JP3445579B2 - Bonding structure between dissimilar metal hollow members and bonding method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining structure between hollow members made of different metals and a joining method thereof, and particularly to abutting the end faces of an Al alloy hollow member and a steel hollow member with each other. The present invention relates to a structure for joining by friction welding and a joining method thereof.

[0002]

2. Description of the Related Art In recent years, vehicles, especially automobiles, have been further reduced in weight in order to improve fuel efficiency. Therefore, power transmission means for vehicles, such as transmissions, axle shafts, propeller shafts, etc. In the same manner, the weight reduction is also attempted.

In these power transmission means, a hollow member is used, and an aluminum base is formed of a hollow member made of steel.
Hollow members (pipes) made of alloy are joined to achieve a significant weight reduction.

There are various methods for joining the end faces of the Al alloy hollow member and the steel hollow member, but one of them is the joining of the end faces of the hollow members. There is a method of joining the parts by friction welding.

[0005]

By the way, when an Al alloy hollow member and a steel hollow member are joined using this friction welding, a brittle metal is formed at the joining interface, especially at the center of the thickness of the joining interface. An intermetallic compound such as Fe ₃ Al is produced, and a heat-affected zone that softens the Al alloy, that is, an oxide and a softened layer produced in the friction process remain. For this reason, in the joining between dissimilar metal materials by friction welding, since the joining strength at the central portion of the wall thickness is low, the joining strength is higher than that between Al alloy materials by friction welding, that is, between similar metal materials. There was a problem that was inferior.

Here, by defining the friction welding conditions,
A method for improving the bonding strength between dissimilar metal materials has been proposed. However, even in this case, there is a problem that it is inevitable that intermetallic compounds, oxides, and the like remain at the bonding interface, particularly at the central portion of the thickness of the bonding interface.

The object of the present invention, which was devised in consideration of the above circumstances, is a joining structure between hollow members of different kinds of metals, in which intermetallic compounds and oxides hardly remain at the joining interface and the joining strength is good. And to provide a joining method thereof.

[0008]

In order to achieve the above object, the joining structure between different metal hollow members according to the present invention is such that the end faces of an Al alloy hollow member and a steel hollow member are butted and the butted end faces are made to come together. In a structure in which the above are joined by friction welding, a slope angle is 1 at the abutting end surface of the steel hollow member from the central portion of the wall thickness to the inner peripheral surface portion and the outer peripheral surface portion.
A downward slope of 5 ° or less is formed.

According to the above construction, the thick center portion of the abutting end surface of the steel hollow member and the thick center portion of the abutting end surface of the Al alloy hollow member are surely butted.

On the other hand, according to the method for joining dissimilar metal hollow members according to the present invention, a downward slope having a slope angle of 15 ° or less is formed on the end face of the steel hollow member from the central portion of the wall thickness to the inner peripheral surface portion and the outer peripheral surface portion. Is formed, and the end surface of the steel hollow member having the descending slope and the flat end surface of the Al alloy hollow member are abutted, and the abutted end surfaces are joined by friction welding.

According to the above method, the end surface of the hollow member made of steel and the flat end surface of the hollow member made of Al alloy are butted against each other and frictionally welded to each other, whereby an intermetallic compound or Since almost no oxides remain,
Good bonding strength.

At the time of the above-mentioned butting, it is preferable to rotate at least one of the steel hollow member and the Al alloy hollow member while applying pressure.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a vertical cross-sectional view of the joining structure of the different metal hollow members according to the present invention before joining, and FIG. 1 is a vertical cross-sectional view of the joining structure of the different metal hollow members according to the present invention after joining. Is shown in FIG. Here, FIG. 1B is an enlarged view of the main part A of FIG.

In order to improve the pressure contact property between the aluminum alloy hollow member and the steel hollow member, generation of a heat-affected zone due to friction welding and an intermetallic compound such as Fe ₃ Al at the joint interface are reduced. Since it is important to do so, attention was paid to the shapes of the abutting end faces (joint end faces) of the aluminum alloy hollow member and the steel hollow member.

That is, as shown in FIGS. 1 (a) and 1 (b), the joining structure between different metal hollow members according to the present invention is made of Al.
The hollow member 1 made of an alloy and the end face 1a of the hollow member 2 made of steel in which a downward slope S having a slope angle θ of 15 ° or less is formed on the end face 2a from the thickness center portion 3 to the inner peripheral surface portion 4 and the outer peripheral surface portion 5, Two
a is abutted against each other, and the abutted end faces 1a, 2a
The two are joined by friction welding. That is, in the end surface 2a of the steel hollow member 2 in the joining structure of the present invention, as shown in FIG. 1 (b), the wall thickness central portion 3 projects by a height H from the inner peripheral surface portion 4 and the outer peripheral surface portion 5. It is a ridge.

The slope angle of the down slope S is not particularly limited as long as it is 15 ° or less, but is preferably 3 to 12.
°, more preferably 6 to 12 °, particularly preferably 10 °
Before and after.

Here, the gradient angle θ of the downward gradient S is 15 °
What is limited to the following is that if the inclination angle θ is larger than 15 °, the protruding height H at the end face 2a of the steel hollow member 2 becomes high, and during friction welding, the Al alloy material at the joint interface becomes the inner peripheral surface portion 4. This is because slip deformation easily occurs on the side and the outer peripheral surface portion 5 side. As a result, it becomes impossible to secure a residence time (friction time) for heating the Al alloy material to a temperature necessary for friction welding, resulting in poor press contact property.

According to the joining structure between hollow members of different metals according to the present invention, a gradient angle θ is provided on the end face 2a of the steel hollow member 2 from the central portion 3 of the wall thickness to the inner peripheral surface portion 4 and the outer peripheral surface portion 5. By forming the descending gradient S of 15 ° or less, the metal components generated at the joint interface between the Al alloy hollow member 1 and the steel hollow member 2 and in the vicinity thereof at the time of joining by friction welding (most of them are metal). The intermetallic compound and the oxide and the softening layer generated in the friction step are easily slip-deformed along the end surface 2a of the steel hollow member 2.

Further, in the conventional joining structure, the metal component near the central portion of the thickness of the joining interface is prevented from sliding deformation by the metal components on the inner peripheral surface side and the outer peripheral surface side of the joint interface.
Often remained at the bonding interface. On the other hand, in the joining structure according to the present invention, in order to positively join the thick center portion, which was not so good in the past, the metal component in the vicinity of the thick center portion 3 at the joining interface is also At the time of friction welding, the member 2 is scraped off by the central portion 3 (protruding portion) of the wall thickness, and is slid along the end surface 2a of the member 2 and toward the inner peripheral surface portion 4 side and the outer peripheral surface portion 5 side. At this time, the steel hollow member 2 is the Al alloy hollow member 1
Since it is harder than the above, the raised portions are hardly worn by the friction welding, and the scraping is surely performed.

Therefore, in the joining structure according to the present invention, the metal component in the vicinity of the joining interface including the metal component in the vicinity of the thickness center portion 3 is slipped and deformed along the end face 2a of the member 2 and the peripheral edge portion of the joining interface is formed. Is pushed out, as shown in FIG.
It is discharged as burr 20. As a result, at the bonding interface between the members 1 and 2, the newly-formed surface, that is, the alloy surface that is not affected by heat is always exposed, and as a result, the pressure contact property is improved and the bonding strength is improved. Here, even in the joining structure according to the present invention, the softening layer is present at the joining interface, but the layer thickness is significantly smaller than the layer thickness of the softening layer in the conventional joining structure, and as a result, the joining strength is improved. Will be done.

Further, on the end face 2a of the member 2, from the thick central portion 3 toward the inner peripheral surface portion 4 and the outer peripheral surface portion 5, respectively,
By forming the descending slope S having the slope angle θ of 15 ° or less, the burr 20 is evenly discharged to the peripheral edge portions on the inner peripheral surface side and the outer peripheral surface side at the joint interface between the members 1 and 2. As a result, it contributes to the improvement of the reliability of the joint interface between the members 1 and 2, particularly the torsional fatigue strength.

Next, a method for joining dissimilar metal hollow members according to the present invention will be described with reference to FIGS.

First, the steel hollow member 2 (or Al alloy hollow member 1) for friction welding is rotated and increased until the rotation speed reaches a predetermined rotation speed r1 (step 31).
After that, while increasing the friction pressure until the pressure reaches a predetermined pressure P1 (step 34), a predetermined time (friction time)
The end surfaces 1a and 2a of the hollow members 1 and 2 are butted against each other and pressed against each other over T1, and the bonding interface is heated to a temperature required for pressure welding. This process is a friction process. At this time, both the members 1 and 2 may be rotated in opposite directions, and the relative number of rotations of the members 1 and 2 may be set to r1.

Next, after the friction process is completed, the rotation is stopped to make the rotation speed zero (step 32), and the pressure is increased until the pressure reaches a predetermined pressure P2 (step 3).
5) Upset pressure is applied to the end surfaces 1a and 2a of the hollow members 1 and 2 for a fixed time (upset time) T2. This process is an upset process. By this upsetting process, the intermetallic compounds, oxides, softening layers, etc. generated at the bonding interface in the friction process are discharged as burrs 20 from the peripheral edge of the bonding interface, and the new surfaces of the bonding interfaces of the members 1 and 2 are joined together. Are joined.

Here, factors affecting the pressure contact property of the friction pressure contact include the height of the rotation speed r1, the magnitudes of the friction pressure P1 and the upset pressure P2, the friction time T1, the length of the upset time T2, and the like. . The rotation speed r1 is too high,
If the friction pressure P1 is too large or the friction time T1 is too long, the joint interface is overheated, and the generation of metal components (intermetallic compound, oxide, and softening layer) at the joint interface and its vicinity is increased. This causes deterioration of the pressure contact property.

In order to improve the pressure contact property of the friction pressure welding, it is important how quickly the metal component is discharged to the peripheral portion of the bonding interface during the friction process and the upsetting process. If this discharge property is not good, the metal component will remain at the bonding interface.

In the present invention, in order to improve this discharge property, the end face (friction pressure welding joining face) 2a of the hollow steel member 2 is formed.
In addition, a downward slope S having a slope angle θ of 15 ° or less is formed from the thickness center portion 3 to the inner peripheral surface portion 4 and the outer peripheral surface portion 5.

Therefore, at the start t1 of the friction process, the contact between the end faces 1a and 2a of the members 1 and 2 is point contact and the "twist" (contact area) is zero. By pressing the thick central portion 3 of the end surface 2a of the member 1 against the end surface 1a of the member 1 at the rotational speed r1 and the friction pressure P1, the margin gradually increases, and at the end of the friction step (at the start of the upset step) t2. Is more than A1
(It is more than friction). Also, in the upset process,
The twist amount gradually increases, and at the time t3 at the end of the upset process, the twist amount becomes A2 (total twist amount).

At the time of increasing the twist, the metal component in the vicinity of the joint interface and in the vicinity thereof, and in the vicinity of the central portion of the wall thickness, becomes a member 2
The central portion 3 (protruding portion) is continuously scraped to the inner peripheral surface portion 4 side and the outer peripheral surface portion 5 side. The metal component scraped off continuously along the end face 2a of the member 2
Further, the inner peripheral surface portion 4 side and the outer peripheral surface portion 5 side are continuously slip-deformed and rapidly discharged to the peripheral edge portion of the bonding interface.

Therefore, according to the method of joining different kinds of metal hollow members according to the present invention, the metal component of the metal component during friction welding is formed by the downward slope S formed on the end face 2a of the member 2 having a slope angle θ of 15 ° or less. It is easily and quickly discharged to the peripheral edge of the bonding interface, and hardly remains at the bonding interface. Further, this descending slope S is effective for discharging the metal component to the peripheral portion of the bonding interface, and as a result, is also effective for always exposing the new surface at the bonding interface of each member 1, 2. . As a result, the pressure contact property by the friction pressure contact is improved, and the joint strength between the members 1 and 2 is improved.

[0032]

Example 1 As an aluminum alloy hollow member, an A having an outer diameter of 101.6 mm, an inner diameter of 96.6 mm and a length of 30 mm was used.
l Alloy pipe (A6061) is used as a steel hollow member and has an outer diameter of 1
Friction welding is performed between dissimilar metal hollow members using a carbon steel pipe for general structure (JIS STK400) having a diameter of 01.6 mm, an inner diameter of 95.2 mm and a length of 55 mm. Here, the joint end surface of the general structural carbon steel pipe is formed with a downward slope having a slope angle of 10 ° from the central portion of the wall thickness to the inner peripheral surface portion and the outer peripheral surface portion. Also,
Friction welding is 1500 rpm, friction pressure 4 kgf / mm ²
(About 39.2MPa), upset pressure 10kgf / mm ² (about 98MPa
a), the friction time was 0.3 seconds, and the upset time was 6 seconds. (Comparative Example 1) Friction welding is performed under the same conditions as in Example 1 except that the joining end face of the carbon steel pipe for general structure is made flat without forming a downward slope.

Joining structure of Example 1 (hereinafter, joining surface angle 8
Various tests were performed on the joint structure of 0 °) and the joint structure of Comparative Example 1 (hereinafter, referred to as a joint structure with a joint surface angle of 90 °) to evaluate the pressure contact property.

Tensile strength (kgf / mm ² (MPa)) was measured for a joint structure having a joint surface angle of 80 ° and a joint structure having a joint surface angle of 90 °. As a result,
As shown in, the joint structure with the joint surface angle of 90 ° has a tensile strength of 18 to 22 kgf / mm ² (about 176.4 to 215.6M).
Pa), average tensile strength is 20.5kgf / mm ² (about 200.9MPa)
Met. On the other hand, in the joint structure with the joint surface angle of 80 °, the tensile strength is 24 to 26 kgf / mm ² (about 235.2
~ 254.8MPa), average tensile strength is 25kgf / mm ² (about 245MPa)
a), and compared with a joint structure with a joint surface angle of 90 °,
The tensile strength is improved by 20% or more.

Further, of the joint interfaces fractured by the tensile test, the amount (%) of Al adhered to the joint interfaces on the carbon steel pipe side was evaluated. as a result,
As shown in FIG. 5, in the joint structure with the joint surface angle of 90 °, Al was hardly attached to the joint interface on the carbon steel pipe side. From this, it is understood that in the joint structure with the joint surface angle of 90 °, the Al alloy and the carbon steel are hardly fused at the joint interface. On the other hand, in the joint structure with the joint surface angle of 80 °, Al adheres to the joint interface on the carbon steel pipe side in an amount of about 100%. Therefore, in the joint structure with the joint surface angle of 80 °, the joint interface It can be seen that the Al alloy and the carbon steel are almost completely fused.

Further, the joint structure with the joint surface angle of 80 ° and the joint structure with the joint surface angle of 90 ° are cut in the long axis direction, and the hardness (HV) in the vicinity of the joint interface is measured, and the hardness decreasing portion in the vicinity of the joint interface. The width (mm) of (softening layer) was examined. As a result, as shown in FIG. 7, the joint surface angle is 90 °.
In the joint structure of No. 3, the width of the softening layer that inhibits the improvement of the joint strength at the joint interface was 2.5 mm. On the other hand, in the joint structure with the joint surface angle of 80 °, the width of the softening layer is 2.0 mm, and compared with the joint structure with the joint surface angle of 90 °, the width of the softening layer, that is, the layer thickness is 20 mm. % Is also thin. This is one of the reasons why the tensile strength shown in FIG. 4 is improved.

It is needless to say that the embodiments of the present invention are not limited to the above-mentioned embodiments but various other embodiments are possible.

[0038]

In summary, according to the present invention, the end face of the hollow member made of steel and the flat end face of the hollow member made of Al alloy are butted against each other and friction welded to each other so that the metal is bonded to the joining interface. The excellent effect that a joint structure between hollow members of different metals with almost no residual intermetallic compound or oxide can be obtained is exhibited.

[Brief description of drawings]

FIG. 1 is a longitudinal cross-sectional view of a joining structure between dissimilar metal hollow members according to the present invention before joining.

FIG. 2 is a vertical cross-sectional view showing a state after joining of the joining structure between dissimilar metal hollow members according to the present invention.

FIG. 3 is a diagram showing a pressure welding cycle in friction pressure welding.

FIG. 4 is a diagram showing the tensile strength of the joint structures of Example 1 and Comparative Example 1.

5 is a diagram showing a degree of Al adhesion at a bonding interface in the bonding structures of Example 1 and Comparative Example 1. FIG.

6 is a diagram showing hardness in the vicinity of a joint interface in the joint structure of Example 1. FIG.

7 is a diagram showing hardness in the vicinity of a joint interface in the joint structure of Comparative Example 1. FIG.

[Explanation of symbols]

1 Al alloy hollow member 1a end face 2 Steel hollow member 2a end face 3 Thickness center part (protrusion) 4 Inner surface 5 outer peripheral surface θ gradient angle S down slope

Continuation of the front page (56) Reference JP-A 63-97381 (JP, A) JP-A 7-40065 (JP, A) JP-A 2000-301364 (JP, A) JP-A 2000-288747 (JP, A) ) JP-A-58-61987 (JP, A) JP-A-48-76761 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B23K 20/12

Claims (3)

(57) [Claims] 1. In a structure in which the end faces of an Al alloy hollow member and a steel hollow member are butted against each other and the butted end faces are joined by friction welding, the butted end faces of the above hollow steel members are joined from the center of the wall thickness. A joint structure between hollow members of different metals, characterized in that a downward slope having a slope angle of 15 ° or less is formed over the inner peripheral surface portion and the outer peripheral surface portion. 2. A steel hollow member having a downward slope having an inclination angle of 15 ° or less from the central portion of the wall thickness to the inner peripheral surface portion and the outer peripheral surface portion on the end surface of the steel hollow member. A method for joining dissimilar metal hollow members, characterized in that the end faces and the flat end faces of the Al alloy hollow member are abutted, and the abutted end faces are joined by friction welding. 3. The method for joining dissimilar metal hollow members according to claim 2, wherein at the time of the butting, at least one of the steel hollow member and the Al alloy hollow member is rotated while applying pressure.