JP2008207245A - Joined product of dissimilar materials of steel and aluminum material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joined product of dissimilar materials formed by melt-welding, which has satisfactory joint or weld strength even in the case of dissimilar material welding of a GA plated steel plate and an aluminum material. <P>SOLUTION: This dissimilar material joined product is produced by melt-welding a zinc plated layer steel product 1 having a specific plate thickness and an aluminum material 2 and forming an aluminum weld metal 3 in a joint interface 6. In a joint interface 6 between the aluminum weld metal 3 and the steel product 1, a joint interface layer 4 is formed which is composed of a mixed layer of an Al<SB>3</SB>Fe-based compound and an Al<SB>5</SB>Fe<SB>2</SB>-based compound formed on the steel product side, and an α-AlFeSi layer formed on the aluminum weld metal side. High weld strength is obtained by thinly and uniformly forming the joint interface layer 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dissimilar material joined body that is a joined body of dissimilar metal members of an iron-based material and an aluminum-based material in the transportation field of automobiles, railway vehicles, and the like, machine parts, and building structures.

  In welding, the same kind of metal members are generally joined together. However, the joining of dissimilar metal members (dissimilar materials joints) of iron-based materials (hereinafter simply referred to as steel materials) and aluminum-based materials (generically referring to pure aluminum and aluminum alloys, hereinafter simply referred to as aluminum alloy materials) If it can be applied to, it can contribute significantly to the weight reduction of the member only of steel materials.

  However, when steel and aluminum alloy materials are welded together, it is easy to form brittle Fe-Al intermetallic compounds at the joint, so it is very difficult to obtain a reliable joint (joint strength) with high strength. It was difficult. Therefore, conventionally, these dissimilar joined bodies (dissimilar metal members) are joined by bolts, rivets or the like, but there are problems such as reliability, air tightness, and cost of the joint joint.

  On the other hand, the strength of steel and aluminum alloy materials has been increased in order to reduce the weight of parts such as automobile bodies, and steel materials are made of high-tensile steel (high-tensile steel), and aluminum alloy materials have less alloying elements and are therefore recyclable. In addition, there is a tendency that an excellent A6000 series aluminum alloy material is used.

  For this reason, even in the welding joining between different materials, the conventional low-strength different materials such as mild steel and pure aluminum alloy or A5000-based aluminum alloy are joined together with high-tensile steel materials and 6000-based aluminum alloy materials. The joining object has been changed to welding joining of different strength materials. In Fe-Al bonding by fusion bonding, since a high heat input is applied, usually an extremely thick and brittle Fe-Al reaction layer exceeding several tens of μm is formed. For this reason, it is generally considered that Fe-Al joining by fusion welding is difficult. In particular, in the case of a high-strength steel material to which various alloys are added, the heat generation on the steel material side is particularly large due to the higher melting point, higher electrical resistance and lower thermal conductivity than mild steel with relatively low strength. Prone. As a result, in the case of such a high-strength steel material, the brittle Fe—Al reaction layer is more easily formed. Therefore, the welding conditions of high strength dissimilar materials are different in the formation conditions of brittle Fe-Al intermetallic compounds at the joint, and in order to obtain reliable high joint strength, New welding conditions are required for welding.

  When joining dissimilar materials of steel and aluminum alloy materials, the steel material has a higher melting point, higher electrical resistance and lower thermal conductivity than the aluminum alloy material. Aluminum melts. Next, the surface of the steel material melts, and as a result, a Fe—Al-based brittle intermetallic compound layer is formed at the interface, so that high bonding strength cannot be obtained.

  For this reason, many examinations and proposals have been made on the fusion welding method of these different types of joined bodies. For example, a method of brazing at a low temperature has been proposed so that a brittle Fe—Al intermetallic compound is not generated at the joint (see Patent Documents 1 and 2).

  In fusion welding of these dissimilar joints that are joined at higher temperatures, a solid wire made of an aluminum alloy to which at least 3 to 15 wt% of silicon is added is used as a welding wire, and an aluminum alloy material and galvanizing are applied to the surface. A method of joining a steel material by pulse MIG welding has been proposed (see Patent Document 3). In this method, along with the melting of the welding wire, silicon is also transferred to the base material, penetrates into the molten pool interface, becomes hot due to the heat of the arc, improves the wettability of the molten metal, and improves the adhesion. .

  Furthermore, it has been proposed to improve the composition of the flux used for fusion welding of dissimilar joints to increase the strength of the welded joint. As an example of this, a flux-cored wire in which a nocollock flux (cesium fluoride, aluminum fluoride, potassium fluoride, and aluminum oxide) is coated with aluminum can be used as a method for continuous welding simply and with the current welding line. Also disclosed is a method of arc welding a mild steel and pure aluminum or a 5000 series aluminum alloy material (see Patent Document 4).

  Further, a method for joining different materials between steel and aluminum is proposed, in which a fluoride-based mixed flux is applied and welded by various welding methods such as magnetic, ultrasonic, high frequency, and spot (Patent Document 5). reference). These methods promote the cleaning action of the steel surface by the chemical reaction of the flux, improve the wettability and adhesion of the molten metal made of aluminum, and prevent the formation of a fragile thick intermetallic compound layer.

Further, a fluoride-based flux having an effect of reducing, dissolving and removing the oxide film from the surface of the aluminum alloy material on which a strong oxide film is formed is applied to the surface of the aluminum alloy material, so that mild steel and 6000 series aluminum alloy material are applied. A method of spot welding the two has also been proposed (see Patent Document 6). Further, these fluoride fluxes are also used for fusion welding joining between aluminum alloy materials (see Patent Documents 7 and 8).
JP 7-148571 A JP 10-314933 A JP 2004-223548 A JP2003-2111270A JP 2003-48077 A JP 2004-351507 A JP 2004-210013 A JP 2004-210023 A

  In low-temperature brazing as in Patent Documents 1 and 2, brazing using an aluminum brazing material or a flux and an aluminum brazing material has been performed. However, in low-temperature brazing, management of the joining temperature range of the material to be joined is strictly higher than the melting temperature of the brazing material and below the melting temperature of the material to be joined, and is applicable to joining large members such as automobile bodies. For this purpose, a large furnace capable of precise temperature control is required. Further, since it takes a long time to join, it cannot be applied to a large-sized member such as an automobile body that requires high productivity.

  The method of MIG welding using a solid wire made of aluminum alloy added with silicon as a welding wire as in Patent Document 3 not only requires an expensive control power source for high-precision control such as heat input conditions, but also a joint. There is a problem that the shape is greatly limited. For this reason, it cannot be applied to a large-sized member such as an automobile body that requires a joint shape to be freely designed.

  Furthermore, in the flux-cored aluminum wire having a fluoride composition as disclosed in Patent Documents 4 and 5, dissimilar material joining of mild steel and pure aluminum or 5000 series aluminum alloy material is possible. However, the flux-cored aluminum wires having a fluoride composition disclosed in Patent Documents 4 and 5 provide high joint strength in the welding of high-strength dissimilar materials between a high-tensile steel material and a 6000 series aluminum alloy material. Absent. The same applies to the flux having the fluoride composition disclosed in Patent Documents 67 and 8.

  In addition, in a flux-cored wire in which a Nocolok flux is coated with aluminum as disclosed in Patent Document 4, the surface of the material itself can be cleaned by the action of a flux having a fluoride composition. However, since the moisture absorption of cesium fluoride contained in this flux is extremely high, it tends to cause blowholes in the weld metal due to moisture, and there is a concern that the corrosion resistance of the weld may be deteriorated. .

  In addition, since the flux filling rate is not properly controlled, workability deteriorates due to the large amount of molten flux scattered, and the wettability of the weld metal by the flux becomes too good and spreads, resulting in failure to form beads. Further, the brittle interfacial reaction layer is thickly formed over a wide range due to the expansion of the beads, resulting in deterioration of joint strength.

  And in the conventional fusion welding using the flux of these dissimilar materials joined bodies, there is a big limit in common in order to increase the joining strength of the steel material in which at least the joint surface with the aluminum material is galvanized.

  In the case of a high-tensile steel plate (GA-plated steel plate), etc., on which the surface of the steel material is galvanized, in particular, hot-dip galvanized, it is extremely difficult to increase the joint strength of the dissimilar material joined body. And this kind GA plating steel plate is widely used for an automobile body as is well known. In this GA plating, it is extremely difficult to increase the joining strength of the dissimilar material joined body by the fusion welding as compared with pure zinc plating (GI plated steel sheet).

  Therefore, this point is also a major factor that the application of the dissimilar material joint of the steel material and the aluminum material does not spread in the structural member application such as the automobile described above.

  In view of such circumstances, the present invention has an object to provide a dissimilar material joined body by fusion welding having sufficient joint strength or joining strength even in the case of dissimilar material joining with an aluminum material using a GA plated steel sheet. And

In order to achieve the above object, the gist of the dissimilar material joined body of steel material and aluminum material in the present invention is that a galvanized steel material having a thickness t ₁ of 0.5 to 5.0 mm and a thickness t ₂ of 0.5. It is a dissimilar material joined body in which an aluminum material having a thickness of ˜4.0 mm is joined by forming an aluminum weld metal at a joint portion by fusion welding, and at the joining interface between the aluminum weld metal and the steel material, Al is provided on the steel material side. A bonding interface layer having a mixed layer of ₃ Fe compound and Al ₅ Fe ₂ compound and an α-AlFeSi layer on the aluminum weld metal side is formed, and the average thickness of the bonding interface layer in the plate thickness direction is formed. Is 0.5 to 5 μm.

  Here, it is preferable that a flux is used in the fusion welding, and this flux is a mixed flux composition of aluminum fluoride and potassium fluoride that does not contain chloride. It is preferable to supply this flux to the fusion welded part as a flux cored wire filled in an aluminum alloy outer skin.

  The α-AlFeSi phase itself in the bonding interface layer defined in the present invention is known as a body-centered cubic intermetallic compound phase of Al, Fe, and Si together with a single crystal β-AlFeSi phase. This α-AlFeSi phase is derived from pure aluminum, Fe of aluminum alloy, impurities of Si, Fe alloy of aluminum alloy, alloy elements of Si, and the like. It is a precipitate.

Incidentally, the α-AlFeSi phase itself has been known as a compound phase that improves the machinability and surface finish of an aluminum alloy photoreceptor (Japanese Patent Laid-Open No. 11-131168, etc.). In addition, due to impurities of Fe and Si in pure aluminum, the amount of solid solution and precipitation varies depending on heat treatment conditions and hot working conditions, and changes to Al ₃ Fe compound, α-AlFeSi phase, and simple substance Si. It is known to affect properties such as work hardening, softening, and texture (Kobe Steel Technical Report / Vol. 56. No. 1. Apr. 2006).

In the present invention, an Al ₃ Fe-based compound inevitably generated on the steel material side at the joint interface between the aluminum weld metal and the steel material in the dissimilar material joined body formed by forming an aluminum weld metal at the joint by fusion welding and In addition to the mixed layer with the Al ₅ Fe ₂ -based compound, an α-AlFeSi layer is formed on the aluminum weld metal side.

  This α-AlFeSi layer is not necessarily formed in the fusion welding of the galvanized steel material and the aluminum material. According to the knowledge of the present inventors, this α-AlFeSi layer is formed on the aluminum weld metal side only under a specific fusion welding condition using a specific flux.

  The fact that the formation of the α-AlFeSi layer depends on the melt welding conditions, as described above, that the solid solution and precipitation amount (solid solution and precipitation state) of Fe and Si in aluminum depend on the heat treatment and hot working conditions of aluminum. This is also supported by the well-known fact that the precipitated compound changes greatly.

  If the present inventors can form an α-AlFeSi layer on the aluminum weld metal side at the joint interface between the aluminum weld metal and the steel material, the α-AlFeSi layer is brittle and thick Fe-Al based at the joint interface. It has been found that it has an effect of suppressing the formation of an intermetallic compound layer. The effect of suppressing the formation of the Fe—Al-based intermetallic compound layer is that the average thickness in the plate thickness direction of the bonding interface layer (intermetallic compound mixed layer) including the α-AlFeSi layer on the aluminum weld metal side is 0. It is possible to reduce the thickness in the range of 5 to 5 μm. As a result, according to the present invention, it is possible to remarkably improve the bonding strength of the dissimilar material joined body of steel and aluminum.

  When joining dissimilar materials of steel and aluminum, the steel has a higher melting point, higher electrical resistance and lower thermal conductivity than the aluminum, so the heat generation on the steel side increases, and the low melting point aluminum melts first. To do. Next, the surface of the steel material is melted, and as a result, an Al—Fe based brittle intermetallic compound layer is formed at the joining interface (welding interface).

Fe-Al intermetallic compounds that are inevitably formed at the joining interface on the steel material side by fusion welding of steel and aluminum are mainly Al ₃ Fe compounds (meaning intermetallic compound Al ₃ Fe) and Al It is known to be a ₅ Fe ₂ -based compound (meaning intermetallic compound Al ₅ Fe ₂ ). Since these Fe-Al based intermetallic compounds are very brittle, it has been conventionally assumed that high bonding strength cannot be obtained.

In addition, in the fusion welding of a galvanized steel material such as GA and an aluminum material, a Zn—Fe-based compound (intermetallic compound Fe ₃ Zn ₇ or the like) derived from this galvanizing is generated, and the above-described Fe—Al-based material It is necessarily contained as an impurity in the intermetallic compound layer. And since this Zn-Fe-type compound layer is still brittle, it is likely to become a starting point of fracture, and the joint strength of the dissimilar material joined body is significantly reduced.

  Therefore, especially when different materials of galvanized steel and aluminum are joined by fusion welding, the thickness and structure of the interface reaction layer at the joining interface (welding interface) is controlled in order to obtain high joining strength. It becomes very important.

  In the present invention, the zinc-plated steel material such as GA produces a Zn-Fe-based compound derived from this galvanizing and, for example, is necessarily included as an impurity in the Fe-Al-based intermetallic compound layer. Even in this case, the formation of the Fe—Al intermetallic compound layer itself can be suppressed by forming the α-AlFeSi layer on the aluminum weld metal side. As a result, even if the galvanization on the steel material side is GA plating, the present invention can remarkably improve the joining strength of the dissimilar material joined body of the steel material and the aluminum material.

(Dissimilar material joint)
The dissimilar material joined body of the present invention will be described. FIG. 1 is a cross-sectional view showing a lap joint (joined) portion of a dissimilar material joined body of the present invention after fusion joining. FIG. 2 is an enlarged view of the bonding interface 6 of the bonding portion 5 in FIG. 1 and 2 are manufactured by the fusion welding method shown in FIG. 3 or FIG. 4 described later.

1 and 2, 1 is a galvanized (GA) steel plate, 2 is an aluminum plate, 3 is an aluminum weld metal (aluminum bead), and 4 is a bonding interface layer (interface reaction layer or bonding interface 6). T ₁ is the thickness of the galvanized steel plate (steel material), and t ₂ is the thickness of the aluminum plate (aluminum material) 2.

(Bonding interface)
2, the α-AlFeSi layer on the aluminum weld metal side is preferentially generated (formed) on the aluminum weld metal side at the initial stage of the reaction at the time of fusion welding under the specific fusion welding conditions described later. It has been made.

On the other hand, the mixed layer of the Al ₃ Fe compound (Al ₃ Fe reaction layer) and the Al ₅ Fe ₂ compound (Al ₅ Fe ₂ reaction layer) on the steel material side in FIG. Inevitably produced if the welding conditions are

However, the α-AlFeSi layer on the aluminum weld metal side is preferentially generated at the beginning of the reaction at the time of fusion welding, so that mutual diffusion of Al and Fe after the beginning of the reaction at the fusion welding at the joint interface 6 is achieved. Is suppressed. For this reason, the time for forming the brittle Fe—Al ₅ reaction layer (Al ₃ Fe compound: Al ₃ Fe, Al ₅ Fe ₂ ) is delayed.

  Thus, the α-AlFeSi layer on the aluminum weld metal side acts as a mutual diffusion suppressing layer of Al and Fe after the initial stage of the reaction at the time of fusion welding, and an interface reaction layer (bonding interface layer 4 including this α-AlFeSi layer). ) Is formed between the aluminum weld metal 3 and the galvanized steel sheet 1 in a thin and uniform manner. As a result, a high bonding strength of the dissimilar material bonded body can be stably obtained.

Note that the bonding interface structure such as the α-AlFeSi layer and the Fe—Al ₅ -based reaction layer (Al ₃ Fe-based compound: Al ₃ Fe, Al ₅ Fe ₂ ) has an electron diffraction pattern analysis of the bonding interface layer 4 and X Can be identified by line diffraction analysis.

(Bonding interface layer)
The thickness of the bonding interface layer (interface reaction layer) to be made thin and uniform is such that the mixed layer of the Al ₃ Fe-based compound and the Al ₅ Fe ₂ -based compound on the steel material side and the α on the aluminum weld metal (aluminum bead) side -Let AlFeSi layer be a bonding interface layer, and the average thickness of these layers in the total thickness direction is 0.5 to 5 m.

  When the thickness of the bonding interface layer is less than 0.5 μm, the metallurgical bonding between the aluminum weld metal 3 and the galvanized steel sheet 1 cannot be performed, and the bonding strength of the dissimilar material bonded body becomes low. On the other hand, when the thickness of the bonding interface layer exceeds 5 μm, the bonding interface 6 becomes fragile, and the bonding strength of the dissimilar material bonded body also decreases.

  The thickness of the bonding interface layer is about 500 times magnification at the bonding interface from the top of the aluminum weld metal 3 to the toe end of the cross section of the dissimilar material joined body, with an optical microscope or SEM (scanning electron). Measure using a microscope.

  In order to increase the joining strength of the dissimilar material joined body, the thin and uniform joining interface layer 4 as shown in FIG. 2 is formed over the entire joining interface 6 between the aluminum weld metal 3 and the galvanized steel sheet 1 as shown in FIG. It is effective to make it.

(Α-AlFeSi layer)
As described above, the α-AlFeSi phase in the bonding interface layer defined in the present invention is a body-centered cubic intermetallic compound phase of Al, Fe, and Si. By X-ray diffraction analysis, the compound composition and the crystal form are clearly distinguished and specified from the single crystal β-AlFeSi phase and the like.

  In order to preferentially generate the α-AlFeSi layer on the aluminum weld metal side at the initial stage of the reaction at the time of fusion welding, it is effective to use a flux at the time of fusion welding. However, in order to preferentially generate the α-AlFeSi layer on the aluminum weld metal side at the initial stage of the reaction at the time of fusion welding, the flux has the effect of reducing and removing the surface oxide film of the welded material such as an aluminum alloy material, It is necessary to have an effect of promoting the formation of the α-AlFeSi layer at the initial stage of welding.

  In this regard, examples of the conventional fluoride flux described above include cesium fluoride and zinc fluoride. Even these fluoride fluxes have a function of cleaning the surface of the aluminum alloy material. However, these fluoride fluxes are extremely hygroscopic. For this reason, moisture that has been absorbed is likely to cause blowholes in the weld metal part, and there is a concern that the corrosion resistance of the weld part may be deteriorated. Moreover, fatally, the effect of promoting the formation of the α-AlFeSi layer at the initial stage of welding is small.

  The α-AlFeSi phase is derived from pure aluminum or aluminum alloy Fe, Si impurities, aluminum alloy Fe, Si alloy elements, etc. Deposit on the metal side.

  However, in this way, in order to preferentially generate the α-AlFeSi layer on the aluminum weld metal side at the initial stage of the reaction at the time of fusion welding, together with the above specific welding conditions, the aluminum material is an impurity, Alternatively, any alloy element may be used, but it is preferable to contain a substantial amount of Fe and Si (a sufficient amount to generate the α-AlFeSi phase).

  On the other hand, depending on the aluminum material to be bonded to the dissimilar material, the amount of Fe and Si contained may be insufficient (or can be predicted to be insufficient) for the formation of the α-AlFeSi phase. In such a case, during welding, Fe and Si are supplied from the outside to the aluminum material side joining interface. That is, using an aluminum solid wire for making an aluminum weld metal (bead), a flux-cored aluminum wire, and the like, Fe and Si are contained therein, and only an amount sufficient to produce an α-AlFeSi phase is sufficient. Si is supplied to the aluminum material side bonding interface.

(Norocrock flux)
On the other hand, among the fluoride-based mixed fluxes, the mixed flux of aluminum fluoride and potassium fluoride (Nocolok flux) has a cleaning effect on the surface of the steel material due to the chemical reaction between aluminum fluoride and potassium fluoride. At the same time, the strong oxide film on the surface of the aluminum plate is reduced, dissolved and removed. As a result, the effect of promoting the formation of the α-AlFeSi layer at the initial stage of welding is further enhanced, and there is also an effect of improving the bonding strength and appearance in order to significantly improve the wettability of the molten metal made of aluminum and the steel material.

  Further, the nocolok flux used in the present invention has the above-mentioned fluoride composition not containing chloride. When chloride remains in the welded part, it acts as a corrosion promoting factor for the welded part or the dissimilar material joined body. For this purpose, the content of chloride in the flux is regulated. In this respect, it is preferable that the nocolok flux contains no chloride at all. However, in consideration of the cost and practicality of the nocolok flux, the inclusion of chloride within the range not promoting corrosion is allowed. As a guide, the amount of chloride is 1 mol% or less with respect to the total amount of Nocolok flux.

  In addition, the above-mentioned Nocolok flux used in the present invention allows the case of containing an oxide as a flux component. Specifically, aluminum oxide, sodium oxide, lithium oxide, phosphorus pentoxide, or the like may be added as appropriate as long as the effect of fluoride is not impaired. Their upper limit is about 30 mol% with respect to the total flux.

(Noroclock flux usage)
FIGS. 3 and 4 are cross-sectional views respectively showing a fusion welding method for joining different materials using Nocolok flux. 3 and 4, the end portion of the aluminum material 2 is overlapped on the end portion of the hot dip galvanized steel material 1 so as to form the lap joint of the end portions.

  Then, using a welding torch, a flux-cored wire, or the like, the welding torch or the like is moved along the welding line 10 that extends along the ends of the steel material 1 and the aluminum material 2 (in the front-rear direction in the figure). Then, the entire length of the weld line 10 is melt welded. At this time, welding conditions such as the inclination angle of the welding torch are appropriately selected.

  As the supply method of the nocolok flux, (1) a method of forming a flux layer on the surface of the aluminum plate, (2) a flux-cored wire in which the flux is encapsulated in an aluminum alloy sheath is used as a filler material, and the flux is supplied. A method is appropriately selected.

  FIG. 3 shows an embodiment in which a Noclock flux 7 is disposed (applied and laminated) in advance between the joint (joint) portions of the galvanized (GA) steel plate 1 and the aluminum plate 2 as the embodiment of (1) above. Indicates. Reference numeral 8 denotes an aluminum solid wire for forming an aluminum weld metal (aluminum bead) 3.

(Flux-cored wire)
FIG. 4 shows, as a mode of the above (2), a flux cored wire (FCW, flux-cored wire) 9 in which a nocolok flux is filled in an aluminum alloy skin, and a galvanized (GA) steel plate 1 and an aluminum plate 2 A mode in which the material is supplied to the joint (joint) is shown. The FCW 9 is made of aluminum for forming an aluminum weld metal (aluminum bead) 3 in an outer shell that fills and accommodates a Nocolok flux.

  It is preferable to relatively reduce the filling amount (filling rate) of the noclock flux into the flux-cored wire, such as 0.1 mass% or more and less than 24 mass% with respect to the total mass of the flux-cored wire. When the flux filling rate is increased to over 24%, as in the case of flux cored wires that are commercially available or widely used in the past, a large amount of melted flux is obtained even under normal AC MIG welding or MIG welding conditions with DC reverse polarity. Scatter. In addition to this, the wettability improving effect is too strong, the weld metal spreads too much, a sound bead is not formed, the welding workability is poor, and the bead is not formed soundly, so the reliability of the welded portion is also impaired.

  On the other hand, the lower limit of the filling rate of the nocolok flux is 0.1%. If the filling rate of Nocolok flux is too small, it is the same as the aluminum welding wire (JIS standard: A4043-WY, A4047-WY, A5356-WY, A5183-WY, etc.) for forming beads commonly used in arc welding Become. For this reason, if the filling rate of the nocolok flux is less than 0.1%, the effect of the nocolok flux such as the wettability improvement effect cannot be exhibited, and a sound and highly reliable welded joint cannot be obtained.

  When a flux-cored wire is used, when joining an aluminum material and a steel material including a hot-dip galvanized steel material, there are few restrictions such as application conditions and excellent versatility, and there are few shape restrictions. Also, joining technology that enables continuous joining necessary for wire welding, with less brittle intermetallic compounds in the joints, blowholes in the welds and deterioration in corrosion resistance, and good welding workability. Can provide. For this reason, it becomes possible to provide a dissimilar material joint (dissimilar material welded joint) applicable to structural members, such as a car.

(Skin aluminum alloy)
In order to suppress the formation of the Fe-Al intermetallic compound layer between the steel and the aluminum alloy material, an aluminum alloy band is used for the tubular outer sheath (also called a hoop) of the flux cored wire. Is used. Under the present circumstances, it is preferable that the aluminum alloy which is an outer shell contains 1-13 mass% of Si, and consists of remainder Al and an unavoidable impurity. This is mainly to ensure the fluidity of the aluminum alloy in the molten state, the strength of the joint after solidification, the strength as the outer skin, and the like. When there is too little Si content, fluidity | liquidity and intensity | strength will fall. Conversely, if the Si content increases too much, the improvement in fluidity tends to be saturated, and the tendency of the weld metal to become brittle increases. For this reason, the amount of Si in the case of containing is made into the range of 1-13 mass%.

  The outer aluminum alloy preferably contains 0.1 to 0.3% by mass of Mn in addition to this Si, and is composed of the balance Al and inevitable impurities. This is mainly for ensuring the fluidity of the aluminum alloy in the molten state, the strength of the joint after solidification, the strength as the outer skin, and the like. As the outer skin having such an aluminum alloy composition, it is preferable to use a standardized and widely used aluminum alloy filler. As the aluminum alloy filler having such an aluminum alloy composition, it is preferable to use A4047 containing 11.0 to 13.0% by mass of Si and 0.15% by mass or less of Mn. Moreover, A4043 which contains Si 4.5 to 6.0 mass% and Mn 0.05 mass% or less can also be used.

(Melting welding method)
Laser, MIG, TIG, electron beam welding, or the like can be used as a heat source for fusion welding in the dissimilar material joining of the present invention. In other words, the melt welding method used is not particularly limited, and a general-purpose melt welding method using a heat source such as an arc or a laser can be used. For example, AC MIG welding, MIG welding with reverse DC polarity, TIG method, laser method, or a hybrid welding method thereof can be applied. In actual fusion welding, the welding method is selected and the welding conditions are optimized in accordance with the type and shape of the material to be welded, the shape and structure of these dissimilar joints, and the required joining characteristics.

  In the present invention, the steel material and the aluminum material can be directly joined. Therefore, as long as an appropriate welding current, voltage condition, joining shape, etc. are adopted, there is no particular limitation. Although it is the same as that of the method, a preferable range is described below.

(Welding current)
When performing AC MIG welding or MIG welding with DC reverse polarity, the larger the current, the more likely the flux is scattered, and the more brittle intermetallic compounds are produced at the joint interface. For this reason, in order to suppress such scattering of flux and intermetallic compounds, it is recommended to perform bonding under a low current condition. Such a welding current is 20 A or more, more preferably 30 A or more, 100 A or less, more preferably 80 A or less.

(Welding voltage)
As with the welding current, it is recommended that the welding voltage be joined under low voltage conditions for both AC MIG welding and MIG welding with reverse DC polarity. In this respect, the welding voltage is 5 V or more, more preferably 7 V or more, 20 V or less, more preferably 18 V or less.

(Laser output)
A carbon dioxide laser with a wavelength of 10.6 μm, a YAG laser with a wavelength of 1.06 μm, and a GA are typical, and the laser output is preferably 3 kW or more.

(Welding speed)
The welding speed for both AC MIG welding and MIG welding with reverse DC polarity, including the laser method, is appropriately determined within a range in which Fe and Al in the base metal are not excessively melted according to the welding current, welding voltage, or output. That's fine. In AC MIG welding, it is preferably 15 cm / min or more and 60 cm / min or less in consideration of welding efficiency and the like. In MIG welding with reverse DC polarity, in order to suppress the generation of fragile intermetallic compounds, it is necessary to increase the welding speed as much as possible to reduce the heat input, so that the welding speed is preferably 30 cm / min or more. It is 150 cm / min or less.

(Shielding gas)
For both MIG welding with AC and MIG welding with reverse polarity, including laser method, a general-purpose gas such as Ar can be used as the shielding gas, and a general-purpose flow rate of 10-50 L / min can be selected as the shielding gas flow rate. There is no particular limitation.

(Welding torch angle)
Welding Torch (Arc Torch) The angle is not particularly limited, and for both AC MIG welding and MIG welding with reverse DC polarity, the angle θ is appropriately selected according to the welding conditions and the welding conditions of the joint.

(Thickness of galvanized steel and aluminum)
Here, in this invention, the range of the plate | board thickness of the galvanized steel materials and aluminum material which mutually join is prescribed | regulated to the practical range which can be practically melt-welded. That is, the plate thickness t ₁ of the galvanized steel material is defined as a range of 0.5 to 5.0 mm, and the plate thickness t ₂ of the aluminum material is defined as a range of 0.5 to 4.0 mm.

(Galvanized steel)
The plate thickness t ₁ of the galvanized steel material to be joined must be selected from the range of 0.5 to 5.0 mm according to the plate thickness t ₂ on the aluminum material side.

If the thickness t _{1 of the} steel material is too thin at less than 0.5 mm, the strength and rigidity necessary for the above-described structural member and structural material cannot be ensured, which is inappropriate. Moreover, when the thermal deformation of the steel material at the time of fusion welding becomes large and this is remarkable, the material of the steel material falls off and a sound welded joint cannot be obtained. On the other hand, if the thickness t _{1 of the} steel material exceeds 5.0 mm and is too thick, the weight reduction which is one of the advantages of the dissimilar material joined body is sacrificed. In addition, it becomes difficult to control the amount of heat input required to produce an interface reaction layer having an appropriate thickness necessary for obtaining the joined body of the present invention. For this reason, the formation of the α-AlFeSi layer is likely to be uneven, and the interface reaction layer (bonding interface layer 4) due to the mixed layer of the Al ₃ Fe compound and the Al ₅ Fe ₂ compound on the steel material side becomes too thick. , Resulting in strength degradation.

  Although the present invention is effective for GA (alloyed hot dip galvanizing), the target galvanizing is not limited to GA plated steel, but also includes GI, electroplated steel, etc. Target the body.

  In the present invention, the shape and material of the steel material to be used are not particularly limited, and an appropriate shape and material, such as a steel plate, a steel shape member, a steel pipe, which are generally used for structural members or selected from structural member applications Can be used. However, when a high-strength steel material is required for the structural member, it is preferable to use a high-tensile steel material (high tensile) having a tensile strength of 400 MPa or more.

(Aluminum material)
The aluminum material used in the present invention is not particularly limited in the type and shape of the alloy, and depending on the required characteristics as each structural member, commonly used plate materials, profiles, forging materials, casting materials, etc. It is selected appropriately. As for the strength of the aluminum material, as in the case of the steel material, a higher structural material is desirable. In this respect, the use of AA (or JIS) 50000 series, 6000 series, etc., which has high strength among aluminum alloys and is widely used as this kind of structural member, is optimal.

In the present invention, the thickness t ₂ of the aluminum material to be used in the range of 0.5 to 4.0 mm. If the thickness t ₂ of the aluminum material is too and thin below 0.5 mm, it is inappropriate to insufficient strength as a structural material. Moreover, when the thermal deformation of the aluminum material at the time of fusion welding becomes large and this is remarkable, the material of the aluminum material falls off and a sound welding joint cannot be obtained. On the other hand, when the plate thickness t ₂ of the aluminum material exceeds 4.0 mm, the weight reduction which is one of the advantages of the dissimilar material joined body is sacrificed. In addition, it becomes difficult to control the amount of heat input required to produce an interface reaction layer having an appropriate thickness necessary for obtaining the joined body of the present invention. For this reason, the formation of the α-AlFeSi layer is likely to be uneven, and the interface reaction layer (bonding interface layer 4) due to the mixed layer of the Al ₃ Fe compound and the Al ₅ Fe ₂ compound on the steel material side becomes too thick. , Resulting in strength degradation.

  Hereinafter, the dissimilar material joined body as shown in FIG. 1 was prepared using laser and AC MIG welding, and the joint interface (interface reaction) layer was analyzed and the joint strength was evaluated. These results are shown in Table 1 for Example 1 using laser welding and in Table 2 for Example 2 using MIG welding.

  In addition, a comparative example dissimilar material joined body (Comparative Example 9 in Tables 1 and 2) having all the same welding conditions, such as a welded material, except that no Noloc Flux is used, was also produced in Examples 1 and 2, and a joining interface ( The interface reaction) layer was analyzed and the bonding strength was evaluated. Moreover, the comparative example dissimilar material joined bodies (Comparative Examples 10 to 13 in Tables 1 and 2) which were all the same welding conditions except that the plate thickness deviated from the plate thickness condition of the present invention were produced in the same manner, and the bonded interface ( The interface reaction) layer was analyzed and the bonding strength was evaluated.

(Welding material conditions)
In each of Examples 1 and 2, Invention Examples 1 to 8 and Comparative Example 9 in Tables 1 and 2 satisfied the present invention thickness conditions and set the same thickness conditions. That is, in FIG. 1, the aluminum material 2 is an aluminum alloy plate (AA6022) having a thickness t ₂ of 1.0 mm, and the steel material 1 is a GA (hot galvanized) steel plate (590 N / mm) having a thickness t ₁ of 1.2 mm. ² ) Used. On the other hand, in Examples 1 and 2, in Comparative Examples 10 to 13 in Tables 1 and 2, the plate thickness on either side of the steel material 1 and the aluminum material 2 in FIG. The invention sheet thickness conditions were not met. In the comparative examples 10 to 13, the types of the steel material 1 and the aluminum material 2 in FIG. 1 are the same as those of the inventive examples 1 to 8 and the comparative example 9 in common with each example, and the GA steel plate (590 N / mm ² ) And AA6022 aluminum alloy plate.
In Comparative Example 10, the thickness t _{1 of the} steel material ₁ was 5.5 mm that was too thick, and the thickness t ₂ of the aluminum material 2 was 3.6 mm within the range.
In Comparative Example 11, the plate thickness t _{1 of the} steel material ₁ was too thin 0.3 mm, and the plate thickness t ₂ of the aluminum material 2 was 1.0 mm within the range.
In Comparative Example 12, the thickness t _{1 of the} steel material ₁ was 0.7 mm within the range, and the thickness t ₂ of the aluminum material ₂ was too thin 0.2 mm.
In Comparative Example 13, the thickness t _{1 of the} steel material ₁ was 4.8 mm within the range, and the thickness t ₂ of the aluminum material 2 was 4.2 mm too thick.
In addition, as for the arrangement | positioning at the time of welding of each of these examples, as shown in the said FIG. 1, the GA steel plate 1 was turned down, the aluminum alloy plate 1 was piled up, and the mutual lap width | variety was 30 mm. .

(Noroclock flux condition)
In both Examples 1 and 2, the types of nocolok flux used were the following four types depending on the mixing ratio of aluminum fluoride (AlF ₃ ) and potassium fluoride (KF). In the column of the type of flux in Tables 1 and 2 below, the symbols (a) to (d) are used.
(A) K ₃ AlF ₆ (25 mol% AlF ₃ , 75 mol% KF)
(B) K ₃ AlF ₆ (33 mol% AlF ₃ , 67 mol% KF)
(C) 75 mol% AlF ₃ , 25 mol% KF
(D) 40 mol% AlF ₃ , 60 mol% KF

(Application conditions)
In both Examples 1 and 2, the flux was supplied in two ways: application of flux 7 in FIG. 3 or use of FCW 9 in FIG. As shown in FIG. 3, when applying the Nocolok flux 7 to the surface of the aluminum plate 2, the flux powder suspended in an ethanol solution was thinly applied to the welded portion of the aluminum plate 2 with a brush. The amount of flux applied was 1-2 g / m ^{2 in} each example. In this application, AA4047WY wire having a diameter of 1.2 mmΦ was used as the filler material.

(FCW conditions)
In both of Examples 1 and 2, when FCW9 of FIG. 4 is used, a flux-cored wire having a wire diameter of 1.2 mmφ is used, and the filling amount (filling rate) of the nocolock flux into the wire is the total mass of the flux-cored wire. The content was 5% by mass. At this time, the above-described A4043 aluminum alloy filler was used as the outer aluminum alloy of the wire.

(Bonding interface layer)
In both Examples 1 and 2, the identification of the intermetallic compound on the galvanized steel sheet 1 side and the intermetallic compound on the aluminum weld metal 3 side in the joint interface structure (joint interface layer) 4 shown in FIG. Ten arbitrary locations were measured by electron beam diffraction image analysis of the interface layer 4. In addition, the thickness of the bonding interface layer 4 is about 500 times at the bonding interface from the top of the aluminum weld metal 3 to the toe portion of the cross section of the bonding interface (dissimilar material bonded body). Then, arbitrary 10 points were measured and averaged.

(Joint strength)
In both Examples 1 and 2, laser and AC MIG welding were performed three times for each example under each condition. In order to measure the bonding strength, a test piece having a width of 30 mm including a bonded portion was cut out from the bonded joint of each of the three dissimilar joints, a tensile test was performed, and each of the breaking strengths per unit weld line was measured. Were averaged and evaluated. When the breaking strength was 250 N / mm or more, ◎, when it was 200-250 N / mm, ◯, when it was less than 100-200 N / mm, Δ, and when it was less than 100 N / mm, it was rated as x. Here, unless the breaking strength is 200 N / mm (◯) or more, it cannot be used as a dissimilar material joined body for a structural material such as an automobile.

(Example 1)
In Example 1, a dissimilar material joined body was manufactured by laser welding. Laser welding used a defocused continuous wave YAG laser. The welding conditions were laser output: 4.0 kW, joining speed: 1.2 m / min, and shielding gas: Ar.

As can be seen from Table 1, the invention of a galvanized steel material and an aluminum material, which satisfy the plate thickness condition and are joined by forming an aluminum weld metal at the joint portion by means of appropriate laser welding using Nocolok flux. Example: The dissimilar material joined body has a mixed interface layer having an α-AlFeSi layer on the aluminum weld metal side together with a mixed layer of Al ₃ Fe compound and Al ₅ Fe ₂ compound on the steel material side. The average thickness of the bonding interface layer in the plate thickness direction is 0.5 to 5 μm. As a result, the inventive different-material bonded body has high bonding strength that can be used for structural materials such as automobiles.

On the other hand, the dissimilar material joined body of Comparative Example 9 under the same conditions except that no nocolok flux was used was only a mixed layer of the steel material side Al ₃ Fe compound and Al ₅ Fe ₂ compound. The α-AlFeSi layer is not formed on the aluminum weld metal side. Further, the average thickness in the plate thickness direction of the bonding interface layer, which is composed only of the mixed layer of the Al ₃ Fe compound and the Al ₅ Fe ₂ compound, is thicker than 5 μm. As a result, the joint strength of the dissimilar material joined body of Comparative Example 9 is low and cannot be used for structural materials such as automobiles.

In Comparative Example 10 to 13, are used to Nocolok fluxes, as described above, the steel material 1 side of the plate thickness t ₁ or the plate thickness t ₂ Kano one of the aluminum material 2 side, the present invention thickness Does not satisfy the conditions. Therefore, in Comparative Examples 10 to 13, even if nocolock flux is used or only one of the plate thicknesses deviates from the plate thickness condition of the present invention, as described above, It is difficult to control the amount of heat. As a result, as shown in Table 1, in Comparative Examples 11 and 12 in which either plate thickness is too thin, thermal deformation during welding is large, the material falls off, and a sound welded joint is not obtained. On the other hand, as shown in Table 1, in Comparative Examples 10 and 13 in which any of the plate thicknesses is too thick, the mixed layer of the Al ₃ Fe compound and the Al ₅ Fe ₂ compound on the steel material side has It exceeds the upper limit of 5 μm in the average thickness in the plate thickness direction and is too thick. In Comparative Examples 10 and 13, although an α-AlFeSi layer was generated, it was non-uniform. From these results, the comparative example that deviates from the plate thickness condition of the present invention cannot be used for structural materials such as automobiles because the bonded material of the dissimilar material itself cannot be created or even if it can be prepared, the bonding strength of the dissimilar material bonded material is low. I understand that.

(Example 2)
In Example 2, a dissimilar material joined body was manufactured by AC MIG welding. The welding conditions were performed within the range of the MIG welding conditions recommended above. Welding speed: AC MIG welding was 35 cm / min, welding current: 75 A, welding voltage: 18 V, welding torch angle was 90 °, and Ar was used as the shielding gas.

As can be seen from Table 2, the invention of a galvanized steel material and an aluminum material, which satisfy the plate thickness condition and are joined by forming an aluminum weld metal at the joint portion by means of appropriate laser welding using Nocolok flux. Example: The dissimilar material joined body has a mixed interface layer having an α-AlFeSi layer on the aluminum weld metal side together with a mixed layer of Al ₃ Fe compound and Al ₅ Fe ₂ compound on the steel material side. The average thickness of the bonding interface layer in the plate thickness direction is 0.5 to 5 μm. As a result, the inventive different-material bonded body has high bonding strength that can be used for structural materials such as automobiles.

On the other hand, the dissimilar material joined body of Comparative Example 9 under the same conditions except that no nocolok flux was used was only a mixed layer of the steel material side Al ₃ Fe compound and Al ₅ Fe ₂ compound. The α-AlFeSi layer is not formed on the aluminum weld metal side. Further, the average thickness in the plate thickness direction of the bonding interface layer, which is composed only of the mixed layer of the Al ₃ Fe compound and the Al ₅ Fe ₂ compound, is thicker than 5 μm. As a result, like Example 1, the joining strength of the dissimilar material joined body of Comparative Example 9 is low and cannot be used for structural materials such as automobiles.

In Comparative Example 10 to 13, are used to Nocolok fluxes, as described above, the steel material 1 side of the plate thickness t ₁ or the plate thickness t ₂ Kano one of the aluminum material 2 side, the present invention thickness Does not satisfy the conditions. Therefore, in Comparative Examples 10 to 13, even if nocolock flux is used or only one of the plate thicknesses deviates from the plate thickness condition of the present invention, as described above, It is difficult to control the amount of heat. As a result, as shown in Table 1, in Comparative Examples 11 and 12 in which either plate thickness is too thin, thermal deformation during welding is large, the material falls off, and a sound welded joint is not obtained. On the other hand, as shown in Table 1, in Comparative Examples 10 and 13 in which any of the plate thicknesses is too thick, the mixed layer of the Al ₃ Fe compound and the Al ₅ Fe ₂ compound on the steel material side has It exceeds the upper limit of 5 μm in the average thickness in the plate thickness direction and is too thick. In Comparative Examples 10 and 13, although an α-AlFeSi layer was generated, it was non-uniform. Also from these results, the comparative example that deviates from the sheet thickness condition of the present invention, as in Example 1, is that the dissimilar material joined body itself cannot be created or even if it can be created, the joining strength of the dissimilar material joined body is low, and the automobile It can be seen that it cannot be used for structural materials such as.

ADVANTAGE OF THE INVENTION According to this invention, even in the case of dissimilar material joining with the aluminum material which uses a GA plating steel plate, the dissimilar material joined body by fusion welding which has sufficient joint strength or joint strength can be provided. Further, it is possible to provide a dissimilar material joined body of a steel material and an aluminum material that can perform fusion welding with high joint strength without greatly changing the conditions on the steel material side, the aluminum material side, or the welding side. Such a joined body can be very usefully applied as various structural members in transportation fields such as automobiles and railway vehicles, machine parts, building structures, and the like. Therefore, the present invention greatly expands the use of the dissimilar material joined body of steel and aluminum.

It is sectional drawing which shows the overlap joint (joining) part of this invention joined material of this invention after melt joining. It is an enlarged view of the joining interface 6 of the junction part 5 in FIG. It is sectional drawing which shows an example of the fusion welding construction method of this invention joined material of this invention of FIG. It is sectional drawing which shows an example of the fusion welding construction method of this invention joined material of this invention of FIG.

Explanation of symbols

1: Galvanized (GA) steel material (steel plate) 2: Aluminum material (plate),
3: Aluminum weld metal (aluminum bead),
4: Bonding interface layer (interface reaction layer), 5: bonding portion, 6: bonding interface,
7: Flux, 8: Aluminum solid wire,
9: Flux-cored wire, 10: Welding wire,
t ₁ : Thickness of galvanized steel (steel plate), t ₂ : Thickness of aluminum (plate)

Claims (3)

A galvanized steel material having a plate thickness t ₁ of 0.5 to 5.0 mm and an aluminum material having a plate thickness t ₂ of 0.5 to 4.0 mm are formed by weld welding to form an aluminum weld metal. Dissimilar materials joined to each other, and at the joining interface between the aluminum weld metal and the steel, a mixed layer of Al ₃ Fe compound and Al ₅ Fe ₂ compound on the steel material side and α- A bonded interface between a steel material and an aluminum material, wherein a bonded interface layer having an AlFeSi layer is formed, and an average thickness of the bonded interface layer in the thickness direction is 0.5 to 5 μm.   The dissimilar material joining of the steel material and aluminum material of Claim 1 which uses the flux in the said fusion welding, and makes this flux the mixed flux composition of the aluminum fluoride and potassium fluoride which does not contain a chloride. body.   The dissimilar-material joined body of the steel material and aluminum material of Claim 2 which supplied the said flux to the fusion welding part as a flux cored wire with which the aluminum alloy outer shell was filled.

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