JPS5851772B2 - Manufacturing method of corrosion-resistant aluminum pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for manufacturing corrosion-resistant aluminum pipe.

In this specification, the aluminum pipe is A70
This refers to pipes made of all aluminum alloys other than aluminum-zinc alloys such as 72 and pure aluminum.

In the case of aluminum pipes, pitting corrosion makes them unusable.

Therefore, an attempt was made to form an aluminum-zinc alloy coating layer on the inner surface of the aluminum pipe, which has a lower electrode potential than aluminum, to prevent pitting corrosion from occurring in the pipe itself due to sacrificial preferential corrosion of this coating layer. The technical idea behind this is already well known.

Incidentally, in the case of a plate, it is easy to form a sacrificial corrosion layer by co-rolling, but in the case of a pipe, it is difficult to form a sacrificial corrosion layer on the inner surface due to its shape.

As a solution to this problem, the applicant has applied a chemical dip plating method to coat the surface of aluminum pipes with 0.0
A zinc layer of 19/d~0.20 p/di is formed and then heated at a temperature above 200°C and below the melting point of aluminum to diffuse the zinc into the surface layer of the aluminum pipe to form a zinc layer of 30~0.20 p/di. A zinc diffusion layer of 300μ is formed, and 0
．． A method for manufacturing a corrosion-resistant aluminum pipe forming an aluminum-zinc alloy layer having a surface zinc concentration of 5 to 5.0% by weight was proposed (see Japanese Patent Publication No. 34103/1983).

According to this method, it is possible to obtain an aluminum pipe with excellent corrosion resistance and no fear of pitting corrosion, but unfortunately, pollution problems still remain because a chemical immersion plating method is applied.

In addition, it is necessary to change the thickness of the sacrificial corrosion layer appropriately depending on the use of the aluminum pipe, and therefore a method is required that can arbitrarily control the thickness of this sacrificial corrosion layer within a predetermined range. be done.

This invention was made in view of the above-mentioned circumstances, and it is possible to arbitrarily control the thickness of the sacrificial corrosion layer without worrying about pollution problems, and to obtain a long aluminum pipe. The purpose of the present invention is to provide a method for manufacturing corrosion-resistant aluminum pipes.

The method of manufacturing corrosion-resistant aluminum pipe according to this invention is as follows:
The first step is to make an aluminum hollow billet, and after the first step, zinc or an aluminum-zinc alloy is thermally sprayed on the inner surface of the aluminum hollow billet to form an inner coating layer made of zinc or aluminum-zinc alloy on the inner surface of the hollow billet. a second step, and a third step in which, after the second step, the hollow billet with the inner surface coating layer is extruded using a conventional method at a temperature lower than the melting point of the metal forming the coating layer to form a pipe.
step, and after the third step, the pipe is subjected to a diffusion treatment at a temperature of 200° C. or higher and lower than the melting point of aluminum to diffuse zinc into the inner surface layer of the pipe to form an inner sacrificial corrosion layer. It is characterized by consisting of a process.

As the above-mentioned thermal spraying method, a wire blast thermal spraying method is suitable, but other methods such as a fire thermal spraying method and a plasma thermal spraying method are also applicable.

When the sprayed metal is an aluminum-zinc alloy, the zinc content is at least about A7072, that is, 1% by weight.
There should be a certain amount of weight, and it is preferable to have a much larger amount than this, and about 10 weight □ is suitable.

In the above, after the pipe is shaped by extrusion, the pipe is subjected to a diffusion treatment to diffuse zinc into the inner surface layer of the aluminum pipe. has an excellent sacrificial corrosion effect because it is appropriately thick.

The reason why the diffusion treatment temperature was limited to 200°C or higher and below the melting point of aluminum is because zinc cannot be sufficiently diffused below 200°C, and when the melting point of aluminum is exceeded, the aluminum pipe will melt. .

The thickness of the zinc diffusion layer formed by the diffusion treatment is 30 to 3
It is preferable that it is about 00μ.

Moreover, the surface zinc concentration of the inner sacrificial corrosion layer is 0.5 to 5.
It is preferably about 0% by weight.

If a thin-walled pipe is required, it is finished to the specified size using a pultrusion method after extrusion molding.

The purpose of performing the first to fourth steps in the above order is to manufacture long and small diameter corrosion-resistant aluminum pipes.

In other words, since the hollow billet is short and the diameter of the hollow part is large, the inner coating layer is coated on the hollow billet by thermal spraying.
Since it can be easily formed into a uniform thickness and then the pipe is formed by extrusion molding, it is possible to produce a long pipe with a small diameter and an inner coating layer of uniform thickness.

Finally, by performing a diffusion treatment, it is possible to obtain a corrosion-resistant aluminum pipe that is long, small in diameter, and has an inner sacrificial corrosion layer of uniform thickness.

On the other hand, when forming an inner coating layer by thermal spraying after extrusion molding a hollow billet to make a long and small diameter pipe, it is necessary to freely control the thickness and make it uniform. It is difficult.

According to the method for manufacturing a corrosion-resistant aluminum pipe according to the present invention, in the fourth step, zinc or aluminum-zinc alloy that forms a sacrificial corrosion layer on the inner surface of the pipe is thermally sprayed on the inner surface of the hollow aluminum billet. Unlike conventional plating methods, no waste liquid is produced, so there is no risk of pollution problems.

Furthermore, since zinc or aluminum-zinc alloy is thermally sprayed onto the inner surface of a short aluminum hollow billet with a large diameter hollow portion, the thickness of the inner surface coating layer can be easily and freely controlled.

Therefore, the thickness of the sacrificial corrosion layer on the inner surface can be freely controlled, and corrosion-resistant aluminum pipes suitable for various uses can be obtained.

Further, after forming the inner surface sprayed coating layer on the hollow billet, the hollow billet provided with the sprayed inner surface coating layer is extruded by a conventional method at a temperature lower than the melting point of the coating layer forming metal to form a pipe,
Since this pipe is subjected to a diffusion treatment at a temperature of 200°C or higher and lower than the melting point of aluminum to diffuse zinc into the inner surface layer of the pipe, a thick inner sacrificial corrosion layer consisting of an aluminum-zinc alloy layer is formed. can form, and its preferential corrosion prevents pitting corrosion in the pipe.

And the inner sacrificial corrosion effect is maintained for a long time.

Furthermore, after making an aluminum hollow billet, an inner coating layer is formed on the hollow billet by thermal spraying, a pipe is then formed by extrusion molding, and finally a diffusion treatment is performed on the pipe to form an inner sacrificial corrosion layer. This makes it possible to manufacture long, small-diameter corrosion-resistant aluminum pipes.

Embodiments of the invention will be described below with reference to the drawings.

As shown in Figure 1, the outer diameter is 300 mm.

An aluminum hollow billet 1 having an inner diameter of 135 mm and a length of 4501 nm was prepared, and zinc was thermally sprayed onto the inner surface of the billet by a wire bombardment spraying method to form an inner surface coating layer 2 with a thickness of 100 μm on the hollow billet 1.

The hollow billet 1 provided with the inner surface coating layer 2 was heated to 350° C. and extruded by a conventional extrusion method to form a pipe having an outer diameter of 127 mm and an inner diameter of 115 mm.

The pipe was heated at 500'C for 3 hours to diffuse zinc into the surface layer of the aluminum pipe to form a 200μ zinc diffusion layer, with a surface zinc concentration of approximately 2 wt □ and an internal layer of An aluminum pipe 3 was obtained which was provided with a zinc diffusion layer, that is, an inner sacrificial corrosion layer 4 in which the degree of zinc corrosion gradually decreased over time (see FIG. 2).

[Brief explanation of drawings]

The drawings show an embodiment of the present invention in the order of steps. Figure 1 is a longitudinal cross-sectional view of a hollow billet with an inner surface coating layer formed by thermal spraying, and Figure 2 is a longitudinal cross-sectional view of a pipe with an inner surface sacrificial corrosion layer. FIG. 1... Hollow billet, 2... Inner coating layer, 3... Pipe, 4... Inner sacrificial corrosion layer.

Claims (1)

[Claims] 1 The first step of making an aluminum hollow billet, and after the first step, forming an inner coating layer made of zinc or aluminum-zinc alloy on the inner surface of the hollow billet by spraying zinc or aluminum-zinc alloy on the inner surface of the hollow billet. A second step of forming a pipe by extruding a hollow billet with an inner surface coating layer by a conventional method at a temperature lower than the melting point of the metal forming the coating layer after the completion of the second step; The pipe is subjected to a diffusion treatment at a temperature of 200°C or higher or lower than the melting point of aluminum,
A method for manufacturing a corrosion-resistant aluminum pipe, comprising a fourth step of diffusing zinc into the inner surface layer of the pipe to form an inner sacrificial corrosion layer.