JPH0510193B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a method for joining dissimilar materials, and in particular,
This invention relates to a dissimilar material joining method suitable for manufacturing transition insert materials used in LNG carriers.

A composite member made by bonding aluminum alloy and stainless steel is usually used as the transition insert material. Since such composite parts cannot be manufactured by fusion welding,
Diffusion welding may be applied, but since the surface oxide of aluminum is very strong, it is difficult to weld not only aluminum and steel, but also diffusion welding between aluminum. Also, it is necessary to raise the diffusion welding temperature to just below the melting point of the aluminum base material. By the way, in joining dissimilar materials between aluminum and steel,
When the welding temperature is increased as described above, a brittle Al-Fe intermetallic compound is generated at the joint.
It is not possible to form a joint with sufficient reliability. Figure 1 shows the tensile test results of a joint obtained by conventional diffusion welding.As shown in the figure, when the diffusion welding temperature is low, the joint strength is almost equal to zero, and when the welding temperature is increased. It is clear that the bonding strength varies over a wide range. In addition, Fig. 2 shows the specimen used for the above-mentioned tensile test, and the dimensions of each part in this case are d1 = 15 mm, d2 = 10 mm, r = 15 mm, l
=25mm is used.

For the reasons mentioned above, transition insert materials are mainly manufactured by explosive welding, and as a result, they are very expensive, despite the economical advantages of diffusion welding. That is the reality. Moreover, in explosive welding, there are restrictions on the types of aluminum alloys etc. that can be used.
The disadvantage is that it is not possible to use any material of choice. Furthermore, due to the limitations on the thickness of plates that can be pressure-welded, it is not possible to manufacture transition insert materials with the desired thickness, and as a result, assembly and welding work is required on-site while taking heat conduction to the joint surfaces into consideration. There are also work-related problems in having to do this.

This invention was made in view of the above, and its purpose is to provide a good joint strength when joining a soft metal made of aluminum or an aluminum alloy to a hard metal such as stainless steel, and to be economical. Another object of the present invention is to provide a method for joining dissimilar materials, which is not limited by the type of alloy or its thickness, and is therefore suitable for manufacturing composite materials such as transition insert materials.

The dissimilar metal joining method of the present invention, which meets the above object, is a dissimilar metal joining method in which both a hard metal and a soft metal made of aluminum or its alloy are joined in a solid state. By cutting and removing the side surface layer, a new surface is formed on the soft metal, and this new surface is continuously coated with the bonding surface of the hard metal during the cutting and removal work and even after the work is finished. The joining surface of the hard metal and the new surface of the soft metal are pressure-welded under a temperature condition of less than 500° C., thereby preventing oxygen contact with the new surface until the end of the joining. Become something.

As mentioned above, the oxide film on the aluminum surface, which is difficult to remove, is removed by using a hard metal edge to form a new surface, and the two are pressed together without the new surface ever coming into contact with air. This makes it possible to bond at a lower temperature than conventional diffusion bonding, and also prevents the formation of intermetallic compounds, resulting in good joint strength. Furthermore, since the construction is such that the work of creating a new surface using a hard metal edge and the subsequent press-welding work of the joint surfaces are performed as a continuous series of work, highly efficient joining work can be performed.

Next, specific embodiments of the dissimilar material joining method of the present invention will be described in detail with reference to the drawings.

First, FIGS. 3a, 3b, and 3c show a hard metal block 1, which has a generally rectangular parallelepiped shape and is made of, for example, stainless steel (SUS304). Tapered portions 2 and 3 are formed on both sides of the block 1 in the longitudinal direction, and are inclined inward toward the bottom.
Also, on the bottom part, there is a cutout part 4 that curves upward in an arc shape.
is formed. As a result, the lower ends of each of the tapered parts 2 and 3 have acute-angled edges 5 and 6, respectively.
will be formed. As will be described later, each of the tapered portions 2 and 3 serves as a bonding surface with a soft metal, and has a smooth surface finish. In this case, the specific dimensions of block 1 are length L1 = 38, thickness H1 = 25, and upper width W1.
= 30, the distance between the edges 5 and 6 w1 = 26, and the depth P1 of the cut portion 4 = 5 (all in mm).

On the other hand, soft metal block 7 is shown in Fig. 4 a, b, and c.
The soft metal block 7 has a substantially rectangular parallelepiped shape, and is made of aluminum alloy (A5083). A tapered portion 8 is formed on one side, and the tapered portion 8 slopes outward toward the bottom.
A concave groove 9 having an inverted triangular cross section and extending in the longitudinal direction is formed near the . The specific dimensions of this block 7 are: length L2 = 40, thickness H2 = 40, upper width W2 = 42, lower width W2 = 45.2, groove width W3 =
2. The depth of the groove P2 is 2, and the distance L3 between the center of the groove and the upper edge of the tapered portion is 2 (all in mm).

FIG. 5 shows an example of a jig used to join the blocks 1 and 7 described above. This jig 10
has four side walls 12, 12, 13, 13 removably assembled with an appropriate number of bolts 11, and one rigid A metal block 1 and two soft metal blocks 7, 7 are arranged. That is, as shown in the figure, each soft metal block 7,
The tapered portions 8 of 7 are arranged to face each other, and the hard metal block 1 is placed above them, and the edges 5 and 6 of the hard metal block 1 are inserted into the respective grooves 9 and 9 of the soft metal blocks 7 and 7. I'm going to put it in there.

Bonding is performed in the above state, and the process will be explained below.

First, set each block 1, 7, 7 to the state shown above.
Place the jig 10 set in the chamber (not shown).
The atmosphere is maintained at a vacuum of about 10 ^-4 Torr.

Next, each block is heated, but the heating temperature is
It is preferably less than 500°C, particularly within the range of 250°C to 450°C. Then, in the heated state, pressure is applied to the hard metal block 1 to push it down. At this time, as the block 1 descends, the edges 5 and 6 of the block 1 move into the tapered portions of the soft metal blocks 7 and 7. As a result, a new surface is formed on the soft metal blocks 7, 7, and this new surface comes into close contact with the surfaces of the tapered portions 2, 3 of the hard metal block 1. In addition, the required pressure P in the above is P = 21.5 tons when the heating temperature is 300°C, P = 20.3 tons when the heating temperature is 350°C, and P = when the heating temperature is 400°C.
In the case of 15.6 tons and 450 degrees Celsius, P=12.6 tons, which gradually decreases as the heating temperature increases.

A new surface is formed on the soft metal block 7 as described above, and when this new surface comes into contact with the tapered parts 2 and 3 that will become the joint surfaces of the hard metal block 1, the pressing force is reduced, and in this state, Hold. In this case, the required holding force is the above-mentioned pressing force P
It is about 1/6 of that. and hold it in this state
Diffusion welding between the two is completed by performing the process for about 30 minutes to 1 hour and then cooling.

FIG. 6a shows the metal structure of both blocks before they are joined, and FIG. 6b shows the metal structure after they are joined. Further, the results of the tensile test of the joint obtained in the above manner are shown in FIGS. 7 and 8. In addition, Fig. 7 shows that a triangular waveform is formed at the tip of the stainless steel in order to destroy the surface oxide of the aluminum and increase the contact area between the stainless steel and the aluminum, and this waveform is applied inside the aluminum. The graph shows the tensile strength of the joint when it is heated while being pushed into the joint. Further, the tensile test in the above examples was conducted in the following manner.
In other words, when a tensile test is performed on a tensile test piece whose center part is made of stainless steel (SUS304) and both ends are made of aluminum alloy (A5083), one joint surface between the aluminum alloy and stainless steel breaks, but after that, A tensile test was also conducted on the other bonded surface to determine the tensile strength of the two bonded surfaces. Therefore, the data on the low strength side in Figure 7 shows the tensile strength of one joint surface that broke first, and the data on the high strength side shows the tensile strength of the remaining joint surface that broke later. . As is clear from FIGS. 7 and 8, it is clear that the above diffusion welding method significantly improves the joint strength compared to the conventional method and the above-mentioned improved method. be. By the way, the normal temperature tensile strength of the explosive bonded clad material made by explosively welding aluminum alloy (A3003) to stainless steel (SUS304) using titanium (Ti) as an insert material is approximately 19 Kgf/mm ² (A3003 base metal fracture). , and an explosion-bonded clad material made of stainless steel (SUS304), an aluminum alloy (A1050) with nickel (Ni) and titanium (Ti) inserted as insert materials, and an aluminum alloy (A5083) on top of it. Tensile strength is approximately 16.5
Kgf/mm ² (A1050 base metal fracture), but when comparing these data with the example data shown in Figure 8, it can be seen that according to the example method, a tensile strength not much different from that of the explosive crund material can be obtained. it is obvious. In Fig. 8 above, the joint strength at a heating temperature of 500°C is significantly reduced, but because this is a high temperature, the reaction of Al-Fe between the new surface of aluminum and the joint surface of stainless steel is rapid. The reasons for this are thought to be that a large amount of intermetallic compounds are formed and that the yield point of aluminum decreases as the temperature rises, resulting in a decrease in the pressure applied during bonding. Therefore, at temperatures in this vicinity, it is possible to improve the strength by shortening the holding time, restraining the aluminum from above and below, and applying pressure from the sides.

A specific example of manufacturing a transition insert material (A5083+SUS304) using the above joining method will be described below. In this case, as shown in FIG. 9, blocks 1 and 7 having the same cross-sectional shape as above but slightly longer are used. The thickness of the blocks 1 and 7 is set to be slightly larger than 150 mm, and the length is set to about 500 mm, and a new surface is formed at a heating temperature of 300° C. and a pressing force of P=283 tons, and the two are joined together. Next, as shown in FIG. 10, the joined composite material is cut as shown by broken lines to produce a transition insert material as shown in FIG. 11. In this case, in order to increase the thickness of the transition insert material, the above-mentioned block 1,
It is only necessary to increase the width of 7, and there is no need to change the bonding conditions or the like. The hard metal block 1 used in the above may be formed integrally as described above, or may include a wedge-shaped plate 15 inserted between a pair of hard metal plates 14, 14, as shown in FIG. It is also possible to form it by.

Although one embodiment of the dissimilar material joining method of the present invention has been described above, the dissimilar material joining method of the present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, in the above example, in order to generate welding pressure, the joint surfaces at two locations were not parallel, but tapers were provided, and this was restrained from all sides with a jig. It is also possible to press the button. In addition, although the above examples show transition insert materials using aluminum alloy as the soft metal and stainless steel as the hard metal, the types of metals and the applications of the products are not limited to these. . For example, we used mild steel (SM41A) as the hard metal and aluminum alloy (A5083) as the soft metal, welded them at a joining temperature of 300°C, and performed a tensile test on this joint, but the fracture occurred in the aluminum alloy base material. Ta. The tensile strength in this case is 31.9 Kgf/mm ² , and it is clear from this that the strength of the diffusion welded joint between mild steel and aluminum alloy by the method of the present invention is higher than the above value at both interfaces. In addition, stainless steel (SUS304) was used as the hard metal, and pure aluminum (A1050) was used as the soft metal, and the joints were joined at a joining temperature of 300°C and tensile tests were conducted. Occurred in wood. The tensile strength in this case is 8.1 Kgf/mm ² , and from this it is clear that the strength of the diffusion welded joint between stainless steel and pure aluminum by the method of the present invention is higher than the above value at both interfaces. Furthermore, in the examples, the formation and bonding of a new surface are performed in a vacuum, but the formation and bonding of a new surface can also be performed in an atmosphere other than the vacuum as described above, such as an inert gas or air. is possible. Furthermore, in the above case, 250
Although the new surface is formed by heating to ~500℃,
This may be done by forming a new surface at room temperature and then heating it to a desired temperature. In this case, if the jig of the embodiment is used, it is possible to expect the generation of pressing force due to thermal expansion of each block due to heating. Of course, there are cases where this heating for bonding is not necessary. In addition, in order to form a new surface as described above, it is not necessary to provide an acute edge as described above on the hard metal side.In short, it is sufficient to have an edge that can remove the surface layer of the soft metal. Similarly, the tapered portions and the grooves on the soft metal side may be omitted.

In the dissimilar metal joining method of the present invention, the oxide film surface of aluminum or its alloy, which is soft and difficult to remove, is removed at the edge of the hard metal joining surface to create a new surface of the aluminum alloy, and the subsequent hard metal By applying pressure on the joining surfaces on the metal side, we have adopted a configuration in which the newly formed surface of the soft metal is joined to the air without ever coming into contact with the air.
Bonding can be performed at lower temperatures than conventional diffusion bonding, and good joint strength can be obtained. Furthermore, since the construction is such that the work of creating a new surface using a hard metal edge and the subsequent press-welding of the joint surfaces are performed as a continuous series of work, highly efficient joining work can be performed. Moreover, restrictions on the type of alloy and its plate thickness are significantly relaxed compared to the past.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the joint strength obtained by conventional diffusion bonding, Fig. 2 is an explanatory diagram of the shape of the test piece used in the above, and Fig. 3 is an example of the hard metal block used in implementing the method of this invention. In the diagram shown,
a is a plan view, b is a front view, c is a side view, and FIG. , FIG. 5 is a perspective view showing an example of a joining jig used in carrying out the method of the present invention and the arrangement of the blocks described above, FIG. 6 a is a diagram showing the metallographic structure of each block in a state before joining, Fig. 6b is a diagram showing the metal structure of both blocks after joining, Fig. 7 is a graph showing the joint strength obtained by the above joining method in comparison with other joining methods, and Fig. 8 is a graph showing the joint strength obtained by the above joining method. Graphs showing the joint strength obtained by the method, Figures 9 to 11 are explanatory diagrams of the manufacturing process of the transition insert material, Figure 9 shows the arrangement of both blocks, and Figure 10 shows the cutting. FIG. 11 shows a state in which manufacturing is completed, and FIG. 12 is an explanatory diagram of a modified example of the hard metal block used in the above. 1... Hard metal block, 5, 6... Edge,
7...Soft metal block.

Claims (1)

[Claims] 1. In a dissimilar metal joining method that joins both a hard metal and a soft metal made of aluminum or its alloy in a solid state, by cutting and removing the surface layer on the soft metal side at the edge of the joint surface of the hard metal. A new surface is formed on the soft metal, and even during the cutting and removal operations described above, this new surface is
In addition, even after the work is completed, the bonding surfaces of the hard metal and the new surface of the soft metal are continuously pressed together, thereby preventing oxygen contact with the new surface until the end of the bonding. 500℃
A method of joining dissimilar materials characterized by pressure welding under temperature conditions below.