JP2541411B2 - Aluminum alloy for brazing sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aluminum alloy used as a skin material for a brazing sheet having excellent corrosion resistance.

[0002]

2. Description of the Related Art Aluminum-based materials are used as heat exchanger components such as condensers and evaporators because of their light weight and excellent corrosion resistance. In particular,
As a lightweight component focused on low fuel consumption, demand for heat exchangers such as radiators for automobiles is expected. In this type of application, a brazing material layer is provided on one surface of the core material in order to facilitate brazing with the radiation fins, and a skin material having excellent corrosion resistance is provided on the other surface in contact with the corrosive liquid. Layered brazing sheets have been developed.

A typical brazing material is an Al--Si alloy. Further, as the core material, an Al-Mn-based alloy excellent in mechanical strength and corrosion resistance is used.
Al-Zn alloys are known as skin materials that come into contact with corrosive liquids.

Brazing sheets are used, for example, as radiator tubes and header plates. The tube is manufactured by making a brazing sheet with the skin material inside and then electro-welding the butt end surfaces. Then, the thin fin is combined with the tube and the header plate, and the radiator in which the tube, the header plate and the thin fin are integrated is assembled by brazing in the furnace.

The tubes and header plates constituting the radiator are required to have excellent corrosion resistance so that through holes due to corrosion do not occur. On the other hand, there is a strong demand for weight reduction of radiators along with the reduction of fuel consumption of automobiles, and thin brazing sheets are desired as materials used for tubes, header plates and the like.

Al-Zn based skin materials, which have shown sufficient corrosion resistance in conventional brazing sheets, cannot provide sufficient internal corrosion resistance to thin brazing sheets. The cause thereof is that Zn is evaporated or diffused during brazing, and the content of Zn exhibiting a sacrificial anticorrosion effect is reduced in the surface layer of the skin material after brazing. The decrease in the Zn content in the surface layer of the skin material did not have a large adverse effect on the corrosion resistance because the conventional thick brazing sheet was expected to supply Zn from the lower layer. However, as the brazing sheet becomes thinner, Zn
, The sacrificial anticorrosive action of Zn is not sufficiently exerted, and through holes are generated due to corrosion.

Therefore, Japanese Patent Laid-Open No. 2-129333 proposes to improve the pitting corrosion resistance in the internal circulating water by adding 0.2 to 1.0% by weight of Mg to the skin material. . It is said that the added Mg contributes to improving the pitting corrosion resistance of the skin material without changing the electrochemical properties of the skin material. In addition, some examples have been reported in which the pitting corrosion resistance of the skin material is improved by adding In.

[0008]

Although the pitting corrosion resistance of the skin material is improved by the addition of Mg, the Zn concentration remaining in the skin material after brazing is insufficient depending on the heating conditions during brazing. Is inevitable. Therefore, the expected sacrificial anticorrosion effect of Zn cannot be obtained, and the required characteristics concerning pitting corrosion resistance cannot be satisfied. To avoid this,
It is necessary to strictly control the heating conditions during brazing, which causes a decrease in productivity.

On the other hand, in the case where the pitting corrosion resistance is improved by adding In, In, which is a low melting point metal, is easily segregated, and In
The self-potential locally becomes base at the segregated area, and the anticorrosion performance of the skin material against the core material becomes unstable. Moreover, since the natural potential becomes too base, the consumption of the skin material increases. As a result, although the sacrificial anticorrosive action is strengthened, corrosion products such as aluminum hydroxide are deposited on the inner surface of the tube as a result of the sacrificial anticorrosion reaction, which promotes the occurrence of defects such as clogging. Moreover, In becomes a major obstacle when recycling scraps to be used as a raw material.

The present invention has been devised in order to solve such a problem. By adding alloy elements such as Y, Ce, La, Nd and Pr to the skin material, the corrosion mode of the skin material can be improved. It is an object of the present invention to provide an aluminum alloy for a brazing sheet, in which pitting corrosion is changed to general corrosion and the progress of corrosion is suppressed.

[0011]

The aluminum alloy for a brazing sheet of the present invention has the following objects and advantages.
Al—Si based brazing filler metal is a skin material laminated on one surface of the Al—Mn based core material laminated on one surface, and Zn: 1.0-3.
0% by weight, Mg: 0.5 to 3.0% by weight, Si: 0.0
5 to 0.5% by weight and Fe: 0.05 to 0.5% by weight, further Y: 0.01 to 0.8% by weight, C
e: 0.01 to 1.5% by weight, La: 0.01 to 1.5
Wt%, Nd: 0.01 to 1.5 wt% and Pr: 0.
It is characterized by containing 01 to 1.5% by weight of one kind or two or more kinds.

The contents of Zn and Mg contained in the skin material are
It is preferable to maintain the Zn% / Mg% ratio in the range of 1 to 6.

[0013]

[Operation] When an aluminum alloy comes into contact with an aqueous solution, it is thought that the following reactions proceed and pitting corrosion occurs. On the aluminum alloy surface, Al → Al ³⁺ + 3e ⁻
Al is eluted according to the anode reaction of. The electron e ⁻ generated along with the elution of Al causes a cathode reaction of O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ with oxygen dissolved in the aqueous solution to generate a hydroxide ion OH ⁻ . The hydroxide ion OH ⁻ is further ^{converted into} Al ³⁺ +3 with the Al ³⁺ ion.
Causes a pitting reaction of OH ⁻ → Al (OH) ₃ . This pitting corrosion reaction is confirmed by the white precipitate Al (OH) ₃ being deposited around the pitting holes.

If an Al-Zn-based skin material intervenes in this corrosion system, a sacrificial anticorrosion reaction occurs in which the skin material preferentially dissolves in the Al alloy core material, and elution of Al itself is suppressed. However, in the case of a material that positively performs the sacrificial anticorrosion reaction, the elution amount of the skin material inevitably increases, and the life of the brazing sheet is shortened.Of course, corrosion products such as aluminum hydroxide are contained in the tube. As described above, defects such as accumulation and clogging occur.

Therefore, it is necessary to suppress the elution of the skin material and the occurrence of pitting corrosion while maintaining the sacrificial anticorrosive action of the Al—Zn based skin material. In the present invention, the evaporation of Zn is suppressed by the addition of Mg, the sacrificial anode effect of the skin material is enhanced by adding alloy elements such as Y, Ce, La, Nd and Pr, and the elution of the skin material is suppressed. are doing. Y,
The elution suppression of the skin material by Ce, La, Nd, Pr, etc. is presumed to be due to the following mechanism.

For example, when Y is added to an aluminum alloy, the spontaneous potential shifts to the base and the difference from the pitting potential widens. Therefore, pitting corrosion is less likely to occur. Further, Y contained in the aluminum alloy reacts with chlorine ions contained in water to become YCl ₃ . YCl ₃ is
It accumulates in the aqueous solution and acts as a corrosion inhibitor by itself, and when it exceeds a certain concentration, it is deposited on the surface of the aluminum alloy as oxide Y ₂ O ₃ or hydroxide Y (OH) ₃ .

Oxide Y ₂ O ₃ or hydroxide Y (OH) ₃
All form a dense film and cover the surface of the aluminum alloy. Therefore, O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻
Since the cathodic reaction is suppressed and the hydroxide ion OH ⁻ is not supplied, the pitting corrosion reaction that produces Al (OH) ₃ does not proceed. Other Ce, La, Nd, Pr, etc. also suppress the pitting corrosion of the aluminum alloy by a similar mechanism.

As a result, on the surface of the aluminum alloy,
In place of the conventional pitting corrosion with a large erosion depth, a relatively shallow pitting corrosion takes the form of general erosion over the entire surface. Then, elution of the skin material is suppressed, and excellent corrosion resistance is exhibited for a long period of time.

Further, Mg contained in the skin material improves the sacrificial anode action in cooperation with Zn. Mg in the skin material diffuses into the core material by heating during brazing. At this time, Mg
Diffusion rate of Zn is higher than that of Zn, and diffusion of Zn into the core material during brazing is suppressed. as a result,
After the brazing, a decrease in the residual Zn concentration that effectively acts on the sacrificial anticorrosion effect is prevented. In this respect, the Mg content is set in the range of 1 to 6 in terms of Zn% / Mg% ratio in relation to the Zn content.

The alloy components and content of the skin material will be described below. Zn: This is an essential alloy component for protecting the tube core material in the liquid contact part by the sacrificial anode action. However, since Zn easily diffuses into the core material during brazing, the residual Zn concentration of the skin material is set to 0.
It is necessary to secure at least 8% by weight. This residual Z
In order to secure the n concentration, the skin material contains Zn in an amount of 1.0 wt% or more. When the Zn content is less than 1.0% by weight, the residual Zn concentration is less than 0.8% by weight due to the heat diffusion during brazing, and the pitting corrosion resistance decreases.

When the Zn content in the skin material exceeds 3.0% by weight, the residual Zn concentration exceeds 1.5% by weight, and the amount of corrosion produced at the time of contact with liquid is the cause of clogging in the tube. Will increase. Therefore, the Zn content of the skin material is suppressed to 3.0% by weight or less, and the sacrificial anticorrosive action is complemented by the addition of Mg.

Mg: The Mg component in the skin material has a function of shifting the natural potential of the skin material to base and enhancing the sacrificial anticorrosion effect of Zn. Further, by heating during brazing, an oxide film MgO is formed on the surface of the skin material to prevent Zn evaporation and scattering. Moreover, Mg diffuses inside the core material and contributes to the strength improvement without impairing the brazing property. In order to obtain such an effect, it is necessary to contain 0.5% by weight or more of Mg in the skin material. However, the Mg content is 3.0% by weight
If it exceeds, the electric potential of the skin material becomes unnecessarily low and the wear of the skin material is promoted. Therefore, the Mg content is 0.5 to
It was defined in the range of 3.0% by weight.

Si: The Si component in the skin material reacts with the Mg component to form a fine intermetallic compound Mg ₂ Si, thereby improving the strength after brazing. This strength improving effect is small when the Si content is less than 0.05% by weight. However, the Si component contained in the skin material is also a factor that forms an Al-Fe-Si-based intermetallic compound. This Al-F
Since the e-Si-based intermetallic compound is electrochemically more noble than the Al-Zn-based intermetallic compound, it acts as a nucleus of pitting corrosion and reduces the sacrificial anode action. The Al-Fe-Si-based intermetallic compound having such an adverse effect is caused by the Si in the skin material.
When the content exceeds 0.5% by weight, it appears remarkably. Therefore, the Si content is restricted to the range of 0.05 to 0.5% by weight.

Fe: The Fe component contributes to improvement of hot rolling property and strength. However, when the Fe content is less than 0.05% by weight, the effect of improving properties is small. On the contrary, if the Fe content exceeds 0.5% by weight, the corrosion resistance is rather impaired. Therefore, the content of Fe in the range of 0.05 to 0.5% by weight is
The content was set.

Y: Y contained in the skin material is changed to yttrium chloride YCl ₃ by reacting chlorine ion Cl ⁻ dissolved in the internal circulating water from the environment with hydrochloric acid generated by the reaction with water. Yttrium chloride YCl _{3 functions} as a corrosion inhibitor by itself, and also forms an oxide film or a hydroxide film to cover the surface of the liquid contact part, and suppress the cathode reaction of aluminum. As a result, a so-called two-step anticorrosive action is exhibited in which both pitting corrosion and general corrosion are suppressed.
This effect remarkably appears when the Y content is 0.01% by weight or more. However, even if Y is contained in an amount exceeding 0.8% by weight, the property improving effect commensurate with the increased amount cannot be obtained. Therefore, the Y content is set to the range of 0.01 to 0.8% by weight.

Ce, La, Nd and Pr: These alloying elements react with chlorine ions Cl ⁻ in the aqueous solution to form CeCl ₃ , LaCl ₃ , NdCl ₃ and PrCl ₃ , respectively.
Generate Each of the produced chlorides has a strong film forming action, and forms an oxide film or a hydroxide film on the surface of the liquid contact part, like Yttrium chloride YCl ₃ . Then, both pitting corrosion and general corrosion are suppressed. This action is Ce, L
When the content of each alloying element such as a, Nd and Pr is 0.01% by weight or more, it appears remarkably. However, even if Ce, La, Nd, Pr or the like is contained in an amount of more than 1.5% by weight, a property improving effect commensurate with the increased amount cannot be obtained. So Ce, L
The content of a, Nd, Pr, etc. was in the range of 0.01 to 1.5% by weight, preferably 0.03 to 1.2% by weight.

The aluminum alloy skin material of the present invention may further contain a trace amount of Ti and / or B as a grain refinement element. The addition of Ti, B, etc. makes the alloy structure a dense crystal structure and improves the mechanical strength. Also,
Ti is an alloying element effective in suppressing the cathode reaction and improving the corrosion resistance. Such property improvement is
Content and B content are 0.01% by weight and 0.
It becomes remarkable at 0001% by weight or more. However, Ti and B
If a large amount of is added, the amount of precipitates such as intermetallic compounds becomes large, and there is a dislike that workability and corrosion resistance are deteriorated. Therefore, when Ti and / or B is contained, the respective contents are 0.01 to 0.2% by weight and 0.000.
The range is 1 to 0.01% by weight.

[0028]

【Example】

Example 1: Various aluminum alloys whose components and contents are shown in Table 1 were used as skin materials. Also, as a core material, C
u: 0.5% by weight, Si: 0.3% by weight, Fe: 0.5
% By weight, Mg: 0.15% by weight, Mn: 1.1% by weight,
Using an aluminum alloy containing Ti: 0.1% by weight,
As the brazing material, 4045 brazing material was used.

A core material, a skin material and a brazing material are separately cast, subjected to soaking for heating at 480 ° C. for 3 hours, respectively, and then hot rolled and then cold rolled. A brazing sheet was manufactured. In addition,
The cold rolling was performed while sandwiching intermediate annealing for heating at 400 ° C. for 1.5 hours.

Using the obtained brazing sheet as a test material, the temperature was raised at 50 ° C./hour to 600 ° C. assuming brazing.
After heating for 3 minutes, it was gradually cooled.

[0031]

[Table 1]

A test piece having a width of 25 mm and a length of 100 mm was cut out from the test material after the heat treatment and subjected to a corrosion resistance test.
The corrosion resistance test is performed by immersing the test piece with the brazing filler metal side and the end surface sealed with resin in a corrosive liquid, 88 ° C × 8 hours → 35 ° C × 16
A beaker test was repeated 14 times with one cycle as time. Etchant used was, Cl pure water ^-: 1000
^{_{ppm, SO 4 2-: 1000ppm,}} HCO 3 -: 100
It was adjusted by adding 0 ppm and Cu ²⁺ : 10 ppm.
The immersion liquid was renewed after the immersion was repeated 7 times. Then, the amount of corrosion was obtained from the weight difference of each test piece before and after the corrosion test, and the depth of pitting corrosion generated in each test piece after the corrosion test was measured by the microscope focal depth method. Table 2 shows the results of the investigation of the amount of corrosion and the maximum pitting depth.

[0033]

[Table 2]

As is clear from Table 2, Zn% / Mg%
It is found that when 0.01% by weight or more of Y and / or Ce is contained under the condition of = 1 to 6, the maximum pitting corrosion depth becomes 100 μm or less, and excellent corrosion resistance is shown after brazing. In addition, the corrosion weight loss was also determined by sample numbers 12 to 15 containing no Y or Ce or containing less than 0.01% by weight.
Compared to, it is less than 10%. Thus, the inclusion of Y and / or Ce suppresses both pitting corrosion resistance and general corrosion.

By the way, when considering the actual usage of the heat exchanger, the acceptable line from the viewpoint of pitting corrosion resistance is 100 μm.
m or less is required. In this regard, Sample Nos. 1 to 11 according to the present invention all satisfy this requirement. Further, the brazing sheets obtained by laminating the aluminum alloys of Sample Nos. 1 to 11 as the skin material also have excellent brazing properties, and the tensile strength after brazing is 17 kgf / m.
It showed excellent mechanical properties of m ² or more.

Example 2 An aluminum alloy containing an alloying element such as La, Nd, Pr or the like added to a skin material is used in Example 1.
A brazing sheet was manufactured in the same manner as in. Table 3 shows the components and contents of the aluminum alloy used as the skin material.

[0037]

[Table 3]

A test piece having a width of 25 mm and a length of 100 mm was cut out from the test material heated in the furnace in the same manner as in Example 1, and the amount of corrosion and the maximum pitting corrosion depth were investigated by the same corrosion resistance test as in Example 1. The survey results are shown in Table 4. As is apparent from Table 4, the aluminum alloys of sample numbers 17 to 25 according to the present invention are compared with the case where the aluminum alloy of sample number 26 containing no La, Nd, Pr, etc. is used as the skin material. When used as a skin material, the pitting corrosion resistance is significantly improved.

[0039]

[Table 4]

[0040]

As described above, according to the present invention, an aluminum alloy having specified Zn content, Mg content and Zn% / Mg% ratio is added to Y, Ce, La, Nd, P.
A material having excellent pitting corrosion resistance and general corrosion resistance is obtained by containing one or more of r and the like. When the obtained aluminum alloy is used as a skin material for brazing sheets, it has excellent corrosion resistance and brazability, so even if it is a thin brazing sheet, it has excellent corrosion resistance and mechanical strength. A heat exchanger having is assembled.

Claims (2)

(57) [Claims] 1. A skin material in which an Al—Si based brazing material is laminated on one surface and an Al—Mn based core material is laminated on the other surface of the Al—Mn based core material.
n: 1.0 to 3.0 wt%, Mg: 0.5 to 3.0 wt%, Si: 0.05 to 0.5 wt% and Fe: 0.05
To 0.5% by weight, and further Y: 0.01 to
0.8% by weight, Ce: 0.01 to 1.5% by weight, La:
Brazing characterized by containing one or more of 0.01 to 1.5% by weight, Nd: 0.01 to 1.5% by weight and Pr: 0.01 to 1.5% by weight. Aluminum alloy for seats. 2. The alloy system according to claim 1, wherein Zn%
Aluminum alloy for brazing sheet, characterized in that the ratio of / Mg% is maintained in the range of 1 to 6.