JP2006026724A - Joined body made of different kinds of metals of iron based alloy member and aluminum based alloy member by welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joined body made of different kinds of metals of an iron based alloy member and an aluminum based alloy member by welding which can obtain advantages such as excellent joining strength and high productivity substantially similar to those by welding the same kind of members, and to provide a joining technique therefor. <P>SOLUTION: This joined body obtained by joining the iron based alloy member and the aluminum based alloy member by welding is characterized in that the joint part between the iron based alloy member and the aluminum based alloy member has a structure including a supersaturated solid solution phase in which aluminum enters into solid solution in iron in a supersaturated manner. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a joined body obtained by joining an iron-based alloy member and an aluminum-based alloy member by welding, and more particularly to a dissimilar metal welded joint having excellent joint strength at the welded portion.

  In recent years, in order to improve the global environment such as exhaust gas regulations, there has been a strong demand for improved fuel consumption by reducing the weight of vehicles.

  Aluminum (hereinafter sometimes abbreviated as “aluminum”) has a specific gravity that is about one-third lighter than steel, and has good corrosion resistance. It is a desirable metal for reducing the weight of a car because it has features such as excellent crushability combined with material properties. On the other hand, aluminum is inferior in rigidity, strength and material cost compared to steel.

  Therefore, if the components of the car can be hybridized by making the best use of the advantages of steel and aluminum, not only the weight of the car but also the recyclability and the safety of the car can be improved.

  For hybridization using both steel and aluminum, it is important to use steel and aluminum in specific parts and material design, but it is essential to join both materials.

  However, when an iron-based alloy and an aluminum-based alloy are dissolved and welded directly to each other, a brittle intermetallic compound is generated, so that a sufficient joint strength cannot be obtained and it is extremely difficult to put it to practical use. For this reason, instead of this welding method, a canonical joining method, a brazing method, a friction welding method, and a joining method using an insert material have been put into practical use.

However, each of these joining techniques has advantages and disadvantages, and has the following disadvantages and problems, and is still not a satisfactory joining method.
(Mechanical joining method)
This is a method of mechanically joining members together such as bolt joining, rivet joining, screw joining, mechanical clinch, hemming, and mechanical molding joining. However, this method is generally inferior to welding of homogeneous materials (such as steels) in terms of shape constraints, joining accuracy, productivity, and versatility of joined parts.
(Brazing method)
In this method, the brazing material that serves as a medium between the members is melted and joined. Although this method has also been proposed as a method for joining steel and aluminum (Patent Document 1, etc.), the active surface of both metals is removed without removing the oxide film of steel and aluminum by flux and dissolving the base metal. It is necessary to produce an appropriate compound with the raw material. In order to obtain this appropriate compound, restrictions are imposed on the reliability of the material of the brazing material, the material and shape of the joined product, the joining strength, and the joining quality. Therefore, the workability, productivity and versatility of joining are generally accompanied by disadvantages compared to welding of homogeneous materials (such as steel).
(Friction welding method)
This is a solid phase bonding that uses frictional heat generated by sliding the members while rotating the members while applying pressure. However, since this method requires pressurization and rotation, there are restrictions on the shape of the joined parts, the treatment of burrs generated in the joining is necessary, longitudinal welding such as beat welding is difficult, and Mg-containing alloys (5000 In the case of the system), it is generally inferior to welding of homogeneous materials (such as steel) in terms of workability, versatility, and productivity, such as the difficulty of welding due to the generation of oxide (MgO).
(Insert material joining method)
In this method, a clad material is inserted between members and joined by spot welding or the like. However, this method has restrictions on the part shape associated with the insert of the clad material, inferior workability and cost problems, and is generally more common than welding of homogeneous materials (such as steel). It is inferior.
JP-A-5-111757

  The present invention eliminates these disadvantages and problems entirely in view of the background of the joining technology of the above-mentioned conventional steel and aluminum-based alloy members such as aluminum and aluminum-based alloy members, and substantially eliminates these disadvantages and problems. The development and commercialization of a revolutionary dissimilar metal joint that can enjoy advantages such as excellent joint strength and high productivity, as well as its joining technology, have been made as its issues.

  The present invention has been completed to solve such a problem, and the gist of the present invention is as follows.

  (1) A dissimilar metal welded joint in which an iron-based alloy member and an aluminum-based alloy member are joined by welding, wherein a welded joint between the iron-based alloy member and the aluminum-based alloy member is fixed to iron in a state where aluminum is supersaturated. A dissimilar metal welded joint of an iron-based alloy member and an aluminum-based alloy member, comprising a structure containing a molten supersaturated solid solution phase.

  (2) The dissimilar metal welded joined body of the iron-based alloy member and the aluminum-based alloy member according to (1), wherein the welded joint has a rapidly solidified structure.

  (3) The iron-based alloy member according to (1) or (2), wherein the welded joint is formed at a boundary where the iron-based alloy member side bites into the aluminum-based alloy member side in a bullet shape. Dissimilar metal welded joint of aluminum alloy member.

  (4) The iron-based alloy member according to any one of the above (1) to (3), wherein the iron-based alloy member is stainless steel, and the aluminum-based alloy member is made of an aluminum alloy. Dissimilar metal welded joints of alloy members.

  (5) The dissimilar metal welded joint of the iron-based alloy member and the aluminum-based alloy member according to any one of (1) to (4) above, wherein the welded joint is formed by laser welding.

  (6) The dissimilar metal welded joint of the iron-based alloy member and the aluminum-based alloy member according to (5) above, wherein laser welding performs heat input from the iron-based alloy member side.

  According to the present invention, it is possible to provide a dissimilar metal joined body of an iron-based alloy member and an aluminum-based alloy member having excellent bonding strength, and can be directly bonded by a welding method such as laser welding. High productivity can be realized, and there are remarkable effects such as advantageous in practical use.

  The present inventors have conventionally abandoned welding methods because of difficulties in joining different metals such as steel (represented as an example of an iron-based alloy member) and aluminum (represented as an example of an aluminum-based alloy member). And decided to try again to see if it could be realized.

As described above, a major obstacle to joining by the welding method is that an aluminum-rich intermetallic compound such as FeAl ₃ or Fe ₂ Al ₅ is generated at the joint, and this greatly reduces the joint strength.

  Therefore, the present inventors have made research and experiments from various viewpoints with the greatest proposition to prevent the generation of this harmful intermetallic compound, and as a result, the following concept is considered as an extremely effective solution. I was convinced that a welded steel / aluminum joint with excellent joint strength could be obtained by welding.

(1) Supersaturated solid solution phase In the present invention, the structure of the joint includes a solid solution phase in which aluminum is supersaturated in a solid solution exceeding its solid solubility limit. Hereinafter, this structure is referred to as an Fe—Al supersaturated solid solution structure or simply a supersaturated solid solution structure. This eliminates the generation of the aforementioned brittle iron-aluminum intermetallic compound and provides excellent bonding strength. Of course, iron-rich intermetallic compounds such as FeAl and Fe ₃ Al are allowed to exist in this structure because their strength can be prevented from decreasing by rapid solidification described later.

  The supersaturated solid solution phase contained in the aluminum parent phase is specifically preferably in a state where aluminum is solid-solved in an amount of 4 to 50% atomic% in iron. This is because if the solid solution is less than 4 atomic%, the harmful intermetallic compounds may be partially mixed in the structure of the joint portion to reduce the joint strength. This is because it is technically difficult and sufficient bonding strength can be maintained with a solid solution amount less than this.

(2) Rapid solidification In order to form the joint structure as the above-described supersaturated solid solution phase, it is important to create a state in which the joint is rapidly solidified. By this rapid solidification, there is no room for the intermetallic compound to precipitate in the cooling process, and solidification occurs while aluminum is supersaturated in iron. In addition, the rapid solidification of the joint becomes a so-called rapid solidification structure in which the grain size of the matrix aluminum and the supersaturated solid solution phase is refined, and a joint having higher strength in combination with the supersaturated solid solution phase structure. Will be obtained.

(3) Laser welding As a preferable welding method for achieving the supersaturated solid solution phase and the rapidly solidified structure, a laser welding method is adopted. Unlike the arc welding method, this laser welding method is characterized in that a weld bead having a very high heat input density (10 ⁶ W / cm ² or more) and an extremely high aspect ratio (penetration depth / penetration width) can be obtained. . Therefore, since the heat input sufficient for melting and joining can be instantaneously performed with the penetration width of the steel-aluminum joint reduced, the cooling after heat input proceeds rapidly and the joint is rapidly solidified. As a result, the joint can be made into a rapidly solidified structure, and at the same time, a supersaturated solid solution phase can be obtained. Moreover, when welding steel and aluminum by laser welding, it is preferable to perform the heat input from the steel side.

  The present invention will be described in further detail below based on typical experimental examples.

(Experimental example 1)
As shown in FIG. 1, a sample obtained by press-fitting a JIS 3003 aluminum rod 2 into a JIS 316L stainless steel pipe (iron) 1 (12Φ × 1.0t × 40L) is a carbon dioxide laser welding machine 4 (YB-L150A8, Matsushita Welding Systems, Using a diameter of 5Φ, a welding speed of 400 mm / min, an output of 700 Wm, and an output form of CW, laser was irradiated from the stainless steel pipe side (above), and heat was applied to join. In the figure, 5 indicates a weld bead. And after joining, when the two prototypes were subjected to a tensile test, it was confirmed that both of them were fractured from the base metal on the aluminum side and had excellent joining strength.

 Therefore, the present inventors conducted various investigations and analyzes in order to elucidate the reason why a joined body having such excellent joint strength was obtained by the welding method.

 First, the cross section of the welded portion of the joined body was macro-observed with a microscope (× 10). FIG. 2 is a schematic diagram of a photomicrograph. As shown in FIG. 1, a stainless steel re-solidification phase A (hereinafter sometimes referred to simply as an iron re-solidification phase) is formed in a region where the stainless steel pipe 1 is welded. It turns out that it becomes the biting part a immersed in the aluminum bar 2. And the junction part C of both is formed in the boundary of this biting part a and the aluminum bar 2 of this stainless steel. B shows the aluminum resolidification phase.

 Furthermore, the schematic diagram of the microscope picture which performed micro observation of this junction cross section with a microscope (x100) is FIG. It can be seen from FIG. 3 that the joint C is an independent boundary phase intricately intertwined with the iron resolidification phase A and the aluminum resolidification phase A on both sides.

 Next, surface analysis and line analysis were performed on this bonding portion (bonding boundary phase) C with an electron beam microanalyzer (EPMA-1400 manufactured by Shimadzu Corp.). Fig. 4 shows the results of surface analysis observation, where black is 100% iron and white is 100% aluminum, and the composition in the meantime is shown in shades. Is shown in the pull-out gland. From this, it was found that the joining boundary phase contains 10 to 50 atomic% of aluminum. FIG. 5 shows the results of measurement along the arrow X in FIG. 3 by line analysis from the steel resolidification phase to the aluminum resolidification phase (aluminum ground). From FIG. 5, the iron resolidification phase A forming the encroaching part a (FIG. 2) contains 4 atomic% or more of aluminum, and at the joint C, iron (Fe) decreases toward the aluminum resolidification phase side. It can be seen that aluminum (Al) increases, and the amount of aluminum rapidly rises to the aluminum resolidification phase of 100 atomic% of aluminum through the point where the amount of iron to aluminum is equal. Nickel (Ni) shows the same change as iron (Fe).

  Further, this joint was subjected to composition analysis at three locations on the iron resolidification phase side, the intermediate portion, and the aluminum resolidification phase side by Auger electron spectroscopy (AES). Table 1 shows the results.

  From the results in Table 1, it is known that 20 to 29 atomic% Al is present in the joint C.

  Further, as a result of observing the structure of the joint C by SEM analysis, a rapidly solidified structure having a size of several to tens of microns was observed.

  The inventors next decided to investigate whether or not the intermetallic compound in question exists in the joint C. FIG. 6 is an X diffraction pattern measured on the polished surface of the joint section using an X-ray diffraction apparatus (RINT 1500 manufactured by Rigaku Corporation). From FIG. 7, the detected peaks correspond to Al, Fe and Fe—Cr—Ni, and no peaks corresponding to the Fe—Al compound were detected.

  From these results, the structure of the joint was in a state that greatly exceeded the solid solubility limit of aluminum (0.15%) with respect to iron, and Fe-Al intermetallic compounds could not be detected. The conviction that it exists as a supersaturated solid solution phase of Fe-Al was obtained.

  In addition, since the shell-like encroaching part a of the iron resolidification phase adjacent to this joint contains 4% or more exceeding its solid solubility limit, it is also a supersaturated solid solution phase of Fe-Al. I know that there is. This is because the Al dissolved in the supersaturation in the encroaching portion a is solidified by being dispersed in the molten iron by the aluminum vapor generated at a high temperature during laser welding.

  The supersaturated solid solution phase in the joint is obtained by rapid solidification as described above. In particular, laser welding is the method in which the joint is most rapidly cooled among the welding methods, and the melting point difference between iron and aluminum. It can be said that the rapid solidification is easily realized by the fact that the temperature is 1000 ° C. or higher and the thermal conductivity of aluminum is extremely high. Here, the cooling rate required for rapid solidification is 10 K / s or more, preferably 100 K / s or more. Thereby, a fine solidified structure of several μ to 10 μm or less is obtained.

  Next, preferred welding conditions for the joined body of the present invention will be described.

  Laser welding conditions that can provide sufficient bonding strength are basically to stably input heat from the iron side at a high energy density, and to allow the molten iron to bite into the aluminum in an appropriate amount in a short time. is there. In order to satisfy this condition, as shown in FIG. 7, first, a laser beam (R) is irradiated from the iron (1) side to perform heat input, and a keyhole (inside the molten iron (M)) ( It is necessary to prevent the metal vapor (V) from being contained in K) and to prevent bumping by the vapor (V). Moreover, it is necessary to adjust heat input so that molten iron (M) does not scatter. When the molten iron (M) is inserted into the aluminum (2), a dent due to shrinkage tends to occur on the iron side surface after solidification. In order to prevent the occurrence of excessive dents on the solidified surface, the heat input needs to be performed not only in the welding depth direction but also in the width direction in order to supplement the amount of molten iron (M) from around the heat input during solidification. The heat input in the width direction causes the metal vapor (V) obtained with the generation of the keyhole (K) to emit plasma on the iron surface, that is, near the upper side of the keyhole (K), and a plasma cloud (P ) It is important to maintain it continuously.

  As specific conditions for achieving such a situation, the laser output is preferably 650 to 850 W (particularly 700 to 750 W), and the welding speed is preferably 375 to 400 mm / min.

Hereinafter, a plurality of experimental examples will be given as examples to clarify the effects of the present invention.
(Example)
A SUS304 standard pipe, an aluminum bar, and a pipe were press-fitted, and a joining test was performed by changing welding conditions with a laser welding machine (YB-L150A8 manufactured by Matsushita Welding Systems; argon seal, nozzle diameter 5φ). The results are shown in Table 2. No1 to No3 are examples of the present invention (No1 is the same as the above experimental example), and No4 to No8 are comparative examples. As the SUS pipes, No. 1 to No. 5 of 12φ × 1.0t × 45L and No. 6 to 7 of 12φ × 1.0t × 45L were used. In addition, aluminum having a size of 10φ × 60L, No3 to 5 and No8 is 10φ × 1.4t × 60L, No6 is 14φ × 40L, and No7 is 17.3φ × 2.0t × 40L. .

  As can be seen from Table 2, according to the examples of the present invention, a bonded body of iron (SUS) and aluminum having a significantly higher bonding strength than the comparative examples is obtained, and the excellent effects of the present invention are obtained. It is to prove.

The perspective view which shows the outline | summary of the laser joining (welding) of the stainless steel pipe and aluminum bar in Experimental example 1. FIG. The schematic diagram based on the microscope (x10) observation result of the junction part (cross section) laser-joined in Experimental example 1. FIG. The schematic diagram based on the microscope (x100) observation result of the junction part (cross section) laser-joined in Experimental example 1. FIG. The Al composition distribution map which shows the surface analysis result of the junction part (cross section) laser-joined in Experimental example 1. FIG. The figure which shows the glandular analysis result of the junction part (cross section) laser-joined in Experimental example 1. FIG. FIG. 3 is an X-ray diffraction diagram of a bonded portion (cross section) laser-bonded in Experimental Example 1. The schematic diagram which shows the state at the time of joining of iron and aluminum by the laser welding in this invention.

Explanation of symbols

1: Stainless steel pipe 2: Aluminum rod A: Iron (stainless steel) resolidification phase B: Aluminum resolidification phase C: Joining part a: Biting part 4: Laser welding machine 5: Welding bead R: Laser beam M: Molten iron K : Keyhole V: Metallic vapor P: Plasma cloud

Claims (6)

A dissimilar metal welded joint obtained by welding an iron-based alloy member and an aluminum-based alloy member by welding, wherein the welded joint between the iron-based alloy member and the aluminum-based alloy member is supersaturated in which aluminum is solid-solved in iron A dissimilar metal welded joint of an iron-based alloy member and an aluminum-based alloy member, characterized by comprising a structure containing a solid solution phase. The dissimilar metal welded joint of an iron-based alloy member and an aluminum-based alloy member according to claim 1, wherein the welded joint has a rapidly solidified structure. 3. The iron-based alloy member and the aluminum-based alloy according to claim 1, wherein the welded joint is formed at a boundary where the iron-based alloy member side bites into the aluminum-based alloy member side in a bullet shape. 4. Dissimilar metal welded joints of members. The dissimilar metal welding of the iron-based alloy member and the aluminum-based alloy member according to any one of claims 1 to 3, wherein the iron-based alloy member is stainless steel and the aluminum-based alloy member is made of an aluminum alloy. Joined body. 5. The dissimilar metal welded joint of an iron-based alloy member and an aluminum-based alloy member according to any one of claims 1 to 4, wherein the welded joint is formed by laser welding. The dissimilar metal welded joint of an iron-based alloy member and an aluminum-based alloy member according to claim 5, wherein the laser welding performs heat input from the iron-based alloy member side.

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