JPS6127679B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum heat exchanger, and in particular has improved pitting corrosion resistance in the parts that come into contact with circulating water. Conventionally, aluminum heat exchangers, such as automobile radiators, have water chambers 2, 2 installed at both ends of a large number of upright parallel water pipes 1, and a large number of fins 3 between each water pipe 1, as shown in Fig. 1. In this installed structure, the cooling water that absorbs heat from the engine enters the radiator through the inlet 4 and is cooled, is sent to the engine section through the outlet 5, and is replenished through the supply port 6. In the figure, 7 indicates a side bar, and 8 indicates a drain pot. The fins of such heat exchangers are JIS3003 (Al
-Mn alloy), JIS1100 (industrial pure aluminum),
JIS5005 (Al-Mg alloy) or sacrificial anode fins made of these added with Zn, Sn, etc. are used, and aluminum composite plates with excellent cathodic protection are used for the water pipes and water chambers. This composite board has Zn0.8~1.3wt
% (hereinafter wt% is simply abbreviated as %), such as JIS7072 (Al-Zn alloy), is used as the skin material, and this is clad on one side of the core material made of JIS3003, and the other side is covered with a filler metal (All-Zn alloy). Si alloy, Al-Si-Mg
The water tubes and water chambers are formed by electric resistance welding or press molding to form water tubes and water chambers with brazing filler metal on the outer surface, and the water tubes are arranged upright and in parallel as shown in Figure 1. Water chambers are attached to both the upper and lower ends, and corrugated press-formed fins are attached between the upright water tubes, which are joined by plating. When the composite board is exposed to a corrosive atmosphere, the skin material, which has a lower potential than the core material, corrodes preferentially and has the effect of preventing corrosion of the core material, that is, has a cathodic protection effect. In order to manufacture a heat exchanger using such a composite plate, conventionally, plating is performed in the atmosphere using flux or plating is performed in molten flux. However, these methods have various drawbacks, such as the use of harmful flux, which poses pollution problems, and the need to completely remove the flux after brazing. In view of this, in recent years a method of brazing in a vacuum has been developed and has become popular. However, when brazing is performed in a vacuum, the Zn contained in the skin material of the composite plate that forms the water pipes and water chambers evaporates into the vacuum, and the Zn concentration on the surface of the skin material decreases extremely, resulting in a loss of cathodic protection. When exposed to a highly corrosive atmosphere such as an automobile radiator, especially cooling water that is not controlled by corrosion inhibitors, pitting corrosion can reach the core material and eventually penetrate the water pipes and water chamber. It had the drawback of creating holes. As a result of various studies on suppressing Zn evaporation during vacuum brazing according to JIS7072, the present inventors found that Zn evaporation can be suppressed by adding a small amount of Ca or Li to JIS7072.
I suggested this. However, although the addition of Ca or Li has a considerable effect, it is impossible to completely suppress Zn evaporation, especially in mass production.
Contamination of the furnace due to Zn evaporation has become a problem. In view of this, as a result of various studies, the present invention has discovered that an alloy made by adding a small amount of Ca to aluminum does not evaporate in a vacuum like Zn or Mg when vacuum brazing, and exhibits excellent cathodic protection effects. As a result of further study, we developed an aluminum heat exchanger with excellent cathodic protection.The multiple parallel water pipes and the water chambers attached to both ends are made of aluminum composite plates with brazing filler metal on the outer surface. form,
In a heat exchanger in which a large number of aluminum fins are attached between water tubes and joined by vacuum brazing, the water tube water chamber is made up of 1.0% Cu or less, 0.8% Mn or less, and a total of 0.5% or more of Cu and Mn. The core material is an aluminum alloy consisting of Al and normal impurities, with a brazing filler metal on one side and Ca0.02 ~ on the other side.
0.2%, the total of Fe and Si is 0.5% or less, and the balance is made of an aluminum composite plate with a skin made of aluminum, and is characterized by using the skin on the inner surface of the water pipe and water chamber. That is, in the heat exchanger of the present invention, water chambers are attached to both ends of a large number of parallel water tubes, a large number of fins are attached between the water tubes, and the water tubes and water chambers are connected by vacuum brazing, and the water tubes and the water chamber are formed by the following composite plate. Ca0.02-0.2%, total of Fe and Si 0.5 on the inner surface of the water pipe and water chamber through which the cooling water passes.
% or less, an aluminum alloy (hereinafter abbreviated as Al-Ca alloy) layer is formed with the remainder being Al. The composite plate has Cu less than 1.0%, Mn less than 0.8%, and Cu and
Aluminum alloy (hereinafter referred to as Al-Cu-Mn
(abbreviated as "alloy") plate is the core material, and one side is filled with a brazing material such as Al-Si alloy or Al-Si-Mg alloy, such as Al-10.
%Si-1.5%Mg alloy or a brazing filler metal with a small amount of Bi added thereto, and the other side is clad with an Al-Ca alloy material. This composite plate is roll-formed and a brazing material 1 is applied to the outer surface as shown in Figure 2.
a and an Al-Ca alloy material 1b on the inner surface, the contact surface is electrically welded to form the water tube 1, and the both ends of the water tube 1 are press-formed as shown in Fig. 3. Brazing material 9a is installed on the outside surface, and on the inside surface.
A water chamber tube plate 9 having an Al-Ca alloy material 9b, a brazing material 10a on the outer surface, and an outer frame 10 for the water chamber having an Al-Ca alloy material 10b on the inner surface are formed. By installing the water chamber 2 consisting of the outer frame 10, the inner surface of the water pipe 1 and the water chamber 2, through which cooling water passes, is
An Al-Ca alloy layer is formed. Ca in the Al-Ca alloy evaporates during vacuum brazing and forms a compound with the impurities Fe and Si contained in the aluminum without contaminating the inside of the furnace, thereby highly purifying the matrix and lowering the potential of the alloy. However, we limited the Ca content to 0.02 to 0.2% and the total content of Fe and Si in the impurities of Al to 0.5% or less.If the Ca content is less than 0.02%, Fe and Si in the impurities contained in aluminum The amount is too low for complete bonding, and the potential to the core material is not low enough to exert a cathodic protection effect, and if it exceeds 0.2%, excess Ca that does not bond with Fe and Si forms a compound with Al, causing damage to the core material. This is because the potential becomes higher. Furthermore, if the total content of Fe and Si exceeds 0.5%, Fe and Si crystallize in the matrix either alone or as a compound with Al, and the potential with respect to the core material does not become sufficiently low. Cu and Mn in the Al-Cu-Mn alloy (core material) have the effect of increasing the potential of the core material and imparting the necessary strength to the core material.
The total content of Cu and Mn within the range of 0.8% or less 0.5
% or more because even if either Cu or Mn exceeds the upper limit, the potential increase effect will be saturated, and in particular an increase in Cu will increase self-corrosion, and an increase in Mn will worsen plastic workability. This is because if the total content of Cu and Mn is less than 0.5%, the potential of the core material cannot be made sufficiently high. In addition, the core material is made by refining the crystals of the ingot.
Even if Ti is added, there is no problem if the amount added is 0.03% or less. The composite ratio of the Al-Ca alloy material to the total thickness of such a composite plate, that is, the cladding ratio, is not particularly limited, but is generally 2 to 20%, and the brazing metal cladding ratio is generally 5 to 15%. % is desirable. The heat exchanger of the present invention has the above-mentioned configuration, and the water pipes, water chambers, and fins formed as described above are combined as shown in Fig. 1, and heated in a vacuum of 1 x 10 ^-5 to 1 x 10 ^-4 Torr.
It is obtained by joining by vacuum brazing at a temperature of 580 to 600°C. Examples of the present invention will be described below. Example 1 Al-Ca alloy (skin material) with the composition shown in Table 1 and Al
- Composite plate for the water chamber of a heat exchanger with a plate thickness of 1.2 mm made of Cu-Mn alloy (core material) (cladding ratio of skin material 10%,
A skin material (thickness: 0.12 mm) was prepared and heated to a temperature of 600° C. for 10 minutes in a vacuum of 5×10 ^-5 Torr to simulate vacuum brazing, and then the following tests were conducted.
For comparison, A3003 (Al−0.15%Cu−1.1%Mn
alloy) as the core material, A7072 (Al-1.1%Zn alloy)
A conventional composite board for a water chamber made of a skin material was subjected to the same heat treatment, and then the following tests were conducted.
These results are also listed in Table 1. (1) The potentials of the skin material and core material were measured with reference to a saturated acetate electrode in 5% saline at 25°C. (2) Seal the surface of the core material with polyester tape,
Immerse it in a corrosive solution of tap water + 10ppmCu ⁺⁺ and keep the temperature of the corrosive solution at 80℃ for 8 hours, then return to room temperature for 16 hours.
The holding time was repeated for two months, and the maximum depth of pitting on the surface of the skin material was measured.

【table】

[Table] As is clear from Table 1, in all of the composite plates of the present invention, the potential of the skin material is sufficiently low compared to the potential of the core material, the maximum pitting depth is 0.12 mm or less, and the thickness of the skin material is (0.12mm), compared to conventional composite board No. 21
It turns out that it is much better than the . On the other hand, comparative skin materials No. 15 and No. 16, which do not contain Ca or have a low content of 0.01%,
Comparative skin material with a high total content of Fe and Si of 0.6%
No.17 or comparative leather material with high Ca content of 0.30%
For No. 18, the potential of the skin material was not low enough, and the depth of pitting corrosion was 0.18 mm or more, indicating that the corrosion penetrated through the thickness of the skin material and reached the core material. In addition, the Cu content and Mn of the core material
Comparative composite board No. 19, which has a low total Cu content of 0.4%, has a low potential in the core material and the depth of pitting corrosion reaches the core material, while comparative composite board No. 20, which has a high Cu content in the core material, Although the potential of the core material was high and the maximum water pitting depth was 0.08 mm, it was excellent, but the plastic working of the composite plate was poor and was not practical. Example 2 Thickness of a plate made of skin material and core material with the composition shown in Table 2
A 0.4 mm composite plate for water pipes of a heat exchanger (cladding ratio of skin material: 15%, skin material thickness: 0.06 mm) was prepared in Example 1.
After heat treatment in vacuum in the same manner as above, each test was conducted. The results are also listed in Table 2.

[Table] As is clear from Table 2, in all of the composite plates of the present invention, the potential of the skin material is sufficiently lower than that of the core material, and the maximum pitting depth remains within the thickness of the skin material. , it is found that it has an excellent cathodic protection effect. In contrast, it can be seen that the maximum pitting corrosion depth of the comparative composite material outside the scope of the present invention reaches the core material through the thickness of the skin material. Example 3 Using core material and skin material having the composition shown in Table 3, cladding the skin material on one side of the core material (cladding ratio of skin material 10%)
and Al-10%Si-1.5%Mg-0.02%Bi on the other side.
Composite plates with thicknesses of 1.6 mm and 0.4 mm were made by cladding brazing metal made of alloy (10% cladding ratio of brazing metal). A water tube as shown in Fig. 2 with a skin material on the outside and a water chamber as shown in Fig. 3 with a brazing material on the outer surface and a skin material on the inner surface are formed from a composite plate with a thickness of 1.2 mm. did. The water pipe was formed into a tubular shape by roll forming a composite plate, and the contact surface was electrically sewn. These were combined as shown in Figure 1, and fins made of ^A3003 plate formed into a corrugated shape were attached between the water tubes, and the aluminum was A manufactured heat exchanger was created. There is corrosion inside this heat exchanger (tap water +
10ppmCu ⁺⁺ ) was circulated at a temperature of 80°C for 8 hours and then at room temperature for 16 hours, which was repeated for 3 months, and then the maximum pitting depth of the water pipe and water chamber was measured. The results are also listed in Table 3. Note that the electrode potentials of the intermediate skin material and the core material in Table 3 are those measured in the same manner as in Example 1 on test pieces taken from the composite board.

[Table] As is clear from Table 3, in all of the heat exchangers of the present invention, the maximum depth of pitting corrosion remains within the skin material, indicating that the cathodic protection effect is excellent. On the other hand, in both the conventional heat exchanger and the comparative heat exchanger outside the scope of the present invention, the maximum depth of pitting corrosion reaches the core material through the skin material, and no cathodic protection effect is observed. In this way, the heat exchanger of the present invention shows excellent cathodic protection effect even after being bonded by vacuum brazing,
This has the remarkable effect of improving the pitting corrosion resistance of the heat exchanger and significantly extending its service life.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of an aluminum heat exchanger, Fig. 2 is a perspective view showing a water tube of the heat exchanger of the present invention, and Fig. 3 is a sectional view showing a water chamber of the heat exchanger of the present invention. . 1... Water pipe, 1a... Brazing metal, 1b... Al-
Ca alloy material, 2, 2'...Water chamber, 3...Fin, 4
...Cooling water inlet, 5...Cooling water outlet, 6...
Water supply port, 7...side bar, 8...drain pot, 9...tube plate for water chamber, 10...outer frame for water chamber.

Claims (1)

[Claims] 1. A heat exchanger in which multiple parallel water tubes and water chambers attached to both ends are formed from an aluminum composite plate with brazing material on the outer surface, and a large number of aluminum fins are attached between the water tubes and joined by vacuum brazing. , water pipes and water chambers should be Cu1.0wt% or less,
An aluminum alloy containing 0.8wt% or less of Mn, a total of 0.5wt% or more of Cu and Mn, and the balance consisting of Al and normal impurities is used as a core material, and a brazing filler metal is provided on one side of the core material.
On the other side, Ca0.02~0.2wt%, total of Fe and Si is 0.5wt
% or less, the aluminum heat exchanger is formed of an aluminum composite plate provided with a skin material of which the balance is aluminum, and the inner surface of the water tube and water chamber is made of the skin material.