JPH06172905A - Aluminum alloy material for heat exchanger excellent in pitting corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an Al alloy material for heat exchanger excellent in strength and pitting corrosion resistance by providing an Al coating layer to a core material composed of an alloy having a specific composition consisting of Cu, Mn, Mg, and Al and forming a specific copper diffused layer. CONSTITUTION:An alloy having a composition consisting of, by weight, 0.2-1.0% Cu, further 0.6-1.4% Mn and/or 0.1-0.8% Mg, and the balance Al with inevitable impurities is used as a core material. One side or both sides of this core material are clad with coating layer consisting of pure Al or Al alloy and, in the course of its manufacture or brazing heating, Cu in the core material is allowed to diffuse in the coating layer, by which a copper diffused layer having sacrificial anode effect is formed in the surface layer part. At this time, the thickness of the diffusion layer, where Cu concentration is gradually reduced from the inner part of the coating material toward the surface, is regulated to 40-300mum, and the difference in Cu concentration between the inner part and the surface is regulated to 0.15-0.6%. By this method, the sacrificial anode effect of the surface layer part of the material can be made sufficient and maintained over a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy material for heat exchangers such as evaporators, condensers and radiators, and more particularly to a material excellent in pitting corrosion resistance and strength.

[0002]

2. Description of the Related Art For example, 3003 alloy is generally used as an aluminum alloy material used as a material for a heat exchanger (evaporator, condenser, radiator, etc.) for automobiles, but as a material for a heat exchanger having higher strength, Thirty
04, 6951 alloy or the like is used.

[0003]

Since the strength of the 3003 alloy after the brazing heat (600 ° C.) does not reach 12 kg / mm ² , it is difficult to reduce the thickness of the heat exchanger in order to reduce its weight. Further, the 3004, 6951 alloys and the like have insufficient pitting corrosion resistance, and there is a problem of penetration leakage due to pitting corrosion of the refrigerant passage pipe material.

Therefore, various anticorrosion methods have been proposed, but they are roughly classified into an anticorrosion method against outer surface (atmosphere side) corrosion and an inner surface (aqueous solution side) corrosion.

External corrosion is a major problem in evaporators, capacitors, radiators and the like. It is considered that a zinc diffusion layer is formed on the outer surface of the tube to prevent corrosion by the sacrificial anode effect. When vacuum brazing is performed for assembling the heat exchanger, zinc having a low vapor pressure is evaporated and scattered, and the sacrificial anode effect is insufficient. It is also considered that the sacrificial anode effect of a fin material (Al-Zn system, Al-Sn system, etc.) having a lower electric potential than that of the pipe material protects the pipe material from corrosion. Since the tank portion of the mold evaporator, the core plate portion of the radiator, and the like are in contact with the fin joint portion, there is no fin effect and pitting corrosion occurs.

Internal corrosion is a major problem in radiators, heater cores and the like. Triple clad material (Al-Si
/ 3003/7072, etc.) may be used to prevent corrosion of the core material by the sacrificial anode effect of the endothelial material (7072 etc.), but since zinc in the 7072 alloy evaporates by vacuum brazing, the sacrificial anode effect of the endothelial material is Will be insufficient. Further, when Zn, Sn, In, Ga, etc. are added in order to give the sacrificial anode effect to the endothelial material, the self-corrosion of the endothelial material is fast and easily consumed due to the inclusion of these elements, and the sacrificial anode effect of the endothelial material is Difficult to sustain for a long time. Although an Al-Sn alloy or the like may be used as the endothelial material, Sn is a low melting point element and is Al.
Since it does not form a solid solution, it is difficult to manufacture because cracks occur during casting and hot working.

As described above, the conventional heat exchanger materials have advantages and disadvantages, and a material satisfying both strength and pitting corrosion resistance is desired.

[0008]

The present invention provides Cu: 0.2.
~ 1.0 wt%, Mn: 0.6 ~ 1.4w
t% and Mg: 0.1 to 0.8 wt% of one type or two types, with the balance being an alloy consisting of Al and unavoidable impurities as a core material, and one or both surfaces of the core material being coated with pure Al or an Al alloy. A diffusion layer having a thickness of 40 to 300 μm in which the copper concentration gradually decreases from the inside to the surface of the coating material provided with the layer is provided, and the difference in copper concentration between the inside and the surface is 0.15 to 0.6 wt%.
The aluminum alloy material for heat exchangers has excellent pitting corrosion resistance.

Copper in the alloy material of the present invention forms a diffusion layer suitable for the sacrificial anode effect on the surface layer of the material. If the internal copper concentration is less than 0.2 wt%, a suitable copper diffusion layer will form on the surface layer. It is difficult to form and pitting occurs, and if it exceeds 1.0 wt%, the self-corrosion of the material becomes severe.

Mn and Mg have the effect of enhancing the strength without impairing the sacrificial anode effect of the copper diffusion layer. If both elements are added in excess of the upper limits, the corrosion resistance deteriorates. Addition of less than the lower limits enhances the strength. Less effective.

When the difference in copper concentration between the inside of the material and the surface is less than 0.15 wt%, the potential difference between the inside and the surface is small, the sacrificial anode effect on the inside of the surface layer portion is insufficient, and deep pitting corrosion occurs. If the concentration difference exceeds 0.6 wt%, the potential difference between the inside and the surface layer is large, the self-corrosion (consumption) rate of the diffusion layer is increased, and the sacrificial anode effect on the inside of the surface layer portion does not last for a long time.

If the thickness of the copper diffusion layer is less than 40 μm,
Since the diffusion layer corrodes in a short period of time, it does not exhibit a sufficient anticorrosion effect, and when it exceeds 300 μm, the diffusion layer has the same effect as that of the lower layer.

The method of forming a copper diffusion layer suitable for the sacrificial anode effect on the surface layers of the plate material and the tube material is as follows.

In the case of a clad plate, Al-Cu- (M
n, Mg) -based alloy core material on one or both sides of Al-S
i-based, Al-Si-Mg-based brazing material or pure Al, A
An Al alloy such as 1-Mn is clad.

In the case of a clad tube, the clad plate material is rolled into a tubular shape and welded. Alternatively, a hollow billet is prepared by casting a brazing material such as Al-Si, Al-Si-Mg or the like, or pure Al, Al alloy such as Al-Mn-based on the inside or inside / outside of the core material. To produce a clad tube.

In the case of an extruded flat multi-hole tube, Al-Cu-
(Mn, Mg) -based extruded flat multi-hole tube
The surface is coated with the brazing material by immersing it in a molten brazing material such as 1-Si-Mg system.

Although the above is just an example and various other methods can be used, copper in the core material is diffused in each of the manufacturing process and the brazing heat treatment process to give a sacrificial anode effect to the surface layer portion. A copper diffusion layer having is formed.

The detailed diffusion layer thickness, internal copper concentration,
Optimum conditions such as the difference in copper concentration between the inside and the surface differ depending on the operating environment, the allowable corrosion depth, etc., and should be determined at the time of design.

As a brazing method for the material of the present invention, any method such as vacuum brazing, inert atmosphere brazing, and flux brazing may be used.

In addition to copper, Mn, and Mg, the alloy material of the present invention contains impurities such as Si, Fe, Cr, Zn, Ti, and Z.
r, V, etc. may be contained in a range that does not impair the sacrificial anode effect of the copper diffusion layer.

[0021]

【Example】

Example 1 Each ingot piece of each alloy of Samples No. 1 to 11 in Table 1 was homogenized at 500 ° C. for 8 hours and then used as a core material on one surface of the brazing material. 4104 alloy pieces,
A 1050 alloy piece was polymerized on the other surface of the plate of the final product so that each clad ratio was 10%, and hot working and cold working were applied to manufacture a soft plate material having a thickness of 0.4 mm.

After heating this plate material at 600 ° C. for 5 minutes in a vacuum of 5 × 10 to ⁵ Torr, the 4104 alloy surface side and the 1050 alloy surface side of each plate material are separately sealed with silicone rubber, and each surface is sealed. A corrosion test was conducted on the. 1050
For alloy surface (ASTM × 10 + 10ppm C
u) Using an aqueous solution, alternately 80 ° C. × 8 hr and room temperature × 1
The test was conducted by immersion for 1 month in a cycle of 6 hours, 410
2 weeks CASS test (JIS-D-
0201). Table 1 also shows the maximum pitting depth of each surface by these tests.

A tensile test was conducted before the silicone rubber seal was applied. The results are also shown in Table 1.

4104 alloy side and 1050 shown in Table 1
The thickness of the copper diffusion layer in the alloy side surface layer was adjusted by variously changing the final softening treatment and the brazing addition heat treatment of the sample material. Table 1 also shows the difference in copper concentration between the inside and the surface of the test material (after the above vacuum heating). Sample No. 12 is 4343 /
Triple clad material 3003/7072 with a thickness of 0.4 m
It is a soft plate of m, and the 7072 alloy surface of this plate is a sample No.
Corrosion tests were performed under the same conditions as the corrosion tests performed on the 1050 alloy surfaces 1 to 11. Table 1 shows the diffusion layer thickness, copper concentration difference, and maximum pit depth.

As is clear from the results of Table 1, the material according to the present invention has excellent pitting corrosion resistance as compared with the comparative example and the conventional example, and is suitable as an aluminum material for heat exchangers.

[0026]

[Table 1]

[0027]

EFFECTS OF THE INVENTION The material of the present invention has a copper diffusion layer suitable for the sacrificial anode effect in the surface layer of the material, and therefore has excellent pitting corrosion resistance as compared with conventional materials, and particularly heat exchange. It also has excellent strength as a dexterous structural material.

Therefore, the material of the present invention is particularly useful as an aluminum material for heat exchangers for automobiles, and can be used for thinning the material and thus for reducing the weight of the heat exchanger.

Claims (1)

[Claims] 1. Cu: 0.2-1.0 wt%, Mn: 0.6-1.4 wt% and Mg: 0.1-
From the inside of a covering material containing 0.8 wt% of one or two kinds and a balance of Al and an unavoidable impurity as a core material and providing a coating layer of pure Al or Al alloy on one or both sides of the core material Thickness 40 to 3 in which the copper concentration gradually decreases toward the surface
An aluminum alloy material for a heat exchanger having excellent pitting corrosion resistance, which is provided with a diffusion layer of 00 μm and has a difference in copper concentration between the inside and the surface of 0.15 to 0.6 wt%.