JP2013133517A - High temperature resistant three-layered brazing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-layered brazing sheet exhibiting both a high strength at a high temperature and an excellent pitting corrosion resistance to various strong acids.SOLUTION: The three-layered brazing sheet excellent in corrosion resistance under strong acid circumstances is formed by cladding a core material containing 1.0 to 1.8% Mn, 0.3 to 1.2% Si, 0.1 to 1.0% Cu, and the balance containing Al and inevitable impurities, with a first brazing material formed on one side of the core material, and containing 5.0 to 9.5% Si, 1.0 to 5.0% Zn, and the balance containing Al and inevitable impurities, and with a second brazing material formed on the other side of the core material, and made of an Al-Si based alloy.

Description

  The present invention relates to a high temperature resistant three-layer brazing sheet, and particularly to a brazing sheet excellent in corrosion resistance under a strong acid environment.

  Various automotive parts constructed by brazing are exposed to high-temperature environments such as EGR (Exhaust Gas Recirculation) cooler, CAC (Charged Air Cooler), muffler, etc. Increasing cases are exposed to a strong acid environment as a component. In these members, exhaust gas concentrated water adheres inside the members. Since this exhaust concentrated water contains various strong acids such as hydrochloric acid, nitric acid and sulfuric acid, each member is required to have corrosion resistance under various strong acid environments in addition to pressure resistance at high temperature.

JP 2009-108761 A

For example, as a conventional CAC tube material, an aluminum alloy is used as described in Patent Document 1. In general, an aluminum alloy in which an Al—Si alloy brazing material is clad on one surface or both surfaces of a core material made of an Al—Mn—Cu alloy is used. The Al—Si brazing material is bonded for integral brazing joining with other members, and brazing is usually performed using a fluoride flux in an inert gas atmosphere.
In a conventional CAC tube material, pitting corrosion resistance is improved by ensuring a certain potential difference between the core material and the brazing material by adding Cu to the core material. However, the pitting corrosion resistance under various strong acid environments such as the above-mentioned exhaust gas concentrated water is not sufficient, and it is possible that through holes are generated in a very short period of time.
Accordingly, the present invention aims to provide a brazing sheet capable of satisfying both high strength at high temperature and pitting corrosion resistance against various strong acids by examining an aluminum alloy having excellent pitting corrosion resistance under various strong acid environments.

The three-layer brazing sheet (hereinafter sometimes simply referred to as a brazing sheet) having excellent corrosion resistance in a strong acid environment of the present invention has the following constitution.
That is, Mn: 1.0-1.8%, Si: 0.3-1.2%, Cu: 0.1-1.0% are contained, and the balance is formed on one surface of the core material composed of Al and inevitable impurities, Si: A first brazing material containing 5.0 to 9.5%, Zn: 1.0 to 5.0%, the balance being made of Al and inevitable impurities, and a second brazing material made of an Al—Si alloy formed on the other surface of the core material, , Is clad.
In the present invention, unless otherwise specified, the amount of element is mass%.

  In addition to the above elements, the core material in the brazing sheet of the present invention further contains one or two of Mg: 0.1 to 0.3% and Zr: 0.05 to 0.20% for corrosion resistance in a strong acid environment. desirable.

In the brazing sheet of the present invention, the potential of the first brazing material after the brazing heat treatment is 100-200 mV lower than the potential of the core material, and the brazing heat treatment was further subjected to a heat treatment at 200 ° C. for 10 hours. Later, it is desirable for the corrosion resistance in a strong acid environment that the potential of the first brazing material is 100-200 mV lower than the potential of the core material.
Further, in the brazing sheet of the present invention, the potential difference between the crystal grains and the crystal grain boundary (intra-grain boundary) in the core material after brazing heat treatment is less than 20 mV, and following the brazing heat treatment, 200 ° C. After the heat treatment for 10 hours, it is desirable for the corrosion resistance in a strong acid environment that the potential difference between the crystal grains and the crystal grain boundaries (intra-grain boundary) in the core material is less than 20 mV.

  ADVANTAGE OF THE INVENTION According to this invention, the brazing sheet | seat which is compatible with the pitting corrosion resistance with respect to various strong acids while being high intensity | strength at high temperature is provided.

Hereinafter, the brazing sheet of the present invention will be described in detail.
(1) Core component [Mn: 1.0-1.8%]
Mn has the effect of increasing the strength of the core material by finely forming an Al—Mn—Si intermetallic compound in the matrix.
However, if the amount of Mn is less than 1.0%, the effect is not sufficiently exhibited, and if it exceeds 1.8%, the castability is inferior, and since a huge intermetallic compound is produced during casting, the subsequent rollability is inferior. Therefore, the Mn content of the core material of the present invention is set to 1.0 to 1.8%. For the same reason, the lower limit is preferably 1.15% and the upper limit is 1.75%, more preferably the lower limit is 1.5% and the upper limit is 1.7%.

[Si: 0.3-1.2%]
Si has the effect of increasing the strength of the core material by finely forming an Al-Mn-Si intermetallic compound in the matrix.
However, if the amount of Si is less than 0.3%, the effect is not sufficiently exhibited, and if it exceeds 1.2%, the melting point of the material is lowered and the brazing property is inferior. Therefore, the Si content of the core material of the present invention is set to 0.3 to 1.2%. For the same reason, it is desirable to set the lower limit to 0.4% and the upper limit to 1.2%, and more preferably to set the lower limit to 0.8% and the upper limit to 1.2%.

[Cu: 0.1-1.0%]
Cu dissolves in the matrix to increase the strength of the material, and when added to the core, the potential difference between the first brazing material and the potential of the core is noble, increasing the corrosion resistance. .
However, if the amount of Cu is less than 0.1%, the effect is not sufficiently exhibited, and if it exceeds 1.0%, the melting point of the material is lowered and the castability is inferior. Therefore, the Cu content of the core material of the present invention is 0.1 to 1.0%. For the same reason, it is desirable to set the lower limit to 0.2% and the upper limit to 0.5%, and it is more desirable to set the lower limit to 0.2% and the upper limit to 0.4%.

The following Mg and Zr are elements that are preferably contained in the core material of the present invention.
[Mg: 0.1-0.3%]
Mg dissolves in the matrix and increases the strength of the material. When added to the core material, Mg increases the potential difference from the first brazing material with the potential of the core material being noble, thus improving the corrosion resistance. .
However, if the amount of Mg is less than 0.1%, the effect is not sufficiently exhibited, and if it exceeds 0.3%, the melting point of the material is lowered and the brazing property is deteriorated. Therefore, the Mg content of the core material of the present invention is 0.1 to 0.3%.

[Zr: 0.05 to 0.20%]
Zr dissolves in the matrix and has the effect of increasing the strength of the material.
However, if the amount of Zr is less than 0.05%, the effect is not sufficiently exhibited, and if it exceeds 0.20%, the castability is inferior, and since a huge intermetallic compound is produced during casting, the subsequent rollability is inferior. Therefore, the Zr content of the core material of the present invention is set to 0.05 to 0.20%.
Other than the above elements in the core material, Al and unavoidable impurities.

(2) First brazing material [Si: 5.0-9.5%]
Si has the effect of improving brazing properties. However, when the Si content is less than 5.0%, the effect of improving the brazing property is insufficient, while when it exceeds 9.5%, the brazing property is lowered. Therefore, the Si content of the first brazing material of the present invention is set to 5.0 to 9.5%. For the same reason, it is desirable that the lower limit is 6.0% and the upper limit is 9.0%, and it is more desirable that the lower limit is 6.0% and the upper limit is 8.0%.

[Zn: 1.0-5.0%]
Zn has the effect of lowering the potential.When added to the first brazing filler metal, the potential difference from the core material increases, creating a potential gradient effective for corrosion resistance, improving the corrosion resistance of the brazing sheet and reducing the corrosion weight. There is a reduction effect. However, if the Zn content is less than 1.0%, the effect is not sufficiently exhibited. If the Zn content exceeds 5.0%, the corrosion rate increases and the corrosion weight loss increases. Therefore, the Zn content of the first brazing material of the present invention is 1.0 to 5.0%. For the same reason, the lower limit is preferably 1.0% and the upper limit is 4.0%, more preferably the lower limit is 1.5% and the upper limit is 3.5%.
In addition, other than the above elements in the first brazing filler metal are Al and inevitable impurities.

(3) Second brazing material The brazing material in the present invention is made of an Al-Si alloy (including JIS 4045 alloy and 4343 alloy). This Al—Si alloy preferably contains 5.0 to 9.5% of Si. If the Si content is less than 5.0%, the content is small, which leads to poor brazing. If the Si content exceeds 9.5%, melting occurs during brazing. A preferable amount of Si is 5.5 to 9.0%, and a more preferable amount is 6.0 to 8.0%.

(4) Potential of core material and first brazing material In the brazing sheet of the present invention, the potential of the first brazing material after brazing heat treatment is 100-200 mV lower than the potential of the core material, and brazing heat treatment Subsequently, after further heat treatment at 200 ° C. for 10 hours (10 hours), it is desirable for the corrosion resistance in a strong acid environment that the potential of the first brazing material is 100-200 mV lower than the potential of the core material.
Here, the potential difference after brazing is specified because the brazing sheet of the present invention is used for brazing. Further, the heat treatment at 200 ° C. for 10 hours performed after brazing has the following meaning. The maximum working temperature of various automobile parts intended by the present invention is about 200 ° C. In actual automobiles, it is exposed to this maximum temperature for several hundred hours. It is stipulated based on the fact that the impact on
The potential of the core material in the three-layer brazing sheet is measured after the first brazing material and the second brazing material are melted by etching after brazing and the core material surface is exposed. On the other hand, since the first brazing material is originally exposed on the surface of the brazing sheet, it can be measured without etching as in the core material. However, in the vicinity of the interface between the first brazing material and the core material, alloy components diffuse to each other due to the brazing heat, and an accurate potential cannot be measured. Therefore, the potential is measured on the surface of the first brazing material as far as possible from the interface. On the other hand, in the case of the core material, the potential at the center of the plate thickness is measured. In Examples described later, the potentials of the core material and the sacrificial material were measured according to the above procedure.
(5) Regarding the potentials in the crystal grains of the core material and the crystal grain boundaries According to the study by the present inventors, by identifying the potential difference between the crystal grains of the core material constituting the brazing sheet and the crystal grain boundaries, a strong acid environment Excellent corrosion resistance below. That is, the potential difference between the crystal grains and the grain boundaries in the core material after brazing heat treatment (intragrain-grain boundaries) is less than 20 mV, and the heat treatment at 200 ° C. for 10 hours is further performed following the brazing heat treatment. After application, it is desirable for the corrosion resistance in a strong acid environment that the potential difference between the crystal grains and the crystal grain boundaries (intra-grain boundary) in the core is less than 20 mV. When the potential difference between the grain boundaries and the grain boundaries is 20 mV or more, grain boundary corrosion occurs in which the potential grain boundaries preferentially corrode, leading to penetration at a relatively early stage.
The potential measurement within the crystal grain and the grain boundary is determined as “intragranular potential = grain boundary potential” when only one peak potential at which the current density increases appears in the anodic polarization curve, and when two points appear, the potential is Is the grain boundary potential, and the noble is the intragranular potential.
The term “grain boundary” was defined as a range of ± 5 μm in width including the crystal grain boundary, and a location away from the grain boundary by more than 5 μm was defined as “inside grain”.

  The brazing sheet of the present invention is used with the first brazing material side inside. The second brazing material serving as the outer surface is used for brazing and joining to the object to be joined.

[Example]
The specific example performed in order to confirm the effect of the brazing sheet of this invention demonstrated above is demonstrated.
[Material manufacturing process]
Aluminum alloy for core material, aluminum alloy for first brazing material, and alloy for second brazing material (JIS A4045 alloy) were cast by semi-continuous casting. The chemical composition of each alloy is as shown in Table 1.
Both the obtained core material alloy and brazing material alloy were subjected to a homogenization treatment at 500 ° C. for 6 hours. The conditions for this homogenization treatment are an example.
After the homogenization treatment, the first brazing material alloy was combined on one surface of the core material alloy and the second brazing material alloy was combined on the other surface and hot rolled to obtain a clad material.
This clad material is cold-rolled to a specified thickness, then subjected to intermediate annealing for 3 hours at 400 ° C, and the final cold-rolling produces a 0.4mm-thick H14 tempered three-layer brazing sheet (sample) did. The clad rate of each element in the clad material is: first brazing material: core material: second brazing material (thickness) = 15%: 75%: 10%. However, this cladding ratio is merely an example, and the cladding ratio of the first brazing material may be 17% or 20%. Moreover, the above is also an example for the intermediate annealing, and the temperature can be selected from the range of 200 to 400 ° C. and the holding time of 1 to 6 hours.
In Comparative Example 2 in Table 1, since the amount of Mn was too large, giant crystals were generated during casting, and this was the starting point, causing frequent breaks during rolling, and a sound clad material could not be produced.

The following evaluation was performed about the sample obtained as mentioned above.
[Potential (mV)]
The following potentials A to D were measured for the core material and the first brazing material.
Potential A: Potential of core material after brazing Potential B: Potential of first brazing material after brazing Potential C: Potential of core material after brazing and heat treatment held at 200 ° C. for 10 hours Potential D; After brazing, the potential E of the first brazing material after heat treatment is maintained at 200 ° C. for 10 hours; the intragranular potential of the core material after brazing; the potential F; the grain boundary potential of the core material after brazing; ; Intragranular potential H of core material after brazing and heat treatment held at 200 ° C. for 10 hours; Grain boundary potential measurement method of core material after brazing and heat treatment held at 200 ° C. for 10 hours Anodic polarization was performed using each sample after brazing equivalent heat treatment. For anodic polarization, a saturated calomel electrode was used as a reference electrode, and measured at a potential sweep rate of 0.5 mV / s in a 2.67% AlCl3 solution at 40 ° C deaerated by blowing nitrogen gas.

[Strength]
Tensile test pieces are prepared from each sample (clad material) subjected to brazing equivalent heat treatment based on JIS H 4000, and the strength (tensile strength) after brazing is obtained by performing a tensile test using these test pieces. Obtained. The results are shown in Table 1.
Tensile strength was judged as ○ when 130 MPa or higher, and × when less than 130 MPa, and the results are shown in Table 1.

[Corrosion resistance]
Each sample subjected to brazing equivalent heat treatment was subjected to an immersion test in various strong acid mixtures (mixtures of hydrochloric acid 200 ppm, nitric acid 200 ppm, sulfuric acid 200 ppm, and acetic acid 200 ppm). Evaluation in the strong acid immersion test was “corrosion depth” and “corrosion weight loss”. The results are shown in Table 1.
Concerning the corrosion depth, “◎” when the penetration life is 100 days or more, “○” when 50 days or more and less than 100 days, “△” when 25 days or more and less than 50 days, “×” when less than 25 days. As evaluated.
Also, regarding corrosion weight loss, those with a weight loss per day of corrosion test of less than 15 mg / dm2 are `` ◎ '', those with 15 mg / dm2 or more and less than 25 mg / dm2 are `` ○ '', those with 25 mg / dm2 or more and less than 30 mg / dm2 Was evaluated as “Δ”, and those with 30 mg / dm 2 or more as “×”.

[Brassability]
A mini-core was made with the brazing sheet and fin material (JIS A3003) obtained and heat-treated at 600 ° C for 3 minutes in a nitrogen gas atmosphere. Brazing properties were evaluated as “joining rate” and “brazing erosion”. As for the joining rate, the mini-core after brazing was disassembled and the joining rate of the brazing sheet / fin joint was determined. Joining rate = Joined length / Overall length x 100. When the joining rate is 95% or more, it is evaluated as “◎”, 80% or more and less than 95% as “◯”, and less than 80% as “×”. did. The brazing erosion property was evaluated by observing the cross section of the brazing sheet / fin joint. The case where almost no wax erosion was observed was indicated as “◎”, the case where wax erosion was observed but not penetrating through the fin was indicated as “◯”, and the case where the fin penetrated was indicated as “×”.

Claims (4)

Mn: 1.0 to 1.8%, Si: 0.3 to 1.2%, Cu: 0.1 to 1.0%, the balance is made of Al and unavoidable impurities,
Formed on one surface of the core material, Si: 5.0-9.5%, Zn: 1.0-5.0% containing, the first brazing material consisting of Al and inevitable impurities,
A second brazing material formed on the other surface of the core material and made of an Al-Si alloy;
Is a three-layer brazing sheet characterized in that it is clad and has excellent corrosion resistance in a strong acid environment. The core material further contains one or two of Mg: 0.1 to 0.3% and Zr: 0.05 to 0.20%.
The three-layer brazing sheet excellent in corrosion resistance under a strong acid environment according to claim 1. The potential of the surface of the first brazing material after brazing heat treatment is 100-200 mV lower than the potential of the core material, and
Following the brazing heat treatment, after further heat treatment at 200 ° C. for 10 hours, the potential of the surface of the first brazing material is 100-200 mV lower than the potential of the core material,
A three-layer brazing sheet excellent in corrosion resistance in a strong acid environment according to claim 1 or 2. The potential difference between the crystal grain boundary and the crystal grain (intra-grain boundary) in the core material after the brazing heat treatment was less than 20 mV, and the heat treatment at 200 ° C. for 10 hours was further performed following the brazing heat treatment. Later, the potential difference between the crystal grain boundary and the crystal grain in the core material (intra-grain boundary) is less than 20 mV,
A three-layer brazing sheet excellent in corrosion resistance under a strong acid environment according to any one of claims 1 to 3.