JP2007216276A - Method for welding iron based material and aluminum based material, and welded joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding method with which, when an aluminum based material and an iron based material are welded, restriction on applying conditions or the like is reduced, versatile applicability is excellent, further, restriction on shape is reduced, also, operability is excellent and, continuous welding is possible, and, while forming a sound bead, production of a brittle intermetallic compound in the welded part is prevented, thus high welding strength can be obtained, and to provide a welded joint obtained using the method. <P>SOLUTION: A flux-cored wire formed by coating flux containing aluminum fluoride and potassium fluoride and further comprising one or more fluorides selected from the group consisting of magnesium fluoride, calcium fluoride, strontium fluoride and barium fluoride with aluminum or an aluminum alloy is used as a filler metal, and an aluminum based material and an iron based material are directly welded by alternating current MIG (metal inert gas) welding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for joining an iron-based material and an aluminum-based material, which is necessary in an assembly process of an automobile structure or the like.

  When joining iron-based materials and aluminum-based materials (a collective term for aluminum and aluminum alloys), it is easy to form brittle intermetallic compounds at the joints, so that it is possible to obtain a reliable joint with high strength It was very difficult.

  As countermeasures against this, a number of conventional techniques have been disclosed as follows.

  For example, a method of vacuum rolling joining (see Patent Document 1), a method of performing seam welding by interposing a two-layer clad material made of an iron-based material layer and an aluminum alloy layer (see Patent Document 2), high-temperature pressurization A method of joining (see Patent Document 3), a method of joining a Ti alloy in advance on the joint surface by HIP treatment (see Patent Documents 4 and 5), a method of friction welding (see Patent Document 6), an iron system in contact with aluminum For example, an aluminum alloy is plated on the surface of the material, or resistance welding is performed by interposing a two-layer clad material made of an iron-based material layer and an aluminum alloy layer (see Patent Documents 7 and 8).

  However, the above prior art has the following problems.

  The method of obtaining a joined member of an iron-based material and an aluminum-based material by joining an iron-based material and an aluminum-based material by vacuum rolling, high-temperature pressurization, and HIP treatment is intended to produce such a composite member. To do. Therefore, this method can be used for joining members having a relatively simple shape such as a flat plate, but cannot be applied when the shape of the member is complicated, so that the applicable range is narrow and the versatility is poor.

  The method of joining an iron-based material and an aluminum-based material by friction welding is inferior in versatility due to the restriction of the member shape, and the joint becomes spot-like so that a continuous joint cannot be obtained. .

  The method of plating an aluminum alloy on the surface of an iron-based material in contact with aluminum and performing resistance welding requires a plating process, and the process is complicated, so that there is a problem that quality stability cannot be ensured.

  In the method of preparing seam welding or resistance welding by preparing two clad materials consisting of an iron-based material layer and an aluminum alloy layer in advance, the clad material is inserted between the iron-based material and the aluminum-based material. The joining of the three plates becomes the joining of the three plates. For this reason, an insert material (cladding material) insertion process and a fixing process are required at the time of actual construction, and the process becomes complicated in the same manner as described above, so that quality stability cannot be ensured.

  In any of the above methods, in addition to the above problems, there is a problem that equipment costs increase because new equipment must be incorporated into the current welding line. Furthermore, in the method using a clad material, the clad material itself must be manufactured by joining an iron-based material and an aluminum-based material. Therefore, the production conditions are severely restricted, and an inexpensive and stable performance clad material is required. It was difficult to obtain.

  As one of the backgrounds in which various methods as described above have been proposed for joining an iron-based material and an aluminum-based material, an intermetallic compound that is brittle at the joint when the iron-based material and the aluminum-based material are directly melt-bonded. May be generated and cracking is likely to occur. Therefore, when directly joining an iron-based material and an aluminum-based material, including the case of joining using a welding wire, how to mix the iron in the iron-based material and the aluminum in the aluminum-based material as much as possible. It is extremely important to ensure the ductility of the molten metal part without making it, and how to prevent the formation of a brittle intermetallic compound layer in the vicinity of the interface between the iron-based material and the aluminum-based material.

  From such a viewpoint, the flux-cored wire 1 formed by coating a flux containing at least cesium fluoride, aluminum fluoride, potassium fluoride and aluminum oxide as a core material with aluminum or an aluminum alloy is used as a filler material. The aluminum or aluminum alloy member and the steel member are joined by arc welding, the joining portion on the aluminum or aluminum alloy member side is melted and joined, and the joining portion on the steel member side is not melted and is a thin intermetallic compound layer A method of joining aluminum and steel that forms and joins is disclosed (see Patent Document 9).

However, the above-mentioned flux obtained by further adding cesium fluoride having a low melting point to a mixture containing aluminum fluoride and potassium fluoride, which originally has a lower melting point than aluminum, has a lower melting point. There is a problem that workability deteriorates such as evaporation of a large amount and generation of fumes and spatters, and a weld metal made of aluminum spreads too much, so that a healthy bead is not formed and high bonding strength cannot be obtained.
JP 2000-94162 A Japanese Patent Laid-Open No. 11-197846 JP-A-10-185040 JP-A-6-198458 JP-A-5-8056 JP-A-8-141755 JP-A-6-39558 JP-A-6-63762 JP2003-2111270A

  Therefore, the present invention has few restrictions such as application conditions when joining an aluminum-based material and an iron-based material, and is excellent in versatility, has few shape restrictions, is excellent in workability, and can be continuously joined. An object of the present invention is to provide a joining method in which a high joining strength is obtained by preventing formation of a brittle intermetallic compound in a joint while forming a sound bead and a joint joint obtained thereby.

  The invention according to claim 1 contains aluminum fluoride and potassium fluoride, and further contains one or more fluorides selected from the group consisting of magnesium fluoride, calcium fluoride, strontium fluoride and barium fluoride. An iron-based material and an aluminum-based material characterized in that a flux-cored wire formed by coating a flux with aluminum or an aluminum alloy is used as a filler material, and an aluminum-based material and an iron-based material are directly joined by AC MIG welding. It is a joining method.

  The invention according to claim 2 is the method for joining the iron-based material and the aluminum-based material according to claim 1, wherein the iron-based material is a galvanized steel sheet.

  The invention according to claim 3 is a joint joint of an iron-based material and an aluminum-based material obtained by the joining method according to claim 1 or 2.

  The present invention is configured as described above, and by using a flux containing a high melting point fluoride in aluminum fluoride and potassium fluoride as a filler material, the evaporation of the flux during welding is suppressed. High workability can be obtained by improving the workability and preventing the formation of fragile intermetallic compounds at the joints while suppressing the excessive expansion of the weld metal made of aluminum and forming a sound bead.

  Furthermore, by using AC MIG welding as a welding means, there are few restrictions such as application conditions and excellent versatility, and there are few geometric restrictions, and continuous joining is possible, and aluminum-based materials and iron-based materials are efficiently used. Can be realized.

  In the present invention, AC MIG welding is adopted as the welding means, but a general-purpose AC MIG welding apparatus may be used for AC MIG welding. Since AC MIG welding equipment can precisely control the heat input to the material to be joined, the heat input can be controlled to suppress the melting and mixing of aluminum in the aluminum-based material and iron in the iron-based material and their reaction. . As a result, the generation of fragile intermetallic compounds at the joint is suppressed, and as a result, strength defects (particularly the occurrence of cracks) at the joint can be prevented. Laser welding can be applied in addition to AC MIG welding as a welding means capable of precise control of the heat input.

  As the welding wire (filler material), a flux-cored wire formed by coating flux with aluminum or an aluminum alloy is used. The wire diameter to be used is preferably 1.6 mm or less because it is necessary to generate a stable arc under low current conditions in order to minimize the amount of heat input. If the wire diameter exceeds 1.6 mm, the current for obtaining a stable arc becomes excessive, and the melting of the base metal becomes excessive, which may lead to the formation of fragile intermetallic compounds (Fe-Al compounds). is there.

  The welding wire flux includes aluminum fluoride and potassium fluoride, and further contains one or more fluorides selected from the group consisting of magnesium fluoride, calcium fluoride, strontium fluoride, and barium fluoride. Is used.

  Conventionally, a flux in which aluminum fluoride and potassium fluoride are mixed has an action of dissolving and removing a strong oxide on the surface of an aluminum-based material. However, since the mixed flux of aluminum fluoride and potassium fluoride has a very low melting point of not more than the melting point of aluminum (660 ° C.), the workability is deteriorated such that a large amount of the flux evaporates and fumes and spatter are generated. Moreover, the weld metal which consists of aluminum spreads too much, a sound bead is not formed, and high joint strength is not obtained. Therefore, the welding wire flux used in the present invention includes a mixed flux of aluminum fluoride and potassium fluoride, magnesium fluoride (melting point 1248 ° C.), which is a high melting point compound among fluorides of group IIA elements, and fluoride. A flux containing one or more of calcium (1403 ° C.), strontium fluoride (about 1400 ° C.) and barium fluoride (1353 ° C.) is used. Since the melting point of the flux can be raised to a temperature range of about 700 to 1000 ° C. by adding these high melting point fluorides, the spread of the weld metal made of aluminum in the initial stage of welding is suppressed, and a healthy bead is formed. At the same time, evaporation and scattering of the flux during welding are suppressed, and generation of fume and spatter can be reduced. If the total content of the high melting point fluoride is too large, the flux is difficult to melt and the effect of improving the wettability is not sufficiently exhibited. On the other hand, if the amount is too small, the effect of increasing the melting point of the flux is insufficient. It is desirable that the content be 10 to 50%.

  The iron-based material to which the joining method of the present invention is applied is not particularly limited as long as it is a material mainly composed of iron, such as a steel material or an iron-based alloy. It is preferable to do this. In addition, the intensity | strength of a steel plate is not specifically limited. Conventionally, in the welding of galvanized steel sheets, the arc has become unstable due to the generated zinc vapor, and the occurrence of spatter and pore defects such as pits and blowholes have become problems. For example, the cleaning effect of the steel plate surface is effectively exhibited by the effect of the flux, and the molten metal covers the steel plate surface with good wettability, so that the generation of zinc vapor is small and the arc stability is also excellent. Therefore, even if the galvanized steel sheet is welded, the occurrence of defects such as blow holes is small, and dynamic characteristics such as fatigue strength can be expected.

  As welding conditions for AC MIG welding in carrying out the present invention, the welding current is 20 A or more, more preferably 30 A or more, 100 A or less, more preferably 80 A or less. The welding voltage is 5 V or more, more preferably 7 V or more, 20 V or less, more preferably 18 V or less.

  The welding speed may be appropriately determined in accordance with the welding current and the welding voltage as long as Fe and Al in the base metal are not excessively melted. In consideration of welding efficiency and the like, it is preferably 15 cm / min or more, more preferably. Is 20 cm / min or more and 60 cm / min or less, more preferably 50 cm / min or less.

  In the present invention, an iron-based material and an aluminum-based material can be directly joined by AC MIG welding, so as long as an appropriate welding current, voltage condition, joining shape, etc. are adopted, there is no particular limitation, and the applicable range is expanded. Therefore, versatility is improved and continuous joining is also possible. In addition, both iron-based and aluminum-based materials can obtain a sound bonded state with the minimum necessary melting amount, and it is difficult for brittle intermetallic compounds to form at the interface between iron-based and aluminum-based materials, resulting in high bonding strength. Is obtained.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to carry out and they are all included in the technical scope of the present invention.

〔Example〕
The joining method of the present invention was employed to conduct a lap fillet welding test between an aluminum alloy plate and an alloy hot-dip galvanized (GA) steel plate.
1140139601343_0
As shown in Fig. 1, a 1.6 mm thick aluminum alloy plate is superimposed on a 1.2 mm thick GA steel plate to form a fillet joint, and various flux-cored wires are used to form an aluminum alloy plate and a GA steel plate. AC MIG welding was performed. Ar was used as the shielding gas. The plane size of the test piece was 100 mm × 300 mm for both the aluminum alloy plate and the GA steel plate, and a flux-cored wire having a diameter of 1.2 mm was used.

As a flux of the flux-cored wire, as a comparative example, a Nocolok (registered trademark) flux which is a mixed flux of aluminum fluoride (AlF ₃ ) and potassium fluoride (KF) is used, and as an example of the invention, this Nocolok (registered trademark). In the flux, the total amount of any one or two of magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), strontium fluoride (SrF ₂ ) and barium fluoride (BaF ₂ ) What was added so that it might become a ratio of 10 to 50% with respect to was used.

  The welding conditions were within the ranges of welding current: 30 to 80 A, welding voltage: 7 to 18 V, and welding speed: 15 to 60 cm / min, which are welding conditions for AC MIG welding recommended in the above-described best mode.

  And the bead stability and joint strength were evaluated by investigating the obtained joint. The bead stability was evaluated by observing the bead shape of the resulting joint joint. The case where the bead was intermittent was judged as bad (X), and the case where the bead width was almost constant and continuous was judged as good (O). (See FIG. 2). The joint strength was evaluated by taking a joint strength evaluation test piece having a plate width of 30 mm from the joint joint, performing a tensile test at a speed of 25 mm / min, and using the shear tensile strength calculated by the following formula (1). I went.

Formula (1) (Fitting strength) = (Maximum load point load) / (Fitting cross-sectional area)
Here, the joint sectional area was the sectional area in the thickness direction of the aluminum alloy plate.

The results of the evaluation test are shown in Table 1. In addition to potassium fluoride and aluminum fluoride, when a flux-cored wire using a flux containing a high melting point compound among fluorides of group IIA elements is used (invention example), these high melting point fluorides are not included. Compared to the conventional product (comparative example), the generation of fume and spatter is small, welding workability is good, bead stability is excellent, and a sound bead with few blowholes is obtained, resulting in high bonding strength. was gotten.

It is a front sectional view showing an outline of a welding test in an example. It is a top view for demonstrating the reference | standard which determines the quality of the bead shape of the joint joint in an Example.

Claims (3)

  A flux containing aluminum fluoride and potassium fluoride and further containing one or more fluorides selected from the group consisting of magnesium fluoride, calcium fluoride, strontium fluoride and barium fluoride is coated with aluminum or an aluminum alloy A method of joining an iron-based material and an aluminum-based material, characterized in that the flux-cored wire formed in this manner is used as a filler material, and an aluminum-based material and an iron-based material are directly joined by AC MIG welding.   The method for joining an iron-based material and an aluminum-based material according to claim 1, wherein the iron-based material is a galvanized steel sheet.   A joint joint of an iron-based material and an aluminum-based material obtained by the joining method according to claim 1 or 2.

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