JPS6249146B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing defects in DCSP-TIG welding of aluminum.

In this specification, aluminum includes both pure aluminum and aluminum alloys. Further, left rotation and right rotation refer to directions seen from the torch side.

DCSP-TIG welding of aluminum is attracting attention as a highly efficient welding method that can achieve a narrower bead width and deeper penetration than MIG welding or AC TIG welding, but due to the presence of an oxide film on the surface unique to aluminum, other methods Deformation blow holes and feather-like crystals that are not seen with welding methods occur, which not only adversely affects joint performance, but also poses an obstacle to non-destructive testing because feather-like crystals generate analytical images on X-ray photographs. It also has the disadvantage of becoming

Deformed blow holes can be eliminated by considering welding conditions and groove pretreatment, but the range of welding conditions is very narrow and there are many practical problems, and feathery crystals can be eliminated by changing welding conditions. However, it is difficult to eliminate it.

The purpose of this invention is to
The object of the present invention is to provide a method for preventing the above-mentioned defects that occur in TIG welding.

In order to achieve the above object, the method for preventing defects in DCSP-TIG welding of aluminum according to the present invention is to provide a method for preventing defects in DCSP-TIG welding of aluminum. applies an alternating magnetic field of 2 to 15 Hz, and the molten pool is stirred by rotating left and right alternately by Lorentz force.

This invention will be explained below with reference to the drawings.

In Fig. 1, 1 is a TIG torch, 2 is its electrode, 3 is a welding arc, 4 is an aluminum material to be welded, and 5 is a coil iron core that is opposed to the TIG torch 1 through the material to be welded 4. A magnetic field generating coil 6 is wound around. 7 is a power source that supplies an alternating current to the coil 6.

In the above, the material to be welded 4 is welded by DCSP-TIG welding as shown by the arrow 18 in FIGS. 3 and 4.
Butt weld in the direction. 8 is the weld metal, 9
is a molten pool, and when an alternating current is supplied to the coil 6, magnetic lines of force 10 generated from the iron core 5 penetrate the material to be welded 4 and apply an alternating magnetic field to the molten pool 9.
At this time, the welding current 11 is concentrated directly below the arc 3, as shown by the arrow in FIG. Rotate and stir as shown at 19. Since an alternating magnetic field is applied to the molten pool 9, the direction of rotation shown in FIG. 4 is then reversed, and thereafter the direction of rotation alternates between left rotation and right rotation, and the rotation is repeated.

The coil 6 is wound around the iron core 5, and the torch 1
The coil 6 is placed opposite the torch 1.
An alternating magnetic field can be applied to the molten pool 9 even if the wire is wound around the molten pool 9.

The reason why the frequency of the alternating magnetic field is limited to 2 to 15 Hz is because
This is due to the following reasons. In other words, if the frequency is less than 2Hz, the molten pool will not be stirred sufficiently because the rotation speed of the left and right alternations is slow, and if it exceeds 15Hz, the molten pool will not be sufficiently stirred because the rotation speed of the left and right alternations is too fast. This is because they cannot be forced to do so. In Figure 8 a to g, JIS, 5083P-0 was used as the aluminum material to be welded, welding speed was 300 mm/min, and welding current was 220 A.
When performing DCSP-TIG welding, in the molten pool,
An alternating magnetic field with a component perpendicular to the welding current flowing through this molten pool and frequencies of 0.2Hz, 5Hz, 10Hz, 15Hz, 20Hz, and 30Hz is applied, respectively, and the molten pool is rotated alternately left and right by Lorentz force. The surface macrostructure of each weld metal is shown.

Figure 8a shows a conventional example where the frequency is 0, that is, no alternating current is applied to the molten pool, and therefore the molten pool is not stirred at all, and feather-like crystals are clearly observed on the surface of the weld metal. . When the frequencies c to e in the same figure are 5 Hz, 10 Hz, and 15 Hz, the molten pool is stirred and the crystals become finer, and as a result, no feathery crystals are generated. When the frequencies f and g in the figure are 20 Hz and 30 Hz, the molten pool is not sufficiently stirred, and the presence of feather-like crystals is observed. In the case of a frequency of 2 Hz as shown in Figure b, the presence of feathered crystals is not recognized. However, from the surface dimple state of the weld metal, the figure shows that the molten pool is not sufficiently stirred at a frequency of less than 2 Hz.

As described above, it can be seen from FIG. 8 that there is an effect of stirring the molten pool within the frequency range of 2 to 15 Hz, and that 5 to 10 Hz is particularly excellent.

Next, we added 0.5% to He as a shielding gas to make it easier to generate blow holes.
DCSP-TIG containing _H2 gas and under the same conditions as above.
Performed welding. The surface condition of the weld metal when no alternating magnetic field was applied to the molten pool at this time is shown in photographs in FIG. 9A, and the cross section thereof is shown in FIG. 9B. Furthermore, the surface condition of the weld metal when an alternating magnetic field with a frequency of 5 Hz is applied to the molten pool is shown in Fig. 10A, and the cross section thereof is shown in Fig. 10B, respectively. Figure 9 A,
In Figure 10 (B), the existence of blow holes is clearly recognized, and in Figure 10 (A) and (B), the generation of blow holes is hardly recognized because the release of blow holes from the weld metal is promoted by the stirring effect of the molten pool. do not have.

Note that normal DCSP-TIG welding does not contain large amounts of H ₂ gas as mentioned above, and blow holes are often caused by dirt in the welding groove or entrainment of oxide film. Therefore, the blow hole appears in a deformed shape.

According to this invention, DCSP of aluminum
During TIG welding, as mentioned above, an alternating magnetic field is applied to the molten pool, and the molten pool is rotated alternately left and right by Lorentz force to stir it, so deformation blow holes due to the presence of an oxide film unique to aluminum are avoided. It is ejected outside the weld metal, or at least forms a blow hole with an acceptable round shape. Furthermore, although the generation of feather-like crystals cannot be prevented by stirring the molten pool by rotation in one direction, the crystal grains become finer by stirring by repeating rotations alternating left and right, thereby suppressing their generation.

By the way, in DCSP-TIG welding of aluminum, when the welding current increases, the welding current generates a magnetic field, which causes the molten pool to rotate clockwise, although the reason is not clear. As a result, as shown in FIG. 5, the bead 12 is deformed and an undercut 13 is created on the right side in the direction of welding progress.

However, in the embodiment of the present invention, the alternating magnetic field applied to the molten pool is a non-balanced alternating magnetic field in which the clockwise rotational force on the molten pool, which occurs as the welding current increases, is canceled out by the counterclockwise rotational force. As a result, a proper bead shape as shown by the chain line 20 in FIG. 5 is obtained.

To generate an unbalanced alternating current, for example, in the alternating current the positive time t ₁ is made longer than the negative time t ₂ or the positive current value It is sufficient to make A ₁ larger than the negative current value A ₂ . Of course, the opposite case is also possible, and in short, the polarity time for generating the magnetic field for counterclockwise rotation may be lengthened or the current value may be increased. Although the power supply current waveform is generally a rectangular wave as shown in the figure, it is not limited to this.

[Brief explanation of the drawing]

Fig. 1 is an overall side view showing the method of the present invention, Fig. 2 is an enlarged vertical cross-sectional view of the main parts, Figs.
The figure is a plan view of the main part, FIG. 3 shows the state of welding current, and FIG. 4 shows the state of stirring of the molten pool. Fifth
The figure is a cross-sectional view showing the state of the bead, Figures 6 and 7 are diagrams each showing the waveform of a nonequilibrium alternating current, and Figures 8 a to g show the results of various changes in the frequency of the alternating magnetic field applied to the molten pool. Figures 9A and 9B are plan views of weld metal showing the presence or absence of feather-like crystals in the case where blowholes are generated when no alternating magnetic field is applied to the molten pool; 10A and 10B are a plan view and a cross-sectional view of the weld metal showing a state in which no blow holes are generated when an alternating magnetic field with a frequency of 5 Hz is applied to the molten pool. 1... TIG torch, 4... Aluminum material to be welded,
6... Magnetic field generating coil, 9... Molten pool.

Claims (1)

[Claims] 1 For DCSP-TIG welding of aluminum,
An aluminum alloy that is characterized by applying an alternating magnetic field to the molten pool with a component perpendicular to the welding current flowing through the molten pool and having a frequency of 2 to 15 Hz, and stirring the molten pool by rotating the molten pool alternately left and right by Lorentz force.
DCSP - Defect prevention method in TIG welding.