JPH04155000A - Zinc-manganese alloy plated steel sheet excellent in spot weldability - Google Patents

Abstract

PURPOSE:To extend the life of an electrode tip and to widen the welding current range by incorporating a component having a lower m.p. than Fe into the plating layer in the Zn-Mn plated steel sheet. CONSTITUTION:One or >=2 kinds among Al, Ni, P, Ce and S are incorporated by <0.0050-5% into the plating layer of a Zn-Mn alloy plated steel sheet. An oxide film consisting essentially of ZnO is formed, as required, on the plating layer on both sides respectively at 30-3000mg/m<2>. Since the plated steel sheet is excellent in spot weldability and the number of continuous spots can be increased, welding can be continued for a long time without changing the electrode tip. Consequently, the quality of the weld zone is secured, and the productivity in welding is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a zinc-manganese alloy coated steel sheet with excellent spot weldability.

[Conventional technology]

For example, Japanese Patent Application Laid-Open No. 62-215211 discloses a method for improving the weldability of galvanized steel sheets, in which the surface of the galvanized steel sheet is coated with a medium film that makes electrode protection metal adhere to the spot. It is disclosed that the life of electrode tips in welding can be significantly extended.

Furthermore, JP-A No. 2-11983 discloses that an oxide film containing 30 to 3000 mg of ZnO as a main component is applied to the surface of a plated steel sheet.
/m2 to similarly improve weldability.

[Problems that the invention attempts to solve]

By the way, although each of the above-mentioned techniques can improve the life of the electrode tip, it cannot necessarily meet the demand for expanding the range of welding current that can be welded.

In view of the above-mentioned problems, the present invention provides a zinc-manganese alloy plated steel sheet with excellent spot weldability that advantageously solves the demands for improvement in electrode tip life and expansion of welding current range.

[Means to solve the problem]

The present invention solves the above problems. (1) Electrolytic zinc-manganese alloy plating and zinc-manganese alloy plated steel sheet (2 ) In item (1) above, as an element with a lower melting point than iron, A
One or more of e, Ni, P, Ce, S
．． Zinc-manganese alloy plated steel sheet with excellent spot weldability with a content of less than 0050 to 5%
The present invention is a zinc-manganese alloy plated steel sheet having excellent spot weldability as described in item 1) or (2).

[For production]

The present invention will be explained in detail below along with its operation.

The galvanized steel sheet that is the subject of the present invention can be produced by electroplating,
There are various manufacturing methods other than hot-dip plating, such as vapor deposition plating and thermal spraying, and the plating composition contains 5 to 95 wt% of 1.In in Zn, and has corrosion resistance,
In order to improve various functions such as adhesion, it contains one or more alloying elements and unavoidable impurity elements, and S
iO2,A (ceramic fine particles such as 1202,
There are plating layers in which oxides such as TiOz and organic polymers are dispersed, and there are those with a single composition in the thickness direction of the plating layer, those with a composition that changes continuously or layered, and even multi-layer plating. In some steel plates, the top layer, middle layer, or bottom layer contains Fe or Ni as a main component and various elements such as Zn or P.

For example, electrolytic zinc-manganese alloy galvanized steel sheets, single plating layers or multiple plating layers, plated steel sheets with organic coatings on these plating layers, vapor deposition of zinc and zinc-containing metals, etc. There is a plated steel plate.

Others 5iOz, Al 20. Ceramic fine particles such as.

There is a dispersion plated steel sheet in which Tiez oxide fine particles, polymers, etc. are dispersed in a zinc alloy plating layer.

An oxide film mainly composed of ZnO may contain, in addition to ZnO, component elements contained in the plating layer, or compounds such as oxides thereof, etc., in the oxide. Further, in the case of forming an oxide film by an electrochemical method, the treatment liquid may contain components or compounds contained in the treatment liquid.

Plating layer and one or two of Ae, Ni, P, Ce, and S
The reason why the life of the electrode tip is improved and the suitable welding current range is expanded, that is, weldability is improved by using the above-mentioned materials, will be described below.

The present inventors have proposed electroplating of zinc-manganese alloy plated steel sheets and an element having a lower melting point than Fe, such as A I
, Ni, P, Ce, and S, or by forming an oxide film mainly composed of ZnO on the surface of the plating layer, the life of the electrode tip in -layer spot welding can be significantly extended. It has been found that it is possible to significantly expand the weldable current range.

In the present invention, the surface of the plating layer made of the above-mentioned low melting point component is coated with an oxide film mainly composed of ZnO and spot welded, so that the plating metal is first melted by the welding heat. However, when this plated metal comes into direct contact with the electrode tip, the copper in the electrode tip composition and the zinc in the plating composition react selectively, forming a low melting point copper-zinc alloy layer and causing wear to the electrode tip. , which will shorten the lifespan.

The plated metal in the molten state is cut off from contact with the electrode tip by the ZnO film coated on the surface of the plated steel sheet, which prevents melting damage caused by direct contact between the plated metal and the electrode tip, and further prevents the plated metal from being in the molten state. The plated metal is alloyed with the iron of the steel plate to become mainly an iron-zinc alloy,
This passes through the cracks in the ZnO film or migrates to the tip of the electrode tip together with the ZnO film and accumulates, forming a protective film for the electrode tip, that is, an electrode protective metal, and even if welding continues, the thickness and shape of the protective film will change. There are no major changes, and good welding is always possible.

This protective film has the effect of keeping the shape of the tip of the electrode tip convex, allowing welding with low current during the process where the electrode tip is softened and damaged, and extending the life of the electrode tip.

Here, the electrode protection metal is mainly an alloy of plating metal and base iron, and has an average concentration of Fe: 20 to 6.
0') (i, Zn: '↓Although it is often about 0 to 80%, it is generally preferable to have a high Fe concentration, and it is not preferable particularly when a high concentration Zn portion is localized.

Further, the electrode protection metal may include components of the plating metal, components of the steel sheet such as Mn and S, components of surface treatment products such as chemical conversion treatment of the plated steel sheet such as Or, and components of the electrode tip such as Cu.

That is, the tip of the electrode tip is coated with a ZnO film that generates an electrode protection metal mainly composed of Fe and Zn on the surface of the plating layer, and the alloy of the plating metal and the steel plate is applied through the ZnO film or with the film using welding heat. This is done by welding while forming them on the electrode tip. Therefore, the reaction between the electrode tip and the Zn component of the plating layer is suppressed and the formation of electrode protective metal is promoted.

Furthermore, the promotion of 111 adhesion onto the electrode tip greatly influences the degree of improvement in the life of the electrode tip.

The generation of the electrode protection metal is caused by the F of the base metal into the hot-dipped metal.
This is due to e-diffusion, but this varies greatly depending on the plating metal components. When a component with a melting point higher than Fe is present together with the plating metal, it is not easy to generate an electrode protective metal.

On the other hand, it has been found that when a component having a melting point lower than that of Fe coexists with the plating metal, the formation of the electrode protective metal becomes easy. In addition, in the process of generating the electrode protection metal, the Fe concentration of the electrode protection metal component increases, raising the melting point and greatly reducing the viscosity of the electrode protection metal, thereby suppressing the transfer of the electrode protection metal to the electrode tip. . Even in such cases, the presence of the plating and components with a lower melting point than Fe makes it possible to greatly reduce the viscosity of the electrode protection metal made of Fe-Zn alloy, which prevents the electrode protection metal from transferring to the electrode tip. It becomes easier.

Furthermore, it has been found that improving the viscosity of the electrode protection metal is effective in avoiding the phenomenon of welding between the electrode tip and the material to be welded, and makes it possible to expand the weldable current range.

In this way, in zinc-manganese plated steel sheets in which a component with a lower melting point than Fe coexists with the plated layer, by forming a ZnO film on the surface of the plated layer, welding II
) It is possible to expand the range of current that can be achieved and to significantly extend the life of the electrode tip.

In addition, in plating containing a component with a lower melting point than Fe, Z
Even in the absence of an nO film, the reaction of ZnO with the Zn component of the plating layer on the electrode tip is not suppressed, but the effect of improving the viscosity of the electrode protective metal is to expand the weldable current range and extend the life of the electrode tip. becomes.

In other words, plated steel sheets with components with a lower melting point than Fe can expand the weldable current range and extend the life of the electrode tip, but in order to further enhance this effect, it is necessary to form an oxide film on the surface of the plating layer. Indicates that granting is valid.

The appropriate amount of oxide film to be produced is 30 to 3,000 mg/m2 of ZnOJil per side of the oxide film; less than 30 mg/m2 is insufficiently effective, and more than 3,000 mg/m2 is This is undesirable because the resistance becomes large, the electrode becomes susceptible to softening and deformation, and the life of the electrode becomes short.

An extremely small amount of oxide film, mainly composed of ZnO, is formed when the plated steel sheet comes into contact with air, but the amount of oxide film is so small that it is difficult to measure.
The above effects are not obtained at all, and since the oxide film is not intentionally produced as in the present invention, it is assumed that substantially no oxide film is produced.

In addition, low melting point components include Ae, Nu, P, Ce, S
etc., containing one or more of these components at 0.0
Coexistence within a range of less than 0.5% to 5% results in a fi effect. If this value is less than 0.0050%, the effect of improving the viscosity of the electrode protective metal is small, and no practical effect can be obtained.

- If the blade metal content exceeds 506, the viscosity of the electrode protection metal increases, which is not preferable because the effect of improving the electrode life and expanding the appropriate welding current range by forming the electrode protection metal disappears.

Figure 1 shows electrolytic zinc-manganese (14n: 15wt%
) is a drawing showing the influence of Ni content on expansion of the appropriate welding current range when Ni is included in the alloy plating layer. Here, 1) Plate thickness CLB mm - double welded double welded two-plate welded lead-monomanganese gold-plated steel plate.

Plating deposition amount: 115ρ15 g/m23) Appropriate welding current range - Welding current (S) - Minimum nugget forming current value (Imin
).

As can be seen from the above description and drawings, not only the life of the electrode tip can be improved, but also the range of appropriate welding current can be significantly expanded with an appropriate Ni1l.

However, as a method of forming the above-mentioned low melting point element and zinc-manganese plating layer, there is a method of adding it to the zinc-manganese plating layer during normal electroplating and incorporating it into the zinc-manganese plating layer, or a method of adding only the low-melting point element to the zinc-manganese plating layer. electrolytic zinc-
Plating before or after manganese plating [7, (”J
”-j may be used.

Effective methods for forming the oxide film include immersion oxidation in an alkaline or acidic solution after plating, and electrochemical oxidation in an alkaline, neutral or acidic solution.

〔Example〕

Next, Examples of the present invention are listed in Table 1 along with comparative examples.

The conditions in Table 1 are as follows.

Note 1 = Contents of plated steel sheet 1) All galvanized zinc-manganese alloy double-sided plated steel sheets. , 2) All steel plates are ordinary steel plates with a thickness of 0.8 mm.

3) In Example 3 and Comparative Example 3, Zn-Mn plating was used as the lower layer, and Zn-Fe plating containing 85 wf% of Fe was used.
Double-layer electrogalvanized steel sheet with 3 g/m2 upper layer plating.

q) Example 5 is a case of a vapor-deposited zinc-manganese alloy plated steel sheet.

Note 2 = The oxide film generation treatment method is Zn (NO3) after plating.

・It was carried out by immersion in a 6H20 aqueous solution. Processing mouth bath <7) 11 degrees Get, Zn(NOx)z・6H20
:600g/l, HNO3:0.5ml! /
I! , the bath temperature was 50°C, and the amount of oxidized film was changed over the treatment time from 0 to 1.
It was controlled in 0 seconds.

Note 3: Measurement of ZnO in oxides ZnOJl, Z calculated from [0] intensity obtained by GD3 analysis (glow discharge optical emission spectrometry) of the surface of the plating layer
For the conversion of nO, a method of estimating from the relationship between the [0] intensity of GDS obtained from standard samples having different ZnO thicknesses and the ZnO thickness was used.

Note 4: Welding conditions The welding conditions are as follows.

1) Pressure force: 250 Kgf 2) Initial pressurization time: 110 Hz 3) Current application time: 12 Hz 4) Holding time: 511z 5) Plate combination: two-ply welding 6) Electrode tip life test welding current, 1IKA7) Chi.
Sib tip diameter: 5.0φ (cone-shaped) 8) Evaluation of appropriate welding current range = s -lm1n S: Welding flow m where the electrode tip is welded Imin: Welding current that makes the nugget diameter 3.6φ 9)
Electrode life end point determination: Number of dots that can ensure a nugget diameter of 3.6 mm at 85% of welding current: 10) Electrode material: Cu-Cr (electrode made of commonly used material) Electrode life welding is performed on one side of a plated steel plate. Two sheets were stacked with one side on top and the other side on the bottom, and 20 points were continuously welded at a speed of 1 point/2 seconds, followed by a 30 second pause.

As is clear from this example, in the alloy plated steel sheet of the present invention, the number of electrode strikes is 9000 or more, which is a dramatic increase compared to the conventional method.

〔Effect of the invention〕

As explained above, the alloy-plated steel sheet of the present invention has excellent spot weldability and can increase the number of consecutive welding points, so it is possible to weld for a long time without replacing the electrode tip, improving the durability of the electrode. be able to. Furthermore, the range of appropriate welding current is maintained at the same level as conventional materials, and the weldability is also good, which has an excellent effect on ensuring the quality of welded parts and improving the productivity of welding work.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the relationship between the appropriate welding current range and the Ni content when Ni is contained in the electrolytic zinc-manganese alloy plating layer. Agent: Patent attorney Masamitsu Akizawa and 1 other person! 6

Claims (3)

[Claims] (1) A zinc-manganese alloy plated steel sheet with excellent spot weldability, consisting of electrolytic zinc-manganese alloy plating and 0.0050 to less than 5% of an element with a lower melting point than iron. (2) Al, Ni, P, and C as elements with lower melting points than iron.
The zinc-manganese alloy plated steel sheet with excellent spot weldability according to claim 1, wherein one or more of e and S is contained in an amount of 0.0050 to less than 5%. (3) The zinc-manganese alloy coated steel sheet with excellent spot weldability according to claim (1) or (2), wherein an oxide film mainly composed of ZnO is formed on the upper layer of the plating layer at a rate of 30 to 3000 mg/m^2 per side. .