JPS63111181A - Method for applying zinc on extruded aluminum stock - Google Patents

Abstract

PURPOSE:To increase peeling strength of a coated Zn layer and to enhance corrosion resistance and also to enable free processing such as blending work after Zn treatment by mechanically subjecting an extruded Al stock to roughened surface processing at the specified surface roughness just after extruding the Al stock and thereafter treating it in a melted ZnF2 bath and then baking it. CONSTITUTION:An extruded stock 5 obtained by extruding a billet 1 of Al (alloy) is worked at 6-30mu surface roughness just after extrusion with a roughener 7 which mechanically performs roughened surface processing such as shot blasting. Then after immersing a short-sized extruded stock 5' which is obtained by cutting it at proper length into a melted ZnF2 bath 9, a Zn diffusion layer is formed by drawing up it from the bath 9 and successively baking it. Further the extruded stock 5 is desirably a flat tube having many holes. By this method, even when performing bending work or the like, free processing can be performed after Zn treatment because pitting corrosion is not caused.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for coating zinc extrusions on aluminum extrusions, and particularly relates to a method for coating zinc extrusions on aluminum extrusions suitable for use in tubes of heat exchangers. .

[Prior Art] Aluminum and aluminum alloys have better corrosion resistance than ordinary steel, and if used in a normal manner, they have sufficient corrosion resistance even when they are taken from raw materials or when they are anodized or painted.

However, it has poor corrosion resistance and is prone to pitting corrosion, mainly in the transportation field, where it is used in areas with strong corrosive atmospheres such as heavy industrial areas, the Middle East, and North America.

■Car air conditioners and heat exchangers are one of the fields where corrosion resistance has been particularly important recently. Car cooler condensers, evaporators, etc. are generally made by bending an extruded multi-hole tube 5 into a serpentine shape with a harmonica cross-sectional shape as shown in Fig. 4, and interposing a very thin aluminum fin 12 material between the tubes 5. The core is fixed to a jig, the melting temperature of the brazing filler metal is maintained at approximately 650° C., and the tube 5 and the fin material 12 are integrated under heating conditions for 2 minutes.

In this case, consideration is given to using the fin material 12 which has a larger ionization tendency than the tube 5, and to obtain a sacrificial corrosion effect in which the fin material 12 is preferentially corroded.

However, since the fin material 12 is not present at the bent portion of the tube 5, the corrosion resistance is poor in a bare state or in a state subjected to alumite treatment or painting, and pitting corrosion is likely to occur.

Therefore, recently, coating the aluminum surface with zinc has been carried out.

That is, an attempt has been made to form a coating layer made of zinc on the surface of aluminum or an aluminum alloy, and to prevent pitting corrosion of aluminum extrusions through the sacrificial corrosion effect of this zinc coating layer.

By the way, the following technique is conventionally known as a method for forming a zinc diffusion layer on an aluminum extrusion material.

Immediately after extrusion, an extruded aluminum or aluminum alloy material is immersed in a molten zinc bath (hereinafter referred to as the immersion method) or vaporized zinc is deposited (hereinafter referred to as the vapor deposition method), and after immersion or vapor deposition, the extruded material is A method of forming a zinc diffusion layer on the surface of an extruded aluminum material by heating the aluminum to 600°C to diffuse zinc into the extruded aluminum material (for example, Japanese Patent Publication No. 59-31588).

[Problems to be Solved by the Invention] However, the method for forming the zinc coating layer described above has the following problems.

(2) In the prior art, the extruded material immediately after extrusion is coated with zinc by immersion or vapor deposition.

However, the surface roughness of the extruded material immediately after extrusion is as small as 0.5 to 5 l, and if it is coated with zinc in that state, the peel strength will be low.

Particularly, for example, when pressing or bending is performed to form a tube for the above-mentioned heat exchanger, cracks occur in the zinc coating layer at the corners.

[Means for solving the problem] The above problem can be solved by extruding aluminum or aluminum alloy material and mechanically roughening the extruded material obtained by extrusion immediately after extrusion to improve the surface roughness of the surface of the extruded material. degree 6-30
After surface roughening, the extruded material is immersed in a bath of molten zinc fluoride.

The problem is solved by a method for coating aluminum extrudates with zinc, which is characterized in that the extrudates are baked after being pulled out of a bath of molten zinc fluoride.

There are no particular limitations on the material of aluminum or aluminum alloy material. For example, pure A sentence, A sentence-CU system, A l
-Mg series, An-Si series, A-Mn series, A1-Mg
-5i system, An-Cu-Mg system, A! ;L-Cu-Ni
system, A l -M g -Z n system, AM-Cu-3i
Applies to each alloy in the series.

In the present invention, the extruded material obtained by extrusion is mechanically roughened immediately after extrusion.

Mechanical roughening is performed immediately after extrusion because the surface of the extruded material is clean and has no oxide film, so it is immersed in a zinc fluoride bath in an activated state! A# A strong zinc layer is easily formed.

As a means for roughening the surface, for example, show blasting or sandblasting may be used.

It is thought that increasing the surface roughness by mechanical roughening increases the surface area, which increases the adhesion of zinc.

The reason why the surface roughness of the extruded material surface is set to 6 to 30 degrees is because the peel strength of the zinc coating layer decreases if the surface roughness is less than 6 degrees. To,
The extruded material is immersed.

The temperature of the bath is preferably 400 to 600°C.

Moreover, the immersion time is preferably 1 to 20 minutes.

Note that if the extruded material is exposed to IFL sound waves during dipping, the delamination strength will be further improved.

After the extruded material to which zinc has been adhered is pulled out of the bath, the baking time may be any time and temperature that is commonly used.

By such baking, zinc is diffused into the aluminum extrusion, and a zinc diffusion layer is formed on the surface of the extrusion.

The shape of the extruded material is not particularly limited, such as a pipe, rod, multi-hole flat tube, etc. In the case of a pipe, the surface of the extruded material to be coated may be either the inner surface, the outer surface, or the inner or outer surface depending on the use. be.

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

FIG. 1 is a plan view for explaining the extrusion process.

In the figure, 1 is a billet and 5 is an extruded material.

The heating temperature of billet 1 was approximately 450°C, and the extrusion speed was 3
A as m/m i in! ; L-Cu-based billet 1 was extruded into a multi-hole flat tube of a heat exchanger.

Immediately after extrusion, the extruded material 5 obtained by extrusion is introduced into a shot blasting device 7, which is a surface roughening device, as shown in FIG. 2, and shot blasting is applied to both surfaces thereof.

In this example, since the extruded material 5 is long, it was cut into an appropriate length after shot blasting to obtain a single length extruded material of 5°.

The extruded piece 5' was then immersed in a bath 9 of molten zinc fluoride. Ultrasonic waves were applied to the mono-length extruded material 5'' during immersion.

The following tests were conducted on the extruded material coated with zinc as described above.

In addition, the same test as in the example was conducted on an extruded aluminum alloy material extruded by the same method as in the above example, and an extrusion material coated with zinc using the dipping method and the vapor deposition method described in the conventional example. I saved up.

(State of Zinc Diffusion Layer) The extruded material was baked at 600° C. for 2 minutes to diffuse zinc, and then the depth and zinc concentration of the diffusion layer were investigated.

-Depth In this example and in the case of the immersion method, a diffusion layer with a depth of 100° from the surface was obtained. On the other hand, in the case of the vapor deposition method, the depth of the diffusion layer was 90 degrees from the surface.

- Zinc concentration In the case of this example, the concentration was 1%, but in the case of the immersion and vapor deposition methods, the concentration was 0.8% or less.

Note that the above results are shown in Table 1.

(Adhesion) Adhesion was evaluated by a bending test. That is, after coating with zinc, the extruded material was bent by 90 to 180', and peeling of the zinc layer at that time was observed.

The results are shown in Table 1.

When the immersion method was used, 211a formed in the tube, and when the vapor deposition method was used, the tube simply peeled off. On the other hand, 'A#' was not recognized in the case of this example.

The results below are shown in Table 1.

(Corrosion resistance) The tube and fin material were brazed (600°C x 2 minutes) in the configuration shown in Figure 5 under the conditions of 600'CXZ, and the brazing was carried out after the salt spray test specified in JISH G661. I did it.

In the case of the immersion method and the vapor deposition method, pitting corrosion occurred after 600 poems. In contrast, in the case of this example, no pitting corrosion was observed even after 8°0 hours had elapsed. In particular, even in the U-bend, only general corrosion was observed, and no pitting corrosion was observed.

[Effects of the Invention] Since the present invention is configured as described above, the following effects can be obtained.

■Corrosion resistance is superior to conventional methods.

- Since pitting corrosion does not occur even when bending is performed, free processing can be performed after zinc treatment.

[Brief explanation of the drawing]

FIG. 1 is a plan view for explaining the extrusion process. Second
The figure is a side view showing the shot blasting process. FIG. 3 is a side sectional view showing a zinc fluoride bath. FIG. 4 is a cross-sectional perspective view showing the tube. FIG. 5 is a side view showing the state in which the fins are brazed to the tube. 1・φ aluminum billet, 2・・Dice, 2′・φ
Dice bearing, 3 @ ii container, 4... Stem, 5... Aluminum extrusion, (tube) 5'... Aluminum single length material, 6... Line out table, 7φ/Roughened case, 8... Rough Surface forming device (shot blasting device ff1)
, 9@・Zinc bath, 10.. Ultrasonic device, 11.. Heating device, 12.. Aluminum fin. Figure 1- Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. Extruding aluminum or aluminum alloy material, and mechanically roughening the extruded material obtained by extrusion immediately after extrusion, so that the surface roughness of the surface of the extruded material is 6 to 30.
μ, and after surface roughening, the extruded material is immersed in a bath of molten zinc fluoride, and after the extruded material is pulled out of the bath of molten zinc fluoride, baking is performed. Zinc coating method. 2. The method for coating an aluminum extruded material with zinc according to claim 1, wherein the extruded material is a multi-hole flat tube of a heat exchanger.