JPH10296472A - Method for laser welding for aluminum plated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify welding of a vehicle fuel tank and the like made of an aluminum plated sheet and to improve welding strength. SOLUTION: In manufacturing a fuel tank 1 through laser welding of peripheral flange parts 2a, 3a of a pair of halved shell bodies 2, 3 made of an aluminum plated sheet with an aluminum plated surface, the flange part 2a, 3a are put together one above the other in close contact, then the superposed part is irradiated with a laser beam and at the same time is subjected to blowing of a gaseous mixture composed of gaseous argon, helium and nitrogen or a gaseous mixture of 38-90% oxygen (vol.%) to gaseous carbon dioxide and thus welded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for laser welding aluminum-plated steel sheets.

[0002]

2. Description of the Related Art The applicant of the present invention has previously proposed in Japanese Patent Application No. 7-311934 a laser welding technique for aluminum-plated steel sheets. In this technology, when manufacturing a fuel tank for a vehicle by joining a pair of half-shells, the steps such as inner rust prevention after welding, outer coating, and the like are omitted, and in order to shorten welding work time, a half-shell is used. The body is made of an aluminum-plated steel plate, and a half-shell made of this aluminum-plated steel plate is laser-welded to manufacture a fuel tank.

[0003] In this technique, when an aluminum-plated steel plate is laser-welded, unnecessary components such as aluminum or silicon may enter the molten metal and cause a reduction in bonding strength. It has been proposed to form a gap between aluminum-plated steel sheets around the laser irradiation part to allow unnecessary components to escape.

[0004] Japanese Patent Publication No. 5-20192 discloses that
Aluminum or aluminum alloy with oxygen gas ratio of 1
A technique for performing laser welding using a shielding gas of 5% to 90% is disclosed.

[0005]

SUMMARY OF THE INVENTION However, Japanese Patent Application No. Hei.
The technique of forming a gap around the laser irradiation location as proposed in 311934 becomes difficult to apply, especially when the product is enlarged and the welding range is widened, and if possible, without forming a gap, It is convenient if welding can be performed even when they are in close contact.

Further, as disclosed in Japanese Patent Publication No. 5-20192, it is actually possible to weld aluminum or aluminum alloy using a shielding gas having an oxygen gas ratio of 15% to 90%. Such welding is limited to build-up welding as disclosed in the publication, and welding of plate-like aluminum or aluminum alloy is insufficient in strength and cannot be applied.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to establish a welding technique capable of securing a required welding strength without forming a gap around a welded portion for releasing unnecessary components when laser-welding an aluminum-plated steel sheet. .

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a laser welding method in which aluminum-plated steel sheets are overlapped and welded with a laser beam. In laser-welding the superimposed portion, a mixed gas of at least one of argon gas, helium gas, nitrogen gas or carbon dioxide gas and oxygen gas as an assist gas, and the ratio of oxygen gas is 38 vol% or more. A mixed gas of 90 vol% or less, preferably 65 vol% or more and 85 vol% or less was used.

In general, in laser welding, as a technique for mixing oxygen into an assist gas blown toward a welded portion, for example, a laser welding technique for a galvanized steel sheet as disclosed in Japanese Patent Application Laid-Open No. Hei 6-79484. According to this technology, when a galvanized steel plate is laser-welded, the boiling point of zinc is low, so that the zinc in the plating layer is explosively vaporized to prevent a blowhole from being generated in the molten portion.
By including oxygen in the assist gas in a volume ratio of 5 to 35%, the oxidation and combustion of the galvanized layer are promoted, and the vapor of the plating is easily released to the outside.

However, it has been found that when the present inventors apply this technique to laser welding of an aluminum-plated steel sheet, the exhaustiveness of unnecessary components such as aluminum and silicon is not sufficient, and the necessary bonding strength cannot be secured. Then, when the experiment was repeated, it was found that when the mixing amount of oxygen was 38 vol% or more and 90 vol% or less with respect to the volume ratio with respect to the whole gas, the discharging property of unnecessary components was improved, and the bonding strength was increased to reach practical strength. . In addition, it was found that the strength was extremely excellent when the ratio of oxygen in the mixed gas was 65 vol% or more and 85 vol% or less.

Here, it is considered that the reason why the welding strength is improved by mixing oxygen in the above ratio is as follows. First, unnecessary components such as aluminum and silicon react with oxygen to be activated as oxides and are easily discharged from the molten portion to the outside. Also the second
In addition, by mixing oxygen, the calorific value of the fusion zone increases, the width of fusion increases, and the welding strength improves. And the first,
Regarding the reason why the second melting width is widened,
As a result of actually verifying the cross-sectional structure of the weld with a micrograph,
It was confirmed that the mixing width of oxygen was wider than that of the case of using a single gas such as argon.

When the amount of oxygen is less than 38 vol%, the amount is insufficient for discharging unnecessary components such as aluminum, although it is sufficient for discharging gas such as vaporized zinc.
It is considered that the effect of discharging unnecessary components is enhanced by setting the content to 8 vol% or more. On the other hand, when the oxygen content is 91 vol% or more, the oxidation of the melted portion becomes remarkable, and the bonding strength decreases.

[0013] In the present invention, the welding method may include:
Includes application to welding of vehicle fuel tanks made of aluminized steel plates. By making the vehicle fuel tank made of aluminum-plated steel sheet in this way, it is possible to save time and effort for processing such as internal rust prevention and external rust prevention. And welding can be performed at a high speed.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIGS. 1 to 4 are a photograph (A) in which a metal structure is photographed by a micrograph of the metal structure of the welded portion and a schematic diagram (B), FIG. 1 shows an oxygen content of 38% in the mixed gas, and FIG. FIG. 3 shows an oxygen content of 70% in the mixed gas, and FIG. 4 shows an oxygen content of 10% in the mixed gas.
FIG. 5 is an overall view of a fuel tank to which the welding method of the present invention is applied, and FIG. 7 is a partial view of a welded portion of the fuel tank.

The laser welding method for an aluminum-plated steel sheet according to the present invention, for example, when manufacturing a vehicle fuel tank 1 made of an aluminum-plated steel sheet as shown in FIG. 3 is applied as a method of superposing the peripheral flange portions 2a, 3a and welding the superposed flange portions 2a, 3a over the entire circumference.

Here, it has been revealed by the present inventors that the joining strength is reduced when the aluminum-plated steel sheet is brought into close contact with the laser welding, and that the joining strength is also related to the moving speed of the laser welding machine. I have. That is, when the present inventors took a micrograph of a cross-sectional photograph of the welded portion and revealed the metallographic structure, when the laser welding speed was high, there was no need for aluminum or the like having melted out of the aluminum plating layer on the contact surface side. It has been found that the components cannot escape from the molten portion and solidify while remaining inside, so that the desired bonding strength cannot be obtained.

As a type of the mixed gas, a mixed gas of argon gas and oxygen, a mixed gas of helium gas and oxygen,
Any of a mixed gas of nitrogen gas and oxygen, a mixed gas of carbon dioxide and oxygen, or a mixed gas of argon gas, a helium gas, a nitrogen gas, and a plurality of carbon dioxide gas and oxygen may be used.

Hereinafter, specific examples and comparative examples which were tested by changing the amount of oxygen in the mixed gas used at the time of welding will be described. (Example 1) FIG. 1 shows two test pieces T, T made of an aluminum-plated steel sheet, which are superimposed on each other in close contact with each other, and irradiated with a laser beam. FIG. 3 is a metallographic diagram obtained by welding at a welding speed of 3.0 m / min while spraying a mixed gas mixed at a ratio of 3: 3 (oxygen volume ratio to the entire gas volume: 38%).

From this figure, from the entrance side to the exit side of the laser irradiation, the melting width becomes almost linear although the middle part becomes narrower, and almost no unnecessary components such as aluminum are mixed into the melting part. It was also confirmed that the welded portion did not break, and that sufficient welding strength was obtained.

(Embodiment 2) FIG. 2 shows two similar test pieces T, T superimposed on each other in close contact with each other, and irradiating the test pieces with a laser beam. FIG. 9 is a metallographic diagram obtained by welding at a welding speed of 3.0 m / min while spraying a mixed gas mixed at a ratio of 9: 9 (volume ratio of oxygen to the entire gas volume: 90%).

From this figure, the melting width becomes almost linear from the entrance side to the exit side of the laser irradiation, and almost no unnecessary components such as aluminum are mixed into the inside of the fusion part. Even the result of the tensile test of
It turns out that sufficient welding strength is obtained.

(Embodiment 3) FIG. 3 shows two similar test pieces T, T superposed on each other in close contact with each other, irradiating them with a laser beam, and applying an argon gas and an oxygen gas at a volume ratio toward an irradiation portion. FIG. 3 is a metallographic diagram obtained by welding at a welding speed of 3.0 m / min while blowing a mixed gas mixed at a ratio of 3: 7 (oxygen volume ratio to the entire gas volume: 70%).

From this figure, it can be seen that from the entrance side to the exit side of the laser irradiation, the melting width becomes almost linear and the outer surface of the melting part becomes almost flat, and furthermore, unnecessary components such as aluminum and the like enter the inside of the melting part. Almost no contamination was found, and the results of the tensile test after welding showed that a more excellent and sufficient welding strength was obtained. In addition, it was confirmed that even when a mixed gas having an oxygen content of 65% to 85% was used, the same welding strength tended to be obtained.

(Comparative Example 1) FIG. 4 shows two similar test pieces T, T superposed on each other in close contact with each other, irradiating the test pieces with a laser beam, and spraying 100% oxygen gas toward the irradiated portions while welding. It is a metallographic chart welded at 3.0 m / min.

From this result, almost no unnecessary components such as aluminum were mixed into the melted portion, but the oxidation of the welded portion became remarkable, the thickness of the welded portion became thinner, and the joining strength was reduced. I was

(Comparative Example 2) FIG. 5 shows two similar test pieces T, T superimposed on each other in close contact, irradiating them with a laser, and applying argon gas (zero oxygen content) toward the irradiated part. FIG. 3 is a metallographic view of a metal welded at a welding speed of 3.0 m / min while spraying.

From this figure, it can be seen that the welding width on the inlet side and the outlet side of the laser irradiation is wide and the melting width of the intermediate portion (overlapping surface portion) is narrow, and the narrowed intermediate portion (overlapping surface portion). It was found that unnecessary components such as aluminum were mixed in the vicinity of the melt, and the desired strength was not reached in the tensile test.

In the above test, the same result is obtained even when helium gas, nitrogen gas or carbon dioxide gas is used in place of argon gas, and all are effective if the oxygen content is set in the range of 38 to 90%. Met. If such laser welding of an aluminum-plated steel plate is applied to welding of the fuel tank 1 of a vehicle, steps such as corrosion-resistant coating after welding can be omitted, and processing can be performed at high speed.

[0029]

As described above, according to the welding method of the present invention, at least a part of an aluminum-plated steel sheet is superposed in close contact,
The laser beam is applied to the part that is superimposed in close contact, and at the same time, welding is performed while spraying a mixed gas containing a predetermined amount of oxygen as an assist gas toward the laser-irradiated part. It is possible to increase the welding strength because it is discharged from the part and the melting width is widened. And such a welding method,
If the present invention is applied to welding of a fuel tank for a vehicle made of an aluminum-plated steel plate, an area where a plated portion is destroyed is limited, post-processing is not required, and welding can be performed at high speed.

[Brief description of the drawings]

FIG. 1 shows the metallographic structure of a weld when the oxygen content in a mixed gas is 38% (A) is a micrograph, and (B) is a mimetic diagram thereof.

FIG. 2 shows a metallographic structure of a welded portion when the oxygen content in the mixed gas is 90% (A) is a micrograph, and (B) is a mimetic diagram thereof.

3A and 3B show a microstructure of a welded portion when the oxygen content in the mixed gas is 70%, and FIG. 3B is a micrograph and FIG.

4A and 4B show a metallographic structure of a weld when the oxygen content in the mixed gas is set to 100%; FIG. 4A is a micrograph, and FIG.

5A and 5B show a microstructure of a welded portion when the oxygen content is set to zero, wherein FIG. 5A is a micrograph, and FIG.

FIG. 6 is an overall view of a fuel tank to which the welding method of the present invention is applied.

FIG. 7 is a partial view of a welded portion of the fuel tank.

[Explanation of symbols]

1 ... Fuel tank, 2,3 ... Semi-shell, T ... Test piece of aluminum plated steel plate.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B62J 35/00 B62J 35/00 A

Claims (3)

[Claims] 1. A laser welding method in which aluminum-plated steel sheets are overlapped and welded with a laser beam, wherein at least a part of the aluminum-plated steel sheets is closely overlapped, and the closely overlapped portion is assisted by an assist gas. When performing laser welding using a gas, the assist gas is a mixed gas of oxygen gas and at least one of argon gas, helium gas, nitrogen gas or carbon dioxide gas, and the ratio of oxygen gas in the mixed gas is 38 vol. % Or less and 90 vol% or less. 2. The laser welding method for an aluminum-plated steel sheet according to claim 1, wherein the ratio of oxygen gas in the mixed gas is 65 vol% or more and 85 vol% or less. 3. The laser welding method for an aluminum-plated steel sheet according to claim 1, wherein the welding method is applied to welding of a fuel tank for a vehicle made of the aluminum-plated steel sheet. Method.