JPH03266640A - Laminated steel sheet with excellent corrosion resistance and welding characteristics - Google Patents

Abstract

PURPOSE:To obtain a laminated steel sheet with excellent corrosion resistance, weld ability, especially spot weld ability by pinching a polymer resin layer between two upper and lower steel sheets and blending a metal powder with approximately spherical shape before it is crushed and pinched between the steel sheets, a specified mean particle diameter, the thickness of the polymer resin layer, a Vickers hardness and a m.p. which is higher than that of an electroplated film. CONSTITUTION:In a laminated steel sheet 1 pinching a polymer resin layer 2 between two upper and lower steel sheets, on each steel sheet, a molten alloy zinc plated layer 5 as a lower layer and an electroplated layer 4 as an upper layer are formed at least on the surface of the side faced to the polymer resin layer 2 are formed. In the polymer resin layer 2, a metal powder 3 with an approximately spherical shape before it is crushed and pinched between the steel sheets, a mean particle diameter D in a range of T D 2T to thickness T of the polymer resin layer, a Vickers hardness of 180 or smaller and a m.p. which is higher than that of the electroplated film, is mixed. It is thereby possible to obtain a laminated steel sheet with excellent corrosion resistance, weld ability, especially spot weld ability and adhesive properties.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laminated steel plate that has excellent weldability and corrosion resistance.

[Conventional technology]

Laminated steel plates, in which a polymer resin is sandwiched between two thin steel plates, have excellent vibration damping properties and light weight.
It is widely used in automobiles, home appliances, construction materials, etc. for purposes such as noise prevention, vibration prevention, and weight reduction. However, since polymer resins have extremely high electrical insulation properties and do not allow current to flow through them, spot welding cannot be performed by direct energization as is. For this reason, many technologies have been proposed in the past that mix conductive materials such as metal powder, graphite powder, or spiral conductors into polymer resin to ensure conductivity between skin steel plates and enable spot welding by direct energization. (For example, JP-A-50-79920, JP-A-60-912, JP-A-6287341, JP-A-57-146649, JP-A-61-29)
No. 261, etc.) In these laminated steel plates that can be spot welded, if the skin steel plate is a cold-rolled steel plate, not only will the surface be susceptible to rust, but the joint surface between the polymer resin and the steel plate will be more likely to rust than the edges of the cut surface. Rust may invade the surface and cause peeling, so it is required to provide corrosion resistance. For this purpose, a method of using an iron-zinc alloy plated steel plate as the skin steel plate (for example,
3-158242), a method in which the bonding surface with the polymer resin is a chromate-treated surface and the outer surface is a galvanized surface (Japanese Patent Application Laid-Open No. 63-205227), A method of limiting the number of atoms and using a steel plate having an amate treatment layer thereon (Japanese Unexamined Patent Publication No. 1-280543) has been proposed.

[Problem to be solved by the invention]

Although conventionally proposed methods are effective in preventing peeling due to rust penetration at the joint surface between the polymer resin and the skin steel plate, they are not necessarily sufficient in terms of spot weldability. Ta. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a laminated steel plate that has excellent corrosion resistance and weldability, particularly spot weldability.

[Means to solve the problem]

It is basically possible to impart spot weldability by adding conductive metal powder or the like to a polymer resin using the various methods described above. The present inventors conducted intensive studies on the mechanism of imparting spot weldability to laminated steel sheets to which conductive metal powder was added, and obtained the following knowledge.

The role of conductive metal powder during spot welding is 1 in total.
In the initial stage of spot welding (within about 2 cycles), which consists of about 0 cycles, a current is passed between the electrodes. In other words, when the laminated steel plate and the material to be welded are sandwiched between welding electrodes while applying pressure, and a voltage is applied to the electrodes, if no conductive metal powder is added, the polymer resin layer is an electrically insulating layer, so as mentioned above, no current will be generated. does not flow, but when conductive metal powder is added, current flows through the conductive metal powder under and around the electrode. When electricity is applied, the skin steel plate generates resistance heat under and around the electrode, and the heat melts the polymer resin. The molten polymer resin layer under the electrode is removed by the pressure of the electrode, and the skin steel plates come into contact with each other, and normal spot welding is performed.

Therefore, if a layer with poor conductivity, such as a chromate film, is present on the bonding surface between the polymer resin and the skin steel plate, the electrical conductivity will deteriorate and the spot weldability will deteriorate.

In addition, the conductive metal powder generates resistance heat when a current flows through the conductive metal powder, although it is for a very short period of time at the initial stage of spot welding. Therefore, if the number of conductive metal powders is small, the conductive metal powders instantly generate resistance heat, melt and scatter, and no current flows. Furthermore, if some of the conductive metal powders are in very good contact with the steel plate, the current will concentrate there and rapidly heat the skin steel plate that is in contact with the conductive metal powder, causing the skin steel plate to melt and scatter. This may result in pinhole-like defects. Even if the number of conductive metal powders is large, if the contact condition with the skin steel plate is poor, the resistance will be high, making it difficult for current to flow, and the spot welding quality will decrease. Furthermore, when using galvanized steel sheets, since zinc has a significantly lower melting point than iron, the Zn plating layer that comes into contact with conductive metal powder may instantly melt, scatter, or evaporate due to resistance heat generation, making it more difficult to use than cold-rolled steel sheets. Best spot weldability is significantly reduced.

The present invention has been made based on the above-mentioned knowledge. In order to solve the above problems, in the present invention, in a laminated steel plate in which a polymer resin layer is sandwiched between two upper and lower steel plates, each of the steel plates has at least one side facing the polymer resin layer. A molten galvanized layer as a lower layer and an electroplated layer as an upper layer are formed on the surface, and the polymer resin layer has a substantially spherical shape before being crushed and sandwiched between steel plates. , the average particle diameter (D) is within the range of T≦D≦2T with respect to the thickness (T) of the polymer resin layer, and the Vickers hardness is 180 or less, and
The electroplated layer is characterized by being mixed with a metal powder having a melting point higher than that of the electroplated layer, and in particular, the electroplated layer is
It is characterized by being made of iron or iron-zinc alloy plating with an iron concentration of 50 to 100%.

[Effect]

Next, the operation of the present invention will be explained with reference to the drawings. FIG. 1 is a sectional view showing the first embodiment of the present invention;
The figure is a sectional view showing the second embodiment, and FIG. 3 is a front view showing the spot welding procedure.

In the drawings, 1 and 11 are laminated steel plates, 2 is a polymer resin layer, 3 is metal powder, 4 is an electroplating layer, 5 is a hot-melting galvanized layer, 6 is a skin steel plate, 7 is an electrode 8 is a single steel plate (material to be welded). In the laminated steel sheet 11 of the second embodiment, the molten galvanized layer 5 as the lower layer and the electroplated layer 4 as the upper layer are formed only on the surface of the surface steel sheet 6 on the side facing the polymer resin 2. .

The reason why the electroplating layer 4 is formed on the upper layer is mainly to prevent the plating layer from melting and scattering due to resistance heat generation. In other words, the iron concentration of the lower layer molten galvanized plating is 4 to 17%.
Although the melting point is higher than that of pure zinc (420°C), it is at most about 800°C, which is not necessarily sufficient. Types of electroplating include iron-zinc,
Zinc-nickel, zinc-manganese alloy plating or N
1. Fe, etc. can be used, but it is desirable to use iron or iron-zinc alloy plating with an iron concentration of 50 to 100% because it has the same composition as molten alloyed galvanized plating.

The effect of forming the electroplated layer 4 on the upper layer is not only the above-mentioned improvement in spot weldability but also the following effects. That is, compared to the molten alloyed galvanized layer 5, the surface of the electroplated layer 4 is smoother, and the contact state with the conductive metal powder 3 is improved. Furthermore, since the iron concentration is high, the wettability is improved and the adhesive strength with the polymer resin is increased.

As the conductive metal powder 3, one whose original size before crushing is larger than the thickness of the polymer resin layer 2 is used. The reason for this is that by crushing the layers to the thickness of the polymer resin layer 2 when laminating them, they are brought into contact with the upper and lower steel plates, and as a result, low resistance can be obtained. As for the size of the conductive metal powder 3, the average particle diameter (D) is within the range of T≦D≦2T with respect to the thickness (T) of the polymer resin layer 2. D is T
If it is smaller, sufficient contact cannot be obtained; on the other hand, D
If it is larger than 2T, it will be difficult to crush. Further, the conductive metal powder 3 used has a spherical shape as its original shape before being crushed. The reason for this is that if the particle size distribution is accurately grasped, the area of the portion where the skin steel plate 6 and the conductive metal powder 3 are in contact with each other when crushed can be easily determined.

The conductive metal powder 3 used has a Vickers hardness of 180 or less. The reason is that the conductive metal powder 3 can be easily crushed. That is, the Vickers hardness of the electroplated layer is approximately 300 for iron-zinc alloy plating with an iron concentration of about 10, for example. Therefore, if hard conductive metal powder is used, the conductive metal powder cannot easily penetrate into the plating layer even if the rolling blade is raised when stacking the layers, and furthermore, if the rolling blade is raised to crush it, Rather, the skin steel plate 6 is deformed, and as a result, the conductive metal powder and the plating layer come into point contact, which results in insufficient contact and tends to reduce spot weldability. Furthermore, in order to prevent the conductive metal powder from being crushed,
Air bubbles enter the bonding surface with the polymer resin, causing problems such as a decrease in adhesion. As mentioned above, by using a conductive metal powder with a Vickers hardness of 180 or less, not only good conductivity can be obtained, but also air bubbles will not form at the joint surface between the polymer resin and the skin steel plate ( Good adhesion can be obtained.

Furthermore, it is desirable that the melting point of the conductive metal powder is higher than that of the electroplated film. That is, the purpose of forming an electroplated film on the upper layer is mainly to increase the melting point of the film and improve spot weldability, and it is necessary that the melting point is higher than that of the electroplated film.

〔Example〕

Next, examples of the present invention will be described together with comparative examples.

The laminated steel plates of the present invention, the comparative laminated steel plates, and a single steel plate (material to be welded) were welded by spot welding. The laminated steel plates, single steel plates, polymer resin, conductive metal powder, lamination conditions, and spot conditions are shown below.

The number of welding defects and shear adhesion were evaluated, and the results are shown in Table 1. In addition, the corrosion resistance of laminated steel plates was evaluated by the salt spray test shown below, and the results were used in the first test.
It is also shown in the table.

(1) Steel plate ■ Iron-zinc hot alloy coated steel plate (both sides plated) (Iron concentration 1O1θ%, coating amount per side 45 g/d and 60 g/rrI, plate thickness 0.4 mm, chromate treatment with or without adhesive, Cr attached) rate 40-50 ■/rd).

■ An iron-zinc electroalloy plating film is formed on the upper layer.
Steel plate of item (1) above (iron concentration of treated film: 80.4 N, adhesion amount: 4.0 g/rrf per side).

■Cold-rolled steel plate (aluminum killed steel plate, plate thickness 0.4 mm).

(2) Polymer resin ethylene-acrylic acid ester copolymer resin in film form. Thickness is 50u0 (3) Conductive metal powder■ Type: Uses spherical nickel powder manufactured by the precipitation method.

■ Average particle size: 82μ (distribution 74-90μ), 68μ
(distribution 63-74μ), 59μ (distribution 44-74μ) and 48μ (distribution 44-53μ) were used.

■ Hardness: Vickers hardness 100, 180 and 2
I used 80.

■ Amount added: Selected within the range of 10 to 30%.

Note that the conductive metal powder was added at the time of molding the film.

(4) Lamination conditions Use a laminator to attach a polymer resin film containing nickel powder to one side of a preheated steel plate (approx.
Using a pair of pinch rolls lined with a heat-resistant resin, a steel plate heated to 80℃) and heated above the melting point of the polymer resin in a separate heating furnace is laminated by applying a linear pressure of 10)cg/a++ or higher. did. After lamination, the layers were slowly cooled to room temperature in air.

(5) Spot welding conditions■ Electrode: Dome-shaped Cu-Cr electrode (tip diameter, 61mφ
).

■ Pressure force: 180 kg f.

■Current: 10.

■　Electrification time: 12 cycles (60Hz).

■ Control method: constant current control (0.5 cycle control) ■ Welding: 30 x 10 (1 m sample and 0.5 cycle control)
8+w thick single steel plate (if the laminated steel plate is a plated steel plate,
Melt-alloyed galvanized steel plates were used (if the laminated steel plates were cold-rolled steel plates, cold-rolled steel plates were used), and the sheets were stacked and welded.

(6) Salt spray test In order to evaluate corrosion resistance, the sample was subjected to a 1000 hour salt spray test (JIS Z 2371), the upper and lower steel plates were peeled off, and the amount of rust infiltration at the joint surface of the polymer resin was determined.
Visually inspected.

〔Evaluation methods〕

Regarding spot weldability, spot welding was performed at one location for every 500 samples of 30×I00m, for a total of 500 welds, and the number of defects such as sparks, non-energization, and melting around the electrodes was determined. Ta. Based on the number of defective pieces, evaluation was made as ◯: good, △: slightly poor, and X: poor.

Corrosion resistance is evaluated by the amount of rust infiltration from the end face. ◎ if the amount of rust intrusion from the end face is 1 m or less, ○ if 1 to 5, 5
The fins and above were defined as ×.

As is clear from Table 1, Examples 1 to 5 within the scope of the present invention had good weldability, corrosion resistance, and shear electrodeposition strength.

On the other hand, Comparative Example Nal had no electroplated layer (upper layer), had somewhat poor weldability, and poor shear electrodeposition strength.

In comparison sidetone 2, the average particle size of the metal powder was DOT, and the weldability was poor.

In Comparative Example Net3, the Vickers hardness of the metal powder exceeded 180, and the weldability was poor.

Comparative Example N114 had no electroplated layer and had chromate treatment, so weldability was poor.

Comparative Example No. 5 had no electroplating layer, was chromate treated, and had a Vickers hardness of over 180, so its weldability was somewhat poor.

Comparative examples N116 and Na3 are cold-rolled steel plates, and the comparison sidetone is 6.
The corrosion resistance is Nu? had poor weldability.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a laminated steel plate that has excellent corrosion resistance and weldability, especially spot weldability, and excellent adhesion, and has been used in conventional corrosion-resistant spot weldability for automobiles, home appliances, construction materials, etc. Industrially useful effects are brought about, such as making it possible to significantly expand the application to applications that could not be applied due to the problem.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a sectional view showing a second embodiment, and FIG. 3 is a front view showing a spot welding procedure. In the drawings: 1.11-1 Laminated steel plate, 2-1 Polymer resin layer, 3-.- Metal powder, 4..., Electroplated layer, 5-9- Melt alloyed galvanized layer, 6-1 Skin steel plate , 7°0. electrode, 811. Single steel plate. Figure 1 Figure

Claims (1)

[Scope of Claims] In a laminated steel plate in which one polymer resin layer is sandwiched between two upper and lower steel plates, each of the steel plates has a molten layer as a lower layer on at least the surface facing the polymer resin layer. An alloyed galvanized layer and an electroplated layer as an upper layer are formed, and the polymer resin layer has an approximately spherical shape before being crushed and sandwiched between steel plates, and has an average grain size. Diameter (D
) is T≦D with respect to the thickness (T) of the polymer resin layer.
≦2T, a Vickers hardness of 180 or less, and a laminated steel sheet having excellent corrosion resistance and weldability, characterized in that it contains a metal powder having a melting point higher than that of the electroplated film. 2. The laminated steel sheet with excellent corrosion resistance and weldability according to claim 1, wherein the electroplated layer is made of iron or iron-zinc alloy plating with an iron concentration of 50 to 100%.