JP2007253172A - Friction stir welding method of aluminum alloy and steel sheet, and friction stir welding member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction stir welding method with which a weld joint of high joint strength is obtained by making a joint boundary greater in friction stir welding of different kinds of metallic materials, and to provide a friction stir welding member. <P>SOLUTION: In the friction stir welding method, in the friction stir welding of the different kinds of metallic materials, a low melting point plated steel sheet 30 as the metallic material of a high melting point has a plating layer 30a of the melting point lower than the melting point of an aluminum alloy as the metallic material of the low melting point. The plating layer 30a is diffused by the plastic flow in a plastic fluid area 20a generated in the aluminum alloy during friction stir welding to diffuse the plating layer 30a, and the steel sheet newly-formed surface 30 of the low melting point steel sheet 30 is exposed and solid phase joining of the surface to the aluminum alloy 20 is performed to obtain the weld joint of the high joint strength. The friction stir welding member is also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a friction stir welding method and a friction stir welding member for different metal materials such as a steel plate and an aluminum alloy.

  Currently, friction stir welding has been established as a joining method for metal materials having relatively low melting points (for example, aluminum alloys). Friction stir welding has the advantage in cost that it can be automated at low cost because it is simple and easy to construct because it stirs and solid phase bonds in a plastic flow state without melting the metal material. Therefore, it is widely used in fields such as automobile manufacturing and railway vehicle manufacturing.

On the other hand, the friction stir welding has a problem that sufficient strength cannot be obtained for the joining of different metal materials (for example, a steel plate and an aluminum alloy). This is mainly due to the fact that there is a difference in the melting points of the metal materials to be joined, so that stirring by plastic flow is not sufficiently performed. As a solution to this problem, a technique has been disclosed in which a joining pin for joining is inserted from the metal material side having a low melting point, the joining pin shape and the insertion depth are adjusted, and different metal materials are friction stir welded. (See Patent Document 1).
JP 2003-266182 A

  However, in view of the current state of friction stir welding using GA steel or SP steel as a metal material with a high melting point and aluminum alloy as a metal material with a low melting point, the friction stir welding of the prior art has a joint joint with sufficient strength. The current situation is that it cannot be obtained.

  The cause is that the solid interface can be solid-phase bonded to the aluminum alloy only in the range where the steel plate contacts the bonding pin during friction stir welding (approximately equivalent to the diameter of the bonding pin), and the bonding interface is very small.

  This is because the steel plate is very easy to oxidize, and the surface of the SP steel plate is always covered with an oxide film, and the GA steel plate is galvanized on the surface to prevent oxidation. To do.

  That is, the friction stir welding of the steel plate and the aluminum alloy is performed by solid-phase joining the steel plate surface and the plastic fluidized aluminum alloy, but the oxide film covering the SP steel plate is not diffused by the plastic fluidized aluminum alloy. The new surface does not appear and solid phase bonding with aluminum alloy is impossible.

  The GA steel sheet has a zinc (Zn) plating layer on the surface, but the GA steel sheet is subjected to an alloying hot dip galvanizing process, and the melting point of the Zn plating layer is about 750 ° C. or higher. Since the aluminum alloy plastically fluidizes at about 450 ° C., the Zn plating layer is not diffused even by the plastic flow of the aluminum alloy, and the new surface of the steel sheet does not appear, so that solid phase bonding with the aluminum alloy cannot be performed.

  And only the part (new surface of a steel plate) which the joining pin rotated and contacted and scraped off the oxide film and Zn plating layer is based on the characteristic that it can carry out solid phase joining with the plastic fluidized aluminum alloy.

  As described above, in the prior art, since the joining is performed only at the portion where the joining pin is in contact with the steel sheet, there is a problem in that a joining joint having a very small joining interface cannot be obtained.

  Accordingly, an object of the present invention is to provide a friction stir welding method and a friction stir welding member capable of performing bonding with a larger bonding interface and higher bonding strength even in the bonding of a steel plate and an aluminum alloy.

  In order to solve the above-mentioned problem, in the invention according to claim 1, in the friction stir welding method by a combination of the first metal material and the second metal material having a melting point lower than the melting point of the first metal material. A film having a melting point lower than the melting point of the second metal material is formed on the surface of the first metal material at least on the surface in contact with the second metal material in the bonding surface region; The first metal material and the second metal material are overlapped to form the joint surface region, and a joint pin that rotates from the surface of the second metal material in the joint surface region is used as the first metal material. And inserted to the vicinity of the joining interface where the second metal material is joined and frictionally stirred, the film is diffused by the plastic flow of the second metal material to expose the new surface of the first metal material, Solid phase on the new surface And the friction stir welding method, characterized in that the coupling. According to the present invention, it is possible to provide a friction stir welding method capable of performing bonding with a large bonding interface and high bonding strength.

  Furthermore, in the invention which concerns on Claim 2, when the said joining pin is inserted from the surface of the said 2nd metal material, the insertion amount to the said 1st metal material of the said joining pin is -0.1mm-0. The friction stir welding method was characterized by being in the range of 2 mm. According to the present invention, it is possible to obtain optimum joint strength without reducing the processing efficiency of friction stir welding.

  Further, in the invention according to claim 3, the first metal material is made of a steel plate, the second metal material is made of an aluminum alloy, and the film has a melting point of 450 ° C. or less. The friction stir welding method was used. According to the present invention, friction stir welding having suitable joint strength can be obtained in friction stir welding of an aluminum alloy and a steel plate.

  Furthermore, in the invention according to claim 4, the friction stir welding method is characterized in that the film is made of a plated layer, and the plated layer is made of an alloy composed of zinc, aluminum, and magnesium. According to the present invention, friction stir welding having suitable joint strength can be obtained in friction stir welding of an aluminum alloy and a steel plate.

  Furthermore, the invention according to claim 5 is the friction stir welding method according to any one of claims 1 to 4, wherein the first metal material and the second metal material having a melting point lower than the melting point of the first metal material are used. A friction stir welding member that is friction stir welded by an intermetallic compound produced by the friction stir welding at a joint interface where the first metal material and the second metal material are joined. Is a friction stir welding member having a granular form with a thickness of 10 nm to 1 μm or a divided layered form and dispersed at the joining interface. According to the present invention, a friction stir welding member having suitable joint strength can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the friction stir welding method and friction stir welding member which can perform joining with a large joining interface and high joining strength between a steel plate and an aluminum alloy can be provided.

  Hereinafter, the best embodiment for carrying out the present invention will be described in detail with reference to the drawings as appropriate.

  FIG. 1 is a view showing a welding tool 1 used for friction stir welding. The joining tool 1 is a substantially cylindrical joining projecting concentrically around the rotational axis A from the bottom of a cylindrical rotor 12 that is rotationally driven around the rotational axis A by a rotational drive device such as a motor (not shown). It has a pin 10. The diameter of the joining pin 10 is smaller than the diameter of the rotor 12, and the shoulder portion 11 is formed by a step portion of the diameter of the joining pin 10 and the rotor 12.

  FIG. 2 illustrates an embodiment of the present invention. FIG. 2 is a view showing that a joining surface region is formed by superimposing an aluminum alloy on a low melting point plated steel sheet in which a plated layer is provided on the steel sheet.

  As shown in FIG. 2, the present invention is a friction stir welding method of a steel plate as a first metal material described in the claims and an aluminum alloy as a second metal material described in the claims. For the steel sheet, a steel sheet (hereinafter referred to as a low melting point plated steel sheet) 30 having a plating layer 30a plated on the surface of the steel sheet that is lower than the melting point of the aluminum alloy 20 was used as the film described in the claims. Features.

  In this embodiment, a steel sheet having a plating layer as a coating described in the claims is used, and hot galvanizing with an alloy composed of zinc, aluminum, and magnesium (Zn—Al—Mg) is applied as the plating layer. However, as long as the condition that the melting point of the film is lower than the melting point of the aluminum alloy 20 is satisfied, the type and components of the film are not limited. Further, unlike the low melting point plated steel sheet 30, it is not necessary to have a plating layer (film) on the entire steel sheet, and the effect of the present invention can be obtained if at least the bonding surface region 21 with the aluminum alloy 20 has a plating layer (film). It is done.

  FIG. 3 is a view showing the position of the tip portion 10a when the joining pin 10 is inserted into the plastic flow region 20a until the shoulder portion 11 contacts the surface 20b of the aluminum alloy 20. As shown in FIG.

  As shown in FIG. 3, while rotating the welding tool 1, the tip part 10a of the joining pin 10 is brought into contact with the surface 20b of the aluminum alloy 20 while being brought close to the surface 20b of the aluminum alloy 20, thereby forming a plastic flow region 20a. However, until the shoulder portion 11 is in sliding contact with the surface 20b of the aluminum alloy 20, the joining pin 10 is rotated and inserted into the plastic flow region 20a of the aluminum alloy 20.

  At this time, the tip portion 10a of the joining pin 10 is within the plastic flow region 20a of the aluminum alloy 20 when the distance L1 from the contact surface 20c between the aluminum alloy 20 and the low melting point plated steel surface 30b is in the range of 0 mm to 0.1 mm. (See FIG. 3A), or the tip portion 10a of the joining pin 10 is inserted into the low melting point plated steel sheet 30 with a distance L2 from the contact surface 20c of 0 mm to 0.2 mm. (See FIG. 3B), the protruding amount of the joining pin 10 from the shoulder portion 11 is set so as to be in any position.

  That is, as described in the claims, the insertion amount of the joining pin 10 into the low melting point plated steel sheet 30 as the first metal material is in the range of −0.1 mm to 0.2 mm.

  The amount of insertion of the joining pin 10 into the low melting point plated steel sheet 30 is a value determined from the joining strength and processing efficiency by friction stir welding.

  That is, as shown in FIG. 3B, when the joining pin 10 is inserted into the low melting point plated steel sheet 30, a portion where the plating layer 30 a of the low melting point plated steel sheet 30 is scraped by the rotational contact of the joining pin 10, and In this way, a new steel plate surface 30d (see FIG. 4C) appears at the portion of the plating layer 30a diffused. Here, since the component of the plating layer 30a can be completely removed in the portion where the plating layer 30a of the low melting point plated steel plate 30 is scraped by the rotational contact of the joining pin 10, the new steel plate surface 30d (FIG. The strength of the friction stir welding with the aluminum alloy 20 is higher than the portion (see (c) of 4).

  Therefore, when a small amount of the joining pin 10 is inserted into the low melting point plated steel sheet 30, a slightly stronger friction stir welding can be obtained as compared with the case where the joining pin 10 is not inserted into the low melting point plated steel sheet 30. However, by inserting the joining pin 10 into the low melting point plated steel plate 30, the hard steel plate must be cut, and the processing resistance increases, so the processing efficiency decreases.

  Since the processing resistance increases as the insertion amount of the joining pin 10 into the low melting point plated steel sheet 30 increases, the insertion amount of the joining pin 10 into the low melting point plated steel sheet 30 is limited to 0.2 mm in consideration of processing efficiency. Become.

  On the contrary, as shown in FIG. 3A, when the front end portion 10a of the joining pin 10 is retained in the plastic flow region 20a of the aluminum alloy 20, the new steel plate surface 30d (diffusion of the plated layer 30a will be described later). 4 (c)) appears, but if the tip 10a is separated from the contact surface 20c by a certain distance or more, sufficient frictional heat cannot be supplied to the plating layer 30a, and the plating layer 30a is not sufficiently diffused. The strength of stir welding will decrease.

  From the above, the distance from the contact surface 20c to the tip 10a is set as a range in which the optimum strength of friction stir welding can be obtained and the influence on the processing efficiency is small, and in FIG. L1 was in the range of 0 mm to 0.1 mm, and L2 in FIG. 3B was in the range of 0 mm to 0.2 mm.

  FIG. 4 is a schematic view showing a joining process of the friction stir welding method according to the present invention. As shown in FIG. 4A, the welding tool 1 continues to rotate at the position where the shoulder portion 11 is in sliding contact with the surface 20b of the aluminum alloy 20, so that heat from friction is generated from the joining pin 10 and the shoulder portion 11 by aluminum. The alloy 20 continues to be supplied to the low melting point plated steel sheet 30, and the plastic flow region 20 a of the aluminum alloy 20 comes into contact with the low melting point plated steel surface 30 b from the surface 20 b of the aluminum alloy 20 in a range substantially equal to the diameter of the shoulder portion 11. The range extends to the contact surface 20c.

  On the other hand, for the low melting point plated steel sheet 30, since the temperature of the plastic flow region 20a of the aluminum alloy 20 is higher than the melting point of the plating layer 30a, the contact surface 20c where the plastic flow region 20a and the low melting point plated steel surface 30b are in contact with each other: As shown in FIG. 4B, the plating layer 30a melts and the plating layer melting portion 30c appears. And since the molten plating component of the plating layer melting part 30c is diffused by the plastic flow in the plastic flow region 20a, the plastic flow region 20a of the aluminum alloy 20 and the low melting point plated steel plate as shown in FIG. A new steel plate surface 30d in contact with 30 appears.

  Since the friction stir welding is performed by solid phase bonding on the surface where the plastic flow region 20a of the aluminum alloy 20 and the steel plate new surface 30d of the low melting point plated steel plate 30 are in contact with each other, as shown in FIG. The joining interface 30e of the low melting point plated steel sheet 30 has a size substantially equal to the plastic flow region 20a generated in the aluminum alloy 20.

  Here, since the plastic flow region 20a extends to a range substantially equal to the diameter of the shoulder portion 11 of the joining tool 1 as described above, the joining interface 30e is substantially equal to the diameter of the shoulder portion 11 of the joining tool 1. It can be said.

  FIG. 5 is a view showing a bonding interface when friction stir welding between a steel plate and an aluminum alloy is performed by the conventional technique. As shown in FIG. 5, the bonding interface 20 d generated when the steel plate 40 such as the SP steel plate or the GA steel plate and the aluminum alloy 20 are friction stir welded by the conventional technique is the joining pin 10 b at the time of the friction stir welding processing as described above. The size is substantially equal to (indicated by an imaginary line in FIG. 5).

  Therefore, the bonding interface 30e generated by the present invention shown in FIG. 4 (d) is larger than the bonding interface 20d generated by the prior art shown in FIG. It can be said that high friction stir welding can be performed.

  In the friction stir welding, if the joining tool 1 is sent along the surface 20b of the aluminum alloy 20 by a necessary length, the friction stir welding having a necessary joining length can be performed.

  The melting point of zinc used for the plating of the GA steel sheet is about 420 ° C., which is lower than about 450 ° C. of the plastic flow region 20a of the aluminum alloy 20 during the friction stir welding process. Since it is a hot dip galvanizing process and the plating layer is partially alloyed with the steel plate, the melting point of the plating surface is about 750 ° C. or higher and is not diffused by the heat supplied from the plastic flow zone 20a of the aluminum alloy 20.

  On the other hand, the plating constituting the plating layer 30a of the low melting point plated steel sheet 30 used in the present embodiment is hot dip galvanizing made of Zn—Al—Mg, and the plating layer 30a is not alloyed with the steel sheet. The melting point of the plating layer 30a is about 400 ° C., and the effects of the present invention are exhibited.

  FIG. 6 is a diagram showing a test material for performing a joint strength test of friction stir welding according to the present embodiment, and FIG. 7 is a diagram showing a tensile shear strength of the friction stir welding by the test material.

Hereinafter, the shape of the test material and the friction stir welding method shown in FIG. 6 were used, and the friction stir welding was performed under the conditions shown in Table 1 and the tensile shear strength was measured. The result shown in FIG. Was obtained.

In addition, the description of the joining member in FIG. 7, and the test material A60 and the test material B61 in FIG. 6 correspond to the test materials (A to D) described in Table 1 as follows.
Joining member: low melting point plated steel sheet Specimen A60: Specimen A shown in Table 1
Specimen B61: Specimen B listed in Table 1
Joining member: GA steel plate Specimen A60: Specimen A shown in Table 1
Specimen B61: Specimen C listed in Table 1
Joining member: SP steel plate Test material A60: Test material A described in Table 1
Specimen B61: Specimen D listed in Table 1
Joining member: Aluminum alloy Specimen A60: Specimen A listed in Table 1
Specimen B61: Specimen A listed in Table 1

  According to FIG. 7, in the friction stir welding of the aluminum alloy and the low melting point plated steel sheet, a tensile shear strength of about 5 kN is obtained, and the tensile shear strength (about 3.0 kN to about 3 k) obtained by the friction stir welding by other combinations is obtained. It can be seen that the bonding strength is high.

  In FIG. 8, the electron micrograph of the joining interface of the friction stir welding member by this embodiment is shown. According to FIG. 8, it was confirmed that an intermetallic compound was formed at the bonding interface between the upper aluminum alloy and the lower steel plate, as indicated by the portion surrounded by the black frame, and the composition was Fe4Al13. It was.

  Furthermore, as shown in FIG. 8, the intermetallic compound has a thickness in the range of 10 nm to 1 μm, and is dispersed in the joint interface as a granular form or a divided layer form rather than a continuous layer form over the entire joint interface. It was confirmed that

  In general, intermetallic compounds are brittle and easily break. Therefore, if it exists in a continuous layered form at the bonding interface, it causes a decrease in the strength of the bonding interface.

  Further, since the strength of the bonding interface decreases even when the thickness of the intermetallic compound is increased, a stronger bonding interface can be obtained when the intermetallic compound is thinner.

  The joint interface of the friction stir welding member according to the embodiment of the present invention has the intermetallic compound dispersed therein as described above, and the thickness can be suppressed in the range of 10 nm to 1 μm. This can be compensated for in the absence of the intercalation compound, and a decrease in the strength of the bonding interface can be prevented.

  As described above, the embodiment of the present invention has been described. However, the film described in the claims is not limited to the plating layer, the melting point is lower than that of the aluminum alloy, and the plasticity of the plastic flow region generated in the aluminum alloy during friction stir welding is described. Any kind of material can be used as long as it satisfies the condition of being diffused by flow.

It is the schematic of the welding tool used for friction stir welding. It is a figure which shows the joining member in the friction stir welding which concerns on embodiment of this invention. It is a figure which shows the state of the joining pin at the time of friction stirring. (A) is a figure which shows that the front-end | tip part of a joining pin exists in the plastic flow area of an aluminum alloy, (b) is a figure which shows that the front-end | tip part of a joining pin is inserted in the low melting-point plated steel plate. It is the schematic which shows the joining process of the friction stir welding method which concerns on embodiment of this invention. (A) is a figure which shows that a plastic flow area is formed by a joining tool, (b) is a figure which shows that a plating layer fusion | melting part is formed by a plastic flow area, (c) is a steel plate new surface. (D) is a figure which shows that a joining interface is formed. It is a figure which shows the joining interface by friction stir welding of a prior art. It is a figure which shows the test material used for the joint strength test which concerns on this embodiment. It is a figure which shows the result of the joint strength test which concerns on this embodiment. The vertical axis shows the tensile shear strength, and the horizontal axis shows the metal material that is friction stir welded to the aluminum alloy. It is an electron micrograph of the joining interface of the friction stir welding member which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Joining tool 10 Joining pin 20 Aluminum alloy 20a Plastic flow area 21 Joining surface area 30 Low melting point plated steel plate 30a Plating layer 30d New steel plate surface

Claims (5)

In a friction stir welding method by a combination of a first metal material and a second metal material having a melting point lower than the melting point of the first metal material,
On the surface of the first metal material, a film having a melting point lower than the melting point of the second metal material is formed at least on the surface on the side where the second metal material is in contact with the bonding surface region;
The first metal material and the second metal material are overlapped to form the bonding surface region;
A joining pin that rotates from the surface of the second metal material in the joining surface region;
Inserting the first metal material and the second metal material to the vicinity of the bonding interface where the first metal material and the second metal material are bonded, and stirring the friction;
Diffusing the film by plastic flow of the second metal material to expose a new surface of the first metal material;
Friction stir welding method, wherein solid phase bonding is performed on the new surface.   When the joining pin is inserted from the surface of the second metal material, an insertion amount of the joining pin into the first metal material is in a range of −0.1 mm to 0.2 mm. The friction stir welding method according to claim 1.   The first metal material is made of a steel plate, the second metal material is made of an aluminum alloy, and the film has a melting point of 450 ° C or lower. Friction stir welding method.   The friction stir welding method according to any one of claims 1 to 3, wherein the film is made of a plated layer, and the plated layer is made of an alloy composed of zinc, aluminum, and magnesium. The friction stir welding member in which the first metal material and the second metal material having a melting point lower than the melting point of the first metal material are friction stir welded by the friction stir welding method according to any one of claims 1 to 4. Because
An intermetallic compound is generated at a bonding interface where the first metal material and the second metal material are bonded,
The friction stir welding member, wherein the intermetallic compound has a granular form having a thickness of 10 nm to 1 μm or a divided layered form and is dispersed at the joining interface.