JP2013215797A - Flux-less brazing method of aluminum material, brazing sheet for flux-less brazing and method for manufacturing the same, brazing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux-less brazing method of aluminum material capable of obtaining a stable joining state excellent in reliability, and a brazing sheet for flux-less brazing.SOLUTION: In a brazing sheet, Al-Si-Mg based brazing material having a composition which contains, by mass%, 5.0-13.0% of Si and 0.1-3.0% of Mg and the rest of which is made of Al and unavoidable impurities clads a core and is positioned at the outermost surface. By using the brazing sheet in which average film thickness of an oxide film on a surface of the Al-Si-Mg based brazing material before brazing is equal to or less than 150 Å and average film thickness of an MgO film in the oxide film is equal to or less than 20 Å, the Al-Si-Mg based brazing material and an object member to be brazed are made to contact and adhere to each other in a non-oxidizing atmosphere not accompanied by decompression and with oxygen concentration of 50 ppm or lower, and the core and the object member to be brazed are joined on an adhesion surface of a contact adhesion part by the Al-Si-Mg based brazing material in a flux-less manner.

Description

  The present invention relates to a brazing sheet for fluxless brazing that can be brazed without using a flux in a non-oxidizing atmosphere, a method for producing the brazing method, a fluxless brazing method for an aluminum material, and a brazed structure.

  In brazing fields such as automotive heat exchangers, brazing is currently performed using a non-corrosive fluoride-based flux such as Nocolok (registered trademark) flux in an inert gas atmosphere such as nitrogen gas. Or, a method of adding 0.5 to 1.5% by mass of Mg to the brazing material and brazing in a vacuum atmosphere has become the mainstream.

However, in the construction method using the above-described fluoride-based flux, when an Mg-added aluminum alloy effective for increasing the strength of the thin wall is used for a member to be joined, MgF ₂ is caused by the reaction between the fluoride-based flux and Mg in the alloy. As a result, the flux is inactivated, and as a result, there is a problem that the brazing property is remarkably lowered.

On the other hand, a fluxless brazing method that is performed under atmospheric pressure in consideration of mass productivity is also being developed. However, these fluxless brazing methods employ special methods such as surface treatment, material specifications, and brazing method, and many have problems in cost and quality stability. For this reason, the fluxless brazing method performed under atmospheric pressure has not yet been put into practical use.
In order to solve the problem of the above fluxless brazing method, Patent Document 1 includes decompression without generating equipment introduction costs and process costs by keeping the amount of Mg added to the brazing material within an appropriate range. Methods have been proposed that allow brazing without the use of flux under no atmosphere.

Japanese Patent No. 4547032

However, in the conventional fluxless brazing method performed under atmospheric pressure, if the oxide film on the surface of the brazing material is not sufficiently broken or divided during the brazing heat treatment, a problem occurs in that bonding failure occurs in a wide range and bonding strength decreases. There is.
In particular, when an Al—Si—Mg brazing material in which Mg is added to an Al—Si brazing material is used, Mg in the brazing material reacts with oxygen in the atmosphere to form an oxide film of Mg. When the film grows, there is a problem that it becomes difficult to obtain a stable bonding state due to a decrease in bonding rate.

  In order to improve the bonding state, it is effective to improve the wettability and fluidity of the molten brazing by dividing the oxide film of the bonded portion into a fine particle form as much as possible before melting the wax. is there. However, in the conventional Al—Si—Mg-based brazing filler metal, the division and removal of the surface oxide film are often insufficient, and it is difficult to ensure the stability of bonding.

  For the problem in the case of using the Al—Si—Mg brazing material, the reliability of joining has been improved by improving the brazing conditions and members. For example, the oxygen concentration in the furnace atmosphere in which brazing is performed is reduced, or the initial oxide film of the brazing target member is thinned by acid cleaning or the like (see Patent Document 1). Furthermore, the shape change of a junction part, optimization of member specification, etc. are also performed. However, it has not yet been possible to stably obtain a joint state necessary for practical use. In particular, in recent years, it has been required to reduce the thickness of members and to increase the pressure resistance of heat exchangers. Therefore, it is indispensable to ensure a stable bonding state at the bonding portion, and improvement of the bonding state is required.

  The present invention has been made against the background of the above circumstances, a fluxless brazing method for aluminum material, a brazing sheet for fluxless brazing, and a method for producing the same, capable of obtaining a stable and excellent reliability. An object is to provide a brazed structure.

That is, in the fluxless brazing method of the aluminum material of the present invention, the first invention of the present invention contains, in mass%, Si: 5.0 to 13.0%, Mg: 0.1 to 3.0%. The Al-Si-Mg brazing material is clad on the core material and located on the outermost surface, the average film thickness of the oxide film on the surface of the Al-Si-Mg brazing material before brazing is 150 mm or less, and Using a brazing sheet in which the average film thickness of the magnesium oxide film in the oxide film is 20 mm or less,
In a non-oxidizing atmosphere with an oxygen concentration of 50 ppm or less without decompression, the Al—Si—Mg-based brazing material and the brazing target member in the brazing sheet are brought into contact and intimate contact with each other, and the Al—Si is fluxless at the adhering portion. -The core material and the brazing target member are brazed and joined with an Mg-based brazing material.

The fluxless brazing method of the aluminum material according to the second aspect of the present invention is the method according to the first aspect, wherein the Al—Si—Mg based brazing material has a liquidus temperature of 610 ° C. or less,
The heating temperature in the brazing joining is 590 ° C. or higher.

The fluxless brazing method for an aluminum material according to a third aspect of the present invention is the method according to the first or second aspect, wherein the Al—Si—Mg-based brazing material has an equivalent circle diameter of 0.25 μm or more on the surface. More than 20,000 particles are present per 1 mm ² .

  In the fluxless brazing method of the aluminum material of the fourth invention, in any one of the first to third inventions, the core material is in% by mass, and Mn: 0.2 to 2.5%. One or more of Cu: 0.05 to 1.0% and Si: 0.1 to 1.0% are contained, and the balance is composed of Al and inevitable impurities.

  In the fluxless brazing method of the aluminum material of the fifth invention, in any one of the first to third inventions, the core material is in mass%, Mg: 0.01 to 1.0%, Contains one or more of Mn: 0.2-2.5%, Cu: 0.05-1.0%, Si: 0.1-1.0%, the balance being Al and inevitable impurities It has the composition which consists of.

The brazing sheet for fluxless brazing according to the sixth aspect of the present invention is a flux that is brought into contact with and closely contacted with a member to be brazed in a non-oxidizing atmosphere with an oxygen concentration of 50 ppm or less without decompression and is used for brazing without flux. A brazing sheet for brazing,
An Al—Si—Mg brazing material containing Si: 5.0 to 13.0% and Mg: 0.1 to 3.0% by mass% is clad by the core material and located on the outermost surface. The average film thickness of the oxide film on the surface of the Al—Si—Mg brazing filler metal before attachment is 150 mm or less, and the average film thickness of the magnesium oxide film in the oxide film is 20 mm or less.

  The brazing sheet for fluxless brazing according to a seventh aspect of the present invention is the brazing sheet according to the sixth aspect, wherein the Al-Si-Mg-based brazing material or the core material is according to any one of claims 2 to 5. It consists of an Al-Si-Mg type brazing material or the core material.

  According to an eighth aspect of the present invention, there is provided a method for producing a brazing sheet for fluxless brazing, without subjecting the material to be the Al—Si—Mg brazing material according to claim 1 or 2 to homogenization, or 500 After performing homogenization at a temperature of ℃ or less, clad rolling with the material to be the core material by performing a soaking treatment with a holding time at 500 ℃ or more within 1 hour, and after the clad rolling, It is characterized by performing rolling and performing intermediate annealing or final annealing at a temperature of 250 to 500 ° C. in an atmosphere having an oxygen concentration lower than the oxygen concentration in the atmosphere, and cooling to 200 ° C. or less in the same atmosphere. To do.

  In the brazing structure of the ninth aspect of the present invention, the brazing sheet for fluxless brazing according to claim 6 or 7 is used as a part of the brazing structure, and the brazing structure according to any one of claims 1 to 5. The brazing sheet for fluxless brazing is joined by the fluxless brazing method for aluminum material.

  Hereinafter, the reasons for limitation of the components defined in the present invention will be described. In addition, each component amount is shown by mass%.

1. In the present invention, an Al—Si—Mg based brazing material made of an Al—Si—Mg based alloy is used. The action of each element in the brazing material and the reasons for limitation are as follows.

Si: 5.0 to 13.0%
When Si is contained in Al, it is an essential element for lowering its melting point and melting at a brazing temperature to form a predetermined joint. Further, on the Si particles existing on the surface of the brazing material, the growth of a dense oxide film of aluminum is suppressed, and a defective portion of the oxide film is generated.
In other words, even if the oxide film on the surface of the aluminum material becomes thick during brazing heat treatment, melting of the brazing filler metal occurs from the periphery of the Si particles, and the oxide film breaks up and breaks off from this site, causing melting. Improves wettability of wax. This makes it possible to obtain a stable joined state.
For these reasons, the Si content needs to be 5.0% or more. If it is less than 5.0%, the amount of liquid phase produced is insufficient, so that sufficient fluidity cannot be obtained. On the other hand, if it exceeds 13.0%, the primary crystal Si rapidly increases and the workability deteriorates, and the brazing erosion of the joint portion is remarkably promoted during brazing. For this reason, Si content shall be 5.0 to 13.0%. For the same reason, the Si content is desirably 6.5% for the lower limit and 12.0% for the upper limit, and more desirably 11.0% for the upper limit.

Mg: 0.1-3.0%
Mg reductively decomposes a dense oxide film (Al ₂ O ₃ ) formed on the surface of the material to change it into a fine particulate oxide (MgAl ₂ O ₄ ), thereby improving the wettability and fluidity of the wax. Thereby improving the bonding rate. Mg has the effect of increasing the metal / metal bonding area at the bonding interface and improving the bonding strength by reducing and decomposing the oxide film. In order to obtain these effects sufficiently, a content of 0.1% or more is necessary. If it is less than 0.1%, the reduction and decomposition action of the oxide film becomes insufficient, so that a sufficient bonding state cannot be obtained. On the other hand, if it exceeds 3.0%, the strength of the brazing material is improved, making the clad rolling difficult, and the Mg oxide film tends to grow thick and brazeability is hindered. For this reason, content of Mg shall be 0.1-3.0%. For the same reason, it is desirable that the lower limit of the Mg content is 0.25% and the upper limit is 2.0%.

  The Al—Si—Mg brazing filler metal may be the balance of Al and inevitable impurities, and may contain other components as long as the above effects are not impaired. Examples of other components include Zn, Bi, Be, Sr, and Ca.

2. In the present invention, in the brazing sheet in which the Al-Si-Mg-based brazing material is clad on the core material and located on the outermost surface, the Al-Si-Mg-based brazing material surface before brazing -The average film thickness of the oxide film on the surface of the Si-Mg-based brazing material and the average film thickness of the magnesium oxide film in the oxide film are each controlled within a predetermined range.
In general, in brazing, a good bonding state cannot be obtained unless the initial oxide film on the surface of the material is destroyed. However, the Al ₂ O ₃ film, which is a typical aluminum oxide oxide film, is reduced and decomposed into an oxide by Mg as described above. For this reason, even if the Al ₂ O ₃ film is somewhat thick, the bonding rate does not significantly decrease.

On the other hand, in an Mg-added aluminum alloy material such as an Al—Si—Mg-based brazing material, a magnesium oxide film is easily formed during manufacturing or brazing heat treatment. Below, the reaction formula in which an oxide etc. are produced | generated in Mg addition aluminum alloy material is shown.
4Al + 3O ₂ → 2Al ₂ O ₃ (1)
2Mg + O ₂ → 2MgO (2)
3Mg + 4Al ₂ O ₃ → 3MgAl ₂ O ₄ + 2Al (3)

The Al ₂ O ₃ film produced according to the formula (1) can be reductively decomposed with Mg as described above. On the other hand, since the MgO film produced according to the formula (2) is very stable and difficult to break, even if the film thickness is relatively thin, the bonding rate is significantly reduced. The reaction represented by the formula (3) is a reaction that occurs when the oxygen concentration is low. As this reaction proceeds, the Al ₂ O ₃ film changes to a granular oxide (MgAl ₂ O ₄ ). As a result, the brazability is improved.
The reactions represented by the above formulas are likely to occur in the order of the formulas (2), (1), and (3), and an MgO film is easily formed. Therefore, in fluxless brazing, it is necessary to suppress the formation of the MgO film in order to obtain a stable bonding state.

Therefore, in the present invention, the average film thickness of the oxide film on the surface of the Al—Si—Mg brazing material before brazing is set to 150 mm or less.
The thinner the oxide film, the easier it is to decompose during brazing heat treatment, and as a result, the bonding rate is improved. Further, the formation of coarse voids is suppressed at the bonding interface, and the bonding strength and durability are remarkably improved. By setting the average film thickness of the oxide film to 150 mm or less, it is possible to improve the bonding rate and further obtain the effects of improving the bonding strength and durability. The type of the oxide film in this case is not limited. In the conventional fluxless brazing method, a portion where the oxide film is not sufficiently divided is formed during brazing, and this portion becomes a poorly bonded portion, resulting in a loss of airtightness or a decrease in pressure resistance. Of course, it is desirable that there is no void at the bonding interface, or a state where it is dispersed as small voids as possible so as not to become a stress concentration portion when an internal pressure or vibration is applied.
Note that the reduction in the thickness of the oxide film also contributes to an increase in cost. For this reason, the lower limit of the average film thickness of the oxide film is not particularly limited, but it is desirable to select the average film thickness in the range of 150 mm or less according to the application site.
On the other hand, when the average thickness of the oxide film exceeds 150 mm, the oxide film is not sufficiently broken during brazing, and as a result, the bonding strength and durability are remarkably reduced, and the bonding rate is also reduced.

Furthermore, in this invention, the average film thickness of the magnesium oxide film in the said oxide film shall be 20 mm or less.
As described above, the magnesium oxide film is very stable and has difficulty in breaking during brazing heat treatment. Therefore, when the average film thickness exceeds 20 mm, brazing joining is hindered, the bonding rate is reduced, and coarse voids are formed. This causes a significant decrease in bonding strength and durability. For this reason, since it is necessary to suppress the initial production of the magnesium oxide film as much as possible, the average film thickness before brazing is set to 20 mm or less. Thereby, the brazing joining inhibition by a magnesium oxide film can be suppressed, and the stable joining state excellent in reliability can be obtained.

  Note that Mg is an element having a very high activity, so that it combines with oxygen on the surface of the brazing material during heat treatment to form a magnesium oxide film in the vicinity of the surface layer of the oxide film. As described above, the magnesium oxide film defining the range of the average film thickness is formed in the vicinity of the surface layer of the oxide film as described above. In addition, the thinner the magnesium oxide film, the better the bonding state, but at the same time, the reduction in the thickness of the magnesium oxide film causes an increase in cost. If the Mg content in the Al—Si—Mg brazing material is reduced, a magnesium oxide film is less likely to be formed, but the effect of decomposition of the oxide film by Mg is also reduced. For this reason, the lower limit of the average thickness of the magnesium oxide film is not particularly limited, but the Mg content and the production process are appropriately selected according to the application site, and within an average range of 20 mm or less, It is desirable to select the optimal one.

3. Distribution of Si particles on the surface of the Al-Si-Mg brazing filler metal In the present invention, in the surface layer of the Al-Si-Mg brazing filler metal, 20,000 or more Si particles having an equivalent circle diameter of 0.25 µm or more exist per 1 mm ^2. It is desirable to do.
In the part where the Si particles are present on the surface of the brazing material, the growth of a dense oxide film (Al ₂ O ₃ film) is suppressed and becomes a defective part of the oxide film. Starting from this defective part, the destruction and splitting of the oxide film are promoted, the wettability of the molten solder is improved, and a more stable joined state can be obtained.
The above phenomenon is more effective as Si particles having a certain size or more are uniformly dispersed on the surface. That is, if the Si particle size on the surface of the brazing material is too small, the effect of causing a defect in the oxide film becomes insufficient. For this reason, it is desirable that the equivalent circle diameter of the Si particles is 0.25 μm or more. Further, when the distribution density of the Si particles is low, the places where the oxide film is broken or divided are reduced, and the effect becomes insufficient. For this reason, the distribution density of Si particles is desirably 20,000 or more per 1 mm ² .

4). In the present invention, the liquidus temperature of the Al—Si—Mg brazing material is preferably 610 ° C. or lower.
When the liquidus temperature is 610 ° C. or less, the brazing material melts in a short time after reaching the solidus temperature of the brazing material when the temperature of brazing is increased, and most of the brazing material is liquid phase in a short time when the temperature of brazing is increased. It becomes. For this reason, the initial oxide film on the surface of the brazing material is finely divided and flows to the outside of the joint surface together with the molten brazing. As a result, the wettability of the molten solder at the joint is improved, and a very stable joined state is obtained. On the other hand, when the liquidus temperature exceeds 610 ° C., the liquid phase ratio near the melting start temperature of the wax is lowered, and it takes time to completely become a liquid phase. Therefore, there is an effect of finely dividing the initial oxide film. It becomes insufficient. Therefore, the liquidus temperature of the Al—Si—Mg brazing material is desirably 610 ° C. or less.

5. Alloy component of core material The alloy component of the core material of the brazing sheet used in the present invention is not particularly limited, and bonding is possible without adding Mg to the core material. However, by realizing fluxless brazing, it is possible to actively add Mg aiming at high strength.
As the core material, one or more of Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, and Si: 0.1 to 1.0% are contained in mass%. It is contained and the remainder has a composition composed of Al and inevitable impurities. Moreover, what contains Mg: 0.01-1.0% by the mass% to the said composition as a core material is shown.
The action of each element in the core material and the reasons for limitation are as follows.

Mn: 0.2 to 2.5%
Mn crystallizes or precipitates as an intermetallic compound, and improves the strength after brazing. In addition, the corrosion resistance is improved by making the potential of the core material noble. In order to sufficiently obtain these functions, Mn is contained in an amount of 0.2% or more. Below the lower limit, these effects are insufficient. On the other hand, when the upper limit is exceeded, a giant intermetallic compound is produced during casting, and rolling becomes difficult. For this reason, the content of Mn is desirably 0.2 to 2.5%. For the same reason, the lower limit of the Mn content is more preferably 1.0% and the upper limit is 1.7%.

Cu: 0.05 to 1.0%
Cu is dissolved in the material to improve the strength after brazing and to improve the corrosion resistance by making the potential of the core material noble. In order to obtain these functions sufficiently, Cu is contained at 0.05% or more. Below the lower limit, these effects are insufficient. On the other hand, if the upper limit is exceeded, cracking occurs during casting, and the rollability deteriorates. For this reason, the content of Cu is desirably 0.05 to 1.0%. For the same reason, the Cu content is more preferably 0.1% at the lower limit and 0.7% at the upper limit.

Si: 0.1 to 1.0%
Si alone dissolves in the matrix to improve the material strength, and in the present invention, the material strength is improved by precipitation of Mg ₂ Si obtained by a synergistic effect with the addition of Mg. This precipitation of Mg ₂ Si contributes to a dramatic improvement in material strength by age hardening after brazing heat treatment. Further, when added simultaneously with Mn, it is dispersed as an Al—Mn—Si compound, and has an effect of improving the material strength. In order to obtain these effects sufficiently, Si is contained by 0.1% or more. Below the lower limit, these effects are insufficient. On the other hand, when the upper limit is exceeded, the melting point decreases, and the core material melts during brazing. For this reason, the content of Si is desirably 0.1 to 1.0%. For the same reason, the lower limit of the Si content is more preferably 0.4% and the upper limit is more preferably 0.8%.

Mg: 0.01 to 1.0%
Mg alone has a solid solution strengthening effect and, when added simultaneously with Si, precipitates as a fine intermetallic compound Mg ₂ Si after brazing and has the effect of significantly improving strength by age hardening. Moreover, it reacts with Si diffused from the brazing material during the brazing heat and has the same strength effect. Further, some of them diffuse into the brazing material and have an effect of contributing to the destruction and alteration of the oxide film on the brazing material surface. In order to obtain these effects sufficiently, Mg is contained in an amount of 0.01% or more. Below the lower limit, these effects are insufficient. On the other hand, when the upper limit is exceeded, the melting point decreases, and the core material melts during brazing. For this reason, the Mg content is desirably 0.01 to 1.0%. For the same reason, the lower limit of the Mg content is more preferably 0.2% and the upper limit is more preferably 0.6%.

6). Brazing sheet In the brazing sheet used in the present invention, it is sufficient that the Al-Si-Mg-based brazing material is clad on at least one side of the core material, and a single-side clad brazing sheet and a double-side clad brazing sheet are appropriately used. Can be used properly. In the double-sided clad brazing sheet, the Al—Si—Mg-based brazing material may be clad on both surfaces of the core material, and the Al—Si—Mg-based brazing material is clad on one side, Another material such as a sacrificial material may be clad on the other surface.

7). Material of brazing target member Any commonly used aluminum alloy can be used as the brazing target member without any problem.

8). Initial oxide film thickness of brazing target member In carrying out the present invention, an aluminum material having an initial oxide film thickness of about 20 to 500 mm, which is usually produced as a mass production coil material of aluminum, can be used as the brazing target member. In order to make the initial oxide film thickness less than 20 mm, acid cleaning or the like as shown in the prior art is required. Even if the initial oxide film thickness exceeds 500 mm, bonding is possible with the material of the present invention, but it is difficult to obtain a good bonded state, so it is desirable to make the initial oxide film as thin as possible.

9. In-furnace atmosphere In carrying out the present invention, the atmosphere in the furnace is an inert gas or a non-oxidizing gas such as a reducing gas, thereby reducing the oxygen concentration and dew point in the atmosphere, and brazing material and brazing target. It is necessary to suppress reoxidation of the member. The type of replacement gas to be used is not particularly limited in obtaining bonding, but from the viewpoint of cost, nitrogen, argon, and hydrogen, ammonia, and carbon monoxide are used as the inert gas and the reducing gas, respectively. Is preferred.
The non-oxidizing atmosphere as described above is not accompanied by reduced pressure. In the present invention, even in a non-oxidizing atmosphere without decompression, it is possible to obtain a stable joint state with excellent reliability by suppressing the joint inhibition by the magnesium oxide film as described above. By not accompanying it, high mass productivity can be secured.
The oxygen concentration in the non-oxidizing atmosphere is 50 ppm or less by volume ratio. By setting the oxygen concentration to 50 ppm or less, it is possible to suppress the deterioration of the brazing property due to the growth of an oxide film on the material surface during brazing. Bonding is possible even when the oxygen concentration is high, but depending on the shape of the joint, an oxide film grows during brazing and the joining state becomes unstable, and the joining rate and particularly the joining strength may decrease. . Desirable oxygen concentration is 20 ppm or less by volume ratio.
In addition, the bonding rate is improved as the oxygen concentration is lowered, but there is a concern that the manufacturing cost is increased, such as using a large amount of gas for managing the atmosphere. For this reason, it is desirable to appropriately set the oxygen concentration according to the required bonding rate.

10. Brazing temperature In the present invention, brazing can be performed at 559 ° C. or higher, which is the lowest solidus temperature of the Al—Si—Mg brazing alloy, but the core is heated to a peak temperature of 590 ° C. or higher It is desirable to join the member to be brazed. In combination with the liquidus temperature of the Al—Si—Mg brazing material, the brazing is favorably generated during the brazing heat.

11. Manufacturing method of brazing sheet The manufacturing method of the brazing sheet in which the Al-Si-Mg brazing material is clad on the core material is not limited to a specific one. However, when an Mg-containing aluminum alloy material such as an Al—Si—Mg-based brazing material is held at a temperature exceeding 500 ° C. in an atmosphere having a high oxygen concentration, an oxide film grows, and particularly a magnesium oxide film grows remarkably. For this reason, it is desirable to optimize the heat load process during the manufacturing process and control the average film thickness of the oxide film before brazing and the average film thickness of the magnesium oxide film in the oxide film as described above.

  Hereinafter, desirable conditions for each of the steps of homogenization, soaking, and intermediate annealing or final annealing, which are heat load steps in the manufacturing process, will be described.

Homogenization treatment When the homogenization treatment for the ingot of the Al-Si-Mg brazing material is carried out at a high temperature for a long time, an oxide film, particularly a magnesium oxide film grows on the surface of the brazing material and the brazing property is lowered. For this reason, it is desirable not to implement a homogenization process or to implement at a temperature below 500 degreeC.

Soaking Treatment When soaking heat treatment for heating the Al—Si—Mg-based brazing material before clad rolling is carried out at a high temperature for a long time, an oxide film, especially a magnesium oxide film grows on the brazing material surface, and the brazing property is lowered. On the other hand, in order to ensure the bonding property at the time of clad rolling, it is necessary to perform soaking at a temperature of 500 ° C. or higher. Therefore, when carrying out soaking at a temperature of 500 ° C. or higher at which the growth rate of the oxide film increases, it is preferable to shorten the holding time as much as possible, and specifically, to keep the holding time within one hour. . Since the rolling temperature of the rolled material is about 500 ° C. and the clad rolling property is ensured, it is desirable to keep the soaking time as short as possible in order to suppress the thickness of the oxide film.

Intermediate annealing and final annealing Intermediate annealing performed after cold rolling after clad rolling or final annealing after cold rolling is performed at a temperature of 250 to 500 ° C. in an atmosphere having an oxygen concentration lower than that in the atmosphere. It is desirable to do. By performing intermediate annealing or final annealing at a relatively low temperature in an atmosphere having a lower oxygen concentration than the atmosphere, it is possible to reduce the thickness of the oxide film of the final product and suppress the formation of the MgO film. .
In addition, as for the oxygen concentration in the atmosphere which implements intermediate annealing or final annealing, it is desirable that it is 1% or less by volume ratio.
Moreover, when the annealing temperature is less than 250 ° C., it is difficult to obtain predetermined mechanical properties without sufficiently softening the material. On the other hand, when the annealing temperature exceeds 500 ° C., the MgO film grows, so that the brazing property is lowered. For this reason, it is desirable that the annealing temperature be 250 to 500 ° C.
Moreover, in the said annealing, it is desirable to cool a brazing sheet to 200 degrees C or less in the atmosphere whose oxygen concentration is lower than the oxygen concentration in the atmosphere which implemented the said annealing. By setting the cooling atmosphere after annealing to an atmosphere having an oxygen concentration lower than that in the air, it is possible to reduce the thickness of the oxide film of the final product and to suppress the formation of the MgO film.
The intermediate annealing and the final annealing are performed as desired, and either one or both can be performed.

  As described above, according to the present invention, the brazing filler metal component and the oxygen concentration in the atmosphere are optimized, and further, the thickness and configuration of the initial oxide film are controlled to suppress the formation of a magnesium oxide film in the oxide film. Thus, the joining state can be remarkably improved.

  In addition, in order to obtain a more stable bonding state, in addition to optimization of the shape of the bonding portion, the composition of the brazing material, the oxygen concentration in the atmosphere, and the composition of the initial oxide film on the surface of the brazing material, the Si particles on the surface of the brazing material It is more effective to control the distribution form, the liquidus temperature of the brazing material and the brazing temperature.

  As described above, in addition to optimizing the brazing material components and brazing conditions, controlling the state of the initial oxide film on the brazing material surface of the brazing sheet dramatically improves the reliability of the joint compared to the conventional method. Can be improved.

Hereinafter, an embodiment of the present invention will be described.
A material to be an Al—Si—Mg based brazing material containing Si: 5.0 to 13.0% and Mg: 0.1 to 3.0% by mass% can be cast by a conventional method. The obtained material is not subjected to homogenization or is subjected to homogenization at a temperature of 500 ° C. or lower.
The remaining part of the Al—Si—Mg brazing material may be Al and inevitable impurities, and may further contain Zn, Bi, Be, Sr, Ca, or the like. The liquidus temperature of the Al—Si—Mg-based brazing material is 610 ° C. or less by adjusting the components.

  Moreover, a core material can be manufactured by a conventional method. As the core material, one or more of Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, and Si: 0.1 to 1.0% are contained in mass%. Examples are those containing and having the balance of Al and inevitable impurities. Moreover, what contains Mg: 0.01-1.0% by the mass% to the said composition as a core material is illustrated.

  Next, as a heat treatment before clad rolling, the brazing material that has not been subjected to the homogenization treatment or has been subjected to the homogenization treatment at a temperature of 500 ° C. or less, a core material, and other materials such as a sacrificial material as necessary Perform soaking treatment. In the soaking process, the holding time at 500 ° C. or higher is set to within 1 hour.

  After the soaking, clad rolling is performed on the brazing material and the core material. The conditions for clad rolling are not particularly limited. Further, the cladding ratio of each layer is not specified as the present invention.

  After clad rolling, cold rolling is performed by a conventional method. At the time of cold rolling, intermediate annealing or final annealing is performed at a temperature of 250 to 500 ° C. in an atmosphere having an oxygen concentration lower than the oxygen concentration in the atmosphere, and cooling is performed to 200 ° C. or less in the same atmosphere.

As described above, a brazing sheet is produced in which a brazing material is clad with a core material. In the obtained brazing sheet, an oxide film is formed on the surface of the Al-Si-Mg brazing material located on the outermost surface, and the average film thickness is 150 mm or less. A magnesium oxide film is formed near the surface layer in the oxide film, and the average film thickness is 20 mm or less. In addition, on the surface of the Al—Si—Mg brazing filler metal, 20,000 or more Si particles having an equivalent circle diameter of 0.25 μm or more exist per 1 mm ² .

The brazing sheet is assembled with a brazing target member such as a bare fin or a solid material connector, and preferably constitutes a heat exchanger assembly or the like. Note that aluminum members having various compositions can be used as the brazing target member, and the present invention is not limited to a specific one.
In the assembly, pressure is applied to the contact contact portion between the Al—Si—Mg-based brazing material and the brazing target member with a jig made of stainless steel or carbon. The higher the applied pressure, the better the stability of the joint. However, if the applied pressure is too high, deformation of the member occurs during brazing and the amount of pressurization is appropriately adjusted depending on the shape of the joint. The applied pressure at the joint is desirably 50 gf / cm ² or more.

The assembly is placed in a heating furnace having a non-oxidizing atmosphere without decompression. The non-oxidizing atmosphere can be configured using an inert gas such as nitrogen or argon, or a reducing gas such as hydrogen, ammonia or carbon monoxide, or a mixed gas thereof. The non-oxidizing atmosphere is not pressure-reduced at the time of brazing addition heat, and is usually atmospheric pressure, but may be a pressure higher than atmospheric pressure. In addition, before obtaining a non-oxidizing atmosphere, you may include a pressure reduction process for the purpose of substitution. The heating furnace does not need to have a sealed space, and may have a carry-in port and a carry-out port for a member to be brazed. Even in such a heating furnace, the non-oxidizing atmosphere is maintained by continuously blowing the inert gas into the furnace. The non-oxidizing atmosphere preferably has an oxygen concentration of 50 ppm or less by volume.
Under the above atmosphere, brazing is performed by heating to 590 ° C. or higher in a state where the Al—Si—Mg-based brazing material and the brazing target member are brought into close contact with each other. In brazing, the core material and the brazing target member are satisfactorily bonded to each other at the close contact surface of the contact close contact portion by the Al—Si—Mg brazing material. Thus, a brazed structure in which the core material and the brazing target member are joined is obtained.

(Brazing test)
An aluminum brazing sheet was prepared in which a brazing material (remainder Al and unavoidable impurities) having the composition shown in Table 1 was bonded to both surfaces of a core material (remainder Al and unavoidable impurities) having the composition shown in Table 1. The brazing alloy was produced by a semi-continuous casting method. The solidification rate during casting was varied in the range of 0.1 to 500 ° C./sec to change the Si particle size. Even with the same component, the faster the solidification rate, the smaller the Si particle size, and the number per unit area increases. The brazing sheet was finished with a brazing material clad rate of 5% on both sides and a 1 mm thick O material with a tempering equivalent to H14. The brazing sheet was cut into 50 mm squares, 5 sheets were laminated, uniformly pressurized at 500 gf / cm ² , and subjected to brazing heat treatment for heating to a predetermined temperature in a nitrogen gas atmosphere. The oxygen concentration in the atmosphere was controlled by changing the flow rate of nitrogen gas.
In the production process of the brazing sheet, each evaluation sample was prepared by appropriately changing the homogenization temperature and holding time of the brazing material, the temperature and holding time of soaking, and the atmosphere and temperature at the final annealing. The manufacturing conditions for each step are summarized in Table 2.

(Joining rate)
The bonding rate was measured with an ultrasonic flaw detector on each bonded surface of each sample produced, and used as an evaluation index for brazing. The ultrasonic measurement can detect the void portion, and the area of the void portion with respect to the entire area is obtained to calculate the bonding rate. The determination of brazeability was evaluated according to the following criteria based on the obtained bonding rate, and the results are shown in Table 1.
◎: Joining rate 95% or more ○: Joining rate 85% or more and less than 95% Δ: Joining rate 75% or more and less than 85% ×: Joining rate less than 75%

(Average film thickness of the initial oxide film and MgO film)
For each sample before brazing, the film thickness of the oxide film on the surface of the brazing material was observed at five arbitrary portions with a TEM (transmission electron microscope), and the average film thickness of the oxide film was determined. Further, the element distribution in the depth direction was measured by XPS (X-ray photomolecular spectroscopy) at three arbitrary portions on the surface of the brazing filler metal. The part where the total of Mg and oxygen exceeds 70% in terms of atomic ratio (at%) was defined as MgO, and the average film thickness of the MgO film was calculated.

(Joint strength)
Each produced sample was processed into a cylindrical shape of φ10 mm × thickness 5 mm, fixed to a jig with an adhesive, a tensile test was performed, and the fracture strength at the laminated joint interface was measured to obtain the joint strength. The determination of brazeability was evaluated according to the following criteria based on the obtained bonding strength, and the results are shown in Table 1.
○: Joining strength 80 MPa or more ×: Joining strength less than 80 MPa

(Si particle size of brazing material surface)
For the Si particle size, the outermost surface of the brazing material is polished with 0.1 μm abrasive grains, etched with 0.5% hydrofluoric acid aqueous solution for 60 seconds, and then fully automatic particle analysis using EPMA (electron beam microanalyzer) from the surface direction. The particle size and number were measured. For each sample, five arbitrary portions were measured in an observation field corresponding to 250 μm square for each sample, and a distribution of Si particles having a circle-equivalent diameter of 0.25 μm or more was obtained.

(Measurement of liquidus temperature of brazing material)
About each brazing alloy, liquidus temperature was measured using DSC (differential scanning calorimetry).

Claims (9)

An Al—Si—Mg brazing material containing Si: 5.0 to 13.0% and Mg: 0.1 to 3.0% by mass% is clad by the core material and located on the outermost surface. Using a brazing sheet in which the average film thickness of the oxide film on the surface of the Al-Si-Mg-based brazing material before attachment is 150 mm or less, and the average film thickness of the magnesium oxide film in the oxide film is 20 mm or less,
In a non-oxidizing atmosphere with an oxygen concentration of 50 ppm or less without decompression, the Al—Si—Mg-based brazing material and the brazing target member in the brazing sheet are brought into contact and intimate contact with each other, and the Al—Si is fluxless at the adhering portion. A fluxless brazing method for an aluminum material, characterized in that the core material and the brazing target member are brazed and joined with an Mg-based brazing material. The Al—Si—Mg brazing material has a liquidus temperature of 610 ° C. or less,
2. The fluxless brazing method for an aluminum material according to claim 1, wherein a heating temperature in the brazing joining is 590 ° C. or more. 3. The aluminum material according to claim 1, wherein the Al—Si—Mg-based brazing material has 20,000 or more Si particles having an equivalent circle diameter of 0.25 μm or more per 1 mm ^{2 on the} surface. Fluxless brazing method.   The core material is, by mass%, Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0.1 to 1.0%, or one or more of them. The fluxless brazing method for an aluminum material according to any one of claims 1 to 3, wherein the aluminum material has a composition comprising Al and inevitable impurities.   The said core material is the mass%, Mg: 0.01-1.0%, Mn: 0.2-2.5%, Cu: 0.05-1.0%, Si: 0.1-1. The fluxless brazing method for an aluminum material according to any one of claims 1 to 3, wherein the aluminum material contains one or more of 0%, and the balance is composed of Al and inevitable impurities. In a non-oxidizing atmosphere with an oxygen concentration of 50 ppm or less without decompression, a brazing sheet for fluxless brazing that is brought into contact and close contact with a member to be brazed and flux-lessly brazed,
An Al—Si—Mg brazing material containing Si: 5.0 to 13.0% and Mg: 0.1 to 3.0% by mass% is clad by the core material and located on the outermost surface. Flux characterized in that the average film thickness of the oxide film on the surface of the Al-Si-Mg brazing filler metal before attachment is 150 mm or less, and the average film thickness of the magnesium oxide film in the oxide film is 20 mm or less. Brazing sheet for brazing.   The said Al-Si-Mg type | system | group brazing material or the said core material consists of the said Al-Si-Mg type | system | group brazing material or the said core material in any one of Claims 2-5. Brazing sheet for fluxless brazing.   The material to be the Al—Si—Mg-based brazing material according to claim 1 or 2 is subjected to homogenization without performing homogenization or at a temperature of 500 ° C. or lower, and then at 500 ° C. or higher. Clad rolling with the material to be the core material is carried out by performing soaking treatment with a holding time of within 1 hour, cold rolling is performed after the clad rolling, and in an atmosphere where the oxygen concentration is lower than the oxygen concentration in the atmosphere A method for producing a brazing sheet for fluxless brazing, wherein intermediate annealing or final annealing is performed at a temperature of 250 to 500 ° C. and cooling to 200 ° C. or less in the same atmosphere.   The brazing sheet for fluxless brazing according to claim 6 or 7 is used for a part of the brazing structure, and the fluxless brazing method for an aluminum material according to any one of claims 1 to 5 is used. A brazing structure characterized in that a brazing sheet for fluxless brazing is joined.