JP3223172B2 - Welding method of laser welded body made of aluminum plated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a technique for manufacturing a fuel tank for a vehicle, for example, by welding.

[0002]

2. Description of the Related Art Conventionally, a material such as a tin-lead plated steel plate or a material such as a zinc-nickel plated steel plate is generally used for an inner tank such as a scooter for the purpose of preventing rust on the inner surface. However, plating using lead is currently
Due to pollution issues and the need for a fuel tank made of a new material is desired, a double-sided hot-dip aluminized steel sheet with both sides aluminized is used, and this double-sided hot-dip aluminized steel sheet is overlapped and joined. By welding the parts, a method is considered that simplifies the rust prevention on the outside as well as the rust on the inside.

[0003]

However, resistance seam welding has conventionally been generally used for welding steel sheets constituting a fuel tank. When this resistance seam welding is used as a welding method for a double-sided hot-dip aluminized steel sheet, There are the following problems. First, since the aluminum plating on the surface adheres to the electrodes during welding, the electrodes must be frequently shaped. Second, since the surface is plated with aluminum, the heat conduction is good, and the conductivity is also good. Therefore, welding cannot be performed unless a large current, for example, 1.5 to 2.0 times that of a normal steel plate is applied. . Thirdly, since the input heat is large and the area where the surface treatment is destroyed is large, the corrosion resistance of the inner surface of the tank is reduced.

[0004] In view of the above, the joint strength of the welded portion is improved while significantly eliminating the steps such as rust prevention on the inner surface and painting on the outer surface.
It is desired to have a welding technique that does not cause a problem such as adhesion of aluminum plating to the electrode and that can minimize the destruction area of the surface treatment.

[0005] Laser (including electron beam) welding is considered as a welding technique in which aluminum plating does not adhere to the electrodes. However, sufficient welding strength cannot be obtained simply by laser welding.

[0006]

Means for Solving the Problems The present inventors have found that in the case of an aluminum-plated steel sheet, the strength greatly changes depending on the metal composition of the welded portion, and have made the present invention based on this finding. Specifically, it has been found that, when an aluminum-plated steel sheet is welded with a laser beam under normal conditions, aluminum segregation occurs in the molten metal at the welded portion, and the welding strength is reduced due to the segregation.

That is, in the laser welded body according to the first aspect, when the superposed double-sided aluminum-plated steel sheets are welded by the laser beam, the relative moving speed of the laser beam is reduced.
By slowing down , A in the molten metal at the welded portion of the welded body
The ratio of 1 was adjusted to 0.65 wt% or less.

As described above, Al in the molten metal at the welded portion
In order to make the ratio of 0.65 wt% or less, the relative moving speed of the laser beam in welding while relatively moving the aluminum-plated steel plate and the laser beam as described in claim 2 Ru a 1.5m / mi n and be <br/>.

[0009] The moving speed by a 1.5 m / mi n, increases the amount of heat input to the weld, A in molten metal
The occurrence of segregation of the l component is suppressed. And by doing in this way, the ratio of Al in the molten metal
It becomes 5 wt% or less. By the way, the ratio of Al is 0.65wt%
When it exceeds, the peel fracture stress of the welded portion becomes smaller than the tensile stress of the base material.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a perspective view showing an example of a fuel tank made of an aluminum-plated steel sheet formed by the manufacturing method according to the present invention, and FIG. 2 is an explanatory view showing various aspects of a welding method.

The fuel tank 1 is formed of a pair of upper and lower half-shells 2 and 3 formed by pressing an aluminum-plated steel plate.
a is welded with a laser beam over the entire circumference, and the welded portions are kept airtight. Small parts such as a lubrication base 4 and stays are laser-welded or fixed to predetermined portions of these half-shells 2 and 3. It is attached by attaching.

The aluminum-plated steel sheet is, for example, SA1E
An aluminum plating layer is formed on the front and rear surfaces of a 60 steel or a SA1E60Y steel obtained by subjecting the SA1E60 steel to a chromate treatment. The SA1E60 steel or the SA1E60Y
Steel is made of Si, M, which is added for refining needs in addition to carbon.
n, and components such as P and S as impurities.
Incidentally, the melting point of Fe is 1540 ° C. and the boiling point is 2750 ° C.
And the melting point of Al is 660 ° C. and the boiling point is 2470 ° C.

As a method of overlapping and welding the flange portions 2a, 3a of the half-shells 2, 3 made of the aluminum-plated steel plate as described above, for example, various methods as shown in FIG. 2 can be adopted. That is, FIG. 2A shows that the laser irradiation direction is substantially perpendicular to the flange surface direction,
It is a method of welding while moving the laser welding machine along the entire circumference along the periphery. It is resistant to misalignment of laser irradiation, but after welding, it is necessary to apply rust-proof coating on the top of the weld bead to maintain appearance quality There is.

FIG. 2 (B) shows the laser irradiation direction substantially parallel to the flange surface, and the welding machine is moved along the peripheral edge while irradiating toward the joining surface end of the flange portions 2a, 3a. This is a method of welding the circumference. This method is not so strong in the positional deviation of the laser irradiation, but has the characteristic that after welding, rust-proof coating of the weld bead is unnecessary. FIG. 2 (C) shows a method of changing the overhang width of the flange portions 2a and 3a and irradiating a laser beam from a diagonal direction toward a joint end having a narrow overhang width. On the other hand, it has a characteristic that it is slightly resistant to the positional deviation of laser irradiation.

By the way, when the welding method shown in FIG. 2A is employed, it has been found that when the flange portions 2a and 3a are brought into close contact with each other and laser-welded, the joining strength is significantly reduced. It was also found that the joining strength was related to the moving speed of the laser welding machine. That is, the present inventors changed the moving speed of the laser welding machine by using the test pieces T, T made of aluminized steel sheet as shown in FIG. 3 and changing the gap between the test pieces T, T by the spacer S. As a result of performing a laser welding while performing the bonding and then performing a tensile test to test a bonding strength, a result as shown in FIG. 4 was obtained.

Here, when the gap was 0, the test was performed by changing the pressing force by the clamper C. The change in the gap was changed by changing the height of the spacer S. And
The horizontal axis in FIG. 4 represents the gap mm (when the gap is 0, the applied pressure kg / cm2), and the vertical axis represents the peel rupture stress kgf / mm2. Also,
△ and △ show an example of welding with a laser welding machine having the same moving speed as seam welding, etc., and △ shows a test piece T with a laser welding machine moving at a speed of 3.5 m / min and the focal point of laser light being upward. Example of a sample welded so that it is tied 4 mm above the above, and ■ indicates that the moving speed of the laser welding machine is 4.0 m / min
This is an example of a sample welded so that the focal point of the laser beam is focused on the upper surface of the upper test piece T. Also,
◆ shows a sample example in which the speed of the laser welding machine is sufficiently reduced. The welding speed is 1.5 m / min, and the laser beam is focused 4 mm above the upper test piece T. did.

In the tensile test, as shown in FIGS. 5A and 5B, each long side of each test piece T, in which each short side bent in an L-shape is overlap-welded, is placed in the opposite direction ( FIG. 5 (b)
(Arrow direction). From these results, for example, when the gap is 0 (the applied pressure is 5 kg / cm 2), as shown in FIG.
10 kgf / mm2 and ■ were less than that (not shown) and extremely weak. On the other hand, Δ indicates that the pressing force is 10
At kg / cm2, it was 22 to 27 kgf / mm2, and a relatively large peeling rupture stress was obtained. On the other hand, when the gap was provided, the peeling rupture stress was close to the base metal rupture stress almost independently of the moving speed of the welding machine and the focal position of the laser beam.

From the above results, by providing the gap, it is possible to obtain sufficient bonding strength to the aluminum-plated steel sheet. On the other hand, when the gap is not provided, the moving speed of the laser welding machine is sufficiently reduced, that is, It has been found that a predetermined bonding strength can be obtained by increasing the amount of heat of the laser beam per unit area.

Therefore, the present inventors thought that the Al component contained in the welded part y might be related to the tensile strength,
The relationship between the content of the Al component in the center of the weld (the center of the weld metal) and the peeling rupture stress was examined. The result is as shown in FIG. FIG. 6 shows the results of examining the joint strength of a test piece T obtained by laser welding with the gap changed under the same conditions as in FIG. 4 by performing the same tensile test as the test in FIG. Things. The horizontal axis indicates the content of the Al component in the welded portion, and the vertical axis indicates the peel fracture fracture stress.

From the test results shown in FIG. 6, when the proportion of the Al component in the welded portion is 0.65% by weight or less, a peeling rupture stress equivalent to the tensile stress (27 to 28 kgf / cm 2) of the base metal is obtained. On the other hand, the ratio of the Al component in the welded portion is 0.6
It was found that when the content was 5 wt% or more, the peeling rupture stress was smaller than the tensile stress of the base material. From the above, it can be seen that the Al component in the welded portion is related to the tensile strength, and that the lower the content of the Al component in the welded portion, the higher the joining strength. Further, in order to keep the content of the Al component in the welded portion y low in order to obtain a predetermined bonding strength, it is necessary to increase the calorific value of the laser beam per unit area by, for example, decreasing the moving speed of the laser welding machine. It turns out to be effective.

If an aluminum-plated steel plate is used as a fuel tank material, the welded portion is protected by the sacrificial corrosion-preventing action of aluminum, and the internal corrosion protection, which is a problem as a fuel tank, can be greatly improved. In laser welding this aluminum-plated steel sheet, the area where the surface treatment layer is broken can be minimized because the beam width is narrow. In addition, high-speed welding is possible because heat can be applied locally and rapidly.

[0022]

According to the present invention as described above,
In the welding method of a laser welded body in which a pair of half-shells made of an aluminum-plated steel sheet is joined by laser beam welding, the welding speed is reduced to reduce the ratio of Al in the molten metal of the welded part to 0.1. Since the content is 65 wt% or less, the welding strength can be significantly improved. Also, the welding speed is 1.5 m / mi.
By setting n to increase the heat input to the welded portion, segregation of the Al component in the weld metal can be suppressed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a fuel tank made of an aluminum-plated steel sheet formed by a manufacturing method of the present invention.

FIG. 2 is an explanatory view showing various aspects of a welding method, and the direction of an arrow is a laser irradiation direction.

FIG. 3 is an explanatory view of a welding state of a test piece.

FIG. 4 is a graph of a result of a tensile test performed for examining a joining strength. A horizontal axis represents a gap mm (when the gap is 0, a pressing force is kg / c).
m2), the vertical axis is the breaking stress kgf / mm2

FIG. 5 is a graph showing the relationship between the amount of Al component in a welded portion and the peel rupture stress.

6A is a front view of a test piece for a tensile test, and FIG. 6B is a side view of the test piece.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-131284 (JP, A) JP-A-56-62688 (JP, A) JP-A-61-74793 (JP, A) JP-A-7-76 155974 (JP, A) JP 4-13077 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/00-26/40

Claims (2)

(57) [Claims] 1. Double-sided aluminum-plated steel laminated without gaps
Weld the plate while moving the laser beam relatively
The method, wherein the relative speed of movement of the laser beam
The ratio of Al in the molten metal at the weld
Aluminum plating characterized by being 0.65 wt% or less
Laser welding method for steel sheet. 2. A method of welding while the double-sided aluminized steel sheet superposed with no gap by relatively moving the laser beam, the relative moving speed of the laser beam by a 1.5 m / mi n, A laser welding method for an aluminum-plated steel sheet, wherein a ratio of Al in a molten metal at a weld portion is 0.65 wt% or less.