JPH0729202B2 - Brazing method of iron material and aluminum material - Google Patents

Description

TECHNICAL FIELD The present invention is used for joining iron materials and aluminum materials in heat exchangers such as bath heaters, water heaters, heaters, and general industrial joints. The present invention relates to a brazing method of an iron material and an aluminum material.

In this specification, the term iron is used to mean not only pure iron but also stainless steel, ordinary steel and other iron-based alloys. The term aluminum is used to include its alloy.

2. Description of the Related Art Brazing of iron materials such as stainless steel and aluminum is an aluminum material used for normal aluminum material brazing.
It is known that this can be done by using a -Si brazing filler metal.

However, when using such a conventional Al-Si brazing filler metal, the melting point of the brazing filler metal is generally high.
There is no choice but to reach a high temperature of 600 ° C or higher. However, when the brazing temperature is high, a brittle alloy layer of FeAl ₃ system having a thickness of 20 to 40 μm is formed at the joint interface between the iron material and the aluminum material,
Due to this, there is a drawback that sufficient strength of the joint surface cannot be obtained. Therefore, the products to which such a brazing method can be applied are naturally limited. Especially, in the case of repeated heating and cooling, such as a bath kettle, a water heater, a cold heat repeater joint, etc., particularly excellent joining strength is required,
Applying brazing to join an iron material and an aluminum material poses a serious problem, and in reality, other complicated joining methods must be used.

This invention has been made in view of such a technical background, in brazing an iron material and an aluminum material,
An object of the present invention is to provide a brazing method capable of suppressing the formation of a brittle alloy layer at the joint interface and realizing sufficient joint strength.

Means for Solving the Problems The above-mentioned object is to braze an iron material and an aluminum material, using an Al-Si-high Zn brazing material as a brazing material, and brazing at a temperature of 570 ° C or less. Is achieved by a brazing method of an iron material and an aluminum material.

The composition of the iron material used in the present invention is not specifically limited, and carbon steel, austenitic stainless steel, ferritic stainless steel, or the like may be appropriately used depending on the application. The composition of the aluminum material is not limited, and in addition to pure aluminum, Al-Mn-based alloys and various other alloys can be used.

The brazing filler metal used in the present invention contains 0.5 to 12 wt% of Si and Zn.
It is an Al-Si-high Zn brazing filler metal containing about 15 to 80 wt%.
As described above, by using the brazing material having a high Zn content, the melting point of the brazing material can be lowered, and by extension, brazing can be performed at a low temperature without forming a brittle FeAl ₃ alloy layer at the joint interface. An example of the specific composition of the brazing material is as follows.

That is, basically, a brazing material containing Si: 0.5 to 12 wt% and Zn: 15 to 80 wt% with the balance aluminum and inevitable impurities may be used. In the above, Si is necessary for lowering the melting point of the brazing material and enhancing the fluidity. However, if the content is less than 0.5 wt%, the effects may be poor. On the other hand, if it is contained in excess of 12 wt%, the melting point may be rather increased, and it may not be used as a brazing material. A particularly preferable content of Si is 4 wt% or more, especially 5 to 8 wt%. Zn is an extremely effective element for lowering the melting point of the brazing material. However, if the content is less than 15 wt%, the effect may be poor, while if it exceeds 80 wt%, the workability may be deteriorated. A particularly preferable Zn content is 55 wt% or less, particularly about 20 to 50 wt%.

In addition to the above Si and Zn as other high Zn content brazing filler metals,
You may use what contained Be in 0.02 to 1.0 wt%. Be contributes to the improvement of mechanical properties such as strength and elongation of the brazing filler metal without impairing the low melting point effect of Si and Zn.
As a result, the brazing joint (fillet) after brazing
Has the effect of improving the mechanical properties of. But 0.
If it is less than 02% by weight, the above effect may not be exhibited, while if it exceeds 1.0% by weight, the effect may be saturated, which may lead to economical waste. A particularly preferable range when Be is contained is 0.10 to 0.5 wt%.

Further, as another brazing filler metal having a high Zn content, in addition to the above Si and Zn, a brazing material containing Cu: 0.2 to 2.0 wt% may be used. C
u plays the role of preventing the natural electrode potential of the fillet from becoming base after brazing due to the high Zn content, and preventing the corrosion of the joint by shifting the potential to the noble side. However, if the content is less than 0.2 wt%, the above effect may be poor, and if it exceeds 2.0 wt%, workability may be deteriorated. When Cu is contained, the preferable range is 0.5 to 1.5 wt%. If Cu is contained,
In order to improve the mechanical properties of the joint, Be may be contained in the range of about 1 wt% or less.

As another high-Zn content brazing material, together with the above Si and Zn
In: 0.02-0.2wt%, Sn: 0.05-0.4wt%, Bi: 0.05-0.4wt
%, One containing one kind or two or more kinds. In the above, In, Sn, and Bi are elements effective in achieving good brazing by making the oxide film on the surface weak and defective when the molten brazing filler metal spreads by wetting. In terms of such effects, these are all evaluated as equivalents, and it is sufficient that at least one kind is contained. However, In is less than 0.02 wt%, Sn is less than 0.05 wt%, Bi is 0.05.
If it is less than wt%, the above effect may not be exhibited. On the other hand, In exceeds 0.2 wt%, Sn exceeds 0.4 wt%, Bi exceeds 0.4 w
Even if it exceeds t%, the effect is saturated and there is a risk of causing economic waste. When containing one or more of In, Sn, and Bi, a particularly preferable content range is In: 0.03 to 0.15 wt.
%, Sn: 0.10 to 0.30 wt%, Bi: 0.10 to 0.30 wt%.

The method for manufacturing the brazing material is not particularly limited, and may be extruded into a wire by an extrusion method according to a conventional method, or may be manufactured into a plate material by hot rolling or cold rolling according to a conventional method, Any other manufacturing means can be applied.

At the time of brazing, the brazing material is placed in the form of a brazing material by placing it near the site where the iron material and the aluminum material are to be joined,
Alternatively, it is supplied in the form of a brazing sheet using aluminum as the core material and brazing material as the skin material. Then, after applying a flux if necessary, the brazing joining is achieved by heating the assembly of the iron material and the aluminum material. Here, brazing needs to be performed at a temperature of 570 ° C. or lower. If the brazing temperature exceeds 570 ° C, a brittle FeAl ₃ alloy layer is formed at the joint interface between the iron and aluminum materials,
This is because the strength of the joint is deteriorated. Of course, since brazing itself becomes impossible at a temperature lower than the melting point of the brazing material, the brazing temperature must be set above the melting point of the brazing material and below 570 ° C. Further, since the alloy layer grows with time, it is preferable that the heating and holding time during brazing be as short as possible within the range where good joining can be obtained. In particular, on the high temperature side of 540 to 570 ° C., the holding time is 10 minutes or less, preferably 5 minutes or less.

Next, an embodiment of the present invention will be described.

Example As shown in FIG. 1, a stainless steel tube (1) made of SUS304 and having a thickness of 0.4 mm and a corrugated fin (2) made of aluminum were temporarily assembled. As the corrugated fin (2), a brazing sheet was used in which a brazing material was clad on both sides of an aluminum core material made of A3003 and having a thickness of 0.5 mm. Then, as shown in Table 1, various brazing materials were used to fabricate a plurality of types of assemblies.
The thickness of the brazing filler metal was 0.1 mm on each side. Further, when the liquidus temperature of the brazing material alone was examined, it was as shown in Table 1.

Then, by brazing in a furnace using chlorine-based flux,
The ambient temperature was set as shown in Table 1 and the above-mentioned assemblies were brazed.

After brazing, the joint portion (3) between the tube (1) and the fin (2) was visually observed. In addition, the presence or absence of the FeAl ₃ alloy layer at the joint interface between the tube (1) and the fin (2) was examined for each assembly with a microscope. The results are also shown in Table 1.

In addition, when an increasing tensile load was applied to each assembly and the strength of the joint strength was examined, it was found that in all the products of the present invention, the fins were released before the separation of the joint surface between the tube (1) and the fins (2). While (2) was cut, in the comparative product, peeling occurred on the joint surface before cutting the fin (2).

In addition, Al-8wt% Si-20wt% Zn, Al-7wt% Si-30wt% Zn-1wt
% Be, Al-10wt% Si-25wt% Zn-0.5wt% Cu, Al-4wt% Si-5
Using a brazing filler metal consisting of 0 wt% Zn-0.15 wt% Sn
When the same brazing as above was performed at a temperature of 0 to 550 ° C,
The FeAl ₃ -based alloy layer at the joint interface was also not recognized.

From the above test results, it was confirmed that according to the present invention, the formation of the FeAl ₃ -based alloy layer at the joint interface can be suppressed and the strength of the joint can be improved.

EFFECTS OF THE INVENTION According to the present invention, as described above, first, as a brazing material, Al-Si-high
Since a Zn-based material is used, good brazing property can be maintained, and only the melting point of the brazing material can be made significantly lower than that of the conventional Al-Si-based material. Moreover, since the brazing material contains a high concentration of Zn, it has good wetting with the iron material,
Good joining is possible. Then, after ensuring good brazing property and lowering the melting point of the brazing material,
Since brazing is performed at a temperature of 570 ° C or less, it is possible to suppress or eliminate the formation of a FeAl ₃ -based brittle alloy layer at the joint interface between the iron material and the aluminum material, and therefore the joint strength of both members due to the existence of the alloy layer. It is possible to provide a brazed product having excellent strength while preventing deterioration of As a result, it is possible to sufficiently join the iron material and the aluminum material by brazing in various products such as bath kettles and water heaters, which have been difficult to apply in the past, and the brazing application range can be expanded.

[Brief description of drawings]

FIG. 1 is a front view of a brazing test piece used in Examples. (1) …… Stainless steel tube, (2) …… Aluminum fin.

Claims (1)

[Claims] 1. When brazing an iron material and an aluminum material, an Al-Si-high Zn brazing material is used as the brazing material, and the brazing material is brazed at a temperature of 570 ° C. or lower. Brazing method with aluminum material.