JPH11106889A - Aluminum alloy member excellent in low temperature erosion and corrosion resistances - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the erosion and corrosion resistances to low temp. and high speed sea stream by specifying the lower limit values of Zn contents in a plurality of phases having different Zn contents in the average Zn content of a thermal-sprayed corrosion-proof film of Al-Zn alloy formed on an Al alloy material for constituting an LNG vaporizer and Zn content in a film. SOLUTION: The average Zn content of the Al-Zn alloy film is made to be 3.6-85% and the Zn content in each phase of an Al-rich phase a1 , b1 , c1 and Zn-rich phase a2 , b2 , c2 having different Zn contents, is made to be >=3.5%. The Zn content in each phase is varied with the thermal-sprayed condition, but this Zn content of 3.6% is the lower limit value for sufficiently displaying a sacrificing corrosion-proof action. That is, even in the case of consuming the Zn-rich phase a2 , b2 , c2 in the film at the initial stage of the corrosion-proof, the sacrificing corrosion-proof action over the long time is displayed even if Zn quantity in the remaining phase having little Zn content is 3.6%. This Al alloy member makes way for large scaling of the LNG vaporizer and using in the continuous long time.

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 having an Al-Zn alloy film formed on a surface thereof, which is used in a low temperature erosion / corrosion environment, and particularly to an Al alloy excellent in low temperature erosion / corrosion by seawater. It relates to members.

[0002]

2. Description of the Related Art Liquefied natural gas (hereinafter referred to as LNG) is usually transported and stored in a liquid state at low temperature and high pressure, and is vaporized before use. To vaporize this large amount of LNG,
Conventionally, an open rack vaporizer (hereinafter referred to as ORV) shown in FIG. 5 has been used. This ORV is a type of heat exchanger that heats and vaporizes LNG by heat exchange with seawater. That is, in FIG. 5, the seawater 9 is
From the header 6 through the watering nozzle 7, it is stored in the trough 8,
The outside of the panel (heat transfer tube) 3 is hung down from both side edges of the trough 8 while being wet. On the other hand, LNG is sent from the manifold 1 to the header 4, heated by heat exchange with the seawater, vaporized in the panel (heat transfer tube) 3 and rises, and led out from the NG header 4 to the NG manifold 5.

[0003] The members for the ORV, especially the members for the panel (heat transfer tube) 3 have good heat conductivity, are easily processed into a complicated shape for gaining a heat transfer area, and have good weldability such as JIS 3203.
Alloys are used. However, Al alloys are naturally susceptible to corrosion when immersed in seawater, and once erosion begins,
There is a disadvantage that the eroded portion is intensively attacked and is susceptible to so-called pitting.

[0004] For this reason, it has been conventionally used for the above-mentioned applications.
Anticorrosion treatments have been actively studied for Al alloys, and at present, anticorrosion methods utilizing a sacrificial anticorrosion effect occupy the mainstream. This sacrificial corrosion protection is to coat the surface of a base metal alloy made of an Al alloy with an alloy that is more susceptible to corrosion than the base metal alloy, that is, an alloy having a higher ionization tendency with a lower corrosion potential in seawater than the base metal alloy. . As a result, the base metal alloy does not come into direct contact with seawater due to the coating action of the coating alloy, thereby maintaining corrosion resistance.Also, a part of the coating alloy is peeled off, so that the base metal alloy is exposed and comes into direct contact with seawater. Even so, the sacrificial corrosion protection of the remaining coating alloy ensures long-term corrosion resistance of the base metal alloy.

Conventionally, an alloy of Al and Zn has been known as a coating alloy having this sacrificial anticorrosion action. Al-2% Zn, Al-3
Alloys such as% Zn are used. As a method of coating the base material alloy with this alloy, for example, as in Japanese Patent Application Laid-Open No. 5-164496, a method of cladding an Al-Zn alloy by a thermal spraying method or the like to extend the surface protection for a long time may be used. Proposed.

[0006] Further, for the purpose of further enhancing the sacrificial anticorrosion action, or Al containing a small amount of Hg, Sn, In, Ga, Cd.
-Zn coated alloy or Zn content was 3.5 to 85.0%
An Al-Zn coating alloy has been proposed in Japanese Patent Application Laid-Open No. 6-317392. According to this technique, the Zn content is increased and the trace element is added, so that the sacrificial anticorrosion action can be further enhanced as compared with the coating alloys such as Al-2% Zn and Al-3% Zn.

[0007]

However, the ORV is
In recent years, the efficiency has been further increased, and there is a tendency that the size of the apparatus is increased or the operation is continued for a long time. For this reason, durability and reliability, such as corrosion resistance for a longer period of time, which is required to increase the velocity of falling seawater due to the increase in the size of the members constituting the ORV, and to withstand continuous continuous operation, are required. In this regard, the present inventors have found that coating alloys such as Al-2% Zn and Al-3% Zn, Al-Zn coating alloys having a Zn content of 3.5 to 85.0%, etc. When applied as an ORV member that has been enlarged or continuously operated for a long time,
There is a problem that corrosion progresses remarkably depending on use conditions. This corrosion phenomenon is particularly severe in the lower part of the panel (heat transfer tube) 3 exposed to the flow of seawater at a low temperature and a high flow velocity. The reason for this is that, with the operation of the ORV becoming larger or continuously longer, the flow of low-temperature seawater that comes into contact with the panel 3 becomes faster, and the water comes into contact for a longer time.
Corrosion environment of erosion and corrosion by seawater,
Due to being more severe. Accordingly, despite the need for better low-temperature erosion / corrosion properties for the Al alloy member of the ORV, in the Al alloy member coated with the conventional Al-Zn alloy,
This is because the required characteristics cannot be met.

If the corrosion caused by the seawater causes corrosion particularly to a part of the Al alloy member of the panel (heat transfer tube), and the possibility of damage or the need for repair arises, the size of the panel (transfer tube) increases. The need to replace all of the heat pipes, or to stop the operation for repair, etc. arises, resulting in an increase in ORV maintenance costs and a significant decrease in NG production efficiency. Therefore, an Al alloy member having better low-temperature erosion / corrosion properties and a longer life is indispensable for the operation of increasing the ORV and extending the operation time continuously.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an Al alloy member that can guarantee long-term corrosion resistance even under a low-temperature erosion / corrosion environment such as seawater. It is intended to provide.

[0010]

In order to achieve this object, the gist of the present invention is to form an Al-Zn alloy film on a surface.
An Al alloy member in which the Al-Zn alloy film is formed from a plurality of phases having different Zn contents, the average Zn content of the Al-Zn alloy film is 3.6 to 85.0%, and the Zn content of all the phases is The amount is to be 3.6% or more.

[0011] The inventors of the present invention have disclosed an Al-Zn coated alloy having a Zn content of 3.5 to 85.0% described in JP-A-6-317392.
As a result of investigating the corrosion mechanism in low-temperature erosion-corrosion environments such as seawater, it was found that the presence of multiple phases with different Zn contents in the Al-Zn alloy film affected low-temperature erosion-corrosion properties. . In other words, when such an Al-Zn alloy film having a Zn content of 3.5% or more is formed by a thermal spraying method or the like, actually, a uniform alloy film in which the composition of Al and Zn is constant cannot be obtained. A plurality of phases in which the composition of Al and Zn in the Al-Zn alloy film is large or slightly different are likely to be formed. From the viewpoint of the Zn content, a film composed of a Zn-rich phase having a relatively high Zn content and an Al-rich phase having a Zn content relatively lower than this phase is formed.

Thus, in the Al-Zn alloy film,
When the Zn-rich phase and the Al-rich phase are mixed, even if the Al-Zn
Even if the average Zn content (or the average Al content) of the alloy film is in an appropriate (desired) range, under the environment of the high-speed flow of the low-temperature seawater, the Zn-rich phase and the Al-rich phase During this time, a contact corrosion phenomenon between different metals occurs. As a result, the Zn-rich phase elutes selectively (preferentially) from the Al-Zn alloy film over time, and only the Al-rich phase remains in the Al-Zn alloy film. On the other hand, the sacrificial corrosion protection, which is an important property of the Al-Zn alloy film, depends on the Zn content. Therefore, if the Zn content of the Al-rich phase remaining in the Al-Zn alloy film after the Zn-rich phase elutes is small, the sacrificial corrosion protection of the Al-Zn alloy film on the base metal alloy is extremely poor. It will be. Therefore, the conventional
It is mainly for this reason that the low-temperature erosion / corrosion properties of the Al-Zn alloy film or the Al alloy member coated therewith are poor. The present inventors have found that the sacrificial corrosion protection effect of the Al-Zn alloy film under the low-temperature erosion-corrosion environment is as follows:
The present invention has been made based on the finding that it depends not only on the average Zn content of the coating but also on the individual Zn content of a plurality of phases having different Zn contents.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The required Zn content of a plurality of phases having different Zn contents will be described in more detail. As described above, in the ORV shown in FIG. 5, corrosion damage is particularly severe in the lower part of the (heat transfer tube) 3 even among panels exposed to the flow of low-temperature seawater. This is because the lowering of the temperature of the seawater and the increasing of the flow velocity in this part are more intense than in other parts.
In such a site, it is inevitable that the Zn-rich phase of the Al-Zn alloy film is preferentially eluted at an early stage by the above mechanism due to the erosion and corrosion of the seawater at a lower temperature and a higher flow rate. I want to. Therefore, in order for the Al alloy member at this portion to maintain excellent erosion and corrosion properties, even after the Zn-rich phase has eluted in the initial stage, the phase remaining in the Al-Zn alloy,
In particular, it is essential to maintain the Zn content of the Al-rich phase in an amount necessary for the remaining phase to exhibit sacrificial corrosion protection on the base alloy in order to maintain excellent erosion and corrosion properties. Becomes

In order to ensure the amount of Zn remaining in the Al-Zn alloy film, particularly the Al-rich phase, in an amount necessary for the remaining phase to exhibit a sacrificial corrosion protection action on the base alloy, First,
The average Zn content of the Al-Zn alloy film is in the range of 3.6 to 85.0%. Then, the Zn content is set to 3.6% or more in all of the plurality of phases having different Zn contents in the Al—Zn alloy film. In other words, the average Zn content is 3.6 to 85.0
%, The Zn-rich phase of the plurality of phases having different Zn contents necessarily has a Zn content of 3.6% or more, but in particular, the Zn content is necessarily reduced. In the Al-rich phase, depending on the coating conditions of the Al-Zn alloy film such as thermal spraying, there is a great possibility that the Zn content will be less than 3.6%. As a result, an excellent sacrificial anticorrosion effect cannot be exhibited. Therefore, even if the Zn-rich phase elutes at an early stage, the Zn content of the phase remaining in the Al-Zn alloy film, particularly the Al-rich phase, is also 3.
It is a feature of the present invention that the content is 6% or more.

When the average Zn content of the Al-Zn alloy film is less than 3.6%, it is difficult to form a phase having a significantly different composition, but considering that the absolute amount of Zn is insufficient, it is possible to consider that a phase having a different Zn content is formed. All Zn content of different phases of Zn content,
In particular, the Zn content of the phase remaining in the Al-Zn alloy film or the Al-rich phase cannot be set to 3.6% or more, and the phase remaining in the Al-Zn alloy film, particularly the Al-rich phase, is superior to the base metal alloy. The sacrificial anti-corrosion effect cannot be exhibited. On the other hand, Al-Zn
When the average Zn content of the alloy film exceeds 85.0%, the Zn-rich phase of the Al-Zn alloy film increases, and the elution amount of the Zn-rich phase in the early stage due to the erosion of seawater at low temperature and high flow rate increases. Al-Zn that should exhibit sacrificial corrosion protection
The amount of the phase itself remaining in the alloy film is reduced, and the erosion / corrosion properties are rather deteriorated. In order to reduce the elution amount of this Zn-rich phase at the initial stage, Al-Zn
It is preferable that the upper limit of the average Zn content of the alloy film is 20%, and the average Zn content is in the range of 3.6 to 20%. Also, Zn
If the content is more than this, it becomes gradually difficult to form a film by a thermal spraying method or the like, and it leads to an increase in raw material costs.

Furthermore, as the Zn content of the Al—Zn alloy film increases, the amount of Zn deposited tends to increase. Particularly, when it exceeds 85.0%, it is difficult to form a structure in which Zn forms a solid solution with Al. There is also a problem. Contained in this Al-Zn alloy film
Zn, in particular, Zn contained in a plurality of phases having different Zn contents including the Al-rich phase, the greater the amount of solid solution in Al, the better the sacrificial corrosion protection action against the base metal alloy be able to. On the other hand, as the Zn content to be precipitated increases, especially
There is a possibility that the Zn content of the Al-rich phase in the Al-Zn alloy film may be insufficient, and the low-temperature erosion / corrosion resistance may be reduced.

The Al-Zn alloy film of the present invention is basically made of Al and Zn.
However, in order to enhance the sacrificial corrosion protection of the Al-Zn alloy film itself, as described in JP-A-5-164496, a further small amount of Hg, Sn, In, Ga, and Cd are added. , Each Hg: 0.020
% Or less, Sn: 0.20% or less, In: 0.20% or less, Ga: 0.50% or less,
Cd: 5.00% or less is allowed.

A plurality of phases having different Zn contents in the Al—Zn alloy film according to the present invention will be described in more detail with reference to FIGS. 1 (a), (b), and (c) have a plurality of phases having different Zn contents according to the present invention, and the average Zn content of the Al-Zn alloy film is 6%, 15%, and 15%. Respectively represent the Al-Zn alloy films a, b, and c. In FIG. 1 (a), (b) , (c), the different phases of Zn content, in FIG. 1 (a), Zn content is Al-rich phase a ₁ and Zn content of 3.6% 3.6% Zn-rich phase a _2, FIG. 1
In (b), Zn content is ₁ and Zn content of 7.0% Al-rich phase b 1
100% of a Zn-rich phase b _2, FIG. 1 (c), Zn content is 0.0
0% Al-rich phase c ₁ and Zn-rich phase c ₂ with 16.0% Zn content
It is. Here, the Al-Zn alloy film shown in Figs. 1 (a) and (b)
In a and b, the Zn content of the Al-rich phases a ₁ and b ₁ is 3.6%, respectively.
7.0%, and in the present invention, the Zn content in all of the plurality of phases having different Zn contents in the Al-Zn alloy film is 3.6% or more, and the Zn rich phases a ₂ and b ₂ are Even after elution, the remaining Al-rich phases a ₁ and b ₁ can exhibit a sacrificial anticorrosion effect on the base alloy, and are excellent in low-temperature erosion and corrosion properties. In contrast, in FIG. 1 (c), Zn content of Al-rich phase c ₁ is 0.00%, Zn content of Al-rich phase c ₁ is too small, Zn content is 16.0% of the Zn-rich phase c _{After 2} elutes, A
sacrificial protection effect against l matrix alloy rich phase c ₁ can not be exerted, so that the low-temperature erosion corrosion is poor.

As described above, a conventional Al—Zn alloy film having a Zn content of 3.5% or more formed by a thermal spraying method or the like is:
In practice, it is easy to form multiple phases with different Zn contents,
In some cases, depending on the method of forming the film, such as the thermal spraying method, a film in which the Zn contents of the multiple phases of the Al-Zn alloy film are substantially the same can be formed. When such an Al-Zn alloy film is formed, the Zn-rich phase of the Al-Zn alloy film is preferentially eluted at an early stage due to the erosion of seawater at a lower temperature and a higher flow rate. Can be suppressed, and the exposed area of the base metal alloy can be suppressed due to the elution of the Zn-rich phase, and even if the base metal alloy is exposed, the sacrificial corrosion prevention action of the Zn-rich phase allows the low-temperature erosion. -It has excellent corrosion resistance and can guarantee long-term corrosion resistance of the base metal alloy. Therefore, in the present invention, on the assumption that the average Zn content of the Al-Zn alloy film is in the range of 3.6 to 85.0%, a plurality of phases of the Al-Zn alloy film are formed.
Films having substantially the same Zn content are also included in the scope of the present invention.

FIGS. 2 (a) and 2 (b) show the Al-Zn alloy film in which the Zn contents of the plurality of phases are substantially the same. FIG.
An ideal state is shown in which the average Zn content of the l-Zn alloy film d is 6%, and the Zn content of all phases d ₁ , d ₂ and d ₃ of the Al-Zn alloy film is 6.00%. However, such an ideal state cannot be achieved, and in fact, even if the film forming conditions such as the thermal spraying method are devised, as shown in FIG. 2 (b), the Al-Zn alloy film e
Has an average Zn content of 6%, and has a plurality of phases e ₁ ,
The Zn content of e ₂ and e ₃ varies about 6.01 to 5.99%. Therefore, in the present invention, the case of the Al-Zn alloy film e shown in FIG.
It is said that the contents are substantially the same. When this Zn content is substantially the same,
Regarding the range of the variation, the variation of the Zn content of each phase with respect to the average Zn content of the Al-Zn alloy film is allowed within a range of ± 0.1%. If the Zn content further varies between the phases, the Zn content of all of the plurality of phases having different Zn contents in the Al-Zn alloy film is set to 3.
When the content is 6% or more, it is necessary to ensure low-temperature erosion / corrosion properties.

Next, a method for evaluating the low-temperature erosion / corrosion properties of the Al—Zn alloy film will be described in detail. The present inventors have studied various Al-Zn alloys under the low-temperature erosion-corrosion environment (under low-temperature high-velocity seawater flow).
The sacrificial corrosion protection of Al-Zn alloy coatings was investigated at high temperatures. This investigation was performed by measuring the spontaneous potential of various Al-Zn alloys. FIG. 3 is a graph illustrating a polarization curve of a metal. In FIG. 3, the horizontal axis represents the value of the potential, and the vertical axis represents the current value. Generally, when a metal (including an alloy) electrode is immersed in a solution containing an electrolyte such as seawater, and is opposed to a reference electrode, the inherent potential of the metal electrode is always measured. Such a potential is called a natural potential. In the graph of FIG. 3, the crosses indicate the natural potential of the metal. Simply immersing a metal (including an alloy) electrode in a solution containing an electrolyte creates an electric potential but does not allow current to flow.

The spontaneous potential differs depending on the type of metal. Generally, a noble metal having a low ionization tendency has a high self potential, and a base metal having a high ionization tendency has a low self potential. That is, as the noble metal has a smaller ionization tendency, the cross mark in FIG. 3 moves to the right, and as the base metal has a higher ionization tendency, the cross mark in FIG. 3 moves to the left. Then, when a potential higher than the natural potential is forcibly applied to the metal in a state where the counter electrode is provided, current flows from the metal electrode toward the counter electrode. The relationship between the applied voltage and the current is plotted in a graph 2 as an anodic polarization curve.
Conversely, when a potential lower than the spontaneous potential is forcibly applied to the metal electrode, a current flows from the counter electrode to the metal electrode. The relationship between the applied voltage and the current is plotted in a graph 2 as a cathode polarization curve. Therefore, if measurement is performed to obtain this polarization curve under specific conditions (under the low-temperature erosion / corrosion environment), it is possible to evaluate the quality of the sacrificial anticorrosion action of the Al-Zn coating alloy film.

That is, in FIG. 3, the natural potential of the Al—Zn alloy is now A (E _corr ), and the natural potential of the Al alloy base material is B (E _corr ).
The pitting potential of the Al alloy base material is C (E _pit ). In this case, as the value of the difference ΔE between the natural potential A of the Al-Zn alloy and the pitting potential C of the Al alloy base material increases, and the value of ΔE does not decrease with time and is maintained at a higher value. In other words, the larger the value of ΔE is, and the longer it is maintained, the better the sacrificial corrosion protection action against the Al alloy base material
= The low temperature erosion / corrosion properties of the Al alloy member are excellent.

The Al alloy used in the Al alloy member of the present invention is LNG
A JIS 3000 series Al alloy, such as JIS 3203 for heat exchangers, is preferred because it has good thermal conductivity required for vaporizers, especially for ORVs, is easy to process into complex shapes that take up the heat transfer area, and has good weldability. . However, a known Al alloy can be appropriately selected according to the application and required characteristics, including mechanical properties such as required strength and proof stress.

Further, as a method of coating the Al-Zn alloy on the Al alloy, known methods such as a thermal spraying method, a vapor deposition method, and a sputtering method can be selected. However, the thermal spraying method is preferable in consideration of the economics of coating a large or large area Al alloy member. However, in these coating methods such as the thermal spraying method, as described above, a plurality of phases having different Zn contents from the conventional Al-Zn alloy coating are likely to occur. Therefore, the Zn content of all phases of the Al-Zn alloy film with different Zn contents was 3.6%.
In order to make the Zn contents of the plurality of phases of the Al-Zn alloy film substantially the same as described above, for example, in the thermal spraying method, the uniformity of the distribution of Al and Zn of the raw material alloy (Al-Zn alloy), The air pressure, the supply conditions of the raw alloy wire to the spray nozzle, etc. have various effects, and these are the same in other coating methods. Therefore, it is necessary to change and adjust these coating conditions in various ways to find the optimum conditions. There is.

[0026]

Next, embodiments of the present invention will be described. Various changes and adjustments of the air pressure, the supply conditions of the raw alloy (Al-Zn alloy) wire to the spray nozzle, etc.
A coated alloy having the composition shown in Table 1 described below was
A test piece was prepared by coating on the alloy substrate. Then, the average Zn content in the Al-Zn coated alloy of these test pieces was determined by inductively coupled plasma mass spectrometry (ICP-MS method), and the Al-Zn content was measured by a scanning electron microscope (SEM, × 1000). The plane of the coated alloy film was analyzed and a photograph of the structure (1 cm
The number of phases with different Zn contents and the Zn content of each phase were determined by measuring the composition distribution of the Al-Zn coated alloy using an X-ray microanalyzer (EPMA). In addition, coating Al
The natural potential A (E _corr ) of the Al-Zn alloy and the pitting potential C (E _pit ) of the Al alloy base material were measured, and the natural potential of the Al-Zn alloy was measured.
The difference ΔE (mV) between A and the pitting potential C of the Al alloy base material was determined. After that, these specimens were immersed in artificial seawater for one month, simulating the environment under high flow velocity of low temperature seawater (low temperature erosion / corrosion environment) of ORV heat transfer tubes.
Similarly, ΔE (mV) was obtained. Table 1 shows the results.

FIG. 4 shows a test apparatus used for this. The test apparatus includes an outer container 10 filled with water for temperature control, and an inner container 20 accommodated in the outer container 10. The temperature of the water for controlling the temperature of the outer container 10 is controlled to a desired temperature by the temperature controller 11, and the temperature of the artificial seawater filled with the inner container 20 and having a salt concentration of 3.5% is controlled to 5 ° C. The upper opening of the inner container 20 is closed by a lid 21, and an electric motor 22 having a stirrer 23 at a lower portion is attached to the lid 21. The test piece 26 is integrally attached to a lower portion of the stirrer 23, and is immersed in the artificial seawater.
Therefore, by driving the electric motor 22 and rotating the stirrer 23 in the horizontal direction at a rotation speed of 5000 rpm, it is possible to generate a flow of artificial seawater that moves circularly in the inner container 20, and the heat transfer tube for the ORV is used. The environment under high flow velocity of low temperature seawater can be simulated. The test piece 26 is attached and detached from the upper opening of the inner container 20 by opening and closing the lid 21.

In such a test apparatus, in the inner container 20, the counter electrode 30 of the base metal Al alloy is inserted from the counter electrode insertion hole 24, and the reference electrode 40 is inserted and immersed in the artificial seawater from the reference electrode insertion hole 25. At the same time, the test pieces 26 are opposed to each other with a certain interval therebetween. The test piece 26, the counter electrode 30, and the reference electrode 40 are electrically connected to a potentiostat M, and the polarization curve of the test piece 26 shown in FIG. From the graph of the polarization curve output to the recording device M1 attached to the potentiostat M, the natural potential A (E _corr ) of the coated Al-Zn alloy and the Al alloy base material of the test piece were obtained. Pitting potential C (E
_pit ), and the difference ΔE (mV) between the natural potential A of the Al—Zn alloy and the pitting potential C of the Al alloy base material can be obtained. The operation of this test apparatus was performed outside the outer container 10.
The operation is performed by the operation panel 50 arranged at (lower).

The measurement was performed using the test apparatus and conditions.
Spontaneous potential A of Al-Zn alloy and pitting potential C of Al alloy base metal
Table 1 shows the difference ΔE (mV) from the above. As is clear from Table 1, the Al-Zn alloy film is formed from a plurality of phases having different Zn contents, and the average Zn content of the Al-Zn alloy film is 3.6 to 85.0%.
In addition, in all of the plurality of phases, the Zn content is 3.6% or more, Invention Examples Nos. 1-4, 6, 7 are Al
The difference ΔE (mV) between the natural potential A of the -Zn alloy and the pitting corrosion potential C of the Al alloy base metal is high immediately after immersion in artificial seawater, and the difference between the It is clear that the film of the Al-Zn coating alloy has excellent sacrificial anticorrosion action and is excellent in low-temperature erosion and corrosion properties. Among the invention examples, the average Zn content, especially
Invention Examples Nos. 3 and 4 in which the Zn content of the Al-rich phase is relatively high are:
In particular, it shows excellent low-temperature erosion-corrosion properties.

On the other hand, the average of the Al-Zn alloy film
In Comparative Example No. 5 where the Zn content itself was low, the difference ΔE (mV) between the natural potential A of the Al-Zn alloy and the pitting potential C of the Al alloy base metal was
The level itself immediately after immersion in artificial seawater is low. Comparative Example No. 8 in which the Zn content of the Al-rich phase was less than 3.6%, or Al-Zn
Comparative Example No. 9 where the average Zn content of the alloy film exceeded 85.0%
The difference ΔE (mV) between the natural potential A of the Al-Zn alloy and the pitting potential C of the Al alloy base metal
After one month, it has dropped significantly. Therefore, it can be seen that in all of these comparative examples, the sacrificial anticorrosion effect of the Al-Zn coating alloy film is weak, and the low-temperature erosion / corrosion properties are poor. As a result, the average Zn of the Al-Zn alloy film of the present invention was
The critical significance of the specified content and the Zn content of each phase in the sacrificial corrosion protection of the Al-Zn coated alloy film is supported.

When the measurement result of ΔE (mV) in this embodiment is applied to the actual use of ORV in a heat transfer tube (use under a high flow rate environment of low-temperature seawater), the invention example is described as a heat transfer tube. Is about twice as long as the comparative example, and has a life difference of about 18 months. Also, the present invention relates to LNG such as ORV.
In addition to the vaporizer, the present invention can be applied as an Al alloy member for a large heat exchanger plant or a large chemical plant under a similar low-temperature erosion / corrosion environment.

[0032]

[Table 1]

[0033]

According to the present invention, it is possible to provide an Al alloy member that can guarantee long-term corrosion resistance even under a low-temperature erosion / corrosion environment such as seawater. This has industrial value in that it opens the way to larger LNG vaporizers, such as ORVs, and longer continuous operation.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a plurality of phases having different Zn contents in an Al—Zn alloy film according to the present invention.

FIG. 2 is an explanatory view showing a plurality of phases having substantially the same Zn content in an Al—Zn alloy film according to the present invention.

FIG. 3 is an explanatory diagram illustrating a polarization curve of a metal.

FIG. 4 shows natural potentials A and Al of an Al—Zn alloy according to an embodiment of the present invention.
FIG. 4 is an explanatory view showing a test device for obtaining a difference ΔE (mV) from a pitting potential C of an alloy base material.

FIG. 5 is a perspective view illustrating a general open rack vaporizer.

[Explanation of symbols]

a ~d: Al-Zn alloy _{coating, a 1, b 1, c} 1: Al -rich _{phase, a 2, b 2, c} 2: Zn -rich phase,

Claims (6)

[Claims] An Al alloy member having an Al-Zn alloy film formed on a surface thereof, wherein the Al-Zn alloy film is formed from a plurality of phases having different Zn contents, and the average Zn content of the Al-Zn alloy film is Is 3.
6-85.0% and the Zn content of all phases is 3.6%
An Al alloy member having excellent low-temperature erosion / corrosion properties, characterized in that: 2. The Al—Zn alloy film having an average Zn content of 3.
The low-temperature erosion according to claim 1, which is 6 to 20.0%.
Al alloy member with excellent corrosion properties. 3. The Al alloy member having excellent low-temperature erosion / corrosion properties according to claim 1, wherein a Zn content of a plurality of phases of the Al—Zn alloy film is substantially the same. 4. The method according to claim 1, wherein said Al-Zn alloy film is formed by thermal spraying.
The Al alloy member having excellent low-temperature erosion / corrosion properties according to any one of claims 1 to 3, wherein the Al alloy member is formed on the surface of the alloy member. 5. The Al alloy member excellent in low-temperature erosion-corrosion properties according to claim 1, wherein the low-temperature erosion-corrosion properties are for seawater. 6. The Al alloy member according to claim 1, wherein the Al alloy member is for an LNG vaporizer.