JPH08290293A - Brazing method of al-plated steel sheet - Google Patents

Abstract

PURPOSE: To achieve the brazing directly to a steel sheet of an Al-plated steel sheet by providing a brazing filler metal of higher melting point than the melting point of Al, and using the chloride containing Al fluoride as the flux in the brazing of the Al-plated steel sheet. CONSTITUTION: A brazing filler metal 14 made of brass, etc., is held between Al-plated steel sheets 10, 10 to be brazed through an Al-plated layer 12 to improve a brazed assembly 20 as a whole. The brazed assembly 20 is heated to the brazing temperature using a gas burner employing oxygen and acetylene, or by placing the assembly in an appropriate heating furnace. In joining the assembly 20, the chloride flux containing Al fluoride is used to prevent the oxidation by the atmosphere, and the wet brazing is achieved on the surface of the steel sheet 10 which is the base metal. Because the temperature of the brazing work is high, the brazing filler metal 14 and the plated layer 12 are melted while the temperature rises, and the plated layer 12 is sublimed or melted in the brazing filler metal 14, and the brazing filler metal 14 is directly joined with the steel sheet 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brazing method for Al-plated steel sheets, and more particularly to a brazing method for Al-plated steel sheets.

[0002]

2. Description of the Related Art When joining metallic materials used for automobiles and home appliances, electric welding (arc and resistance welding) is generally performed.

If the mating material to be joined is a non-ferrous metal, electric welding may not be possible. In that case, a resin bonding method or brazing is mainly carried out, and brazing is widely carried out especially when bonding strength is required or when it is used in a hot atmosphere.

Here, "Brazing" means joining metals by using a brazing material, and the joining form at that time is metal-brazing material-metal. Generally, a metal braze is a metal or an alloy that melts more easily than a base metal (melts at a lower temperature than the joining metal) when heated,
It has the property of wetting the base metal.

As described above, brazing enables precise joining by a simple means, and it is particularly required to put it into practical use for joining Al-plated steel sheets for automobile bodies. For example, application to a part of a car body (door sash), a fuel tank, a fuel circuit, and the like is strongly demanded from the viewpoint of reducing manufacturing cost. Particularly recently, since it has been attempted to construct such a member from an Al-plated steel sheet or an Al alloy-plated steel sheet, application of brazing to such a material, particularly brazing technology capable of ensuring high strength Established is required.

According to the conventional idea, when brazing an Al-plated steel sheet or an Al alloy-plated steel sheet (generally referred to as an Al-based plated steel sheet in the present specification), soldering is performed in accordance with the brazing of Al and Al alloy materials. It is generally considered that brazing using Al-Si alloy brazing or Al-Si alloy brazing is performed, but in both cases, the bonding strength is low. This is because the strength of the solder and the brazing material itself is low.

Incidentally, when brazing an Al or Al alloy material, conventionally, soldering or brazing using an Al-Si alloy as a brazing material has been generally performed. Metals with a lower melting point than Al and Al alloys are Al-Si alloys (melting points 580-615
This is because it is limited to low melting point metals and low melting point alloys called brazing filler metal or solder.

[0008]

SUMMARY OF THE INVENTION Here, an object of the present invention is to develop a brazing method for an Al-plated steel sheet, the application of which has been expanding for automobiles in recent years, and in particular, a brazing method with which high joint strength can be obtained. It is to be.

[0009]

[Means for solving the problem] When we examined there,
Conventionally, it is becoming common knowledge that a brazing material having a melting point lower than that of the materials to be joined is used for brazing, and as a result, even if brazing Al-based plated steel sheet, Metals having a lower melting point than Al and Al alloys, that is, Al-Si alloy brazing filler metals, low melting metal called solder, and low melting alloys must be used.

By the way, there are soft brazing materials and hard brazing materials as the brazing materials, which are defined by the melting point of the brazing material, and the lower one is distinguished from the soft brazing material at 450 ° C. and the above is distinguished from the hard brazing material. . In Japan, soft brazing material is called solder and hard brazing material is simply called brazing material. Therefore, the term "brazing material" as used herein means a hard brazing material.

On the other hand, there is a method of performing brazing under the atmosphere and under vacuum, and a flux is used for the brazing work under the atmosphere. The flux consists of various salts, and is used properly according to the melting point and etching performance.

The flux is required to have the property of preventing high temperature oxidation of the materials to be bonded at the brazing work temperature and removing the oxide film existing on the surfaces of the materials to be bonded. No flux is used under vacuum.

Summarizing the contents of such a prior art,
High melting point metal brazing materials, brass and silver brazing alloys have excellent bonding strength, but in the case of Al-based plated steel sheets, the base material, that is, the Al-based plating layer, cannot be used in the bonding temperature range. Moreover, since the brazing temperature of the hard brazing material is higher than the melting point of the plating metal, it is expected that the aluminum will be dissolved and the alumina will be generated by the oxidation to make the brazing difficult. In fact, in the case of the above-mentioned brass braze, although the brazing metal itself has the strength, the brazing operation is performed at a high temperature, so that the Al of the plating metal is melted and becomes an oxide to form a barrier coating. Can not.

Therefore, the present inventors have conceived that such a problem can be solved by using an appropriate combination of fluxes, and in the brazing method of an Al-based plated steel sheet,
The present invention has been completed, knowing that the above problems can be effectively achieved by directly brazing the Al-based plated steel sheet to the steel sheet by eliminating the Al-based plating layer.

Here, the gist of the present invention is that Al is
In the brazing of system-plated steel sheets, a metal having a melting point higher than the melting point of Al is used as a brazing material, and a chloride containing aluminum fluoride is used as a flux, and the plating metal is sublimated by heating or melted into the brazing metal, This is a brazing method for an Al-based plated steel sheet, characterized by brazing to an Al-based plated steel sheet. Furthermore, a preferred embodiment of the present invention is a brazing method for an Al-based plated steel sheet using brass brazing as a brazing material.

[0016]

Next, the brazing method according to the present invention will be specifically described together with its operation with reference to the drawings.

FIG. 1 is an explanatory view of a brazing method according to the present invention. In the figure, an Al-based plated steel sheet 10, 10 to be brazed is shown.
A brazing material 14 is sandwiched between the Al-based plating layers 12 to form a brazing assembly 20 as a whole.

The brazing assembly 20 is heated to the brazing temperature by a gas burner method such as oxygen acetylene or in a heating furnace (including high-frequency heating furnace). In the case of the present invention, since the temperature of the brazing operation is high, the brazing material and the plating layer 12 are melted in the process of raising the temperature, the plating metal is sublimated or melts into the brazing material 14, and the brazing material 14 and the steel plate 10 are melted. And are directly joined. Then, a kind of diffusion layer is formed at the boundary portion. The structure of the joint region obtained at this time is shown in FIG. 2 with its schematic view.

In the case of the present invention, a chloride flux (not shown) containing aluminum fluoride is used for joining, which prevents oxidation by the atmosphere and wets the surface of the steel sheet 10 as a base material. Make a mark. Of course, since the Al-based plating layer 12 was present on the surface in advance, wetting of the brazing material is easily performed, and mutual diffusion from the brazing material and the base material also progresses, and as shown in FIG. Further, the steel plate 10 and the brazing filler metal 14 are directly and strongly bonded to each other via the diffusion layer 18.

Thus, considering the cross section of the joining region according to the present invention, the joining region has a structure of steel sheet-diffusion layer-brazing material layer-diffusion layer-steel sheet, and the steel sheets on both sides are directly joined via the brazing material. .

The plated metal may be melted at the brazing temperature and melted in the brazing material or evaporated to sublimate. As a result, the steel plate and the brazing material are directly brazed without interposing the plated metal.

The brazing filler metal used in the present invention may be a metal having a melting point higher than that of Al, which is for securing particularly high temperature strength of the brazing filler metal. For example, brass brazing material, JI
S Z3262, BCuZn-1 (Cu-Zn 40%) and the like. As in one embodiment, as in the case of an Al-plated steel sheet, the use of Al, that is, a brazing material having a melting point higher than that of the plated metal facilitates direct bonding between the brazing material and the steel sheet.

In the present invention, the flux component is not particularly limited as long as the above-mentioned action is exhibited,
According to a preferred embodiment of the present invention, when performing the above-mentioned brazing by heating in an air atmosphere, a flux is used in order to prevent oxidation of the surface of the Al plating layer and to activate it. Uses a mixture of aluminum fluoride and chloride.

According to the preferred embodiment, the following combinations are preferred: Brazing material: Copper-zinc alloy (40-70% by weight Cu-remaining Zn) Flux component Aluminum fluoride: 1-10% by weight or 2-6% by weight Sodium chloride: 30-80% by weight, preferably 35-68% by weight Potassium chloride: 10 to 60% by weight, preferably 26 to 59% by weight.

The Al-based plated steel sheet according to the present invention is pure
There are many examples such as Al plating, Al-alloy plating (eg: Al-Mn, Al-Si alloy plating), and plating means include vapor deposition plating, hot dipping, electroplating, etc. The present invention also applies, but preferably,
An Al-Mn alloy molten salt electroplated steel sheet is preferred.

Further, it is preferable that the mating members to be brazed are brazed with the same Al-based plated steel sheets with their plated surfaces facing each other, but the mating surface may be a bare steel surface or an electric Zn.
Other metals such as a plated steel plate, a hot dip Zn plated steel plate, an electric Zn-Ni plated steel plate, etc. may be used. Next, the working effects of the present invention will be described more specifically by way of examples.

[0027]

[Example] Preliminary test (Evaluation of brazing property) In this example, as a preliminary test, base metal plating for brazing (steel plate)
The above brazability evaluation was performed as follows.

2-3 g on Al-based plated steel plate (50 x 50 mm)
And a brazing metal of about 1 to 2 g were placed and heated from below the steel plate with an acetylene gas burner. The evaluation was carried out in five stages according to the extent of the wetting (familiarity) spread area of the brazing metal and the steel sheet.

Specimen: a) Evaporated Al-plated steel sheet (adhesion amount 2 g / m ^{2 on} one side) b) Hot-dip Al-plated steel sheet (adhesion amount 80 g / m ^{2 on} one side, Al-10% S)
i) c) Al-Mn alloy molten salt electroplated steel sheet (deposition amount: 20 g / m ²
One side, composition: Al-25% Mn) Wax wettability evaluation: ⊚ (good)-○-△-× -xx × (bad).

[0030]

[Table 1]

As can be seen from the results shown in Table 1, when the commercial flux and the brass brazing material are used, the wettability of the brazing material with respect to the Al-plated steel sheet is very poor. In addition, in the heating in this example, the Al-based plating layer is dissolved and then oxidized to form an alumina coating. The above-mentioned wettability means the wettability with respect to the steel sheet directly. This is the same in the following examples.
Therefore, this time, various fluxes were mixed and the wettability to the Al-based plated steel sheet was evaluated. The results are summarized in Table 2.

[0032]

[Table 2]

Next, the flux composition was changed to a fluorinated Al-containing chloride system, and the wettability when the composition ratio was changed was evaluated. The results are summarized in Table 3. It can be seen that even if a brass brazing material is used, the above-mentioned flux exhibits sufficient wettability.

[0034]

[Table 3]

Brazing Test Further, the shear strength of the brazed portion was evaluated according to JIS Z 3192 (shear test method for brazing joints). The results are summarized in Table 4.

Brazing material: Bron 68 (Cu-Zn-Sn series) manufactured by Nice Co., Ltd. is used. Flux: Compounded flux (Na chloride: K chloride: Al fluoride 40 = 50:10) Commercial flux [A] = F87 (Zn chloride system) Nice [B] = F19 (Chloride system) Nice [C] = F68 (Boric acid-borax system) Nice Brazing method: Oxygen-Torch brazing method using acetylene gas Produce a test piece with wax.

[0037]

[Table 4]

[0038]

As described above, according to the present invention,
By brazing Al-plated steel sheets, a high joint strength (shear strength) of 169 N / mm ² or more can be realized, and Al-plated steel sheets can be used in the field of automobile bodies, which could not be applied until now. As a result, the practical significance of the present invention is great.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a brazing assembly of Al-based plated steel sheets.

FIG. 2 is a schematic explanatory view of a structure of a bonding area when the brazing assembly of FIG. 1 is heated and brazed.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location // B23K 103: 16 (72) Inventor Katsuro Hirayama 4-53-3 Kitahama, Chuo-ku, Osaka Sumitomo Inside the metal industry

Claims (2)

[Claims] 1. When brazing an Al-based plated steel sheet,
A metal having a higher melting point than the melting point of is used as a brazing material, and a chloride flux containing aluminum fluoride is used as a flux to eliminate the plating layer and braze directly to a steel sheet of an Al-based plated steel sheet. How to attach. 2. The brazing method according to claim 1, wherein brass brazing is used as the brazing material.