JP5904853B2 - Fluxless brazing method for aluminum material and method for manufacturing brazed structure - Google Patents

Description

  The present invention relates to a fluxless brazing method of an aluminum material that can be brazed without using a flux in a non-oxidizing atmosphere, and a method of manufacturing 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.

  For example, in Patent Document 1, in order to enable brazing in the air and under a flux-free condition, in the case of performing brazing by inserting an aluminum thin laminated plate material in advance at the overlapping interface of a plurality of aluminum base materials. In addition, it is described that the aluminum thin laminated plate material has a five-layer or three-layer structure in which a skin material is formed on a brazing material to prevent oxidation of the brazing material. However, this method has a problem that the material cost increases because it is necessary to produce a clad material in which a film for preventing oxidation is separately formed on the brazing material. Further, the brazing material located in the second layer from the outermost surface melts and oozes out the outermost surface layer in the brazing process, so that the molten brazing is supplied to the joint surface. However, if variation occurs in the molten state of the outermost surface layer within the joint surface due to uneven pressurization or the like, there is a problem that an unjoined portion is formed within the joint surface.

  In order to solve the problem of the above fluxless brazing method, Patent Document 2 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. 3701847 Japanese Patent No. 4547032

  However, in the conventional fluxless brazing method described in Patent Document 2, it is necessary to add a considerable amount of Mg to the brazing material in order to obtain stable brazing properties. In addition, in terms of production of a material for clad the high-strength brazing material containing Mg to the core material, there is a problem that the productivity is slightly inferior to the case of producing a clad material for nolock rock brazing not containing Mg. . In addition, when using a clad material, there is a restriction on the clad rate of the brazing material due to requirements in production quality control, for example, it is difficult to supply a very small amount of brazing material with respect to the base material thickness. There is also a problem.

  On the other hand, a method in which only the brazing material portion is taken out and an Al—Mg—Si alloy brazing material sheet is used can be considered. However, in this method, both surfaces of the brazing filler metal sheet containing Mg become joint surfaces, and the contact adhesion portion is also exposed to the atmosphere strictly. For this reason, in the brazing heat treatment process, there is a problem that the MgO film, which is a bonding inhibiting factor, grows on both surfaces of the brazing material sheet, and as a result, the brazing quality is deteriorated.

  The present invention has been made against the background of the above circumstances, and a fluxless brazing method and brazing structure for an aluminum material capable of obtaining a stable joint state excellent in reliability without increasing the material cost. It aims at providing the manufacturing method of.

That is, in the fluxless brazing method of the aluminum material of the present invention, the first present invention includes an Mg-containing aluminum alloy member containing 0.15 to 1.0% Mg by mass%, and Si by mass%. A fluxless brazing method of an aluminum material using an Al-Si aluminum alloy brazing material sheet containing 5.0 to 13.0%,
The average film thickness of the oxide film on the surface before brazing of the Mg-containing aluminum alloy member and the aluminum alloy brazing material sheet is 15 nm or less, and the average of the magnesium oxide film in the oxide film of the Mg-containing aluminum alloy member The film thickness is 2 nm or less,
Contact adhesion between the Mg-containing aluminum alloy member, the aluminum alloy brazing material sheet, and the member to be brazed in a non-oxidizing atmosphere without pressure reduction or in a non-oxidizing atmosphere under a pressure range of atmospheric pressure to 0.1 Pa And the Mg-containing aluminum alloy member and the brazing target member are joined by brazing at the contact close contact portion.

The fluxless brazing method for aluminum material according to the second aspect of the present invention is the method according to the first aspect of the present invention, wherein the number of Si particles having an equivalent circle diameter of 0.25 μm or more is 20 per 1 mm ^{2 on} the surface of the aluminum alloy brazing material sheet. It is characterized by the presence of 000 or more.

  A 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 Mg-containing aluminum alloy member is in% by mass, and Mn: 0.2 to 2.5%. Cu: 0.05-1.0%, Si: 0.1-1.0% of 1 type or 2 types or more are contained.

  A fluxless brazing method for an aluminum material according to a fourth aspect of the present invention is characterized in that, in any of the first to third aspects of the present invention, the brazing target member is an Al material to which no Mg is added. And

  The fluxless brazing method for an aluminum material according to a fifth aspect of the present invention is characterized in that, in any of the fourth aspects of the present invention, the brazing object member is pure aluminum having an aluminum purity of 99.9% or more. And

  The fluxless brazing method for an aluminum material according to the sixth aspect of the present invention is the method according to any one of the fourth aspects of the present invention, wherein the brazing target member is in mass%, Mn: 0.2 to 2.5%, Cu : 0.05-1.0%, Si: 0.1-1.0% of 1 type or 2 types or more are contained, and the remainder has the composition which consists of Al and an unavoidable impurity.

  A fluxless brazing method for an aluminum material according to a seventh aspect of the present invention is the Mg constituting the brazed structure by the fluxless brazing method for an aluminum material according to any one of the first to sixth aspects of the present invention. The containing aluminum alloy member and the brazing target member are joined.

  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. Aluminum alloy brazing material sheet In the present invention, an Al-Si based aluminum alloy brazing material sheet is used.

Si: 5.0 to 13.0%
Si, when contained in Al, is a basic element that lowers its melting point and melts 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.
In order to obtain these functions, the Si content needs to be 5.0% or more. If the Si content is less than 5.0%, the amount of liquid phase produced is insufficient and 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 these reasons, the Si content is set to 5.0 to 13.0%. For the same reason, it is desirable that the lower limit of the Si content is 6.5% and the upper limit is 11.0%.

The aluminum alloy brazing material sheet may be composed of the above-mentioned Si as a basic component, with the balance being Al and inevitable impurities. Moreover, you may contain another component in the range which does not impair the said effect | action. The Al—Si-based aluminum alloy brazing material sheet is not added with Mg. Those not containing Mg are substantially free of Mg. In addition to those not containing Mg, those containing 0.01% or less of Mg as an impurity are allowed.
By substantially not containing Mg, it is possible to prevent the formation of a magnesium oxide film on the brazing filler metal surface at the bonding interface, preventing the bonding inhibition by the magnesium oxide film, and providing a stable bonding state with excellent reliability. Can be obtained.

2. Distribution of Si particles on the surface of the aluminum alloy brazing material sheet In the surface layer portion of the aluminum alloy brazing material sheet, it is preferable that 20,000 or more Si particles having an equivalent circle diameter of 0.25 μm or more exist per 1 mm ² .
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 sheet is too small, the effect of causing a defective portion in the oxide film becomes insufficient. For this reason, it is preferable that the equivalent-circle diameter of Si particle | grains is 0.25 micrometer 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, it is preferable that the distribution density of Si particles is 20,000 or more per 1 mm ² .

3. Mg-containing aluminum alloy member In the present invention, an Mg-containing aluminum alloy member containing Mg is used as one of the members to be brazed.
The Mg-containing aluminum alloy member is brought into contact with the aluminum alloy brazing sheet at the joint, thereby suppressing the formation of a magnesium oxide film in the brazing process at the joint interface, and Mg added to the Mg-containing aluminum alloy member A good brazed joint can be obtained by the action of decomposing the oxide film.

Mg: 0.15-1.0%
Mg has an effect of promoting the destruction of the oxide film by reducing and embrittlement the dense oxide film (Al ₂ O ₃ film) generated on the material surface. In the end, it comes into contact with the molten solder and the entire oxide film is destroyed by the flow of the wax. Moreover, Mg also embrittles the oxide film on the surface of the aluminum alloy brazing material sheet that is in contact and in close contact with the part where the oxide film of the Mg-containing aluminum alloy member itself has been destroyed. Further, a part of Mg is diffused in the molten brazing material and has an effect of embrittlement of the oxide film on the surface of the brazing target member.
Further, Mg alone has a solid solution strengthening effect, and when added at the same time as Si, it precipitates as a fine intermetallic compound Mg ₂ Si after brazing and has an 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 effect of improving the strength. In order to obtain these effects sufficiently, it is necessary to contain 0.15% or more. If it is less than 0.15%, the reduction and embrittlement action of the oxide film becomes insufficient, and a sufficient bonding state cannot be obtained. On the other hand, if it exceeds 1.0%, the melting point is lowered and it is susceptible to wax erosion, which causes problems in the dimensional accuracy, structural strength, corrosion resistance, etc. of the brazed structure, and the magnesium oxide film tends to grow thick. As a result, brazability is inhibited. For this reason, content of Mg shall be 0.15-1.0%. For the same reason, it is desirable that the lower limit of the Mg content is 0.2% and the upper limit is 0.6%.

  The Mg-containing aluminum alloy member may contain the above Mg, and the balance may be made of Al and inevitable impurities, but may contain other components as long as the upper action is not impaired. Hereinafter, other components that the Mg-containing aluminum alloy member may contain will be described.

Mn: 0.2 to 2.5%
Mn crystallizes or precipitates as an intermetallic compound, and improves the strength after brazing. Further, the potential of the Mg-containing aluminum alloy member is made noble to improve the corrosion resistance. If the amount is less than the lower limit, these effects are insufficient. If the upper limit is exceeded, a giant intermetallic compound is produced during casting, which makes rolling difficult. For this reason, the said range can be selected as content of Mn. For the same reason, the lower limit of the Mn content is more preferably 1.0, and the upper limit is more preferably 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 Mg-containing aluminum alloy member potential noble. If it is less than the lower limit, these effects are insufficient, and if it exceeds the upper limit, cracking occurs during casting or the rollability is lowered. For this reason, the said range can be selected as content of Cu. For the same reason, the lower limit of the Cu content is more preferably 0.1%, and the upper limit is more preferably 0.7%.

Si: 0.1 to 1.0%
Si alone dissolves in the matrix to improve the material strength, and also improves the material strength 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. Moreover, it has an effect of improving the material strength by dispersing as an Al—Mn—Si compound contained simultaneously with Mn. Below the lower limit, these effects are insufficient. When the upper limit is exceeded, the melting point is lowered, and the core material melts during brazing. For this reason, the said range can be selected for content of Si. 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%.

4). In the present invention, the average film thickness of the oxide film on the surface before brazing of the Mg-containing aluminum alloy member and the aluminum alloy brazing material sheet is 15 nm. It is as follows.
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 making the average film thickness of the oxide film on the pre-brazing surface of the Mg-containing aluminum alloy member and the aluminum alloy brazing material sheet both 15 nm or less, the bonding rate is improved, and further the bonding strength and durability are improved. Can be obtained.
In addition, although a joining state improves, so that an oxide film is thin, at the same time, the thin film of an oxide film also contributes to a cost increase. For this reason, the lower limit of the average thickness of the oxide film is not particularly limited, but it is preferable to select it appropriately within a range of 15 nm or less.
On the other hand, if the average film thickness of the oxide film exceeds 15 nm, the destruction of the oxide film becomes insufficient at the time of brazing, and as a result, the bonding strength and durability are remarkably reduced, and the bonding rate is also reduced.

5. In the present invention, the average film thickness of the magnesium oxide film in the oxide film of the Mg-containing aluminum alloy member is 2 nm or less.

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, an aluminum alloy material to which Mg is added tends to form a magnesium oxide film 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 Mg-added aluminum alloy member before brazing is set to 15 nm 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 15 nm or less, it is possible to obtain an effect of improving the bonding rate and further 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 thickness of the oxide film is not particularly limited, but it is desirable to select the average thickness within the range of 15 nm or less depending on the application site.
On the other hand, if the average film thickness of the oxide film exceeds 15 nm, the destruction of the oxide film becomes insufficient at the time of 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 2 nm or less. As described above, the magnesium oxide film is very stable and has difficulty in breaking during the brazing heat treatment. Therefore, when the average film thickness exceeds 2 nm, the brazing bonding is hindered, the bonding rate is reduced, and the coarse void is formed. This causes a significant decrease in bonding strength and durability. For this reason, since it is necessary to suppress an initial production | generation as much as possible for a magnesium oxide film, the average film thickness before brazing shall be 2 nm 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. At the same time, the reduction in the thickness of the magnesium oxide film also contributes to the cost increase. When the Mg content of the Mg-added aluminum alloy member is reduced, the magnesium oxide film is hardly 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 manufacturing process should be appropriately selected according to the application site, and should be selected within a range of 2 nm or less. Is desirable.

6). Brazing object member For the other brazing object member to be joined to the Mg-containing aluminum alloy member by brazing, an Al material to which no Mg is added can be preferably used.
Those not containing Mg are substantially free of Mg, and in addition to those not containing Mg, those containing 0.01% or less of Mg as an impurity are allowed.
Even when a brazing target member that does not contain Mg is used, as described above, Mg diffuses from one Mg-containing aluminum alloy member into the molten brazing material during the brazing heat treatment process. The decomposition | disassembly effect | action of a film | membrane can be obtained and the stable brazing state excellent in reliability can be obtained.
Examples of the brazing target member not containing Mg include pure aluminum having an aluminum purity of 99.9% or more, Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0 0.1-1.0% of 1 type or 2 types or more are contained, and the balance can be exemplified by Al and inevitable impurities. In addition, the effect | action and content of each component in the latter 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%
In addition to improving the strength of the material, Si is dissolved in the matrix by itself, and in the present invention, Mg and Mg ₂ Si precipitates diffused from the other member through the liquid phase brazing during brazing are formed. Improve strength. 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%.

7). 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 2 to 50 nm, which is usually produced as a mass production coil material of aluminum, can be used for the brazing target member. In order to make the initial oxide film thickness less than 2 nm, acid cleaning or the like as shown in the prior art is required. Even if the initial oxide film thickness exceeds 50 nm, bonding is possible with the material of the present invention, but it is difficult to obtain a good bonding state, so it is desirable to make the initial oxide film as thin as possible. However, this is a case where the brazing target member is an Mg-free alloy, and when the Mg-added alloy is used, it is desirable to control the magnesium oxide film as described above.

8). 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 or a mixed gas thereof, thereby reducing the oxygen concentration and dew point in the atmosphere. It is necessary to suppress reoxidation of the material sheet and the brazing target member. The type of atmospheric gas to be used is not particularly limited, but it is economically preferable to use nitrogen, argon as the inert gas, and hydrogen, ammonia, or carbon monoxide as the reducing gas.
Further, the oxygen concentration in the non-oxidizing atmosphere as described above is preferably 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. . A more preferable oxygen concentration is 20 ppm or less by volume ratio.

9. Manufacturing method of aluminum alloy member and brazing material sheet The manufacturing method of the aluminum alloy member and brazing material sheet used in the present invention is not limited to a specific method. However, when the Mg-containing aluminum alloy 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 Mg-added aluminum alloy 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 If soaking treatment for heating the Mg-added aluminum alloy before hot rolling 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.
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. .

Intermediate annealing, final annealing Intermediate annealing performed at the time of cold rolling after hot 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 the oxygen concentration in the atmosphere. It is desirable to implement. 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 the substantial temperature of material 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.

The brazing according to the present invention can be carried out in a non-oxidizing atmosphere at atmospheric pressure, and further under a low vacuum. If performed in a low-vacuum non-oxidizing atmosphere that can be obtained with simple vacuum equipment, the oxygen concentration in the atmosphere will decrease. A more stable joined state can be obtained. That is, the brazing of the present invention can be performed under a pressure range from atmospheric pressure to 0.1 Pa.
Under a high vacuum at a pressure of less than 0.1 Pa, Mg evaporates, and evaporated Mg tends to accumulate on the closed joint surface, so that coarse voids are likely to be formed at the joint interface. For this reason, a joining rate falls under high vacuum. Moreover, in order to obtain a high vacuum, the installation and maintenance cost of equipment increases.

  As described above, according to the fluxless brazing method of the present invention, the Mg-containing aluminum alloy member containing 0.15 to 1.0% Mg by mass% and 5.0 to 13. A fluxless brazing method of an aluminum material using an Al-Si-based aluminum alloy brazing material sheet containing 0%, wherein the Mg-containing aluminum alloy member and the oxide film on the surface before brazing of the aluminum alloy brazing material sheet The average film thickness is 15 nm or less, and the average film thickness of the magnesium oxide film in the oxide film of the Mg-containing aluminum alloy member is 2 nm or less, and is 0 in a non-oxidizing atmosphere or no atmospheric pressure without decompression. In the non-oxidizing atmosphere under a pressure range of 1 Pa, the Mg-containing aluminum alloy member, the aluminum alloy brazing material sheet, and the object to be brazed Since the Mg-containing aluminum alloy member and the brazing target member are joined by brazing at the contact and adhesion portion, a stable joining state excellent in reliability is achieved without increasing the material cost. Can be obtained.

It is the schematic which shows the state before brazing in one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described.
An Mg-containing aluminum alloy member containing 0.15 to 1.0% Mg by mass is a target for brazing. For the Mg-containing aluminum alloy member, it is preferable that the balance is Al and inevitable impurities, and if desired, in mass%, Mn: 0.2 to 2.5%, Cu: 0.05 to 1 Those containing one or more of 0.0% and Si: 0.1 to 1.0% can be used. The brazing target member to be the counterpart material is not limited to a specific composition, but is preferably not added with Mg, for example, pure aluminum having an aluminum purity of 99.9% or more, mass %, Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0.1 to 1.0% of one or more, and the balance is Al And those having a composition comprising inevitable impurities can be used.

The production method of the Mg-containing aluminum alloy member and the brazing target member is not particularly limited, and any of them can be produced by a conventional method. In manufacturing the Mg-containing aluminum alloy member, various conditions for heat treatment such as homogenization treatment, soaking treatment, and annealing are appropriately set. Thereby, the average film thickness of the oxide film on the surface of the Mg-containing aluminum alloy member before brazing is controlled to 15 nm or less, and the average film thickness of the magnesium oxide film in the oxide film is controlled to 2 nm or less. For the brazing target member, the average film thickness of the oxide film may be similarly controlled.
Specifically, in the thermal history in the manufacturing process, the homogenization is not performed or the homogenization is performed at a temperature of 500 ° C. or lower in order to set conditions for suppressing the growth of the oxide film. In addition, when soaking is performed before hot rolling, the holding time at 500 ° C. or higher is set to be within 1 hour. In addition, intermediate annealing and final annealing in cold rolling can be 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 can be cooled to 200 ° C. or less in the same atmosphere.

  Moreover, as an aluminum alloy brazing material sheet, what contains 5.0 to 13.0% of Si by mass% and the balance is made of Al and inevitable impurities is used. The aluminum alloy brazing material sheet may not contain Mg.

The above-mentioned aluminum alloy brazing material sheet can also be produced by a conventional method, but in the production thereof, by appropriately setting various conditions of heat treatment such as homogenization treatment, soaking treatment, annealing, etc. The average film thickness of the oxide film on the surface before brazing is controlled to 15 nm or less.
Specifically, in the thermal history in the manufacturing process, the homogenization is not performed or the homogenization is performed at a temperature of 500 ° C. or lower in order to set conditions for suppressing the growth of the oxide film. In addition, when soaking is performed before hot rolling, the holding time at 500 ° C. or higher is set to be within 1 hour. In addition, intermediate annealing and final annealing in cold rolling can be 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 can be cooled to 200 ° C. or less in the same atmosphere.

Moreover, in the aluminum alloy brazing material sheet, the distribution of Si particles can be controlled by the solidification rate at the time of casting, the temperature and time of the homogenization treatment, the maximum rolling rate at the time of hot rolling, and the like.
By controlling these conditions in a complex manner, the distribution of Si particles in the surface layer of the aluminum alloy brazing material sheet (size, the ratio of the number of coarse particles) is adjusted, so that the Si particles having an equivalent circle diameter of 0.25 μm or more are 1 mm. it can be those present over 20,000 per ^2.

  As shown in FIG. 1, the above-mentioned members are assembled so that the aluminum alloy brazing material sheet 3 is sandwiched between the Mg-containing aluminum alloy member 1 and the brazing target member 2 and brought into close contact with each other. Make up the body.

The assembly is disposed in a heating furnace having a non-oxidizing atmosphere. 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 may be at atmospheric pressure without reducing pressure during brazing addition heat, or may be reduced to 0.1 Pa.
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 brazing material carry-in port and a carry-out port. Even in such a heating furnace, a non-oxidizing atmosphere is maintained by blowing an inert gas into the furnace. The non-oxidizing atmosphere preferably has an oxygen concentration of 50 ppm or less by volume. It brazes by heating above 590 degreeC under the said atmosphere. During the brazing, a uniform pressure of about 10 to 1000 gf / cm ² is applied to the assembly in a direction in which the aluminum alloy brazing material sheet 3 is sandwiched between the Mg-containing aluminum alloy member 1 and the brazing target member 2. It is preferable to keep it.
In brazing, the Mg-containing aluminum alloy member 1 and the brazing target member 2 are satisfactorily joined without flux via the contact adhesion portion 4. Thus, a brazed structure in which the Mg-containing aluminum alloy member 1 and the brazing target member 2 are joined is obtained.

  In the present embodiment, an aluminum alloy brazing material sheet that can supply an appropriate amount of brazing material only to the joint and its vicinity as required is used, and a magnesium oxide film that is a factor for inhibiting joining in the brazing process is used. Generation can be minimized.

Aluminum alloy brazing material sheets and Mg-containing aluminum alloy members shown in Tables 2 and 3 were prepared.
The brazing alloy was produced by a semi-continuous casting method, but 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.
Both the Mg-containing aluminum alloy member and the brazing target member, which are brazing target members, were finished to a thickness of 2 mm with a tempering equivalent to H14. Table 1 shows the heat treatment conditions used when producing each material.

(Brazing test)
Brazing structure in which Mg-containing aluminum alloy member is cut into 50 mm square, aluminum alloy brazing material sheet and brazing object member are cut into 30 mm square, and the aluminum alloy brazing material sheet is sandwiched between Mg-containing aluminum alloy member and brazing object member The body. At the time of brazing, a brazing heat treatment was performed by applying a uniform pressure of 30 gf / cm ² to the brazed structure and heating it to a predetermined temperature in a nitrogen gas atmosphere (pressure: atmospheric pressure to 0.1 Pa).

(Surface bonding rate)
The joining surface of the produced sample was scanned with an ultrasonic imaging device, and the surface joining rate was determined. In the ultrasonic measurement, the void portion can be detected. The void area ratio with respect to the entire area to be bonded is obtained, and the surface bonding ratio is calculated. In addition, the surface bonding rate of 95% or more was evaluated as ◎, 85% or more and less than 95% as ○, 75% or more and less than 85% as Δ, and less than 75% as ×.

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

(Average film thickness of the initial oxide film and magnesium oxide film)
About the average film thickness of the oxide film on the surface before brazing of the Mg-containing aluminum alloy member and the aluminum alloy brazing material sheet, the film thickness of the oxide film can be arbitrarily set by TEM (transmission electron microscope) for each sample before brazing. Observation was made at five locations, and the average film thickness of the oxide film was determined. Regarding the average film thickness of the magnesium oxide film in the oxide film of the Mg-containing aluminum alloy member, the elements in the depth direction by XPS (X-ray photomolecular spectroscopy) are used for three arbitrary portions on the surface of each sample before brazing. Distribution was measured. 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. The measurement results of each average film thickness are shown in Table 2 and Table 3.

(Joint strength)
Each produced sample was processed into a cylindrical shape of φ10 mm × thickness 4 mm, fixed to a jig with an adhesive, a tensile test was performed, the fracture strength at the laminated joint interface was measured, and the joint strength was determined. In addition, evaluation was made by judging that the bonding strength (breaking strength) was 80 MPa or more and that the bonding strength (breaking strength) was less than 80 MPa.

DESCRIPTION OF SYMBOLS 1 Mg containing aluminum alloy member 2 Brazing object member 3 Aluminum alloy brazing material sheet 4 Contact adhesion part

Claims (7)

Aluminum using Mg-containing aluminum alloy member containing 0.15 to 1.0% Mg by mass and Al-Si aluminum alloy brazing material sheet containing 5.0 to 13.0% Si by mass A fluxless brazing method for a material,
The average film thickness of the oxide film on the surface before brazing of the Mg-containing aluminum alloy member and the aluminum alloy brazing material sheet is 15 nm or less, and the average of the magnesium oxide film in the oxide film of the Mg-containing aluminum alloy member The film thickness is 2 nm or less,
Contact adhesion between the Mg-containing aluminum alloy member, the aluminum alloy brazing material sheet, and the member to be brazed in a non-oxidizing atmosphere without pressure reduction or in a non-oxidizing atmosphere under a pressure range of atmospheric pressure to 0.1 Pa A fluxless brazing method for an aluminum material, wherein the Mg-containing aluminum alloy member and the brazing target member are joined by brazing at the contact and adhesion portion. ^2. The fluxless brazing method for an aluminum material according to claim 1, wherein 20,000 or more Si particles having an equivalent circle diameter of 0.25 μm or more are present per 1 mm ^{2 on} the surface of the aluminum alloy brazing material sheet. .   The Mg-containing aluminum alloy member is in% by mass, and one of Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0.1 to 1.0% or The fluxless brazing method for an aluminum material according to claim 1 or 2, comprising two or more kinds.   The fluxless brazing method for an aluminum material according to any one of claims 1 to 3, wherein the brazing target member is an Al material to which Mg is not added.   5. The fluxless brazing method for an aluminum material according to claim 4, wherein the brazing target member is pure aluminum having an aluminum purity of 99.9% or more.   The brazing target member is one or two of mass%, Mn: 0.2 to 2.5%, Cu: 0.05 to 1.0%, Si: 0.1 to 1.0%. The fluxless brazing method for an aluminum material according to claim 4, wherein the aluminum material has a composition comprising Al and inevitable impurities.   The aluminum-containing flux alloy brazing method according to any one of claims 1 to 6, wherein the Mg-containing aluminum alloy member constituting the brazing structure and the brazing target member are joined together. Manufacturing method of attached structure.

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