JP2002224857A - Joining structure and joining method between hollow members made of respectively different kinds of metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joining structure and a joining method between hollow members made of respectively different kinds of metals in which an intermetallic compound and oxide or the like hardly remain in the joined boundary and joining strength is excellent. SOLUTION: In the joining structure between the hollow members of different kinds of metals, wherein the end face 1a of A1 alloy-made hollow member 1 is butted against the end face 2a of steel-made hollow member 2 each other and the butted end face 1a is joined to the butted end face 2a by friction welding each other, down gradients S that the gradient angle θ of which is 15 deg. or less are formed over from the center of the thick part 3 to the inner peripheral part 4 and the outer peripheral part 5 in the butted end face 2a of the steel-made hollow member 2.

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 different kinds of metal hollow members and a joining method thereof, and more particularly, to joining end surfaces of an aluminum alloy hollow member and a steel hollow member, and joining the joined end surfaces. The present invention relates to a structure joined 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 and the like. Therefore, power transmission means for vehicles, such as transmissions, axle shafts, propeller shafts, etc. In such cases, weight reduction is also achieved.

[0003] In these power transmission means, a hollow member is used, and an Al base is formed on a base made of a steel hollow member.
By joining hollow members (pipe) made of alloy, significant weight reduction is achieved.

Here, there are various methods for joining the end surfaces of the aluminum alloy hollow member and the steel hollow member. One of the methods is to join the end surfaces of the hollow members to each other. And joining the parts by friction welding.

[0005]

When an aluminum alloy hollow member and a steel hollow member are joined by using this friction welding, a brittle metal is formed at the joining interface, particularly at the center of the joining interface in the thickness direction. An intermetallic compound, for example, Fe ₃ Al is generated, and a heat affected zone that softens the Al alloy, that is, an oxide or a softened layer generated in a friction process remains. For this reason, in joining between dissimilar metal materials by friction welding, since the joining strength at the thick central portion is low, compared with joining between Al alloy materials by friction welding, that is, joining between similar metal materials, the joining strength is higher. 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 center of the thickness of the bonding interface.

SUMMARY OF THE INVENTION An object of the present invention, which has been made in view of the above circumstances, is that an intermetallic compound, an oxide, or the like hardly remains at a joint interface, and a joint structure between dissimilar metal hollow members having good joint strength. And a joining method thereof.

[0008]

In order to achieve the above object, a joining structure between dissimilar metal hollow members according to the present invention comprises an aluminum alloy hollow member and a steel hollow member whose end faces are joined to each other, and the joined end faces are joined to each other. Are joined by friction welding, the slope angle of the butt end face of the steel hollow member from the center to the inner peripheral surface and the outer peripheral surface is 1
A downward gradient of 5 ° or less is formed.

According to the above configuration, the center of the thickness of the butted end face of the hollow member made of steel and the center of the thickness of the butted end face of the hollow member made of Al alloy are securely butted.

On the other hand, the method for joining dissimilar metal hollow members according to the present invention is characterized in that a slope angle of 15 ° or less is applied to the end surface of the steel hollow member from the thick central portion to the inner peripheral surface portion and the outer peripheral surface portion. The end face of the hollow member made of steel having a downward slope and the flat end face of the hollow member made of Al alloy are butted, and the butted end faces are joined by friction welding.

According to the above method, the end surface of the steel hollow member having the thick central portion raised and the flat end surface of the Al alloy hollow member are abutted and friction-welded, whereby an intermetallic compound or Since oxides and the like hardly remain,
Good bonding strength.

Further, at the time of the 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 EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing a state before joining a joining structure between dissimilar metal hollow members according to the present invention, and FIG. 1 is a longitudinal sectional view showing a state after joining the joining structure between dissimilar metal hollow members according to the present invention. Is shown in FIG. Here, FIG. 1B is an enlarged view of a main part A of FIG. 1A.

In order to improve the pressure contact property between the aluminum alloy hollow member and the steel hollow member, the generation of a heat affected zone and the generation of an intermetallic compound such as Fe ₃ Al due to friction welding at the joining interface are reduced. Since it is important to perform this, attention was paid to the shape of the butted end surface (joining end surface) 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 kinds of metal hollow members according to the present invention is
The end surface 1a of the hollow member 1 made of alloy and the end surface 1a of the hollow member 2 made of steel in which the end surface 2a has a downward slope S having a slope angle θ of 15 ° or less extending from the thick central portion 3 to the inner peripheral surface portion 4 and the outer peripheral surface portion 5. 2
a, butted end faces 1a, 2a
These are joined by friction welding. That is, in the end surface 2a of the steel hollow member 2 in the joint structure of the present invention, as shown in FIG. 1B, the thick central portion 3 protrudes by the height H from the inner peripheral surface portion 4 and the outer peripheral surface portion 5. It is a ridge.

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

Here, the inclination angle θ of the descending gradient S is 15 °.
The limitation is as follows: When the gradient angle θ is larger than 15 °, the protruding height H at the end face 2a of the steel hollow member 2 increases, and during friction welding, the Al alloy material at the joining interface becomes less than the inner peripheral surface portion 4. This is because slip deformation easily occurs on the side and the outer peripheral surface 5 side. As a result, a dwell time (friction time) for heating the Al alloy material to a temperature required for friction welding cannot be secured, and the weldability deteriorates.

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

Further, in the conventional joining structure, the metal components near the center of the thickness of the joining interface are prevented from sliding deformation by the metal components on the inner peripheral surface side and the outer peripheral surface side of the joining interface.
It 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 central portion, which was not so good in the past, the metal component near the thick central portion 3 at the joining interface is also At the time of friction welding, the member 2 is squeezed by the thick central portion 3 (raised portion), and slides along the end surface 2a of the member 2 toward the inner peripheral surface portion 4 and the outer peripheral surface portion 5 side. At this time, the hollow member 2 made of steel is replaced with the hollow member 1 made of Al alloy.
Since it is harder, the raised portion hardly wears due to friction welding, so that it can be surely separated.

Therefore, in the joint structure according to the present invention, the metal component near the joining interface including the metal component near the thick central portion 3 slides and deforms along the end face 2a of the member 2 and the peripheral portion of the joining interface. , And as shown in FIG.
It is discharged as burrs 20. As a result, at the joining interface between the members 1 and 2, a new surface, that is, an alloy surface that has not been affected by heat is always exposed, so that the pressure contact property is good and the joining strength is improved. Here, also in the joint structure according to the present invention, a softening layer is present at the joint interface, but the layer thickness is significantly smaller than the layer thickness of the softening layer of the conventional joint structure, and as a result, the joining strength is improved. Will do.

Further, on the end surface 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 downward gradient S having the gradient angle θ of 15 ° or less, the burrs 20 are uniformly discharged to the inner peripheral surface side and the outer peripheral surface side of the joining interface between the members 1 and 2. As a result, it contributes to the improvement of the strength of the joint interface between the members 1 and 2, particularly the reliability of 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 the Al alloy hollow member 1) for performing friction welding is rotated and raised until the rotation speed reaches a predetermined rotation speed r1 (step 31).
Thereafter, while increasing the friction pressure until the pressure reaches the predetermined pressure P1 (step 34), a constant time (friction time)
Over T1, the end surfaces 1a and 2a of the hollow members 1 and 2 are pressed against each other and pressed to heat the bonding interface to a temperature required for pressure welding. This step is a friction step. At this time, both the members 1 and 2 may be rotated in opposite directions, and the relative rotation speed of the members 1 and 2 may be set to r1.

Next, after the end of the friction step, the rotation is stopped to reduce the number of rotations to zero (step 32), and the pressure is increased while the pressure reaches a predetermined pressure P2 (step 3).
5) An upset pressure is applied to the end surfaces 1a and 2a of the hollow members 1 and 2 for a predetermined time (upset time) T2. This step is an upset step. By this upset process, intermetallic compounds, oxides, softening layers, and the like generated at the joining interface in the friction process are discharged from the peripheral edge of the joining interface as burrs 20, and new surfaces of the joining interfaces of the members 1 and 2 are joined together. Are joined.

Here, factors that affect the pressure contact property of the friction welding include the height of the rotational speed r1, the magnitudes of the friction pressure P1 and the upset pressure P2, the friction time T1, and the length of the upset time T2. . The rotational speed r1 is too high,
If the friction pressure P1 is too large or the friction time T1 is too long, the joining interface is overheated, and the generation of metal components (intermetallic compounds, oxides, and softening layers) at and near the joining interface increases. As a result, the pressure contact property is deteriorated.

In order to improve the pressure contact property of the friction welding, it is important how quickly the metal component is discharged to the peripheral edge of the joining interface during the friction step and the upset step. If the discharging property is not good, the metal component remains at the bonding interface.

In the present invention, in order to improve the dischargeability, the end face (friction welding surface) 2a of the hollow member 2 made of steel is used.
A gradient S having a gradient angle θ of 15 ° or less is formed from the thick central portion 3 to the inner peripheral surface portion 4 and the outer peripheral surface portion 5.

For this reason, at the start t1 of the friction step, the contact between the end faces 1a and 2a of the members 1 and 2 is a point contact, and the "margin" (contact area) is zero. Is pressed against the end surface 1a of the member 1 at the rotation speed r1 and the friction pressure P1 at the end surface 2a, the margin gradually increases, and at the end of the friction process (at the start of the upset process) t2 Is more than A1
(Beyond friction). Also, in the upset process,
The margin gradually increases, and at the end t3 of the upset process, the margin becomes A2 (all the margins).

When the margin is increased, the metal component in the vicinity of the bonding interface and in the vicinity thereof and in the vicinity of the central portion of the thickness of the member 2
Of the inner peripheral surface portion 4 and the outer peripheral surface portion 5 by the thick central portion 3 (raised portion). The metal component that has been continuously scraped off along the end face 2a of the member 2
In addition, the sliding deformation continuously occurs toward the inner peripheral surface portion 4 side and the outer peripheral surface portion 5 side, and is quickly discharged to the peripheral edge portion of the bonding interface.

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

[0032]

(Example 1) A hollow member made of an Al alloy having an outer diameter of 101.6 mm, an inner diameter of 96.6 mm, and a length of 30 mm was used.
1 alloy pipe (A6061) as steel hollow member with outer diameter 1
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, friction welding between different kinds of metal hollow members is performed. Here, a downward gradient having a gradient angle of 10 ° is formed on the joint end face of the carbon steel pipe for general structure from the central part of the wall thickness to the inner peripheral surface part and the outer peripheral surface part. Also,
The friction welding was performed at a rotational speed of 1500 rpm and a friction pressure of 4 kgf / mm ²
(About 39.2 MPa), upset pressure 10 kgf / mm ² (about 98MP
a), the friction welding time was 0.3 seconds and the upsetting time was 6 seconds. (Comparative Example 1) Friction welding is performed under the same conditions as in Example 1 except that a flat surface is formed without forming a downward slope on the joint end surface of the carbon steel pipe for general structure.

The joint structure of the first embodiment (hereinafter, joint surface angle 8
Various tests were carried out 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.

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

Further, the degree (%) of the amount of Al adhering to the bonding interface on the carbon steel pipe side among the bonding interfaces broken by the tensile test was evaluated. as a result,
As shown in FIG. 5, in the joint structure having a joint surface angle of 90 °, almost no Al was attached to the joint interface on the carbon steel pipe side. From this, it can be seen that in the joint structure with a joint surface angle of 90 °, almost no Al alloy and carbon steel are fused at the joint interface. On the other hand, in the joint structure with a joint surface angle of 80 °, Al is approximately 100% adhered to the joint interface on the carbon steel pipe side. It can be seen that the Al alloy and the carbon steel are almost completely fused.

Further, the joining structure at the joining surface angle of 80 ° and the joining structure at the joining surface angle of 90 ° were cut in the longitudinal direction, and the hardness (HV) near the joining interface was measured. The width (mm) of the (softening layer) was examined. As a result, as shown in FIG.
In the bonding structure of No. 1, the width of the softening layer that hinders the improvement of the bonding strength at the bonding interface was 2.5 mm. On the other hand, the width of the softening layer is 2.0 mm in the bonding structure with the bonding surface angle of 80 °, and the width of the softening layer, that is, the layer thickness is 20 mm, as compared with the bonding structure with the bonding surface angle of 90 °. The percentage is also thin. This is one of the reasons for the improvement in tensile strength shown in FIG.

As described above, the embodiments of the present invention are not limited to the above-described embodiments, and it is needless to say that various other embodiments are also conceivable.

[0038]

In summary, according to the present invention, the end surface of a hollow steel member having a raised central portion and the flat end surface of an aluminum alloy hollow member are brought into contact with each other and frictionally welded to each other to form a metal at the joining interface. An excellent effect is obtained in that it is possible to obtain a joint structure between dissimilar metal hollow members having little residual intermetallic compounds and oxides.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a state before joining of a joining structure between different kinds of metal hollow members according to the present invention.

FIG. 2 is a longitudinal sectional view showing a state after joining of a joining structure between different kinds of metal hollow members according to the present invention.

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

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

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

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

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

[Explanation of symbols]

 Reference Signs List 1 Hollow member made of Al alloy 1a End face 2 Hollow member made of steel 2a End face 3 Center of thickness (raised portion) 4 Inner peripheral surface part 5 Outer peripheral surface part θ Slope angle S Slope down

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshihisa Hamanaka 4-3-1 Kamigo, Ebina-shi, Kanagawa F-term (Reference) in Automotive Parts Industry Co., Ltd. 4E067 AA02 AA05 AA26 BG00 DA00 EA07 EC06

Claims (3)

[Claims] 1. A structure in which end faces of an aluminum alloy hollow member and a steel hollow member are abutted against each other, and the abutted end faces are joined by friction welding. A joining structure between dissimilar metal hollow members, wherein a downward gradient having a gradient 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 a slope angle of 15 ° or less from the center of the thickness to the inner peripheral surface and the outer peripheral surface at the end surface of the steel hollow member. A method for joining dissimilar metal hollow members, wherein the end surfaces and the flat end surfaces of the Al alloy hollow member are butted, and the butted end surfaces are joined by friction welding. 3. The method for joining dissimilar metal hollow members according to claim 2, wherein at least one of the steel hollow member and the Al alloy hollow member is rotated while applying pressure during the butting.