JP2022142944A - Aluminum brazing sheet for brazing, and manufacturing method thereof - Google Patents

Abstract

To provide an aluminum brazing sheet for flux free brazing, and a manufacturing method thereof.SOLUTION: An aluminum brazing sheet for brazing is an aluminum brazing sheet having a multilayered structure with at least two or more layers of a core material and a braze filler material. In the aluminum brazing sheet for brazing, an Al-Si-Mg-Bi-based braze filler material is positioned on the outermost surface by being cladded on one surface or both surfaces of the core material. In an oxide film on a surface of the Al-Si-Mg-Bi-based braze filler material after brazing, a part with the highest Bi concentration in a various element concentration distribution in the thickness direction, which is acquired using glow discharge optical emission spectrometry, is 1.0% or more in mass%.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an aluminum brazing sheet for flux-free brazing that performs flux-free joining and a method for producing the same.

Aluminum automotive heat exchangers, such as radiators, are becoming smaller and lighter, and aluminum materials are becoming thinner and stronger. In the manufacture of aluminum heat exchangers, brazing is used to join joints. In the current mainstream brazing method that uses fluoride-based flux, the flux reacts with Mg in the material to deactivate it, resulting in The use of Mg-added high-strength members is limited due to the tendency of poor adhesion to occur. Therefore, a brazing method for joining Mg-added aluminum alloys without using flux is desired.

In flux-free brazing using an Al-Si-Mg brazing filler metal, Mg in the brazing filler metal that has become active after melting reduces and decomposes the Al oxide film (Al ₂ O ₃ ) on the joint surface, making joining possible. Become. In closed face-joint joints, etc., joints that combine brazing sheets with brazing material due to the decomposition of oxide films by Mg, and joints that combine brazing sheets and members to be joined (bare materials) that do not have brazing material A good joint state can be obtained at the joint.

JP 2014-50861 A

However, in a joint shape that is easily affected by the atmosphere, such as a tube and fin joint, an MgO film tends to grow on the surface of the Mg-added brazing filler metal. is significantly inhibited. Therefore, there is a strong demand for a flux-free brazing method capable of obtaining a stable joint state in joints having open portions.

As a method for stabilizing the bonding state of flux-free brazing, for example, the Al-Si-Mg-Bi brazing material shown in Patent Document 1 is used, and the technology of controlling the distribution state of Bi particles and Bi-Mg compounds in the brazing material. is proposed. According to this technique, by dispersing elemental Bi or a Bi—Mg compound having an equivalent circle diameter of 5.0 to 50 μm in the brazing material, the elemental Bi or the Bi compound is exposed on the surface of the brazing material during material production. be able to. Further, the presence of elemental Bi or a Bi compound can suppress the formation of an oxide film on the exposed portion, and the short-time brazing addition heat can improve the flux-free brazeability.
However, it is difficult to say that the conventional technology provides stable bondability that can replace the current mainstream brazing method that uses fluoride-based flux. requires further technical improvement.

Therefore, the present inventors have made intensive studies in view of the above problems, and as a result, in order to further improve the brazeability of the Bi-added Al-Si-Mg brazing filler metal, the surface Bi concentration after melting the brazing filler metal should be uniform. It was found that it is important to adjust the content to a certain value or more to promote the dividing action of the oxide film by Bi. Furthermore, joining starts at the start of brazing melting, but in order to sufficiently fill the joint with molten brazing, the surface Bi concentration at the start of brazing melting should be set to a certain value or higher, and the starting point of splitting of the oxide film should be set. I found it important to increase

Further, the inventors' research has revealed that metal Bi produced by melting Mg—Bi compound particles is concentrated on the surface of the brazing filler metal in the brazing temperature rising process. Furthermore, as a result of research, it was found that by dispersing fine Mg—Bi compound particles with a circle equivalent diameter of 0.01 μm or more and less than 5.0 μm distributed within a depth of 10 μm from the surface of the brazing filler metal at a predetermined number density or more, The inventors have confirmed that the surface Bi concentration equal to or higher than the above constant value can be achieved, and have arrived at the present invention.

The present invention has been made in view of the background described above, and an object of the present invention is to provide an aluminum brazing sheet for brazing and a method for producing the same, which can obtain good bondability in flux-free brazing.

The present inventors focused on the surface layer of the Al-Si-Mg-Bi brazing filler metal before brazing, and finely and densely dispersed the Mg-Bi compound particles to obtain a non-oxidizing brazing material without reducing pressure. It has been found that flux-free brazing in an atmosphere provides excellent joints.

(1) The aluminum brazing sheet of the first embodiment is an aluminum brazing sheet for flux-free brazing that is subjected to brazing in a non-oxidizing atmosphere without reduced pressure without using flux, and comprises at least a core material and a braze. An aluminum brazing sheet having a multilayer structure of two or more layers of material, comprising an Al-Si-Mg-Bi brazing material located on the outermost surface of the multilayer structure, and the Al-Si- after brazing In the oxide film on the surface of the Mg—Bi brazing material, the portion with the highest Bi concentration in the concentration distribution of various elements in the thickness direction obtained by glow discharge emission spectrometry is 1.0% or more by mass. Characterized by

(2) In the aluminum brazing sheet of the second embodiment, the Al-Si-Mg-Bi brazing material contains 1.5 to 14.0% by mass of Si and 0.01 to 2.0% by mass of Mg. %, and 0.005 to 0.5% Bi.

(3) The aluminum brazing sheet of the third form is Mg-Bi-based compound particles contained in the Al-Si-Mg-Bi-based brazing material, and observation of a cross section (RD-ND) parallel to the rolling direction 2, wherein 10 or more fine Mg—Bi compound particles having an equivalent circle diameter of 0.01 μm or more and less than 5.0 μm are present per 10000 μm ² visual field within 10 μm depth from the outermost surface of the brazing material. do.

(4) In the aluminum brazing sheet of the fourth embodiment, the oxide film on the surface of the Al-Si-Mg-Bi brazing material that has reached the brazing melting start temperature (solidus temperature) in the brazing temperature rising process has a glow. It is characterized in that the portion having the highest Bi concentration in the concentration distribution of various elements in the thickness direction obtained by discharge emission spectrometry is 0.08% or more in terms of mass %.

(5) The aluminum brazing sheet of the fifth embodiment is characterized in that the average oxide film thickness on the surface of the Al--Si--Mg--Bi brazing material before brazing is 20 nm or less.
(6) The aluminum brazing sheet of the sixth embodiment is characterized in that the impurity Ca contained in the Al--Si--Mg--Bi based brazing material before brazing is 50 ppm or less by mass ppm.
(7) A seventh aspect of the aluminum brazing sheet is the aluminum brazing sheet for brazing according to any one of (1) to (6), wherein at least Si particles and a part of the Mg—Bi compound are present on the outermost surface. It is characterized by being an exposed etching surface.
(8) A method for producing an aluminum brazing sheet according to the eighth aspect, wherein alkali or acid is added before brazing is performed using the aluminum brazing sheet according to any one of (1) to (7). is used to etch the surface of the aluminum brazing sheet.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to perform good and stable flux-free brazing joining.

It is a figure which shows the aluminum brazing sheet for flux-free brazing in one Embodiment of this invention, and a brazing object member. 1 is a perspective view showing an aluminum automotive heat exchanger according to an embodiment of the present invention; FIG. FIG. 4 is a diagram showing a brazing model in one embodiment of the present invention; 4 is a graph showing an example of glow discharge surface analysis results for an example sample.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on embodiments.
The aluminum brazing sheet for flux-free brazing of the first embodiment is an aluminum brazing sheet having a multi-layered structure of at least two or more layers, comprising a sheet-shaped core material and one or both sides of the core material clad with an outermost surface Al--Si--Mg--Bi based brazing material located.
The brazing sheet of this embodiment may be an aluminum brazing sheet having a three-layer structure in which one side of a core material is clad with an Al--Si--Mg--Bi brazing material and the other side of the core material is clad with a sacrificial material.
The aluminum brazing sheet of the present embodiment may have a four-layer structure of brazing material/core material/sacrificial material/brazing material, or a five-layer structure of brazing material/sacrificial material/core material/sacrificial material/brazing material. A four-layer structure of first brazing material/second brazing material/core material/brazing material, or a six-layer structure of first brazing material/second brazing material/sacrificial material/core material/sacrificial material/brazing material The cladding configuration, such as structure, is not particularly limited.
The aluminum brazing sheet of the present embodiment is produced in a sheet form by clad rolling a sheet-like core material and the above brazing material, sacrificial material, and the like.

In the aluminum brazing sheet of the present embodiment, in the oxide film on the surface of the Al—Si—Mg—Bi brazing material after brazing, Bi It is preferable that the portion with the highest concentration is 1.0% or more in mass %. In addition, the brazing material contains 1.5 to 14.0% Si, 0.01 to 2.0% Mg, 0.005 to 0.5% Bi, and the balance Al. Al--Si--Mg--Bi based brazing material having
Hereinafter, in the brazing sheet of the present embodiment, all descriptions of contents are indicated by mass ratios, and when the range of mass ratios is indicated using "~", unless otherwise specified, the expression includes the lower limit and the upper limit. do. Therefore, for example, 1.5 to 14.0% means 1.5% by mass or more and 14.0% by mass or less.

The Mg--Bi compound particles contained in the Al--Si--Mg--Bi brazing filler metal have an equivalent circle diameter of 0.01 μm or more and 5.0 μm in observation of a cross section (RD-ND) parallel to the rolling direction. It is preferable that 10 or more fine Mg—Bi compound particles having a diameter of less than 10 μm are present per 10000 μm ² visual field within a depth of 10 μm from the outermost surface of the brazing filler metal.
In addition, in the oxide film on the surface of the Al-Si-Mg-Bi brazing material that has reached the brazing melting start temperature (solidus temperature) in the brazing temperature rising process described later, the thickness obtained by glow discharge emission spectrometry It is preferable that the portion having the highest Bi concentration in various element concentration distributions in the direction is 0.08% or more in terms of mass %.

Further, in the brazing sheet of the present embodiment, it is preferable that the average thickness of the oxide film on the surface of the Al—Si—Mg—Bi based brazing material before brazing is 20 nm or less.
Further, in the brazing sheet of the present embodiment, it is preferable that the impurity Ca contained in the Al-Si-Mg-Bi brazing filler metal before brazing is 50 ppm or less in mass ppm.

“Brazing material (brazing material layer)”
Mg: 0.01-2.0%
Mg reductively decomposes the Al oxide film (Al ₂ O ₃ ). However, if the content of Mg is too small, the effect is insufficient. Since it becomes brittle, it becomes difficult to manufacture the material. Therefore, the content of Mg in the brazing filler metal of this embodiment is set within the above range.
For the same reason, it is more desirable to set the Mg content at a lower limit of 0.05% and an upper limit of 1.5%.

Si: 1.5-14.0%
Si forms a molten braze during brazing and forms a fillet at the joint. However, if the Si content is too low, there will be insufficient molten solder to form fillets. In particular, since the maximum solid solubility limit according to the Al-Si binary equilibrium diagram is about 1.65%, in the range where the Si content is less than 1.65%, the amount of liquid phase generated at the brazing temperature is almost There is no molten braze that contributes to joining. However, even if the amount of Si is below the maximum solid solubility limit, if the difference from the maximum solid solubility limit is small, molten solder will be generated partially at places where Si is locally concentrated, contribute to
On the other hand, an excessive Si content not only saturates the effect, but also makes the material hard and brittle, making it difficult to manufacture the material. Therefore, in the brazing filler metal of this embodiment, the Si content is set within the above range. For the same reason, it is more desirable to set the lower limit of the Si content to 3.0% and the upper limit to 12.0%.

Bi: 0.005 to 0.5%
Bi condenses on the surface of the material during the process of increasing the brazing temperature and penetrates into the oxide film, thus inhibiting the growth of a dense oxide film. Al ₂ O ₃ in the oxide film is reductively decomposed by Mg in the brazing filler metal when the brazing material is melted. However, the oxide film becomes brittle due to entry of Bi, and the oxide film is easily destroyed. Furthermore, Bi lowers the surface tension of the molten brazing filler metal, thereby improving gap-filling properties. However, if the Bi content is too small, the effect will be insufficient. On the other hand, when Bi is contained excessively, not only does the effect saturate, but Bi, which has a small solid solubility limit in the base material Al, segregates on the material surface in the low temperature range during the heat treatment and brazing temperature rising process during material production, Oxides of Bi are likely to be generated, and bonding is hindered. Therefore, the content of Bi in the brazing filler metal of this embodiment is set within the above range.
For the same reason, it is more desirable that the lower limit of the Bi content is 0.05% and the upper limit is 0.3%.

Ca: 50 ppm by mass or less Ca exists as an impurity in the Al base material, Mg, Si mother alloy, etc., and is usually mixed in about 100 ppm by mass or less as an unavoidable impurity when melting the brazing material, but forms high-melting point compound particles with Bi. However, since it lowers the action of Bi, it is desirable to limit the content. If the Ca content exceeds 50 mass ppm, the action of Bi is reduced and the brazeability becomes insufficient, so it is desirable to set the upper limit to 50 mass ppm.
For the same reason, it is more desirable to set the Ca content to 20 ppm by mass or less.
When the amount of impurities such as the master alloy that is the basis for manufacturing the brazing filler metal is large and the amount of Ca in the brazing filler metal exceeds 50 ppm by mass, it is necessary to inject Cl gas or add a fluoride-based flux during the melting of the brazing filler metal. The amount of impurity Ca in the brazing filler metal can be reduced to a predetermined value or less by the molten metal treatment.

A necessary amount of Zn can be added to the brazing material in order to form a sacrificial anticorrosive layer after brazing.
Zn: 0.1-9.0%
Zn is included as desired because it provides a sacrificial anti-corrosion effect by making the potential of the material base. However, when Zn is contained, if the content is too small, the sacrificial anti-corrosion effect will be insufficient, while if the content is too large, the effect will saturate. Therefore, when the brazing filler metal of the present embodiment contains Zn, the content can be within the above range.
For the same reason, it is desirable to set the Zn content at a lower limit of 0.5% and an upper limit of 7.0%. Even when Zn is not intentionally added, Zn may be contained as an impurity in an amount of less than 0.1%.

In addition, the brazing material may contain, as other elements, one or more of In, Sn, and Mn in an amount of 2.0% by mass or less each, but a total of 2.0% by mass or less. 0% by mass or less, but may contain one or more of Fe, Ni, Ce, and Se in a total amount of 1.0% by mass or less, and each of 0.3% or less, but a total of 0.3% or less of Be , Na, Sb, Ti, Zr, P, S, K, and Rb.

"Fine Mg-Bi compound particles"
In the brazing filler metal of this embodiment, fine Mg—Bi compound particles having an equivalent circle diameter of 0.01 μm or more and less than 5.0 μm are present within a depth of 10 μm from the outermost surface of the brazing filler metal, and 10 or more per 10000 μm ² field of view. preferably included.
By dispersing the fine Mg—Bi compound particles on the surface of the brazing filler metal, when the fine Mg—Bi compound particles are melted during the process of increasing the brazing temperature, Bi tends to be uniformly concentrated on the surface of the material, resulting in better bonding. The dividing action of the oxide film that inhibits the If the number of the fine Mg—Bi compound particles is less than 10, the effect of dividing the oxide film tends to be insufficient, resulting in poor brazeability. For the same reason, it is more desirable that the number of fine Mg—Bi compound particles is 20 or more.

The number of fine Mg—Bi compound particles in the surface layer of the brazing material was determined by mirror-finishing the cross section (RD-ND) of the produced aluminum brazing sheet parallel to the rolling direction with abrasive grains of 0.1 μm. from the outermost surface to a depth of 10 μm (if the thickness of the brazing layer is less than 10 μm, the total thickness of the brazing layer) can be determined by fully automatic particle analysis using an EPMA (electron probe microanalyzer). Furthermore, in order to measure fine Mg—Bi compound particles of 1 μm or less, a cross section (RD-ND) of the cut brazing material layer parallel to the rolling direction was subjected to mechanical polishing and electrolytic polishing to prepare a thin film, and a TEM ( Observe a field of view equivalent to 10000 μm ² (100 μm square) from the outermost surface of the brazing layer to a depth of 10 μm (the total thickness of the brazing layer if the thickness of the brazing layer is less than 10 μm) using a transmission electron microscope). and by counting the number of Mg—Bi compound particles having an equivalent circle diameter of 0.01 to 5.0 μm (0.01 μm or more and 5.0 μm or less).
In the above (RD-ND), RD indicates Rolling Direction, and ND indicates Normal Direction (rolling surface normal direction).

In addition, as a means for finely and densely distributing the Mg-Bi-based compound particles, during casting, the molten metal temperature is high, and the cooling rate is high. It can be adjusted by appropriately combining the rolling time in the region, lowering the hot rolling finishing temperature by a certain level or more and increasing the subsequent cooling rate, and reducing the reduction amount per cold rolling load. .

"Average oxide film thickness on brazing material surface before brazing: 20 nm or less"
Al ₂ O ₃ , which is the main composition of the pre-brazing oxide film, is reduced by Mg in the brazing material during the brazing process and decomposed into MgAl ₂ O ₄ and the like, but MgAl ₂ O ₄ is re-decomposed during brazing. Since it is a stable oxide that is difficult to dissolve, if it is formed in large amounts, the active molten brazing surface will decrease, and the filling property of the molten brazing material will deteriorate. Therefore, in order to reduce the amount of Al ₂ O ₃ used as the raw material of MgAl ₂ O ₄ , it is desirable to set the average thickness of the oxide film on the surface of the brazing material to 20 nm or less in the brazing sheet before brazing.
For the same reason, it is more desirable that the brazing sheet before brazing has an average oxide film thickness of 10 nm or less.
However, if sufficient bondability can be ensured even with the above-mentioned average oxide film thickness or more depending on the selected joint shape, brazing conditions, etc., the average oxide film thickness is not limited to the above-mentioned average oxide film thickness.

The thickness of the oxide film in the brazing sheet before brazing shows the element distribution in the depth direction while sputtering from the surface direction (RD-TD) of the brazing sheet to the inner direction by glow discharge optical emission spectrometry (GD-OES). It can be obtained by obtaining a diagram and defining the distance from the outermost surface to the point where the line indicating the O content from the outermost surface and the line indicating the Al content from the outermost surface intersect as the oxide film thickness. In the above (RD-TD), TD indicates the transverse direction (direction perpendicular to rolling).

The composition and thickness of the oxide film in the brazing sheet before brazing can be controlled by the heat treatment conditions during the preparation of the material that is the basis of the brazing sheet. In the Mg-added material used in the present invention, if the heat treatment temperature is too high or the heat treatment time is too long, an MgO film that is difficult to decompose during brazing will grow, significantly impeding bonding. For this reason, for example, in the heat treatment performed in the intermediate annealing and final annealing after cold rolling, the main composition of the pre-brazing oxide film is made of Al by setting the maximum temperature to 400 ° C. or less and the holding time at the maximum temperature to less than 12 hours. ₂ O ₃ and can be controlled to a predetermined thickness.
It should be noted that the method for obtaining the material that is the basis of the brazing sheet of the present invention is not limited to the above method, as long as the target oxide film composition and thickness in the brazing sheet before brazing can be achieved. do not have.

"In the oxide film on the surface of the brazing filler metal when the brazing melting start temperature is reached, the part with the highest Bi concentration in the concentration distribution of various elements in the thickness direction is 0.1% or more by mass."
Bi condensed on the surface of the brazing filler metal penetrates into the oxide film and divides the oxide film, thereby improving the braze bondability. In the brazing process, the synergistic effect of the oxide film splitting action of Bi and the reductive decomposition action of the Al ₂ O ₃ film by Mg in the brazing material provides excellent brazing jointability. At this time, if the Bi concentration in the oxide film at the start of brazing melting is less than 0.1%, the starting points for dividing the oxide film become insufficient, and the brazing bondability deteriorates. It is desirable to make it 1% or more.
For the same reason, it is more desirable that the surface Bi concentration at the start of solder melting is 0.5% or more.

FIG. 4 shows the results of elemental analysis of an aluminum brazing sheet sample obtained in an example to be described later, which was subjected to a heat treatment equivalent to brazing and reached the brazing melting start temperature, taken out from the brazing furnace, and rapidly cooled. .
The melting start temperature of the brazing filler metal is defined as the solidus temperature of the aluminum alloy constituting the brazing filler metal -5°C. The solidus temperature of an aluminum alloy can be calculated from the alloy composition using thermodynamic calculation software (Jmat Pro).
FIG. 4 is a graph showing an example of the result of obtaining the element concentration distribution in the depth direction from the surface of the sample by glow discharge emission spectrometry on the sample after the sample was taken out of the furnace and quenched.
As shown in FIG. 4, in this sample, the oxygen concentration (oxygen content) is high on the sample surface (material surface) side, and the Al concentration (Al content) is low. and the oxygen concentration gradually decreases. In the specification of the present application, the thickness of the oxide film is defined as the depth to the intersection of the profile indicating the O atomic concentration and the profile indicating the Al atomic concentration in the results of glow discharge emission spectrometry in the depth direction. In the example of FIG. 4, the oxide film thickness can be estimated to be 4 nm.

As is clear from the graph shown in FIG. 4, a concentration gradient of Bi is formed in the oxide film. It was found that a mountain-shaped Bi concentration gradient was formed in which the Bi concentration gradually decreased toward (back side).
In the specification of the present application, the portion having the highest Bi concentration in the element concentration distribution in the thickness direction means the Bi concentration (% by mass) at the peak position of the mountain-shaped Bi concentration gradient.
In addition, in the graph shown in FIG. 4, only the concentration profile of Bi is displayed by enlarging the concentration by 20 times, so the concentration peak of Bi can be read as 0.68 atomic % (at %). The Bi content at the peak position is 6.7% by mass when converted to % by mass.
As described above, the Bi concentration at the part with the highest Bi concentration in the oxide film on the surface of the brazing filler metal when it reaches the brazing melting start temperature (solidus temperature) in the brazing temperature rising process is the means the peak concentration of Bi on the surface of the sample quenched with

"In the oxide film on the surface of the brazing material after brazing, the part with the highest Bi concentration in the concentration distribution of various elements in the thickness direction is 1.0% or more by mass."
The effect of dividing the oxide film by the surface-concentrated Bi is enhanced by promoting the surface concentration of Bi when the temperature exceeds the brazing melting temperature. By setting the Bi concentration on the surface of the brazing filler metal to 1.0% or more afterward, a good brazing joint state can be obtained. As an example of the material, the brazing sheet of this embodiment can be suitably selected, and as an example of the brazing conditions, the brazing temperature rise time is 3 to 60 minutes, the maximum temperature is 580 to 610 ° C., and the maximum temperature is 5 ° C. For example, the holding time during temperature rise from a low temperature is 3 to 10 minutes.
For the same reason, it is more desirable to adjust the surface Bi concentration after brazing to 5.0% or more.

The surface Bi concentration of the brazing sheet taken out from the brazing furnace immediately after brazing melting or the brazing sheet after brazing was measured by glow discharge optical emission spectroscopy (GD-OES) in the surface direction (RD-TD) of the brazing sheet. The element distribution in the depth direction is obtained while sputtering inward from the oxide film, and the portion showing the highest concentration in the Bi concentration distribution in the oxide film is defined as the surface Bi concentration.

"Heartwood (heartwood layer)"
Although the composition of the core material in the brazing sheet of the present embodiment is not limited to a specific one, the following components are preferred.
As an example, the core material, in mass%, is Si: 0.05 to 1.2%, Mg: 0.01 to 2.0%, Mn: 0.1 to 2.5%, Cu: 0.01 to 2 .5%, Fe: 0.05-1.5%, Zr: 0.01-0.3%, Ti: 0.01-0.3%, Cr: 0.01-0.5%, Bi: It can be composed of an aluminum alloy containing one or more of 0.005 to 0.5% and 0.1 to 9.0% Zn, with the balance being Al and unavoidable impurities.

Si: 0.05-1.2%
Si has the effect of improving the strength of the material by solid solution, and also improving the strength of the material by being precipitated as Mg ₂ Si or an Al--Mn--Si compound. However, if the Si content is too small, the effect will be insufficient. On the other hand, if the Si content is too high, the solidus temperature of the core material will drop and the core material will melt during brazing. For these reasons, when the core material contains Si, the Si content is set within the above range. For the same reason, it is desirable that the lower limit of the Si content is 0.1% and the upper limit is 1.0%. Incidentally, even when Si is not positively contained, it may be contained, for example, less than 0.05% as an unavoidable impurity.

Mg: 0.01-2.0%
Mg improves material strength by precipitating a compound with Si or the like. Part of it diffuses into the brazing material and reductively decomposes the oxide film (Al ₂ O ₃ ). However, if the content of Mg is too small, the effect is insufficient. For these reasons, when the core material contains Mg, the Mg content is set within the above range.
For the same reason, it is desirable to set the Mg content at a lower limit of 0.05% and an upper limit of 1.0%. Even when Mg is not positively contained, it may be contained, for example, less than 0.01% as an unavoidable impurity.

Mn: 0.1-2.5%
Mn precipitates in the structure as an intermetallic compound and improves the strength of the material. Furthermore, the solid solution makes the potential of the material nobler and improves the corrosion resistance. However, if the content of Mn is too small, the effect is insufficient, while if the content of Mg is too large, the material becomes hard and the rollability of the material deteriorates. For these reasons, when Mn is contained, the Mn content is set within the above range.
For the same reason, it is desirable to set the Mn content at a lower limit of 0.3% and an upper limit of 1.8%. Even when Mn is not positively contained, for example, less than 0.1% of Mn may be contained as an unavoidable impurity.

Cu: 0.01-2.5%
Cu forms a solid solution in Al to improve the strength of the material. However, if the Cu content is too small, the effect is insufficient, while if the Cu content is too large, the solidus temperature of the core material is lowered and melted during brazing. For these reasons, when Cu is contained in the core material, the Cu content is set within the above range.
For the same reason, it is desirable to set the Cu content at a lower limit of 0.02% and an upper limit of 1.2%. Even when Cu is not positively contained, it may contain, for example, less than 0.01% as an unavoidable impurity.

Fe: 0.05-1.5%
Fe precipitates in the structure as an intermetallic compound and improves the strength of the material. Furthermore, it promotes recrystallization during brazing and suppresses solder erosion. However, if the Fe content is less than the lower limit, the effect is insufficient, while if it is too high, the corrosion rate after brazing increases. For these reasons, when the core material contains Fe, the Fe content is set within the above range.
For the same reason, it is desirable to set the Fe content at a lower limit of 0.1% and an upper limit of 0.6%. Even when Fe is not intentionally contained, Fe may be contained, for example, less than 0.05% as an unavoidable impurity.

Zr: 0.01-0.3%
Zr forms fine intermetallic compounds and improves material strength. However, when the Zr content is less than the lower limit, the effect is insufficient, while when it is too large, the material becomes hard and workability deteriorates. For these reasons, when the core material contains Zr, the Zr content is set within the above range.
For the same reason, it is desirable that the lower limit of the Zr content is 0.05% and the upper limit is 0.2%. Even when Zr is not positively contained, it may be contained as an unavoidable impurity, for example, less than 0.01%.

Ti: 0.01-0.3%
Ti forms fine intermetallic compounds to improve material strength. However, when the Ti content is less than the lower limit, the effect is insufficient, while when the Ti content is excessive, the material becomes hard and workability is lowered. For these reasons, when the core material contains Ti, the Ti content is set within the above range.
For the same reason, it is desirable that the lower limit of the Ti content is 0.05% and the upper limit is 0.2%. Even when Ti is not positively contained, it may be contained, for example, less than 0.01% as an unavoidable impurity.

Cr: 0.01-0.5%
Cr forms fine intermetallic compounds and improves material strength. However, when the Cr content is less than the lower limit, the effect is insufficient, while when the Cr content is excessive, the material becomes hard and workability is lowered. For these reasons, when the core material contains Cr, the Cr content is set within the above range. For the same reason, it is desirable to set the Cr content at a lower limit of 0.05% and an upper limit of 0.3%. Even when Cr is not intentionally contained, it may be contained, for example, less than 0.01% as an unavoidable impurity.

Bi: 0.005 to 0.5%
Bi lowers the surface tension of the molten brazing filler metal by partly diffusing into the brazing filler metal layer. In addition, Bi concentrates on the surface of the material during the process of increasing the temperature for brazing and penetrates into the inside of the oxide film, thus inhibiting the growth of a dense oxide film. Al ₂ O ₃ in the oxide film is reductively decomposed by Mg in the brazing filler metal when the brazing material is melted. However, the oxide film becomes brittle due to the entry of Bi, and the oxide film is easily destroyed. However, if the Bi content is less than the lower limit, the effect is insufficient. On the other hand, if the Bi content is excessive, the effect saturates and Bi oxide tends to form on the surface of the brazing filler metal. Conjugation is inhibited. For these reasons, when the core material contains Bi, the Bi content is set within the above range.
For the same reason, it is desirable that the lower limit of the Bi content is 0.05% and the upper limit is 0.3%. Even when Bi is not intentionally contained, it may contain, for example, less than 0.005% as an unavoidable impurity.

Zn: 0.1-9.0%
Zn makes the pitting potential of the material more base than other members, and exhibits a sacrificial anticorrosion effect. However, if the Zn content is less than the lower limit, the effect is insufficient, while if the Zn content is excessive, the effect saturates. For these reasons, when the core material contains Zn, the Zn content is set within the above range.
For the same reason, it is desirable to set the Zn content at a lower limit of 0.5% and an upper limit of 7.0%. Even when Zn is not actively contained, it may be contained as an unavoidable impurity, for example, less than 0.1%.

"Sacrificial material (sacrificial material layer)"
In this embodiment, it can be an aluminum brazing sheet in which the core material is clad with a sacrificial material. Although the composition of the sacrificial material in the present invention is not particularly limited, the following components are preferred.
The sacrificial material is, for example, Zn: 0.1 to 9.0%, Si: 0.05 to 1.2%, Mg: 0.01 to 2.0%, Mn: 0.01 to 2.0%, in mass%. 1-2.5%, Fe: 0.05-1.5%, Zr: 0.01-0.3%, Ti: 0.01-0.3%, Cr: 0.01-0.5% , and Bi: 0.005 to 0.5%, and the balance is Al and inevitable impurities.

Zn: 0.1-9.0%
Zn is added to the sacrificial material in order to make the self-potential of the material more base than other members, exert a sacrificial anti-corrosion effect, and improve the pitting corrosion resistance of the clad material. If the Zn content is less than the lower limit, the effect is insufficient, and if the Zn content exceeds the upper limit, the potential becomes too base and the corrosion consumption rate of the sacrificial material increases, leading to early disappearance of the sacrificial material. The pitting corrosion resistance of the clad material is lowered.
For the same reason, it is desirable that the amount of Zn contained in the sacrificial material is 1.0% at the lower limit and 8.0% at the upper limit.

Si: 0.05-1.2%
Si precipitates in the structure as intermetallic compounds such as Al-Mn-Si and Al-Mn-Si-Fe, and disperses the starting points of corrosion to improve the pitting corrosion resistance of the clad material. is added to If the Si content is less than the lower limit, the effect is insufficient, and if the Si content exceeds the upper limit, the corrosion rate increases and the sacrificial material quickly disappears, resulting in a decrease in the pitting resistance of the clad material.
For the same reason, it is desirable that the amount of Si contained in the sacrificial material is 0.3% at the lower limit and 1.0% at the upper limit. Incidentally, even when Si is not positively contained, it may be contained, for example, less than 0.05% as an unavoidable impurity.

Mg: 0.01-2.0%
Mg is optionally added to the sacrificial material in order to improve corrosion resistance by strengthening the oxide film. When the content is less than the lower limit, the effect is insufficient, and when the content exceeds the upper limit, the material becomes too hard and the rollability deteriorates.
For the same reason, it is desirable to set the Mg content at a lower limit of 0.05% and an upper limit of 1.5%. For the same reason, it is desirable that the amount of Mg contained in the sacrificial material is 0.1% at the lower limit and 1.0% at the upper limit. Even when Mg is not positively contained, it may be contained, for example, less than 0.01% as an unavoidable impurity.

Mn: 0.1-2.5%
Mn precipitates as intermetallic compounds such as Al--Mn, Al--Mn--Si, Al--Mn--Fe and Al--Mn--Si--Fe and disperses the starting points of corrosion, thereby increasing the pitting resistance of the clad material. It is optionally added to the sacrificial material for enhancement. When the content is less than the lower limit, the effect is insufficient, and when the content exceeds the upper limit, the corrosion rate increases, and the sacrificial material disappears early, thereby reducing the pitting resistance of the clad material.
For the same reason, it is desirable to set the lower limit to 0.4% and the upper limit to 1.8%. Even when Mn is not positively contained, it may be contained as an unavoidable impurity, for example, less than 0.1%.

Fe: 0.05-1.5%
Fe precipitates in the structure as an intermetallic compound such as Al-Mn-Fe and Al-Mn-Si-Fe, and disperses the starting points of corrosion to improve the pitting corrosion resistance of the clad material. is added to If the Fe content is less than the lower limit, the effect is insufficient, and if the Fe content exceeds the upper limit, the corrosion rate increases and the sacrificial material disappears early, resulting in a decrease in the pitting resistance of the clad material.
For the same reason, it is desirable that the Fe content be 0.1% at the lower limit and 0.7% at the upper limit. Even when Fe is not intentionally contained, Fe may be contained, for example, less than 0.05% as an unavoidable impurity.

Zr: 0.01-0.3%
Zr is precipitated in the structure as an Al—Zr intermetallic compound to disperse the starting points of corrosion, and the pitting corrosion resistance of the clad material is improved by making the corrosion mode layered by forming a dark and light part of solid solution Zr. is optionally added to the sacrificial material to improve the If the Zr content is less than the lower limit, the effect is insufficient, and if it exceeds the upper limit, a huge intermetallic compound is formed during casting and the rollability deteriorates.
For the same reason, it is desirable to set the lower limit to 0.05% and the upper limit to 0.25%. Even when Zr is not intentionally contained, it may be contained as an unavoidable impurity, for example, less than 0.01%.

Ti: 0.01-0.3%
Ti precipitates as an Al-Ti-based intermetallic compound to disperse the starting points of corrosion, and forms a thick and thin portion of solid solution Ti to make the corrosion mode layered, thereby improving the pitting resistance of the clad material. It is optionally added to the sacrificial material in order to If the Ti content is less than the lower limit, the effect is insufficient, and if it exceeds the upper limit, a huge intermetallic compound is formed during casting, resulting in a decrease in rollability.
For the same reason, it is desirable to set the lower limit to 0.05% and the upper limit to 0.25%. Even when Ti is not positively contained, it may be contained, for example, less than 0.01% as an unavoidable impurity.

Cr: 0.01-0.5%
Cr precipitates as an Al—Cr-based intermetallic compound to disperse the starting points of corrosion and to form dark and light portions of solid solution Cr, thereby making the corrosion mode layered and improving the pitting resistance of the clad material. Therefore, it is added to the sacrificial material if desired. When the Cr content is less than the lower limit, the effect is insufficient, and when the Cr content exceeds the upper limit, a huge intermetallic compound is formed during casting and the rollability deteriorates.
For the same reason, it is desirable that the lower limit of the Cr content is 0.1% and the upper limit is 0.4%. Even when Cr is not intentionally contained, it may be contained, for example, less than 0.01% as an unavoidable impurity.

Bi: 0.005 to 0.5%
Bi reduces the surface tension of the molten brazing material by diffusing into the molten brazing material when the molten brazing material contacts the surface of the sacrificial material. In addition, it condenses on the surface of the material during the process of increasing the temperature for brazing and penetrates into the oxide film, inhibiting the growth of a dense oxide film. During brazing, Al ₂ O ₃ in the oxide film is reduced and decomposed by Mg in the sacrificial material and/or Mg in the brazing material when the brazing is melted, but Bi enters and the oxide film becomes brittle. Therefore, the oxide film is easily destroyed. However, when the Bi content is less than the lower limit, the effect is insufficient.
For the same reason, it is desirable that the lower limit of the Bi content is 0.05% and the upper limit is 0.3%. However, even if Bi is not actively added, it may contain, for example, less than 0.005% of Bi as an unavoidable impurity.

The aluminum alloy material used for the aluminum brazing sheet according to this embodiment can be produced, for example, by the following method.
As an aluminum alloy for brazing material, it contains 0.01 to 2.0% by mass of Mg, 1.5 to 14.0% of Si, and 0.005 to 0.5% of Bi. An Al--Si--Mg--Bi brazing filler metal having a composition containing 0.1 to 9.0% Zn with the balance being Al and unavoidable impurities is prepared. At this time, the molten aluminum alloy is adjusted by blowing chlorine gas into the molten aluminum alloy so that the impurity Ca is 50 mass ppm or less.

In addition, in the aluminum alloy for brazing material, at least one or two or more of In, Sn and Mn, each of which is 2.0% or less but the total is 2.0% or less as other elements, and each of which is 1.0% or less At least one or more of Fe, Ni, Ce, and Se with a total of 1.0% or less, each of 0.3% or less, but a total of 0.3% or less of Be, Na, Sb, Ti, Zr, and P , S, K, and Rb. Further, the brazing material may be positioned in the outermost layer of the brazing sheet, and the brazing material having a different composition may be included in the inner layer. That is, the brazing material may be composed of multiple layers.
In the case of having an inner layer of brazing material, the composition of the inner layer of brazing material is not particularly limited.

In addition, as the aluminum alloy for the core material, in mass%, Si: 0.05 to 1.2%, Mg: 0.01 to 2.0%, Mn: 0.1 to 2.5%, Cu: 0.01 ~2.5%, Fe: 0.05-1.5%, Zr: 0.01-0.3%, Ti: 0.01-0.3%, Cr: 0.01-0.5%, Bi: 0.005 to 0.5% and Zn: 0.1 to 9.0%, one or more of which are contained, and the balance is adjusted to a composition consisting of Al and unavoidable impurities.

In addition, in flux-free brazing that does not use fluoride-based flux, flux does not become inactive due to reaction with Mg. can. At this time, rather than containing Mg alone, it is expected to coexist with Si and precipitate fine Mg ₂ Si particles by aging or the like, so that a significant improvement in strength can be expected. is valid.

Furthermore, when a sacrificial material is used, the aluminum alloy for the sacrificial material contains, for example, Zn: 0.1 to 9.0% by mass, Si: 0.05 to 1.2%, Mg : 0.01-2.0%, Mn: 0.1-2.5%, Fe: 0.05-1.5%, Zr: 0.01-0.3%, Ti: 0.01-0 .3%, Cr: 0.01 to 0.5%, Bi: 0.005 to 0.5%, one or more of which are contained, and the balance is adjusted to a composition consisting of Al and unavoidable impurities.

An aluminum alloy is melted by adjusting the composition of the present embodiment. The melting can be performed by a semi-continuous casting method.
In this embodiment, in order to disperse fine Mg—Bi compounds before brazing, Mg and Bi are supersaturated and dissolved in the ingot by quenching from a high molten metal temperature during casting of the brazing filler metal. Specifically, the solid solubility of Mg and Bi can be increased by increasing the temperature of the molten metal to 700° C. or higher and increasing the cooling rate during casting.
The obtained aluminum alloy ingot is subjected to homogenization treatment under predetermined conditions. If the homogenization treatment temperature is low, a coarse Mg-Bi compound precipitates, making it difficult to obtain the distribution state of the Mg-Bi compound of the present invention at the time before brazing, so the treatment temperature is 400 ° C. or higher for 1 to 10 hours. is desirable.

Further, in the present embodiment, the Mg—Bi compound particles contained in the brazing material and having an equivalent circle diameter of 0.01 μm or more and less than 5 μm are within a depth of 10 μm from the outermost surface of the brazing material. It is desirable to have 10 or more per 10000 μm ² field of view.
In producing the brazing sheet of the present embodiment, when preparing the brazing material before clad, in addition to the above casting conditions, the Mg-Bi compound particles are finely crushed by increasing the rolling reduction during hot rolling. do.

Next, the brazing material of the aluminum alloy having the above composition is assembled with the core material of the aluminum alloy having the above composition, etc., and is hot clad-rolled. The equivalent strain from start to finish, hot-rolling finish temperature, cooling rate after hot-rolling, and rolling reduction during cold-rolling are controlled to adjust the fine Mg—Bi compound particles to a predetermined size and number density.

First, by satisfying the rolling time in a predetermined temperature range during hot rolling, precipitation of Mg—Bi compound particles having a predetermined size defined in the present embodiment is promoted in an environment in which dynamic strain is applied. Specifically, the precipitation of fine Mg—Bi compound particles is promoted by setting the rolling time to 10 minutes or longer while the material temperature is between 400 and 500° C. during hot rolling.

Further, by controlling the equivalent strain from the start to the end of hot rolling, it is possible to crush and refine coarse Mg—Bi crystallized substances generated during casting. Specifically, the equivalent strain ε shown in the following formula (1) is sufficiently refined by adjusting the slab thickness and the finished thickness so that ε>5.0. can be done.
ε=(2/√3) ln(t ₀ /t) Expression (1)
t ₀ : Thickness at the start of hot rolling (thickness of slab)
t: hot rolled finish thickness

Furthermore, if the finish temperature of hot rolling is high and a state without dynamic strain is maintained, or if the cooling rate after hot rolling is slow, coarser Mg Since -Bi compound particles are precipitated, the hot rolling finishing temperature is lowered to a predetermined temperature, and the precipitation of coarse Mg-Bi compound particles is suppressed by ensuring a cooling rate of a certain level or higher. Specifically, the hot rolling finishing temperature is 250 to 350 ° C., and the cooling rate from the finishing temperature to 200 ° C. is controlled to be faster than -20 ° C./hr to prevent precipitation of coarse Mg-Bi compounds. Suppress.
Further, with respect to rolling during hot rolling, it is preferable to perform multi-pass rolling under as low a pressure as possible. By reducing the rolling reduction per pass, rolling strain tends to concentrate near the surface layer, and shear strain tends to be introduced. Therefore, dynamic precipitation is promoted in the vicinity of the surface layer. Moreover, the crushing and refinement|miniaturization of a crystallized substance are accelerated|stimulated.

Moreover, in the cold rolling process, rolling is performed at least once with a low rolling reduction with respect to the material plate thickness. When the rolling reduction is low, strain tends to concentrate on the surface layer of the material, and fine Mg—Bi particles tend to precipitate on the surface layer of the brazing filler metal during the subsequent heat treatment. Specifically, relatively low cold rolling with a rolling reduction of 25% or less is performed at least once, and then annealing is performed at 200 to 400° C. to remove Mg—Bi particles from the outermost surface of the brazing material to a depth of 10 μm. Precipitate finely. Even if heat treatment is not performed during material production, fine Mg—Bi particles can be precipitated on the surface layer of the brazing filler metal during the brazing temperature rise process. It can be a thing.
Hot rolling and cold rolling are performed to obtain a clad material in which a brazing material is superimposed and bonded to one or both surfaces of a core material.
Through the above steps, as shown in FIG. 1, an aluminum brazing sheet 1 for a heat exchanger is obtained, in which one surface of a core material 2 made of an aluminum alloy is clad with an aluminum alloy brazing material 3 . In FIG. 1, one side of the core material 2 is clad with the brazing material 3, but both sides of the core material 2 may be clad with the brazing material. Alternatively, the other surface of the core material 2 may be clad with a sacrificial material 10 or the like.

Furthermore, the brazing filler metal 3 may have a multi-layer structure of two or more layers, for example, as shown in FIG. A two-layer structure may be adopted. In this case, the first brazing filler metal 3A may be composed of an Al--Si--Mg--Bi based brazing filler metal that satisfies the Bi concentration condition described above. Further, the first brazing material 3A and the second brazing material 3B may be formed on both sides of the core material 2. FIG. For example, a structure in which the first brazing material 3A and the second brazing material 3B are laminated outside the sacrificial material 10 can be adopted.
As the brazing target member 4, for example, aluminum containing 0.1 to 0.8% by mass of Mg, 0.1 to 1.2% by mass of Si, and the balance being Al and unavoidable impurities An alloy is prepared and processed into joining members as appropriate. In the present invention, the composition of the member to be brazed is not particularly limited.

When the fin material for a heat exchanger is obtained by the cold rolling or the like, it is then subjected to corrugating or the like as necessary. Corrugating can be carried out by passing between two rotating molds, which enables good working and exhibits excellent moldability.

The fin material obtained in the above process is used as a component of a heat exchanger, and is used as an assembly combined with other components (tube, header, etc.) for brazing.
The assembly is placed in a heating furnace in a non-oxidizing atmosphere under normal pressure. The non-oxidizing gas can be nitrogen gas, an inert gas such as argon, a reducing gas such as hydrogen or ammonia, or a mixed gas thereof. The pressure of the atmosphere in the brazing furnace is basically normal pressure, but for example, in order to improve the gas replacement efficiency inside the product, it is set to a medium-low vacuum of about 100 kPa to 0.1 Pa in the temperature range before melting the brazing material. Alternatively, the pressure may be about 5 to 100 Pa higher than the atmospheric pressure to suppress outside air (atmosphere) from entering the furnace. These pressure ranges are included in the scope of "without pressure reduction" in the present invention.

The heating furnace does not need to have an enclosed space, and may be of a tunnel type having inlets and outlets for the brazed assembly. Even in such a heating furnace, the non-oxidizing property is maintained by continuously blowing inert gas into the furnace. The non-oxidizing atmosphere preferably has an oxygen concentration of 100 ppm or less by volume.

Under the above atmosphere, for example, heating is performed at a temperature rising rate of 10 to 200° C./min, and brazing is performed under heat treatment conditions such that the assembled body reaches a temperature of 559 to 630° C. In brazing conditions, the faster the rate of temperature rise, the shorter the brazing time, so the growth of oxide film on the surface of the material is suppressed and the brazeability is improved. Brazing is possible if the reaching temperature is at least higher than the solidus temperature of the aluminum alloy brazing filler metal described above, but by bringing it closer to the liquidus temperature, the amount of fluid brazing filler metal increases, and joints with open parts are good. It becomes easier to obtain a bonded state. However, if the temperature is too high, corrosion of the brazing tends to proceed, and the structural dimensional accuracy of the assembled body after brazing is lowered, which is not preferable.

FIG. 2 shows an aluminum heat exchanger 5 in which the aluminum brazing sheet 1 is used to form the fins 6 and aluminum alloy tubes 7 are used as brazing material. The fins 6 and the tubes 7 are assembled with the reinforcing material 8 and the header plate 9, housed in the above-mentioned brazing furnace, heated to the brazing temperature and then cooled to obtain an aluminum heat exchanger for automobiles or the like by flux-free brazing. A vessel 5 can be obtained.

FIG. 3 shows the width W of the joint 13 consisting of the fillet formed between the curved portion of the fin 11 and the tube 12 (the length of the tube 7 so as to sandwich the contact portion of the curved portion of the fin 6 and the tube 12). direction).
FIG. 3 shows an example in which the width W of the joint portion 10 is formed large and an example in which the width W is formed small, side by side.
If the width W of the joint 10 is large as shown in FIG. 3, it means that a good brazing joint has been achieved.
If the heat exchanger 5 is manufactured by brazing using the fins 6 made of the brazing sheet 1 according to the present embodiment, a sufficiently large fret can be formed at the brazing joint portion, so good brazing A heat exchanger 5 can be provided with a joint.

In addition, in the brazing sheet of this embodiment, the surface may be etched with an alkali or an acid, if necessary. By etching, the oxide film formed during the material manufacturing process such as hot rolling and annealing can be removed, and as a result, the brazing properties of the brazing sheet can be further improved.
The timing of etching may be any time after hot rolling and before the brazing heat treatment using the brazing sheet. It may be performed after parts are processed.

Although the composition of the etchant used for etching and the etching conditions are not particularly limited, it is desirable that the surface layer of the brazing sheet is removed by about 0.05 to 3 μm by etching.
In the case of alkali etching, an aqueous solution of sodium hydroxide can be used, and in the case of acid etching, an aqueous solution of sulfuric acid, nitric acid, hydrochloric acid, or the like can be used.
By removing the surface layer of the brazing sheet by about 0.05 to 3 μm, the unnecessary oxide film on the surface of the Al—Si—Mg—Bi brazing material located on the outermost surface of the brazing sheet can be removed. The Si--Mg--Bi brazing material can be exposed on the outermost surface of the brazing sheet. In addition, the exposure of the Mg—Bi compound to the surface promotes the enrichment of Bi. These effects can further improve the brazeability.

Various brazing sheets having compositions shown in Tables 1 to 12 (core material, brazing material, sacrificial material; balance being Al and inevitable impurities) were produced from hot rolled sheets under the casting conditions and hot rolling conditions shown in Table 13. It should be noted that the test materials whose sacrificial material component is indicated by "-" do not use the sacrificial material.
After that, by cold rolling including intermediate annealing, a cold-rolled sheet with a thickness of 0.30 mm with a temper equivalent to H14 was produced. The cladding ratio of each layer was 10% brazing material and 15% sacrificial material. A corrugated fin made of A3003 alloy and H14 aluminum bare material (0.06 mm thick) was prepared as a member to be brazed.

"Thickness of oxide film on brazing material surface before brazing"
For each aluminum brazing sheet produced, while sputtering from the surface direction (RD-TD) of the brazing sheet in the inner direction by glow discharge optical emission spectrometry (GD-OES), a diagram showing the element distribution in the depth direction was obtained, and the outermost surface The distance from the outermost surface to the point where the line indicating the O content (oxygen content) and the line indicating the Al content from the outermost surface intersect was measured as the thickness of the oxide film on the surface of the brazing material before brazing. The thickness of the oxide film was similarly measured at five points on the surface of the brazing sheet, and the average values are shown in Tables 1, 4, 7 and 10.

"Number of fine Mg—Bi compound particles with an equivalent circle diameter of 0.01 to 5.0 μm in the surface layer of the brazing material"
A cross section (RD-ND) parallel to the rolling direction was prepared from the produced aluminum brazing sheet, mirror-finished with 0.1 μm abrasive grains, and the range from the outermost surface of the brazing material layer to a depth of 10 μm was subjected to EPMA (electron beam Fully automated particle analysis was performed with a microanalyzer). JXA-8530F manufactured by JEOL Ltd. was used as EPMA, and a particle analysis program attached to JXA-8530F was used as analysis software. The observation magnification is 1000 times and the acceleration voltage is 15 kV.
In addition, since the X-ray generation region is wider than the compound size, there is a concern that solid solution Mg in the matrix may be picked up and elemental Bi may be misidentified as an Mg—Bi compound. Therefore, separately, a region without crystal precipitates is analyzed, the solid solution Mg concentration is specified (for example, the region without crystal precipitates is analyzed with N = 10 to calculate the average Mg concentration), and the specified solid Compounds where dissolved Mg concentration<Mg concentration of compound were defined as Mg—Bi compounds.

Furthermore, in order to measure fine compound particles of 1 μm or less, a cross section (RD-ND) of the cut brazing material layer parallel to the rolling direction was mechanically polished and electropolished to prepare a thin film.
The Mg—Bi compound was measured for this thin film by TEM (transmission electron microscope) and EDS (energy dispersive X-ray spectroscopy) analysis.
A 10000 μm ^square (100 μm square) area from the outermost surface of the brazing material layer to a depth of 10 μm was observed by TEM, and the number of fine Mg—Bi compound particles with an equivalent circle diameter of 0.01 to 5.0 μm was counted. The observation magnification is 10,000 times (50,000 times especially for minute objects). SAED (Selected Area Electron Diffraction) analysis was also used as necessary when it was unclear whether or not it was a Mg—Bi compound in component analysis by EDS.
Each measurement was made at 5 points on the aluminum brazing sheet, and the average values of the measurement results are shown in Tables 1, 4, 7 and 10.

A flat tube with a width of 25 mm was manufactured using the aluminum brazing sheet, and the tube and corrugated fins were combined so that the tube brazing material and the corrugated fins were in contact with each other. A core was produced. The core was heated to 600° C. in a brazing furnace in a nitrogen atmosphere (oxygen content: 20 ppm), held for 5 minutes, and cooled to room temperature. Evaluation criteria are shown below.

"Brazability"
The bonding rate of the fins was obtained by the following formula, and the superiority or inferiority between each core sample was evaluated.
Fin bonding ratio = (total brazing length of fins and tubes/total contact length of fins and tubes) x 100
Judgments were made according to the following criteria, and the results are shown in Tables 14 to 17.
Fin bonding rate after brazing ◎: 98% or more, ○: 90% or more and less than 98%, △: 80% or more and less than 90%,
x: Less than 80%.

"Junction fillet length"
A portion of each brazed core sample was cut out, embedded in resin, mirror-polished, and the fillet length at the joint was measured using an optical microscope. The measurement method was to measure the width W of the joint 13 shown in FIG. Judgments were made according to the following criteria and shown in Tables 14 to 17.
◎: 1.0 mm or more, ○: 0.8 mm or more and less than 1.0 mm,
Δ: 0.6 mm or more and less than 0.8 mm, ×: less than 0.6 mm.

"Strength after brazing"
Each brazing sheet was placed in a furnace in a drop form and subjected to heat treatment corresponding to brazing under the above brazing conditions. After that, samples were cut out and subjected to a tensile test at room temperature by a method conforming to JIS Z2241 to evaluate tensile strength. The results are shown in Tables 14 to 17 as post-brazing strength. Evaluation of post-brazing strength is shown in Tables 14 to 17 based on the following criteria.
A: over 145 MPa, O: 140 to 145 MPa, x: less than 140 MPa.

"Brazil melting start temperature or Bi concentration on brazing material surface after brazing"
Immediately after the brazing melted or after brazing, each brazing sheet taken out from the brazing furnace was analyzed by glow discharge optical emission spectrometry (GD-OES) while sputtering from the surface direction (RD-TD) of the brazing sheet in the depth direction. was acquired, and the portion showing the highest concentration in the Bi concentration distribution in the oxide film was measured as the surface Bi concentration. The measurement was performed at 5 points on each brazing sheet, and the average value was obtained and shown in Tables 14 to 17.

"corrosion resistance"
A brazing sheet having a sacrificial material was placed in a furnace in the form of a drop, and a heat treatment equivalent to brazing was performed under the above brazing conditions. Thereafter, each brazing sheet was cut into a size of 30 mm×80 mm, masked except for the surface of the sacrificial material, and subjected to SWAAT (Sea Water Acetic Acid. Test, ASTM G85-A3) for 40 days. After the corrosion test, the corrosion product was removed from the sample with chromic acid phosphate, and the cross section of the maximum corroded portion was observed to measure the depth of corrosion. Judgments were made according to the following criteria and shown in Tables 14 to 17.
◎: within the sacrificial material layer, ○: within half the plate thickness, △: no penetration, ×: penetration.
The above results are shown in Tables 1 to 17 below.

Test material Nos. 1 to 120 are examples in which the concentration of the surface Bi after brazing is 1.0% by mass or more as shown in Tables 14 to 16, but all of them have a high brazing joining rate. , the fillet length of the brazed joint was also good. In addition, it is considered that the brazing strength of these test materials is sufficient.

As shown in Table 7, test material Nos. 92 to 96 and 100 are test materials of examples in which less than 10 fine Mg—Bi compound particles of 0.01 μm or more and less than 5.0 μm are present. , the fillet length is slightly shorter than the other test materials.
Test material Nos. 98 and 99, as shown in Table 7, are test materials having a pre-brazing oxide film thickness of more than 20 μm, but as shown in Table 16, they are less than other example test materials. The bonding rate is slightly lower.

Test material Nos. 92 to 99 are manufactured under the manufacturing conditions shown in Table 13, and the casting condition molten metal temperature, homogenization condition temperature, rolling time at 400 to 500 ° C., equivalent strain as hot rolling conditions during clad, finishing temperature , the cooling rate, the lowest rolling reduction, the intermediate annealing temperature, and the time, any one of which is outside the desirable range.
If the conditions shown in Table 13 are exceeded for these test materials, the number of fine Mg--Bi compound particles tends to decrease.

Test material Nos. 121, 122, and 126 have less than 10 fine Mg—Bi compound particles of 0.01 μm or more and less than 5.0 μm as shown in Table 10, but as shown in Table 17, Although the comparative example has a post-brazing surface Bi concentration of less than 1.0%, as shown in Table 17, either or both of the bonding ratio and the fillet length did not provide the required characteristics.
Test material No. 123, as shown in Table 10, cannot be manufactured as shown in Table 17 when the Mg content is out of the desirable range.
Comparative Example 127 has excellent properties such as brazeability, but the high Bi content of 0.8% results in a poor yield during production, and was industrially judged as NG.

Test material Nos. 128 to 136, as shown in Table 11, are samples in which the core material composition is outside the desired composition range. does not achieve the desired performance.
Test material Nos. 136 to 145, as shown in Table 12, are samples in which the composition of the sacrificial material is outside the desired composition range. I couldn't.

Next, Example No. shown in Table 1. 3, 8 and 21 samples were etched.
Specifically, the final material was subjected to alkali etching (immersion in 5% NaOH solution heated to 50° C. for 30 s, followed by desmutting (immersion in 30% HNO ₃ solution at room temperature for 60 s).
As a result, the following results were obtained.
Example No. 3: 18% surface Bi concentration after brazing, 1.7% surface Bi concentration at the start of brazing melting, fillet length ◎
Example No. 8: 48% surface Bi concentration after brazing, 4.5% surface Bi concentration at the start of brazing melting, joining ratio ◎
Example No. 21: 19% surface Bi concentration after brazing, 1.8% surface Bi concentration at the start of brazing melting, fillet length ◎
By subjecting the samples of Examples 3, 8, and 21 to the etching treatment, the fillet length was improved or the bonding rate was improved. Therefore, it was found that the brazeability can be further improved by subjecting the above sample to etching treatment.

INDUSTRIAL APPLICABILITY The brazing sheet according to the present invention can be widely used for brazing heat exchangers such as indoor units and outdoor units of air conditioners, heat exchangers for automobiles, and the like.

DESCRIPTION OF SYMBOLS 1... Aluminum brazing sheet 2... Core material 3... Brazing material 3A... First brazing material 3B... Second brazing material 4... Member to be brazed 5... Aluminum heat exchanger 6... Fin, 7... tube, 11... fin, 12... tube, 13... junction, W... width of junction 13.

Claims (8)

An aluminum brazing sheet having a multi-layered structure comprising at least two layers of at least a core material and a brazing material, comprising an Al-Si-Mg-Bi-based brazing material located on the outermost surface of the multi-layered structure, In the oxide film on the surface of the Al-Si-Mg-Bi brazing material, the part with the highest Bi concentration in the concentration distribution of various elements in the thickness direction obtained by glow discharge optical emission spectrometry is 1.0% or more by mass. An aluminum brazing sheet for brazing characterized by: The Al-Si-Mg-Bi-based brazing filler metal contains 1.5 to 14.0% Si, 0.01 to 2.0% Mg, and 0.005 to 0.5% Bi by mass. The aluminum brazing sheet for brazing according to claim 1, characterized in that The Mg—Bi compound contained in the Al—Si—Mg—Bi brazing filler metal, which has an equivalent circle diameter of 0.01 μm or more and less than 5.0 μm in observation of a cross section (RD-ND) parallel to the rolling direction. The brazing material for aluminum brazing according to claim 1 or claim 2, wherein 10 or more fine Mg-Bi compounds having diameters are present per 10000 µm ² visual field within 10 µm depth from the outermost surface of the brazing material. sheet. Various elements in the thickness direction obtained by glow discharge emission analysis in the oxide film on the surface of the Al-Si-Mg-Bi brazing material that has reached the brazing melting start temperature (solidus temperature) in the brazing temperature rising process. 4. The aluminum brazing sheet for brazing according to any one of claims 1 to 3, wherein the highest Bi concentration in the concentration distribution is 0.08% by mass or more. 5. The aluminum brazing sheet for brazing according to any one of claims 1 to 4, wherein the Al-Si-Mg-Bi based brazing material has an average oxide film thickness of 20 nm or less. The aluminum brazing sheet for brazing according to any one of claims 1 to 5, wherein the Ca impurity contained in the Al-Si-Mg-Bi brazing material is 50 ppm by mass or less. The aluminum brazing sheet for brazing according to any one of claims 1 to 6, characterized in that at least Si particles and part of the Mg-Bi compound are exposed on the uppermost surface of the etched surface. Aluminum brazing sheet for brazing. Etching the surface of the aluminum brazing sheet with an alkali or acid before performing brazing using the aluminum brazing sheet for brazing according to any one of claims 1 to 7 A method for producing an aluminum brazing sheet for brazing according to any one of claims 1 to 7.

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