JP7165315B2 - Friction stir welding method for aluminum alloy plate and steel plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for joining an aluminum alloy plate and a steel plate, and more specifically to a friction stir welding method for overlapping and joining an aluminum alloy plate and a steel plate.

In recent years, in the field of transportation equipment such as automobiles, where weight reduction is required, structures and parts (hereinafter referred to as "members") have been developed by combining aluminum alloys and steel and making full use of the characteristics of each material. It is In a member that combines aluminum alloy and steel, it is necessary to join dissimilar metal materials. There is a problem that a brittle intermetallic compound composed of the main elements that do not exist is often formed, and sufficient joint strength cannot be obtained.

Therefore, as a method for strongly joining an aluminum alloy and steel, a solid phase joining method such as a diffusion joining method, which does not form a molten layer, has been developed. However, the diffusion bonding method requires a preparatory step for keeping the surface of the mating surface of the materials clean, which leads to an increase in cost, and thus has the problem of being difficult to implement industrially.

As another diffusion bonding method, there is a friction bonding method. A technique of joining metal materials by agitating the joined parts to cause plastic flow is disclosed. However, since this technique requires rotating the metal materials to be joined, there are limitations on the shape and size of the metal materials to which this method is applied.

By the way, in recent years, friction stir welding has been developed as a new solid phase welding method, and has been widely used mainly for butt welding of metal materials of the same kind or similar to each other. For example, in Patent Document 2, a rotating tool made of a material harder than the metal plate is inserted into an unbonded portion of the metal plate, and the rotating tool is moved in the joining direction while rotating to move between the rotating tool and the metal plate. A method has been proposed for continuously joining metal sheets in the longitudinal direction by generating heat and plastic flow in the joint. In this method, the metal plates are joined by rotating and moving the rotating tool while the metal plates are fixed. Therefore, there is an advantage that even an infinitely long member can be continuously solid-phase-bonded along the bonding direction. In addition, since this is a solid-state joining utilizing the plastic flow of metal due to frictional heat between the rotating tool and the metal plate, the joint can be joined without melting, and no filler material is required. Furthermore, since the temperature at which the joint is heated is low and it does not melt, there are many advantages such as less deformation of the joint and fewer defects.

Friction stir welding has been widely used in fields such as aircraft, ships, railway vehicles and automobiles as a method for joining low melting point metals such as aluminum alloys and magnesium alloys. The reason for this is that it is difficult to obtain satisfactory weld characteristics for these low-melting-point metals using the conventional arc welding method. This is because not only can it be obtained, but also productivity can be improved. Furthermore, since the joining interface is agitated by a rotating tool, clean surfaces can be created and the clean surfaces can be brought into contact with each other.

As mentioned earlier, this friction stir welding method is an extremely excellent method for joining metal materials of the same kind or similar to each other. In this case, the two metals are mixed at the joint interface, the melting point is lowered, a molten phase is generated, a coarse solidification structure is generated, and brittle intermetallic compounds are generated during solidification.

As a means of solving this problem, in Patent Document 3, an aluminum alloy plate and a steel plate are superimposed via a Zn-5Al layer or a Zn hot-dip layer, and the surface of the joint is pressed with a rotary tool to rub the aluminum alloy. A diffusion layer consisting of Al, Al-Zn, Zn-Al, Fe-Zn and Fe is formed by stirring and plastically flowing to cause mutual diffusion of the Zn-5Al layer or Zn hot-dip plated layer and the aluminum alloy. Then, a method of joining an aluminum alloy plate and a steel plate is disclosed by forming an Al--Zn--Fe alloy layer through plastic flow, without forming a brittle intermetallic compound.

Further, Patent Document 4 describes a friction stir welding method in which dissimilar metals such as an aluminum alloy and steel are superimposed on each other. Using a melting point plated steel sheet, a joining pin that rotates during friction stir welding is pressed from the surface of the aluminum alloy and inserted to the vicinity of the joining interface where the aluminum alloy and the low melting point plated steel sheet are joined, and is formed on the aluminum alloy side. A friction stir welding method for obtaining a high-strength welded joint by solid-phase joining an aluminum alloy and a low-melting-point plated steel plate by diffusing the coating layer by plastic flow in the plastic flow region and exposing a new surface on the surface of the low-melting-point plated steel plate. and friction stir welding members are disclosed.

On the other hand, as a rotating tool, a double-acting friction stir welding method using a welding tool including a pin member and a substantially cylindrical shoulder member having a hollow into which the pin member is inserted is known. Since the joining tool consisting of the pin member and the shoulder member can independently control the rotation and advance/retreat motions, by adjusting the timing of the advance/retreat motion of the pin member and the advance/retreat motion of the shoulder member, the pin member can be press-fitted. It makes it possible to backfill the formed concave portion.

As the double-acting friction stir welding method, for example, in Patent Document 5, a press-fitting pin harder than an aluminum alloy plate is press-fitted into a plurality of superimposed aluminum alloy plates with a friction welding tool with a triple structure and stirred. After that, the aluminum alloy spilled out from the press-fitting hole that was generated was confined between the press-fitting pin and the outer ring. A method for point joining an aluminum alloy is disclosed in which the surface of the alloy plate is pressed and the aluminum alloy overflow portion is flowed and embedded in the press-fitting hole.

Furthermore, as another method for joining dissimilar metal members by a double-acting friction stir welding method, for example, in Patent Document 6, from the side of an aluminum plate superimposed on a steel plate, a probe of a rotary tool reaches directly above the steel plate. When inserting the aluminum plate and the steel plate by friction stir welding, a double-acting rotary tool in which the probe and the shoulder member can be moved separately in the axial direction is used as the rotary tool, and the probe is inserted into the aluminum plate. After performing friction stir welding, the probe is pulled out from the friction stir part formed in the aluminum plate, and the probe hole created by such pulling out is filled by material flow from other parts of the friction stir part. A method for joining metal members is disclosed.

JP-A-62-183979 Japanese Patent Publication No. 07-505090 JP-A-2002-066759 JP 2007-253172 A Japanese Patent Application Laid-Open No. 2001-259863 JP 2010-260109 A

By the way, in Patent Documents 3 and 4, there is a method for solving the generation of brittle intermetallic compounds at the joint interface, which is a problem when dissimilar metals such as an aluminum alloy plate and a steel plate are joined by friction stir welding. Although disclosed, Patent Documents 5 and 6 relating to the double-acting friction stir welding method do not consider the above problems at all. For example, Patent Document 5 discloses a technique related to a member in which aluminum alloy plates are superimposed, and Patent Document 6 discloses a technique related to a joining method of a member in which an aluminum alloy plate and a steel plate are superimposed. It only discloses that the joint characteristics are improved by backfilling the recess formed by press-fitting, and does not disclose any solution to the problem of formation of fragile intermetallic compounds at the joint interface.

The present invention was developed in view of the above-mentioned problems of the conventional double-acting friction stir welding method. The object of the present invention is to propose a double-acting friction stir welding method capable of suppressing the formation of an intermetallic compound at the joint interface where the two come into contact with each other and efficiently forming a joint having sufficient joint strength.

In order to solve the above problems, the inventors made extensive studies on bonding conditions from the viewpoint of suppressing the temperature rise at the bonding interface, and as a result, obtained the following new knowledge.
a) A rotating tool is inserted into an object to be joined in which an aluminum alloy plate and a steel plate are superimposed from the surface of the aluminum alloy plate while being rotated, and the rotating tool is moved in the joining direction to disperse the joining material by friction stirring. When aluminum alloy plate and steel plate are friction stir welded by plastic flow, inserting the tip of the probe from the mating surface of the aluminum alloy plate and steel plate to the steel plate side causes the new surfaces of both materials to come into contact with each other. It is possible to form a bonding interface that is compatible with each other, and to ensure a metallurgical bonding state.
b) In the process of forming the joint interface and achieving a metallurgical joint state, iron and aluminum, which are the main components of both materials, diffuse and become distributed in both materials across the joint interface. If a brittle intermetallic compound composed of iron and aluminum is generated within this diffusion range, it causes a decrease in bonding strength.
c) In order to suppress the formation of the intermetallic compound, it is necessary to suppress the diffusion of iron and aluminum distributed in both materials across the bonding interface. It is necessary to control the peak temperature (maximum temperature reached) immediately after heating and the subsequent cooling rate within an appropriate range.
d) In friction stir welding, the joint is heated by frictional heat and plastic heat generated when the material to be welded is friction-stirred by a rotating tool. The heat generated by the probe and the shoulder can be independently controlled by using a double-acting rotary tool in which the shoulder and the shoulder are separately constructed and each can independently control the rotation speed. Therefore, by applying the above-described double-acting rotary tool to friction stir welding of an aluminum alloy plate and a steel plate, the peak temperature and cooling rate of the weld interface can be controlled within appropriate ranges.
e) Specifically, when the rotation speed of the shoulder of the rotary tool is set higher than the rotation speed of the probe, frictional stirring of the mating surface between the aluminum alloy plate and the steel plate by the tip of the probe is minimized, and the above By supplementing the insufficient heat input due to the rotation of the probe with friction stirring due to the shoulder, the peak temperature at the joint interface can be suppressed. Conversely, when the rotational speed of the probe of the rotating tool is set higher than the rotational speed of the shoulder, the tip of the probe sufficiently friction stirs the mating surfaces of the aluminum alloy plate and the steel plate, while minimizing the friction stir caused by the shoulder. Since it can be held, the cooling rate of the bonding interface can be increased.
The present invention has been developed based on the above new findings.

Based on the above knowledge, the present invention has a probe and a shoulder in which an object to be welded, which is made by laying an aluminum alloy plate and a steel plate on top of each other and fixing them by abutting a backing jig on the steel plate side, is coaxially arranged at the tip as a rotating tool. is configured separately, and a double-acting rotary tool whose rotational speed can be set separately is used, and the probe of the double-acting rotary tool is rotated and inserted from the aluminum alloy plate side of the object to be joined to the steel plate side. In addition, while the shoulder of the double-acting rotary tool is in contact with the surface of the aluminum alloy plate while being rotated, the rotary tool is moved in the joining direction to frictionally stir and plastically flow the object to be joined. A friction stir welding method is proposed in which the rotation speed SS (rotations/minute) of the shoulder of the rotary tool is different from the rotation speed PS (rotations/minute) of the probe.

The friction stir welding method of the present invention is characterized in that the rotational speed SS (rotations/minute) of the shoulder is higher than the rotational speed PS (rotations/minute) of the probe.

In the friction stir welding method of the present invention, the welding speed JS is set to 50 to 200 mm/min, and the shoulder rotation speed SS (times/minute) and the probe rotation speed PS (times/minute) are set to the following (1 ) and (2).
Note 1000≦SS≦1700 (1)
300≦PS≦500 (2)

Further, the friction stir welding method of the present invention is characterized in that the rotation speed PS (rotations/minute) of the probe is set higher than the rotation speed SS (rotations/minute) of the shoulder.

In the friction stir welding method of the present invention, the welding speed JS is set to 50 to 200 mm/min, and the shoulder rotation speed SS (times/minute) and the probe rotation speed PS (times/minute) are set to the following (3 ) and (4).
Note 300≦SS≦500 (3)
1000≦PS≦1700 (4)

Further, the friction stir welding method of the present invention is characterized in that the shoulder diameter SD (mm) and the probe diameter PD (mm) are set to values that satisfy the following equations (5) and/or (6) respectively. and
Note 12≤SD≤18 (5)
4≦PD≦8 (6)

In addition, in the friction stir welding method of the present invention, the probe tip of the rotating tool that is inserted from the surface of the aluminum alloy plate while rotating is inserted into the steel plate side from the mating surface of the aluminum alloy plate and the steel plate. It is characterized by being more than 0 mm and 0.5 mm or less.

Further, in the friction stir welding method of the present invention, the rotating shaft of the rotating tool that is rotated and inserted from the surface of the aluminum alloy plate is set at an angle exceeding 0° and 5° on the side opposite to the welding direction with respect to the perpendicular line to the surface of the aluminum alloy plate. It is characterized by tilting at a tilt angle α of less than °.

According to the present invention, in the friction stir welding method in which an aluminum alloy plate and a steel plate are superimposed and joined by pressing a rotating tool from the aluminum alloy plate side, a probe and a shoulder are coaxially arranged at the tip as the rotating tool. By using a double-acting rotating tool that is configured separately and whose rotational speed can be set separately, the rotational speed of the shoulder and the rotational speed of the probe are set to different and different values, thereby measuring the temperature history of the joint interface. Since it is controlled, it is possible to suppress the generation of intermetallic compounds at the joint interface and stably obtain a high-strength joint.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the double-acting friction stir welding method of this invention used for joining an aluminum alloy plate and a steel plate. FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, and is a diagram for explaining a region where a jointed body in which an aluminum alloy plate and a steel plate are superimposed is friction-stirred by a double-acting rotating tool. It is a figure explaining the shape of the double-acting rotary tool used in the Example, and a dimension. It is a figure explaining the tensile test piece which measures a shear strength.

The present invention relates to a technique for joining an object to be joined in which an aluminum alloy plate 1 and a steel plate 2 are superimposed on each other by friction stir welding, and as shown in FIG. As shown in FIG. The rotating tool 3 is moved in the joining direction to frictionally agitate the object to be joined and cause plastic flow to join the two materials. By inserting to the steel plate side from 6, a joint interface 7 is formed in which the new surfaces of the aluminum alloy plate 1 and the steel plate 2 are in contact with each other on the mating surface 6 of the aluminum alloy plate 1 and the steel plate 2, and further, the probe 4 of the rotary tool 3 and the shoulder 5 By setting the rotation speed separately and separately controlling the friction heat and plastic deformation heat generated by the rotation of the probe and shoulder, the peak temperature (maximum temperature reached) of the joint interface 7 and the subsequent cooling rate are controlled, It is a technique for obtaining a joint 8 having excellent joint strength between an aluminum alloy plate and a steel plate by suppressing the diffusion of iron and aluminum elements across the joint interface 7 and suppressing the formation of brittle intermetallic compounds. be. In addition, 9 shown in the figure is a jig backing the steel plate side of the object to be joined, in which the aluminum alloy plate 1 and the steel plate 2 are superimposed, and 10 is joined by the probe 4 and the shoulder 5 of the rotary tool 3. It shows the region where the material flows plastically.

First, the plate thickness of the aluminum alloy plate 1 and the steel plate 2 constituting the object (member) to be joined to which the friction stir welding method of the present invention is applied is determined from the viewpoint of maximizing the effect of the present invention. is preferably in the range of 1 to 3 mm, and the steel plate is preferably in the range of 1 to 3 mm. However, the plate thickness may be outside the above range.

In addition, the double-acting rotary tool 3, which is used in the friction stir welding method of the present invention and has a probe 4 coaxially arranged at the tip and a shoulder 5, is configured separately from the mating surfaces of the aluminum alloy plate and the steel plate. The tip of the probe that is inserted to the steel plate side and directly contacts the steel plate is made of a material that is at least harder than the steel plate, and the probe and shoulder other than the tip that contacts the aluminum alloy plate are at least harder than the aluminum alloy plate. It must be made of material.

The rotating directions of the probe 4 and the shoulder 5 constituting the double-acting rotating tool 3 used in the present invention may be the same or opposite.

Further, the present invention is characterized in that the rotation speed PS of the probe 4 and the rotation speed SS of the shoulder, which constitute the double-acting rotary tool 3 used for joining an aluminum alloy plate and a steel plate, are separately set to different speeds. With this, the heat generated by the rotation of the probe and the heat generated by the rotation of the shoulder are controlled separately, and the maximum temperature and cooling rate at the joint interface between the aluminum alloy plate and the steel plate are controlled appropriately, and the fragile metal at the joint interface is controlled. It is possible to suppress the generation of intermetallic compounds.

Furthermore, in the double-acting friction stir welding method for superimposing and joining an aluminum alloy plate and a steel plate according to the present invention, as described below, the joining conditions are limited to an appropriate range to prevent the formation of intermetallic compounds at the joining interface. It has been found that suppression is more effective in improving the bonding strength.

First, in the present invention, the joining speed JS (mm/min), that is, the speed at which the double-acting rotary tool 3 inserted while rotating from the surface of the aluminum alloy plate 1 is moved in the joining direction is 50 mm/min or more. The range should be 200 mm/min or less. When the welding speed is changed while the rotational speed of the shoulder of the rotating tool and the probe is kept constant, the amount of heat generated per unit welding length due to the frictional stirring of the rotating tool changes. , the amount of heat generated per unit length due to friction stirring on the surface of the aluminum alloy plate due to the shoulder becomes excessive, and an excessive amount of heat is input around the joint interface between the aluminum alloy plate and steel plate, resulting in an increase in the peak temperature of the joint interface. Alternatively, it promotes the reduction of the cooling rate and promotes the formation of brittle intermetallic compounds. On the other hand, if the welding speed exceeds 200 mm/min, the amount of heat generated per unit length due to frictional stirring of the shoulder and probe becomes insufficient, and sufficient plastic flow of the material cannot be obtained, resulting in defects in the joint. Otherwise, it becomes impossible to form a joint interface where the aluminum alloy plate and the steel plate are metallurgically joined to each other. A preferred joining speed JS is in the range of 75 to 150 mm/min.

Next, in order to effectively enjoy the effects of the present invention, it is necessary to differentiate the rotational speed SS of the shoulder 5 from the rotational speed PS of the probe 4 at the welding speed JS within the group. , the rotation speed SS of the shoulder 5 may be higher than the rotation speed PS of the probe 4, or conversely, the rotation speed PS of the probe 4 may be higher than the rotation speed SS of the shoulder 5, each with a different mechanism. The effects of the invention can be obtained.

First, when the shoulder rotation speed SS is higher than the probe rotation speed PS, the shoulder rotation speed SS and the probe rotation speed PS are controlled within a range that satisfies the following equations (1) and (2), respectively. It is important to.
Note 1000≦SS≦1700 (1)
300≦PS≦500 (2)

By making the rotation speed SS of the shoulder higher than the rotation speed PS of the probe, the frictional stirring of the mating surfaces of the aluminum alloy plate and the steel plate by the tip of the probe can be minimized, and the insufficient amount of heat can be supplemented by the frictional stirring caused by the shoulder. can. As a result, an excessive rise in the peak temperature of the joint interface can be suppressed, the diffusion of iron and aluminum elements across the joint interface can be suppressed, and the formation of brittle intermetallic compounds can be suppressed. and the strength of the joints of steel plates can be improved.

However, when the rotation speed PS of the probe is limited to 300 to 500 times/minute, if the rotation speed SS of the shoulder is less than 1000 times/minute, heat generation due to friction stirring of the surface of the aluminum alloy plate by the shoulder becomes insufficient, and the aluminum alloy It becomes difficult to form a joint interface in a state of being metallurgically joined to the mating surfaces of the plate and steel plate. On the other hand, if it exceeds 1700 times/min, the amount of heat generated by friction stirring on the surface of the aluminum alloy plate due to the shoulder becomes excessive, and an excessive amount of heat is input around the joint interface between the aluminum alloy plate and the steel plate, and the joint interface is heated. It raises the peak temperature and lowers the cooling rate, and promotes the formation of brittle intermetallic compounds.

In addition, when the rotation speed SS of the shoulder is limited to 1000 to 1700 times/minute, if the rotation speed PS of the probe is less than 300 times/minute, frictional stirring of the material by the aluminum alloy plate around the probe becomes insufficient, defects are more likely to occur. On the other hand, if the speed exceeds 500 times/min, the tip of the probe frictionally agitates the steel plate side of the mating surface excessively, causing a rise in the temperature of the joint interface and promoting the formation of brittle intermetallic compounds.

When the shoulder rotation speed SS is higher than the probe rotation speed PS, more preferable shoulder rotation speed SS and probe rotation speed PS are SS: 1000 to 1350 times/minute and PS: 300 to 400 times/minute. is in the range.

On the other hand, when the rotation speed PS of the probe is higher than the rotation speed SS of the shoulder, the rotation speed SS of the shoulder and the rotation speed PS of the probe must be within the ranges satisfying the following equations (3) and (4), respectively. Control is important.
Note 300≦SS≦500 (3)
1000≦PS≦1700 (4)

By making the rotation speed PS of the probe higher than the rotation speed SS of the shoulder, it is possible to sufficiently frictionally stir the mating surfaces of the aluminum alloy plate and the steel plate by the tip of the probe while minimizing the frictional stirring caused by the shoulder. By increasing the cooling rate of the joint interface, suppressing the diffusion of iron and aluminum across the joint interface and suppressing the formation of brittle intermetallic compounds, the strength of the lap joint between the aluminum alloy plate and the steel plate is improved. be able to.

However, when the rotation speed PS of the probe is limited to 1000 to 1700 times/minute, if the rotation speed SS of the shoulder is less than 300 times/minute, heat generation due to friction stirring of the surface of the aluminum alloy plate by the shoulder becomes insufficient, and the aluminum alloy It becomes impossible to form a joint interface in a state of being metallurgically joined to the mating surfaces of the plate and steel plate. On the other hand, if it exceeds 500 times/minute, heat generation due to friction stirring on the surface of the aluminum alloy plate due to the shoulder becomes excessive, and an excessive amount of heat is input around the joint interface between the aluminum alloy plate and the steel plate, resulting in excessive heat at the joint interface. It raises the temperature, slows down the cooling rate, and promotes the formation of brittle intermetallic compounds.

In addition, when the rotation speed SS of the shoulder is limited to 300 to 500 times/minute, if the rotation speed PS of the probe is less than 1000 times/minute, the friction stirring of the aluminum alloy plate around the probe becomes insufficient, resulting in defects in the joint. becomes more likely to occur. On the other hand, if it exceeds 1700 times/min, the steel plate side of the mating surface is excessively friction-stirred by the tip of the probe, which causes an excessive temperature rise at the joint interface and promotes the formation of brittle intermetallic compounds. .

When the probe rotation speed PS is higher than the shoulder rotation speed SS, more preferable shoulder rotation speed SS and probe rotation speed PS are SS: 300 to 400 times/minute and PS: 1350 to 1700 times/minute. is in the range of

Further, in order to enjoy the effects of the present invention more, the diameter SD (mm) of the shoulder 5 of the double-acting rotary tool 3 and the diameter PD (mm) of the probe 4 should be the following formula (5) and/or ( 6) It is preferable that the formula is satisfied.
Note 12≤SD≤18 (5)
4≦PD≦8 (6)

The shoulder of the double-acting rotary tool is brought into contact with the surface of the aluminum alloy plate while being rotated to frictionally stir the object to be joined, thereby generating frictional heat and plastic heat to heat the joint. Then, by setting the shoulder diameter SD to an appropriate range, specifically preferably in the range of 12 to 18 mm, the joint interface formed on the mating surfaces of the aluminum alloy plate and the steel plate is metallurgically joined. A necessary and sufficient amount of heat can be supplied, and the temperature distribution in the thickness direction from the surface of the aluminum alloy plate can be made uniform, thereby suppressing the occurrence of defects in the joint. If the shoulder diameter SD is less than 12 mm, uniform plastic flow cannot be obtained in the thickness direction. On the other hand, if it exceeds 18 mm, the area where plastic flow occurs is unnecessarily widened, and an excessive load is applied to the device, which is not preferable. A more preferred shoulder diameter SD is in the range of 14-16 mm.

In addition, the probe of the double-acting rotary tool is used when lap jointing aluminum alloy plate and steel plate by inserting the tip of the probe to the steel plate side from the mating surface of the aluminum alloy plate and steel plate. It is possible to form a bonding interface in which the new surfaces of the materials are in contact with each other, thereby ensuring a metallurgical bonding state. Then, by setting the diameter PD of the probe within an appropriate range, specifically within a range of 4 to 8 mm, the area of the bonding interface where the metallurgical bonding state is ensured between the mating surfaces of both materials is sufficiently large. can be secured and the bonding strength can be increased. However, if the diameter PD of the probe is less than 4 mm, it is not possible to secure the bonding interface area for obtaining the necessary and sufficient bonding strength. On the other hand, if it exceeds 8 mm, the distance that the material flows around the probe during joining becomes too long, it becomes difficult to maintain the material in a highly plastic state, and defects are likely to occur in the joint. A more preferred probe diameter PD is in the range of 5-7 mm.

Further, in the present invention, the insertion amount P (mm) of the tip of the probe 3 inserted from the surface of the aluminum alloy plate 1 while being rotated from the mating surface of the aluminum alloy plate and the steel plate to the steel plate side is more than 0 mm and 0.5 mm. It is preferable to:

When joining an aluminum alloy plate and steel plate, inserting the tip of the probe to the steel plate side of the mating surfaces of the aluminum alloy plate and steel plate forms a joint interface where the new surfaces of the two materials come into contact with each other. It is possible to secure a metallurgical bonding state. However, when the insertion amount P is 0 mm or less, the tip of the probe does not reach the mating surfaces of the aluminum alloy plate and the steel plate, and the tip of the probe does not agitate the steel plate, so no new surface is formed. On the other hand, if it exceeds 0.5 mm, the tip of the probe frictionally stirs the steel plate excessively, causing an excessive temperature rise and promoting the formation of brittle intermetallic compounds. A more preferable insertion amount P is in the range of 0.1 to 0.3 mm.

Further, in the friction stir welding method of the present invention, the rotation axis of the rotating tool 3 inserted while rotating from the surface of the aluminum alloy plate is set to 0° on the side opposite to the welding direction with respect to the perpendicular to the surface of the aluminum alloy plate 1. It is preferable to incline at an inclination angle α of more than 5° or less.

By tilting the rotation axis of the rotary tool within the range of the inclination angle α, the load received by the rotary tool is divided into compressive stress in the direction of the rotation axis and bending stress in the direction perpendicular to the rotation axis. Since the force in the bending direction received can be reduced, damage to the rotary tool can be prevented. The above effect can be obtained by setting the inclination angle α to exceed 0°. Contact with the surface is biased, and it becomes impossible to form a homogeneous new surface. A more preferable angle of inclination α is in the range of 2 to 4°.

In the above description of the present invention, the tip of the probe of a double-acting rotary tool in which the rotation speeds of the probe and the shoulder are set separately and at different speeds is inserted while being rotated from the surface of the aluminum alloy plate. Although the method of friction stir welding by moving the tool in the welding direction has been described, the present invention can also be applied to lap point welding of both materials without moving the rotating tool in the welding direction. Specifically, the tip of the probe is inserted to the steel plate side of the mating surfaces of both materials, and when forming a joint interface where the new surfaces of both materials come into contact with each other, a double-acting rotation is performed in the same manner as above. By setting the rotation speed of the tool probe and shoulder separately, the heat generated in the probe and shoulder is controlled, and the formation of brittle intermetallic compounds is suppressed, thereby reducing the overlapping point of the aluminum alloy plate and the steel plate. The joint strength of the joint can be improved.

A double-acting friction stir welding method was applied to the object to be joined, in which an aluminum alloy plate and a steel plate having the plate thickness, chemical composition, tensile strength, and hardness shown in Table 1 were superimposed, and one time of welding was performed. A joining experiment with a length of 0.3 m was performed.
For the double-acting friction stir welding, a double-acting rotary tool having the shape and dimensions shown in FIG. 3 was used. The shoulder and probe of the rotary tool are made of tool steel (SKD61) with a Vickers hardness Hv of 530, which is harder than the aluminum alloy plates and steel plates listed in Table 1, which are the joining materials. board. During joining, both the shoulder and the probe of the double-acting rotary tool were rotated clockwise. Table 2 shows other bonding conditions.

With respect to the bonded joint thus obtained, confirmation of the success or failure of the bonding state, measurement of the thickness of the intermetallic compound at the bonding interface, and tensile test of the bonded joint were performed in the following manner.
<Success or failure of bonding state>
The success or failure of the bonded state was confirmed by checking whether or not the manufactured bonded joint was in a state of spontaneous separation after bonding. When there was no peeling, the bonding state was established, and "O" was indicated.
<Thickness of intermetallic compound>
The thickness of the intermetallic compound is determined by cutting the prepared joint in the direction across the joint (perpendicular to the joint direction), and examining the central portion of the joint interface exposed in the cross section with a scanning electron microscope at a magnification of 5000. , the thickness of the intermetallic compound was measured at three or more locations, and the average value was obtained.
<Tensile test of bonded joint>
In the tensile test of the bonded joint, a tensile test piece with a width of 20 mm including the joint perpendicular to the tensile direction is taken from the manufactured bonded joint as shown in FIG. 4, and the tensile test is performed. , the shear strength was measured.

The results of the above evaluation test are also shown in Table 2. The results show the following.
First, No. 1, which satisfies the conditions of the present invention. Joints Nos. 1 , 3 and 4 all have a jointed state, the thickness of the intermetallic compound at the joint interface is 0.7 μm or less, and the tensile strength (shear tensile strength) is 4.6 kN or more. I was able to gain strength.
On the other hand, No. In the joints of Comparative Examples 8, 10, 12, and 14 to 17, the insertion amount P from the mating surface of the Al alloy plate and the steel plate at the tip of the probe to the steel plate side was smaller than the range of the present invention, so a joint interface was not formed. However, the bonding state was not established because the bonding state was such that the substrates were peeled off by themselves after bonding.
Also, No. In the joints of Comparative Examples 7, 9, 13, 19 and 20, either the rotational speed SS of the shoulder or the rotational speed PS of the probe exceeded the upper limit of the range of the present invention. Although the bonding state was established, the thickness of the intermetallic compound at the bonding interface became 0.9 μm or more, and the tensile strength of the joint became 4.4 kN or less.
Also, No. In the joint of Comparative Example 11, the insertion amount P from the mating surface of the probe tip to the steel plate side was too large for the range of the present invention, so the heat generated by the frictional stirring of the steel plate side by the probe tip became excessive, and the peak temperature of the joint interface increased. was excessively increased, although the joint state was established, the intermetallic compound at the joint interface became 0.9 μm or more, and the tensile strength of the joint became 4.4 kN or less .
Also, No. In the joint of Comparative Example 18, the rotation speed SS of the shoulder was below the lower limit of the range of the present invention. Therefore, the joint state was established and the intermetallic compound at the joint interface was suppressed to 0.7 μm or less, but the tensile strength of the joint was 4.4 kN or less.
Also, No. In the joint of Comparative Example No. 21, since the inclination angle α of the rotary tool exceeded 5°, the surface became concave and the tensile strength of the joint was 4.4 kN or less.
No. In the joint of Comparative Example No. 22, since the joining speed JS exceeded 200 mm/min, the heat generation due to friction stirring was insufficient, and sufficient plastic flow was not obtained, and the joining state was not established.

The technology of the present invention can be applied not only to automobile members, but also to railway vehicles, aircraft, ships, building structures, electrical equipment, and the like.

1: aluminum alloy plate 2: steel plate 3: double-acting rotary tool 4: probe 5: shoulder 6: mating surface of aluminum alloy plate and steel plate 7: joint interface 8: joint 9: backing jig 10: plastic flow region

Claims (5)

An aluminum alloy plate and a steel plate are superimposed on each other, and a backing jig is abutted on the steel plate side to fix the object to be joined. Using a double-acting rotating tool whose speed can be set independently, the probe of the double-acting rotating tool is inserted from the aluminum alloy plate side of the object to be joined to the steel plate side while rotating, and the double-acting rotating tool is rotated. In a method for friction stir welding by moving the rotating tool in the welding direction in a state where the shoulder of the tool is in contact with the surface of the aluminum alloy plate while rotating, friction stir welding is performed on the object to be welded and plastic flow is performed,
A friction stir welding method, wherein the rotation speed SS (rotations/minute) of the shoulder of the rotating tool is higher than the rotation speed PS (rotations/minute) of the probe. The joining speed JS is 50 to 200 mm/min, and the shoulder rotation speed SS (times/minute) and the probe rotation speed PS (times/minute) are set to values that satisfy the following equations (1) and (2), respectively. The friction stir welding method according to claim 1 , characterized in that:
Note 1000≦SS≦1700 (1)
300≦PS≦500 (2) 3. The friction according to claim 1 or 2 , wherein the shoulder diameter SD (mm) and the probe diameter PD (mm) are set to values satisfying the following equations (5) and/or (6), respectively. Stir joining method.
Note 12≤SD≤18 (5)
4≦PD≦8 (6) The insertion amount P (mm) of inserting the probe tip of the rotating tool that is inserted from the surface of the aluminum alloy plate while rotating it from the mating surface of the aluminum alloy plate and steel plate to the steel plate side is more than 0 mm and 0.5 mm or less. The friction stir welding method according to any one of claims 1 to 3 . The rotation axis of the rotating tool that is inserted while rotating from the surface of the aluminum alloy plate is inclined at an inclination angle α of more than 0° and 5° or less in the opposite direction to the joining direction with respect to the perpendicular to the surface of the aluminum alloy plate. The friction stir welding method according to any one of claims 1 to 4 .

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