Method for producing joined body of dissimilar materials

Abstract

A method for manufacturing a dissimilar material joined body (10), in which a rivet (40) is driven into a first member (20), protrusions (43B) and recesses (43C) of the rivet (40) are fitted to the first member (20), and a center shaft part (42) of the rivet (40) is inserted into the first member (20), the rivet (40) having a head part (41) and the center shaft part (42), the center shaft part (42) having a substantially cylindrical shape and a plurality of protrusions (43B) and recesses (43C) on an outer peripheral surface (43A). A center shaft portion (42) of a rivet (40) inserted through a first member (20) is brought into contact with a second member (30) made of a material different from that of the first member (20), a gap between a head portion (41) of the rivet (40) and the second member (30) is pressurized and energized, and the rivet (40) and the second member (30) are welded to form a dissimilar material joined body (10).

Description

Technical Field

[0001] The present invention relates to a method for producing a dissimilar material joint body. Background Art

[0002] Conventionally, there is a known method for manufacturing a dissimilar material joint body by joining two members of different materials, and one example thereof is described in Patent Document 1. Patent Document 1 discloses the following manufacturing method: in order to join a steel material and an aluminum alloy material, a rivet for joining dissimilar materials made of steel is driven into the aluminum alloy material to perform riveting and fixing, and a pair of electrodes are used to clamp the rivet and the steel material and conduct electricity, thereby spot welding the rivet and the steel material.

[0003] The rivet described in Patent Document 1 has a groove formed on the lower surface of the rivet head (the surface overlapping the aluminum alloy material), and when the rivet is driven into the aluminum alloy material, the aluminum alloy material plastically deforms and enters the groove, thereby riveting the rivet. Prior Art Literature Patent Literature

[0004] Patent Document 1: Japanese Patent Application Publication No. 2010-207898 Summary of the invention

[0005] Technical problem to be solved by the invention However, if a groove is provided on the lower surface of the head of the rivet as in Patent Document 1, the dissolved aluminum alloy material sometimes does not fully flow into the groove when the rivet is spot welded to the steel material. As a result, the joint strength is reduced, or the joint strength varies depending on the individual. In addition, due to the formation of the groove, sometimes a shunt occurs during spot welding, and the current does not flow to the desired joint portion in a concentrated manner. In fact, this also leads to a reduction in joint strength and instability.

[0006] The present invention has been made based on the above-mentioned actual situation, and an object of the present invention is to increase and stabilize the joining strength of a dissimilar material joint.

[0007] Technical solutions for solving technical problems <1> A method for manufacturing a dissimilar material joint body, comprising driving a rivet into a first member so that a protruding portion and a recessed portion of the rivet are engaged with the first member, and inserting a central axis portion of the rivet through the first member, wherein the rivet comprises a head portion and the central axis portion, the central axis portion is roughly cylindrical and has a plurality of the protruding portions and the recessed portions on the outer peripheral surface, the central axis portion of the rivet inserted through the first member is brought into contact with a second member made of a material different from that of the first member, pressurizing and energizing between the head portion of the rivet and the second member, and welding the rivet to the second member to form a dissimilar material joint body.

[0008] <2> According to the above <1> In the method for manufacturing a dissimilar material joint body, the protrusion and the recess are provided on the outer peripheral surface of the middle shaft portion over the entire circumference.

[0009] <3> According to the above <1> or <2> In the method for manufacturing a dissimilar material joint body, the protrusions and the recesses are arranged at equal intervals.

[0010] <4> According to the above <1> to <3> According to any one of the methods for manufacturing a dissimilar material joint, the central axis portion includes: a first central axis portion having the protrusion and the recess; and a second central axis portion not having the protrusion and the recess, and the axial diameter of the first central axis portion is larger than the axial diameter of the second central axis portion.

[0011] <5> According to the above <1> to <4> According to any one of the methods for manufacturing a dissimilar material joint, when the rivet and the second member are pressurized and energized, the current density flowing in the middle axis portion of the rivet is 397 MA / m 2 Above and 597MA / m 2 Below, the surface pressure applied to the middle axis portion of the rivet is greater than 119 MPa and less than 279 MPa, the dissimilar material joint body solidified after welding has a casting structure formed by combining the rivet and the second component metal, namely, a weld nugget, the height of the weld nugget along the axial direction of the middle axis portion is greater than 0.34 and less than 0.8 compared with the dissimilar material joint body as a whole, and the value obtained by dividing the radial length of the weld nugget along the middle axis portion by the height is greater than 1.7 and less than 5.4.

[0012] <6> According to the above <1> to <5> In any one of the methods for producing a dissimilar metal joint, the protrusions are each protruded in a triangular prism shape.

[0013] <7> According to the above <1> to <6> In the method for producing a dissimilar metal joint body described in any one of the preceding claims, the first member is made of aluminum or an aluminum alloy.

[0014] Effects of the Invention According to the present invention, the joining strength of a dissimilar metal joint can be increased and stabilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an enlarged cross-sectional view of the vicinity of a rivet of the dissimilar metal joint product according to the first embodiment. Figure 2 It is a three-dimensional diagram of a rivet. Figure 3 This is a top view of the rivet. Figure 4It is a side view of the rivet. Figure 5 It is a cross-sectional view showing the stamping process. Figure 6 It is a cross-sectional view showing a state where a rivet is driven into a first member. Figure 7 It is a cross-sectional view showing the welding process. Figure 8 This is a cross-sectional view showing a state where the rivet and the second member are pressurized and energized. Fig. 9 This is a perspective view of a rivet according to Comparative Example 1. Fig.10 yes Fig. 9 AA line section view. Fig.11 It is a cross-sectional view showing a state in which the rivet and the second member according to Comparative Example 1 are fixed by caulking. Fig.12 This is a table showing the evaluation results of the dissimilar metal joined products according to Example 1. Fig.13 This is a table showing the evaluation results of the dissimilar metal joined products according to Comparative Example 1. Fig.14 This is a table showing the evaluation results of the dissimilar metal joined products according to Example 2. Fig.15 This is a table showing the evaluation results of the dissimilar material joined products according to Comparative Example 2. DETAILED DESCRIPTION

[0016] <Implementation Method 1> Reference Figures 1 to 15 The dissimilar material joint body 10 and the manufacturing method of the dissimilar material joint body 10 according to the first embodiment are described. In some figures, the X-axis, Y-axis and Z-axis are shown, and the directions of the axes are drawn in such a way that they are the same in each figure. In addition, the Z-axis direction is set as the up-down direction, but the above directions are determined only for convenience and should not be interpreted in a limiting manner.

[0017] like Figure 1 As shown in FIG. 1 , the dissimilar material joint body 10 includes a first member 20, a second member 30 made of a material different from that of the first member 20, and a rivet (nail) 40 for joining the first member 20 and the second member 30. The dissimilar material joint body 10 is used, for example, in a panel structure of a vehicle, but the use is not limited. The rivet 40 is deformed during the process of manufacturing the dissimilar material joint body 10 as described later, but Figure 1 , the deformed rivet 40 included in the manufactured dissimilar metal joint body 10 is shown.

[0018] The first member 20 is made of a lightweight material, such as a metal material such as aluminum or an aluminum alloy. The second member 30 is made of a metal material that is heavier and stronger than the first member 20, such as steel commonly used in the panel structure of the vehicle. By overlapping the first member 20 and the second member 30 to form the dissimilar material joint 10, it is possible to ensure strength through the second member 30 and achieve lightweighting through the first member 20. In addition, by using a material with aluminum as the main component in the first member 20, recycling becomes easy. In the present embodiment, the first member 20 and the second member are plate materials, but the shape is not limited to plate materials. As long as the shape has a shape that allows at least a portion of the first member 20 and the second member to overlap, it can also be a hollow cylindrical shape, for example.

[0019] Generally, if the first member 20 and the second member 30 composed of different materials are simply overlapped and spot welded, a brittle compound is generated at the interface between the first member 20 and the second member 30, and they cannot be properly joined. Therefore, the dissimilar material joint body 10 is provided with a rivet 40 in order to join the first member 20 and the second member 30. The rivet 40 is made of the same material as the metal material constituting the second member 30 (for example, steel), or a metal material having the same main component as the metal material constituting the second member 30 (for example, iron). As described later, a cast structure (a weld nugget 60 described later) that can be metal-joined with high strength by welding can be formed at the interface between the rivet 40 and the second member 30.

[0020] like Figures 2 to 4 As shown, the rivet 40 has a disc-shaped head 41 and a central axis portion 42 extending in a roughly cylindrical shape from one surface (first surface) 41A of the head 41. The rivet 40 as a whole has a T-shaped cross-section, and each part is formed integrally. The central axis C of the central axis portion 42 is the same as that of the head 41, and the outer diameter is smaller than that of the head 41. The central axis portion 42 is composed of a first central axis portion 43 on the side of the head 41 (the extended base side) and a second central axis portion 44 on the opposite side of the head 41 (the extended end side). The length of the central axis portion 42 along the central axis C (the length in the Z direction) is formed to be greater than or equal to the thickness (the length in the Z direction) of the first component 20, thereby, as described later, the central axis portion 42 can be inserted through the first component 20.

[0021] like Figures 2 to 4As shown, the first central axis portion 43 is the portion between the head portion 41 and the second central axis portion 44, and the outer peripheral side surface 43A is concave-convex. The first central axis portion 43 has a plurality of protrusions 43B throughout the circumference of the outer peripheral side surface 43A. A plurality of protrusions 43B are arranged at equal intervals (16 in this embodiment), and each protrudes from the outer peripheral side surface 43A in a triangular prism shape along the radial direction (the direction intersecting the central axis C). The adjacent protrusions 43B arranged at equal intervals are recessed into a valley shape, thereby forming recessed portions 43C at equal intervals. Regarding the axial diameter (outer diameter dimension) of the first central axis portion 43, the portion including the recessed portion 43C is the minimum value Φ1, and the portion including the protrusion 43B is the maximum value Φ2.

[0022] like Figures 2 to 4 As shown, the second central axis portion 44 extends from the first central axis portion 43 to the opposite side of the head portion 41. The outer peripheral side surface 44A of the second central axis portion 44 is different from the first central axis portion 43 and does not have a concave-convex shape. The maximum value Φ3 of the axial diameter of the second central axis portion 44 is formed to be smaller than the minimum value Φ1 of the outer shape of the first central axis portion 43 mentioned above. The front end (extended end) 44B of the second central axis portion 44 is a circular surface with an axial diameter of Φ4. The corners from the outer peripheral side surface 44A of the second central axis portion 44 to the front end 44B are rounded and gently inclined. The front end 44B gradually becomes thinner, and the axial diameter Φ4 of the front end 44B of the second central axis portion 44 is smaller than the axial diameter Φ3 of the main body of the second central axis portion 44.

[0023] Next, a method for manufacturing the dissimilar metal joint 10 will be described. The manufacturing method includes a stamping process and a welding process performed after the stamping process. Figures 5 and 6 As shown in FIG. 1 , in the punching process, a punching machine having a punch 81 as a support and a die 82 as a press unit is used. The punch 81 has a recess 81A on the upper surface, and the recess 81A is formed in the shape and size of the head 41 of the rivet 40. In addition, the die 82 is formed with an opening 82A into which the second middle shaft portion 44 of the rivet 40 can be inserted. Figure 5 As shown, in the punching process, first, the head 41 of the rivet 40 is placed on the concave portion 81A of the punch 81. Then, the first member 20 ( Figure 5 ), pressurize the die 82 in the clamped state ( Figure 6 ). In this way, the rivet 40 is driven into the first member 20. Figure 6 The fragments of the first member 20 generated in the pressing process are removed.

[0024] like Figure 6As shown, the rivet 40 drives the central axis portion 42 (the first central axis portion 43 and the second central axis portion 44) into the first member 20 through a stamping process, and the front end 44B of the second central axis portion 44 is inserted into the first member 20. The strength (rigidity) of the material of the first member 20 is smaller than that of the rivet 40, so the first member 20 is plastically deformed due to the driven central axis portion 42. By driving, the protrusion 43B and the recessed portion 43C of the second central axis portion 44 bite into the first member 20 and fit together, and are riveted and fixed to the first member 20. The protrusions 43B protrude in the shape of triangular prisms, and the protruding ends are sharp at acute angles, so they are easily fitted with the first member 20. In addition, the protrusions 43B and the recessed portions 43C are formed at equal intervals throughout the circumference of the outer peripheral side surface 43A, so they are evenly riveted and fixed to the first plate 20 throughout the circumference.

[0025] After the rivet 40 is driven into the first member 20 by a stamping process and riveted to fix, as shown in FIG. Figure 7 As shown, a welding process is performed. In the welding process, the first component 20 with the rivet 40 driven into it is placed on the second component 30, so that the front end 44B of the second central axis portion 44 of the rivet 40 is in contact with the first main surface 30A (the main surface on the first component 20 side) of the second component 30. Then, the rivet 40, the first component 20 and the second component 30 are clamped between a pair of electrodes 90 and a voltage is applied, so that the head 41 of the rivet 40 and the second component 30 are pressurized and energized at the same time. Thus, a pressure P is applied between the electrodes 90, and an electric current I flows in the up and down directions along the Z direction. As a result, resistive heating is generated at the interface between the contact portion of the rivet 40 and the second component 30, that is, the front end 44B of the rivet 40 and the first main surface 30A of the second component 30. Thus, as shown Figure 8 As shown in FIG. 1 , the interface is melted and joined by spot welding (resistance welding). The front end 44B of the second middle axis portion 44 of the rivet 40 is deformed by melting due to the pressurized current flow, and is flattened against the second member 30 to form a shape that is widely expanded on the first main surface 30A. In addition, a metal-joined casting structure, i.e., a weld nugget 60, is formed at the contact portion between the rivet 40 and the second member 30. Figure 1 As shown, the dissimilar metal joint body 10 solidified after welding has a weld nugget 60 having a height (length along the direction of the center axis C) H60 and an outer diameter R60 (length along the radial direction intersecting the center axis C).

[0026] When the first member 20 is melted by applying pressure and electricity, it flows in a manner that fills the gap between the protrusion 43B and the recessed portion 43C of the rivet 40. The protrusion 43B and the recessed portion 43C are formed at equal intervals throughout the entire circumference of the outer peripheral side surface 43A, so the first member 20 flows in a manner that fills the gap throughout the entire circumference. As a result, the first member 20 easily flows into the recessed portion 43C that is the groove of the rivet 40, and the gap between the first member 20 and the rivet 40 is filled, thereby improving the bonding strength.

[0027] In addition, when the middle shaft portion 42 of the rivet 40 is melted and flattened due to the pressurized electricity, the portion of the head portion 41 of the rivet 40 connected to the middle shaft portion 42 sinks slightly toward the first member 20 (below). Figure 8 As shown, the outer peripheral portion of the head 41 is slightly floated upward, and a small gap is generated between the first surface 41A of the head 41 and the main surface 20B of the first member 20 (the main surface 20B on the opposite side of the second member 30 among the main surfaces 20A and 20B). As a result, the current flowing between the electrodes 90 is likely to flow to the central axis portion 42 of the rivet 40 in a concentrated manner, and the current can be concentrated to the contact portion between the front end 44B of the rivet 40 and the first main surface 30A of the second member 30 to be spot welded. Assuming that the first surface 41A of the head 41 is in contact with the main surface 20B of the first member 20, part of the current flowing between the electrodes 90 is likely to be diverted to the contact portion. As a result, the current flowing between the front end 44B of the rivet 40 and the first main surface 30A of the second member 30 is reduced, and the resistance heating and further melting become insufficient, which may lead to a reduction in the bonding strength and instability. According to the present embodiment, it is possible to suppress such dissolution failure due to the split flow, thereby achieving improvement and stabilization of the joining strength of the dissimilar metal joined product 10 .

[0028] It should be noted that the current I flowing between the electrodes 90 during spot welding is appropriately adjusted according to the materials of the rivet 40 and the second member 30. If the current I is too small, the resistance heating becomes insufficient, and the welding nugget 60 may not be formed. On the contrary, if the current I is too large, so-called internal dispersion may occur, resulting in a decrease in the quality of the dissimilar material joint 10. The current density J of the current I flowing between the electrodes 90 is preferably 430 (MA / m 2 ) and above 517(MA / m 2 ) below.

[0029] <Comparative Experiment 1> In order to evaluate the performance of the above-mentioned dissimilar material joint body 10, a comparative experiment 1 was conducted. In the comparative experiment 1, the dissimilar material joint bodies involved in Examples 1 and 2 and Comparative Examples 1 and 2 were manufactured and evaluated respectively. Examples 1 and 2 are evaluation samples of the above-mentioned dissimilar material joint body 10, and Comparative Examples 1 and 2 are evaluation samples of the dissimilar material joint body 910 manufactured by the same method as the dissimilar material joint body 10 using a rivet 940 of a different shape.

[0030] like Figures 9 and 10 As shown, the rivet 940 of the dissimilar material joint body 910 involved in Comparative Examples 1 and 2 includes a disk-shaped head 941 and a central axis portion 942 extending from a first surface 941A of the head 941 in a substantially cylindrical shape. The central axis portion 942 is different from the rivet 40 involved in Embodiment 1, and does not have a first central axis portion 43 whose outer peripheral side surface is concave and convex. The outer peripheral portion 941B of the first surface 941A of the head 941 of the rivet 940 protrudes downward along the central axis C. An annular groove 941C is formed between the outer peripheral portion 941B and the central axis portion 942.

[0031] If the rivet 940 is driven into the first member 20, Fig.11 As shown, the first member 20 is plastically deformed and enters the groove 941C, and the rivet 940 is riveted and fixed to the second member 30. Afterwards, if welding is performed by pressurizing and energizing, the first member 20 flows into the groove 941C. However, this inflow is not as easy as the rivet 40 involved in the present embodiment described above, and sometimes the gap between the first member 20 and the rivet 940 cannot be fully buried. In addition, even if the middle axis portion 942 is melted and flattened and slightly sinks to the side (below) of the first member 20, since the peripheral portion 941B protrudes downward, it still contacts the main surface 20B of the first member 20, and it is easy to generate a diversion in this contact portion.

[0032] <Conditions> First member 20: Aluminum plate Thickness of the first member 20: 1.2 (mm) Second member 30: Steel plate (Example 1 and Comparative Example 1 are JIS standard SPCC270, Example 2 and Comparative Example 2 are JIS standard SPCC440) The thickness of the second member 30 is 0.8 (mm) in Example 1 and Comparative Example 1, and 1.4 (mm) in Example 2 and Comparative Example 2. Material of rivet 40 and rivet 940: steel The shaft diameter of the rivet 40 Φ3 and the shaft diameter of the middle shaft portion 942 of the rivet 940: 4 (mm) Pressure P: 1.5 (kN) or 3.5 (kN) Current I: Examples 1 and 2 are in the range of 5 (kA) or more and 12.5 (kA) or less, and Comparative Examples 1 and 2 are in the range of 5 (kA) or more and 10 (kA) or less

[0033] <Evaluation method> For Examples 1 to 2 and Comparative Examples 1 to 2, tensile shear tests, confirmation of defects (interface peeling, rivet crushing, pore generation, etc.), and confirmation of the formation and size measurement of the weld nugget 60 were conducted. In the tensile shear test, the first component 20 and the second component 30 of each dissimilar material joint are stretched in opposite directions along a direction intersecting the center axis C, and the tensile load value when shearing occurs is measured. The larger the tensile load value, the greater the joint strength can be evaluated. In the confirmation of defects, the appearance of each dissimilar material joint is observed, and defects such as interface peeling, rivet crushing, and pore generation are confirmed. The case where the defect occurs is set to yes, and the case where the defect does not occur is set to no. The confirmation of the formation and size measurement of the weld nugget 60 are performed by corroding and grinding each dissimilar material joint with picric acid, and observing the exposed cross section containing the center axis C under a microscope. The case where the weld nugget 60 is formed can be evaluated as a good spot welding. In addition, when the weld nugget 60 is formed, the height H60 and the outer diameter R60 ( Figure 1 ) are measured, and their ratio (R60 / 60) and the ratio (H60 / H10) to the height H10 of the entire dissimilar material joint body are calculated. Then, the results of the above-mentioned tensile shear test, defect confirmation, and the formation state of the weld nugget 60 are comprehensively evaluated and classified into three stages: A (good), B (acceptable), and C (unacceptable).

[0034] <Evaluation Results> The evaluation results of the comparative experiment 1 are shown in Figure 12 to Figure 15 It is confirmed that the range of current I and pressure P applicable to welding is wider in Examples 1 and 2 than in Comparative Examples 1 and 2, and that the joint strength can be improved and stabilized. In addition, it is confirmed that in Examples 1 and 2, the current density J flowing in the middle shaft portion 42 of the rivet 40 is 397 (MA / m 2 ) and above 597(MA / m 2 ) or less, and the surface pressure obtained by dividing the pressure P by the cross-sectional area of ​​the middle axis portion 42 of the rivet 40 is within the range of 119 MPa or more and less than 279 MPa, the weld nugget 60 is well formed. Specifically, the weld nugget 60 is well formed when H60 / H10 is within the range of 0.34 or more and less than 0.8, and R60 / H60 is within the range of 1.7 or more and less than 5.4.

[0035] <Other Implementation Methods> The present invention is not limited to the embodiments described in the above description and drawings, and for example, the following embodiments are also included in the technical scope of the present invention.

[0036] (1) The shapes, sizes, and intervals of the protruding portion 43B and the recessed portion 43C of the rivet 40 are not limited to those shown in the figure, and can be changed as appropriate.

[0037] (2) The protruding portion 43B and the recessed portion 43C of the rivet 40 may not be provided over the entire circumferential direction of the outer peripheral side surface 43A.

[0038] (3) The first member 20 is not limited to a metal material, and may be made of a lightweight material such as carbon fiber reinforced plastic. Description of Reference Numerals

[0039] 10…joint of dissimilar materials, 20…first member, 30…second member, 40…rivet, 41…head, 42…central axis, 43…first central axis, 44…second central axis, 43A…peripheral side (peripheral surface), 43B…protrusion, 43C…recess, 60…welding nugget.

Claims

1. A method for manufacturing a dissimilar material joint body, comprising driving a rivet into a first member, engaging a protruding portion and a recessed portion of the rivet with the first member, and inserting a central axis portion of the rivet through the first member, wherein the rivet comprises a head portion and the central axis portion, the central axis portion is substantially cylindrical and has a plurality of the protruding portions and a plurality of the recessed portions on an outer peripheral surface, The middle axis portion of the rivet inserted through the first member is brought into contact with the second member made of a material different from that of the first member. The rivet and the second member are welded by applying pressure and passing electricity between the head of the rivet and the second member to form a dissimilar material joint body.

2. The method for producing a dissimilar material joint according to claim 1, wherein: The protrusion and the recess are provided on the outer peripheral surface of the middle shaft portion over the entire circumference.

3. The method for producing a dissimilar material joint body according to claim 1, wherein: The protrusions and the recesses are arranged at equal intervals.

4. The method for producing a dissimilar material joint body according to claim 1, wherein: The middle shaft portion includes: a first middle shaft portion having the protruding portion and the recessed portion; and a second middle shaft portion not having the protruding portion and the recessed portion. The first middle shaft portion has a larger shaft diameter than the second middle shaft portion.

5. The method for producing a dissimilar material joint body according to claim 1, wherein: When the rivet and the second member are pressurized and energized, the current density flowing in the middle axis of the rivet is 397 MA / m 2 Above and 597MA / m 2 Below, the surface pressure applied to the middle axis portion of the rivet is greater than 119 MPa and less than 279 MPa, The dissimilar metal joint body solidified after welding has a welding nugget, and the welding nugget is a casting structure formed by the metal bonding of the rivet and the second member. The height of the weld nugget along the axial direction of the middle axis portion is 0.34 or more and less than 0.8 compared with the entire dissimilar metal joint body, A value obtained by dividing a length of the weld nugget along the radial direction of the central axis portion by the height is 1.7 or more and less than 5.

4.

6. The method for producing a dissimilar material joint body according to claim 1, wherein: The protrusions are respectively protruding in a triangular prism shape.

7. The method for producing a dissimilar metal joint according to any one of claims 1 to 6, wherein: The first member is made of aluminum or an aluminum alloy.

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