JP2005059089A - Laser welding method of galvanized steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method in which generation of blowholes is suppressed by eliminating a harmful effect of zinc vapor that is produced in laser welding of a galvanized steel sheet. <P>SOLUTION: In laser welding of an object to be welded in which galvanized steel sheets are combined with each other or in which a galvanized steel sheet is combined with other metal, by containing Al in the molten metal formed, a vapor-like zinc produced at the time of welding by lowering viscosity of the molten metal is made easy to discharge from in the molten metal, and as a result the blowholes are suppressed from remaining in the molten metal. As a means to contain Al, a galvanized steel sheet containing Al is used, or metallic Al is separately supplied to a laser emitting zone preliminarily or during the irradiation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of laser welding in a state where galvanized steel sheets or galvanized steel sheets and other metals are overlapped.

Zinc-based galvanized steel sheets are used in many industrial fields such as building materials, home appliances, and automobiles because they have excellent corrosion resistance. In addition, as a method of joining parts using the steel plate, conventionally, after forming a zinc-based plated steel plate with a press or the like, it is generally joined by spot welding or arc welding. However, in recent years, there is an increasing tendency to replace with laser welding in order to increase production efficiency and design freedom.
By the way, when attempting to laser weld a zinc-based plated steel sheet, zinc in the welded portion and the plating layer around the welded portion may vaporize and enter the welded portion, which may cause defects such as blow holes. For example, as shown in FIG. 1, these defects are caused by the laser beam 3 from above the welded material 2 in which the zinc-based plated steel plates 1 or between the zinc-based plated steel plates and another metal plate 1 ′ are closely overlapped. When welding is performed, there is a tendency to increase due to the generation of zinc vapor from the overlapped plates 4. For this reason, a method is adopted in which a spacer is inserted between the stacked steel plates to form a gap, and zinc vapor is released from the gap.

However, since it takes a considerable amount of time to insert the spacer, there is a problem in that the production time is increased when there are many welds. For this reason, many methods have been proposed so far to reduce the amount of defects such as blow holes due to the generation of zinc vapor without spacers.
For example, in Patent Document 1, by controlling the output of laser light, the first laser light having a low peak pulse and the second laser light having a high peak pulse are alternately irradiated to the welded part, A method has been proposed in which the galvanized layer is removed with the laser beam and the two steel plates are welded with the second laser beam. Moreover, in patent document 2, after carrying out spot welding locally on the centerline which should irradiate a laser beam, and forming the clearance gap between plates by a thermal strain, a laser beam is irradiated along the said centerline. There has been proposed a method of welding while continuously irradiating and escaping zinc vapor from the gap. Further, Patent Documents 3 and 4 propose a method in which irregularities and depressions are formed in advance on the surface of a galvanized steel sheet, and the galvanized steel sheet is laser-welded while releasing zinc vapor generated from the gap.

JP-A-4-251684 Japanese Patent Laid-Open No. 7-80669 JP 2002-361455 A JP 2002-346780 A

However, in the method proposed in Patent Document 1, it is necessary to adjust the laser light output, and further, since the welded portion is irradiated twice, the equipment cost increases and it takes time, resulting in cost. Get higher. Further, the method of Patent Document 2 also needs to perform laser irradiation a plurality of times, which takes time and cost. Furthermore, the methods proposed in Patent Documents 3 and 4 also require a separate process for forming irregularities and depressions, and thus take time and cost.
The present invention has been devised to solve such problems, and eliminates the harmful effects of zinc vapor generated during laser welding of galvanized steel sheets and suppresses the generation of blowholes. An object is to provide a welding method.

In order to achieve the object, the laser welding method of the galvanized steel sheet according to the present invention uses laser irradiation when laser welding the galvanized steel sheets to each other or a welded body in which the galvanized steel sheet and other metals are combined. It is characterized by including Al in the produced molten metal.
As a means for including Al in the molten metal, a steel plate having a zinc-based plating containing Al as a plating layer can be used. Further, an Al coating layer may be separately formed on the plating layer or on another metal surface in advance. Further, Al is placed on the laser irradiation surface of the object to be welded, or Al is preliminarily interposed between the materials to be welded in the form of a plate, foil, wire, or powder, or the irradiation site at the time of laser irradiation A linear or powdery Al material may be supplied to or added to the molten metal.

When laser welding the zinc-based plated steel sheet, the present inventors apply laser light 3 from above the workpiece 2 in a state where the zinc-based plated steel sheets 1 and 1 are overlapped as shown in FIG. We observed and examined the blowhole occurrence in welding. As a result, the inventors have found that the amount of blowholes generated depends on the amount of Al entering the molten metal during laser welding, that is, the amount of Al contained in the molten metal.
In laser welding, the base material steel plate that is the plating base plate of the zinc-based plated steel plate is also melted. It is known that when iron, which is a main component of a base steel plate, is in a molten state, the viscosity changes when various metal components are added. FIG. 2 shows the effect of various additive metals on the viscosity of iron in the molten state. Al greatly affects the viscosity of iron in a molten state, and even when a small amount of Al is added, the viscosity tends to decrease rapidly. The present invention makes the best use of the tendency to reduce the viscosity of the molten metal by including Al in the molten metal generated during laser welding, thereby reducing the viscosity of the vapor generated during welding. Zinc can be easily discharged from the molten metal, and as a result, the remaining blowholes in the weld metal can be suppressed. For this reason, it is possible to obtain a welded joint of good quality without blowholes by a simple method.

In the coupling and laser light irradiation mode shown in FIG. 1, zinc-plated steel sheets 1 and 1 having a plate thickness of 0.8 mm and a single-side plating thickness of 20 μm are used, and Al is added, interposed or inserted in various ways. Then, the amount of blow holes generated when laser welding was performed was investigated.
First, laser welding was performed by changing the amount of Al contained in the plated layer of the galvanized steel sheet. And the transition of the blowhole amount to generate | occur | produce was calculated | required by performing X-ray inspection from the upper surface of a welding part. The result is shown in FIG. It was found that the amount of blowholes tended to decrease as the amount of Al contained in the plating layer increased.
In order to investigate the cause of the decrease in the amount of blowholes generated, the amount of Al contained in the welded portion is compared with the portion that is not welded. As shown in FIG. It has been found that the amount of Al contained in the weld increases as the amount of Al increases.

As described above, in the laser welding, the base steel plate that is the plating base plate of the zinc-based plated steel plates 1 and 1 is also melted. When iron, which is the main component of the base steel sheet, is in a molten state, the viscosity changes according to the type and amount of the added metal component as seen in FIG. The influence of Al on the change is much larger than other metal components. And even if it is addition of a trace amount Al, the viscosity is reduced rapidly.
As shown in FIG. 5, when the plating layer of the galvanized steel sheets 1, 1 is laser welded with Al, the Al in the plating layer enters the molten base steel sheet and lowers its viscosity. The vaporous zinc 5 generated from the inter-plate space 4 during welding is easily discharged from the molten metal 6. Therefore, the amount of blowholes 8 remaining in the welded portion 7 can be reduced.

Next, laser welding was performed on the zinc-based plated steel sheet 1 and the cold-rolled steel sheet 1 ′ not plated in the state shown in FIG. Even in that case, the transition comparison of the amount of blowholes generated by variously changing the amount of Al contained in the plated layer of the zinc-based plated steel sheet was compared. As a result, although the same tendency as the tendency shown in FIG. 3 was shown, the thickness of the plating layer existing between the plates, that is, the amount of zinc is smaller than when the zinc-based plated steel plates 1 and 1 are welded together. The amount of blowholes is decreasing.
In the molten metal 6, the amount of blow holes generated by laser welding between the galvanized steel sheet 1 and the cold-rolled steel sheet 1 ′ that has not been plated showed the same tendency as in the case of the galvanized steel sheets 1, 1. This is because Al is mixed in and the viscosity is lowered.

Furthermore, when the galvanized steel sheets 1 and 1 were installed in the state shown in FIG. 1 and laser welding was performed, an Al plate was placed on the irradiation position of the laser beam 3 and welded. The amount of blowholes generated at that time also tended to decrease as the thickness of the Al plate increased, indicating the same tendency as in the state shown in FIG.
Furthermore, when laser welding was similarly performed using a steel sheet coated with Al on the coating layer of the zinc-based plated steel sheet at the laser beam 3 irradiation position, the amount of blowholes generated also increased the sprayed film thickness of the coated Al. It showed a tendency to decrease the more. The tendency was the same as shown in FIG. Al coating at the laser beam 3 irradiation position was performed on one side and both sides, but the decrease in blowhole generation was the same, but the absolute number of blowholes generated tends to be smaller when coated on both sides. there were.
In these cases as well, the reason is that zinc 5 evaporated by mixing Al in the molten metal 6 is easily discharged from the molten metal 6.

Rather than having Al present in advance, the same action and effect can be achieved even if linear and powdered Al material is separately supplied and added to the molten metal part melted by laser during laser welding. can do.
The above-described tendency is that welding is performed by irradiating laser beams from the upper surfaces of the welded materials in which the Zn-based plated steel plates as shown in FIG. The present inventor has confirmed that the same applies not only to cases but also to overlay fillet welding and butt joint welding.

As shown in FIG. 1, Zn—Al-based plated steel sheets 1 and 1 having a plate thickness of 0.8 mm, a plate width of 50 mm, a total length of 200 mm, and a plating adhesion amount of 120 g / m ^{2 on} one side are closely stacked. Laser welding was performed. At this time, as the Zn-Al-based plated steel sheet, the Al concentration in the plating layer is 7 kinds of 6 mass%, 10 mass%, 20 mass%, 30 mass%, 55 mass%, 70 mass% and 80 mass%. A plated steel sheet was prepared. In addition, the base material steel plate which is an original plate of a plated steel plate is C: 0.037 mass%, Si: 0.002 mass%, Mn: 0.26 mass%, S: 0.011 mass%, Al: 0.04. It is a cold-rolled steel sheet having a mass%.
A YAG laser welder with a beam mode of multimode was used, and the laser output was 2.5 kW, the focal length was 200 mm, and the welding speed was 2 m / min. The focal position of the laser beam was the surface of the upper Zn-Al-based plated steel sheet 1 and the laser beam spot system at the focal position was 0.6 mm.
The welded sample was subjected to X-ray inspection from the upper surface of the weld bead, and the number of blow holes was measured. The blowhole generation amount is expressed as the number of weld beads per 100 mm, and the result is shown by a solid line in FIG.
The amount of blowholes generated decreases as the amount of Al contained in the plating layer increases. Further, as shown by the solid line in FIG. 7, the amount of Al contained in the welded portion 7 tended to increase as the amount of Al contained in the plating layer increased.

FIG. 1 shows a Zn—Al-based plated steel sheet 1 having a plate thickness of 0.8 mm, a sheet width of 50 mm, a total length of 200 mm, and a coating adhesion amount of 120 g / m ^{2 on} one side, and a cold-rolled steel sheet 1 ′ having the same dimensions. Thus, laser welding was performed by overlapping closely. As the Zn-Al-based plated steel sheet at this time, the Al concentration in the plating layer is 7 types of 6 mass%, 10 mass%, 20 mass%, 30 mass%, 55 mass%, 70 mass% and 80 mass%. A plated steel sheet was prepared. In addition, both the plated steel plate and the cold-rolled steel plate are the same as those in Example 1.
A YAG laser welder with a beam mode of multimode was used, and the laser output was 2.5 kW, the focal length was 200 mm, and the welding speed was 2 m / min. The focal position of the laser beam was the surface of the upper Zn-Al-based plated steel sheet 1 and the laser beam spot system at the focal position was 0.6 mm.
The welded sample was subjected to X-ray inspection from the upper surface of the weld bead, and the number of blow holes was measured. The blowhole generation amount is expressed as the number of weld beads per 100 mm, and the result is indicated by a broken line in FIG.
The amount of blowholes generated decreases as the amount of Al contained in the plating layer increases, and the number of blowholes is smaller than when laser welding the Zn—Al-based plated steel sheets of Example 1 to each other. Further, as shown by the broken line in FIG. 7, the amount of Al contained in the welded portion 7 tended to increase as the amount of Al contained in the plating layer increased.

Laser welding with a plate thickness of 0.8 mm, a plate width of 50 mm, a total length of 200 mm, and Zn-plated steel plates 1 and 1 having a coating adhesion amount of 120 g / m ^{2 on} one side are closely stacked as shown in FIG. Went. At this time, an Al plate having a plate width of 50 mm, a total length of 200 mm, and a plate thickness of 0.05 mm, 0.1 mm, and 0.15 mm was placed on the upper Zn-plated steel plate, and the surface of the Al plate was laser-treated. The irradiated surface was used. The original plate of the plated steel plate is the same as that in Example 1.
A YAG laser welder with a beam mode of multimode was used, and the laser output was 2.5 kW, the focal length was 200 mm, and the welding speed was 2 m / min. The focal position of the laser beam was the surface of the upper Al plate 1 and the laser beam spot system at the focal position was 0.6 mm.
The welded sample was subjected to X-ray inspection from the upper surface of the weld bead, and the number of blow holes was measured. The blowhole generation amount is expressed as the number of weld beads per 100 mm, and the result is shown by a solid line in FIG.
The amount of blowhole generation decreases as the thickness of the Al plate increases. Further, as shown by the solid line in FIG. 9, the amount of Al contained in the welded portion 7 tended to increase as the plate thickness of the Al plate increased.

As shown in FIG. 1, a Zn-plated steel plate 1 having a plate thickness of 0.8 mm, a plate width of 50 mm, a total length of 200 mm, and a plating adhesion amount of 120 g / m ^{2 on} one side, and a cold-rolled steel plate 1 ′ having the same dimensions as shown in FIG. Then, laser welding was performed by superimposing them. At this time, an Al plate having a plate width of 50 mm, a total length of 200 mm, and a plate thickness of 0.05 mm, 0.1 mm, and 0.15 mm was inserted between the plates of the plated steel plate, and the surface of the plated steel plate was irradiated with laser. The surface. In addition, both the plated steel plate and cold-rolled steel plate used in this example are the same as those in Example 1.
A YAG laser welder with a beam mode of multimode was used, and the laser output was 2.5 kW, the focal length was 200 mm, and the welding speed was 2 m / min. The focal position of the laser beam was the surface of the upper Al plate 1 and the laser beam spot system at the focal position was 0.6 mm.
The welded sample was subjected to X-ray inspection from the upper surface of the weld bead, and the number of blow holes was measured. The blowhole generation amount is expressed as the number of weld beads per 100 mm, and the result is indicated by a broken line in FIG.
The amount of blow holes generated decreases as the plate thickness of the Al plate increases, and the number of blow holes is reduced as compared with the case where the Zn-plated steel plates of Example 3 are laser welded together. Further, as shown by the broken line in FIG. 9, the amount of Al contained in the welded portion 7 tended to increase as the plate thickness of the Al plate increased.

Comparative example

As a comparative example, laser welding was performed under the same conditions as in Example 1 using Zn-plated steel sheets 1 and 1 that did not contain Al in the plating layer. The base material of the Zn-plated steel sheet was also the same as in the example, and the amount of plating adhesion on one side was set to the same 120 g / m ² . The welded sample was measured for blowhole generation by the same method as in the example.
As a result, as shown by the black circle plots in FIG. 6, the amount of blowholes generated was larger than when laser welding was performed on a Zn—Al plated steel sheet in which Al was contained in the plating layer. Further, it was found that the Al content contained in the welded portion was the same as the Al content of the base material, which is the plating original plate, and did not increase, as shown by the black circle plot in FIG.

Schematic showing an example of a mode for laser welding Diagram showing the effect of contained metal components on the viscosity of molten metal The figure which shows the amount of blowhole generation to the amount of Al contained in the plating layer Diagram comparing the amount of Al contained in the weld and base metal It is a figure explaining the generation | occurrence | production situation of zinc vapor | steam and a blowhole, (a) shows a molten state, (b) shows a solidification state. The figure explaining the difference in the amount of blowhole generations by the difference in Al content in a present Example The figure which showed the amount of Al contained in a welding part in a present Example by the ratio with the amount of Al of a base material. The figure explaining the difference in the amount of blowhole generation by the difference in the amount of Al when placing and inserting the Al plate The figure which showed the amount of Al contained in the welded part in the case of placing and inserting the Al plate as a ratio with the amount of Al of the base material

Explanation of symbols

1: Zinc-based plated steel sheet 1 ': Metal other than zinc-based plated steel sheet 2: Welded material
3: Laser beam 4: Between plates 5: Zinc vapor 6: Molten metal 7: Welded part
8: Blow hole

Claims (5)

  Zinc-based galvanized steel sheet characterized by including Al in molten metal generated by laser irradiation when welding welded objects in which galvanized steel sheets or zinc-plated steel sheets and other metals are combined. Laser welding method.   The laser welding method for a zinc-based plated steel sheet according to claim 1, wherein a steel sheet subjected to zinc-based plating containing Al is used as means for including Al in the molten metal.   The method for laser welding a zinc-based plated steel sheet according to claim 1, wherein an Al coating layer is separately formed on the plating layer or on another metal surface in advance as a means for including Al in the molten metal.   As means for including Al in the molten metal, plate-like, foil-like, wire-like, or powder-like Al is previously placed on the laser irradiation surface of the welded body, or a plate-like, foil is placed between the materials to be welded. The method for laser welding a zinc-based plated steel sheet according to claim 1, wherein Al in the form of a wire, wire, or powder is interposed.   The laser welding method for galvanized steel sheets according to claim 1, wherein as a means for including Al in the molten metal, a linear or powdery Al material is supplied to and added to the molten metal at the irradiation site during laser irradiation.

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