JP2007075872A - Laser brazing welding process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser brazing welding process, in which welding strength sufficient for welding of an alloyed hot dip galvanized steel sheet and an aluminum based sheet material is obtained. <P>SOLUTION: The surface of an alloyed hot dip galvanized steel sheet as a base material W1 on the lower side is overlapped with an aluminum based sheet material as a base material W2 on the upper side. Then, the corner part formed by the base material W1 on the lower side and the edge face e of the base material W2 on the upper side is irradiated with laser light L1, L2 in a twin spot form, and by the melting and solidifying of a wire 8, a bead 11 is formed, thus the base materials W1, W2 are welded in the form of a lap fillet-welded joint. Prior to the melting of the wire 8 by the irradiation of the laser light L2 on the rear side, the plated layer at the weld zone of the base material W1 on the lower side is removed by the laser light L1 on the front side. Directly after that, by allowing the laser light L2 to follow the part from which the plated layer is removed, the wire 8 is melted and solidified. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a joining method for laser brazing a steel plate and an aluminum-based plate material, which are different metals, through, for example, a Zn-Al-based brazing material (a filler metal), and particularly an alloy among galvanized steel plates. The present invention relates to a laser brazing joining method suitable for joining a galvannealed steel sheet and an aluminum-based sheet.

  For the purpose of reducing the weight of an automobile body, a part of the body panel using an aluminum-based material has been put to practical use. Joining is required. The melting point of aluminum materials is around 600 ° C, the melting point of steel is about 1300-1500 ° C, and the melting points of the two materials are very different, and when both materials are melted, a brittle intermetallic compound of aluminum and iron is produced. Since the bonding strength is lowered, it is difficult to perform high-strength bonding by the welding method described in Patent Document 1, for example.

On the other hand, in automobile body parts, steel sheet parts are often galvanized for the purpose of rust prevention. For example, aluminum-based materials and steel sheets via Zn-Al brazing filler metal A joining method for brazing (brazing) has been developed, and a so-called laser brazing method using a laser capable of finely controlling the amount of heat input as a heat source for melting the brazing material, for example, as described in Patent Document 2 By adopting a simple laser brazing method, bonding strength is secured while suppressing the formation of intermetallic compounds.
JP-A-4-231190 JP 2003-205382 A

  However, high bonding strength can be obtained under the laser brazing method only when hot-dip galvanized steel sheet is used. When alloyed hot-dip galvanized steel sheet is used, the processing conditions on the laser side are controlled. However, there is a problem in that the formation of intermetallic compounds cannot be suppressed only by this, and sufficient bonding strength cannot be obtained.

  In addition, the alloyed hot-dip galvanized steel sheet is a steel sheet in which an alloy layer is formed by Fe-Zn interdiffusion by performing an alloying treatment after hot-dip galvanizing to the steel sheet in order to suppress the activity of the galvanized layer. That is, it means that the hot-dip galvanized steel sheet is heated to diffuse Fe in the base steel sheet into the Zn plating layer to form an Fe—Zn alloy.

  More specifically, in the conventional laser brazing method, the combination of a hot-dip galvanized steel sheet and an aluminum-based plate material and a combination of an alloyed hot-dip galvanized steel plate and an aluminum-based plate material are to be joined, for example, in the form of a lap fillet joint. If (in any case, the lower base metal is a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet), the laser power, laser spot diameter, joining speed, etc. can be selected appropriately. Even in this combination, it is possible to obtain a good bonding state in appearance.

  On the other hand, when both are compared in terms of the joint strength after brazing, when the alloyed hot-dip galvanized steel sheet is used as the base material, the joint strength is only about 60% as compared with the case where the hot-dip galvanized steel sheet is used as the base material. I can't get it. This is because, when a hot-dip galvanized steel sheet is used as a base material, for example, a boundary portion between a bead formed by melting a Zn-Al-based brazing material (a filler metal) and a hot-dip galvanized steel sheet as a base material However, although a brittle alloy layer of Al and Zn is formed, the thickness is as small as about 0.5 μm and cannot be a factor for reducing the bonding strength.

  On the other hand, when the alloyed hot-dip galvanized steel sheet is used as a base material, since the plating layer from the beginning is an alloy of Zn and Fe as a special property of the base material, The thickness of the alloy layer formed at the boundary with the alloyed hot-dip galvanized steel sheet, which is the base material, is remarkably increased to about 20 μm, and this is presumed to be a factor that decreases the bonding strength. This phenomenon cannot be avoided even if the joining conditions such as the laser output described above are changed, and particularly in the case of the lap fillet joint having the base material of the alloyed hot-dip galvanized steel sheet and the aluminum-based sheet. It is difficult to improve the bonding strength.

  The present invention has been made paying attention to such a problem, and in particular, laser brazing bonding capable of obtaining a necessary and sufficient bonding strength for bonding the above-mentioned galvannealed steel sheet and aluminum-based sheet. Is to provide a method.

  The invention according to claim 1 is a laser brazing joint in which a brazing filler metal is melted with a laser beam and a galvanized steel sheet as a base material and an aluminum-based sheet material are joined in the form of a fillet joint. In this method, prior to laser brazing, the plating layer on the galvanized steel sheet side is removed, and immediately after that, the brazing material is melted by laser light irradiation so as to follow the removed portion. The base materials are joined together.

  Specifically, as described in claim 2, after the aluminum-based plate material is overlaid on the galvanized steel plate that is the base material, the corner portion formed by the end surface of the galvanized steel plate and the aluminum-based plate material, A bead is formed with the molten brazing material to join the base materials.

  More specifically, the removal of the plated layer of the galvanized steel sheet can be performed by mechanical means such as polishing. Here, the removal of the plated layer of the galvanized steel sheet is also performed by laser as described in claim 3. In particular, in terms of simplifying the equipment configuration, a pair of laser beams are irradiated to the base material with a pair of laser beams before and after the brazing traveling direction as described in claim 4. Relative movement of light and base material in the direction of brazing, so that the brazing material is melted with the laser beam on the rear side and the base materials are joined together while removing the plating layer of the galvanized steel sheet with the front side laser beam It is desirable to do.

  In this case, as described in claim 5, the pair of front and rear laser beams that are offset from each other in the brazing progression direction are offset from each other in the width direction of the bead so that the front laser beam irradiates only the galvanized steel sheet. It is more desirable to prevent the aluminum-based plate material from melting.

  Further, as the brazing material (melting material), for example, a zinc-aluminum (Zn-Al) material is used.

  Therefore, in at least the invention described in claim 1, for example, after removing the Fe—Zn alloy, which is the plating layer on the surface of the alloyed hot-dip galvanized steel sheet, which is one base material, When brazing (brazing) with the aluminum base plate, which is the other base material, by melting the brazing material, the production of intermetallic compounds accompanying the brazing is suppressed, and a hot dip galvanized steel sheet was used as the base material. The joint strength equivalent to the case can be obtained.

  According to the first aspect of the present invention, when a galvanized steel sheet and an aluminum-based sheet material are joined by brazing in the form of a lap fillet joint, alloying and melting is performed as a galvanized steel sheet as one base material. Even when a galvanized steel sheet is used, necessary and sufficient bonding strength can be obtained.

  FIG. 1 and the subsequent drawings show a more specific embodiment of the laser brazing joining method according to the present invention. As shown in FIG. 2, the galvannealed steel sheet as the lower base material W1 and the upper galvanized steel sheet as shown in FIG. The example in the case of carrying out brazing joining (laser brazing joining) by laser beam irradiation in the form of a fillet joint joint with the aluminum-type board | plate material which is base material W2 is shown. In particular, FIG. 1 shows an example of a laser processing head 1 used in the laser brazing joining method.

  As shown in FIGS. 1A and 1B, the laser processing head 1 is attached to the tip of an arm 3 of an articulated robot via a mounting bracket 2, and the laser processing head 1 is connected to an optical fiber cable 4. Is connected to the laser oscillator 5. The laser processing head 1 incorporates a predetermined optical system such as a condenser lens and a prism, and before and after the laser light introduced into the laser processing head 1 via the optical fiber cable 4 is adjacent in the joining traveling direction. The laser beam L1 is divided into a pair of laser beams L1 and L2, and then condensed and then irradiated to the processing points P1 and P2 on the base materials W1 and W2 in a so-called twin spot system.

  A wire feeding device 7 is attached to the mounting bracket 2 via an auxiliary bracket 6. The wire feeder 7 is connected with a conduit tube 9 for guiding a wire 8 which is a brazing material (a filler metal) and an assist gas supply hose 10 for supplying, for example, argon gas as an assist gas. Yes, as shown in FIG. 2 in addition to FIG. 1, while continuously supplying a wire (for example, Zn-Al-based) 8 at a predetermined speed toward the irradiation position of the laser beam L2 on the rear side that is the processing point P2, At the same time, argon gas is blown as an assist gas. The blowing direction and the blowing amount are set so that the argon gas reaches not only the rear processing point P2 but also the front processing point P1.

  Therefore, according to the present embodiment, as shown in FIGS. 1 and 2, the upper base material W2 is superimposed on the lower base material W1, and then the robot is applied to the base materials W1 and W2. The laser processing head 1 held on the side arm 3 is moved at a constant speed, and a corner portion C (see FIG. 3B) formed by the lower base material W1 and the end surface e of the upper base material W2. )) So that the twin-spot laser beams L1 and L2 are radiated along with each other, and the bead 11 is formed by melting the wire 8 which is a brazing material, thereby brazing the base materials W1 and W2 to each other (brazing). Join with.

  In this case, the laser light excited and amplified by the laser oscillator 5 is introduced into the laser processing head 1 via the optical fiber cable 4. The laser beam introduced into the laser processing head 1 is divided into a pair of front and rear laser beams L1 and L2 that are offset from each other in the bonding traveling direction by an internal optical system as described above, and is of a so-called twin spot type. Then, at the corner portion C formed by the lower base material W1 and the end surface e of the upper base material W2 described above, the front laser light L1 is the processing point P1, and the rear laser light L2 is the processing. Each point P2 is irradiated.

  Since the laser beam L1 is set in advance so as to irradiate only the lower base material W1 without reaching the upper base material W2, as will be described later, the front side laser beam P1. The plating layer of the galvannealed steel sheet which is the lower base material W1 is removed by heat input by the irradiation of L1. The portion from which the plating layer has been removed is immediately irradiated with the rear laser beam L12 at the rear processing point P2, and at the same time, the wire 8 is supplied to the laser beam L2 irradiation site. For this irradiation, the wire 8 is melted to form a bead 11, and the lower base material W1 and the upper base material W2 from which the plating layer has been removed are brazed and joined together.

  At this time, since both the processing points P1 and P2 which are the irradiated portions of the laser beams L1 and L2 are set so that argon gas reaches the assist gas, the removal of the plating layer by the irradiation of the front laser beam L1 and Since both brazing joining by irradiation with the laser beam L2 on the rear side is performed in an argon gas atmosphere, generation of an oxide film in a portion where the plating layer is removed is suppressed.

  3A shows a plan view of FIG. 2, FIG. 3B shows a cross-sectional view of FIG. 3A, and Table 1 shows various laser beams L1 and L2 on the front and rear sides. Indicates conditions. Table 1 shows an alloyed hot-dip galvanized steel sheet having a thickness of 0.8 mm as the lower base material W1, and a 6000 series aluminum alloy plate (corrosion-resistant aluminum plate) having a thickness of 1.2 mm as the upper base material W2. ) Shows the data when each is used.

  The irradiation condition of the front side laser beam L1 is an indispensable condition that only the lower base material W1 is given laser energy without melting the upper base material W2 and only the plating layer on the surface is removed. The irradiation condition of the rear laser beam L2 is an essential condition that brazing having the required bonding strength is possible. Table 1 shows the laser energy density, the moving speed, and the laser spot diameter R2 in terms of the laser output of the rear laser beam L2 that is directly involved in the laser brazing.

  Here, in order to apply appropriate laser energy to the upper base material W2 and the lower base material W1 so as to input heat, the center of the irradiation position of the rear laser light L2 is set to the end surface of the upper base material W2. In FIG. 3, the offset amount c is set to 1.2 mm, and 20% of the spot diameter R2 (= 4.0 mm) of the laser light L2 is the upper base material. That is, the offset amount c of the rear laser beam L2 is set to 30% of the laser spot diameter R2 so as to achieve good bonding with an appropriate amount of heat input.

  On the other hand, the laser energy density, moving speed, and laser spot diameter R1 in terms of laser output of the front laser beam L1 are also as shown in Table 1. As the irradiation condition of the front laser beam L1, it is necessary to remove the plating layer of the lower base material W1 in advance in a range equal to or larger than the irradiation range of the rear laser beam L2, and the spot diameter of the front laser beam L1 R1 is set to R1 = 4.2 mm based on the equation (1). Here, it is assumed that the plating layer of the lower base material W1 is removed 1 mm wider than the range where brazing is performed with the rear laser beam L2.

R1 = (1-0.2) × R2 + 1 (1)
In addition, as described above, the laser beams L1 and L2 on the front side and the rear side need to be offset from each other not only in the bonding progress direction but also in the width direction of the bead 11, as described above. The irradiation position offset amount d between L1 and L2 is set to d = 2 mm from d = R2 × 0.5.

  Further, the inter-spot distance b in the direction in which the front and rear laser beams L1 and L2 travel is set to b = 4.1 mm based on b = (R1 + R2) × 0.5.

  In FIG. 4, the example which compared the shear strength in the junction part of various lap fillet joints is shown. Conventional methods (1) and (2) are both based on the conventional laser brazing joining method. In the conventional methods (1), (2) and the present invention, a 6000 series aluminum alloy plate is used as the upper base material W2, and in the conventional method (1), an alloyed hot-dip galvanized steel sheet is used as the lower base material W1. In the conventional method (2), similarly, a hot dip galvanized steel sheet is used as the lower base material W1.

  In the conventional laser brazing method, when an alloyed hot-dip galvanized steel sheet is used as the other base material combined with the aluminum-based plate (conventional method (1)), a hot-dip galvanized steel sheet was used as the other base material. As described above, only about 60% of bonding strength can be obtained compared to the conventional method (conventional method (2)). However, when the conventional method (1) and (2) in FIG. ing.

  On the other hand, according to the laser brazing joining method of the present invention, even when one base material W2 is used as an aluminum-based plate and the other base material W1 is used as an galvannealed steel sheet, at least the conventional method ( 2) That is, it can be understood that the bonding strength is improved to the same level as when a hot-dip galvanized steel sheet is used as the base material W1 combined with the aluminum-based plate material. Prior to laser brazing, the plating layer of the alloyed galvanized steel sheet which is the lower base material W1 is removed in advance, and as shown in FIG. It is greatly influenced by the fact that the alloy layer formed at the boundary between the bead 11 formed by melting and solidifying and the alloyed galvanized steel sheet as the lower base material W1 is not as thick as the conventional method. Guessed.

It is a figure which shows an example of the laser processing head used for the laser brazing joining method of this invention, (A) is the side explanatory drawing, (B) is the front explanatory drawing similarly. The principal part expansion perspective view of the laser brazing junction part in FIG. It is a figure which shows the detail of a laser brazing junction part, (A) is plane explanatory drawing of FIG. 2, (B) is sectional explanatory drawing of the figure (A). Explanatory drawing which compared the shear strength in a laser brazing junction part by the conventional construction method and this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser processing head 3 ... Arm of robot 5 ... Laser oscillator 7 ... Wire feeder 8 ... Wire (brazing material or filler material)
DESCRIPTION OF SYMBOLS 11 ... Bead C ... Corner part e ... End surface of upper side base material L1 ... Front side laser beam L2 ... Rear side laser beam P1 ... Front side processing point P2 ... Rear side processing point W1 ... Lower side base material (alloy) Galvanized steel sheet)
W2 ... Upper base material (aluminum-based plate material)

Claims (7)

A laser brazing joining method in which a brazing material is melted with a laser beam, and a galvanized steel sheet and an aluminum-based sheet material as a base material are joined in the form of a fillet joint,
Prior to laser brazing, the plating layer on the galvanized steel sheet side is removed, and immediately after that, the brazing material is melted by laser light irradiation so as to follow the part from which the plating layer has been removed. A laser brazing joining method characterized by joining.   Overlay the aluminum base material on the galvanized steel sheet, which is the base material, and then form a bead with the molten brazing material at the corner formed by the end face of the galvanized steel sheet and the aluminum base material. The laser brazing joining method according to claim 1, wherein joining is performed.   3. The laser brazing joining method according to claim 2, wherein the removal of the plating layer of the galvanized steel sheet is performed by laser light irradiation. Irradiate the base material with a pair of laser beams before and after the brazing direction, and relatively move the pair of laser beams and the base material in the brazing direction,
The laser brazing method according to claim 3, wherein the base material is joined by melting the brazing material with the rear laser beam while removing the plating layer of the galvanized steel sheet with the front laser beam.   5. The pair of front and rear laser beams that are offset from each other in the direction of brazing progression are offset from each other in the width direction of the bead so that the front laser beam irradiates only the galvanized steel sheet. Laser brazing joining method.   The laser brazing joining method according to any one of claims 1 to 6, wherein the removal of the plating layer of the galvanized steel sheet and the joining of the base materials by melting the brazing material are performed in an assist gas atmosphere.   7. The laser brazing joining method according to claim 1, wherein the one base material is an alloyed hot-dip galvanized steel sheet.

Images