JP7311337B2 - Brazing wire for flux-free brazing and flux-free brazing method - Google Patents

Description

The present invention relates to a brazing wire for flux-free brazing and a flux-free brazing method for performing flux-free brazing.

In flux-free brazing using Al-Si-Mg brazing filler metal in a non-oxidizing gas atmosphere without reduced pressure, Mg in the brazing filler metal activated by melting forms an Al oxide film (Al ₂ O ₃ ) is reductively decomposed to enable bonding. In closed face joints, etc., joints that combine brazing sheets with brazing material due to the decomposition of oxide films by Mg, and joints that combine brazing sheets and members to be joined (bare materials) that do not have brazing material. A good bonding state can be obtained.
However, in a joint shape that has an open portion that is easily affected by the atmosphere, an MgO film tends to grow on the surface of the Mg-added brazing filler metal, but the MgO film is a stable oxide film that is difficult to decompose, which significantly hinders joining. be. For this reason, a flux-free brazing method that can obtain a stable joint state in a joint having an open portion is desired.
Furthermore, in heat exchangers for automobiles, aluminum members of various shapes are joined, but if the clearance between the members of the joint is wide, there is a problem that it is difficult to obtain a sufficient joint state with only the amount of brazing material supplied from the brazing sheet. . For this reason, when joining wide-clearance joints by flux-free brazing, it is sometimes important to use a brazing wire that compensates for the shortage of brazing material and realizes a good joining state.

In order to suppress the growth of the MgO film on the surface of the brazing filler metal, in order to solve the above problems, the surface layer is made of a Mg-free alloy and the core part is made of a brazing filler metal alloy with Mg added to improve the bonding state. A brazing wire for free brazing has been proposed (see Patent Document 1).

JP 2012-96264 A

However, in the method of Patent Document 1, the solidus temperature of the surface layer is about the same as that of the core material alloy (generally the solidus temperature is 600 ° C. or higher) of the brazing sheet that is the structural member of the heat exchanger. Because of this high temperature, in normal brazing performed at a reaching temperature of about 600° C., there is a problem that the melting of the surface layer portion does not proceed sufficiently and the flow of the core portion brazing material is hindered. In the brazing temperature rising process, Si diffuses from the core to the surface layer, and the solidus temperature of the surface layer decreases. , it is difficult for the melted core brazing material to flow out, and a stable fillet is difficult to form.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a brazing wire for flux-free brazing and a flux-free brazing method that can obtain good flux-free brazeability.

That is, among the brazing wire for flux-free brazing of the present invention, the first embodiment is a brazing wire for flux-free brazing in which a surface layer portion is laminated on a core portion and is used for flux-free brazing of aluminum members. is a wire,
The core portion is made of an Al-Si-Mg alloy containing 4 to 13% by mass of Si and 0.1 to 5.0% by mass of Mg, and the surface layer portion is composed of 2 to 13% by mass of Si. Consists of an Al-Si alloy containing
Si particles contained in the core portion have less than 3,000 Si particles having an equivalent circle diameter of 0.25 μm or more per 10000 μm ² in cross-sectional observation , and the Si particles contained in the surface layer portion are on the surface layer surface In observation of the direction, the ratio of the number of objects having a diameter of 1.75 μm or more in the number of objects having an equivalent circle diameter of 0.8 μm or more is 10% or more,
The thickness of the surface layer portion is 30 μm or more,
The liquidus temperature difference between the Al—Si—Mg-based alloy in the core portion and the Al—Si-based alloy in the surface layer portion is the liquidus temperature of the Al—Si-based alloy in the surface layer portion−Al in the core portion. The liquidus temperature of the -Si-Mg alloy is -60°C to 71°C .

Another aspect of the invention of a brazing wire for flux-free brazing is a brazing wire for flux-free brazing in which a surface layer is laminated on a core and used for flux-free brazing of an aluminum member,
The core part is made of an Al-Si-Mg alloy containing 1% or more and less than 4% by mass of Si and 0.1 to 5.0% of Mg, and the surface layer part is 2 to 13% by mass. Made of an Al-Si alloy containing Si,
The core portion contains less than 3,000 Si particles with an equivalent circle diameter of 0.25 μm or more per 10000 μm ² when observed in a cross section, and the Si particles contained in the surface layer portion are on the surface. When observed in the layer surface direction, the ratio of the number of particles having an equivalent circle diameter of 0.8 μm or more to the number of particles having a diameter of 1.75 μm or more is 10% or more,
The surface layer portion has a thickness of 30 μm or more,
A liquidus temperature difference between the Al—Si—Mg alloy in the core portion and the Al—Si alloy in the surface layer portion is 60° C. or less.

Another embodiment of the invention of a brazing wire for flux-free brazing is the invention of the above embodiment, wherein the Al-Si-Mg-based alloy in the surface layer portion further contains 0.1 to 1.0% Fe by mass%. It is characterized by containing

Another embodiment of the invention of a brazing wire for flux-free brazing is characterized in that, in the invention of the above embodiment, the surface layer portion has a thickness of 30 μm or more.

Another form of the invention of a brazing wire for flux-free brazing is the invention of the above form, in which the Al-Si-Mg alloy of the core portion further contains 0.01 to 0.5% by mass of Bi It is characterized by containing

Another form of the invention of a brazing wire for flux-free brazing is the invention of the above form, wherein the Al—Si alloy of the surface layer portion further contains 0.01 to 0.1% by mass of Bi. characterized by

Among the flux-free brazing methods of the present invention, the first embodiment uses the brazing wire for flux-free brazing according to any one of the above embodiments, in a non-oxidizing gas atmosphere having an oxygen concentration of 100 ppm or less. It is characterized in that the aluminum members are joined together without using the method.

The effects and reasons for limitation of the component compositions defined in the present invention will be described below. In addition, in the following description, the component composition is shown in mass %.
(Core part composition)
Si: 4-13%
Si forms a liquid phase in the core during brazing and promotes diffusion of Mg added to the core to the surface layer. If the Si content is insufficient, the effect will be insufficient, and if the Si content is excessive, the material will be hard and brittle, and breakage will easily occur during wire processing or wire bending, making production difficult.
From these points, it is desirable to set the Si content to 4 to 13%.
For the same reason, it is more desirable to set the lower limit of the Si content to 5% and the upper limit to 11%.
Si: less than 1 to 4% As described above, Si forms a liquid phase in the core portion during brazing and promotes diffusion of Mg added to the core portion to the surface layer portion. By the way, if the clearance of the joint to be joined is particularly large, such as exceeding 600 μm, for example, if the amount of Si added to the core is reduced, the liquid phase ratio during brazing will decrease and the core will remain undissolved, so there is an effect of filling the clearance. . If the Si content is insufficient, the effect of diffusing Mg will be insufficient, and if the Si content is excessive, the proportion of the core portion remaining undissolved will decrease and the effect of filling the clearance will be insufficient. However, when the Si content is reduced to less than 4%, the amount of Mg diffused into the surface layer during brazing tends to be lower than in the case of 4 to 13% Si. It is desirable to make it 5% or more. Furthermore, for the same reason, it is more desirable to set the Mg content to 0.8% or more.
From these points of view, it is desirable to set the Si content to less than 1 to 4%. For the same reason, it is more desirable to set the lower limit of the Si content to 1.5% and the upper limit to 3%.

Mg: 0.1-5.0%
Mg reductively decomposes the Al oxide film (Al ₂ O ₃ ). However, if the Mg content is insufficient, the effect is insufficient, and if the Mg content is excessive, the effect saturates and the material becomes hard and brittle, making wire production difficult. For these reasons, the Mg content should be 0.1 to 5.0%. For the same reason, it is desirable to set the lower limit to 0.3% and the upper limit to 3.0%, and more preferably set the lower limit to 0.8% and the upper limit to 2.5%.

Bi: 0.01-0.5%
Bi lowers the surface tension of the molten brazing filler metal and improves gap-filling properties, so it is optionally contained. If the Bi content is insufficient, the effect is insufficient, and if the Bi content is excessive, the effect is saturated. For these reasons, the Bi content is preferably 0.01 to 0.5%. For the same reason, it is desirable to set the lower limit to 0.02% and the upper limit to 0.2%.

(Surface layer composition)
Si: 2-13%
In the surface layer, molten solder is formed from Si during brazing to form a fillet of the joint. Insufficient Si content results in insufficient molten braze to form fillets. Moreover, diffusion of Mg from the core portion is delayed, and sufficient bonding cannot be obtained. On the other hand, if the Si content becomes excessive, the effect is saturated. Moreover, since the material becomes hard and brittle, it becomes difficult to manufacture the material.
For these reasons, the Si content in the surface brazing filler metal is set to 2 to 13%. For the same reason, it is more desirable to set the lower limit of the Si content to 3% and the upper limit to 11%.

Bi: 0.01-0.1%
Bi concentrates on the surface of the material during the process of raising the brazing temperature, suppresses the growth of a dense oxide film, lowers the surface tension of the molten brazing filler metal, and improves the gap-filling properties, so it is contained as desired. If the Bi content is insufficient, the effect is insufficient, and if the Bi content is excessive, the effect saturates. Furthermore, in the surface layer where Mg is not added, if Bi is added excessively, Bi concentrates on the material surface during heat treatment during material production, making the oxide film brittle, and the oxide film that inhibits bonding tends to grow during storage. I don't like it. For these reasons, it is desirable to set the Bi content to 0.01 to 0.1%. For the same reason, it is more desirable to set the lower limit of Bi to 0.02% and the upper limit to 0.07%.

Fe: 0.1-1.0%
Fe hardly dissolves in Al, and exists as a single substance or an intermetallic compound with Al, Mn, Si, or the like in the surface layer. Since these particles present on the surface of the material become defects in the oxide film, they suppress the growth of the oxide film that inhibits bonding, and are oxidized when Mg diffused from the core decomposes Al ₂ O ₃ . It has the effect of making the film easier to destroy. If it is less than 0.1%, the effect is insufficient, and if it exceeds 1.0%, the effect saturates. %.

(Surface layer thickness)
Mg added to the core part diffuses to the surface layer in the brazing temperature rising process, but if Mg reaches the surface of the material at an early stage below the brazing melting temperature, it reacts with oxygen in the atmosphere and easily grows a MgO film. Therefore, the growth of the MgO film is suppressed by setting the thickness of the surface layer to a certain value or more. For this reason, the thickness of the surface layer is preferably 30 μm or more.

(Surface portion Si particles)
In carrying out the present invention, it is preferable that relatively coarse Si particles are present on the surface of the surface brazing material. Normally, a dense oxide film such as Al ₂ O ₃ exists on the surface of an aluminum material, and this film grows further during the brazing heat treatment process to form a thick film. It is a general opinion that the greater the thickness of the oxide film, the stronger the tendency to inhibit the destructive action of the oxide film. In the present invention, since coarse Si particles are present on the surface of the brazing filler metal in the surface layer, a dense oxide film of aluminum does not grow on the surface of the coarse Si particles, and this portion acts as an oxide film defect on the surface of the aluminum material. In other words, even if the oxide film on the surface of the aluminum material becomes thick during the brazing heat treatment, the brazing filler material will seep out from the Si particle portion, and the oxide film breaking action will proceed starting from this portion. Conceivable. The Si particles referred to here include Si particles composed of a single component of Si in terms of composition, and also include, for example, Fe—Si compounds and Al—Fe—Si based intermetallic compounds containing Fe—Si as a main component. shall be taken. In the description of the present invention, these are referred to as Si particles for convenience. Specifically, when Si particles on the surface of the brazing filler metal are regarded as equivalent circle diameters and the number of Si particles of 0.8 μm or more is counted, if the proportion of Si particles of 1.75 μm or more is 10% or more, this effect is sufficiently obtained. Although the density of Si particles is not mentioned in the present invention, it is believed that the number of Si particles of 0.8 μm or more in a 10000 μm ² field of view ranges from several tens to several thousands, depending on the range of alloy composition and manufacturing conditions. , Since it is difficult to define it, in the present invention, it is confirmed that if the ratio of the number of Si particles with a diameter of 1.75 μm or more is 10% or more in this Si particle number range, the above definition is desirable. I assumed.

(Core portion Si particles)
Furthermore, in carrying out the present invention, it is preferable that the Si particles in the core brazing material are finely dispersed. In the present invention, when the Mg-added core brazing filler metal reaches the solidus temperature during the brazing temperature rising process, Mg ₂ Si particles and the like begin to melt, and Mg diffuses easily into the surface layer brazing filler metal. However, if the Si particles in the core brazing filler metal are coarse and roughly distributed, the diffusion of Mg to the surface brazing filler metal becomes uneven, resulting in an oxide film ( Al ₂ O ₃ , etc.) also becomes non-uniform and the joining state becomes unstable. The Si particles referred to here include Si particles composed of a single component of Si, and intermetallic compounds such as Mg ₂ Si compounds, for example. In the description of the present invention, these are referred to as Si particles for convenience. Specifically, the Si particles viewed from the cross section of the brazing filler metal in the core are regarded as circle-equivalent diameters, and the Si particles having a diameter of 0.25 μm or more are less than 3,000 per 10,000 μm ² to obtain the effect. It is desirable that the Si particles have finer particle diameters and are densely dispersed within the range that satisfies the above.
As a means for making Si particles finer, it is possible to apply ultrasonic waves during casting, control the solidification rate (0.1 to 500 ° C./sec), adjust the temperature conditions during annealing, and make fine Si particles in the brazing material. For example, adding Sr, etc., which has a quenching effect, is an example, but the method is not limited.

(liquidus temperature difference)
Due to the addition of Mg, the solidus temperature of the core brazing filler metal is lower than that of the Al-Si brazing filler metal in the surface layer. Therefore, in the process of raising the brazing temperature, the core brazing filler metal begins to melt earlier than the surface layer brazing filler metal and approaches the liquidus temperature. The higher the liquid fraction, the greater the amount of Mg diffused into the brazing filler metal in the surface layer. However, if the liquidus temperature of the core brazing filler metal is much lower than that of the surface layer brazing filler metal, the core brazing filler metal will flow out from the wire ends, etc., and the temperature will be sufficient to decompose the Al ₂ O ₃ film on the surface of the material. Insufficient amount of Mg and insufficient flow of effective braze flowing into the joint. Conversely, if the liquidus temperature of the surface layer brazing material is too lower than the liquidus temperature of the core part brazing material, the amount of Mg sufficient to decompose the Al ₂ O ₃ film on the surface layer part brazing material is insufficient for the core. Since the liquid phase ratio of the surface brazing filler metal increases and becomes active before it diffuses from the brazing filler metal, the brazeability deteriorates due to reoxidation of the outermost surface and unstable brazing flow. Therefore, it is desirable that the liquidus temperature difference between the core brazing material and the surface layer brazing material is 60° C. or less. Furthermore, for the same reason, it is more desirable to set the temperature to less than 35°C.

(Brazing conditions)
If the oxygen concentration exceeds 100 ppm, re-oxidation at the joint tends to proceed, resulting in deterioration of the bondability. Therefore, it is desirable to limit the oxygen concentration.
The brazing wire can be flux-free brazed in a non-oxidizing gas atmosphere with an oxygen concentration of 100 ppm or less.
The pressure of the atmosphere in the brazing furnace is basically normal pressure, but for example, in order to improve the gas replacement efficiency inside the product, it is set to a medium-low vacuum of about 100 kPa to 0.1 Pa in the temperature range before melting the brazing material. Alternatively, the pressure may be about 5 to 100 Pa higher than the atmospheric pressure to suppress outside air (atmosphere) from entering the furnace.
The non-oxidizing gas atmosphere includes nitrogen gas, reducing gas, or mixed gas thereof. The type of replacement gas to be used is not particularly limited for bonding aluminum materials, but from the viewpoint of cost, nitrogen gas, argon as an inert gas, and hydrogen and ammonia as a reducing gas are used. is preferred. The oxygen concentration control range in the atmosphere is desirably 100 ppm or less. If it exceeds 100 ppm, the reoxidation of the brazed member is likely to proceed. For the same reason, it is preferably 30 ppm or less, and more preferably 10 ppm or less.

That is, according to the present invention, the surface layer portion is made of Mg-free brazing material and the core portion is made of Mg-added brazing material, thereby suppressing the growth of MgO film on the surface of the material during the process of brazing temperature rise, and further, By optimizing the Si particle distribution of each brazing material layer, Mg, which decomposes the Al oxide film (Al ₂ O ₃ ), can be efficiently supplied to the material surface when the brazing material is melted. The molten brazing filler metal is easily wetted and spread, and a good joining state can be obtained even in a joint having an open portion.
With the present invention, it is possible to obtain a good joint condition with a joint having an open part under practical oxygen concentration control, so that it is equivalent to or better than the conventional brazing method for tube root parts such as radiators, condensers, evaporators, heater cores, and intercoolers. The joint strength and durability are ensured.

1 shows a brazing wire for flux-free brazing in one embodiment of the invention; FIG. 1 is a perspective view showing an aluminum automotive heat exchanger in one embodiment of the present invention; FIG. It is a figure which shows the brazing evaluation model in the Example of this invention.

A brazing wire for flux-free brazing of an aluminum alloy according to one embodiment of the present invention will be described below.
By mass, Si: 4 to 13%, or Si: less than 1 to 4%, Mg: 0.1 to 5.0%, and optionally Bi: 0.01 to 0.5% The aluminum alloy is melted to obtain an alloy material for the core portion. As a melting method, a semi-continuous casting method or a continuous casting method can be used.
Furthermore, in mass%, Si: 2 to 13%, optionally Fe: 0.1 to 1.0%, Bi: Al- containing one or two of 0.01 to 0.1% A Si-based alloy is melted to obtain an alloy material for the surface layer.

In addition, as the aluminum alloy for the core part and the surface layer part brazing material, Cu: 0.05-2.0, Mn: 0.05-2.5, Ca: 0.001-0. 5, Li: 0.001 to 0.5, Be: 0.001 to 0.1, and the like. Cu adjusts the melting temperature of the brazing material, Mn adjusts the fluidity of the molten brazing material, and Ca, Li, and Be are appropriately selected as elements that promote decomposition of the oxide film on the surface of the material during brazing and are added within the above ranges. be able to.

For these alloys, for example, a billet having a double structure of a core portion and a surface layer portion is produced, and the brazing wire of the present invention is obtained by extrusion processing such as backward extrusion. The method of manufacturing the brazing wire is not particularly limited. In addition, after manufacturing a wire by extruding the core alloy alone, the core alloy wire is coated with the melted surface alloy by dipping or thermal spraying. There is a method of manufacturing In addition, after the core alloy and surface alloy are clad by hot rolling to form a sheet material with a double structure, cold rolling is performed as appropriate, and the sheet material is roll-formed so that the surface layer alloy is on the front side. It can also be manufactured by processing into a hollow wire shape. In addition, after working into a wire shape, a drawing process or the like may be added in order to adjust the diameter and dimensional accuracy.
The brazing wire of the present invention is obtained by the method described above.
FIG. 1 is a cross-sectional view of a brazing wire 1, in which a surface layer portion 1B is positioned around a core portion 1A.

In the obtained brazing wire, the Si particles contained in the core portion were less than 3,000 Si particles per 10,000 μm ² having an equivalent circle diameter of 0.25 μm or more as a result of cross-sectional observation of the brazing material. Furthermore, when observing the Si particles contained in the surface layer in the surface direction, the proportion of particles having a diameter of 1.75 μm or more among the number of particles having an equivalent circle diameter of 0.8 μm or more is 10%. That's it. The thickness of the surface layer is ensured to be 30 μm or more.

Although the aluminum member to be brazed is not particularly limited, for example, the following can be applied.
The brazing alloy contains Si: 4 to 12%, Mg: 0.1 to 5.0%, optionally Bi: 0.01 to 0.5%, and the balance is Al. And an aluminum alloy consisting of inevitable impurities is melted, and as an aluminum alloy for core material, in mass%, Mn: 0.1 to 3.0%, Si: 0.1 to 1.2%, Cu: 0.1 ~3.0%, Mg: 0.2 to 1.0%, and the balance is Al and unavoidable impurities. A brazing sheet is formed by cladding a brazing alloy and a core alloy by hot rolling, and is processed into the shape of a heat exchanger member by press forming or the like. The brazing aluminum alloy may also contain Fe, Cu, Zn, Mn, Ca, Li, and Be, and the core aluminum alloy may contain Fe, Zn, Ca, Li, Be, etc. in known amounts. may be contained in Alternatively, an aluminum alloy to which Zn is added may be clad as a sacrificial anticorrosion layer between any of the clad layers or on the surface of the core material that is not clad with brazing material.

Moreover, the aluminum alloy for the core material may be processed into a plate material by rolling or into a rod shape by extrusion as a bare material, and then processed into a heat exchanger member by pressing or cutting.
In _the present invention, the alloy composition of the aluminum member to be brazed is not particularly limited. An added alloy can be preferably used. In the conventional brazing method using a fluoride-based flux, the flux reacts with Mg to generate Mg fluoride with a high melting point, which inactivates the flux. Therefore, it was difficult to apply to high-strength Mg-added alloys, but high-strength Mg-added alloys can be used in flux-free brazing.

For example, a heat exchanger member of a radiator is processed as described above and assembled into a product shape. At that time, the brazing wire of the present invention is installed in the tube netting where the clearance of the joint is large. As for the wire, it is possible to appropriately select an installation method such as one that is processed into a ring shape, one that is bent into a U-shape, or one that is wound with a rod-shaped wire more than once. Although the brazing conditions are not particularly limited, for example, brazing can be performed by heating to 600° C. in a nitrogen gas atmosphere with an oxygen concentration of 30 ppm.
A heat exchanger product obtained by brazing has a sufficient fillet formed at all joints, including joints with large clearances, and exhibits excellent durability and heat exchange performance in a usage environment such as automobiles.

In FIG. 2, using the brazing wire 1, an aluminum alloy fin 2 and an aluminum alloy tube 3 are brazed at a joint 5, and the tube 3 is brazed and joined at a root portion 6 of a header plate 4. ing. An aluminum automobile heat exchanger 10 is obtained by these joinings. The root portion 6 is a joint that tends to have a large clearance.
Further, in the above embodiments, the heat exchanger for automobiles is described as an application of the present invention, but heat exchangers other than those for automobiles may be used, and the application of the present invention is not limited to heat exchangers.

After the billets of the surface brazing filler metal having the composition shown in Table 1 (the balance being Al and unavoidable impurities) and the core brazing filler metal having the composition shown in Table 2 (the balance being Al and unavoidable impurities) were melted by semi-continuous casting. , In order to change the thickness of the surface layer brazing material, the inside of the surface layer brazing material is cut to form a hollow billet with various inner diameters, and the core part is cut from the outside of the core part brazing material to have various outer diameters. A braze billet was prepared. Thereafter, a core brazing material billet having an outer diameter equal to the inner diameter of the hollow billet was assembled to form a double-structured billet, and a round bar having an outer diameter of 10 mm having various compositions was produced by backward extrusion. After that, the round bar was drawn to prepare various wire brazing filler metals having an outer diameter of 1.0 mm.

A JIS A3003 plate with a plate thickness of 1.5 mm and tempered O material is drilled with a hole of 7.5 to 8.5 mm, and a JIS A3003 pipe with an outer diameter of 7.0 mm and an inner diameter of 6.0 mm is assembled as shown in Fig. 3. , Various wire brazing materials processed into a ring shape with an inner diameter of about 7.02 mm were installed in the root portion.
Various assembled bodies were brazed in a nitrogen gas atmosphere with an oxygen concentration of 10 ppm at a reaching temperature of 600 ° C. for a holding time of 3 minutes, and the brazability was evaluated according to the following criteria. The results are shown in Tables 3 to 5. .

Brazeability evaluation method ◎: The clearance of the plate hole diameter 8.5 mm was filled ○: The clearance of the plate hole diameter 8.0 mm was filled △: The clearance of the plate hole diameter 7.5 mm was filled Those that could be filled ×: Those that could not fill the clearance of the plate hole diameter 7.5 mm

Although the present invention has been described above based on the above embodiments and examples, the present invention is not limited to the contents of the above description, and appropriate modifications to the above embodiments can be made without departing from the scope of the present invention. is possible.

REFERENCE SIGNS LIST 1 brazing wire 1A core portion 1B surface layer portion 2 fins 3 tube 4 header plate 5 joint 6 root portion 10 aluminum heat exchanger for automobiles

Claims (7)

A flux-free brazing brazing wire for use in flux-free brazing of an aluminum member, wherein a surface layer portion is laminated on a core portion,
The core portion is made of an Al-Si-Mg alloy containing 4 to 13% by mass of Si and 0.1 to 5.0% by mass of Mg, and the surface layer portion is composed of 2 to 13% by mass of Si. Consists of an Al-Si alloy containing
Si particles contained in the core portion have less than 3,000 Si particles having an equivalent circle diameter of 0.25 μm or more per 10000 μm ² in cross-sectional observation, and the Si particles contained in the surface layer portion are on the surface layer surface In observation of the direction, the ratio of the number of objects having a diameter of 1.75 μm or more in the number of objects having an equivalent circle diameter of 0.8 μm or more is 10% or more,
The thickness of the surface layer portion is 30 μm or more,
The liquidus temperature difference between the Al—Si—Mg-based alloy in the core portion and the Al—Si-based alloy in the surface layer portion is the liquidus temperature of the Al—Si-based alloy in the surface layer portion−Al in the core portion. - A wire brazing material for flux-free brazing, characterized in that the liquidus temperature of the Si--Mg alloy is -60°C to 71°C. A flux-free brazing brazing wire for use in flux-free brazing of an aluminum member, wherein a surface layer portion is laminated on a core portion,
The core part is made of an Al-Si-Mg alloy containing 1% or more and less than 4% by mass of Si and 0.1 to 5.0% of Mg, and the surface layer part is 2 to 13% by mass. Made of an Al-Si alloy containing Si,
The core portion contains less than 3,000 Si particles with an equivalent circle diameter of 0.25 μm or more per 10000 μm ² when observed in a cross section, and the Si particles contained in the surface layer portion are on the surface. When observed in the layer surface direction, the ratio of the number of particles having an equivalent circle diameter of 0.8 μm or more to the number of particles having a diameter of 1.75 μm or more is 10% or more,
The surface layer portion has a thickness of 30 μm or more,
A wire brazing material for flux-free brazing, wherein a liquidus temperature difference between the Al--Si--Mg-based alloy in the core portion and the Al--Si-based alloy in the surface layer portion is 60.degree. C. or less. The wire brazing material for flux-free brazing according to claim 1 or 2, wherein the Al-Si alloy in the surface layer further contains 0.1 to 1.0% by mass of Fe. . Cu: 0.05 to 2.0, Mn: 0.05 to 2.5, Ca: 0.001 to 0 in % by mass in the core portion, the surface layer portion, and both the core portion and the surface layer portion .5, Li: 0.001 to 0.5, Be: 0.001 to 0.1, or any one or more of 0.001 to 0.1. The wire brazing material for flux-free brazing described in 1. above . The flux according to any one of claims 1 to 4 , wherein the Al-Si-Mg alloy of the core portion further contains 0.01 to 0.5% by mass of Bi. Wire brazing material for free brazing. The flux-free brazing filler metal according to any one of claims 1 to 5 , wherein the Al-Si alloy of the surface layer portion further contains 0.01 to 0.1% by mass of Bi. Wire brazing material for attachment. Using the wire brazing material for flux-free brazing according to any one of claims 1 to 6 , aluminum members are joined together without using flux in a non-oxidizing gas atmosphere with an oxygen concentration of 100 ppm or less. A flux-free brazing method for an aluminum member, characterized by:

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