JP6786977B2 - Laminated joint and its manufacturing method - Google Patents

Description

The present invention relates to a lap joint and a method for manufacturing the lap joint, and more particularly to a lap joint for a high-strength steel sheet used for an automobile body and a method for manufacturing the same.

In recent years, in the automobile field, it has been required to reduce the weight of the vehicle body in order to reduce fuel consumption and CO ₂ emissions, and to increase the strength of the vehicle body member in order to improve collision safety. In order to satisfy these requirements, it is effective to use high-strength steel plates for vehicle body members and various parts.

In processes such as assembling a car body made of such a high-strength steel plate and attaching parts, spot-shaped melt bonding using resistance heating has become widespread, but in recent years, instead of this resistance spot bonding, Molten bonding (hereinafter, simply referred to as bonding) using light rays having high power density (hereinafter, referred to as light rays) has come to be used in some parts. Joining using light rays enables high-speed construction, and since the joining current does not shunt to the existing joint, the pitch interval of the joint can be shortened, and the rigidity of the vehicle body due to multi-point joining can be achieved. Improvement is also possible.

The joint strength, which is one of the quality indicators of joints formed by melt joints (hereinafter referred to as joint joints), includes tensile shear strength (TSS) measured by applying a tensile load in the shear direction and peeling direction. There is a cross tensile strength (CTS) measured by applying a tensile load to. In joints using light rays, CTS tends to be as low as or lower than that of conventional resistance spot joints, and in the case of high-strength steel sheets with a large amount of carbon, CTS may be particularly low. .. Therefore, a technique for improving the joint strength of CTS or the like when joining a high-strength steel sheet using a light beam has been desired.

Under such circumstances, as a technique for improving the joint strength in joining using light rays, a technique for forming another joint in the vicinity of the joint (see Patent Document 1), a closed loop-shaped main bead. A technique for forming another bead for the purpose of tempering the present bead on the inside (see Patent Documents 2 and 3) is known.

On the other hand, in the assembly process of an automobile body, spot joining is often used, and a method of obtaining a shape similar to a point-shaped lap joint in a plan view by joining with light rays, which is formed by this joining method, is patented. It is disclosed in 4. Point-shaped lap joints using light rays are attracting attention as an alternative technique to spot joints when electrodes cannot be sandwiched from both sides of a lap steel plate.

Japanese Unexamined Patent Publication No. 2010-012504 Japanese Unexamined Patent Publication No. 2012-241986 International Publication No. 2012/05007 Japanese Unexamined Patent Publication No. 60-68185

However, the point-shaped lap joint formed by the above-mentioned light rays has a problem that sufficient cross tensile strength (CTS) cannot be obtained, particularly in the case of a lap joint made of high-strength steel plate, and the joint strength is improved. Was desired.

In view of such circumstances, it is an object of the present invention to provide a lap joint with excellent joint strength.

The present inventors are means for improving the toughness in the vicinity of the melting boundary of the point-shaped joint in order to improve the joint strength of the joint in which the metal plate is joined by a light beam to form the point-shaped joint. Diligently examined.

The present inventors have conceived of heat-treating a point-shaped joint, and have investigated various heat-treated locations and heat-treated methods. As a result, when the melt-solidified portion of the point-shaped joint is viewed in a plan view from the irradiation side of the light beam, the light beam is irradiated to the inside of the melt-solidified portion, the outer contour is substantially circular, and the melt-solidified portion is re-melted and solidified to the center. The substantially central portion of the shape (hereinafter referred to as "dotted") is remelted and solidified across a plurality of metal plates to form a remelted solidified portion, and near the melting boundary of the dotted joint. It was found that CTS is improved by forming a coagulation reheating portion by reheating so as to reheat.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) In a lap joint that is composed of a plurality of lapped metal plates and has point-shaped joints.
The point-shaped joint has a melt-solidified portion that straddles the plurality of metal plates.
The melt-solidified portion has a remelt-solidified portion and a solidified / reheated portion.
When the melt-solidified portion is viewed in a plan view, the re-melt-solidified portion has a point shape including a circular equivalent center of the melt-solidified portion and straddles the plurality of metal plates.
The solidification reheating portion is located around the remelt solidification portion, includes a melting boundary of the point-shaped joint portion, and is softened from the remelt solidification portion. ..
(2) Of the solidification and reheating portions, the average value of Vickers hardness in the range of 0.5 mm from the melting boundary of the overlapping surface of the metal plates toward the remelting and solidifying portion is Hv390 or less. The lap joint joint according to (1) above, wherein the Vickers hardness of the remelted solidified portion is lower than the average value of Hv70 or more.
(3) The lap joint according to (1) or (2) above, wherein the plurality of metal plates include one or more metal plates having a surface treatment film.
(4) In a method for manufacturing a lap joint, in which a plurality of metal plates are overlapped and joined by irradiating a light beam.
One of the overlapped metal plates is irradiated with light rays to form a point-shaped joint having a melt-solidified portion that is melt-solidified in a dot shape over the plurality of metal plates.
When the melt-solidified portion is viewed in a plan view from the irradiation side of the light beam, the light beam is re-irradiated to the inside of the melt-solidified portion, and the plurality of metal plates are formed into dots including the circular equivalent center of the melt-solidified portion. A remelt solidification portion is formed by remelting and solidifying across the remelt solidification portion, and a solidification reheating portion including a melting boundary of the point-shaped joint portion is formed around the remelt solidification portion, and reheating at that time is performed. A method for manufacturing a lap joint, which comprises adjusting conditions to soften the solidified and reheated portion from the remelted solidified portion.
(5) In the re-irradiation of the light beam, the distance from the outer end portion of the remelted solidified portion of the remelted solidified portion to the melting boundary of the point-shaped joint portion is 1 in the plate thickness direction cross section of the plurality of metal plates. The method for manufacturing a lap joint according to (4) above, wherein the thickness is 0 to 3.0 mm.
(6) The method for manufacturing a lap joint according to (4) or (5) above, wherein one or more metal plates having a surface treatment film formed on the plurality of metal plates are used.

According to the present invention, since the solidification reheating portion having excellent toughness is provided near the melting boundary of the point-shaped joint portion, the joint strength of the lap joint, particularly the cross tensile strength (CTS) can be improved. it can. Then, by applying the joint of the present invention to an automobile part, the reliability of the automobile part can be improved.

It is a figure which shows the outline of the Vickers hardness distribution of a joint joint which has a punctate joint part. (A) schematically shows the structure of the cross section of the joint, and (b) shows the Vickers hardness distribution of the joint. It is a figure which shows the outline of the Vickers hardness distribution of a joint joint which irradiated the central part of the point-like joint part with a light beam. (A) schematically shows the structure of the cross section of the joint, and (b) shows the Vickers hardness distribution of the joint. It is a figure which shows typically the structure of the cross section of the joint of this invention. It is a perspective view which shows the outline of formation of the point-like joint part. (A) shows a schematic diagram of irradiating light rays with different irradiation diameters, (b) shows a schematic diagram of irradiating light rays with a wide condensing area, and (c) shows a schematic diagram of formed point-shaped joints. A perspective view is shown. It is a perspective view which shows the outline of the heat treatment of a punctate joint part. (A) shows a schematic diagram of irradiating light rays with different irradiation diameters, (b) shows a schematic diagram of irradiating light rays with a wide condensing area, and (c) shows a remelt solidification portion and a solidification reheating portion. The perspective view of the point-shaped joint portion having and is shown.

The lap joint of the present invention (hereinafter referred to as "joint of the present invention") is a lap joint having a point-shaped joint formed by irradiating a plurality of metal plates with light rays, and is the above-mentioned point. The joint portion has a melt-solidified portion, and the melt-solidified portion is composed of a re-melted solidified portion and a solidified and reheated portion, and the solidified and reheated portion is softened from the remelted solidified portion. It has the characteristics of.

Hereinafter, the background of the study leading to the joint of the present invention will be described, and the joint of the present invention will be described.
In a lap joint having a point-shaped joint, it has been desired to further improve the joint strength. Therefore, the present inventors examined heat treatment on the punctate joints, and investigated the heat treatment points and the heat treatment method of the punctate joints.

When a load is applied to the joint portion in the peeling direction of the lap joint, stress is concentrated in the vicinity of the melting boundary, and the lap joint is likely to break. Therefore, when the melt-solidified portion of the point-shaped joint portion having a diameter of about 6.0 mm is viewed in a plan view from the irradiation side of the light beam, the light beam having a ray diameter of about 3.0 mm is re-irradiated in a dot shape inside the melt-solidified portion. In addition to remelting and solidifying in dots, heat treatment was performed on the molten boundary of the melted and solidified part, and the Vickers hardness distribution of the joint was investigated. As a result, it was confirmed that the melting boundary was tempered by re-irradiation and the toughness was improved. This test will be described with reference to the drawings.

FIG. 1 shows a schematic view of the Vickers hardness distribution of a joint having a point-shaped joint. FIG. 1A shows a schematic view of a cross section of a joint joint having a melt-solidified portion, and FIG. 1B shows a schematic diagram of a Vickers hardness distribution of the joint joint in the melt-solidified portion and its vicinity. FIG. 2 shows a schematic diagram of the Vickers hardness distribution of the joint joint in which the central portion of the point-shaped joint portion is re-irradiated with light rays. FIG. 2A shows a schematic view of a cross section of the joint joint, and FIG. 2B shows a schematic view of the Vickers hardness distribution of the joint joint.

First, a joint joint whose distribution of Vickers hardness has been investigated will be described with reference to FIGS. 1 (a) and 2 (a). 1 (a) and 2 (a) show a schematic view of a cross section of a joint joint cut in the plate thickness direction so as to include a melt-solidified portion of the point-shaped joint portion. The joint joint 1 is formed by superimposing and joining metal plates 2a and 2b. The metal plates 2a and 2b are hot stamped steel plates having a tensile strength of 1500 MPa, and are joined by a melt-solidified portion 3 of a point-shaped joint portion.

The joint joint 1 shown in FIG. 1A is before the heat treatment for re-irradiating the melt-solidified portion 3 of the point-shaped joint portion with light rays. In the joint joint 1 shown in FIG. 2A, when the melt-solidified portion of the point-shaped joint is viewed in a plan view from the light irradiation side, the inside of the melt-solidified portion 3 is re-irradiated with light rays and re-melted in a dot shape. It has a solidified remelt solidification unit 3a and a solidification / reheating unit 3b reheated thereby.

Next, the Vickers hardness distribution of these joints will be described with reference to FIGS. 1 (b) and 2 (b). The Vickers hardness distribution diagrams shown in FIGS. 1 (b) and 2 (b) are the positions of the dotted lines X (measurement of Vickers hardness in the plate thickness direction) shown in FIGS. 1 (a) and 2 (a), respectively. It is a schematic diagram which obtained the position) over the measurement range L1 of the Vickers hardness in the direction parallel to the surface of a metal plate. The dotted line X is a position 0.2 mm from the overlapping surface of the metal plates 2a and 2b to the metal plate 2a side in the plate thickness direction. Further, L2 is a measurement range of Vickers hardness of the melt-solidified portion. L3 is a measurement range of Vickers hardness of the remelted solidified portion.

As shown in FIG. 1 (b), the Vickers hardness of the joint joint 1 before the heat treatment for re-irradiating the melt-solidified portion 3 with light rays is as hard as about HV460 inside the melt-solidified portion 3 (L2). It is almost constant. Immediately outside of L2 is not a melt-solidified portion, but it is heated to a high temperature range and hardened, so that it has a high hardness. In addition, although there is a portion having a low hardness on the outer side, this is a HAZ softened portion of the hot stamped steel sheet which is the base material.

On the other hand, as shown in FIG. 2B, the Vickers hardness of the joint joint 1 having the remelt solidification portion 3a and the solidification reheating portion 3b is determined by re-irradiating the inside of the melt solidification portion 3 with light rays. Inside the portion 3a (L3), the HV is as high as about 460. Immediately outside of L3 is not the remelt and solidification portion 3a, but it is heated to a high temperature range and hardened, so that it has a high hardness. Further, a portion having a low Vickers hardness was formed on the outside. The average hardness of the melting boundary (around a radius of about 3 mm) and the inside thereof up to a little less than 1 mm was reduced to about HV320. The HAZ softened portion of the base material on the outer side of the melt-solidified portion 3 remains as it is.

Then, when the cross tensile strength (CTS) of both joints was investigated, the cross tensile strength of the joint having the solidified and reheated portion formed by re-irradiating the inside of the molten solidified portion was found. It turned out to be higher. As a result, in the case where the point-shaped joint shown in FIG. 2A has a solidification / reheating portion that is softened from the remelting / solidifying portion, the melting boundary is tempered to reduce the hardness and improve the toughness. It was found that it was something to do. Further, even if the combination of the metal plates was changed, the improvement of CTS was confirmed in the case where the point-shaped joint portion had a solidification reheating portion softened from the remelt solidification portion.

The present invention has led to the invention described in (1) above through the above-mentioned examination process, and necessary requirements and preferable requirements will be sequentially described for such an invention.

Next, the joint joint of the present invention will be described with reference to FIG. FIG. 3 shows a cross-sectional view of the joint joint of the present invention cut in the plate thickness direction so as to include the joint portion.

In the joint 10 of the present invention, a plurality of metal plates 20a and 20b are overlapped and a light beam is irradiated from the metal plate 20a side into a limited area on the surface of the metal plate 20a to form a point-shaped joint. Then, a plurality of metal plates 20a and 20b are laminated and joined. The metal plates 20a and 20b are joined by the melt-solidified portion 30 of the point-shaped joint portion. When the melt-solidified portion 30 is viewed in a plan view from the light irradiation side, the melt-solidified portion 30 has a remelted solidified portion 30a which is a structure which remains melt-solidified in the central portion and a solidified reheated portion 30b which is reheated after solidification. , 30c.
Hereinafter, the point-shaped joints and the plurality of metal plates will be described in detail in this order.

<Dot-shaped joint>
The point-shaped joint portion has a melt-solidified portion 30 in which a plurality of metal plates 20a and 20b are superposed and melt-solidified by irradiation with light rays. The melt-solidified portion 30 of the point-shaped joint portion may or may not penetrate the plurality of metal plates as long as it is formed so as to straddle the plurality of metal plates 20a and 20b.

The point-like shape means that when the melt-solidified portion is viewed in a plan view from the irradiation side of the light beam, the outer peripheral contour of the melt-solidified portion is circular or polygonal, and melt-solidified to the center of the contour. The circular shape includes not only the case where the melt-solidified portion is circular or elliptical when the melt-solidified portion is viewed in a plan view from the light irradiation side, but also a combination of semicircles or semi-ellips having different diameters. Further, the shape of the melt-solidified portion formed by irradiating the metal plate with light rays in a spiral shape from the outer peripheral side to the center side or from the center side to the outer peripheral side is also included in a dot shape.

The width W of the melt-solidified portion 30 of the point-shaped joint (the equivalent circle diameter of the melt-solidified portion when the melt-solidified portion is viewed in a plan view from the light irradiation side) may be adjusted according to the joint strength and the like, and in particular. By way of example, but not limited to, 3 to 12 mm. It is preferably 4 to 10 mm.

(Remelt solidification part)
The remelting and solidifying portion 30a is a portion obtained by re-irradiating the inside of the melting and solidifying portion 30 of the point-shaped joint portion with light rays to melt and solidify the dots, and has a structure as it is melted and solidified. The point-like shape means that when the remelted solidified portion is viewed in a plan view from the irradiation side of the light beam, the outer peripheral contour of the remelted solidified portion is circular or polygonal, and the remelted solidified portion is melted and solidified to the center of the contour. The circular shape includes not only the case where the remelted solidified portion is circular or elliptical when the remelted solidified portion is viewed in a plan view from the irradiation side of light rays, but also a combination of semicircles or semicircles having different diameters. In addition, the shape of the remelted solidification portion formed by irradiating the metal plate with light rays in a spiral shape from the outer peripheral side to the center side or from the center side to the outer peripheral side is also included in a dot shape.

The remelt and solidified portion 30a is formed so as to include the center corresponding to the circle of the melt and solidified portion and not to include the melting boundary of the melt and solidified portion 30 when the melt and solidified portion is viewed in a plan view from the irradiation side of the light beam. However, when the melt-solidified portion is viewed in a plan view from the irradiation side of the light beam, the center corresponding to the circle of the melt-solidified portion and the center corresponding to the circle of the re-melt-solidified portion 30a do not have to coincide with each other.

Further, the remelt solidification portion 30a is formed so as to straddle the plurality of metal plates 20a and 20b in the plate thickness direction of the joint joint 10. That is, as shown in FIG. 3, the remelting and solidifying portion 30a may or may not penetrate the metal plate 20b as long as it is formed so as to straddle at least a plurality of metal plates.

The upper limit of the width Wa of the remelt solidification portion 30a (the equivalent circle diameter of the remelt solidification portion when the melt solidification portion is viewed in a plan view from the light irradiation side) is not particularly limited, and the remelt solidification portion 30a It is determined by the relationship with the width Wb of the solidifying and reheating portions 30b and 30c in the surroundings.

(Coagulation and reheating section)
The solidification and reheating portions 30b and 30c are portions formed by re-irradiating the melt and solidification portion 30 of the point-shaped joint portion with light rays so as to include a fusion boundary around the remelt and solidification portion 30a, and are formed so as to include a fusion boundary. It includes a portion softened from the portion 30a. The solidification / reheating unit 30b adjacent to the remelt / solidification unit 30a is a portion that has been reheated to a temperature equal to or lower than the melting point of the base metal and above the Ac1 point temperature. The solidification / reheating portion 30c is a portion that has been reheated to an Ac 1 point temperature or lower, has a tempered structure, and is formed at least around a melting boundary near the overlapping surface of the metal plate. When a load is applied to the joint 10 in the peeling direction, stress concentrates on the melting boundary near the overlapping surface of the metal plate, leading to fracture, so that at least the toughness of the solidification reheating portion 30c is improved.

Further, since stress tends to concentrate in the solidification / reheating portion 30c near the melting boundary of the overlapping surfaces of the metal plates, the average value of the Vickers hardness is set to Hv390 or less, and the Vickers hardness of the remelting solidification portion 30a. It is preferable that Hv70 or more is lower than the average value of. Further, by setting the width Wc of the solidification / reheating portion 30c to at least 0.5 mm, the toughness in the vicinity of the melting boundary can be improved. In order to make the width Wc of the solidification / reheating portion 30c at least 0.5 mm, the width Wb of the solidification / reheating portions 30b and 30c is preferably 1.0 to 3.0 mm.

In the measurement of the average value of the Vickers hardness of the remelt solidification section 30a and the solidification reheating section 30c, the melt solidification section 30 in contact with the overlapping surface of the metal plate is melted in the cross section in the plate thickness direction including the central axis C. Measure on the line connecting the boundaries. Then, in the remelt and solidification section 30a and the solidification and reheating section 30c, the Vickers hardness is measured at three or more points including the center and the vicinity of both ends of each portion at equal intervals, and the average value is obtained. As an example of specific measurement conditions, the hardness is measured at a pitch of 0.15 mm from both ends with a test force of 0.3 kg, and the average value of the hardness at 0.15 mm, 0.30 mm, and 0.45 mm is obtained. The vicinity of both ends is a range of 5 to 10% of the width from both ends. When there are a plurality of overlapping surfaces of the metal plates, the measurement is performed on the line connecting the fusion boundaries of the melt solidification portions 30 in contact with the overlap surfaces of the metal plates. The remelted solidified portion and the solidified and reheated portion can be distinguished by observing the microstructure.

<Multiple metal plates>
Next, a plurality of metal plates constituting the joint of the present invention will be described.

(Type and composition of metal plate)
The metal plate is not particularly limited and may be a plate of various metals, but a steel plate is preferable. The composition of the steel sheet is not particularly limited, and a steel sheet having a composition that can obtain mechanical properties and the like according to the intended use may be used. Further, when a high-strength steel sheet having a carbon content of 0.10% by mass or more is applied to the joint of the present invention, the cross tensile strength is remarkably improved, and such a steel sheet is preferably targeted.

(Thickness of metal plate)
The thickness of the metal plate is not particularly limited and can be in the range of 0.5 to 3.2 mm. Even if the plate thickness is less than 0.5 mm, the effect of improving the joint strength of the joint can be obtained, but since the joint strength affects the plate thickness, the effect of improving the strength of the entire joint is reduced, and the joint is joined. The scope of application is limited. Further, even if the plate thickness exceeds 3.2 mm, the effect of improving the joint strength of the joint portion can be obtained, but the applicable range of the joint joint is limited from the viewpoint of weight reduction of the member.

(Surface treatment film of metal plate)
The plurality of metal plates may include at least one metal plate having a surface treatment film formed on both sides or one side of the joint. The surface treatment film includes a plating film, and may further include a coating film and the like. Examples of the plating film include zinc plating, aluminum plating, zinc / nickel plating, zinc / iron plating, zinc / aluminum / magnesium-based plating, and the plating manufacturing method includes hot-dip plating and electroplating. It may also be hot stamped galvanized or aluminum plated.

(Metal plate form)
The form of the metal plate may be at least as long as the portion forming the joint is plate-shaped, and the entire metal plate does not have to be a plate. For example, it includes a flange portion of a member press-molded into a specific shape having a hat-shaped cross section, a flat portion of a pipe, and the like. The number of metal plates to be stacked is not limited to two, and may be three or more. Further, the type, composition and thickness of each metal plate may be the same or different from each other. Further, the joint is not limited to those composed of separate metal plates, and may be a lap joint joint formed by molding one metal plate into a predetermined shape such as a tubular shape and overlapping the ends.

Hereinafter, an example of a lap joint in an automobile is shown, although not limited to this.
In the case of A-pillar, it is a combination of 270-340 MPa class alloyed hot-dip galvanized steel sheet, 590-1800 MPa class non-plated steel sheet or hot stamped steel sheet, and 590-1800 MPa class non-plated steel sheet or hot stamped steel sheet. A lap joint is exemplified.

In the case of B-pillar, it is a combination of three layers of alloyed hot-dip galvanized steel sheet with tensile strength of 270-340 MPa class, 590-1800 MPa class non-plated steel sheet or hot stamped steel sheet, and 440-980 MPa class non-plated steel sheet. A lap joint is exemplified.

In the case of side sill, a lap joint joint consisting of a combination of 270-340 MPa class alloyed hot-dip galvanized steel sheet, 590-1800 MPa class alloyed hot-dip galvanized steel sheet, and 590-1800 MPa class alloyed hot-dip galvanized steel sheet. Is exemplified.

In the case of floor members, the floor panel of 270-590 MPa class alloyed hot-dip galvanized steel sheet and the floor member of 440-1800 MPa class non-plated steel sheet or alloyed hot-dip galvanized steel sheet are lap-bonded in a double-layered combination. A joint is exemplified.

Next, the manufacturing method of the lap joint of the present invention (hereinafter, referred to as "the manufacturing method of the present invention") will be described.
The manufacturing method of the present invention
(A) When a plurality of metal plates are superposed, irradiated with light rays, and viewed in a plan view from the surface side of the metal plates, the outer contour is substantially circular, and a punctate joint formed by melting and solidifying to the center thereof. as well as,
(B) When the inside of the point-shaped joint is re-irradiated with a light beam and the melt-coagulated portion is viewed in a plan view from the irradiated side of the light beam, the outer contour is substantially circular and re-melted to the center. It includes solidifying and reheating the molten boundary so that it softens from the remelted solidified portion.

First, (a) when a plurality of metal plates are superposed, irradiated with light rays, and viewed in a plan view from the surface side of the metal plates, the outer contour is substantially circular, and a point-like joint formed by melting and solidifying to the center thereof is formed. This will be described with reference to FIG.

FIG. 4 is a perspective view showing an outline of the formation of a point-shaped joint. FIG. 4A shows an outline of irradiating light rays with different irradiation diameters, FIG. 4B shows an outline of irradiating light rays with a wide condensing area, and FIG. 4C is formed. A dotted joint is shown.

FIG. 4A shows an example of a method of irradiating the light ray 50, which irradiates the light ray 50 with different irradiation diameters. In this figure, the planned irradiation points 60a of the light beam 50 are shown by dotted lines, and three planned irradiation points 60a having different irradiation diameters are shown.

In the formation of the point-shaped joint portion, first, a plurality of metal plates 20a and 20b are overlapped, and light rays 50 are irradiated from one of the metal plates 20a side to perform the joint. In the irradiation of the light ray 50, when the planned irradiation portion 60a is viewed in a plane from the irradiation side of the light ray 50, the light ray is scanned in a substantially circular shape as shown by a white arrow. At that time, the light beam 50 is irradiated to the outer scheduled irradiation portion 60a, and then to the inner scheduled irradiation portion 60a, but also to the inner scheduled irradiation portion 60a, and then to the outer scheduled irradiation portion 60a. You may go. The scanning direction of the light beam is not particularly limited, and may be clockwise or counterclockwise.

Further, when the planned irradiation point 60a from the irradiation side of the light beam 50 is viewed in a plan view, the outer peripheral shape of the planned irradiation point 60a of the light beam 50 is a circle, but a semicircle or a semicircle having an elliptical shape, a polygonal shape, or a different diameter is used. It may be a combined shape or a spiral shape. When the planned irradiation point 60a of the light ray 50 has a spiral shape, the light beam 50 is irradiated from the outer end portion of the spiral irradiation planned irradiation portion 60b toward the inner end portion or in a spiral shape. The light beam is scanned in a spiral shape from the inner end of the planned portion 60b toward the outer end. The direction of the spiral is not particularly limited, and may be clockwise or counterclockwise.

In FIG. 4A, three planned irradiation points having different diameters are illustrated, but the number of planned irradiation points having different diameters can be increased or decreased according to the focal area of the light beam and the joint area of the point-shaped joints. Can be done.

FIG. 4B shows another example of the method of irradiating the light ray 50, which irradiates the light ray 50 with a wide condensing area. In this figure, the planned irradiation portion 60b of the light beam 50 is shown by a dotted line. Then, the light beam 50 is irradiated at one time by widening the light collecting area.

By irradiating the light beam 50 as shown in FIG. 4 (a) or FIG. 4 (b), the melted melted portion solidifies from the outside to the center side, and the point-shaped joint is formed as shown in FIG. 4 (c). The melt-solidified portion 30 of the above can be formed.

Further, when one or more metal plates having a surface treatment film formed on the plurality of metal plates are used, the light beam 50 may be irradiated to the outer scheduled irradiation portion 60a and then to the inner scheduled irradiation portion 60a. preferable. As a result, it becomes easy to collect the film which has become a gas that causes defects in the joint portion near the center of the molten portion and remove it by stirring. Even if the light beam 50 is irradiated to the inner scheduled irradiation portion 60a and then to the outer scheduled irradiation portion 60a, or if the light collecting area of the light ray 50 is widened, the film that has become a gas is formed. Since it can be removed from the molten portion, it does not exclude the adoption of these light beam irradiation methods.

Next, (b) when the inside of the point-shaped joint is re-irradiated with a light beam and the melt-solidified portion is viewed in a plan view from the light-emitting side, the outer contour is substantially circular and the shape is re-melt-solidified to the center. It will be described that the molten boundary is reheated so as to be softened from the remelted solidified portion while being remelted and solidified (dotted).

In the heat treatment of the punctate joint, the temperature of the melt-solidified portion 30 of the punctate joint obtained by the method shown in FIG. 4 is below a predetermined temperature, for example, in the case of a steel plate, the Ms point is −50 ° C. (Ms point: marten). Wait until the temperature becomes lower than the site transformation start temperature), and then irradiate the inside of the melt solidification portion 30 with the light beam 50 from the metal plate 20a side. The inside means the inside of the melt-solidified portion 30 excluding the melt boundary of the melt-solidified portion 30.

When the temperature of the melt-solidified portion 30 is Ms point −50 ° C. or lower, a certain amount or more of martensite is generated in the steel sheet. Therefore, by heat-treating the melt-solidified portion 30 of the point-shaped joint, the martensite is formed. Is tempered and softened, improving joint strength. The lower limit of the temperature of the melt-solidified portion 30 at the start of the heat treatment of the melt-solidified portion 30 of the point-shaped joint is not particularly limited, but is preferably Ms point −250 ° C. or lower. This is because a general steel sheet completes martensitic transformation at an Ms point of −250 ° C.

Next, among the irradiations of the light rays 50 in the heat treatment of the point-shaped joints, the scanning of the light rays 50 will be described with reference to FIG.
FIG. 5 is a perspective view showing an outline of heat treatment of the point-shaped joint. FIG. 5 (a) shows an outline of irradiating light rays with different irradiation diameters, FIG. 5 (b) shows an outline of irradiating light rays with a wide condensing area, and FIG. 5 (c) shows remelting. A punctate joint having a solidified portion and a solidified and reheated portion is shown.

FIG. 5A shows an example of a method of irradiating the planned remelting portion with the light beam 50, and irradiates the light beam with different irradiation diameters. In this figure, the planned irradiation points 70a of the light beam 50 are shown by dotted lines, and two planned irradiation points 70a having different irradiation diameters are shown inside the melt-solidified portion 30.

In the irradiation of the light beam 50, the light beam is scanned in a substantially circular shape as indicated by the white arrow. At that time, the light beam 50 is irradiated to the inner scheduled irradiation portion 70a, and then to the outer scheduled irradiation portion 70a, but also to the outer scheduled irradiation portion 70a, and then to the inner scheduled irradiation portion 70a. You may go. The scanning direction of the light beam is not particularly limited, and may be clockwise or counterclockwise.

When the melt-solidified portion 30 is viewed in a plan view from the irradiation side of the light beam 50, the planned irradiation portion 70a of the light beam 50 is remelted into a dot shape including the center corresponding to the circle of the melt-solidified portion 30, and the melting boundary of the melt-solidified portion 30 is formed. Set to be burned back.

Further, when the joint portion is viewed in a plan view from the irradiation side of the light ray 50, the outer peripheral shape of the planned irradiation portion 70a of the light ray 50 is a circle, but a shape obtained by combining an ellipse, a polygonal shape, and a semicircle or a semicircle having different diameters. , May have a spiral shape. Further, although two planned irradiation points having different diameters are illustrated, the number of planned irradiation points having different diameters can be increased or decreased depending on the focal area of the light beam and the area of the melt-solidified portion of the point-shaped joint. ..

FIG. 5B shows another example of a method of irradiating the planned remelting portion with the light beam 50, in which the light collecting area is widened and the light beam 50 is irradiated. In this figure, the planned irradiation portion 80b of the light beam 50 is shown by a dotted line inside the melt-solidifying portion 30. Then, the light beam 50 is irradiated at one time by widening the light collecting area. Also in this example, the planned irradiation portion 80b of the light beam 50 is remelted into a point shape including the circular equivalent center of the melt solidification portion 30 when the melt solidification portion 30 is viewed in a plan view from the irradiation side of the light ray 50, and the melt solidification portion 30 is formed. The melting boundaries of 30 are set to be burned back.

By irradiating the light beam 50 as shown in FIGS. 5 (a) and 5 (b), the melt-solidified portion 30 is viewed in a plan view from the irradiation side of the light beam 50 as shown in FIG. 5 (c). The remelt and solidification portion 30a is formed in a dot shape including the circular equivalent center of the melt and solidification portion, and the solidification and reheating portions 30b and 30c are formed around the remelt and solidification portion 30a. Then, the solidification / reheating portion 30c including the melting boundary is tempered, and the toughness is improved.

Further, in the formation of the point-shaped joint and the heat treatment of the molten boundary of the point-shaped joint, the light beam irradiation method may be the same irradiation method or different irradiation methods. For example, even if light rays are irradiated with different irradiation diameters to form point-shaped joints, and light rays are irradiated with different irradiation diameters to heat the melting boundary of the point-shaped joints, the condensing area is widened. Then, the point-shaped joint may be formed by irradiating the light beam, and the molten boundary of the point-shaped joint may be heat-treated by irradiating the light with different irradiation diameters.

Next, among the irradiations of the light beam 50, the heating temperatures of the solidification and reheating portions 30b and 30c will be described.
Of the melt-solidified portions 30 of the point-shaped joints, at least the region within 0.5 mm from the melt boundary near the overlapping surfaces of the metal plates 20a and 20b is tempered (the solidified reheated portion 30c is obtained). It is better to reheat (so that it can be done).

In order to burn back a region in the range of 0.5 mm from the melting boundary near the overlapping surface, the maximum temperature reached in this range is a predetermined temperature of Ac 1 point or less (for example, 500 ° C. or higher and 700 ° C. or lower). The light beam 50 is applied to the inside of the melt-solidified portion 30. As the temperature of the solidification reheating unit 30c, the temperature measured on the surface of the steel sheet can be used as a representative value. The temperature can be measured using a radiation thermometer or a thermocouple.

In order to obtain such a temperature, the diameter equivalent to the circle of the planned remelting portion (the portion scheduled to be irradiated with the light beam) or the width Wb of the solidified reheating portion to be formed and the temperature in the above range during the re-irradiation of the light beam are obtained in advance. The relationship between the above and the relationship between the re-irradiation time of the light beam and the temperature in the above range, etc., the circle-equivalent diameter of the planned remelting location (the planned irradiation location of the light beam), the width Wb of the solidification reheating part, and the light beam This can be done by adjusting the re-irradiation time and the like. Further, in order to set the solidification / reheating portion 30c to 500 ° C. or higher and 700 ° C. or lower, it is exemplified that the irradiation of light is adjusted so that the width Wb of the solidification / reheating portion is 1.0 to 3.0 mm. It is preferably 1.5 to 2.5 mm.

Next, the light rays used in the formation of the point-shaped joints and the heat treatment of the point-shaped joints will be described. A laser is generally used as the light beam, and the type thereof is not particularly limited, but a remote joining device is preferable. The remote joining device uses a galvano mirror attached to the tip of the robot arm to move light rays between joining points at high speed, which makes it possible to significantly reduce the joining work time. Further, as the oscillator, a gas excitation type, a solid excitation type, a semiconductor type and the like can be used.

Further, as the joining conditions, the conventional conditions can be adopted. For example, the bonding conditions can be such that the output is 2 to 30 kW, the light beam diameter of the condensing surface is 0.1 to 8.0 mm, and the bonding speed is 0.1 to 60 m / min.

Further, assembling an automobile consists of a plurality of joining steps, but when the manufacturing method of the present invention is carried out in one step, joining and remelting by light irradiation are carried out at each joining point. However, in order to reduce the waiting time for cooling to the Ms point of −250 ° C. or lower, more preferably, a plurality of melt bondings are carried out by light irradiation, and then a plurality of remelts are carried out by light irradiation. Is preferable. Further, when the manufacturing method of the present invention is carried out in a plurality of joining steps, the waiting time for cooling can be eliminated by setting the melt joining step by light irradiation and the remelting step by light irradiation as separate steps.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Table 1 shows steel plates to be joined.

Two steel plates of the same type shown in Table 1 were superposed and joined by a fiber laser using a remote joining device having a galvanometer mirror to prepare a test piece having a point-shaped joint. Table 2 shows the conditions for forming the point-shaped joints. The ray diameter is the diameter of the ray on the condensing surface.

Next, the point-shaped joints of each test piece were heat-treated. In this heat treatment, when the melt-solidified portion is viewed in a plan view from the light irradiation side, the center of the melt-solidified portion and the re-melted-solidified portion are aligned with each other, and the re-melted-solidified portion is formed so as to penetrate the test piece. It was. Table 3 shows the heat treatment conditions for the point-shaped laser joint. The ray diameter is the diameter of the ray on the condensing surface. In the heat treatment, the same remote joining device as for forming the point-shaped joint was used.

Table 4 shows the width Wb of the solidification / reheating portion, the average Vickers hardness A of the remelted solidification portion (excluding shrinkage cavities), and the average of 0.5 mm from the melting boundary of the melt solidification portion for the test pieces after the heat treatment. The Vickers hardness B, the difference between the average Vickers hardness A and B, and the cross tensile strength (CTS) are shown.

For CTS, the method described in JIS Z3137 as a strength test method for spot bonding was adopted. After joining, the steel sheet was cut and polished through the center of the punctate joint and perpendicular to the plate surface, the size of the shrinkage cavities was observed, and the Vickers hardness was measured. The Vickers hardness A of Comparative Examples 1, 5 and 14 is the average Vickers hardness of the central portion of the melt-solidified portion.

No. In Nos. 2, 4, 6 to 8, 10 to 13, the point-shaped joints are heat-treated, and in order to satisfy the configuration specified by the joint of the present invention, the range is 0.5 mm from the melting boundary of the melt-solidified portion. The toughness is improved and the cross tensile strength (CTS) is high.

On the other hand, No. 1, No. 5 and No. In No. 14, since the point-shaped joints were not heat-treated, the toughness of the melt boundary of the melt-solidified portion was not improved, and the cross tensile strength (CTS) was low. In addition, No. In No. 9, since the entire melt-solidified portion was heat-treated, the toughness of the melt boundary of the melt-solidified portion was not improved, and the cross tensile strength (CTS) was low.

According to the present invention, since the solidification reheating portion having excellent toughness is provided near the melting boundary of the point-shaped joint portion, the joint strength of the lap joint, particularly the cross tensile strength (CTS) can be improved. It is possible to improve the reliability of the joint joint. Then, by applying the joint of the present invention to an automobile part, the reliability of the automobile part can be improved. Therefore, the present invention has high industrial applicability.

1 Joint joint 2a, 2b Metal plate 3 Point-shaped joint melt solidification part 3a Remelt solidification part 3b Solidification reheating part 10 Joint joint 20a, 20b Metal plate 30 Point-shaped joint melt solidification part 30a Remelt solidification Part 30b Solidification reheating part 30c Solidification reheating part 50 Rays 60a, 60b Scheduled irradiation location 70a, 70b Scheduled irradiation location X Vickers hardness measurement position in the plate thickness direction L1 Vickers hardness measurement range in the direction parallel to the metal plate surface L2 Measuring range of Vickers hardness of melt-solidified part L3 Measuring range of Vickers hardness of re-melted-solidified part C Central axis W Width of melt-solidified part Wa Width of re-melted-solidified part Wb Width of solidifying and reheating part Width of solidification and reheating part of

Claims (6)

In a lap joint that is composed of a plurality of lapped metal plates and has a point-shaped light irradiation joint.
The point-shaped joint has a melt-solidified portion that straddles the plurality of metal plates.
The melt-solidified portion has a remelt-solidified portion and a solidified / reheated portion.
When the melt-solidified portion is viewed in a plan view, the re-melt-solidified portion has a dot shape including the center of the melt-solidified portion and straddles the plurality of metal plates.
The solidification and reheating portion is located around the remelt and solidification portion, and is 0.5 mm from the fusion boundary between the fusion and solidification portion and the base metal and the fusion boundary toward the remelt and solidification portion. A lap joint that includes a range and includes a portion that is softened from the remelted and solidified portion. Among the solidification and reheating portions, the average value of Vickers hardness in the range of 0.5 mm from the melting boundary of the overlapping surface of the metal plates toward the remelting and solidifying portion is Hv390 or less and The lap joint joint according to claim 1, wherein the Vickers hardness of the remelted solidified portion is lower than the average value of Hv70 or more. The lap joint according to claim 1 or 2, wherein the plurality of metal plates include one or more metal plates having a surface treatment film. In a method for manufacturing a lap joint, in which a plurality of metal plates are superposed and irradiated with a light beam having a high power density to join them.
One of the overlapped metal plates is irradiated with a light beam having a high power density to form a dot-shaped joint having a melt-solidified portion that is melt-solidified in a dot shape over the plurality of metal plates.
When the melt-solidified portion is viewed in a plan view from the irradiation side of the light beam having a high power density, the light beam having the high power density is re-irradiated inside the melt-solidified portion, and includes the circular equivalent center of the melt-solidified portion. A remelt solidification portion is formed by remelting and solidifying across the plurality of metal plates in a dotted manner , and a melting boundary between the melt solidifying portion and the base metal is formed around the remelting and solidifying portion. to form a solidified reheating portion from the fusion boundary includes the range of 0.5mm toward the remelted and solidified portion, further to the re-melt the solidified reheating portion by adjusting the re-heating conditions at that time A method for manufacturing a lap joint, which is characterized by being softened from a solidified portion. The re-irradiation of the light beam having a high power density is the distance from the outer end portion of the remelt solidified portion of the remelted solidified portion to the melting boundary of the point-shaped joint portion in the plate thickness direction cross section of the plurality of metal plates. The method for manufacturing a lap joint according to claim 4, wherein the lap joint is set to 1.0 to 3.0 mm. The method for manufacturing a lap joint according to claim 4 or 5, wherein one or more metal plates having a surface treatment film formed on the plurality of metal plates are used.

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