JPH06649A - Welding method for galvanized steel sheets - Google Patents

Abstract

PURPOSE:To suppress the occurrence of a blowhole caused by gasification of zinc. CONSTITUTION:Galvanized layers 3 of the galvanized steel sheets 1 are oxidized by shielding gas 11 and the galvanized steel sheets 1 are joined together by filler metal 10 having the lower melting point than the gasification temperature of zinc oxide generated by this shielding gas 11 and having the higher boiling point than the melting point of zinc not oxidized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding a galvanized steel sheet, and more particularly to a method for welding a galvanized steel sheet capable of suppressing the formation of blowholes due to vaporization of zinc.

[0002]

2. Description of the Related Art Galvanized steel sheets are widely used for automobile bodies and the like because of their excellent corrosion resistance. Joining of galvanized steel sheets is usually performed by melting the steel sheets by gas shielded arc welding using a shield gas. In the welding of galvanized steel sheet by the gas shield arc welding method, there occurs a phenomenon that zinc on the surface of the steel sheet becomes a gas during welding and the gas remains in the weld metal. Therefore, there is a problem that blowholes are generated in the weld metal and the strength of the joint is lowered.

As a prior art relating to the welding of galvanized steel sheets, for example, Japanese Patent Application Laid-Open No. 57-209778 is known. In the gas shielded arc welding method of the present gazette, the effect on the shielding gas and the welding atmosphere is reduced by oxidizing the plated zinc with the shielding gas and suppressing the evaporation of zinc.

[0004]

However, even if zinc oxide is oxidized by a shield gas to oxidize zinc, the vaporization temperature of zinc oxide cannot be significantly increased, and if zinc oxide comes into contact with a molten pool at about 1500 ° C. After all, the problem that the zinc oxide is evaporated and the blowhole is generated cannot be solved yet.

The theoretical sublimation point of zinc oxide is 1725.
Although it was ℃, it was found from the experiment that it actually vaporizes considerably even at about 1300 ℃. Therefore, when the steel sheet itself of the galvanized steel sheet is simply melted and joined, since the melting point of iron is about 1500 ° C., even if zinc is oxidized, vaporization of zinc oxide causes blowholes. The contents of the experiment that confirmed that zinc oxide evaporates at about 1500 ° C are described in "Working method in arc welding of galvanized steel sheet" in the material of the 105th welding arc physics research committee of the Japan Welding Society (1992 1 24).

In view of the above problems, it is an object of the present invention to provide a method for welding a galvanized steel sheet capable of suppressing the formation of blowholes due to vaporization of zinc.

[0007]

According to the present invention, there is provided a method for welding a galvanized steel sheet according to the present invention, which is a method for welding a galvanized steel sheet whose surface is galvanized by arc welding using a shield gas. A method for welding a plated steel sheet, wherein zinc coated on the steel sheet is oxidized by a shield gas, and has a melting point lower than the vaporization temperature of zinc oxide produced by the shield gas and is higher than the boiling point of unoxidized zinc. It is a method of joining galvanized steel sheets with a filler material having a high melting point.

[0008]

In the welding method for a zinc-plated steel sheet having such a structure, the zinc plated on the steel sheet is oxidized by the shield gas and changed to zinc oxide which is difficult to vaporize.
Since the steel plates are joined by a welding material having a melting point lower than the vaporization temperature of zinc oxide, the melting amount of the steel plates can be suppressed to a small level. Therefore, the temperature of the molten pool can be lowered, and the evaporation of zinc oxide can be prevented. As described above, since the steel plates can be joined at a low temperature, the vaporization of zinc oxide is less likely to occur, and the generation of blowholes due to the vaporization of zinc is suppressed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the galvanized steel sheet welding method according to the present invention will be described below with reference to the drawings.

1 to 3 show an embodiment of the present invention. In the figure, 1 indicates a galvanized steel sheet in which a galvanized layer 3 is formed on the surface of the steel sheet 2. A welding torch 5, which is a part of the MIG welding machine, is arranged above the galvanized steel sheet 1. The welding torch 5 has a conductive tip 7 for supplying power to a welding wire 10 as a filler material. A shield nozzle 8 for flowing the shield gas 11 toward the welded portion is arranged on the outer periphery of the conductive tip 7.

The shield gas 11 is an argon gas (A
r) at least oxygen gas (O ₂ ) and carbon dioxide gas (C
One of O ₂ ) is mixed. FIG. 2 shows the component ratios when three gases of Ar, CO ₂ and O ₂ are mixed. Here, assuming that the ratio of CO ₂ (volume ratio) is A% and the ratio of O ₂ is B%, 6 ≦
It is desirable to mix Ar with a composite gas satisfying A + 3B ≦ 18. Further, in the case of mixing only CO ₂ and Ar, it is desirable that the proportion of CO _{2 be} 6 to 18%.
_In the case of mixing only ₂ and Ar, the proportion of O ₂ is preferably 2 to 6%.

In the above, the ratio O of CO ₂ is O
The coefficient of the ratio B of ₂ is set to 3 because the gas is decomposed in the arc to generate oxygen atoms and the oxidizing ability is O ₂ is CO.
_This is because there are about 3 times as many as ₂ . Further, in the above, if the gas ratio inequality is less than 6 for A + 3B, the cathode spot of the arc moves remarkably on the surface of the material to be welded, the arc is not stabilized, and the weld bead shape becomes uneven. Further, zinc is not reliably oxidized, and the effect of reducing blowholes is not sufficiently obtained. If the gas ratio A + 3B exceeds 18, the molten metal is violently oxidized and the effect of reducing blowholes is obtained, but the weld metal becomes brittle and the strength of the joint decreases, so the above composition ratio must be strictly observed. Will be required.

The welding wire 10 as a filler material is made of a material having a melting point lower than the vaporization temperature of zinc oxidized by the shield gas 11 and higher than the boiling point of zinc. That is, the welding wire 10
It is made of a material having a melting point of 950 ° C to 1400 ° C. In the present embodiment, the welding wire 10 is made of copper (Cu), but of course other materials such as copper,
You may comprise from nickel and a titanium (Cu-65Ni-5Ti) alloy.

Next, the welding method of galvanized steel sheet and its operation will be described. When the galvanized steel sheet 1 is positioned at a predetermined position, an arc 12 is generated between the joint portion of the galvanized steel sheet 1 and the welding wire 10, and welding is started. Further, a shield gas 11 is ejected from the shield nozzle 8 with the start of welding, and the periphery of the arc 12 is shielded by the shield gas 11.

The galvanized layer 3 of the galvanized steel sheet 1 is oxidized by the arc heat and the shield gas 11 to produce zinc oxide which is difficult to vaporize. The welding wire 10 is melted by arc heat, and the galvanized steel sheet 1 is joined by the molten metal generated by the melting of the welding wire 10.

Here, since the welding wire 10 having a low melting point is used as the filler material, the melting of the welding wire 10 by the arc heat is promoted, and the melting amount of the steel sheet 1 is the welding wire 1.
The amount is smaller than the melting amount of 0. Then, the molten steel plate 1 is thinned by being mixed with the welding wire 10 which is a filler material. Therefore, the temperature of the molten pool is almost determined by the low melting point filler material, and the molten pool does not rise to the temperature at which zinc oxide is vaporized.

As described above, according to the present invention, since the steel sheets 1 are joined while oxidizing the zinc plating layer 3 and suppressing the temperature rise of the molten pool, the vaporization of zinc is suppressed, and the vaporized zinc is converted into the molten metal. Mixing is almost eliminated. As a result, the generation of blowholes in the weld bead 13 is significantly suppressed, and the strength of the joint is increased.

FIG. 3 shows three kinds of welding wires 1 having different melting points.
The result of investigating the number of blowholes inside the weld bead by using 0 is shown. The welding conditions in this case were set as follows. Galvanized steel plate SGAC-45 / 45 Steel plate thickness 2.0 mm Welding speed 750 mm / min Gap between steel plate joints 0 mm Shield gas Ar + O ₂ (2%) Consumable electrode wire (A) Cu (B) Cu-65Ni-5Ti (C) Fe-60Ni (D) Steel The shield gas when Steel is used as the welding wire is different from the other shield gas components in Ar +.
CO ₂ (20%) was used.

As shown in FIG. 3, in the case of a welding wire having a melting point of 1380 ° C. or less, almost no blowholes are found. This is because the galvanized layer 3 is almost oxidized by the shield gas 11 during welding, and 1380
It is considered that the vaporization of zinc oxide (ZnO) can be reliably prevented at a temperature of not higher than ° C. And the melting point is 140
It can be seen that the number of blowholes sharply increases when the temperature exceeds 0 ° C.

[0020]

According to the present invention, the following effects can be obtained.

(1) Zinc coated on a steel sheet is oxidized by a shield gas, and has a melting point lower than the vaporization temperature of zinc oxide produced by the shield gas and higher than the boiling point of unoxidized zinc. Since the galvanized steel sheets are joined by the filler material, the vaporization of zinc can be suppressed.

Therefore, the vaporized zinc is hardly mixed into the molten metal, and the generation of blow holes can be greatly suppressed. As a result, the joint strength of the joint can be sufficiently increased.

Since the joining can be performed with a lower heat input than that of the usual arc welding, the thermal deformation can be suppressed to a small level even when joining thin plates.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a welding state of a galvanized steel sheet according to an embodiment of the present invention by a welding method.

FIG. 2 is a characteristic diagram showing the ratio of the components of the shield gas in FIG.

FIG. 3 is a characteristic diagram showing the relationship between the filler material and the number of blowholes generated.

[Explanation of symbols]

 1 Galvanized Steel Sheet 3 Galvanized Layer 5 Welding Torch 8 Shield Nozzle 10 Welding Wire as Filler Material 11 Shield Gas

Claims (1)

[Claims] 1. A method of welding a galvanized steel sheet, the method comprising welding a galvanized steel sheet whose surface is galvanized by arc welding using a shield gas, wherein the zinc plated on the steel sheet is shielded by a shield gas. Characterized in that the galvanized steel sheet is joined by a filler material which is oxidized and has a melting point lower than the vaporization temperature of zinc oxide generated by the shield gas and a melting point higher than the boiling point of unoxidized zinc. Welding method for galvanized steel sheet.