JPH03238170A - Method for joining aluminum or aluminum alloy to stainless steel - Google Patents

Abstract

PURPOSE:To furnish laminated material of high quality by forming titanium films having the specified thickness on the surface to be joined of stainless steels, superposing Al thereon via brazing filler metals and heating these for the specified holding time in a vacuum. CONSTITUTION:First material to be joined of Al or an Al alloy 3 and second materials to be joined of stainless steels la and 1b are joined together with brazing filler metals 4a and 4b. The titanium films 2a and 2b having >= 1mum film thickness are then formed by the PVD method on the surfaces to be joined of the second materials to be joined of the stainless steels la and 1b. The first material to be joined of Al3 is superposed on the titanium films 2a and 2b via the brazing filler metals 4a and 4b and heated in the vacuum or insert gas and the brazing filler metals 4a and 4b are molten to join the first and second materials to be joined together. The fusion holding time Y(sec) of the brazing filler metals an the film thickness X(mum) of the titanium films 2a and 2b satisfy the inequality. By this method, the laminated material having high joining strength can be obtained stably.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an aluminum product (A1) or an aluminum alloy (
The present invention relates to a method of joining A7 material and stainless steel to obtain a composite material by joining the AJ material (hereinafter referred to as AJ material) and stainless steel by brazing.

[Conventional technology] A composite material of aluminum material and stainless steel has the features of lightweightness, high thermal conductivity, corrosion resistance, and good workability that AI material has, and
It has both the excellent corrosion resistance that stainless steel has, and is used in fields such as appliances such as electromagnetic cookers, parts for vehicles and ships, electrical parts, parts for heat exchangers, contact materials, and kitchen supplies. is being expanded.

Conventionally, as a technique for joining such an AI material and stainless steel, there is a rolling clad method in which the two are rolled in an overlapping state. However, the scrap material generated during the manufacturing stage of rolled crat material has no economic value, and
It has drawbacks such as not being able to be partially combined.

Also) AI! Another technique for joining materials and stainless steel is a method of joining aluminum materials and stainless steel by brazing. In this case, if the Al material and stainless steel are brazed directly, it is difficult to obtain high bonding strength through such direct brazing because fragile intermetallic compounds are likely to be generated at the interface. It is. On the other hand, there is a method (Japanese Unexamined Patent Publication No. 133971) in which stainless steel is coated with tin or silver, pretreated, and then vacuum brazed. There is a drawback that bonding strength cannot be obtained.

In addition, a joining method using Ti foil as an insert material (
li! (Metal Vol. 37, No. 6, pp. 413-418), but this method involves joining Ti and stainless steel and bonding Ti to stainless steel.
Since the bonding with Al and the bonding with Al are performed in separate heat treatment steps, the manufacturing method has the disadvantage of being complicated. Furthermore, in this case, for joining Ti and stainless steel, 850
Since it is necessary to heat to a high temperature of ℃, there is a drawback that the corrosion resistance of the stainless steel base material deteriorates.

Therefore, recently, a method has been proposed in which an ion brazing layer made of Ti or TiN is provided on the stainless steel material, and an A1 brazing material is interposed between the stainless steel material and the A1 material and the stainless steel material are brazed. (Japanese Unexamined Patent Publication No. 1-143788).

[Problems to be Solved by the Invention] However, in the method of brazing and joining the stainless steel material provided with the ion brazing layer made of Ti or TiN and the Al material using the A1 brazing material, the ion brazing layer is insufficient. If the brazing process is not thick enough, or if brazing takes a long time to join large parts, this brazing process may require A7-
Ti intermetallic compounds may be generated and the ion blating layer may be locally lost. Then, Al
There is a problem in that the bonding strength between the aluminum material and the stainless steel material decreases because a weak intermetallic compound is generated at the bonding interface when the aluminum material and the stainless steel material come into contact with each other.

The present invention has been made in view of such problems, and includes:
No fragile intermetallic compounds are formed at the bonding interface.
The object of the present invention is to provide a method for joining aluminum or aluminum alloy and stainless steel, which provides extremely high joining strength.

[Means for Solving the Problems] The method for joining aluminum or aluminum alloy and stainless steel according to the present invention includes a first workpiece made of aluminum or an aluminum alloy, and a second workpiece made of stainless steel. The method includes the steps of: forming a titanium thin film having a thickness of 1 μm or more on the surface of the second material to be joined by PVD; joining the first and second materials by stacking the first materials to be joined and heating them in vacuum or in an inert gas to melt the brazing material and joining the first and second materials to be joined; It is characterized in that the melting retention time Y (seconds) and the film thickness X (μm) of the titanium thin film satisfy the following inequality.

Y≦(1,3X2-2.[iX+ 5.0) XIO2
5- [Function] The inventors of the present application have conducted various studies on methods of joining aluminum or aluminum alloy and stainless steel material via a titanium thin film. As a result, by correlating the thickness of the titanium thin film and the holding time at the heating temperature that melts the brazing metal, that is, the brazing time, and keeping it within a specified range, the relationship between Al material and stainless steel can be improved. It was discovered that high bonding strength could be obtained between the two. The present invention has been made based on the results of such research.

That is, in the present invention, first, a titanium thin film is formed on the surface to be joined of the second material to be joined made of stainless steel by the PVD method. In this case, since the titanium thin film is formed by the PVD method, the stainless steel base material is not exposed to high temperatures, and problems such as deterioration of its corrosion resistance and strength do not occur.

Next, a first material to be joined made of aluminum or aluminum alloy (A7 material) is placed on top of the titanium thin film with a brazing material sandwiched between the titanium thin film and heated in a vacuum or inert gas atmosphere. The first and second materials to be joined are joined by melting the brazing material. Therefore, since the titanium thin film is interposed between the Al material and the stainless steel, the two do not come into direct contact with each other, and a fragile intermetallic compound is not generated at the bonding interface.

However, in this brazing process, if the thickness of the titanium coating is small or if the brazing time is long,
In brazing, Af and Ti in the brazing material or the second material to be joined react with each other due to heating in the brazing process, and an A1-Ti intermetallic compound is generated, and the thickness of the titanium thin film decreases, causing the titanium The thin film may disappear locally. In this case, the first and second materials to be joined come into direct contact, and a fragile intermetallic compound is generated at the joining interface.

Therefore, in the present invention, in order to prevent the titanium thin film from disappearing, the thickness of the titanium coating is set to 1 μm or more. In other words, if the thickness of the titanium thin film is less than 1 μm, the titanium thin film will locally disappear even if brazing is performed with the minimum necessary melting and holding time, so the thickness of the titanium thin film should be 1 μm. limited to the above.

Further, the relationship between the melting retention time Y (seconds) of the brazing filler metal and the film thickness X (μm) of the titanium thin film is limited within the range shown by the inequality in the following equation.

Y≦(1,3X2-2.6X+5.0) XIO2...
・■ This equation 0 was obtained based on the experimental results of the inventors of the present application.

Figure 1 shows the melting retention time Y of the brazing filler metal and the film thickness X of the titanium thin film.
It is a graph diagram showing the relationship between the two, in which the horizontal axis shows the thickness of the titanium thin film, and the vertical axis shows the melting retention time of the brazing material.

In Fig. 1, when X≧1 and the melting retention time Y of the brazing filler metal and the film thickness X of the titanium thin film are within the range that satisfies the above equation 0 (hatched area in the figure), the brazing process is The titanium thin film will not disappear.

Therefore, the first and second materials to be joined do not come into direct contact with each other, and a fragile intermetallic compound is not generated at the joining interface.

For example, even if brazing takes a long time due to the size or shape of the first and second materials to be joined, that is, even if the melting retention time Y of the brazing filler metal becomes long, the titanium thin film When the film thickness X is set to be thicker than the minimum value obtained by substituting the above Y into the above equation, disappearance of the titanium thin film in the brazing process can be avoided. That is, if the thickness X of the titanium thin film is set within the hatched area in FIG. 1 in relation to the holding time Y, then
Even if the thickness of the titanium thin film decreases due to the growth of Af-Ti intermetallic compounds during the brazing process, the titanium thin film is sufficiently thick (formed) and will not disappear.

Therefore, in the present invention, the film thickness X of the titanium thin film is set to 1 μm.
m or more, and the brazing time is limited according to the thickness of the titanium thin film based on the above formula 0, or the brazing thickness of the titanium thin film is defined according to the time. This can prevent the titanium thin film from disappearing. For this reason, the first
Moreover, a fragile intermetallic compound is not generated at the bonding interface of the second material to be bonded. Thereby, a composite material having high bonding strength can be stably obtained.

In addition, as a brazing material, AI! -8i alloy or -〇- AI! -8t-Mg alloy, etc. can be used.

In addition, when this brazing material is used as a plating sheet that has been joined to the Al material in advance and is integrated, the joining process can be simplified.

[Example 2] Next, a method for joining stainless steel with aluminum porcelain according to an example of the present invention will be described with reference to the attached drawings.

Fig. Φ is a sectional view showing a composite material of Al material and stainless steel in which stainless steel plates are provided on both sides of materials A and ff.

Ti thin films 2a + 2b each having a film thickness of 1 μm or more are deposited on the surfaces to be joined of the stainless steel plates 1a and 1b by PVD.
(Physical Vapor Depositio
n: Deposited by physical vapor deposition) method. Specific examples of such PVD methods include vacuum deposition, sputtering, and ion blasting.

On the other hand, brazing materials 4a and 4 are provided on the front and back surfaces of the Al material 3, respectively.
b is applied. This brazing material 4a.

4b and 7! tA7-8i alloy or Al-8i -1
0-Mg based alloys can be used. In addition, it is better to use a commercially available plating sheet 5 for the A7 material 3 and the brazing materials 4a, 4b than to use separate materials. This is preferable because the bonding process between them can be simplified.

Therefore, brazing filler metal 4 a + 4 b is applied to the front and back surfaces of A1 material 3.
The plating sheet 5 coated with Ti thin film 2a,
The Ti thin films 2 a + 2 b are sandwiched between the stainless steel plates 1 a and 1 b to which the Ti thin films 2 a and 2 b are applied, respectively, in contact with the brazing materials 4 a and 4 b. And a pair of stainless steel plates 1
While applying a constant pressure between a and lb, these laminates are heated to a predetermined brazing temperature in a vacuum or in an inert gas for a predetermined time.

As a result, the brazing filler metals 4a and 4b are melted, and when cooled after a predetermined period of time, the stainless steel plates 1a and lb and the Al material 3 are brazed. In this case, the melting retention time of the brazing materials 4a, 4b at the brazing temperature is set in accordance with the thickness of the Ti thin films 2a, 2b, as specified in the present invention. Further, the thickness of the Ti thin films 2a and 2b may be set in accordance with the melting and holding time of the brazing filler metals 4a*4b.

In this way, in the method of this embodiment, since the Ti thin films 2a and 2b are interposed between the A7 material 8 and the stainless steel plates 1a and 1b, respectively, the Al material 3 and the stainless steel plates 1a,
There is no direct contact with lb. In addition, T 1 thin film 2
By mutually limiting the film thicknesses a and 2b and the melting retention time of the brazing materials 4a and 4b, it is possible to prevent the Ti thin films 2a and 2b from disappearing during the brazing process.

Therefore, fragile intermetallic compounds are not generated at the interface between the Ai7 material 3 and the stainless steels 1a and 1b, so the Al
Sufficiently high bonding strength can be obtained between the material 3 and the stainless steel plates 1a, lb.

The above-mentioned brazing process is carried out in a vacuum or an inert gas atmosphere, but in consideration of brazing properties, it is preferable to heat the above-mentioned laminate in a vacuum rather than in an inert gas atmosphere.

On the other hand, since the Ti thin films 2a, 2b are deposited on the surfaces to be joined of the stainless steel plates 1a, lb by the PVD method, the base metal stainless steel plates 1a, lb are not exposed to high temperatures during this deposition process. No loss of material performance. Therefore, the excellent property of high corrosion resistance of stainless steel is sufficiently maintained.

Further, the Ti thin films 2a, 2b are adhered to the surfaces to be joined of the stainless steel plates 1a, lb as in the above embodiment,
It does not adhere to the front and back surfaces of AAAs2. When brazing stainless steel and Al material, it is necessary to use a brazing material whose melting point is lower than that of the base materials stainless steel and Al material, and the brazing material 4 a r 4 b is usually as described above. Af-8t alloy or AI! -8t-Mg
Use alloys of this type. For this reason, the Ti thin films 2a and 2b are
When formed on the front and back surfaces of l material 3, brazing material 4 containing AI
Since a and 4b come into contact with stainless steel plates 1a and lb, stainless steel plates ta and 11) and brazing filler metals 4a and 4b
Intermetallic compounds are formed at the interface with the metal. On the other hand, without using the brazing filler metal 4a + 4b, the stainless steel plate 1a
, lb and the Al material 3 with the 13-Ti thin films 2a and 2b sandwiched between them,
It is necessary to join by diffusion bonding at high temperature instead of brazing, which results in deterioration of the base material stainless steel, as in the conventional technology. For this reason, stainless steel plate 1a
, 1b with Ti thin 11i2 a.

2b is deposited by the PVD method, and Ti thin films 2a, 2b and A
It is necessary to braze and join the l material 3 with the brazing filler metals 4a + 4b.

Next, we will compare the results of actually joining stainless steel and Al material by changing the film thickness of the titanium thin film formed by the PVD method and the holding time at the brazing temperature in the method of this example. I will explain by comparing. Tables 1 and 2 below show stainless steel (SIIS 304) and A
1 material (A 3003A ffi alloy), the results of the tensile test of the brazed section, and the presence or absence of intermetallic compounds are shown. Note that the intermetallic compounds in Tables 1 and 2 refer to fragile intermetallic compounds that are generated by the reaction between the components of the Al material and the components of the stainless steel at the bonding interface.

14- Also, Table 1 shows the case where Af-8t-Mg alloy (BA 4004) is used as the brazing material, and Table 2 shows the case where Al-8i alloy (BA 4343) is used as the brazing material. In either case, the above A, I! A plating sheet was prepared in which the front and back surfaces of the material were clad with an Af-8t-Mg alloy layer or an Af-8i alloy layer. Furthermore,
The temperature for brazing is 620°C, and during this brazing, the brazing material is 0.02 kg f/ca 2 or 5 kg f/
Pressure was applied at a pressure of c+m''.

As is clear from Tables 1 and 2, in the cases of Examples 1 to 35 that satisfy the relationship defined by the Ti thin film thickness and waxing time in the present invention, the shear strength is 4k.
A healthy joint with high gf/mm2 and high joint strength was obtained. Also, if the waiting time is relatively long,
Correspondingly, since the Ti thin film is formed thickly, T1
The thin film did not disappear, and almost no fragile intermetallic compounds were formed at the bonding interface between the Al material and stainless steel.

Table 1 (Part 2) 17- Table 1 (Part 1) Table 2 (Part 1) 18- Table 2 (Part 2) On the other hand, the thickness of the Ti thin film and the waxing time are defined in the present invention. In the case of Comparative Examples 1 to 12 that do not satisfy the relationship, the shear strength was low at less than 4 kgf/mm2 (and the bonding strength was low. In particular, the thickness of the Ti thin film was 1.0 kgf/mm2).
In Comparative Examples 1, 2° 7, and 8, which are micrometers, the A7 material and the stainless steel were not completely bonded, so peeling occurred at the bonded portion during the tensile test. Furthermore, in both cases, a fragile intermetallic compound was formed at the bonding interface.

[Effects of the Invention] As explained above, according to the present invention, the process of forming a titanium thin film on the surface of the second material to be joined made of stainless steel by the PVD method, and the step of forming the titanium thin film on the surface of the second material to be joined made of stainless steel, Alternatively, a step of joining the first and second materials to be joined by stacking the first material made of A1 alloy and the titanium thin film via a brazing material and melting them in a vacuum or inert gas atmosphere. Since the thickness of the titanium thin film and the melting retention time of the brazing filler metal are limited in relation to each other, fragile intermetallic compounds are not generated at the bonding interface between the stainless steel and the A1 material due to the titanium thin film. It is possible to reliably prevent this, and to stably obtain a composite having high bonding strength.

Therefore, in the field of heat exchangers, electromagnetic cookers, etc., it is possible to provide a high-quality composite material that takes advantage of the excellent characteristics of both stainless steel and Al material.

[Brief explanation of drawings]

Fig. 1 is a graph showing the relationship between the melting holding time of the brazing filler metal and the thickness of the titanium thin film according to the present invention, and Fig. 2 shows a composite material of Al material and stainless steel according to an embodiment of the present invention. FIG. 1a+1b; Stainless steel plate, 2a, 2b; Titanium thin film, 3; A1 material, 4a+4b; Brazing metal, 5; Beak piece X (μm) of plating sheet through Ti film.

Claims (1)

[Claims] (1) First made of aluminum or aluminum alloy
In the method of joining a material to be joined and a second material to be joined made of stainless steel by brazing, a titanium thin film having a thickness of 1 μm or more is applied to the surface of the second material to be joined by a PVD method. the first and second materials are stacked on the titanium thin film via a brazing material and heated in a vacuum or inert gas to melt the brazing material and bond the first and second materials together; an aluminum or aluminum alloy comprising the step of joining materials to be joined, wherein the melting retention time Y (seconds) of the brazing filler metal and the film thickness X (μm) of the titanium thin film satisfy the following inequality: How to join with stainless steel. Y≦(1.3X^2-2.6X+5.0)×10^2