JP2014184468A - Brazing method for aluminium material and brazed structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable successful brazing without using flux without requiring flux and a vacuum facility.SOLUTION: An aluminum alloy material including Al-Si-Mg-based brazing filler metal is heated within a brazing furnace in a pressure reduction state lower than the atmospheric pressure, is heated in a first reduced-pressure atmosphere preferably having 50 ppm or less of an oxygen concentration at least in a temperature range from 450°C until before melting of the brazing filler metal during temperature rise, and is heated in a second reduced-pressure atmosphere preferably having 25 ppm or less of the oxygen concentration and preferably 10 vol.% or less of a nitrogen gas concentration at least at a temperature equal to or higher than that enabling the brazing filler metal to start to melt, so that a brazing object including the aluminum alloy material is joined by using the Al-Si-Mg-based brazing filler metal without using flux. Thus the oxygen concentration and the nitrogen concentration in the atmosphere in the middle of brazing are controlled, so as to suppress cost increase and dramatically improve reliability of joined portions, compared to a conventional brazing method without using flux.

Description

  The present invention relates to a brazing method for an aluminum material in which a brazing object including an aluminum alloy material is bonded using an Al—Si—Mg-based brazing material without using a flux, and a brazing structure joined by the brazing method. About the body.

  In addition to radiators and condensers, automotive heat exchangers such as intercoolers, and other heat exchangers and radiators manufactured from aluminum alloys are currently non-corrosive fluorides in an inert gas atmosphere. The mainstream method is brazing using a flux or brazing in a vacuum atmosphere by adding about 0.5 to 1.5% by mass of Mg to the brazing material.

  When using the above-mentioned flux, many members to be brazed are processed by press molding or the like, and then put into a desired assembled state. A turbid liquid in which flux powder is dissolved in a solvent is applied to the assembled body and dried, and high purity nitrogen gas is used. Heat brazing in a non-oxidizing atmosphere. In this case, there is a problem that the use of the flux itself, or the installation and management of the coating process, requires cost.

Further, it is known that a part of the flux evaporates in the process of brazing heat and adheres to and accumulates on the inner wall of the furnace, and periodic maintenance of the furnace for the purpose of removing the deposit also occurs as a necessary cost. And nowadays, with the promotion of weight reduction of automobiles, there is a demand for further thinning and strengthening of materials in automobile heat exchangers. Addition of Mg to an aluminum alloy is very effective for increasing the strength of aluminum materials. However, brazing using a flux reacts with Mg to produce a high melting point MgF ₂ , which is brazed. As a result, the Mg added in the material does not contribute to the increase in strength. That is, in flux brazing, there are restrictions on the site and amount of Mg added in the product, and the current situation is that it cannot be actively used as a technique for increasing the strength of materials. In recent years, in inverter coolers and the like used for hybrid vehicles and electric vehicles, the use of flux may be restricted because the flux residue itself hinders the solderability of semiconductor components.

  On the other hand, in high-vacuum brazing such that the pressure is 0.01 Pa or less, Mg added to the brazing material evaporates from the material in the process of raising the brazing temperature. The oxide film is destroyed, and the atmosphere in the furnace can be brazed by the getter action combined with moisture and oxygen in the atmosphere. Although this method does not require a flux coating process, there is a problem that a high-vacuum vacuum furnace is an expensive facility, and there is a corresponding cost in managing the airtightness of the furnace. In addition, in heat exchangers for automobiles, Zn is added for the purpose of ensuring the corrosion resistance of products. However, since Zn evaporates under high vacuum heating, sufficient Zn does not remain in the material, and sufficient corrosion resistance is achieved. There is also a demerit that it cannot be secured. Furthermore, since evaporated Mg and Zn are deposited on the inner wall of the furnace, periodic cleaning in the furnace is also required.

On the other hand, fluxless brazing under atmospheric pressure has recently been proposed as a brazing method that can solve the above problems (see Patent Documents 1 to 5).
For example, Patent Document 1 proposes flux-less brazing under a non-oxidizing atmosphere and atmospheric pressure by placing an Mg-containing material on a brazed member or other part and covering the brazed material. doing.

Patent Document 2 proposes a mechanism in which a brazing member (cover) heated in advance in a brazing furnace is used to cover a brazed member in the furnace, thereby improving the decrease in the heating rate.
On the other hand, as fluxless brazing that does not require a cover, in Patent Document 3, Mg is added to a clad brazing material, and the inside of the heat exchanger tube formed by the clad material is set to atmospheric pressure in an inert atmosphere. A fluxless brazing method has been proposed below.
Also, as a device that does not require a cover, Patent Document 4 also proposes a method in which a brazing material surface is clad with an antioxidant layer and the clad material is laminated to enable brazing in an air atmosphere. is there.

  Furthermore, in Patent Document 5, if the surface of the core material is clad with a brazing material made of an Al—Si—Mg-based alloy, and the material surface is acid-washed before brazing and the thickness of the oxide film is 20 mm or less, There is a proposal that fluxless brazing in a non-oxidizing atmosphere becomes possible.

JP-A-9-85433 JP 2006-175500 A Japanese Patent No. 4037477 Japanese Patent No. 3701847 Japanese Patent Laid-Open No. 10-180489 International Publication No. 2012-057197

However, in the technique proposed in Patent Document 1, it is indispensable to cover, and it is necessary to prepare a cover for each product size, to prepare a number to be used for mass production, and to cover Maintenance is required, and there is a problem that it takes time and cost for mass production. Moreover, there is also a problem that the temperature rise rate of the brazed object is lowered by covering, and the productivity is lowered.
Moreover, in the method shown in Patent Document 2, it is necessary to provide a mechanism for controlling the operation of the windbreaker in the furnace, and there is a problem that it takes cost and labor to install and maintain the equipment.

Further, Patent Documents 3 to 5 that enable brazing under atmospheric pressure without requiring a cover also have the following problems.
In the method proposed in Patent Document 3, a flux is used to join the outer surface of the tube and the fin, and there is a problem that the disadvantages of using the flux are not completely eliminated.
Moreover, in the technique proposed in Patent Document 4, it is necessary to prepare a clad material in which an anti-oxidation layer is provided on the surface of the brazing material with respect to the material used for the conventional high vacuum brazing or nocolok brazing, and the material cost In addition, there is a problem of versatility that the product shape is limited to a laminated structure.
Furthermore, the method disclosed in Patent Document 5 has a problem that the process management of the acid cleaning becomes complicated and the cost for the acid cleaning process increases.

  Further, in the conventional fluxless brazing method, the oxide film on the surface of the brazing material is not sufficiently broken or divided during the brazing heat treatment, and thus there is a problem that bonding failure occurs and the bonding strength is remarkably reduced. In addition, when the oxygen concentration in the atmosphere during the manufacturing process and brazing heat treatment is high, Mg in the member reacts with oxygen in the atmosphere, an Mg oxide film (MgO) grows, and the bonding rate decreases significantly. There is also a problem that it is difficult to obtain a stable bonded state.

  In view of such a problem, the present invention does not generate new operation costs such as introduction operation costs such as flux application process and vacuum equipment, secondary material costs such as a cover used at the time of brazing, material acid cleaning, And it aims at providing the versatile fluxless brazing method of the aluminum material which can obtain the stable joining state in all the parts irrespective of shapes, such as a heat exchanger.

Aluminum is very easily oxidized by the reaction of the following formula (1), and when an oxide film is formed, the brazing property is lowered.
2Al + 3 / 2O ₂ → Al ₂ O ₃ (1)
In fluxless brazing, it is necessary to improve the wettability and fluidity of the molten brazing by dividing the oxide film at the joint into fine particles as much as possible. Further, it has been confirmed that the reduction of the oxygen concentration in the furnace atmosphere is effective in terms of improving the brazeability.
Even when Mg is added to a material such as a brazing material or a brazing target member for dividing an oxide film, if the oxygen concentration in the atmosphere is high at the time of brazing, the member as shown in the following formula (2) The oxidation of Mg is promoted and a stable MgO oxide layer is formed thick on the surface, so that the brazing property is remarkably lowered. During brazing, the oxide film on the surface grows as it is stored at a high temperature for a long time, but the oxidation reaction proceeds rapidly at 550 ° C. or higher, and the reaction occurs even in the solid phase.
Mg + 1 / 2O ₂ → MgO (2)
On the other hand, in the state where the oxygen concentration is low, as shown in the following formula (3), the oxide film Al ₂ O ₃ on the aluminum surface is reduced and decomposed by Mg in the material to be changed into granular MgAl ₂ O ₄ , which is fine. Since it is dispersed as an oxide, good bonding is performed.
3Mg + 4Al ₂ O ₃ → 3MgAl ₂ O ₄ + 2Al (3)
Therefore, in order to obtain a good bonding state, it is desirable to control the oxygen concentration in the atmosphere as low as possible.

In general, the cheapest nitrogen gas is used to lower the oxygen concentration. However, in the molten brazing containing Mg, since the surface oxide film is destroyed and activated, the following equation (4) is obtained. In addition, it is considered that when the wax is melted, it reacts with nitrogen in the atmosphere, and a reaction layer mainly composed of nitride is formed on the surface of the molten wax, so that the gap filling property is lowered and the wettability of the wax is remarkably lowered. However, this reaction is a reaction between molten brazing (liquid phase) and atmospheric gas (gas phase) and does not occur in the solid phase, so the O ₂ and N ₂ concentrations in the atmosphere are lowered in the brazing melting region in the furnace. It becomes important.
M (Al, Mg, Si) + N ₂ → M _x N _y (4)
In the reactions of the above formulas (1) to (4), the reactions are likely to occur in the order of (2), (1), (3), and (4).

Argon has been proposed as a gas other than N ₂ gas that is effective for improving brazing properties (see Patent Document 6). However, since argon is more expensive than N ₂ , the cost of brazing increases. By efficiently using these gases only in the region where the wax is melted, the amount used can be reduced, and the improvement in brazing and cost can be achieved.

  Therefore, as a result of intensive studies in view of the above problems, the present inventors added an appropriate amount of Mg to the Al—Si brazing material and heated in a reduced pressure atmosphere. The present inventors have found that the oxygen concentration and the nitrogen gas concentration are optimally managed according to the temperature range, and that the joining state can be remarkably improved while suppressing an increase in cost, and the present invention has been completed.

That is, among the brazing methods for an aluminum material of the present invention, the first invention is that an aluminum alloy material provided with an Al—Si—Mg-based brazing material is heated in a brazing furnace at a reduced pressure lower than atmospheric pressure. A brazing method,
Heating is performed in a first reduced-pressure atmosphere having an oxygen concentration equal to or lower than a first predetermined value at a temperature range of at least 450 ° C. before the wax melting at the time of temperature rise, and at least above the temperature at which the wax starts melting The Al—Si—Mg-based brazing material is heated without using a flux by heating in a second reduced pressure atmosphere having a nitrogen gas concentration equal to or lower than a second predetermined value lower than the first predetermined value. The brazing object containing the aluminum alloy material is joined by the above.

  The method for brazing an aluminum material according to a second aspect of the present invention is the method according to the first aspect, wherein the Al—Si—Mg brazing material and the aluminum alloy material are clad using the aluminum alloy material as a core material. It is characterized by constituting a brazing sheet.

  The 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 first reduced-pressure atmosphere has a first predetermined value of oxygen concentration of 50 ppm and a pressure of 1 Pa or more. The second reduced-pressure atmosphere is characterized in that a second predetermined value of oxygen concentration is 25 ppm, a predetermined value of the nitrogen gas concentration is 10% by volume, and a pressure is 0.01 Pa or more.

  In the method of brazing an aluminum material according to a fourth aspect of the present invention, in the third aspect of the present invention, the first reduced-pressure atmosphere has a pressure of 10,000 Pa or less, and the second reduced-pressure atmosphere has a pressure of 5 , 000 Pa or less.

  The aluminum material brazing method according to the fifth aspect of the present invention is the method according to the third or fourth aspect of the present invention, until the brazing is cooled to 400 ° C. in the cooling process after the step of heating at a temperature higher than the temperature at which melting starts. The oxygen concentration is maintained at 50 ppm or less in a temperature range of

  The aluminum material brazing method of the sixth aspect of the present invention is the method according to any one of the first to fifth aspects of the present invention, wherein the second reduced-pressure atmosphere forms a rare gas or a mixed gas containing a rare gas as a carrier gas. It is characterized by being.

  The aluminum material brazing method according to a seventh aspect of the present invention is the method according to any one of the first to sixth aspects, wherein the first reduced-pressure atmosphere is formed by using a rare gas or a mixed gas containing a rare gas as a carrier gas. It is characterized by being.

  An aluminum material brazing method according to an eighth aspect of the present invention is characterized in that, in the sixth or seventh aspect of the present invention, the rare gas is argon.

  A brazing method for an aluminum material according to a ninth aspect of the present invention is the method according to any one of the first to eighth aspects, wherein the brazing material is in mass%, Si: 5.0 to 13.0%, Mg: It contains 0.1 to 3.0%, and the balance is made of Al and inevitable impurities.

  The brazing method for an aluminum material according to a tenth aspect of the present invention is the method according to the ninth aspect of the present invention, wherein the brazing material further contains Be: 0.0001 to 0.1% and Bi: 0.01 to 0.0. It is characterized by containing one or more of 3% and Ca: 0.002 to 0.3%.

  The aluminum material brazing method of the eleventh aspect of the present invention is the aluminum alloy material according to any one of the first to tenth aspects of the present invention, wherein the aluminum alloy material is Mn: 0.2 to 2.5% by mass, Cu: It is characterized by containing one or more of 0.05 to 1.0% and Si: 0.1 to 1.0%, with the balance being composed of Al and inevitable impurities.

  The aluminum material brazing method according to a twelfth aspect of the present invention is the aluminum material according to any one of the first to eleventh aspects, wherein the aluminum alloy material contains Mg: 0.01 to 1.0% by mass. Further, Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0.1 to 1.0%, or one or more of them are contained, with the balance being Al. It has a composition comprising inevitable impurities.

  The brazing structure of the thirteenth aspect of the present invention is characterized in that a brazing object is joined by the brazing method of any of the first to twelfth aspects of the present invention.

Since the oxidation of the aluminum member progresses as the temperature rises during brazing addition heat, it is essential to lower the oxygen concentration in the atmosphere, but aluminum and nitrogen gas are not reactive at the stage before the brazing melts Therefore, it is advantageous in terms of cost to suppress oxidation using the least expensive nitrogen gas. However, if the nitrogen gas concentration in the atmosphere is high after the wax is melted, a nitride layer is formed on the surface of the molten solder, so that the wettability of the solder is remarkably lowered and sufficient bonding cannot be obtained. That is, the reaction layer with nitrogen is a reaction between the liquid phase melting wax and the gas phase nitrogen gas. According to the present invention, under reduced pressure, the oxygen concentration and atmosphere before wax melting and the oxygen in the atmosphere after wax melting. By controlling the concentration and the nitrogen concentration, the stability of bonding is improved, the amount of expensive argon gas used is reduced, and both brazability and cost can be achieved. In addition, by controlling the oxygen concentration and the nitrogen concentration, the degree of vacuum at the time of decompression can be lowered, and evaporation of Mg and the like can be suppressed.
When the amount of argon gas used can be reduced, it is also effective to use a carrier gas containing argon gas or the like from the first reduced pressure atmosphere. Note that the reduced-pressure atmosphere gas in the first reduced-pressure atmosphere and the second reduced-pressure atmosphere may be the same type or different types.
Below, the conditions prescribed | regulated by this invention are demonstrated.

(Atmosphere control during brazing process)
Reduce the pressure inside the brazing furnace to reduce the amount of gas (atmosphere) brought into the heat exchanger and the adsorbed substances (residual oil, moisture, etc.) on the material surface to improve brazing.
Temperature range from 450 ° C to before melting, oxygen concentration and reduced pressure atmosphere (first reduced pressure atmosphere)
It is necessary to regulate the oxygen concentration in order to prevent the oxide film on the surface of the material from growing during brazing addition heat at 450 ° C. or higher and reducing brazing. Bonding is possible even when the oxygen concentration is high, but depending on the shape of the bonded portion, the bonding rate and bonding strength are reduced.
In addition, since the nitrogen gas and the aluminum material have no reactivity before the solder melting, it is advantageous in terms of cost to reduce the oxygen concentration in an inexpensive nitrogen gas atmosphere, but the type of the reduced-pressure atmosphere gas is particularly defined. It is not a thing. In addition, when using arbitrary decompression atmosphere gas, it is not necessary to regulate nitrogen gas concentration in particular.
The upper limit of the temperature of the first reduced-pressure atmosphere is not particularly limited as long as it is before the wax melting, but it is preferably as close to the wax melting as possible, and more preferably just before the wax melting temperature.

The upper limit of the oxygen concentration in the first reduced pressure atmosphere is a first predetermined value higher than the second predetermined value of the oxygen concentration in the second reduced pressure atmosphere. Since the oxygen concentration restriction in the first reduced-pressure atmosphere is to suppress the oxidative growth in the solid phase, it can be made more lenient than the oxidation restriction at the time of melting. Specifically, for example, the oxygen concentration can be 50 ppm or less. When the oxygen concentration exceeds 50 ppm, the growth of the oxide film of Al or Mg proceeds during the heat of brazing addition, and the wettability during the melting of the braze decreases, so that the joining state becomes unstable, and particularly the gap filling property and the joining strength are lowered. Note that the growth of the oxide film is suppressed when the oxygen concentration is lower in the region where the temperature is higher. For this reason, in the temperature range from 500 degreeC or more to wax melting, you may make it regulate oxygen concentration to 25 ppm or less. The oxygen concentration in the first reduced pressure atmosphere is more preferably 20 ppm or less.
As the oxygen concentration in the atmosphere is lowered, the bonding rate is improved. However, it is necessary to improve the air tightness of the furnace and to significantly increase the amount of use of the reduced-pressure atmosphere gas, which causes a cost increase.
Further, the first reduced-pressure atmosphere is brought into a reduced pressure state lower than the atmospheric pressure to prevent the brazed surface from being oxidized. The pressure is desirably 10,000 Pa or less. If it exceeds 10,000 Pa, it is difficult to lower the oxygen concentration, and the surface cleaning effect of the brazing object cannot be sufficiently obtained, so that the brazing property is lowered. For the same reason, 5,000 Pa or less is more desirable.
Further, it is desirable that the first decompressed atmosphere has a pressure of 1 Pa or more. This is because the lower the pressure, the lower the oxygen concentration and the surface cleaning effect, but the airtightness of the brazing furnace and the capacity of the vacuum pump are required, and the furnace maintenance and production maintenance management costs increase. .
In addition, from the viewpoint of brazing furnace management and productivity as described above, the first reduced-pressure atmosphere is more preferably a pressure of 100 Pa or more, and more preferably a pressure of 5,000 Pa or less. It is.

Note that as a gas for forming the first reduced-pressure atmosphere, one kind or a mixed gas of a rare gas such as argon, helium, and xenon that is not reactive with aluminum is used, and argon is most preferable from the viewpoint of cost. It is also possible to use different rare gases at different times. The above gas can be used as a carrier gas.
Since there are many methods for obtaining the atmosphere, such as providing a partition plate in the furnace and optimizing the gas blowing method, the structure of the brazing furnace is not particularly defined here. In addition, a method of recovering the argon gas used for cost reduction and performing recirculation is also effective.

At least the temperature at which the wax begins to melt ・ Oxygen concentration and nitrogen gas concentration (second reduced pressure atmosphere)
Above the temperature at which the wax starts to melt, the oxygen concentration and the nitrogen gas concentration are regulated as the second reduced pressure atmosphere, and the pressure is reduced to a low vacuum. Since higher pressure is better for suppressing evaporation of Zn, Mg, etc., the degree of vacuum is desirably 5,000 Pa or less. If it exceeds 5,000 Pa, it is difficult to lower the oxygen concentration, and a large amount of carrier gas is required. The degree of vacuum is more preferably 2,500 Pa or less. The second reduced-pressure atmosphere can be relatively lower in vacuum, that is, higher pressure than the first reduced-pressure atmosphere. The second reduced pressure atmosphere may start below the temperature at which the wax begins to melt.
Further, it is desirable that the second reduced pressure atmosphere has a pressure of 0.01 Pa or more. In order to ensure brazing, it is better to have a low pressure, but an expensive vacuum pump is required, and if the pressure is low, Zn will evaporate from the member during brazing, ensuring corrosion resistance. This is because it becomes difficult.
For the same reason as described above, it is more desirable that the second reduced-pressure atmosphere has a pressure of 0.1 Pa or more, and it is more desirable that the pressure be 2,500 Pa or less.

  When the molten wax is formed, the reaction with the gas in the atmosphere is significantly accelerated. That is, unless the oxygen concentration and the nitrogen concentration above the temperature range where the wax starts to melt are not lowered, a reaction layer is formed and the wettability is remarkably lowered. In the case of a brazing material containing Mg, since the brazing material surface is activated, it is necessary to control not only the oxygen concentration but also the nitrogen concentration to suppress the growth of the reaction layer.

  The oxygen concentration in the second reduced-pressure atmosphere is determined to be lower than the restriction value for the oxygen concentration in the first reduced-pressure atmosphere because it is an oxidation suppression during melting. Specifically, for example, it is 25 ppm or less. When the oxidation concentration exceeds 25 ppm, the magnesium oxide film (MgO) grows remarkably, making it difficult to sufficiently advance the reaction of the formula (3). A more desirable oxygen concentration is 20 ppm or less. However, further reduction in the oxygen concentration causes an increase in the airtightness of the furnace and an increase in the amount of reduced-pressure atmospheric gas used, which increases the cost.

  Further, in the second reduced-pressure atmosphere, by restricting the nitrogen concentration, the cause of the brazing property inhibition by the atmospheric gas is eliminated so that the reaction of the formula (4) does not proceed. Specifically, for example, the nitrogen concentration in the atmosphere is set to 10% by volume or less. If it exceeds 10% by volume, the reaction of the formula (4) tends to proceed, the growth of the nitride layer is remarkably promoted, and the brazing property is lowered. Desirably, it is 5 volume% or less. When the nitrogen gas concentration in the atmosphere is further reduced, the bonding rate is improved. However, since the amount of the use of a more expensive reduced-pressure atmosphere gas such as argon or helium is increased, it is not desirable from the viewpoint of cost.

In addition, as a gas for forming the second reduced pressure atmosphere, one kind or a mixed gas of rare gas such as argon, helium, and xenon which is not reactive with aluminum is used, but argon is most preferable from the viewpoint of cost. It is also possible to use different rare gases at different times.
In other words, by efficiently using only gas such as argon and helium only in the region where the wax is melted, the amount of these gases used can be reduced, and improvement in brazing and cost can be achieved. The above gas can be used as a carrier gas.
Since there are many methods for obtaining the atmosphere, such as providing a partition plate in the furnace and optimizing the gas blowing method, the structure of the brazing furnace is not particularly defined here. In addition, a method of recovering the argon gas used for cost reduction and performing recirculation is also effective.

  In addition, although the regulation value of oxygen concentration differs in the 1st decompression atmosphere and the 2nd decompression atmosphere, the magnitude relationship of density | concentration itself is not specifically limited. However, the first reduced-pressure atmosphere is usually obtained by replacing the atmospheric atmosphere with a reduced-pressure atmosphere gas such as nitrogen gas, and the second reduced-pressure atmosphere is obtained by adjusting the atmosphere from the first reduced-pressure atmosphere. It is more efficient that the oxygen concentration in the first reduced pressure atmosphere is higher than the oxygen concentration in the second reduced pressure atmosphere.

In the present invention, the components of the brazing material and the aluminum alloy material are not limited to specific ones, but suitable compositions are exemplified below. All of the following components are shown in mass%.
The brazing material and the aluminum alloy material can be provided as a brazing sheet in which the brazing material is clad with the aluminum alloy material as a core material. In addition, a brazing material alone or an aluminum alloy material alone can be used as a brazing structural member in combination with the brazing sheet or the like.

  Further, in the cooling process after the brazing addition heat, it is desirable to regulate the oxygen concentration in the heating furnace until it reaches 400 ° C., specifically 50 ppm or less. Thereby, the growth of the surface oxide film when the wax solidifies can be suppressed, and the surface discoloration and the like can be suppressed.

(Brazing alloy component)
Mg: 0.1-3.0%
Mg in the brazing material reduces the dense oxide film (Al ₂ O ₃ ) generated on the surface of the material to form a fine particulate oxide, which improves the wettability and fluidity of the brazing and joins. The rate is improved. As a result, the metal / metal bonding area at the bonding interface is increased, and the bonding strength is improved. For these effects, a content of 0.1% or more is desirable. If the content is less than 0.1%, the reduction and decomposition action of the Al ₂ O ₃ oxide film becomes insufficient, and it becomes difficult to obtain a sufficient bonding state. On the other hand, if the content exceeds 3.0%, the strength of the brazing material increases and rolling becomes difficult. Further, the Mg oxide film becomes thick and easy to grow, and the brazing property is hindered. For these reasons, the Mg content is preferably within the above range. For the same reason, it is more desirable to set the lower limit to 0.25% and the upper limit to 2.0%.

Si: 5.0 to 13.0%
When Si is contained in the Al brazing material, it is an essential element for lowering its melting point and melting as a brazing material at a brazing temperature to form a predetermined joint. Further, the growth of a dense oxide film of aluminum is suppressed on the Si particles existing on the surface of the brazing filler metal, and a defective portion of the oxide film is generated. That is, even if the oxide film on the surface of the aluminum material becomes thick during brazing heat treatment, melting of the brazing filler metal begins to occur from the periphery of the Si particles, and the oxide film breaks up and breaks off starting from this site. Since the wettability of the wax is improved, a more stable joined state can be obtained. In order to obtain these effects, a content of 5.0% or more is desirable. If the content is less than 5.0%, the amount of liquid phase to be produced is insufficient, so that sufficient bonding cannot be obtained. On the other hand, if it exceeds 13.0%, the primary crystal Si rapidly increases, the workability as a raw material deteriorates, and the brazing erosion of the joint is remarkably promoted during brazing. For this reason, the above range is desirable for the Si content. For the same reason, it is more desirable to set the lower limit to 6.5% and the upper limit to 11.0%.

Be: 0.0001 to 0.1%
Be suppresses generation and growth of a reaction layer (oxide or nitride) mainly composed of Mg formed on the surface of the molten brazing, and is good even when the oxygen concentration and nitrogen concentration in the atmosphere at the time of brazing are high. Since joining becomes easy to obtain, it is contained as desired. In order to acquire the said effect | action, it is desirable to contain 0.0001% or more. If the content is less than 0.0001%, the effect is insufficient. On the other hand, even if the content exceeds 0.1%, the effect is saturated. For these reasons, the content of Be is preferably in the above range. For the same reason, it is more desirable to set the lower limit to 0.0002% and the upper limit to 0.01%.

Bi: 0.01 to 0.3%
Bi has a lower melting point due to coexistence with Mg, and exudation of wax occurs from a low temperature. Oxide film breaks up and breaks away from this site, improving the wettability of the molten wax and making it more stable. Since it becomes possible to obtain the joined state, it is contained if desired. In order to acquire the said effect | action, containing 0.01% or more is desirable, and an effect will become inadequate if it contains less than 0.01%. On the other hand, when it contains exceeding 0.3%, the rolling property of a brazing material will fall. For these reasons, the Bi content is preferably within the above range. For the same reason, it is more desirable to set the lower limit to 0.05% and the upper limit to 0.2%.

Ca: 0.002 to 0.3%
Ca is contained as desired because it reduces and decomposes the oxide film of Al and Mg formed on the surface of the brazing material and improves the wettability of the molten braze. In order to acquire this effect | action, it is desirable to contain 0.002% or more, and if it is less than 0.002%, the effect will be insufficient. On the other hand, if the content exceeds 0.3%, oxidation of the brazing filler metal surface is promoted and the joining rate is lowered. For these reasons, the Ca content is preferably within the above range. For the same reason, it is more desirable to set the lower limit to 0.005% and the upper limit to 0.2%.

(Aluminum alloy material component)
Mn: 0.2 to 2.5%
Mn crystallizes or precipitates as an intermetallic compound, and improves the strength after brazing. Further, since the potential of the core material is made noble and the corrosion resistance is improved, it is contained as desired. In order to acquire this effect | action, it is desirable to contain 0.2% or more. If it contains less than 0.2%, the said effect will become inadequate. On the other hand, when it contains exceeding 2.5%, a huge intermetallic compound will produce | generate at the time of casting, and castability and rolling property will be inhibited. For these reasons, the Mn content is desirably 0.2 to 2.5%. For the same reason, it is more desirable to set the lower limit to 1.0% and the upper limit to 1.7%.

Cu: 0.05 to 1.0%
Cu is dissolved in the material to improve the strength after brazing and to increase the corrosion resistance by making the potential of the core material noble, so it is contained as desired. In order to acquire this effect | action, it is desirable to contain 0.05% or more, and the said effect will become inadequate if it contains less than 0.05%. On the other hand, when it contains exceeding 1.0%, a crack will arise at the time of casting, or rolling property will fall. For these reasons, the Cu content is desirably 0.05 to 1.0%. For the same reason, it is more desirable to set the lower limit to 0.1% and the upper limit to 0.8%.

Si: 0.1 to 1.0%
Si alone dissolves in the matrix to improve the material strength. When Si is contained together with Mn, it is dispersed as an Al—Mn—Si compound and has the effect of improving the material strength. If Mg is present, Mg ₂ Si precipitates after the brazing heat treatment, and the material strength is dramatically improved by age hardening. In order to obtain these actions, it is desirable to contain 0.1% or more. If the content is less than 0.1%, the above effect is insufficient. On the other hand, when it contains exceeding 1.0%, since melting | fusing point falls, a core material will fuse | melt at the time of brazing. For these reasons, the Si content is desirably 0.1 to 1.0%. For the same reason, it is more desirable to set the lower limit to 0.4% and the upper limit to 0.8%.

Mg: 0.01 to 1.0%
Mg alone has the effect of solid solution strengthening, and if it is contained simultaneously with Si, it precipitates as a fine intermetallic compound Mg ₂ Si after brazing and has the effect of significantly improving the material strength by age hardening. Moreover, the same strength effect is exhibited with Si diffused from the brazing material during the brazing heat. Further, a part thereof diffuses into the brazing material and has an effect of promoting the destruction of the oxide film on the surface of the brazing material. It is desirable to contain 0.01% or more for the said effect | action, and if it contains less than 0.01%, the said effect will become inadequate. On the other hand, when it contains exceeding 1.0%, melting | fusing point will fall and a core material will fuse | melt at the time of brazing. For these reasons, the Mg content is set to 0.01 to 1.0%. For the same reason, it is more desirable to set the lower limit to 0.2% and the upper limit to 0.6%.

  As described above, according to the present invention, the oxygen concentration and the nitrogen concentration in the atmosphere during brazing are controlled, and the reduced pressure atmosphere gas is reduced to a reduced pressure state lower than the atmospheric pressure. It is possible to significantly reduce the amount used, and by reducing the pressure, the introduction of gas inside the heat exchanger and the adsorbed substances (residual oil, moisture, etc.) on the surface of the material are reduced, and brazing performance is dramatically improved. In addition, in conventional vacuum brazing in a high vacuum atmosphere, Zn in the material evaporates, so ensuring corrosion resistance due to the inclusion of Zn has been a problem. However, in the present invention, the object can be achieved with low vacuum, and brazing. It is possible to suppress evaporation of components such as Zn and maintain good corrosion resistance. In addition, since the structure of the brazing furnace can be simplified, the equipment cost of the furnace is reduced and the maintainability is improved, so that it is possible to improve productivity and improve the reliability of brazing.

It is a schematic diagram of the sample material in the Example of this invention.

Although the manufacturing method of the aluminum member used for this brazing is not specifically limited, It is desirable that the oxide film thickness of the material before brazing is as thin as possible. Although the oxide film grows slightly even during heat load during the manufacturing process, it is desirable to perform the heat treatment process at a low temperature and in a short time as much as possible. Also, it is effective to reduce the oxygen concentration in the atmosphere during heat treatment such as annealing.
Hereinafter, an embodiment of the present invention will be described.

Preferably, an Al—Si—Mg-based brazing material containing Si: 5.0 to 13.0%, Mg: 0.1 to 3.0%, the balance being Al and inevitable impurities, and an aluminum alloy member The core material can be manufactured by a conventional method, and both or another material such as a sacrificial material is overlapped with each other and hot-rolled and clad-rolled. The production conditions in the clad rolling are not particularly limited as the present invention. Further, the cladding ratio of each layer is not specified as the present invention.
In addition, as a core material, it is 1 type (s) or 2 or more types in Mn: 0.2-2.5%, Cu: 0.05-1.0%, Si: 0.1-1.0% in the mass%. In addition, if desired, Mg: 0.01 to 1.0% is contained, and the balance is composed of Al and inevitable impurities.

  The hot-rolled clad material can be further cold-rolled to a predetermined final thickness, and then subjected to heat treatment for structure control and tempering as desired.

(Content of heat treatment)
Intermediate annealing and final annealing for adjusting the physical properties of the material are usually carried out in a batch furnace or a continuous annealing furnace, but the heat treatment temperature is generally in the range of 100 to 420 ° C. The manufacturing method of the aluminum member used for the brazing is not particularly limited, but the oxide film grows even during the annealing, but the heat treatment process should be performed at a low temperature and in a short time as much as possible. Is desirable. However, in consideration of soaking of the material, it is desirable to give a certain holding time, and in the case of batch-type annealing, it is held at a predetermined temperature for 1 to 3 hours. Even if the atmosphere such as annealing is carried out in the air, the oxide film does not grow remarkably, but the oxygen concentration in the furnace is adjusted using DX gas (exothermic metamorphic gas), nitrogen gas, hydrogen gas, etc. It is also effective to reduce and suppress the growth of the oxide film.

  In the aluminum clad material obtained by a conventional method, the Al—Si—Mg-based brazing material is located on the outermost surface, and an oxide film having an initial oxide film thickness of 20 to 500 mm is formed. The aluminum clad material is assembled with a member to be brazed such as a bare fin or a solid material connector, and preferably constitutes a heat exchanger assembly or the like. Note that aluminum materials having various compositions can be used as the brazing target member, and the present invention is not limited to a specific one.

The assembly is disposed in a heating furnace, and the inside of the heating furnace is in a reduced pressure state at a temperature range from at least 450 ° C. to before melting of the solder when the temperature is raised. This reduced pressure state corresponds to the first reduced pressure atmosphere of the present invention, and the reduced pressure state is set using a rotary pump or the like. In the first reduced pressure atmosphere, it is desirable that the oxygen concentration is 50 ppm or less by volume and the pressure is 1 Pa or more and 10,000 Pa or less. The first reduced-pressure atmosphere can be formed using a rare gas or a mixed gas containing a rare gas as a carrier gas.
The reduced pressure state can be obtained by using only a rotary pump as described above without using a mechanical booster pump or the like.
Further, in the heating furnace, in the region where the temperature of the brazing material is melted, a second reduced pressure atmosphere is formed by using a carrier gas and a rare gas or a mixed gas containing a rare gas that is not reactive with the molten solder. In the second reduced pressure atmosphere, it is desirable to adjust the oxygen concentration to 25 ppm or less, the nitrogen concentration to 10% by volume or less, and the pressure to 0.01 Pa or more and 5,000 Pa or less. The reduced pressure state can be obtained by using only a rotary pump as described above without using a mechanical booster pump or the like.
It brazes by heating at 559-620 degreeC under the said atmosphere. In brazing, the contact and adhesion portion with the brazing target member is satisfactorily joined without flux.
Further, in the cooling process after the brazing heat, it is desirable that the oxygen concentration in the heating furnace be 50 ppm or less until reaching 400 ° C.

  In the above description, the brazing sheet and the aluminum alloy member are provided as a brazing sheet clad. can do.

  The core material (corresponding to the aluminum alloy member of the present invention, the balance being Al and unavoidable impurities) of the composition shown in Table 1, and the brazing material (the balance being Al and unavoidable impurities) similarly shown in Table 1 were bonded to the surface. An aluminum brazing sheet was prepared. The brazing material clad rate was set to 10%, and finished to an 0.25 mm-thickness O material having a tempering equivalent to H14. This brazing sheet 1 is combined with a corrugated fin 2 made of Al-1% Mn-1.5% Zn bare material having a thickness of 0.1 mm, and has a shape shown in FIG. 1 having a width (W) of 50 mm and a depth (D) of 25 mm. A brazing test was performed on the specimen. The corrugated fin 2 corresponds to the brazing object of the present invention.

At the time of brazing, a reduced pressure atmosphere with a rotary pump is used for heating and heating, and the oxygen concentration in the atmosphere until brazing is reduced with an inert gas such as nitrogen or argon. A mixed gas was used. The pressure, oxygen concentration, and nitrogen concentration in the atmosphere at each temperature range during brazing were measured, and the relationship with brazing properties was investigated. The pressure was measured by a broadband vacuum meter, the oxygen concentration was measured by a zirconia oxygen meter, and the nitrogen gas concentration was measured by gas chromatography.
Brazing property was determined by obtaining the bonding rate of fins by the following formula.
Fin joint rate = (total brazed joint length of fin and tube / total contact length of fin and tube) × 100

Moreover, the Zn residual rate on the fin material surface after brazing was calculated by the following formula using EPMA (electron beam analyzer).
Fin material surface Zn residual ratio = (surface Zn concentration after brazing) / (surface Zn concentration before brazing) × 100

1 Brazing sheet 2 Corrugated fin

Claims (13)

A brazing method for heating an aluminum alloy material including an Al-Si-Mg brazing material in a brazing furnace at a reduced pressure lower than atmospheric pressure,
Heating is performed in a first reduced-pressure atmosphere having an oxygen concentration equal to or lower than a first predetermined value at a temperature range of at least 450 ° C. before the wax melting at the time of temperature rise, and at least above the temperature at which the wax starts melting The Al—Si—Mg-based brazing material is heated without using a flux by heating in a second reduced pressure atmosphere having a nitrogen gas concentration equal to or lower than a second predetermined value lower than the first predetermined value. A method of brazing an aluminum material, comprising joining a brazing object containing the aluminum alloy material by the method described above.   The brazing sheet for an aluminum material according to claim 1, wherein the Al-Si-Mg-based brazing material and the aluminum alloy material are clad with the aluminum alloy material as a core material to constitute a brazing sheet. Method.   The first depressurized atmosphere has a first predetermined value of oxygen concentration of 50 ppm and a pressure of 1 Pa or more, and the second depressurized atmosphere has a second predetermined value of oxygen concentration of 25 ppm and the nitrogen gas concentration. The method for brazing an aluminum material according to claim 1 or 2, wherein the predetermined value is 10% by volume and the pressure is 0.01 Pa or more.   4. The aluminum material brazing method according to claim 3, wherein the first reduced pressure atmosphere has a pressure of 10,000 Pa or less, and the second reduced pressure atmosphere has a pressure of 5,000 Pa or less.   5. The oxygen concentration is maintained at 50 ppm or less in a temperature range until cooling to 400 ° C. in a cooling process after the step of heating at a temperature higher than the temperature at which the wax starts to melt. 5. Brazing method of aluminum material.   The method for brazing an aluminum material according to any one of claims 1 to 5, wherein the second reduced-pressure atmosphere is formed using a rare gas or a mixed gas containing a rare gas as a carrier gas.   The aluminum material brazing method according to claim 1, wherein the first reduced-pressure atmosphere is formed using a rare gas or a mixed gas containing a rare gas as a carrier gas.   The method for brazing an aluminum material according to claim 6 or 7, wherein the rare gas is argon.   The brazing material contains, by mass%, Si: 5.0 to 13.0% and Mg: 0.1 to 3.0%, and the balance is made of Al and inevitable impurities. The brazing method of the aluminum material in any one of -8.   The brazing material further contains at least one of Be: 0.0001 to 0.1%, Bi: 0.01 to 0.3%, and Ca: 0.002 to 0.3% by mass%. It contains, The brazing method of the aluminum material of Claim 9 characterized by the above-mentioned.   The aluminum alloy material contains at least one of Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, and Si: 0.1 to 1.0% by mass%. The aluminum material brazing method according to claim 1, wherein the aluminum material has a composition comprising Al and inevitable impurities.   The aluminum alloy material contains Mg: 0.01 to 1.0% by mass, Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0.00. The brazing of an aluminum material according to any one of claims 1 to 11, wherein the brazing material contains one or more of 1 to 1.0%, and the balance is composed of Al and inevitable impurities. Method.   A brazing structure in which a brazing object is joined by the brazing method according to claim 1.

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