming a corrosion resistant coating applied to the Al alloy heat exchanger and a method for using the Al alloy heat exchanger. INDUSTRIAL APPLICABILITY The Al alloy member of the present invention is suitably used for a heat exchanger that uses ground water or hard water such as rivers as a heat medium.

[0002]

2. Description of the Related Art A heat exchanger made of an Al alloy is lightweight and has excellent properties such as thermal conductivity and cutting workability, and in addition, since it is possible to use a shaped material such as an extruded material, it is possible to use it on site. Has good workability and is therefore used very often.
As the heat medium used in this heat exchanger, ground water and hard water such as rivers that are abundant in industrial areas are mainly used because they are inexpensive and harmless.

However, hard water useful as a heat medium contains a large amount of oxidizing anions such as carbonate ions, hydrogen carbonate ions and sulfate ions; and high valent metal ions such as Fe ³⁺ and Cu ^2+. Has been. These ions act as an oxidizing agent, and due to, for example, local nonuniformity of the solution, the spontaneous potential of the Al alloy partially rises to form a local battery. Corrosion occurs when the natural potential of Al exceeds the pitting corrosion generation potential, and as a result, pitting corrosion, which is one of the typical corrosion in Al alloys, is caused, resulting in water leakage of the heat medium and stress corrosion cracking. However, it will cause a great adverse effect on the operation of the heat exchanger.

Therefore, a method of adding an anticorrosion inhibitor to the heat medium has been carried out for the purpose of suppressing the harmful effects caused by such corrosion, but the cost is increased and a harmful substance is added to these inhibitors. Therefore, problems such as difficulty in waste liquid treatment occur. Alternatively, Al
A method of coating the surface of the alloy member with an organic resin to improve the anticorrosion effect has also been attempted, but it is necessary to enlarge the heat exchange area for coating, and accordingly, complicated design changes and reduction of heat transfer efficiency are required. And the like, and inconveniences such as an increase in cost occur.

[0005]

The present invention has been made in view of the above circumstances, and an object thereof is an Al alloy member for a heat exchanger excellent in corrosion resistance, an Al alloy heat exchanger, and It is an object of the present invention to provide not only a method for efficiently producing these, but also a method for operating the heat exchanger while maintaining high corrosion resistance.

[0006]

The Al alloy member for a heat exchanger of the present invention, which has been able to solve the above problems, has an Al oxide and / or an Al hydroxide on the surface of the Al alloy member for a heat exchanger. The main point is that a corrosion-resistant film (hereinafter sometimes abbreviated as a corrosion-resistant film) containing at least one metal element that is mainly composed of Al and is less than Al is formed.

Here, the metal element that is less base than Al is M
g, Li or Ca, and those in which the thickness of the corrosion-resistant coating is 0.2 μm or more are preferred embodiments of the present invention. Further, the Al alloy heat exchanger of the present invention which has been able to solve the above problems has a gist in that the above corrosion resistant coating is formed on the surface of the Al alloy member for a heat exchanger.

Al alloy member for heat exchanger of the present invention and A
The method for producing a heat exchanger made of 1-alloy is as follows.
The point is to form the above-mentioned corrosion resistant film on the surface of the alloy member by immersing the alloy member.

Here, in manufacturing the Al alloy heat exchanger of the present invention, in addition to the above method, the Al alloy heat exchanger is operated while being immersed in hard water as a heat medium. A method of forming the above corrosion resistant film on the surface is also adopted. The preferred solution used is hard water.

Further, the method of forming the corrosion resistant film is as follows.
While the alloy heat exchanger is being operated, the heat exchanger is immersed in a heat medium containing at least one metal element that is baser than Al to form the above corrosion-resistant coating on the surface thereof. Have. Hard water is preferred as the heat medium used.

Further, according to the method of using the Al alloy heat exchanger of the present invention, at least one metal element which is baser than Al is 0.01 m in total while operating the Al alloy heat exchanger.
The point is to operate while forming the above-mentioned corrosion resistant film on the surface of the heat exchanger by immersing the heat exchanger in a heat medium containing ol / L or more. Hard water is preferred as the heat medium.

[0012]

As described above, hard water suitably used as the heat medium for the heat exchanger contains a large amount of oxidizing anions such as hydrogen carbonate ions; high valent metal ions such as Fe ³⁺ and Cu ^2+. Therefore, it is considered that due to their oxidizing action, the spontaneous potential of the Al alloy rises and corrosion (particularly pitting corrosion) occurs.

Then, the inventors of the present invention studied a method of lowering the spontaneous potential of the Al alloy member. As a result, a film containing a metal element (eg, Mg, Li, Ca, etc.) that is baser than Al was formed on the surface. Thus, the present invention has been completed by finding that corrosion can be suppressed by suppressing the action of the above-mentioned oxidizing agent that adversely affects corrosion.

That is, according to the present invention, A
1 oxide and / or Al hydroxide as a main component,
Moreover, it has the greatest feature in forming a highly corrosion-resistant film (hereinafter, may be represented again by a corrosion-resistant film) containing at least one kind of metal element that is baser than Al. Specifically, A
l pH of an aqueous solution of a water-soluble salt containing a base metal element
After the adjustment, if the Al alloy member is dipped in this solution for a predetermined time, the above corrosion resistant film is formed on the surface thereof. As described above, the above corrosion-resistant film can be easily formed only by the dipping treatment, and even during the operation of the heat exchanger, the film can be rapidly formed by adding the water-soluble salt containing the metal element to the heating medium. It can be seen that this is a very excellent method in terms of both manufacturing efficiency and operating efficiency. Furthermore, once formed, the corrosion-resistant film exerts a stronger action as a barrier layer against an oxidizing agent than when Al ₂ O ₃ alone is used. As a result, groundwater containing an oxidizing agent such as carbonate ion is used as a heat medium. Even when heat exchange is performed by heat, excellent corrosion resistance can be exhibited. The features of the present invention will be described below while sequentially explaining the process of forming this corrosion-resistant coating.

First, as a metal element that is baser than Al, M
g, Ca, Sr, Ba, Li, Na, K, Rb, Cs, etc., but if considering corrosion resistance, easiness of forming a water-soluble salt, low cost, versatility, etc., Mg, Ca and Li is preferred, and Mg and Li are more preferred. These metal elements may be used alone or in combination of two or more.

Next, the above metal element is contained in the solution in the form of a water-soluble salt. The existence form of this water-soluble salt depends on the type of metal used, sulfate or hydroxide. It is preferable to appropriately select a form that readily dissolves, such as carbonate, hydrogen carbonate, and the like. For example, in the case of Mg, MgSO ₄
Etc. In the case of Ca, Ca (HCO ₃ ) ₂ or the like is preferable, and in the case of Li, salt forms such as LiCO ₃ or the like are preferable.

Next, after adjusting the pH of the aqueous solution containing the water-soluble salt of the metal element to a suitable pH, the Al alloy member for the heat exchanger is dipped in this solution for a predetermined time to form a corrosion resistant film.

In the present invention, the corrosion resistance can be enhanced by controlling the film thickness of the corrosion resistant coating. That is, the film thickness of the film is preferably 0.2 μm or more in order to effectively exhibit the corrosion resistance effect due to the addition of the metal element described above without causing the film discontinuity. More preferably, it is 2 μm or more. However, even if formed in a large amount, not only is the effect saturated, which is economically wasteful, but powdering may occur on the film surface. Therefore, the upper limit is preferably 7 μm or less. More preferably, it is 4 μm or less.

The thickness of such a suitable corrosion resistant coating can be obtained by controlling the immersion conditions. Specifically, the desired film thickness is obtained by appropriately changing the immersion time, the immersion temperature, the concentration of the metal ions used, and the like.

Specifically, for example, the film thickness: M of 3 to 4 μm
When forming a g-containing film, MgS is used as a water-soluble salt.
O ₄ (Mg ion concentration: 0.01 to 0.05 mol /
L), pH: 6 to 7, immersion temperature: 60 to 90 ° C., and treatment time: 15 to 120 minutes.

It is not known in detail in what form the metal element exists in the corrosion-resistant coating thus formed, but in any case, the corrosion-resistant coating contains Al.
The Al alloy member and the heat exchanger of the present invention, which mainly contain the oxide of Al and / or the hydroxide of Al and contain at least one metal element that is baser than Al, and have such a film are It is possible to exhibit extremely excellent corrosion resistance as compared with the examples (those not provided with the corrosion resistant film according to the present invention).

The corrosion-resistant coating is made of Al for heat exchanger.
It can be said to be a very simple and efficient method because it is easily formed by immersing the alloy member in an aqueous solution containing a water-soluble salt of a metal element less base than Al (may be simply referred to as a solution). .

The time when the corrosion resistant coating is formed on the surface of the Al alloy member for a heat exchanger (that is, immersed in the solution) is not particularly limited, and the Al alloy member is dissolved in the solution before the heat exchanger is assembled. It may be immersed in water, or it may be immersed in a solution after assembling a heat exchanger (without corrosion-resistant coating), or after assembling the heat exchanger (without corrosion-resistant coating). The corrosion resistant film may be formed by operating while being immersed in hard water as a medium.

As described above, the corrosion-resistant coating of the present invention can be formed at any stage before, after, and after operation of the heat exchanger (not only at the beginning of operation but also during the entire period). . Here, the film forming process in each step may be performed separately, or the film forming process is performed at the same time in each of the above steps for the purpose of enhancing the corrosion resistance (for example, after performing the process before assembling, further performing the operation. Of course, it is also effective to treat the inside. Further, the heat exchanger subjected to the film formation process does not necessarily have to be a new one, and a heat exchanger whose corrosion resistance has deteriorated after being used for many years may be used, which enables effective use of resources.

The above metal element is dissolved to form a water-soluble salt.
Solution and heat used to operate the heat exchanger
Groundwater is particularly preferable as the medium. Groundwater is more than surface water
In general, the amount of high-valent metal ions is low and carbonate ions are low.
Since it contains a large amount of
The causative substance is considered to be carbonate ion. And
This carbonate ion is a metal element that is more base than Al such as Mg
Easily reacts with MgCO ₃ Form insoluble salts such as
It does not adversely affect the Al alloy member. Like this
In addition, groundwater is trapped by the metal elements used in the present invention.
Corrosion resistance according to the present invention because it contains a lot of easy oxidizing agents
The effect can be exerted more effectively.

The Al alloy member used in the present invention can be applied to various Al alloys including pure Al. Among them, the most versatile alloy is Al-Mg.
-Based alloys (Al alloys in the JIS 5000 series) and Al
-Mg-Si system alloy (Al alloy of JIS6000 series)
Is mentioned. These alloys are also suitable as extruded profiles.

The method of forming the corrosion-resistant coating according to the present invention has been mainly described above, but the Al alloy member for a heat exchanger according to the present invention has the corrosion-resistant coating applied to the surface thereof. The heat exchanger made of Al alloy of the invention is A for heat exchanger.
The corrosion resistant coating is formed on the surface of the 1-alloy member. The corrosion-resistant film formed as described above also effectively acts as a barrier layer against the oxidizing agent, so that even if it is further exposed to the oxidizing agent during heat exchange or the like, it effectively corrodes the Al alloy. Can be suppressed. Although the detailed reason for this is not clear, the following can be considered, for example, when groundwater containing a large amount of carbonate ions is used as the heat medium. That is, the heat exchanger of the present invention is exposed to an oxidizing agent such as carbonate ion during heat exchange, but the insoluble salt such as MgCO ₃ present in the corrosion-resistant film formed on the surface thereof is converted into Al. On the other hand, since it acts as an anode, it has the effect of lowering the potential, and as a result, suppresses the occurrence of pitting corrosion (elevation of the potential) and prevents carbonate ions from entering the Al alloy member and causing corrosion. It is thought that it can be done.

In order to effectively exhibit the action of such a corrosion-resistant coating as a barrier layer, the thickness of this coating should be controlled within the above-mentioned preferred range (preferably 0.2 μm or more, more preferably 3 μm or more). Is preferred.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification or implementation is within the scope of the present invention without departing from the gist thereof. It is included in the technical scope of.

[0030]

[Example] A 50 × 50 mm JIS 6063 Al extruded material (thickness: 2.5 mm) was applied to wet emery paper (# 60).
0) polished with the test materials (No. 1, 1 ', 1''and 2
To 11) were used to perform the film forming processes 1 to 11 below to form a film having a film thickness shown in Table 1 on the surface thereof.

[0031]

[Table 1]

Nos. 1, 2 to 6 and 7 to 11 are shown in Table 1.
The salt solution containing the metal ion concentration shown in [[Mg _{4 for} Mg, LiCO _{3 for} Li, C for Ca]
a (HC0 ₃ ) ₂ ] under the treatment conditions shown in Table 1 to form a film. No. 1'is No. 1 after performing the above film forming process.
A film was formed by immersing in the underground aqueous solution of the Mg salt containing the metal ion concentration used in 1 at 90 ° C. for 20 hours. The groundwater used for this treatment was collected in the southern part of Kyoto Prefecture, and its composition is as shown in Table 2.

[0033]

[Table 2]

No. 1 '' was processed without performing the film forming process in the above method to form a film. No. 7 is a conventional example in which such a film forming process is not performed at all.

The corrosion resistance of each test material treated in this way was evaluated. In the evaluation of corrosion resistance, these test materials were immersed in the groundwater used above at 32 ± 1 ° C. for 20 days in the open air, and then the presence or absence of pitting corrosion was visually observed. Regarding No. 1'and 1 '', the corrosion resistance was similarly evaluated using the metal element-containing groundwater used in the film formation process. The results are also shown in Table 1.

As is apparent from the table, in all the examples of the present invention, the corrosion resistance is improved as compared with the conventional example, and the corrosion resistance effect is remarkably improved by setting the thickness of the corrosion resistant film to 0.2 μm or more. I was able to. Further, it was found that the formation time of the corrosion resistant coating has no effect on the corrosion resistance improving effect by adopting any one of the above film forming treatment conditions.

[0037]

As is apparent from the above description,
The Al alloy member for a heat exchanger and the Al alloy heat exchanger of the present invention have Al oxide and / or Al oxide on the surface thereof.
Since it has a corrosion-resistant film mainly containing hydroxide and containing at least one kind of metal element that is baser than Al, it can be efficiently operated during operation of the heat exchanger without degrading corrosion resistance. .

The corrosion-resistant coating can be formed at any stage before, after, and after operation of the Al alloy heat exchanger, and the forming method is a solution containing a metal element less base than Al. This is a very simple and efficient method because it can be applied simply by immersing the Al alloy member for heat exchanger therein.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area F28F 19/06 F28F 19/06 A

Claims (13)

[Claims] 1. A surface of an Al alloy member for a heat exchanger is coated with Al.
Excellent in corrosion resistance, characterized by being formed of a corrosion-resistant coating mainly containing oxide of Al and / or hydroxide of Al and containing at least one metal element that is baser than Al. Alloy material. 2. A metal element which is baser than Al is Mg, L
The Al alloy member according to claim 1, which is i or Ca. 3. The Al alloy member according to claim 1, wherein the thickness of the corrosion-resistant coating is 0.2 μm or more. 4. An Al alloy heat exchanger having excellent corrosion resistance, characterized in that the corrosion resistant coating according to any one of claims 1 to 3 is formed on the surface of an Al alloy member for a heat exchanger. . 5. The corrosion resistant coating according to any one of claims 1 to 3 is formed on the surface of an Al alloy member for a heat exchanger by immersing it in a solution containing at least one metal element that is baser than Al. A method of manufacturing an Al alloy member for a heat exchanger, which comprises forming the Al alloy member. 6. The manufacturing method according to claim 5, wherein the solution is hard water. 7. The corrosion resistant coating according to any one of claims 1 to 3 is formed by immersing an Al alloy member for a heat exchanger in a solution containing at least one metal element that is baser than Al. A method for manufacturing an Al alloy heat exchanger, which is characterized in that the heat exchanger is formed. 8. The manufacturing method according to claim 7, wherein the solution is hard water. 9. An Al alloy heat exchanger is operated while being immersed in hard water as a heat medium to form the corrosion resistant film according to any one of claims 1 to 3 on its surface. A method for manufacturing a heat exchanger made of a characteristic Al alloy. 10. While operating the Al alloy heat exchanger,
The corrosion resistant coating according to any one of claims 1 to 3 is formed on the surface of the heat exchanger by immersing the heat exchanger in a heating medium containing at least one metal element that is baser than Al. And a method for forming a corrosion resistant coating applied to an Al alloy heat exchanger. 11. The method according to claim 10, wherein the heating medium is hard water. 12. While operating the Al alloy heat exchanger,
A total of at least one metal element that is baser than Al is 0.0
By immersing the heat exchanger in a heat medium containing 1 mol / L or more, the Al alloy is operated while forming the corrosion-resistant coating according to any one of claims 1 to 3 on its surface. How to use the heat exchanger. 13. The method according to claim 12, wherein the heating medium is hard water.