JP2012152786A - Dissimilar metal welding method of steel sheet and aluminum alloy sheet, and dissimilar metal welded joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the dissimilar metal welding method of a steel sheet and an aluminum alloy sheet for suppressing formation of an intermetallic compound on a weld interface, and can improve joint strength, fatigue strength and corrosion resistance, and dissimilar metal welded joint.SOLUTION: When a steel sheet 1 and an aluminum alloy sheet 2 are subjected to resistance spot welding, energizing time Bt(ms) and stop time Rt(ms) are made into the conditions satisfying expressions {2≤Bt≤10} and {1≤Rt≤5}, pulsation energizing under pressurizing force EF(kN) is performed in the range of 2 to 8 times, after the final energizing stop for the stop time Rt(ms) is completed, immediately, the pressurizing force is increased to pressurizing force FF(kN) after the completion of the energizing satisfying an expression {1.2×EF≤FF≤2.0×EF}, subsequently, the pressurizing is held for a holding time Ht(ms) satisfying an expression {50≤Ht≤300}, and thereafter, the pressurizing force is unloaded.

Description

  The present invention relates to a dissimilar metal joining method and a dissimilar metal joining joint between a steel plate and an aluminum alloy plate, and in particular, manufacture of automobile parts reduced in weight by application of a partial aluminum alloy plate, assembly of a vehicle body, and the like. In this process, the present invention relates to a dissimilar metal joining method for joining a steel plate and an aluminum alloy plate, and a dissimilar metal joint joint obtained thereby.

In recent years, in the automobile field, there has been a growing need to partially use aluminum alloy plates for car bodies and parts in order to reduce vehicle weight for the purpose of reducing fuel consumption and reducing carbon dioxide (CO ₂ ) emissions. In particular, it is prominent in the field of hybrid vehicles and the like. On the other hand, spot welding is mainly used in processes such as vehicle body assembly and parts mounting. However, when an aluminum alloy plate is partially used, it is necessary to spot weld the steel plate and the aluminum alloy plate. Sex occurs.

  Here, in general, the important characteristics of a welded joint obtained by spot welding include tensile strength and fatigue strength, but the most important is tensile strength. The tensile strength of a welded joint includes a tensile shear strength (TSS) measured by applying a tensile load in the shear direction and a cross tensile strength (CTS) measured by applying a tensile load in the peeling direction.

However, when the steel plate and the aluminum alloy plate are spot-welded, the following problems occur.
As shown in FIG. 6, when the steel plate 101 and the aluminum alloy plate 201 are spot-welded, an intermetallic compound 203 made of brittle Fe ₂ Al ₅ or the like is generated in the welded portion. The intermetallic compound 203 is generated at the interface between the Al molten portion 201a generated on the steel plate 101 and the aluminum alloy plate 201 side. In particular, when the Fe molten portion 101a is large, the generation amount of the intermetallic compound 203 also increases. . When such a large amount of intermetallic compound 203 is produced, there arises a problem that the tensile strength of the spot welded portion (welded joint) 110, particularly the cross tensile strength in the peeling direction, is extremely lowered. In addition, when an impact is applied to the welded joint in which the intermetallic compound 203 as described above is generated, there is a problem that breakage easily occurs. Furthermore, in the welded portion where the intermetallic compound 203 is generated, corrosion preferentially progresses, so that there is a problem that the corrosion resistance is inferior.

  Many methods have been proposed so far in order to suppress the formation of intermetallic compounds when welding a steel plate and an aluminum alloy plate and increase the joint strength. For example, a method of suppressing the formation of intermetallic compounds by setting the energization pattern during welding to a large current and a short time energization (see, for example, Patent Document 1), and an intermetallic compound by devising the electrode tip shape A method (for example, see Patent Document 2) has been proposed. Moreover, the method of suppressing the production | generation of an intermetallic compound is proposed by optimizing the composition of the steel plate and aluminum alloy plate which are to-be-welded materials, or content of Mn and Si in an oxide film (for example, (See Patent Document 3).

  In addition, when welding a steel plate and an aluminum alloy plate, a method has been proposed in which an adhesive layer or the like is provided in advance between the joint surfaces, and joint strength and corrosion resistance are improved by using adhesion and welding together (for example, Patent Documents). See 4). Moreover, in welding a steel plate and an aluminum alloy plate, a method of performing welding using a eutectic reaction has been proposed (see, for example, Patent Document 5). In addition, a method for securing joint strength by defining the thickness and area ratio of an intermetallic compound generated at a welded portion between a steel plate and an aluminum alloy plate has also been proposed (see, for example, Patent Document 6). .

Also, for example, there are a method of increasing the joint strength after welding by inserting and welding an aluminum clad steel plate between a steel plate and an aluminum alloy plate, and a method of using mechanical joining by a self-piercing rivet or the like. There is also a method using a friction stir welding method in which a frictional heat is generated by pressing against a workpiece to be welded with a pressure while rotating the pin, and the frictional heat is joined by the rotation of the pin and the plastic flow generated in the axial direction. is there. Moreover, in joining pipes or rods, a method of using friction stir welding that joins by rotating the materials to be joined with strong pressure by pressing the members to be joined together with a strong pressure is also conceivable. In addition, for example, a method for joining a steel plate and an aluminum alloy plate by allowing an aluminum alloy plate to penetrate through a steel pin to contact the steel plate and resistance-welding the contact portion by energizing between the steel pin and the steel plate. Etc. are also conceivable.
However, in any of the above methods, there is a problem that a large amount of brittle intermetallic compound is generated in the welded portion between the steel plate and the aluminum alloy plate, and the bonding strength and corrosion resistance are lowered. These methods also have a problem that the joining method is complicated.

  Here, a method has been proposed in which an aluminum-plated steel plate is used as the steel plate and the composition of components such as Si in the aluminum plating is optimized (for example, see Patent Document 7). According to the method described in Patent Document 7, it is said that the joint strength of the welded portion can be increased by using an aluminum-plated steel sheet in which components during plating are optimized. However, even if the method described in Patent Document 7 is used, a large amount of Fe—Al-based intermetallic compound is produced at the interface between molten steel (Al melted part) produced by a steel plate and an aluminum alloy plate. For this reason, similarly to the above, there has been a problem that the joint strength after welding, particularly the cross tensile strength in the peeling direction, the impact resistance, and the corrosion resistance are lowered.

JP 2004-114108 A JP 2007-326146 A JP 2006-336070 A JP 2008-080394 A JP 2010-099672 A JP 2009-061500 JP 2006-198679 A

  The present invention has been made in view of the above problems, and even when a steel plate and an aluminum alloy plate are spot-welded, it is possible to suppress the formation of an Fe-Al intermetallic compound at the bonding interface, It is an object of the present invention to provide a dissimilar metal joining method between a steel plate and an aluminum alloy plate, which can improve joint strength, fatigue strength and corrosion resistance, and a dissimilar metal joint joint obtained thereby.

When the present inventors have eagerly studied to solve the above-mentioned problem, when conducting dissimilar metal joining by spot welding between a steel plate and an aluminum alloy plate, energization conditions for conducting pulsation energization for a large current and for a short time are performed. By increasing the applied pressure immediately after the end of energization, the formation and growth of intermetallic compounds at the bonding interface is suppressed, and even if metal compounds are generated, they are discharged from the interface between the steel plate and the aluminum alloy plate. I found out. That is, by spot welding a steel plate and an aluminum alloy plate under appropriate welding conditions, the joint strength, particularly the cross tensile strength in the peeling direction, can be improved, and the fatigue strength and corrosion resistance can be improved. The headline and the present invention were completed.
That is, the gist of the present invention is as follows.

[1] A steel plate in which one or more steel plates and aluminum alloy plates are superposed, and a total of two or more plates are superposed, and resistance spot welding is performed while applying pressure with electrodes arranged above and below the steel plates and aluminum alloy plates. Is a dissimilar metal joining method between an aluminum alloy plate and the resistance spot welding, the energization time Bt (ms), the rest time Rt (ms) is a condition satisfying the following formulas (1) and (2): The pulsation energization with the applied pressure EF (kN) is performed in the range of 2 to 8 times, and immediately after the final energization suspension with the rest time Rt (ms) is completed, the applied pressure is expressed by the following formula (3) The pressure is increased to the applied pressure FF (kN) after completion of energization satisfying the condition, and after that, the pressure is held for a holding time Ht (ms) that satisfies the following formula (4), and then the applied pressure is unloaded. Steel plate and aluminum alloy Dissimilar metal joining method with plate.
2 ≦ Bt ≦ 10 (1)
1 ≦ Rt ≦ 5 (2)
1.2 x EF ≤ FF ≤ 2.0 x EF (3)
50 ≦ Ht ≦ 300 (4)
{However, in the above formulas (1) to (4), Bt: energization time (ms), Rt: rest time (ms), EF: applied pressure during pulsation energization (kN), FF: applied after completion of energization Pressure (kN), Ht: holding time (ms). }

[2] Before conducting the pulsation energization, pre-energization is performed in advance under the conditions of the pre-energization time Pt (ms) satisfying the following (5) and (6) and the pressure PF (kN) during the pre-energization. Thus, the dissimilarity between the steel plate and the aluminum alloy plate according to the above [1] is characterized in that minute scattering is generated between the joining interfaces between the steel plate and the aluminum alloy plate, and then the pulsation energization is performed. Metal joining method.
5 ≦ Pt ≦ 20 (5)
0.6 × EF ≦ PF ≦ 0.8 × EF (6)
{However, in the above formulas (5) and (6), Pt: pre-energization time (ms), EF: pressure applied during pulsation energization (kN), PF: pressure applied during pre-energization (kN). }

  [3] A dissimilar metal joint obtained by joining a steel plate and an aluminum alloy plate by the dissimilar metal joining method according to [1] or [2], wherein the joint is formed between the steel plate and the aluminum alloy plate. A dissimilar metal between a steel plate and an aluminum alloy plate, characterized in that a Fe-Al intermetallic compound layer having a thickness of 0.5 μm or less at a position corresponding to the center of the electrode at the time of applying pressure is formed Joint joint.

  According to the dissimilar metal joining method of a steel plate and an aluminum alloy plate of the present invention, as described above, a method for optimizing the welding conditions when spot-welding the steel plate and the aluminum alloy plate, that is, energization and pressure conditions Is adopted. This makes it possible to form a highly reliable joint with excellent weldability, that is, joint strength, fatigue strength, and corrosion resistance, while ensuring good workability when joining a steel plate and an aluminum alloy plate. Is possible.

  Further, according to the dissimilar metal joint according to the present invention, it is obtained by joining the steel plate and the aluminum alloy plate by the dissimilar metal joining method, and the thickness of the intermetallic compound is suppressed to a predetermined value or less. In addition, the joint strength, fatigue strength and corrosion resistance are excellent and highly reliable.

Therefore, for example, in the automotive field, by applying the present invention to the process of manufacturing parts for automobiles that are lightened by applying a partial aluminum alloy plate, assembling the body, etc., low fuel consumption due to weight reduction of the entire body Benefits such as gasification and carbon dioxide (CO ₂ ) emission reduction can be fully enjoyed, and its social contribution is immeasurable.

It is a figure explaining typically an example of a dissimilar metal joining method of a steel plate and an aluminum alloy plate concerning the present invention, and a dissimilar metal joining joint, and is a sectional view showing a process of joining a steel plate and an aluminum alloy plate by spot welding is there. It is a figure explaining typically an example of a dissimilar metal joining method of a steel plate and an aluminum alloy plate concerning the present invention, and a dissimilar metal joint joint, and shows a welded part after joining a steel plate and an aluminum alloy plate by spot welding It is sectional drawing. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining typically an example of the dissimilar metal joining method and dissimilar metal joining joint of the steel plate and aluminum alloy plate which concern on this invention, and the pulsation electricity supply pattern at the time of forming a welding part by spot welding, and an electrode It is a graph which shows the pattern of the applied pressure by. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which illustrates typically an example of the dissimilar metal joining method of the steel plate and aluminum alloy plate which concerns on this invention, and a dissimilar metal joint joint, and the dissimilarity formed by joining one steel plate and one aluminum alloy plate It is the schematic which shows the measuring method of the cross tensile strength of a metal joining joint. It is a figure which illustrates typically an example of a dissimilar metal joining method of a steel plate and an aluminum alloy plate concerning the present invention, and a dissimilar metal joining joint, and is a different kind formed by joining two steel plates and one aluminum alloy plate It is the schematic which shows the measuring method of the cross tensile strength of a metal joining joint. It is a figure which illustrates typically the dissimilar-metal joining method and dissimilar-metal joining joint of the conventional steel plate and an aluminum alloy plate, and shows the intermetallic compound produced when welding a steel plate and an aluminum alloy plate by spot welding It is sectional drawing.

  Hereinafter, embodiments of a dissimilar metal joining method and a dissimilar metal joining joint (hereinafter simply referred to as a dissimilar metal joining method, sometimes referred to as a dissimilar metal joining joint) between a steel plate and an aluminum alloy plate of the present invention will be described with reference to This will be described with reference to FIG. The present embodiment is described in detail for better understanding of the purpose of the dissimilar metal joining method and dissimilar metal joint in the present invention, and does not limit the present invention unless otherwise specified. .

In recent years, particularly in the automobile field, there has been a need to partially use aluminum alloy plates for vehicle bodies and parts in order to reduce vehicle weight for the purpose of reducing fuel consumption and reducing carbon dioxide (CO ₂ ) emissions. This tendency is particularly noticeable in the field of hybrid vehicles and the like. In addition, spot welding methods are mainly used when assembling the vehicle body or attaching parts, but when an aluminum alloy plate is partially used, it is necessary to spot weld the steel plate and the aluminum alloy plate. Sex occurs. Conventionally, when a steel plate and an aluminum alloy plate are welded, the tensile strength (cross tensile strength) in the peeling direction of the welded portion is reduced particularly by the Fe-Al intermetallic compound produced at the joint interface. There is a problem that fatigue strength and corrosion resistance are reduced. For this reason, a method that can suppress the formation of intermetallic compounds when spot welding the steel plate and the aluminum alloy plate with the expansion of the application area of the aluminum alloy plate in the automobile field and realize excellent joint characteristics is desired. It was rare.

  In response to such demands, the dissimilar metal joining method of the steel plate and the aluminum alloy plate of the present invention employs the energization condition for conducting pulsation energization for a short time with a large current as described above, and further, after energization is completed. Immediately increase the applied pressure. This makes it possible to suppress the formation of intermetallic compounds while properly controlling the welding energization and pressure pattern within the range of practical welding conditions using resistance spot welding equipment similar to the conventional one, and the joint strength It is possible to obtain a dissimilar metal joint having excellent fatigue strength and corrosion resistance. Below, the dissimilar metal joining method and dissimilar metal joining joint of the steel plate and aluminum alloy plate of this invention are demonstrated in detail.

[Dissimilar metal joining method between steel plate and aluminum alloy plate]
As shown in FIG. 1, the dissimilar metal joining method of the steel plate 1 and the aluminum alloy plate 2 according to the present invention includes one or more steel plates 1 and two aluminum alloy plates 2 in total (one each in the illustrated example). In this method, resistance spot welding is performed while applying pressure with the electrodes 5 (5A, 5B) arranged above and below the steel plate 1 and the aluminum alloy plate 2. In the present invention, when the steel plate 1 and the aluminum alloy plate 2 are subjected to resistance spot welding, the energizing time Bt (ms) and the downtime Rt (ms) are set to satisfy the following expressions (1) and (2). The pulsation energization at the pressure EF (kN) is performed in the range of 2 to 8 times, and immediately after the last energization stop at the stop time Rt (ms) is completed, the applied pressure satisfies the following formula (3). A method is adopted in which the pressure is increased to FF (kN) after completion of energization, and after that, pressure is held for a holding time Ht (ms) that satisfies the following expression (4), and then the pressure is unloaded.
2 ≦ Bt ≦ 10 (1)
1 ≦ Rt ≦ 5 (2)
1.2 x EF ≤ FF ≤ 2.0 x EF (3)
50 ≦ Ht ≦ 300 (4)
However, in the above formulas (1) to (4), Bt: energization time (ms), Rt: rest time (ms), EF: applied pressure during pulsation energization (kN), FF: applied pressure after completion of energization (KN), Ht: holding time (ms).

"Resistance spot welding"
FIG. 1 is a schematic diagram for explaining a resistance spot welding method used for welding a steel plate 1 and an aluminum alloy plate 2 in the present invention.
In the resistance spot welding described in the present invention, first, a steel plate 1 and an aluminum alloy plate 2 which are welded materials are overlapped. In the illustrated example, the steel plate 1 and the aluminum alloy plate 2 are overlapped one by one. And by energizing while pressing the welding electrodes 5A, 5B made of a copper alloy so as to be sandwiched from both sides with respect to the overlapping portion of the steel plate 1 and the aluminum alloy plate 2, that is, from the vertical direction in FIG. Molten metal is formed between the steel plate 1 and the aluminum alloy plate 2. After the welding energization by pulsation energization is completed, the molten metal is rapidly cooled and solidified by heat removal by the water-cooled welding electrodes 5A and 5B and heat conduction to the steel plate 1 and the aluminum alloy plate 2, and the steel plate 1 is solidified. A solidified portion is formed between the aluminum alloy plate 2 and the aluminum alloy plate 2.

  In the present invention, as in the example shown in FIG. 2, the Fe molten portion 1 a and the Al molten portion 2 a that are thin molten metal layers are formed at the joint interface between the steel plate 1 and the aluminum alloy plate 2. When the Fe melt part 1a and the Al melt part 2a are solidified to form a nugget, the steel plate 1 and the aluminum alloy plate 2 are welded. In addition, it is not always necessary to melt at the interface between the steel plate 1 and the aluminum alloy plate 2, and both or one of them may be joined in a solid state.

  Moreover, in the example shown in FIG. 2, the intermetallic compound layer 3 which consists of Fe-Al type metal is produced | generated between the Fe fusion | melting part 1a and the Al fusion | melting part 2a in a joining interface. Although details will be described later in the present invention, the thickness of the intermetallic compound layer 3 is 0.5 μm or less at the thickness t1 at the central position 31 corresponding to the central portion 51 of the electrodes 5A and 5B when applying pressure. Limited. Note that the thickness t1 of the intermetallic compound layer 3 may be a thickness when both or one of the steel plate 1 and the aluminum alloy plate 2 are joined in a solid state.

  In the dissimilar metal joining method according to the present invention, in the resistance spot welding as described above, the energization condition is such that pulsation energization is performed for a short time with a large current by the electrodes 5A and 5B, and the applied pressure is increased immediately after energization. The method is a combination of conditions. And by defining these conditions in the optimum ranges as described below, the generation of the Fe molten portion 1a on the base metal side of the steel plate 1 is particularly suppressed. Thus, the production | generation of the Fe-Al type intermetallic compound produced | generated from this Fe fusion | melting part 1a and Al fusion | melting part 2a is also suppressed by suppressing the production | generation of the Fe fusion | melting part 1a in the steel plate 1 side. And by suppressing the formation so that the thickness of the intermetallic compound layer 3 made of Fe-Al-based intermetallic compound is in the above range, the joint strength, in particular, the cross tensile strength that is the strength in the peeling direction is reduced. It is possible to improve the fatigue strength and corrosion resistance, and to form a highly reliable welded portion.

"steel sheet"
Below, the characteristic of the steel plate 1 which is one to-be-welded material in the dissimilar metal joining method of this invention is explained in full detail.

(Steel grade)
In the present invention, the steel type of the steel sheet to be welded is not particularly limited, and for example, extremely low C type (ferrite main structure), Al-k type (structure including pearlite in ferrite), two-phase structure type ( For example, steel sheets of any type such as a structure containing martensite in ferrite, a structure containing bainite in ferrite, a work-induced transformation type (structure containing residual austenite in ferrite), a fine crystal type (ferrite main structure), etc. It may be. By applying the dissimilar metal joining method of the present invention to any steel type, the steel plate and the aluminum alloy plate are welded while suppressing the formation of intermetallic compounds without impairing the properties of the steel plate. Therefore, a highly reliable dissimilar metal joint (welded part) can be obtained.

(Tensile strength)
In the present invention, the tensile strength of the steel plate is not particularly limited, and any steel plate having any tensile strength can be applied. For example, a steel plate having a tensile strength of about 270 to 1470 MPa, which is generally used in an automobile body or the like, can be used without any limitation.

(Plating)
In the present invention, it is possible to employ a steel plate in which a plating layer is further provided on the surface layer, but the type of the plating layer applied at this time is not limited at all. For example, as a kind of plating layer, Zn type (Zn, Zn-Fe, Zn-Ni, Zn-Al, Zn-Al-Mg, Zn-Al-Mg-Si, etc.), Al type (Al-Si, etc.) Any of these may be used. Further, the basis weight of these plating layers is not particularly limited, but the basis weight on both sides is preferably 100 g / 100 g / m ² or less. If the plating weight per unit area exceeds 100 g / m ² , the plating layer may become an obstacle during welding.

(Thickness)
In the present invention, the thickness of the steel plate is not particularly limited, and a steel plate having a thickness of about 0.50 to 2.3 mm, which is generally used in an automobile body or the like, can be employed without any limitation. it can.

"Aluminum alloy plate"
Hereinafter, the characteristic of the aluminum alloy plate 2 which is the other material to be welded in the dissimilar metal joining method of the present invention will be described in detail.

(Alloy type)
In the present invention, the type of alloy of the aluminum alloy plate 2 is not particularly limited. For example, any type of aluminum alloy such as 5000 (Al—Mg) or 6000 (Al—Mg—Si) commonly used in automobile bodies can be used without any limitation. .

(Tensile strength)
In the present invention, the tensile strength of the alloy of the aluminum alloy plate 2 is not particularly limited. For example, a material of about 100 to 400 MPa class generally used in an automobile body or the like can be used without any limitation. it can.

(Thickness)
In the present invention, the thickness of the aluminum alloy plate 2 is not particularly limited. For example, an aluminum alloy plate having a thickness of about 0.55 to 2.0 mm, which is generally used in an automobile body or the like, is used. It can be employed without any restrictions.

"Superposition of steel plate and aluminum alloy plate"
In this embodiment, regarding the dissimilar metal joining method, a case will be described in which spot welding is performed on two sheets of steel plates 1 and an aluminum alloy plate 2 as illustrated mainly in FIG. 2 (see also FIG. 1). However, the present invention is not limited to this. In the present invention, spot welding may be performed by stacking three or more sheets as long as a steel sheet is present on one side and an aluminum alloy sheet is present on the other side as a material to be welded. In the schematic diagram for explaining the test conditions of the cross tension test shown in FIG. 5, an example in which two steel plates 1 are overlapped and one aluminum alloy plate 2 is used, and a total of three are overlapped and welded. Show. The steel plate 1 and the aluminum alloy plate 2 may be made of different thickness or different materials when two or more of them are overlapped.

"Reasons for limiting welding conditions"
Below, the reason for limitation is explained in full detail about the welding conditions prescribed | regulated with the dissimilar-metal joining method of this invention.

  First, the energization / pressurization pattern when spot welding the steel plate 1 and the aluminum alloy plate 2 described below is shown in the graphs of FIGS. The energization / pressurization patterns shown in FIGS. 3A and 3B are examples of energization patterns applicable to spot welding in the dissimilar metal joining method of the present invention. In the example shown in FIG. The pattern is such that the pulsation energization is performed for a short time with an electric current, the applied pressure (EF) of the electrode is normal, and the applied pressure (FF) is increased immediately after the energization is completed. In the graphs shown in FIGS. 3A and 3B, the vertical axis represents the applied pressure (kN) or current (kA), and the horizontal axis represents time (ms).

  Conventionally, when a steel plate is welded by a general spot welding method, detailed illustration is omitted, but the current is cut off after a predetermined time (t) at a predetermined current (I) for a predetermined time (t). The energization pattern shows a current waveform having a shape, and the pressurizing force of the electrodes is also a rectangular pressurization pattern. On the other hand, in the present invention, as described above, first, regarding welding energization, pulsation energization is performed in which energization (energization time Bt) and pause (rest time Rt) are repeated in a range of 2 to 8 times. The applied pressure (applied pressure EF during pulsation energization) is constant. Then, immediately after the energization, the applied pressure (the applied pressure FF after completion of energization) is immediately increased.

  In the present invention, as in the example shown in FIG. 3 (b), before performing pulsation energization under the above conditions, pre-energization is performed in advance as energization and pressurization at a pressure lower than that during pulsation energization. It is also possible.

(Pressurizing force during pulsation energization: EF)
In the present invention, the pressure EF (kN) applied to the steel plate 1 and the aluminum alloy plate 2 of the electrodes 5A and 5B when performing welding energization by pulsation energization is not particularly limited. In the present invention, for the pressurizing force EF during pulsation energization, the conditions conventionally used when spot welding a steel plate and an aluminum alloy plate can be employed without any limitation. The applied pressure EF can be in the range of about 47 to 4.5 (kN). In the present invention, by setting the applied pressure EF (kN) within the above range, for example, spot welding is performed by stacking two or more mild steel plates or aluminum alloy plates having a plate thickness of about 1 mm, which are used for automobile bodies and the like. In this case, high weldability and productivity can be ensured.

  Here, the applied pressure EF during pulsation energization of the electrodes 5A and 5B also affects the strength of the welded portion, particularly the strength in the peeling direction. For this reason, in this invention, it is more preferable to make this pressurizing force EF into the said range also from a viewpoint of suppressing the production | generation of the intermetallic compound layer 3 effectively. If the applied pressure EF during pulsation energization exceeds the above range, the dent of the welded portion becomes large, which not only impairs the appearance but also may reduce the joint strength. Moreover, when the applied pressure EF is less than the above range, defects may occur in the weld metal.

  In the dissimilar metal joining method of the present invention, for example, a conventionally known resistance spot welding equipment provided with electrodes 5 (5A, 5B) illustrated in FIG. 1 can be used without any limitation. . Moreover, what is necessary is just to use the thing of the structure currently used also about electrode 5A, 5B.

  Further, the welding power source for supplying current to the electrodes 5A and 5B may be either an AC power source or a DC power source. Specifically, an inverter type DC power source, an inverter type AC power source, a single phase AC power source, etc. Among them, an inverter type DC power supply is preferable.

(Pulsation energization current: BC)
In the present invention, the current BC (kA) at the time of pulsation energization can be set to the same level as the current value conventionally employed when resistance steel plate and aluminum alloy plate are subjected to resistance spot welding. An energization current BC in the range of about 20 to 30 (kA) can be obtained. If the energization current BC is less than 20 kA, sufficient bonding strength may not be obtained, and if it exceeds 30 kA, an intermetallic compound layer may be easily generated and grown. In addition, when the energization current BC exceeds 30 kA, a large transformer for generating a large current is required in the power supply device, which causes an increase in the cost of equipment.

(Energization time for pulsation energization: Bt)
In the present invention, the energization time Bt (ms) in pulsation energization is defined within a range that satisfies the following expression (1).
2 ≦ Bt ≦ 10 (1)
However, in the above equation (1), Bt: energization time (ms) is shown.

  If the energization time Bt in pulsation energization is less than 2 ms, sufficient bonding strength cannot be obtained. If the energization time exceeds 10 ms, the intermetallic compound layer is easily formed and grown, and the entire bonding time in the process is also long. Therefore, productivity is reduced.

(Pause time during pulsation energization: Rt)
In the present invention, the rest time Rt (ms) in pulsation energization is defined within a range that satisfies the following equation (2).
1 ≦ Rt ≦ 5 (2)
However, in the above equation (2), Rt: pause time (ms) is shown.

  If the pause time Rt in pulsation energization is less than 1 ms, a sufficient cooling effect cannot be obtained, so that an intermetallic compound layer is easily formed and grows. If it exceeds 3 ms, the temperature of the molten metal is too low. In addition, sufficient bonding strength cannot be obtained, and the entire bonding time in the process becomes longer, resulting in lower productivity.

(Number of pulsation energization patterns: 2 to 8 times)
In the present invention, the number of repetitions (number of pulses) of the pulsation energization pattern that repeats the energization time Bt and the pause time is specified in the range of 2 to 8 times. If the number of energization patterns is less than 2, sufficient bonding strength cannot be obtained. If the number of energization patterns exceeds 8, the intermetallic compound layer is likely to be generated and grown, and the entire bonding time in the process becomes longer. , Productivity decreases.

(Pressure force after completion of pulsation energization pattern: FF)
In the present invention, after the welding energization by the pulsation energization pattern under the above conditions is completed, that is, after the last energization suspension at the above-described rest time Rt (ms) is completed, the steel plate 1 and the aluminum alloy plate 2 are immediately The applied pressure of the electrodes 5A and 5B is increased to the applied pressure FF (kN) after completion of energization satisfying the following expression (3).
1.2 x EF ≤ FF ≤ 2.0 x EF (3)
However, in the above equation (3), FF represents the applied pressure (kN) after completion of energization.

  As shown in the above equation (3), in the present invention, immediately after the completion of the pulsation energization pattern, immediately after the completion of the pulsation energization pattern, the applied pressure FF (kN) in the range of 1.2 to 2.0 times the applied pressure EF during pulsation energization To do. Thus, after the welding energization pattern by pulsation energization is completed, the intermetallic compound layer 3 produced | generated by the joining interface is raised by raising the applied pressure with respect to the steel plate 1 and the aluminum alloy plate 2 of electrode 5A, 5B. Discharged from. Thereby, the thickness of the intermetallic compound layer 3 produced | generated in the dissimilar metal joint joint 10 can be controlled thinly to 0.5 micrometer or less, and it can aim at the improvement of joint strength, fatigue strength, and corrosion resistance. It becomes.

  When the applied pressure FF (kN) after completion of the pulsation energization pattern is less than the above range, the intermetallic compound layer at the bonding interface is insufficiently discharged. The dent becomes larger and the cross tensile strength of the joint decreases.

(Retention time: Ht)
In the present invention, the pressure FF (kN) applied to the steel plate 1 and the aluminum alloy plate 2 of the electrodes 5A and 5B is increased to the above range, and then the pressure is held for a holding time Ht (ms) that satisfies the following expression (4). Then, the applied pressure is unloaded.
50 ≦ Ht ≦ 300 (4)
In the above formula (4), Ht: holding time (ms) is shown.

  In the present invention, immediately after the completion of the pulsation energization pattern, the steel plate 1 and the aluminum alloy plate 2 are held at the joining interface by holding the steel plate 1 and the aluminum alloy plate 2 with the holding time Ht in the range of 30 to 300 (ms) as the pressure FF in the above range. The generated intermetallic compound layer 3 is effectively discharged from the weld. Thereby, as described above, the thickness of the intermetallic compound layer 3 can be controlled to 0.5 μm or less, and it is possible to improve joint strength, fatigue strength, and corrosion resistance.

After the pulsation energization pattern is completed, if the holding time Ht at the pressure FF is less than 50 ms, the intermetallic compound layer at the bonding interface is insufficiently discharged, and if it exceeds 300 ms, the entire bonding time in the process As a result, the productivity decreases.
Note that the holding time Ht described above indicates an actual holding time and is usually longer than the time set on the apparatus side although it depends on the welding apparatus.

  According to the present embodiment, as described above, the welding energization pattern that optimizes the energization time Bt and the rest time Rt and performs short-time pulsation energization with a large current is adopted, and immediately after the pulsation energization ends, In this method, the pressure is maintained with the increased pressure FF and the optimized holding time Ht. Thereby, especially the production | generation of the Fe fusion | melting part 1a in the base material side of the steel plate 1 can be suppressed notably. And in connection with this, the production | generation of the intermetallic compound layer 3 can be suppressed in the joining interface of the steel plate 1 and the aluminum alloy plate 2, and the dissimilar metal joint joint 10 excellent in joint strength, fatigue strength, and corrosion resistance is obtained. It becomes possible.

  In the present embodiment, the method of performing pressure holding under the above conditions after the last energization stop at the rest time Rt in the pulsation energization pattern has been described, but the present invention describes such a method. The pattern is not limited. For example, after completion of the last energization in the energization time Bt in the pulsation energization pattern, it may be a method of starting the pressure holding without taking a rest time, and in any method, the above-described effects of the present invention can be obtained. It is done.

The welding conditions described above are indispensable conditions in the dissimilar metal joining method of the present invention. In the present invention, it is more preferable to perform a pre-energization in advance before performing pulsation energization. Prior to pulsation energization, pre-energization is performed to generate minute scattering between the joining interface between the steel plate 1 and the aluminum alloy plate 2, thereby allowing foreign matter such as oxide to intervene between the steel plate 1 and the aluminum alloy plate 2. The effect of removing is obtained.
Hereinafter, in the dissimilar-metal joining method of this invention, each condition in the case of performing pre-energization before performing pulsation energization is explained in full detail.

(Pre-energization time: Pt)
In the present invention, when the pre-energization is performed before the pulsation energization, the pre-energization time Pt (ms) is defined in a range that satisfies the following equation (5).
5 ≦ Pt ≦ 20 (5)
However, in the above equation (5), Pt: pre-energization time (ms).

  As shown in the above equation (5), when pre-energization is performed in the present invention, the pre-energization time Pt is set to a range of 5 to 20 (ms). If the pre-energization time Pt is less than 5 (ms), minute scattering is unlikely to occur at the bonding interface, and the above-described cleaning effect cannot be obtained. Moreover, when the pre-energization time Pt exceeds 20 ms, the dent of the joint interface on the aluminum alloy plate 2 side becomes large, and the joint strength (cross tensile strength) decreases.

(Pressurizing force during pre-energization: PF)
In the present invention, when the pre-energization is performed before the pulsation energization, the pressure PF at the time of energization during the above-described pre-energization time Pt is defined within a range that satisfies the following expression (6).
0.6 × EF ≦ PF ≦ 0.8 × EF (6)
However, in the above equation (6), EF represents the pressure (kN) during pulsation energization, and PF: the pressure (kN) during pre-energization.

  As shown in the above equation (6), when pre-energization is performed in the present invention, the pre-energization time Pt is set to the above-described range, and the pressure PF at the time of pre-energization is changed to the pressure EF during pulsation energization. Of 0.6 to 0.8 times, and lower than the pressurizing force EF when welding energization is performed. Thus, prior to the pulsation energization, by performing the pre-energization with a low pressure PF, it is possible to effectively generate minute scattering between the bonding interfaces and to clean the bonding interface.

  If the applied pressure PF during pre-energization is less than the above range, the current concentration when energized becomes too high, and the explosion phenomenon may occur, which may cause defects such as perforations in the steel plate or aluminum alloy plate to be joined. There is. Further, if the pressure PF during pre-energization exceeds the above range, heat generation is insufficient, and it is difficult for fine scattering to occur from the bonding interface, so that it is difficult to remove oxides and the like as scattering.

  In the dissimilar metal joining method of the present invention, before conducting pulsation energization, pre-energization under the above-described conditions can be performed in advance to clean the bonding interface between the steel plate 1 and the aluminum alloy plate 2. As described above, by performing pulsation energization under the above-described conditions in a state where the bonding interface is cleaned, generation of the Fe melted portion 1a on the steel plate 1 side as described above is remarkably suppressed. Thus, the formation of the intermetallic compound layer 3 can be effectively suppressed. Therefore, the dissimilar metal joint 10 having excellent joint strength (cross tensile strength), fatigue strength, and corrosion resistance can be obtained.

Prior to the pulsation energization, the pre-energization current PC (kA) in the case where the above-described pre-energization is performed in advance can be approximately the same as the energization current BC (kA) in the pulsation energization.
In the pattern shown in FIG. 3B, the electrodes 5A and 5B are pressed against the steel plate 1 and the aluminum alloy plate 2 before the pre-energization current PC is supplied to the electrodes 5A and 5B. Although it pressurizes with PF (kN), it is not limited to this. For example, the timing for starting pressurization during pre-energization may be simultaneous with the supply of the pre-energization current PC, and may be determined as appropriate.

[Dissimilar metal joints]
The dissimilar metal joint 10 of the present invention is obtained by joining the steel plate 1 and the aluminum alloy plate 2 by resistance spot welding by the dissimilar metal joining method of the present invention as described above. Further, as illustrated in FIG. 2, the dissimilar metal joint 10 of the present invention has a center corresponding to the central portion 51 of the electrodes 5A and 5B at the time of applying pressure to the joint interface between the steel plate 1 and the aluminum alloy plate 2. The intermetallic compound layer 3 made of Fe—Al-based metal having a thickness t1 at the position 31 of 0.5 μm or less is generated.

“Thickness of intermetallic compound layer: t1”
As shown in FIG. 2, in the dissimilar metal joint 10, an intermetallic compound layer 3 made of Fe—Al-based metal is generated between the Fe melt part 1 a and the Al melt part 2 a at the joint interface. And in this invention, the thickness of this intermetallic compound layer 3 is restrict | limited to 0.5 micrometer or less by thickness t1 in the above-mentioned center position 31. FIG. Thus, regarding the intermetallic compound layer 3 produced by the dissimilar metal joining method using resistance spot welding, excellent joint strength, fatigue strength and corrosion resistance can be obtained by reducing the production as much as possible and making it thin. It is done.
When the thickness of the intermetallic compound layer 3 exceeds 0.5 μm at the thickness t1 at the center position 31, the joint strength, particularly the strength in the peeling direction (cross tensile strength) decreases.

  According to the dissimilar metal joining method of the steel plate 1 and the aluminum alloy plate 2 according to the present invention as described above, the welding conditions when the steel plate and the aluminum alloy plate are spot welded as described above, that is, energization In addition, a method of optimizing the pressurizing condition is adopted. Thereby, while ensuring good workability when joining the steel plate 1 and the aluminum alloy plate 2, a highly reliable joint excellent in the characteristics of the welded portion, that is, joint strength, fatigue strength and corrosion resistance is formed. It becomes possible to make it.

  Moreover, according to the dissimilar metal joint 10 according to the present invention, it is obtained by joining the steel plate 1 and the aluminum alloy plate 2 by the dissimilar metal joining method, and the thickness of the intermetallic compound layer 3 is less than a predetermined value. Since it is suppressed, it is highly reliable with excellent joint strength, fatigue strength, and corrosion resistance.

Therefore, for example, in the automotive field, by applying the present invention to the process of manufacturing parts for automobiles that are lightened by applying a partial aluminum alloy plate, assembling the body, etc., low fuel consumption due to weight reduction of the entire body Benefits such as gasification and carbon dioxide (CO ₂ ) emission reduction can be fully enjoyed, and its social contribution is immeasurable.

  Hereinafter, examples of the dissimilar metal joining method and dissimilar metal joining joint between the steel plate and the aluminum alloy plate according to the present invention will be given and described in more detail, but the present invention is originally limited to the following examples. However, the present invention can be carried out with appropriate modifications within a range that can meet the gist of the preceding and following descriptions, and these are all included in the technical scope of the present invention.

As described above, in the present invention, the pressing force EF (kN) at the time of pulsation energization is not particularly limited, but in this embodiment, two sheets of a mild steel plate and an aluminum alloy plate having a plate thickness of about 1 mm are used. A representative pressurizing force was selected in the range of 1.47 to 4.5 kN used during lap welding. By selecting such a pressing force, even if the setting change of the pressing force in the present invention does not deviate from the setting range of a general robot-mounted spot welder, the example data In addition to being appropriate, the actual process has the advantage of not hindering productivity. In the present embodiment, the selection is made by the following formula {F = α × plate thickness × (TS / 270) ^0.5 } [kN], which is frequently used from the base material strength and the plate thickness.

  In the present invention, the welding current BC (kA) at the time of pulsation energization is not particularly limited, but the welding current BC is usually related to the electrode shape, the applied pressure, the energization time, and the like. Determined. In this example, a dome radius type electrode made of a Cr—Cu alloy and having a tip diameter of 6.0 mm was used as the welding electrode. Further, the applied pressure is the same as the applied pressure EF at the time of energizing the pulsation, and when the energized time is 100 msec and welding is performed once by energization, the tensile strength in the shear direction of the welded joint is 2. The welding current was selected so that it would be 5 kN or more and no large scattering or defects would occur.

[Example 1]
In Example 1, first, a steel plate having a tensile strength of 270 MPa as shown in Table 1 below and an aluminum alloy plate (5000 series) similarly shown in Table 1 below. As well as 6000 series). And based on the cross tension test method (JIS Z3137) of a resistance spot welded joint, the sample piece of the size of 50x150 mm used for a cross tension test piece was cut out from each of these steel plates and aluminum alloy plates.

  Next, using the above sample pieces, based on the cross tension test method (JIS Z3137) for resistance spot welded joints, the test pieces were superposed in a cross shape as shown in FIG. Then, spot welding was performed using an inverter type DC spot welder, and cross-tension test pieces in which each sample piece was joined by a welded joint were produced. At this time, a dome radius type electrode made of a Cr—Cu alloy and having a tip diameter of 6.0 mm was used as a welding electrode for resistance spot welding. Here, the welding energization by pulsation energization and the pressure holding conditions after the completion of the pulsation energization pattern were changed within the ranges shown in Tables 2 to 6 below. In addition, test No. shown in Table 4 below. 81-No. In Example 110 of the present invention, pre-energization was performed in advance under the conditions shown in Table 4 below before performing pulsation energization.

  Next, a cross tension test was performed on the obtained cross tension test piece based on a cross tension test method (JIS Z3137) of a resistance spot welded joint. At this time, by applying a load in the peeling direction, that is, as shown by reference numeral 6 in FIG. 4, the upper test piece is upward and the lower test piece is downward and peels from each other. A cross tensile test was performed and the cross tensile strength (CTS) was measured. Then, with respect to the cross tensile strength (peeling load), 1.0 (kN) or more is “◯” and less than 1.0 (kN) is “ The results are shown in Tables 2 to 6 below.

Moreover, regarding the intermetallic compound layer produced | generated in the joining interface of a steel plate and an aluminum alloy plate, the thickness in the position corresponding to the electrode center part at the time of pressurization energization was measured. In this measurement, first, a spot weld sample for cross-sectional observation was prepared by performing resistance spot welding under the same conditions using the same sample piece as that of the cross tension test described above. Next, the vicinity of the center of the welded portion of this sample was cut, embedded in a resin and subjected to cross-sectional polishing, and then the thickness was measured by observing the cross-section with a scanning electron microscope. In the intermetallic compound layer, the thickness corresponding to the electrode center portion is 0.3 μm or less, “」 ”, more than 0.3 μm to 0.5 μm or less“ ◯ ”, and more than 0.5 μm“ × ” The results are shown in Tables 2 to 6 below.
Simultaneously with the measurement of the thickness of the intermetallic compound layer, the presence or absence of the formation of an Fe melt at the bonding interface between the steel plate and the aluminum alloy plate was confirmed by cross-sectional observation, and the results are shown in Tables 2 to 6 below. .

  As a comprehensive evaluation, the thickness of the intermetallic compound layer at the corresponding position in the center of the electrode is 0.5 μm or less (◎ or ○), and the cross tensile strength (peeling excess) is 1.0 kN or more (◯). The case where the thickness of the intermetallic compound layer is more than 0.5 μm (x) or the cross tensile strength is less than 1.0 kN is evaluated as “x”, and the results are shown in Table 2 below. -6.

Test Nos. Shown in Tables 2-4. 1-No. 110 is an example of the present invention. 111-No. 210 is a comparative example.
As shown in the results of Tables 2 to 4, test No. 1 was conducted in which welding energization was performed with the pulsation energization pattern defined in the present invention, and then pressure holding was performed under the conditions defined in the present invention. 1-No. In 110 of the present invention examples, the formation of an Fe melt zone is not observed between the steel plate and the aluminum alloy plate, and the intermetallic compound layer generated between the joining interfaces has a thickness of 0.5 μm or less. It was suppressed (evaluation of ◎ or ○). Moreover, all the cross tensile strengths were also 1.0 kN or more, and it has confirmed that joining strength was high. Based on the above results, test No. 1-No. In all 110 inventive examples, the overall evaluation was “◯”.

  On the other hand, as shown in the results of Tables 5 and 6, a test in which welding energization is performed with a pulsation energization pattern outside the range specified in the present invention, or the subsequent pressurizing and holding conditions are outside the specified range of the present invention. No. 111-No. In the comparative example of 210, the production | generation of the Fe fusion | melting part was seen between the steel plate and the aluminum alloy plate. Along with this, there was a large variation in the thickness of the intermetallic compound layer produced between the bonding interfaces, and in most of the comparative examples, the thickness of the intermetallic compound layer exceeded 0.5 μm. Most of these comparative examples have a cross tensile strength of less than 1.0 kN. As a result, at least one of the thickness of the intermetallic compound layer or the cross tensile strength is evaluated as “x”. The joint strength was inferior. As a result, test no. 111-No. In all of the 210 comparative examples, the overall evaluation was “x”.

[Example 2]
In Example 2, similarly to Example 1, first, a steel plate having a tensile strength of 270 MPa as shown in Table 1 and an aluminum alloy plate (Table 1) having a thickness as shown in Table 1 ( 5000 series and 6000 series) were prepared. And based on the cross tension test method (JIS Z3137) of a resistance spot welded joint, the sample piece of the size of 50x150 mm used for a cross tension test piece was cut out from each of these steel plates and aluminum alloy plates.

  Next, based on the cross tension test method for resistance spot welded joints defined in JIS Z3137, in which the above sample pieces are used as a stack of two sample pieces, and as shown in FIG. After two sample pieces were stacked, one sample piece of the aluminum alloy plate was used, and spot welding was performed with a total of three stacked pieces. At this time, in the same manner as in Example 1, the test pieces were overlapped in a cross shape as shown in FIG. 5 and spot welding was performed using an inverter type DC spot welder under the conditions shown in Tables 7 and 8 below. A cross tensile test piece in which each sample piece was joined by a welded joint was prepared.

  As a welding electrode for resistance spot welding, a dome radius type electrode made of a Cr—Cu alloy and having a tip diameter of 6.0 mm was used as in Example 1. Here, the welding energization by pulsation energization and the pressure holding conditions after the completion of the pulsation energization pattern were also changed within the ranges shown in Tables 7 and 8 below as in Example 1. In addition, test No. shown in Table 7 below. 325-No. In Example 334 of the present invention, pre-energization was performed in advance under the conditions shown in Table 7 below before performing pulsation energization.

  Next, a cross tension test was performed on the obtained cross tension test piece based on a cross tension test method (JIS Z3137) of a resistance spot welded joint. At this time, as shown by the reference numeral 6 in FIG. 5, the upper test piece, that is, the test piece on the steel sheet side which is two-layered is directed upward, and the lower test piece (aluminum alloy). A cross tension test was performed by applying a load in a direction in which the sheet was peeled downward and peeled from each other, and a cross tensile strength (CTS) was measured. Then, with respect to the cross tensile strength (peeling load), 1.0 (kN) or more is “◯” and less than 1.0 (kN) is “ The results are shown in Tables 7 and 8 below.

Moreover, regarding the intermetallic compound layer produced | generated in the joining interface of a steel plate and an aluminum alloy plate, the thickness in the position corresponding to the electrode center part at the time of pressurization energization was measured. In this measurement, the same method as in Example 1 was used, and among the two pieces of steel plate sample pieces stacked, the sample piece on the side in contact with the sample piece of the aluminum alloy plate, and the sample piece of the aluminum alloy plate The thickness of the intermetallic compound layer formed at the bonding interface with the substrate was measured. In the intermetallic compound layer, the thickness corresponding to the electrode center portion is 0.3 μm or less, “」 ”, more than 0.3 μm to 0.5 μm or less“ ◯ ”, and more than 0.5 μm“ × ” The results are shown in Tables 7 and 8 below.
In addition, as in Example 1, the presence or absence of the formation of an Fe melt at the joining interface between the steel plate and the aluminum alloy plate was confirmed by cross-sectional observation, and the results are shown in Tables 7 and 8 below.

  As a comprehensive evaluation, the thickness of the intermetallic compound layer at the corresponding position in the center of the electrode is 0.5 μm or less (◎ or ○), and the cross tensile strength (peeling excess) is 1.0 kN or more (◯). The case where the thickness of the intermetallic compound layer is more than 0.5 μm (x) or the cross tensile strength is less than 1.0 kN is evaluated as “x”, and the results are shown in Table 7 below. , 8.

Test No. shown in Table 7 301-No. 334 is an example of the present invention, and condition No. 335-No. 364 is a comparative example.
As shown in the results of Table 7, the pulsation energization pattern defined in the present invention is made by superposing three sample pieces of steel sheets and one sample piece of aluminum alloy plate, and making a total of three pieces. The test No. 1 was conducted with welding energization and then held under pressure under the conditions specified in the present invention. 301-No. In all of the examples of the present invention of 334, the formation of an Fe melt zone was not observed between the steel plate and the aluminum alloy plate, and the intermetallic compound layer generated between the joining interfaces had a thickness of 0.5 μm or less. It was suppressed (evaluation of ◎ or ○). Moreover, all the cross tensile strengths were also 1.0 kN or more, and it has confirmed that joining strength was high. Based on the above results, test No. 301-No. In all of the 334 invention examples, the overall evaluation was “◯”.

  On the other hand, as shown in the results of Table 8, after the three sheets are stacked as described above, welding energization is performed with a pulsation energization pattern outside the range defined by the present invention, or the subsequent pressurization holding condition Is outside the specified range of the present invention. 335-No. In the comparative example of 364, a part of the Fe melt part was observed between the steel plate and the aluminum alloy plate. Along with this, there was a large variation in the thickness of the intermetallic compound layer produced between the bonding interfaces, and in most of the comparative examples, the thickness of the intermetallic compound layer exceeded 0.5 μm. Most of these comparative examples have a cross tensile strength of less than 1.0 kN. As a result, at least one of the thickness of the intermetallic compound layer or the cross tensile strength is evaluated as “x”. The joint strength was inferior. As a result, test no. 335-No. In all of the 364 comparative examples, the overall evaluation was “x”.

  In Examples 1 and 2, the results were the same as above when the experiment was performed with the plate thickness changed or when the experiment was performed with the plating type, the basis weight, etc. changed. It was. That is, regardless of the thickness of the plate, the presence or absence of plating, etc., by adopting the dissimilar metal bonding method of the present invention, it is possible to suppress the formation of an intermetallic compound layer between the bonding interfaces, the joint strength, fatigue strength characteristics and It was confirmed that the effect of improving the corrosion resistance was obtained.

According to the present invention, by applying the present invention to the manufacturing process of automobile parts and the assembly of a vehicle body that have been reduced in weight by applying a partial aluminum alloy plate, the joint can be secured while ensuring good workability. The characteristics can be improved. Therefore, in the automobile field, it is possible to fully enjoy merits such as fuel efficiency reduction by reducing the weight of the entire vehicle body and reduction of carbon dioxide (CO ₂ ) emissions, and the social contribution is immeasurable.

1 (1A, 1B) ... steel plate,
2 ... Aluminum alloy plate,
3 ... intermetallic compound layer (intermetallic compound),
31 ... Center position (position corresponding to the electrode center),
5 (5A, 5B) ... electrode,
51 ... Center part (electrode center part),
10 ... Joint metal joint,
t1 ... the thickness of the intermetallic compound layer at the position corresponding to the center of the electrode,

Claims (3)

A steel plate and an aluminum alloy in which resistance steel is welded while pressing with electrodes arranged above and below the steel plate and the aluminum alloy plate in a state where one or more steel plates and one or more aluminum plates are overlapped. A dissimilar metal joining method with a plate,
When performing the resistance spot welding, the energization time Bt (ms) and the rest time Rt (ms) are set to satisfy the following formulas (1) and (2), and the pulsation energization with the applied pressure EF (kN) is 2 to 2. Immediately after the last energization stop at the rest time Rt (ms) is completed, the applied pressure is increased to the applied pressure FF (kN) after completion of energization satisfying the following expression (3). Then, after pressurizing and holding for a holding time Ht (ms) that satisfies the following formula (4), the applied pressure is unloaded, and the dissimilar metal joining method of the steel plate and the aluminum alloy plate is characterized by:
2 ≦ Bt ≦ 10 (1)
1 ≦ Rt ≦ 5 (2)
1.2 x EF ≤ FF ≤ 2.0 x EF (3)
50 ≦ Ht ≦ 300 (4)
{However, in the above formulas (1) to (4), Bt: energization time (ms), Rt: rest time (ms), EF: applied pressure during pulsation energization (kN), FF: applied after completion of energization Pressure (kN), Ht: holding time (ms). } Before conducting the pulsation energization, by performing pre-energization in advance under the conditions of the pre-energization time Pt (ms) and pre-energization pressure PF (kN) that satisfy the following (5) and (6), The dissimilar metal joining method of the steel plate and aluminum alloy plate of Claim 1 which produces | generates a fine scattering between the joining interfaces of a steel plate and an aluminum alloy plate, and performs the said pulsation electricity supply after that.
5 ≦ Pt ≦ 20 (5)
0.6 × EF ≦ PF ≦ 0.8 × EF (6)
{However, in the above formulas (5) and (6), Pt: pre-energization time (ms), EF: pressure applied during pulsation energization (kN), PF: pressure applied during pre-energization (kN). } A dissimilar metal joint obtained by joining a steel plate and an aluminum alloy plate by the dissimilar metal joining method according to claim 1 or 2,
An Fe-Al intermetallic compound layer having a thickness of 0.5 μm or less at a position corresponding to an electrode center portion at the time of applying pressure is generated at a bonding interface between the steel plate and the aluminum alloy plate. Dissimilar metal joint between steel plate and aluminum alloy plate.

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