JP5222014B2 - Manufacturing method of MIG welded joint of steel and aluminum - Google Patents

Description

The present invention relates to a steel material and an MIG aluminum material (Metal Inert Gas) welding fittings production how, in particular, the material is superposed plate portions of different steel and an aluminum material, MIG welding the overlapping portion It is related to the technology.

  In recent years, from the viewpoint of protecting the global environment and saving energy, there has been a demand for suppression of generation of harmful gases and carbon dioxide emitted from automobiles, improvement of fuel consumption, and the like. And in order to meet such a demand, since the weight reduction of an automobile is the most effective, in the body member and various parts, the conversion of the material from a steel material to an aluminum material is actively studied. However, it is difficult in terms of cost to make all the materials of the body members and various parts constituting the automobile into an aluminum material. For this reason, when using an aluminum material, the dissimilar metal between steel and aluminum is used. This so-called hybrid joining is inevitable, and this dissimilar metal joining is an important issue. In addition, the joining of such steel materials and aluminum materials is strongly demanded not only in the field of transport aircraft represented by automobiles as described above, but also in various fields such as home appliances, structures such as building materials, There, there is a demand for strong bonding.

  For this reason, in the joining of steel and aluminum, mechanical joining such as caulking, rivet joining, and bolt joining has been studied in order to ensure sufficient joining strength. Even if it exists, some problems are inherent in the workability | operativity of joining, the reliability of a junction part, joining cost, etc. more or less.

In addition, in melt welding methods such as arc welding, which are conventionally used for joining metal materials, a dramatic improvement in productivity can be expected. When welding materials, the heat input during welding becomes too high, and molten aluminum and steel react metallurgically, and brittle and hard intermetallic compounds (Fe ₂ Al ₅ , FeAl _3, etc.) ) Is formed thick, and cracks are easily formed therefrom, and there is a problem that a joint strength at a practical level cannot be obtained.

  By the way, Patent Documents 1 to 7 propose various methods for welding dissimilar metals such as a steel material and an aluminum material by a MIG welding method which is a kind of arc welding. However, in Patent Document 1, since a steel material and an aluminum material are directly welded by a MIG brazing method using a copper alloy or Ni alloy wire, the welding cost is increased and sufficient welding is performed. It was difficult to say that the strength was obtained, and there was room for improvement. In Patent Document 2, a flux-cored wire in which a flux containing at least cesium fluoride, aluminum fluoride, potassium fluoride, and aluminum oxide as a component is coated with an aluminum material is used as a filler material. Although the formation of the intermetallic compound layer is suppressed, the flux remains as a slag in the welded portion and remains on the surface. For this reason, it is necessary to remove the slag covering the surface, resulting in poor productivity. At the same time, the problem of high product costs is inherent.

  In Patent Documents 3 to 7, a solid wire made of an aluminum alloy is employed as a welding wire, not a brazing material or a flux-cored wire. However, in these documents, the relationship between the thickness of the aluminum material and the thickness of the steel material is not examined at all, and the steel material and the aluminum material having the same thickness are welded or a steel material thicker than the aluminum material is used. Are welded. For this reason, even if the heat input is controlled to be low, the rigidity of both materials is greatly different, and the rigidity of the aluminum material is smaller than that of the steel material. There was a possibility that stress due to thermal strain concentrated and local deformation occurred in the weld.

  Further, in Patent Documents 3 to 7, surface-treated steel materials subjected to zinc or zinc alloy plating, aluminum or aluminum alloy plating are used as steel materials, and steel materials not subjected to such surface treatment are used. The method of welding with an aluminum material by the MIG welding method is not clarified at all. For this reason, a joining method capable of ensuring a sufficient joint strength by providing a healthy joint between an aluminum material and a steel material regardless of the presence or absence of a surface treatment layer (metal coating layer) on the surface of the steel material has been strongly desired. It is.

  Under such circumstances, the present inventors superimpose the aluminum material and the steel material vertically so that the aluminum material faces upward, and when MIG welding the end surface portion of the aluminum material, the material and thickness of the aluminum material Special welding conditions that set the steel material thickness, welding wire material, diameter, welding wire centerline placement position, number of droplets per pulse, pulse frequency, etc. within a specified range By adopting, it becomes possible to control the heat input at the time of welding moderately low, thereby forming a sound joint (welded part) regardless of the presence or absence of the surface treatment layer on the steel surface The patent application was filed first (Japanese Patent Application No. 2007-47766 and Japanese Patent Application No. 2007-47767). Thus, the inventors changed the arrangement of the aluminum material and the steel material so that the steel material faces up and the end surface portion of the steel material not subjected to surface treatment (metal coating treatment) such as plating is applied first. When MIG welding was carried out under the same conditions as in the above application, it was found that a continuous bead straddling the steel material and the aluminum material could not be provided in the welded portion, and joining itself could be impossible. . Specifically, a bead cannot be formed without interruption at the end surface portion of the steel material, the bead is cut off in the middle and becomes discontinuous, and the edge portion (upper side corner portion) of the steel material is exposed or welded. It has been found that the droplets of the wire are repelled at the end face of the steel material, and a bead may not be formed on the steel material.

JP2003-2111270A JP 2003-33865 A JP 2004-223548 A JP 2006-88174 A JP 2006-116599 A JP 2006-224145 A JP 2006-224147 A

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is to superimpose a steel material and an aluminum material on top and bottom so that the steel material is on top. In the method of manufacturing a lap fillet joint of steel material and aluminum material by performing MIG welding on the end surface part of the steel, a bead straddling the steel material and the aluminum material is applied to the welded portion regardless of the presence or absence of surface treatment of the steel material end surface. An object of the present invention is to provide a method of manufacturing a steel and aluminum MIG welded joint that can be continuously formed along the end face of the steel material, and to provide a MIG welded joint formed with such a continuous bead. It is to provide.

  And, as a result of repeated diligent studies for solving such problems, the present inventors, as in the previous application in which MIG welding was performed on the end surface portion of the aluminum material with the aluminum material facing up, While controlling the heat input to be moderately low, a relational expression configured by combining the radius of the welding wire, the distance from the base point of the welding wire, the thickness of the steel material, and the welding speed is within a predetermined range. With this setting, a bead straddling the steel material and the aluminum material can be continuously formed along the end surface of the steel material in the welded portion regardless of whether or not the surface treatment of the steel material end surface is performed. The present invention is completed by finding that a predetermined number of surface ripples are formed in the welded portion of the MIG welded joint of steel material and aluminum material so as to straddle the steel material and the aluminum material. Than it came in.

That is, the present invention provides (i) a steel material and an aluminum material, which are superposed one above the other so that the steel material is on top, and an MIG welding operation is performed on the end surface portion of the steel material, whereby the steel material and the aluminum material. (Ii) As the steel material, the thickness: t is 0.50 to 2.0 mm, and 0.6 to 0.8 times the thickness of the aluminum material. And (iii) a welding wire made of a 4000 series or 5000 series aluminum alloy having a radius r of 0.4 to 0.8 mm, and (iv) the center line of the welding wire. However, the upper surface side corner of the end face of the steel material is defined as a base point: 0, and is positioned within a distance of 4r on the side opposite to the overlapping portion of the steel material and the aluminum material in the horizontal direction from the base point: 0. , In a state where the welding wire is arranged, (v) the welding wire is relatively moved along the end surface of the steel material so that A represented by the following formula (I) is 4.0 to 6.0. (Vi) MIG welding is performed by applying a DC welding pulse current with a spray frequency of 0.5 to 5 times per 1 mm of welding length to spray transfer of one pulse per droplet to the welding wire. The gist of the present invention is a method for manufacturing a MIG welded joint of a steel material and an aluminum material, which is characterized by performing the operation.
A = L / r + (t / α) × V (I)
[In the formula, L is the base point: distance from 0 to the center line of the welding wire (mm), r is the radius (mm) of the welding wire, t is the thickness (mm) of the steel material, and α is the coefficient (= 21 mm · cm / Min), and V is the welding speed (cm / min). ]

  In addition, according to one of the preferable aspects of the manufacturing method of the MIG welded joint of the steel material and the aluminum material according to the present invention, as the steel material, mild steel, carbon steel, high-tensile steel, and stainless steel not subjected to surface treatment are used. Is used.

  Moreover, according to one of the other preferable aspects in the manufacturing method of the MIG welded joint of the steel material and aluminum material according to this invention, as said steel material, hot dip galvanized steel, alloyed hot dip galvanized steel, aluminum alloy plated steel, and Any of electrogalvanized steel is used.

  Furthermore, according to one of the desirable aspects in the manufacturing method of the MIG welded joint of the steel material and aluminum material according to this invention, the aluminum material whose tensile strength in the O material is 90 MPa or more is used.

  In addition, according to one of the other desirable aspects in the manufacturing method of the MIG welded joint of the steel material and the aluminum material according to the present invention, among the aluminum alloy materials of 5000 series, 6000 series, and 7000 series as the aluminum material. Either is used.

  In the present invention, the steel material and the aluminum material are overlapped, and the steel material and aluminum obtained by performing MIG welding using a welding wire made of a 4000 series or 5000 series aluminum alloy on the end surface portion of the steel material. MIG welded joint of the material, wherein the thickness of the steel material: t is 0.50 to 2.0 mm, and 0.6 to 0.8 times the thickness of the aluminum material, A steel and aluminum MIG welded joint characterized in that a surface ripple having a height difference of 10 μm or more is formed at 5 to 50 ridges per 1 cm of welding length so as to straddle between steel and aluminum. This is the gist.

  Thus, in the manufacturing method of the MIG welded joint of the steel material and the aluminum material according to the present invention, as the steel material, the thickness: t is 0.50 to 2.0 mm, and the thickness of the aluminum material is 0.6 to 0.8 times, and a welding wire made of a 4000 series or 5000 series aluminum alloy having a radius: r of 0.4 to 0.8 mm is used. Distance to the center line: In a state where the welding wire is arranged so that L is 0 to 4r, the welding wire is a steel material so that A represented by the above formula (I) is 4.0 to 6.0. DC welding pulse current that is relatively moved along the end surface of the welding wire, and further, is a spray transfer of one pulse per droplet on the welding wire, and the pulse frequency is 0.5 to 5 times per mm of welding length. Is washed away Therefore, a combination of the effects of these conditions, regardless of whether or not the surface treatment of the steel material end surface, the bead straddling the steel material and the aluminum material is applied to the welded part of the steel material and the aluminum material on the end surface of the steel material. It can be formed continuously along. That is, according to the method of the present invention, it is possible to advantageously manufacture a MIG welded joint in which the soundness of the joint portion is effectively enhanced.

  Moreover, in the steel material and aluminum material MIG welded joint according to the present invention, the steel material has a thickness: t of 0.50 to 2.0 mm and an aluminum material thickness of 0.6 to 0.00 mm. In addition to being used 8 times, a predetermined surface ripple is formed at 5 to 50 peaks per 1 cm of the weld length so as to straddle the steel and aluminum materials at the weld. Deformation due to thermal strain is unlikely to occur, and the soundness of the welded portion can be advantageously increased.

  Hereinafter, in order to clarify the present invention more specifically, representative embodiments of the present invention will be described in detail with reference to the drawings.

  First, FIG. 1 and FIG. 2 schematically show an example of a steel material and an aluminum material MIG welded joint according to the present invention in a perspective view and a longitudinal sectional view, respectively. As shown in FIGS. 1 and 2, the MIG welded joint 10 includes a flat steel material 12 and a flat aluminum material 14 having different thicknesses, and the steel material 12 is positioned upward at each end portion. So that the end face 16 portion on the front end side of the steel material 12 is overlapped and welded by the MIG welding technique to form the welded portion 18 in a state where the steel material 12 is superposed vertically. It is made up and composed.

  In addition, as shown in FIG. 1, here, the steel material 12 and the aluminum material 14 are welded over the entire length of the overlapping portion, whereby the welded portion 18 extends along the end surface 16 of the steel material 12. Thus, it is formed to extend continuously. Further, as shown in FIG. 2, the welded portion 18 has a bead having a substantially triangular cross section that connects two orthogonal surfaces, that is, the end surface 16 of the steel material 12 and the upper surface of the aluminum material 14. And the aluminum material 14.

  And as for the material of the steel material 12 arrange | positioned upwards among the two to-be-welded materials (12, 14) piled up and down in that way, it does not restrict | limit in particular, In the target joint It can be appropriately selected according to required characteristics and the like, and examples thereof include mild steel, carbon steel, high-tensile steel, and stainless steel. In addition, on the upper and lower surfaces of such steel material, conventionally known zinc or zinc alloy, such as hot dip galvanizing (GI), alloyed hot dip galvanizing (GA), aluminum alloy plating, and electrogalvanizing, Surface treatment (metal coating treatment) with aluminum or an aluminum alloy may be performed. In addition, even if it is the steel material by which surface treatment was given to the upper and lower surfaces, the surface treatment layer (metal coating layer) is not normally provided in the end surface, but in the present invention, the surface treatment layer of the end surface is not provided. It can be used as it is, with or without it.

  On the other hand, the material of the aluminum material 14 disposed below is not particularly limited as long as it is aluminum or an aluminum alloy, and is appropriately selected according to the characteristics required for the intended joint. Preferably, the tensile strength in the case of an O material (an aluminum material having a classification symbol defined by JIS H 0001 that is O and which has become the softest state by annealing) is 90 MPa or more. Some are advantageously used. However, the quality of the aluminum material to be subjected to MIG welding is not limited to the O material, and materials having various qualities such as O, H, and T can be used. Here, the tensile strength refers to the strength measured in accordance with the “metal material tensile test method” defined in JIS Z 2241. When the tensile strength is less than 90 MPa, the welded portion 18 is used. Even if the weak intermetallic compound layer is not formed and the decrease in the strength of the welded portion 18 can be suppressed, the aluminum material 14 as the base material is likely to break. This is because even if an aluminum material (for example, H material) tempered to increase the strength is used, the heat affected zone in the vicinity of the welded portion by welding (the portion that is not melted but is affected by heat) However, this is because the strength is generally the same as that of the O material. Among such aluminum materials, in particular, JIS series alloy numbers are 5000 series (Al-Mg series), 6000 series (Al-Mg-Si series), and 7000 series (Al-Zn-Mg series). In addition to being suitable as a structural material such as a vehicle body panel or a decorative panel for automobiles, it has excellent strength and high melt weldability, so that it is more suitable. Will be adopted.

  Further, the shapes of the steel material 12 and the aluminum material 14 are not limited to a flat plate shape, and any overlapping portion to be subjected to the MIG welding operation may be at least a flat plate shape. Any of various shapes manufactured by a known method such as forging will be employed. In general, a plate material or an extruded shape whose welded portion is a flat plate shape is advantageously used.

  In the present embodiment, the thickness t of the steel material 12 superimposed above the aluminum material 14 is set to a thickness in the range of 0.50 to 2.0 mm. This is because when the thickness t of the steel material 12 is less than 0.50 mm, the steel material 12 is easily melted, the amount of dissolution increases, and a brittle intermetallic compound layer is formed in the welded portion 18. In addition, when the thickness exceeds 2.0 mm, the steel material 12 is not easily heated, and the welding wire (melting material) droplets are placed on the steel material 12 having a low temperature. This is because 16 does not get wet and the droplets are struck in a ball shape.

  Moreover, in the present embodiment, the thickness t of the steel material 12 is 0.6 to 0.8 times the thickness u of the aluminum material 14, that is, 0.6 u to 0.8 u. In other words, the thickness u of the aluminum material 14 is larger than the thickness t of the steel material 12 and is 1.25 to about 1.67 times the thickness t of the steel material 12. As a result, the rigidity of the steel material 12 and the aluminum material 14 is moderately aligned, so that stress due to thermal strain is concentrated at the time of solidification shrinkage after welding, causing local deformation in the welded portion 18 and breaking. This can be advantageously prevented. That is, when the thickness t of the steel material 12 is out of the above range, stress concentrates on the material to be welded with lower rigidity, local deformation occurs, and the material to be welded with lower rigidity preferentially breaks. Will come to do. In addition, when using what surface treatment was given as steel materials, the thickness which added the thickness of the bare steel materials before surface treatment and the thickness of a surface treatment layer from a practical viewpoint is the steel materials 12 Thickness: t.

  Moreover, although the overlap margin W of the steel material 12 and the aluminum material 14 can be appropriately set according to the thickness of the steel member 12, if the overlap margin W is too small, the heat applied to the welded portion 18 is Since the heat is transmitted to the end face 22 of the aluminum material 14 and the heat does not escape and becomes reflected heat and is applied to the welded portion 18, the thickness of the steel material 12 is preferably 3 mm when t is 1 mm or less. In addition, when the thickness t of the steel material 12 exceeds 1 mm, it is desirable that the thickness of the steel material 12 is three times or more, that is, 3 t or more.

  Thus, as described above, the MIG welded joint 10 of the present embodiment has the end surface 16 portion of the steel material 12 in the MIG state in a state where the steel material 12 and the aluminum material 14 having different thicknesses are overlapped with each other. In this case, the bead of the welded portion 18 is 4000 series (Al-Si series) or 5000 series (Al--) without using brazing material or flux. It is formed by MIG welding using a welding wire (melting material) made of an Mg alloy. For this reason, the strength of the weld metal 24 is high, so that the steel material 12 and the aluminum material 14 can be firmly welded compared to the case of using a welding wire of another material, and the slag removal work and large scale are not required. No equipment is required, and the cost can be kept lower than when brazing, flux-cored wire, or the like is used.

  Moreover, in the welded portion 18 of the MIG welded joint 10 of the present embodiment, the surface ripple having a height difference of 10 μm or more is 5 to 50 peaks per 1 cm weld length so as to straddle the steel material 12 and the aluminum material 14. It is formed continuously. Here, the surface ripple means a scale-like uneven pattern formed on the bead surface of the welded portion 18, as shown in FIGS. In the present invention, the number of surface ripples is measured in the welding direction as follows. That is, the measurement position of the surface ripple is the center portion C (between the corner 14 on the aluminum material 14 (lower surface corner 26) on the end surface 16 of the steel material 12 and the toe 28 of the weld metal 24 on the aluminum material 14). In FIG. 3, a thick line portion) is defined, and the uneven shape in the welding direction (left and right direction in FIG. 3) is measured using a measuring device such as a tracer. And when any one of the height difference between one peak (convex) and two valleys (concave) adjacent to it is 10 μm or more, the peak is counted as one peak and welding The number of surface ripples per 1 cm length is calculated. At this time, the number of surface ripples is obtained by obtaining the number of surface ripples in the steady welding part where the welding state is stable, excluding the welding unsteady part. And when such surface ripple is less than 5 ridges per 1 cm of weld length, it indicates that the temperature of the molten metal contacting the steel material 12 during MIG welding was too high. Since the steel material 12 is deeply melted by the molten metal and a brittle intermetallic compound layer is formed thick, sufficient joint strength cannot be obtained. On the other hand, when it exceeds 50 peaks, the heat input per unit length is excessive.

  Thus, in this embodiment, the surface ripple which has a height difference of 10 micrometers or more is formed in the welding part 18 in 5-50 peaks per 1 cm of welding length so that the steel material 12 and the aluminum material 14 may be straddled. Therefore, the soundness of the welded portion 18 is effectively enhanced as compared with the conventional one. As a result, the MIG welded joint 10 according to the present embodiment is advantageously used for automobile body panels, joining of brackets, building materials such as decorative panels, and the like.

  By the way, as described above, the MIG welded joint 10 of the steel material 12 and the aluminum material 14 according to the present embodiment is manufactured, for example, according to the following manufacturing method.

  That is, in order to manufacture the MIG welded joint 10 of the present embodiment, first, as shown in FIG. 4, the flat steel material 12 and the flat aluminum material 14 having the thicknesses as described above, In the end portion, the steel material 12 is overlaid so as to be positioned above. Then, the steel material 12 and the aluminum material 14 and the aluminum material are appropriately used as necessary by an appropriate restraining jig (not shown) so that the superposed state is maintained and the steel material 12 and the aluminum material 14 do not move relative to each other. The material 14 is fixed. Then, under such a fixed state, the MIG welding operation is performed on the end surface 16 portion of the steel material 12 under the conditions as described later.

  Specifically, when performing this MIG welding operation, the welding wire 30 that is a consumable electrode is projected as a predetermined length from the tip opening 34 of the nozzle 32 as a welding machine in the same manner as in the prior art. A MIG welder is used. In such a MIG welding machine, the welding wire 30 can be moved independently in the axial direction with respect to the nozzle 32 by a wire supply device (not shown). Can be supplied to the welded portion 18 side (downward in FIG. 4). Further, in order to cut off the molten metal from the atmosphere, an inert gas 36 made of a mixed gas obtained by combining one or more inert gases such as argon gas, helium gas, neon gas and the like from the inside of the nozzle 32 during arc welding. (Indicated by a two-dot chain line in FIG. 4) is sprayed on a portion to be welded. Further, the welding wire 30 is connected to the + pole side of a welding power source device (not shown) through a contact tip 38 to be a + pole (anode), while the materials to be welded (12, 14) are connected to the −pole side. And negative electrode (cathode).

  Then, by operating a welding power source device (not shown) and applying a predetermined current and voltage between the welding wire 30 and the material to be welded (12, 14), the tip of the welding wire 30 and the object to be welded are applied. While an arc 40 (indicated by a one-dot chain line in FIG. 4) is generated between the welding materials (12, 14), a nozzle 32 (welding wire) is formed along the end surface 16 of the steel material 12 as shown in FIG. 30) is moved relatively, so that the MIG welding of the steel material 12 and the aluminum material 14 proceeds.

  At this time, the arc 40 generated between the workpieces (12, 14) and the welding wire 30 warms the end surface 16 portion of the steel material 12, and the welding wire 30 is melted, so that the droplets 42 of the welding wire 30 are melted. The steel material 12 and the aluminum material 14 are welded by the molten aluminum (molten metal), and a bead made of the weld metal 24 is formed in the welded portion 18.

  In such a MIG welding operation, as described above, the welding wire 30 is made of 4000 series (Al-Si series) or 5000 series (Al-Mg series) in order to firmly join the steel material 12 and the aluminum material 14. Solid wire formed using an aluminum alloy material. In the present embodiment, the radius r of the welding wire 30 is 0.4 to 0.8 mm. This is because when the radius r of the welding wire 30 is smaller than the above range, the current density is increased and the arc 40 is concentrated, so that the heat input is excessive at the concentrated portion of the arc 40 and the steel material deeply melts. When the embrittlement layer made of an intermetallic compound is formed thick, while its radius: r is larger than the above range, it is necessary to increase the heat input in order to melt the welding wire 30, thereby the welding wire 30. This is because the temperature of the droplet 42 itself increases, and a thickened embrittlement layer is formed in the welded portion 18.

  In such MIG welding operation, the torch aiming position, that is, the nozzle position is set too far away from the end face 16 of the steel material 12 in the horizontal direction (direction perpendicular to the welding direction, left-right direction in FIG. 4). As a result, a bead straddling the steel material 12 and the aluminum material 14 is not formed, and a sound weld 18 having a cross-sectional shape as shown in FIG. 2 cannot be formed. Therefore, in the present embodiment, the center line X of the welding wire 30 is such a base point in the horizontal direction with the upper surface side corner 20 on the end face 16 of the steel material 12 as the base point 0 as shown in FIG. : Welding wire so that it is always located within the distance of 4r from 0 to the overlapping portion side (in FIG. 4, the base point: to the left side of 0) opposite side (in FIG. 4, the base point: to the right side of 0) 30 (nozzle 32) is arranged. In other words, as shown in FIG. 4, the distance (L) from the base point: 0 (upper side corner 20) to the center line: X of the welding wire 30 is 0 to 4r (0 ≦ L ≦ 4r). Thus, the welding wire 30 is arranged. Here, the center line: X of the welding wire 30 means the center line of the welding wire at the portion protruding from the tip opening 34 of the nozzle 32.

  When the center line X of such a welding wire 30 is arranged at the position of the overlapping portion side (left side in FIG. 4) from the base point 0, in other words, when L becomes less than 0, the arc 40 concentrates on the steel material 12. On the other hand, when L exceeds 4, the arc 40 does not reach the steel material 12, and in any case, the sound welded portion 18 as described above cannot be formed.

  On the other hand, the arrangement position of the nozzle 32 (welding wire 30) in the vertical direction can be appropriately set according to the power supply characteristics of the welding machine, the material of the welding wire 30, the radius, and the like. It is desirable that the distance between the tip and the surface of the upper plate (steel material 12) be about 3 to 17 mm, more preferably about 3 to 12 mm, and this ensures a high shielding property by the inert gas 36. It becomes possible to do.

Then, while maintaining the position as described above, the nozzle 32 (welding wire 30) is relatively moved in the welding direction (direction perpendicular to the paper surface in FIG. 4), and MIG welding is performed. However, in the present embodiment, the nozzle 32 (welding wire 30) is arranged so that A represented by the following formula (I) is 4.0 to 6.0 (4.0 ≦ A ≦ 6.0). The steel material 12 is relatively moved along the end surface 16.
A = L / r + (t / α) × V (I)

  In the above formula (I), L is the distance (mm) from the base point 0 to the center line X of the welding wire 30 as described above. More specifically, L is the distance from the base point: 0 to the intersection point: p between the center line: X of the welding wire 30 and the extended surface 13 ′ of the upper surface 13 of the steel material 12. Here, the base point: 0 Of the steel material 12 and the aluminum material 14 is negative (base point: left side of 0 in FIG. 4), while the opposite side of the overlap portion (base point: in FIG. 4). The right side of 0) is positive. Moreover, in the said Formula (I), r shows the radius (mm) of the welding wire 30, and it is set as 0.4 mm <= r <= 0.8mm as mentioned above. L / r, which is the first term of the above formula (I), indicates how far the center line X of the welding wire 30 is away from the end of the steel material 12 with respect to the radius of the welding wire 30: r. ing. In the present embodiment, as described above, since the welding wire 30 (nozzle 32) is arranged so that L satisfies 0 ≦ L ≦ 4r, L / r is in a range of 0 ≦ L / r ≦ 4. If the radius: r of the welding wire 30 is large, the upper limit of the distance: L can be increased. Conversely, if the radius: r of the welding wire 30 is small, the upper limit of the distance: L is decreased.

  Moreover, in the said Formula (I), t shows the thickness (mm) of steel materials, and is set as the range of 0.50 mm <= t <= 2.0mm as mentioned above. Α is a coefficient (mm · cm / min), and α = 21 mm · cm / min. V indicates the welding speed (cm / min), and is at least more than 0 (V> 0). The second term (t / α) × V in the above formula (I) is obtained by multiplying the thickness 12 of the steel material 12 by the welding speed V. Thus, the reason for multiplying the thickness t of the steel material 12 and the welding speed V is that the molten metal is accumulated in the stepped portion of the overlapped steel material 12 and the aluminum material 14, that is, the end surface 16 portion of the steel material 12. In order to form a sound weld 18, it is necessary to reduce the thickness t of the steel material 12 when the welding speed V is high, while it is necessary to increase the thickness t of the steel material 12 when the welding speed is low. This is because they are inversely related.

  The nozzle 32 (welding wire 30) is connected to the end surface of the steel material 12 so that A, which is the sum of the first term and the second term of the formula (I), satisfies 4.0 ≦ A ≦ 6.0. By performing the MIG welding by relatively moving along the end 16, a healthy weld 18 extending continuously along the end face 16 is formed. In addition, when A is less than 4.0, there is a possibility that a hole is formed in the base material due to excessive heat input, and when it exceeds 6.0, a discontinuous bead is formed.

  In addition, in the MIG welding operation of this embodiment, direct current welding in which one pulse per droplet is transferred to the welding wire 30 and the pulse frequency is 0.5 to 5 times per 1 mm weld length. A pulse current (see FIG. 6) is passed. By flowing such a direct current pulse current, a cleaning action (cleaning action) for removing the oxide film on the surface of the base material can be exhibited, the weldability is improved, and the heat input is controlled to be moderately low. The penetration of 12 and thus the formation of fragile intermetallic compounds can be advantageously prevented. When such a DC welding pulse current is adopted, the pulse shape (waveform), peak current value, base current value, etc. are always determined by the arc 40 between the tip of the welding wire 30 and the material to be welded. In order to generate | occur | produce, according to the welding voltage value to be applied, the kind of welding wire 30, a radius, etc., it adjusts suitably.

  In addition, in the MIG welding operation, the reason why the welding current changed in a pulse shape is flowed is low because the average welding current value becomes high and heat input to the base metal becomes excessive in the case of direct current without pulse. This is to stably perform regular droplet transfer at the average welding current value, to control heat input at a low level, and to prevent excessive heat from being applied to the material to be welded. In addition, the direct current pulse current is used instead of the alternating current pulse current because the welding wire 30 is always set to the positive electrode, so that the cleaning action is always exerted on the welded material, and the welded portion is a clean metal. This is because the surface is a surface (new surface), and the droplets 42 are easily and effectively spread at the welding site. In the case of alternating current, the cleaning action is not exhibited at the timing when the welding wire 30 is switched from the positive electrode to the negative electrode, which may cause defects in the welded portion 18. In addition, spray transfer that occurs at a current higher than the critical current value during droplet transfer is a globule transfer that occurs at a current lower than the critical current value. This is because no heat is applied and the steel material 12 is not sufficiently wetted, and a sound welded portion 18 cannot be obtained.

  In addition, here, a spray transfer state in which one droplet 42 regularly disengages from the tip of the welding wire 30 in one pulse, as described above, for the direct current welding pulse current that results in such spray transfer. And the adjustment is made so that the pulse frequency is 0.5 to 5 times per 1 mm of the weld length, the above-mentioned cleaning action is effectively exerted, and the wettability of the steel material 12 is enhanced. The molten metal of the welding wire 30 is not repelled at the end surface 16 portion of the steel material 12, and the end surface 16 of the steel material 12 is wetted well. Moreover, heat input is controlled and the surface of the aluminum material 14 is appropriately melted, while the steel material 12 can be effectively prevented from being melted deeply.

  In addition, when one droplet does not cause spray transfer of one droplet, specifically, in the case of one droplet of several pulses, a continuous bead cannot be obtained and an incomplete portion is generated. In the case of several droplets in one pulse, the pulse current density becomes high and the heat input becomes excessive, whereby a brittle intermetallic compound layer is formed thickly in the welded portion 18.

  On the other hand, when the pulse frequency as described above is less than 0.5 times / mm, a continuous bead cannot be obtained and a sound welded portion 18 cannot be obtained as in the case of one droplet with a few pulses. When the pulse frequency exceeds 5 times / mm, the heat input to the material to be welded becomes excessive, and a brittle intermetallic compound layer is formed thickly on the welded portion 18. In this case, the welded portion 18 is easily broken or peeled off. The pulse frequency (times / mm) is changed by changing the pulse frequency (times / s) according to the welding speed (mm / s), or vice versa. Therefore, it can be adjusted appropriately.

  Here, in FIG. 6, an example of a DC welding pulse current waveform is shown side by side along with the corresponding voltage waveform. For example, while flowing such a DC welding pulse current, By performing MIG welding at a welding speed of V, 60 cm / min (= 10 mm / sec), the spray transfer of one pulse per droplet as described above can be advantageously realized. Further, in FIG. 6, since there are 28 peaks per second, the pulse frequency is 2.8 times per 1 mm weld length at a welding speed of 60 cm / min.

  Thus, as described above, the steel material 12 and the aluminum material 14 having a predetermined thickness are superposed, and the welding wire 30 made of a 4000 series or 5000 series aluminum alloy is placed at a predetermined position, and the above formula (I) is satisfied. The welding wire 30 is relatively moved along the end surface 16 of the steel material 12 so that A shown in FIG. 4 becomes 4.0 to 6.0, and spray transfer of one pulse / one droplet is performed, and the pulse frequency is welded. By applying a DC welding pulse current of 0.5 to 5 times per 1 mm length and carrying out the MIG welding operation, the steel material 12 and the aluminum material 14 are arc-welded, integrated, and the target MIG The welded joint 10 will be manufactured. And in the MIG welded joint 10 obtained in this way, the heat input during welding is controlled, and it is advantageously prevented that the temperature of the molten metal becomes too high. Regardless of the presence or absence of treatment, the molten metal accumulates as beads on the end surface 16 portion of the steel material 12, so that a bead straddling the steel material 12 and the aluminum material 14 is continuously formed along the end surface 16 of the steel material 12. It will be. Further, by performing the MIG welding operation so as to satisfy the above-described conditions, the traces of the droplets 42 that have fallen on the material to be welded from the distal end portion of the welding wire 30 become scale-like on the bead surface of the weld portion 18. As a result, the number of surface ripples is approximately the same as the number of spray transfer droplets. That is, in this MIG welding operation, since the MIG welding operation is performed so that one pulse per droplet and a pulse frequency of 0.5 to 5 times / mm, the MIG welding joint 10 is welded. A bead having a surface ripple of 5 to 50 peaks per 1 cm length is continuously formed on the welded portion 18 so as to straddle the steel material and the aluminum material.

  Moreover, by performing the MIG welding operation under the above-described conditions, the penetration of the steel material 12 is also advantageously suppressed, and it is effectively prevented that the intermetallic compound layer is formed thick on the surface of the steel material 12. In addition, deformation due to thermal strain is less likely to occur in the welded portion 18.

  Therefore, when the MIG welding operation is performed under the above-described conditions to manufacture the MIG welded joint between the steel material 12 and the aluminum material 14, discontinuous beads are not formed or the beads are not formed on the steel material end face 16. This is advantageously prevented, and a MIG welded joint with improved soundness as compared with the prior art can be advantageously manufactured.

  The exemplary embodiments of the present invention have been described in detail above. However, the embodiments are merely examples, and the present invention is limited in any way by specific descriptions according to such embodiments. It should be understood that it is not interpreted.

  For example, in the above-described embodiment, as the steel material 12, the upper surface side corner portion 20 and the lower surface side corner portion 26 have a right angle (90 °), but as shown in FIG. Of course, it is also possible to manufacture a MIG welded joint by using a groove whose end is subjected to groove processing so that the upper surface side corner portion 20 'has an obtuse angle and the lower surface side corner portion 26' has an acute angle. In addition, regarding the embodiment shown in FIG. 7 and FIG. 8 to be described later, in order to facilitate understanding thereof, the same structure as that in the embodiment shown in FIGS. The code | symbol was attached | subjected.

  Moreover, in the said embodiment, the nozzle 32 (welding wire 30) is arrange | positioned so that the centerline: X of the welding wire 30 may become parallel with respect to the end surface 16 of the steel material 12, as evident also from FIG. However, as shown in FIG. 8, the MIG welding operation can be performed by tilting the nozzle 32 (welding wire 30) with respect to the end surface 16 of the steel material 12. Also in this case, as described above, the distance from the base point 0 (upper surface side corner portion 20) to the intersection point p of the center line X of the welding wire 30 and the extended surface 13 'of the upper surface 13 of the steel material 12 ( The nozzle 32 (welding wire 30) is arranged so that L) satisfies 0 ≦ L ≦ 4r.

  Further, in FIG. 5, the angle formed by the vertical line Y extending in the direction (vertical direction in FIG. 5) where the nozzle 32 (welding wire 30) intersects the horizontal direction at right angles and the center line X of the welding wire 30. The state in which MIG welding is performed in a posture inclined toward the traveling direction so that the magnitude of θ is in a range of 5 ° or less is shown. The inclination angle of the wire 30) can be set appropriately as in the conventional MIG welding.

  In addition, although not enumerated one by one, the present invention is carried out in a mode to which various changes, modifications, improvements, etc. are added based on the knowledge of those skilled in the art. It goes without saying that any one of them falls within the scope of the present invention without departing from the spirit of the present invention.

  Some examples of the present invention will be shown below to clarify the present invention more specifically. However, the present invention is not limited by the description of such examples. Needless to say.

<Example 1>
First, as shown in Table 1 below, a hot-dip galvanized steel sheet (GI steel sheet) having a thickness (t): 1.3 mm was prepared as the steel material (12). The metal coating layer was not provided in the end surface (16) of this steel material (12). On the other hand, as an aluminum material (Al material), a 7000 series aluminum plate material (7003) having a thickness (u): 1.6 mm and a tensile strength of the O material of 90 MPa or more was prepared. And these steel materials (12) and the aluminum material (14) were overlap | superposed and fixed so that the overlap allowance (W) might be 3 t or more.

  Next, as the MIG welding machine, a precision control type MIG welding machine equipped with a welding wire (30) made of a 5000 series aluminum alloy (5554) having a radius (r): 0.4 mm is used, and the welding wire (30) is + After connecting to the welding power source device so that the electrode and the material to be welded become negative, an arc is generated between the electrode and the material to be welded, and the nozzle (32) of the MIG welding machine is welded at a welding speed of 67 cm / min ( The MIG welding joint according to Example 1 was manufactured by performing relative movement along the end face (16) portion of the steel material (12) at approximately 11 mm / s).

  At this time, as shown in Table 1 below, the number of droplets per pulse: 1 and the number of pulses per 1 mm of welding length (pulse frequency): DC welding pulses so that 3.4 spray transitions occur. The nozzle (32) is arranged so that the center line (X) of the welding wire is positioned at the upper surface side corner (20) of the steel material (12), that is, L = 0 mm while the current is passed. In the state which maintained the nozzle position, it was moved relatively along the end surface (16) portion of the steel material (12).

  Then, using the obtained MIG welded joint according to Example 1, the number of surface ripples of the beads formed in the welded portion (18) was measured, and the joint state was evaluated, and the obtained results were obtained. The results are shown in Table 1 below.

[Measurement of surface ripple number]
The number of surface ripples is measured by using a tracer (CV-3100 manufactured by Mitutoyo Corporation) to measure the shape of the steady welding part, and the difference in height between one peak and two valleys (recesses) adjacent to it. When any one of these became 10 μm or more, the peak portion was counted as one peak, and the number of surface ripples per 1 cm of weld length was determined.

[Evaluation of bonding state]
Moreover, the evaluation of the bonding state was evaluated according to the following evaluation criteria.
○: The welded portion (18) is continuously formed with a bead straddling the steel material (12) and the aluminum material (14) ×: Other than the above, the welded portion (18) has a discontinuous bead, Or what is not formed so that a bead may straddle steel materials (12) and aluminum materials (14).

<Examples 2-83, Comparative Examples 1-83>
Similar to Example 1, plate materials shown in Tables 1 to 6 below were prepared as the steel material (12) and the Al material (14). In addition, the tensile strength of each Al material in the O material was 90 MPa or more. And, when the thickness (t) of the steel material (12) is 1 mm or less, the overlap allowance (W) of 3 mm or more, and when the thickness (t) of the steel material (12) exceeds 1 mm, Overlap was fixed so that the overlap allowance (W) was 3t or more.

  Next, using a MIG welding machine equipped with a welding wire (30) made of an aluminum alloy having the radius (r) and the material shown in Tables 1 to 6 below, the welding wire (30) side becomes a positive pole. An electric current and voltage are applied to generate an arc that becomes a spray transfer between the workpiece and the nozzle (32) of the MIG welding machine at a welding speed (V) shown in Tables 1 to 6 below. MIG welding was performed by relatively moving along the end face (16) portion of the steel material (12), and MIG welded joints according to Examples 2 to 83 and Comparative Examples 1 to 83 were obtained. In this MIG welding operation, the distance (L) of the center line (X) of the welding wire (30), the welding speed (V), the number of droplets per pulse, and the pulse frequency are shown in Tables 1 to 1 below. The conditions shown in Table 6 were adopted.

  And using the obtained MIG welded joint, while measuring the number of surface ripples of the bead formed in the welded portion (18) and evaluating the joining state, the results obtained are shown in Tables 1 to 1 below. Table 6 shows.

  As is apparent from the results of Tables 1 to 3, in the MIG welded joint according to Examples 1 to 83, the number of surface ripples per 1 cm of weld length is in the range of 5 to 50 peaks, The evaluation result of the joined portion is ◯, and it can be seen that the steel material and the aluminum material are well welded regardless of the presence or absence of a surface treatment layer (metal coating layer) such as plating on the steel material end face.

  On the other hand, as is clear from the results of Tables 4 to 6, in the MIG welded joints according to Comparative Examples 1 to 83, the evaluation results of the joints are all x.

Further, “A” was plotted against “(t / α) × V” for Examples 1 to 83 and Comparative Examples satisfying the following conditions (1) to (6). The obtained graph is shown in FIG. Here, assuming that “A” is y and “(t / α) × V” is x, the following formula (I) is y = x + L / r, the slope is 1, and the intercept is L / r. It becomes a straight line. The L / r is in the range of 0 ≦ L / r ≦ 4 as described above. Furthermore, A represented by the following formula (I) is in a range of 4.0 ≦ A ≦ 6.0. Therefore, the range surrounded by the four lines a to d shown in FIG. 9 satisfies the condition defined by the present invention.
A = L / r + (t / α) × V (I)

Condition (1) 0.50 mm ≦ t ≦ 2.0 mm
(2) 0.6 ≦ t / u ≦ 0.8
(3) 0.4 mm ≦ r ≦ 0.8 mm
(4) V> 0 cm / min (5) Number of droplets per pulse: 1
(6) Pulse frequency: 0.5-5 times / mm

  As is apparent from the graph of FIG. 9, the examples indicated by ◯ are all within the range surrounded by four lines a to d (the hatched range in FIG. 9), while indicated by ●. It can be seen that the comparative example exists outside the range. Therefore, even if the above conditions (1) to (6) are satisfied, L / r is not in the range of 0 to 4 and A represented by the above formula (I) is 4.0 to 6.0. It turns out that the thing which is not in a range cannot obtain a sound welded part.

It is an isometric view explanatory drawing which shows an example of the MIG welded joint of steel materials and aluminum materials according to this invention. It is II-II sectional explanatory drawing in FIG. It is a plane explanatory view in FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is longitudinal cross-sectional explanatory drawing which shows one process of manufacturing the MIG welded joint of steel materials and aluminum materials according to this invention method, Comprising: Steel materials and aluminum materials which are to be welded are mutually piled up so that steel materials may become upper, The state which has arrange | positioned the nozzle of MIG welding machine is shown. It is a perspective explanatory view showing one process which manufactures a MIG welded joint of steel materials and aluminum materials according to the method of the present invention, and shows the state where a droplet moves from a welding wire. It is explanatory drawing which shows an example of the waveform of DC welding pulse current and voltage employ | adopted in the MIG welding method according to this invention, Comprising: While showing the waveform of DC pulse current upwards, the waveform of the voltage corresponding to this welding current is shown. Shown side by side. It is longitudinal cross-sectional explanatory drawing which shows the process of manufacturing the MIG welded joint of steel materials and aluminum materials according to this invention method, Comprising: As the steel materials which should be welded, what performed the groove process on the end surface is employ | adopted. It is longitudinal cross-sectional explanatory drawing which shows the process of manufacturing the MIG welded joint of steel materials and aluminum materials according to this invention method, Comprising: The state arrange | positioned in the state which inclined the nozzle of the MIG welding machine with respect to the end surface of steel materials is shown. . In an Example, it is the graph which plotted "A" with respect to "(t / (alpha)) * V" which is the 2nd term of the said Formula (I).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 MIG welded joint 12 Steel material 13 Upper surface 13 'extension surface 14 Aluminum material 16 End surface of steel material 18 Welded part 20,20' Upper surface side corner 22 End surface of aluminum material 24 Weld metal 26, 26 'Lower surface side corner 28 Stop end 30 Welding wire 32 Nozzle 34 Tip opening 36 Inert gas 38 Contact tip 40 Arc 42 Droplet X, X ': Center line of welding wire Y: Perpendicular

Claims (5)

A method of manufacturing MIG welded joints of steel and aluminum by superimposing steel and aluminum on top and bottom so that the steel is on top, and performing MIG welding operation on the end surface portion of the steel. There,
As the steel material, a thickness: t is 0.50 to 2.0 mm, and 0.6 to 0.8 times the thickness of the aluminum material,
As the welding wire, a wire made of a 4000 series or 5000 series aluminum alloy having a radius: r of 0.4 to 0.8 mm is used.
The center line of the welding wire has a distance of 4r on the side opposite to the overlapping portion of the steel material and the aluminum material in the horizontal direction from the base point: 0, with the upper surface side corner portion on the end face of the steel material as the base point: 0. In a state where the welding wire is arranged so as to be located in
The welding wire is moved relatively along the end surface of the steel material so that A represented by the following formula (I) is 4.0 to 6.0, and
By carrying out a MIG welding operation by applying a direct welding pulse current with a pulse frequency of 0.5 to 5 times per 1 mm of welding length, with respect to the welding wire, spray transfer of one pulse per droplet The surface ripple having a height difference of 10 μm or more is welded so that a bead straddling the steel material and the aluminum material is continuously formed along the end surface of the steel material and further straddling the steel material and the aluminum material. A method of manufacturing a MIG welded joint of steel and aluminum, characterized by being formed at 5 to 50 peaks per 1 cm length.
A = L / r + (t / α) × V (I)
[In the formula, L is the base point: distance from 0 to the center line of the welding wire (mm), r is the radius (mm) of the welding wire, t is the thickness (mm) of the steel material, and α is the coefficient (= 21 mm · cm / Min), and V is the welding speed (cm / min). ]   The steel material according to claim 1, wherein the steel material is any one of mild steel, carbon steel, high-tensile steel, and stainless steel that has not been surface-treated. Production method.   The steel material according to claim 1 or 2, wherein the steel material is any one of hot-dip galvanized steel, alloyed hot-dip galvanized steel, aluminum alloy-plated steel, and electrogalvanized steel. Manufacturing method of MIG welded joint of aluminum material.   The method for manufacturing a MIG welded joint between a steel material and an aluminum material according to any one of claims 1 to 3, wherein the aluminum material has a tensile strength in the O material of 90 MPa or more. . 5. The steel material and the aluminum material according to claim 1, wherein the aluminum material is any one of 5000 series, 6000 series, and 7000 series aluminum alloy materials. Manufacturing method of MIG welded joint.

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