JP2019177406A - Welded structure and method for manufacturing the same - Google Patents

Abstract

To provide a welded structure in which an aluminium material and a steel material are welded to different materials by a single-phase AC-type resistance spot welding method, which is excellent in corrosion resistance.SOLUTION: In a welded structure (1A), a molted Al nugget (51) is formed at a boundary between an aluminium material (10) and a molten aluminium-system plated steel plate (30) and a shortest distance between the molted Al nugget (51) and an electrode pressing surface (11) of the aluminium material (10) is 0.01 mm or more.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a bonded structure bonded to different materials by resistance spot welding and a method for manufacturing the bonded structure.

  Aluminum-based materials such as aluminum and aluminum alloys (hereinafter referred to as aluminum materials) are used in various fields because they are lightweight and excellent in corrosion resistance. For example, in the automobile field, an aluminum material may be used as a structural material of a vehicle body to reduce the weight of the vehicle body.

  The aluminum material may be used only for a part of the vehicle body from the viewpoint of manufacturing cost, productivity, and the like. For example, the aluminum material is used for a part (roof or the like) that does not require much strength. In this case, it is necessary to join the aluminum material constituting a part of the vehicle body and the steel material constituting the other part to each other.

  In general, among various methods used for joining different materials, the resistance spot welding method has advantages such as a reduction in the weight of the joint and high productivity as compared with the mechanical joining method. However, usually, when spot welding is performed on an aluminum material and a steel material, there is a problem in that joint strength may be reduced due to formation of a brittle intermetallic compound at the joint interface between them.

  Patent Document 1 describes a spot welding method for increasing the bonding strength of a plurality of steel plates having different plate thicknesses. In this method, spot welding is performed using electrodes of different materials, and the nugget is formed in the vicinity of the interface between the steel plates to increase the bonding strength.

JP2013-173155A (issued on September 5, 2013)

  However, in general, an aluminum material is a material that is difficult to spot weld compared to steel for various reasons. Therefore, the method described in Patent Document 1 cannot be directly applied to spot welding of an aluminum material and a steel material.

  By the way, as a spot welding method, a single-phase alternating current method is widely used. On the other hand, when spot welding an aluminum material, since a large welding current is required, a single-phase AC method is rarely used.

  If a bonded structure can be manufactured by spot welding an aluminum material and a steel material by a single-phase alternating current method, the manufacturing cost can be reduced. This is because the equipment is relatively inexpensive and the existing equipment can be used.

  In order to increase the bonding strength of such a bonded structure, it is necessary to increase a molten nugget formed by melting an aluminum material (hereinafter sometimes referred to as an aluminum material molten nugget). When the welding current at the time of spot welding is increased, the heat input increases, so that the molten nugget of the aluminum material can be increased. On the other hand, the molten nugget of the aluminum material may reach the surface layer of the aluminum material, and in this case, the corrosion resistance of the bonded structure is lowered.

  One aspect of the present invention has been made in view of the above-described conventional problems, and is a joined structure in which an aluminum material and a steel material are joined to each other by a single-phase alternating current resistance spot welding method, and is resistant to corrosion. The object is to provide an excellent bonded structure.

  The bonded structure in one aspect of the present invention is a bonded structure bonded by spot welding an aluminum material and a molten aluminum-based plated steel plate, and is a boundary portion between the aluminum material and the molten aluminum-based plated steel plate A molten nugget of aluminum is formed on the surface of the aluminum material opposite to the surface facing the molten aluminum-based plated steel sheet, the outer surface of the molten nugget, and the aluminum material The shortest distance from the first surface is 0.01 mm or more.

  Further, in the bonded structure according to one aspect of the present invention, the aluminum material and the molten aluminum-based plated steel plate are laminated in this order on the steel material and spot-welded, whereby the steel material and the molten aluminum-based plated steel plate And the aluminum material are joined, the molten nugget is the first nugget, and the nugget formed at the boundary between the molten aluminum-based plated steel sheet and the steel material is the second nugget, the second nugget The ratio of the nugget diameter of the first nugget to the nugget diameter is preferably 1.1 or more and 2.0 or less.

  The manufacturing method of the joining structure in one mode of the present invention is a manufacturing method of a joining structure including the spot welding process of carrying out spot welding of an aluminum material and a molten aluminum system plating steel plate, and is the above-mentioned molten aluminum of the above-mentioned aluminum material. The surface opposite to the surface facing the plated steel sheet is the first surface, and in the spot welding step, the applied pressure of the electrode is 1.4 kN or more and 4.9 kN or less, and the welding current and energization time are A value represented by a product is in a range of 54 to 240, an outer edge portion of a molten nugget formed at a boundary portion between the aluminum material and the molten aluminum-based plated steel sheet, and a first surface of the aluminum material; Spot the aluminum material and the molten aluminum-based plated steel sheet in a single-phase alternating current method so that the shortest distance between them is 0.01 mm or more. It is characterized in that contact.

  Moreover, the manufacturing method of the junction structure in one aspect of the invention preferably has a joint strength of 0.8 kN or more as a measurement result of a cross tensile test of the junction structure formed in the spot welding process.

  A bonded structure in which an aluminum material and a steel material are bonded to each other by a single-phase alternating current type resistance spot welding method, which is excellent in corrosion resistance, can be provided.

It is the schematic which shows the structure of the spot welding machine of the single phase alternating current system used for manufacture of the joining structure in Embodiment 1 of this invention. It is the schematic which shows the shape of the electrode with which the said spot welder is provided. It is a figure which expands and shows the interface vicinity of the base-material steel plate and aluminum plating layer of the hot-dip aluminum type plated steel plate in sectional drawing shown in FIG. It is sectional drawing which shows typically the junction part of the joining structure body in Embodiment 1 of this invention. It is a top view which omits this aluminum material at the time of seeing the above-mentioned joined structure object from the aluminum material side, and is shown typically. It is a figure for demonstrating the method to measure the residual Al thickness in the said junction structure. It is sectional drawing which shows typically the junction part of the joining structure body in Embodiment 2 of this invention. It is a figure for demonstrating the method to measure the residual Al thickness in the said junction structure. It is sectional drawing which shows typically the junction part of the junction structure in Embodiment 3 of this invention. It is sectional drawing which shows typically the junction part of the junction structure in Embodiment 4 of this invention. It is a schematic diagram for demonstrating the cross tension test in an Example, (a) is a top view of a joining structure body, (b) is sectional drawing of a joining structure body.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is for better understanding of the gist of the invention and does not limit the present invention unless otherwise specified. Unless otherwise specified, “A to B” representing a numerical range means “A or more (including A and greater than A) and B or less (including B and less than B)”. The shape and dimensions (length, depth, width, etc.) of the configuration described in each drawing in the present application do not necessarily reflect the actual shape and dimensions, and are appropriately changed for clarity and simplification of the drawings. is doing.

  The joint structure in the embodiment of the present invention is, for example, a vehicle component formed by joining a roof panel and a roof side portion of a vehicle body in the automobile field. However, the bonded structure of the present invention is not necessarily limited to this. INDUSTRIAL APPLICABILITY The present invention can be appropriately applied to a joining structure for use in which there is a demand for joining different materials of an aluminum material and a steel material by a single-phase alternating current type resistance spot welding method.

  In the following description, for simplification of description, description will be given focusing on one joint portion formed by spot welding in the joint structure. However, it goes without saying that a joined structure including a plurality of joined portions is also included in the scope of the present invention.

  Moreover, since a plated layer is formed in the surface of a base-material steel plate, a molten aluminum type plated steel plate may be handled as a kind of steel materials in this specification.

<Knowledge of the present invention>
Conventionally, in the automobile field, the use of aluminum materials for roofs and the like has been promoted as described above. On the other hand, when spot welding is performed on an aluminum material and a steel material, a fragile Fe—Al binary alloy layer is generated at the joint interface. There is a problem in that the bonding strength of the bonded structure decreases due to the occurrence of peeling at the Fe-Al binary alloy layer.

  Until now, the technique regarding the joining structure which joined the aluminum material and the hot dip galvanized steel sheet has been reported (refer to patent 4280671 etc.). This type of prior art mainly aims to increase the bonding strength of the bonded structure by suppressing the formation of the Fe—Al binary alloy layer at the bonded interface. Therefore, during spot welding, the heat input to the welded portion becomes excessive, and the molten nugget of the aluminum material reaches the surface layer of the aluminum material, which may reduce the corrosion resistance of the bonded structure.

  The inventors of the present invention have intensively studied and tried to produce a joint structure having excellent joint strength while maintaining corrosion resistance when joining aluminum materials and steel materials to each other by a single-phase alternating current resistance spot welding method. It was. Then, the present inventors have found a condition as to what kind of structure as a bonded structure can provide a bonded structure excellent in corrosion resistance and bonding strength, and have achieved the present invention.

[Embodiment 1]
One embodiment of the present invention will be described below with reference to FIGS.

  In the present embodiment, a bonded structure (hereinafter sometimes referred to as a two-piece bonded structure) in which an aluminum material and a hot-dip aluminum-plated steel sheet are bonded will be described as an example of the bonded structure of the present invention.

  First, a spot welder used for manufacturing the joint structure of the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing a configuration of a single-phase alternating current type spot welder 100 used for manufacturing a bonded structure 1A (see FIG. 3) in the present embodiment. FIG. 2 is a schematic view showing the electrode 120 provided in the spot welder 100.

  In addition, a well-known apparatus can be used for each member with which the spot welding machine 100 is provided except describing below. Therefore, in FIG. 1 and FIG. 2, illustration of each part of the spot welder 100 and the electrode 120 is abbreviate | omitted suitably in order to avoid the description redundancy. Members not shown and described may be understood to be similar to known members.

(Spot welder)
As shown in FIG. 1, the spot welder 100 includes a welding control device 110 and a pair of electrodes 120 connected to the welding control device 110 so as to be energized. The welding control device 110 includes a single-phase AC power source 111 and a control unit 112.

  Between the pair of electrodes 120, the molten aluminum-based plated steel sheet 30 and the aluminum material 10 are disposed so as to overlap each other. 1A (refer FIG. 3) is formed by energizing these plate materials using the electrode 120 and performing resistance spot welding.

  The spot welder 100 has an electrode 120 supported by, for example, an arm (not shown), and includes an electrode pressurizing mechanism (not shown) for pressing the electrode 120 against the molten aluminum-based plated steel plate 30 or the aluminum material 10. ing.

  The single-phase AC power supply 111 is formed by connecting one phase of, for example, a commercial three-phase power supply to a welding transformer via a thyristor, and supplies power to the electrode 120.

  The control unit 112 comprehensively controls each unit of the spot welder 100 based on the welding conditions set by the user. The control unit 112 controls spot welding between the molten aluminum-based plated steel sheet 30 and the aluminum material 10 by controlling, for example, the pressure of the electrode, pressurization time, current, energization time, and the like.

(electrode)
The shape of the electrode 120 with which the spot welder 100 of this embodiment is provided is demonstrated roughly using FIG. FIG. 2 is a schematic view showing the shape of the electrode 120.

  As shown in FIG. 2, the electrode 120 is a DR (Dome Radius) type electrode tip. The DR-shaped electrode tip is a D-shaped electrode tip (the tip of the electrode is a curved surface, and the radius of curvature of the curved surface is ½ of the outer diameter of the electrode). Curved surface). The DR-type electrode tip has good shapeability by a tip dresser (electrode polishing tool) and is widely used in the automobile industry.

  The electrode 120 has an outer diameter D1 of the body portion of 16 mm. The tip of the electrode 120 is a curved surface having a tip diameter D2 of 6 mm and a curvature radius of 40 mm. Moreover, the surface of the shoulder part between the trunk | drum of the electrode 120 and the said front-end | tip part is a curved surface with a curvature radius of 8 mm.

  The material of the electrode 120 is a chromium copper alloy (Cr—Cu alloy) containing 0.4 mass% to 1.2 mass% of Cr. The chromium copper alloy may contain about 1% by mass of Cr, for example, 0.8% by mass to 1.1% by mass of Cr.

  The electrode 120 is not limited to the above dimensions and materials as long as it is a DR-type electrode chip. The outer diameter D1 of the electrode 120 is not limited to 16 mm, and may be an outer diameter appropriately designed according to the shape of the tip. The tip diameter D2 of the tip portion of the electrode 120 is preferably 5 mm to 7 mm. Further, the radius of curvature of the tip of the electrode 120 and the radius of curvature of the surface of the shoulder are not particularly limited, and are appropriately designed according to the values of the outer diameter D1 and the tip diameter D2 of the tip. It's okay.

(Aluminum material)
In this specification, the term aluminum material is used to include both pure aluminum (however, it is allowed to contain inevitable impurities) and an aluminum alloy.

  The aluminum material 10 may be a wrought material, and the material is not particularly limited. Various aluminum alloys can be used as the aluminum material 10. For example, various 1000 series, 3000 series, 5000 series, 6000 series, and 7000 series aluminum alloys may be used.

The aluminum material 10 preferably has a Fe concentration of 1.0% by mass or less in consideration of corrosion resistance, workability, and the like. In addition, it is preferable that the aluminum material 10 has about 1.0% by mass of Si and 0.01 to 1.5% by mass of Mg and fine Mg ₂ Si is precipitated by heat treatment such as aging treatment. . In this case, the strength of the aluminum material 10 is improved. From this viewpoint, it is preferable to set the lower limit of the Si content to 0.1% by mass. Moreover, when 1.5-6.0 mass% Mg is added, high intensity | strength will be obtained by solid solution strengthening.

  On the other hand, when the aluminum material 10 contains an excessive amount of Mg exceeding 6.0% by mass, defects are likely to occur during spot welding. Further, if an excessive amount of Si exceeding 3.0% by mass is included, coarse precipitates or crystallized substances may be generated inside the aluminum material 10 to reduce the bonding strength. Therefore, the aluminum material 10 preferably has an Mg concentration of 0.01 to 6.0 mass% and an Si concentration of 3.0 mass% or less.

  The aluminum material 10 may be, for example, an aluminum alloy 6022. Aluminum alloy 6022 is, by mass%, Si: 0.90% or more and 1.20% or less, Fe: 0.20% or less, Cu: 0.05% or less, Mn: 0.04% or more and 0.12% or less. Cr: 0.05% or less, Zn: 0.05% or less, Mg: 0.45% or more and 0.70% or less, Ti: 0.05% or less, and the balance is made of Al and inevitable impurities Composition.

  The aluminum material 10 may be, for example, an aluminum alloy 5052. Aluminum alloy 5052 is, by mass%, Si: 0.25% or less, Fe: 0.4% or less, Cu: 0.1% or less, Mn: 0.1% or less, Cr: 0.15% or more, and 0.005% or less. 35% or less, Zn: 0.1% or less, Mg: 2.2% or more and 2.8% or less, and the balance is composed of Al and inevitable impurities.

  The plate | board thickness of the aluminum material 10 may be suitably set according to the intensity | strength calculated | required as the aluminum material 10, and although it does not specifically limit, For example, it may be 0.6 mm-1.4 mm. In general, when an aluminum material is used for a roof panel of an automobile, the thickness is about this. Moreover, the plate | board thickness of the aluminum material 10 may be 0.8 mm-1.3 mm, and 1.0 mm-1.3 mm may be sufficient.

(Molten aluminum-based plated steel sheet)
The molten aluminum-based plated steel sheet 30 will be described with reference to FIGS. 1 and 3. FIG. 3 is an enlarged view of a part (A1) of the cross-sectional view shown in FIG.

  As shown in FIGS. 1 and 3, a molten aluminum-based plated steel sheet 30 includes a base steel sheet (base steel) 31 and an aluminum plating layer 32 formed on the surface of the base steel sheet 31. The aluminum plating layer 32 includes an alloy layer 33 formed at the interface between the base steel plate 31 and the aluminum plating layer 32. The alloy layer 33 includes a nitrogen enriched layer (hereinafter referred to as an N enriched layer) 34 formed at the interface between the alloy layer 33 and the base steel plate 31.

  As the base steel plate 31, low carbon steel, medium carbon steel, low alloy steel, stainless steel, or the like can be used. Depending on the application, steel types to which Si, Mn, Cr, Ni, etc. are added may be used. Moreover, 25 ppm or more and 200 ppm or less of N are added to the base steel plate 31 in this embodiment. Thus, when heat treatment is performed under specific conditions after plating, an N enriched layer 34 is generated at the interface between the base steel plate 31 and the alloy layer 33. An example of the specific condition is a heat treatment that is held at a temperature of 520 ° C. for 6 hours.

  The N enriched layer 34 is a very thin layer formed on the surface portion of the base steel plate 31, and is a layer having a thickness of about 5 nm, for example. The N enriched layer 34 is more concentrated than the base steel sheet 31 (N is concentrated), and contains, for example, 3.0 atomic% or more of N. The N enriched layer 34 suppresses interdiffusion of Al and Fe. The effect of suppressing the interdiffusion of Fe—Al by the N-concentrated layer 34 is improved as the N content of the base steel sheet 31 is increased when the heat treatment conditions after plating are made constant. However, when the base steel plate 31 contains an excessive amount of N exceeding 200 ppm, the manufacturability of the base steel plate 31 itself decreases.

  Further, the molten aluminum-based plated steel sheet 30 is manufactured as follows. That is, the base steel plate 31 is immersed and passed through a molten aluminum plating bath containing aluminum as a main component. Thereby, the aluminum plating layer 32 is formed on the surface of the base steel plate 31. The thickness of the aluminum plating layer 32 is adjusted, for example, by spraying a wiping gas onto a steel strip immediately after being pulled up from a molten aluminum plating bath and controlling the amount of plating adhesion. By making the thickness of the aluminum plating layer 32 in the range of 5 μm or more and 70 μm or less, the workability of the molten aluminum-based plated steel sheet 30 can be improved.

  The composition of the aluminum plating layer 32 is the same as the composition of the molten aluminum plating bath. Therefore, the composition of the aluminum plating layer 32 can be adjusted by adjusting the composition of the molten aluminum plating bath.

  The aluminum plating layer 32 in the present embodiment is an aluminum layer containing 3 mass% or more and 12 mass% or less of Si and 0.5 mass% or more and 5 mass% or less of Fe (note that unavoidable impurities are contained). Is acceptable). When the aluminum plating layer 32 contains an excessive amount of Si, the workability of the molten aluminum-based plated steel sheet 30 may be impaired. Therefore, the upper limit of Si concentration is regulated to 12% by mass.

  By generating the Fe—Al—Si ternary alloy layer in the alloy layer 33, the bonding strength of the bonded structure 1A can be improved. In order to sufficiently generate the Fe—Al—Si ternary alloy layer, the amount of Fe and Si eluted from the base steel sheet 31 to the molten Al is insufficient when immersed in the aluminum plating bath. Therefore, Fe and Si are replenished from the aluminum plating layer 32 to the bonding interface by increasing the Fe and Si contents of the aluminum plating layer 32. In particular, for Si having a large diffusion coefficient, the Si content of the aluminum plating layer 32 is set as high as 3% by mass or more. Thereby, the amount of Si necessary for generating the Fe—Al—Si ternary alloy layer is ensured.

  Adjusting the composition of the aluminum plating layer 32 as described above not only promotes the formation of the Fe—Al—Si ternary alloy layer, but also increases the Fe and Si concentration of molten Al generated during spot welding. This also occurs. The nugget formed by rapidly cooling molten Al having a high Fe and Si concentration is hardened by the effect of solid solution strengthening of Fe and Si and the rapid cooling effect. Therefore, the joint strength of the joined structure 1A can be increased. And generation | occurrence | production of a weak Fe-Al binary alloy layer is suppressed, and 1 A of joining structures with a highly reliable joint strength are obtained.

  The composition of the above-described aluminum plating layer 32 is a composition of a region that does not include the alloy layer 33 formed at the interface between the base steel plate 31 and the aluminum plating layer 32.

  When it is necessary to further improve the characteristics of the bonded structure 1A (characteristics different from those related to spot welding), such as Ti, Sr, B, Cr, Mn, Zn, etc. that do not significantly affect the Fe-Al interdiffusion reaction. Elements can be appropriately included in the aluminum plating layer 32.

(Joint structure)
The bonded structure 1A of the present embodiment is formed by spot welding the aluminum material 10 and the molten aluminum-based plated steel sheet 30 using the spot welding machine 100 in a state where the respective plate materials are laminated as described above. The joint portion 2A of the joint structure 1A will be described with reference to FIGS. FIG. 4 is a cross-sectional view schematically showing the joint portion 2A of the joint structure 1A in the present embodiment. FIG. 5 is a plan view schematically showing the bonded structure 1 </ b> A with the aluminum material 10 omitted when viewed from the aluminum material 10 side. In FIG. 4, one plate surface of the base steel plate 31 is omitted.

  As shown in FIG. 4, a molten Al nugget 51 is formed at the joint 2A of the joint structure 1A. The molten Al nugget 51 joins the aluminum material 10 and the molten aluminum-based plated steel sheet 30. In the cross-sectional view shown in FIG. 4, the molten Al nugget 51 is an aluminum molten nugget formed in the vicinity of the boundary between the aluminum material 10 and the molten aluminum-based plated steel sheet 30, and rises toward the inside of the aluminum material 10. It is formed in a substantially fan shape (convex upward).

  In addition, the aluminum material 10 has a depression on the surface as the electrode 120 bites into the aluminum material 10 by the applied pressure. A portion where the depression on the surface of the aluminum material 10 is generated is defined as an electrode pressing surface (first surface) 11. In other words, the electrode pressing surface 11 is a surface on the opposite side of the surface of the joining portion 2A that faces the molten aluminum-based plated steel sheet 30 of the aluminum material 10.

  As shown in FIG. 4, the bonded structure 1 </ b> A has a strong heat input region (central region) 70 formed at the interface between the molten Al nugget 51 and the base steel plate 31. As shown in FIG. 5, the strong heat input region 70 is formed in the central portion of the molten Al nugget 51 when the bonded structure 1 </ b> A is seen through from the aluminum material 10 side. A center point 51A shown in FIG. 5 is a central part of energization of the pair of electrodes 120 during spot welding.

  In the bonded structure 1A, a weak heat input region (outer peripheral region) 80 is formed at the interface between the outer edge of the molten Al nugget 51 and the base steel plate 31, and the weak heat input region 80 and the strong heat input region 70 are formed. An intermediate region 60 is formed between the two.

  If it demonstrates on the basis of the center point 51A, as shown in FIG. 5, the fusion | melting Al nugget 51 will be formed so that it may expand in circular shape from 51 A of center points. At the interface between the molten Al nugget 51 and the base steel plate 31, a region having a certain range including the center point 51A is the strong heat input region 70, and the intermediate region 60 and the weak heat input region 80 are outside this region. It exists in order.

(Molten Al nugget)
The molten Al nugget 51 is formed as follows. That is, when the electrode 120 (see FIG. 1) is energized, the boundary surface between the aluminum material 10 and the molten aluminum-based plated steel sheet 30 is resistance-heated. Thereby, aluminum melts. As the molten aluminum solidifies, a molten Al nugget 51 is formed. Therefore, the molten Al nugget 51 is mainly made of aluminum and is affected by the composition of the aluminum material 10 and the aluminum plating layer 32.

  Further, the Fe and Si concentrations of the molten Al nugget 51 can vary depending on the combination of the thickness of the aluminum plating layer 32, the welding current, the energization time, and the electrode shape. The thicker the aluminum plating layer 32 serving as the Fe and Si supply source to the molten Al nugget 51, the higher the Fe and Si concentration of the molten Al nugget 51.

  For example, consider a case where spot welding is performed using a 1% chromium copper alloy tip having a curved surface with a diameter of 6 mm and a curvature radius of 40 mm under the conditions of welding current: 12.5 kA and energization time: 12 cycles. In this case, if the thickness of the aluminum plating layer 32 is 5 μm or more, the average Fe and Si concentrations of the molten Al nugget 51 are both higher by 0.1 mass% or more than the Fe and Si contents of the aluminum material 10. As a result, the molten Al nugget 51 is hardened and the bonding strength of the bonded structure 1A is improved.

  The nugget diameter of the molten Al nugget 51 can be measured as follows. That is, the size of the molten Al nugget 51 (boundary with surrounding materials) in the bonded structure 1A can be visually defined using, for example, an electron micrograph obtained by imaging a cross section as shown in FIG. . The width from one end to the other end at the boundary between the molten Al nugget 51 and the alloy layer 33 is defined as a nugget diameter W1.

  When the extension line of the center axis of each of the pair of electrodes 120 (see FIG. 1) is an electrode center line, the heat input tends to be higher at a position closer to the electrode center line at the joint interface during spot welding. It is in. The weak heat input region 80 is a position far from the electrode center line, and is a portion where the heat input during spot welding is small. On the other hand, the strong heat input area | region 70 is a location with large heat input at the time of spot welding. The intermediate region 60 is a portion that has received an amount of heat input between the heat input in the weak heat input region 80 and the heat input in the strong heat input region 70.

(Strong heat input area)
In the strong heat input region 70, the aluminum material 10 and the aluminum plating layer 32 are melted by being heated at a relatively high temperature, and the N enriched layer 34 of the alloy layer 33 is also melted so that various elements are interdiffused. Thus, the base steel plate 31 is melted. As a result, a molten Al nugget 51 having an Fe concentration higher than that of the aluminum material 10 is formed.

  Although the molten Al nugget 51 is hardened by the enrichment of Fe, a fragile Fe—Al binary alloy layer that lowers the joint strength is likely to occur at the joint interface. That is, when molten Al is rapidly cooled during spot welding to become molten Al nugget 51, in the strong heat input region 70, Fe reprecipitates at the joint interface, and a fragile Fe—Al binary alloy layer is generated.

  Therefore, in the strong heat input region 70, an Fe—Al-based intermetallic compound is mainly formed. However, it is allowed to include various elements supplied from the composition of the aluminum material 10 and the molten aluminum-based plated steel sheet 30 and to include an alloy formed by these elements. In this specification, “mainly Fe—Al-based intermetallic compounds are formed” means that, for example, the intense heat input region 70 is formed using nanoprobe electron beam analysis and energy dispersive X-ray analysis (EDX). When analyzed, it means that data showing that the abundance ratio of the Fe—Al intermetallic compound is the most is obtained.

(Weak heat input area)
On the other hand, the weak heat input region 80 is a region that is heated at the time of spot welding although it is relatively cooler than the strong heat input region 70. Thereby, in the weak heat input area | region 80, Fe and Si melt | dissolve somewhat from the alloy layer 33 (Fe-Al-Si ternary alloy layer), and a Fe-Al type intermetallic compound produces | generates. In the weak heat input region 80, an Fe—Al—Si intermetallic compound is mainly formed. In the present specification, “mainly Fe—Al—Si intermetallic compounds are formed” means the presence of Fe—Al—Si intermetallic compounds as described above for the strong heat input region 70. This means that data indicating that the ratio is the highest can be obtained.

  The weak heat input region 80 is formed in a region having a width of about 0.2 mm from the end of the molten Al nugget 51. The width of this region does not vary much even if the nugget diameter W1 of the molten Al nugget 51 changes.

(Intermediate area)
In the intermediate region 60, at the time of spot welding, the alloy layer 33 (Fe—Al—Si ternary alloy layer) is melted while the N-enriched layer 34 remains while the heat input. Therefore, in the intermediate region 60, the Fe—Al—Si intermetallic compound and the N enriched layer 34 are mixed. In this specification, “Fe—Al—Si intermetallic compound and N enriched layer 34 coexist” means that when the intermediate region 60 is analyzed, the Fe—Al—Si intermetallic compound and N This means that data indicating the presence of the concentrated layer 34 (for example, data detecting the presence of Fe, Al, Si, and N) is obtained, and the following data is obtained. That is, in the intermediate region 60, it is meant that almost no Fe is detected on the molten Al nugget 51 side, and data indicating that no Fe—Al intermetallic compound is generated is obtained. The analysis means is not particularly limited as long as it can analyze a very small region, and for example, nanoprobe electron beam analysis and EDX can be used.

  The intermediate region 60 has, for example, a crack that develops from the weak heat input region 80 that is the outer peripheral portion of the molten Al nugget 51 when a force that peels off the aluminum material 10 is applied to the bonded structure 1A. Work to stop. Thereby, when a further force is applied to the aluminum material 10, the bonded structure 1A is likely to be a button break rather than a shear break. In other words, the molten Al nugget 51 has a high bonding strength because the intermediate region 60 works to increase the bonding strength.

(Remaining Al thickness)
FIG. 6 is a diagram for explaining a method of measuring the residual Al thickness in the bonded structure 1A.

  As shown in FIG. 6, in the bonded structure 1 </ b> A of the present embodiment, the aluminum material 10 remains on the top of the molten Al nugget 51. The shortest distance between the outer edge of the molten Al nugget 51 and the electrode pressing surface 11 of the aluminum material 10 is defined as the remaining Al thickness L1. In the bonded structure 1A of the present embodiment, the remaining Al thickness L1 is 0.01 mm or more.

  Here, the position of the electrode pressing surface 11 (the position in the thickness direction of the bonded structure 1 </ b> A) can vary depending on the depth of depression from the surface of the aluminum material 10. This depth is affected by the applied pressure and heat input (the magnitude of the welding current, the energization time, etc.) during spot welding. In addition, the applied pressure at the time of spot welding is related to the adhesiveness (micro contact area) between the aluminum material 10 and the molten aluminum-based plated steel sheet 30, and is also related to the current density of energization. Therefore, the height of the molten Al nugget 51 is also affected by the applied pressure and heat input during spot welding. The relationship between the welding conditions, the position of the electrode pressing surface 11 and the height of the molten Al nugget 51 also changes depending on the thickness and type of the aluminum material 10 and the thickness and type of the molten aluminum-based plated steel sheet 30. .

  Therefore, (i) while increasing the bonding strength of the bonding portion (for example, the bonding strength when the cross tensile test is performed is 0.8 kN or more), (ii) the residual Al thickness L1 is 0.01 mm or more. It is not easy to satisfy both conditions.

  1 A of joining structures of this embodiment are implement | achieved with the following manufacturing methods.

(Method of manufacturing a joined structure)
The manufacturing method of 1 A of joining structures in this embodiment includes the spot welding process of spot-welding the aluminum material 10 and the hot-dip aluminum type plated steel plate 30 using the spot welding machine 100 of a single phase alternating current system.

(Spot welding process)
The heat input in spot welding can be adjusted by the product of the welding current and the energization time. Here, one cycle of the energization time in spot welding is a time determined from the power frequency of the commercial power source connected to the spot welding machine 100. The commercial power supply may have a power frequency of 50 Hz or a power frequency of 60 Hz. Other power supply frequencies may be used. Heat input can be controlled by adjusting the welding current according to the difference in power supply frequency.

  In the spot welding process, the pressure applied to the electrode 120 is 1.4 kN or more and 4.9 kN or less, and the value represented by the product of the welding current and the energization time is controlled to be within the range of 54 to 240. The Then, the aluminum material 10 and the molten aluminum-based plated steel sheet 30 are spot-welded by a single-phase alternating current method so that the remaining Al thickness L1 is within the range of the present invention.

  A value (that is, heat input) represented by the product of the applied pressure of the electrode 120 and the welding current and the energization time affects the value of the remaining Al thickness L1 in a complicated manner. For example, an appropriate heat input value for changing the remaining Al thickness L1 to 0.01 mm or more varies depending on various conditions.

  In the range where the applied pressure of the electrode 120 is 1.4 kN or more and 4.9 kN or less, when the value represented by the product of the welding current and the energization time is smaller than 54, the remaining Al thickness L1 is increased, The nugget diameter W1 of the molten Al nugget 51 becomes too small, and sufficient bonding strength cannot be obtained. When the value represented by the product of the welding current and the energization time is larger than 240, the nugget diameter W1 of the molten Al nugget 51 can be increased, while the heat input becomes excessive, and the molten Al nugget 51 It will reach the electrode pressing surface 11.

  In the spot welding process, when a commercial power source with a power frequency of 60 Hz is used, the initial pressurization is, for example, 35 cycles and the hold is 24 cycles. The initial pressurization may be 10 cycles or more, and the hold may be 5 cycles or more. The term “hold” means forging pressurization in which a material to be welded is pressed using the electrode 120 while the electrode 120 is cooled after the electrode 120 is energized.

  Further, in the manufacturing method of the present embodiment, the above-described DR-type electrode 120 (see FIG. 2) is used as the electrode. While using such an electrode, spot welding is performed under the above-described conditions. According to such a manufacturing method of this embodiment, even if the plate thickness and material of the aluminum material, the plate thickness of the hot-dip aluminum-based plated steel plate, and the like change, the remaining Al thickness L1 is set to 0.01 mm or more. Thus, the bonded structure 1A having excellent corrosion resistance can be manufactured. And the joining strength of 1A of joining structures can be made high, for example, the joining structure which has a joining strength of 0.8 kN or more as a measurement result of a cross tension test can be manufactured. Such a high bonding strength is an effect obtained by increasing the nugget diameter W1 of the bonded structure 1A and forming a specific region (intermediate region 60) in the bonded portion 2A.

[Embodiment 2]
Another embodiment of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above embodiment are given the same reference numerals, and the description thereof will not be repeated.

  In the first embodiment, the two-piece joined structure has been described. In contrast, in this embodiment, a three-piece joined structure including a steel material in addition to the aluminum material 10 and the molten aluminum-based plated steel plate 30 will be described. Note that the present invention is not limited to a three-piece joined structure, and a four-or-more joined structure is also included in the scope of the present invention. In this specification, the value obtained by summing the plate thickness of the base steel plate in the molten aluminum-based plated steel plate 30 and the plate thicknesses of the plurality of steel materials is referred to as the total steel plate thickness in the bonded structure. In the bonded structure according to one aspect of the present invention, the upper limit of the total thickness of the steel material is 4.3 mm. The number of steel materials is not particularly limited as long as the joining structure has a total steel thickness of 4.3 mm or less. In addition, if the total thickness of the steel material exceeds 4.3 mm, it is difficult to generate a nugget between the molten aluminum-based plated steel plate 30 and the steel material therebelow. In this case, when a cross tensile test is performed, the cross tensile strength tends to be not easily obtained at the interface portion between the molten aluminum-based plated steel sheet 30 and the steel material and 0.8 kN or more.

  For example, when manufacturing a vehicle component, it may be necessary to weld an aluminum material and a plurality of steel materials. Aluminum materials need to be welded in a short time with a relatively large welding current because of their low specific resistance and high thermal conductivity.

  The bonded structure of the present embodiment is a bonded structure in which different materials are bonded by further laminating steel materials in addition to an aluminum material and a molten aluminum-based plated steel sheet and spot welding them by a single-phase alternating current method. . About manufacturing such a joining structure using the spot welding machine of a single phase alternating current system, there was no past result and there was no knowledge. Moreover, the case where there are a plurality of steel materials was completely unknown.

(Joint structure)
A bonded structure 1B and a bonded portion 2B according to the present embodiment will be described with reference to FIGS. FIG. 7 is a cross-sectional view schematically showing a joint portion 2B of the joint structure 1B according to Embodiment 2 of the present invention. FIG. 8 is a diagram for explaining a method of measuring the remaining Al thickness L1 in the bonded structure 1B.

  The bonded structure 1 </ b> B in the present embodiment is manufactured by laminating a molten aluminum-based plated steel plate 30 and the aluminum material 10 in this order on the steel material 20 and performing spot welding.

(Steel)
For example, in the automotive field, the body is assembled by changing the strength of the material at the right place, and the SPC 440 class and SPC 590 class having higher strength than the SPC 270 class having general material strength may be used. The steel type and thickness of the steel material 20 may be appropriately set according to the strength required for the steel material 20, and are not particularly limited.

  The steel material 20 may be a general cold-rolled steel plate, a special cold-rolled steel plate, a high-strength steel plate, a hot-rolled steel plate, or the like, or may be a plated steel plate. The steel material 20 may be, for example, SPC270C, SPC270D, SPC440, SPC590, galvannealed steel sheet (GA steel sheet), and the like. The plate | board thickness of the steel material 20 exists in the range of 0.8 mm-1.4 mm, for example.

(Joint part)
As shown in FIG. 7, a molten Al nugget (first nugget) 51, a lower nugget (second nugget) 52 that joins the molten aluminum-based plated steel sheet 30 and the steel material 20 to the joint 2 </ b> B of the joint structure 1 </ b> B And are formed. In the cross-sectional view shown in FIG. 7, the lower nugget 52 is formed at the boundary between the molten aluminum-based plated steel sheet 30 and the steel material 20, and is formed in an elliptical shape extending to both of them.

  The lower nugget 52 is formed by resistance heating of the boundary surface between the molten aluminum-based plated steel sheet 30 and the steel material 20 by energization, and solidification of the molten iron by raising the temperature to the melting point of Fe.

  It is not easy to form both the molten Al nugget 51 and the lower nugget 52 so as to satisfy a desired bonding strength for the three-piece bonded structure 1B. This is because the behavior of the two nuggets during spot welding is different due to the difference in melting point between iron and aluminum.

  As a result of intensive studies, the present inventors have found the following requirements for the joint portion 2B in order that the three-piece joint structure 1B has high joint strength.

  That is, in the bonded structure 1B of the present embodiment, the ratio of the nugget diameter W1 of the molten Al nugget 51 to the nugget diameter W2 of the lower nugget 52 (the ratio of W1 / W2) is 1.1 or more and 2.0 or less. Yes. Here, the length of the major axis in the elliptical shape of the lower nugget 52 is defined as a lower nugget diameter W2.

  The nugget diameter W2 of the lower nugget 52 can be measured in the same manner as the nugget diameter W1 of the molten Al nugget 51 described above. That is, the size of the lower nugget 52 (boundary with surrounding materials) in the bonded structure 1B can be visually defined using, for example, an electron micrograph of a cross section as shown in FIG.

  The lower nugget 52 is not necessarily elliptical as shown in FIG. Therefore, the lower nugget diameter W2 of the lower nugget 52 is defined in more detail as follows. That is, the lower nugget diameter W2 is a length from one side to the other of the boundary between the lower nugget 52 and the surface of the molten aluminum-based plated steel sheet 30 on the interface where the molten aluminum-based plated steel sheet 30 and the steel material 20 contact each other. .

  When the ratio of W1 / W2 is less than 1.1, the heat input at the time of spot welding is large, so that the nugget diameter W1 of the molten Al nugget 51 becomes too large and the aluminum material 10 is greatly reduced in thickness. Therefore, a bonded structure having a bonding strength of less than 0.8 kN can be obtained as a measurement result of the cross tension test. That is, when the heat input at the time of spot welding is increased, the nugget diameter W1 is increased while the aluminum material 10 is thinned, so that the aluminum material 10 is easily broken at the electrode pressing surface 11 portion.

  On the other hand, when the ratio exceeds 2.0, the heat input during spot welding is small, and the nugget diameter of the lower nugget 52 is not sufficiently large. Therefore, the joint structure is easily broken at the lower nugget 52 in the cross tension test, and the joint strength can be less than 0.8 kN.

  As shown in FIG. 8, in the bonded structure 1 </ b> B of the present embodiment, the aluminum material 10 remains on the top of the molten Al nugget 51. The shortest distance between the outer edge of the molten Al nugget 51 and the electrode pressing surface 11 of the aluminum material 10 is defined as the remaining Al thickness L1. In the bonded structure 1A of the present embodiment, the remaining Al thickness L1 is 0.01 mm or more.

(Method of manufacturing a joined structure)
In the manufacturing method of the bonded structure 1B in the present embodiment, the molten aluminum-based plated steel sheet 30 and the aluminum material 10 are laminated in this order on the steel material 20, and spot welding is performed using the single-phase AC spot welding machine 100. Including a spot welding process.

  In the spot welding process, the pressure applied to the electrode 120 is 1.4 kN or more and 4.9 kN or less, and the value represented by the product of the welding current and the energization time is controlled to be within the range of 54 to 240. The Then, the aluminum material 10 and the molten aluminum-based plated steel sheet 30 are spot-welded by a single-phase alternating current method so that the remaining Al thickness L1 is within the range of the present invention.

  As a result, even in the triple bonded structure 1B, the remaining Al thickness L1 can be set to 0.01 mm or more, and a bonded structure excellent in corrosion resistance can be manufactured. And the junction strength of junction structure 1B can be made high, for example, the junction structure which has the junction strength of 0.8 kN or more as a measurement result of a cross tension test can be manufactured.

[Embodiment 3]
Another embodiment of the present invention will be described below with reference to FIG. The configurations other than those described in the present embodiment are the same as those in the first and second embodiments. FIG. 9 is a cross-sectional view schematically showing a joint portion 2C of the joint structure 1C in the present embodiment.

  In the second embodiment, the three-piece joined structure 1B has been described. In contrast, the bonded structure 1 </ b> C of the present embodiment is a four-piece bonded structure including a steel material 21 in addition to the steel material 20.

  As shown in FIG. 9, in the bonded structure 1 </ b> C of the present embodiment, the steel material 21, the steel material 20, the molten aluminum-based plated steel plate 30, and the aluminum material 10 are stacked in this order, and each plate material is stacked. It is formed by spot welding using a single phase alternating current type spot welding machine 100.

  The steel material 21 and the steel material 20 may be the same steel type as each other or may be different from each other. Also, the same plate thickness may be used, or different plate thicknesses may be used. The plate | board thickness of the steel material 21 exists in the range of 0.8 mm-1.4 mm, for example.

  A lower nugget 55 that extends to the steel material 21, the steel material 20, and the molten aluminum-based plated steel sheet 30 is formed in the joint portion 2 </ b> C of the joint structure 1 </ b> C.

  In this case, the length from one side of the boundary between the lower nugget 55 and the surface of the molten aluminum-based plated steel sheet 30 to the other on the interface where the molten aluminum-based plated steel sheet 30 and the steel material 20 abut is determined as the nugget diameter (first steel). Nugget diameter) W2. Further, the length from one side of the boundary between the lower nugget 55 and the surface of the steel material 20 (or the steel material 21) to the other on the interface where the steel material 20 and the steel material 21 abut is defined as a second steel nugget diameter W3.

  In the bonded structure 1C of the present embodiment, the ratio W1 / W2 is 1.1 to 2.0. The length of the second steel nugget diameter W3 has little influence on the bonding strength of the bonded structure 1C. In the bonded structure 1 </ b> C, an intermediate region 60 is formed at the bonded interface between the molten Al nugget 51 and the base steel plate 31.

  The steel material 21, the steel material 20, the hot-dip aluminum-based plated steel sheet 30, and the aluminum material 10 are spot-welded by a single-phase alternating current method so that the remaining Al thickness L1 falls within the scope of the present invention.

  Thereby, also in 1 C of 4 sets of joining structures, residual Al thickness L1 can be 0.01 mm or more, and the joining structure excellent in corrosion resistance can be manufactured. For example, a bonded structure 1C having a bonding strength of 0.8 kN or more can be manufactured as a measurement result of the cross tension test.

[Embodiment 4]
Another embodiment of the present invention will be described below with reference to FIG. The configurations other than those described in the present embodiment are the same as those in the first to third embodiments. FIG. 10 is a cross-sectional view schematically showing a joint 2D of the joint structure 1D in the present embodiment.

  In the third embodiment, the four-piece joined structure 1C has been described. On the other hand, the joined structure 1D of the present embodiment is a five-piece joined structure including the steel material 22 in addition to the steel material 20 and the steel material 21.

  As shown in FIG. 10, the bonded structure 1 </ b> D includes a steel material 22, a steel material 21, a steel material 20, a hot-dip aluminum-based plated steel plate 30, and an aluminum material 10 that are stacked in this order, and each plate material is stacked. Then, it is formed by spot welding using a spot welding machine 100 of a single-phase alternating current method.

  The steel material 22, the steel material 21, and the steel material 20 may be the same steel type or different steel types. In addition, each may have the same thickness or may have a different thickness. The plate | board thickness of the steel material 22 exists in the range of 0.8 mm-1.4 mm, for example.

  A lower nugget 58 that extends to the steel material 22, the steel material 21, the steel material 20, and the molten aluminum-based plated steel sheet 30 is formed in the joint portion 2 </ b> D of the joint structure 1 </ b> D. The length from one side of the boundary between the lower nugget 58 and the surface of the steel material 21 (or the steel material 22) to the other on the interface where the steel material 21 and the steel material 22 abut is defined as a third steel nugget diameter W4.

  In the bonded structure 1D, the ratio W1 / W2 is 1.1 to 2.0. The lengths of the second steel nugget diameter W3 and the third steel nugget diameter W4 have a small influence on the bonding strength of the bonded structure 1D. In the bonded structure 1 </ b> D, an intermediate region 60 is formed at the bonded interface between the molten Al nugget 51 and the base steel plate 31.

  The steel material 22, the steel material 21, the steel material 20, the molten aluminum-based plated steel sheet 30, and the aluminum material 10 are spot-welded by a single-phase alternating current method so that the remaining Al thickness L1 is within the range of the present invention.

  As a result, even in the five-piece bonded structure 1D, the remaining Al thickness L1 can be set to 0.01 mm or more, and a bonded structure excellent in corrosion resistance can be manufactured. For example, a bonded structure 1D having a bonding strength of 0.8 kN or more can be manufactured as a measurement result of a cross tension test.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  Hereinafter, the bonded structure of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Spot welder]
In the example shown below, spot welding was performed using the spot welder 100 described above. The initial pressurization was 35 cycles and the hold was 24 cycles. A commercial power source having a power frequency of 60 Hz was used. As the electrode 120, a DR-shaped electrode tip (see FIG. 2) having a diameter of 16 mm DR, a tip R of 40 mm, and a tip diameter of 6 mm was used.

(Cross tension test)
FIGS. 11A and 11B are schematic diagrams for explaining the cross tension test, in which FIG. 11A is a plan view of the joined structure, and FIG. 11B is a cross-sectional view of the joined structure. Here, a four-piece joined structure is shown.

  As shown in FIGS. 11A and 11B, the steel material 21 and the steel material 20 are laminated, and the molten aluminum-based plated steel sheet 30 and the aluminum material 10 are laminated thereon in this order. As the aluminum material 10, a material having a width W10 of 50 mm and a length L10 of 150 mm is used. Similarly, the molten aluminum-based plated steel sheet 30, the steel material 20, and the steel material 21 are 50 mm × 150 mm.

  The molten aluminum-based plated steel sheet 30 and the aluminum material 10 are laminated so as to form a cross. Then, an electrode is applied to the welding point 3 and spot welding is performed. Thereby, a joined structure is formed.

  A cross tension test is performed by applying an upward force to the aluminum material 10 of the bonded structure and applying a downward force to the molten aluminum-based plated steel sheet 30. This evaluated the cross tensile strength (kN). A cross tensile strength of 0.8 kN or more was determined to be acceptable and evaluated as o. The cross tension test was conducted in accordance with JIS Z 3137.

[Cross-section observation]
Each of the manufactured bonded structures was embedded in an epoxy resin so that the center of the welded portion could be observed, and was polished. After the polishing treatment, etching was performed with 3% NaOH aqueous solution, and further etching was performed with ethanol in which 3% nitric acid was dissolved. This made it possible to measure the nugget diameter at the weld. By observing the cross section using an optical microscope, the nugget diameter of the aluminum molten nugget and the steel molten nugget and the remaining Al thickness L1 were measured.

[Corrosion resistance]
About each of the manufactured joining structure, the salt spray test (SST) prescribed | regulated to JISZ2371: 2000 was done, and white rust generation | occurrence | production time was measured. The corrosion resistance of the bonded structure was evaluated according to the following criteria, and the evaluation was determined to be acceptable.

○: No white rust generated in 10 hours ×: White rust generated in 10 hours.

(Example 1: 2 sheets)
An aluminum alloy 6022 having a plate thickness of 1.0 mm, an aluminum alloy 5052 having a plate thickness of 1.0 mm or 3.0 mm (aluminum material), a hot-dip aluminum-based plated steel plate having a plate thickness of 0.5 mm, 1.0 mm, or 1.6 mm Were spot welded under the conditions shown in Table 1 or Table 2 below. And about each sample, the cross-sectional observation, the cross tension test, and the salt spray test were done.

  As the molten aluminum-based plated steel sheet, the aforementioned molten aluminum-based plated steel sheet 30 was used. Therefore, the base steel plate contains a predetermined amount of N, and the molten aluminum-based plated steel plate includes an N enriched layer. The same applies to the description of other embodiments below.

  Table 1 shows the results when aluminum alloy 6022 is used as the aluminum material. In addition, the Al molten nugget diameter described in Table 1 below corresponds to the nugget diameter W1 of the molten Al nugget 51 described above with reference to FIG. 4, and the distance from the top of the molten Al nugget to the surface layer of the aluminum alloy is the remaining Al It corresponds to the thickness L1. The same applies to the description of other embodiments below.

  No. in Table 1 As shown to 1-6, the joining structure body of the Example whose residual Al thickness L1 is in the range of this invention showed the outstanding cross tensile strength while showing the outstanding corrosion resistance.

  On the other hand, the comparative example No. in which the molten nugget of the aluminum material reaches the surface layer of the aluminum material. In 7-9, although it is excellent in cross tensile strength, it is inferior to corrosion resistance.

  Table 2 shows the results when aluminum alloy 5052 is used as the aluminum material.

  No. in Table 2 As shown to 11-14, the joining structure body of the Example whose residual Al thickness L1 is within the range of the present invention showed excellent corrosion resistance and excellent cross tensile strength.

  On the other hand, the comparative example No. in which the molten nugget of the aluminum material reaches the surface layer of the aluminum material. 15 and 16 are excellent in cross tensile strength but inferior in corrosion resistance.

  In addition, Example No. 14 and Comparative Example No. 16 shows the following. That is, even when the thickness of the aluminum material is as thick as 3 mm, when the heat input during spot welding becomes higher than a specific value, the molten nugget of the aluminum material reaches the surface layer of the aluminum material and the corrosion resistance decreases. obtain.

(Example 2: 3-disc set)
An aluminum alloy (aluminum material) having a plate thickness of 1.2 mm, a molten aluminum-based plated steel plate having a plate thickness of 0.5 mm, and steel materials of various steel types having a plate thickness of 0.8 mm to 1.4 mm are laminated. Spot welding was performed under the conditions shown in FIG. The total steel plate thickness was 1.3 mm to 1.9 mm. The steel melt nugget diameter shown in Table 3 below corresponds to the nugget diameter W2 of the lower nugget 52. Aluminum alloy 6022 was used as the aluminum material.

  No. in Table 3 As shown to 21-34, the joining structure body of the Example whose residual Al thickness L1 is in the range of this invention showed the outstanding cross tensile strength while showing the outstanding corrosion resistance.

  On the other hand, the comparative example No. in which the molten nugget of the aluminum material reaches the surface layer of the aluminum material. 35 and 36 are excellent in cross tensile strength but inferior in corrosion resistance.

(Example 3: 4-disc set)
An aluminum alloy (aluminum material) having a thickness of 1.2 mm, a hot-dip aluminum-based plated steel plate having a thickness of 0.5 mm, a GA steel plate having a thickness of 0.8 mm (first steel material), and various types having a thickness of 1.0 mm A second steel material of the above steel type was laminated and spot welded under the conditions shown in Table 4 below. The total thickness of the steel plate was 2.3 mm. Aluminum alloy 6022 was used as the aluminum material.

  In a four-piece joined structure, (i) the diameter of the molten Al nugget, and (ii) the diameter of the molten steel nugget between the molten aluminum-based plated steel sheet and the steel material adjacent to the steel sheet (in the above-described nugget diameter W2) The ratio of the nugget diameter was calculated using

  No. in Table 4 As shown to 41-44, the joining structure of the Example whose ratio of residual Al thickness L1 and nugget diameter is in the range of the present invention showed the outstanding cross tensile strength while showing the excellent corrosion resistance.

(Example 4: 5-disc set)
An aluminum alloy (aluminum material) having a plate thickness of 1.2 mm, a molten aluminum-based plated steel plate having a plate thickness of 0.5 mm, and three steel materials were laminated and spot-welded under the conditions shown in Table 5 below. The three steel materials are a first steel material of various steel types with a plate thickness of 0.8 mm or 1.4 mm, a second steel material of various steel types with a plate thickness of 1.0 mm, and a plate thickness of 1.0 mm or 1. It is a third steel material of various steel types of 4 mm. The total steel plate thickness was 3.3 mm or 4.3 mm. Aluminum alloy 6022 was used as the aluminum material.

  In the case of a five-piece bonded structure, as in the case of the four-sheet set, it is formed between (i) the diameter of the molten Al nugget and (ii) the molten aluminum-based plated steel sheet and the steel material adjacent to the steel sheet. The ratio of the nugget diameter was calculated using the diameter of the steel material melted nugget (corresponding to the aforementioned nugget diameter W2).

  No. in Table 5 As shown to 51-56, the joining structure of the Example in which the ratio of residual Al thickness L1 and nugget diameter is within the range of the present invention showed excellent corrosion resistance and excellent cross tensile strength.

1A-1D Joining structure 2A-2D Joining part 10 Aluminum material 11 Electrode pressing surface (first surface)
20 Steel 30 Hot-dip aluminum-based plated steel 31 Base steel (base steel)
34 N enriched layer 51 Molten Al nugget (first nugget)
52 Lower nugget (second nugget)
120 electrodes

Claims (4)

A joined structure joined by spot welding an aluminum material and a molten aluminum-based plated steel sheet,
A molten nugget of aluminum is formed at the boundary between the aluminum material and the molten aluminum-based plated steel sheet,
The surface of the aluminum material opposite to the surface facing the molten aluminum-based plated steel sheet is the first surface,
The joining structure characterized by the shortest distance between the outer edge part of the said fusion | melting nugget and the 1st surface of the said aluminum material being 0.01 mm or more. The aluminum material and the molten aluminum-based plated steel sheet are laminated in this order with respect to the steel material and spot-welded, so that the steel material, the molten aluminum-based plated steel sheet and the aluminum material are joined,
When the molten nugget is a first nugget and the nugget formed at the boundary between the molten aluminum-based plated steel sheet and the steel material is a second nugget,
2. The bonded structure according to claim 1, wherein a ratio of a nugget diameter of the first nugget to a nugget diameter of the second nugget is 1.1 or more and 2.0 or less. A method for manufacturing a joined structure including a spot welding step of spot welding an aluminum material and a molten aluminum-based plated steel sheet,
The surface of the aluminum material opposite to the surface facing the molten aluminum-based plated steel sheet is the first surface,
In the spot welding process,
The pressure of the electrode is 1.4 kN or more and 4.9 kN or less, and the value represented by the product of the welding current and the energization time is in the range of 54 or more and 240 or less,
Single phase so that the shortest distance between the outer edge of the molten nugget formed at the boundary between the aluminum material and the molten aluminum-based plated steel sheet and the first surface of the aluminum material is 0.01 mm or more. A method for manufacturing a joint structure, characterized by spot welding the aluminum material and the molten aluminum-based plated steel sheet by an alternating current method.   The method for manufacturing a joined structure according to claim 3, wherein a joining strength is 0.8 kN or more as a measurement result of a cross tensile test of the joined structure formed in the spot welding process.

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