JP2581369B2 - Laminated steel sheet with excellent corrosion resistance and weldability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated steel sheet having excellent weldability and corrosion resistance.

[0002]

2. Description of the Related Art Laminated steel sheets in which a polymer resin is sandwiched between two thin steel sheets are used for automobiles, It is widely used for home appliances and building materials. However, polymer resins have extremely high electrical insulation properties and do not allow current to flow, so that spot welding by direct energization cannot be performed as it is. For this reason, there have been many proposals for technologies that add conductive materials, such as metal powder, graphite powder, and spiral conductors, to polymer resins to ensure conductivity between skin steel plates and enable spot welding by direct energization. (For example, Japanese Patent Application Laid-Open No. 50-79920).
JP, JP-B-60-912, JP-A-62-87
No. 341, JP-A-57-146649, JP-B-61-29261 , and JP-A-3-266640.
Gazette ).

[0003] In these laminated steel sheets capable of spot welding, when the skin steel sheet is a cold rolled steel sheet, not only the surface is easily rusted, but also the joining surface between the polymer resin and the steel sheet from the end of the cut surface. In some cases, rust may enter and cause peeling, and it is required to impart corrosion resistance. For this purpose, a method of using an iron-zinc alloy-plated steel sheet as a skin steel sheet (for example, JP-A-63-158242), a bonding surface side with a polymer resin is a chromate treated surface, and an outer surface is a galvanized surface. (JP-A-63-205227), a method in which the number of zinc atoms with respect to aluminum in the outermost layer of a plating coating is limited, and a steel sheet having a chromate-treated layer on its surface is used (JP-A-1-228)
No. 0543) has been proposed. Also, in the resin layer
An electrogalvanized plating layer as an upper layer
A method of providing the same (JP-A-3-266640) has also been proposed.
Have been.

[0004]

In the prior art,
Although effective in preventing peeling due to rust intrusion at the joint surface between the polymer resin and the skin steel plate, spot weldability is not necessarily sufficient. The present invention has been made to solve the above-described problems, and has as its object to provide a laminated steel sheet having excellent corrosion resistance and excellent weldability, particularly excellent continuous spot weldability.

[0005]

Means for Solving the Problems It is basically possible to add a conductive metal powder or the like to a polymer resin to impart spot weldability by the above-mentioned various conventional techniques. The present inventors have conducted intensive studies on the mechanism of imparting spot weldability to laminated steel sheets to which conductive metal powder has been added,
The following findings were obtained. That is, apply these laminated steel sheets
When performing a continuous spot melting of 2000 to 3000
If the skin steel sheet is plated steel,
For example, if the number of hits exceeds 1,000, the electrode is extremely damaged.
Wear, poor welding or reduced weld strength
Occurs. On the other hand, on the surface facing the resin layer,
In the case of plated steel sheets, the plating layer has a low melting point.
Therefore, it is said that defects occur due to vaporization of the plating layer
There's a problem. Therefore, plated steel sheets should be used to improve corrosion resistance.
When applied, prevent electrode wear and
It is necessary to prevent vaporization of the plating layer in contact with the layer.
The weldability from both sides of the outer layer and the plating layer on the resin layer side.
Need to improve.

The role of the conductive metal powder during spot welding is to supply a current between the welding electrodes sandwiching the laminated steel plate in the initial stage of spot welding consisting of about 10 cycles in total (within about 2 cycles). It is in. That is, when the laminated steel sheet and the material to be welded are sandwiched while being pressed by the welding electrode, and a voltage is applied to the electrode, when the conductive metal powder is not added, the polymer resin layer is an electric insulating layer as described above. No current flows, but when conductive metal powder is added,
An electric current flows through the conductive metal powder immediately below and around the electrode. Then, the energization causes the skin steel plate to generate resistance heat immediately below and around the electrode, and the heat melts the polymer resin. The molten polymer resin layer immediately below the electrode is removed by the pressing force of the electrode, the skin steel plates come into contact with each other, and spot welding is performed similarly to a normal steel plate.

[0007] Therefore, if a poorly conductive film such as a chromate film is interposed on the joint surface between the polymer resin and the skin steel plate, the electric conductivity is deteriorated and the spot weldability is reduced. Also, although very short time in the initial stage of spot welding, when current flows through the conductive metal powder,
The conductive metal powder generates resistance heat. Therefore, when the number of the conductive metal powder is small, the conductive metal powder instantaneously generates resistance heat,
Electric current stops flowing due to melting and scattering. In addition, among conductive metal powders, if there is one with extremely good contact with the steel sheet, the current concentrates there, rapidly heating the skin steel sheet in contact with the conductive metal powder, and the skin steel sheet melts and scatters, May cause pinhole-like defects. Even if the number of conductive metal powders is large, when the contact state with the skin steel plate is poor, the resistance becomes high, so that the current hardly flows, and the spot weldability decreases. Furthermore, when using galvanized steel sheet, zinc has a lower melting point than iron, so the galvanized layer that comes into contact with the conductive metal powder may melt or scatter or evaporate instantaneously due to resistance heat, and compared to cold-rolled steel sheet. Spot weldability is significantly reduced.

On the other hand, galvanized steel sheets and zinc-based alloys
In continuous spot welding of a gold-plated steel sheet , copper and zinc, which are the main materials of the electrode, react with each other to form a copper-zinc alloy layer at the electrode tip. Since this copper-zinc alloy layer is brittle, it peels off from the electrode at the next welding point. This phenomenon is repeated, and as a result, the tip of the electrode is worn in a concave shape. Alternatively, it is known that the electrode tip diameter may increase. Due to the aforementioned wear of the electrode tip, the welding of the laminated steel sheet delays the removal of the resin directly below the electrode, during which time a large amount of current flows through the skin steel sheet around the electrode, and the skin steel sheet around the electrode forms a ring. It may be blown. On the other hand, since the electrode diameter is large, the current density immediately below the electrode is reduced, and a sufficiently large nugget may not be formed. The inventors have developed various zinc-based
Spot welding test of laminated steel sheet with galvanized steel sheet
After conducting the test, there is no problem at all up to 500 points
In addition, welding spots at more than
It was confirmed that the phenomena of the occurrence of the fall were significantly different.

The present invention has been made based on the above findings. In a laminated steel sheet in which a polymer resin layer is sandwiched between upper and lower two steel sheets, each of the steel sheets is formed of the polymer resin layer. Only on the surface facing the side, a two-layer plating formed by an alloyed hot-dip galvanized layer as a lower layer and an electroplating layer as an upper layer is formed, and the other side not in contact with the polymer resin layer An alloyed hot-dip galvanized layer is formed on the surface of the polymer resin layer. In the polymer resin layer, the shape before being crushed and sandwiched between the steel sheets is substantially spherical, and the average particle diameter D is With respect to the thickness T of the polymer resin layer, T ≦ D ≦
It is within the range of 2T, characterized in that conductive metal powder having a Vickers hardness of Hv180 or less and a melting point higher than that of the electroplating layer is added.

[0010]

Next, the operation of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing one embodiment of the present invention,
FIG. 2 is a front view showing a spot welding procedure. In the drawing, 1 is a laminated steel sheet, 2 is a polymer resin layer, 3 is a conductive metal powder, 4 is an electroplated layer, 5 is an alloyed hot-dip galvanized layer,
Reference numeral 6 denotes a skin steel plate, 7 denotes an electrode, and 8 denotes a single steel plate (material to be welded).

In the laminated steel sheet according to the present invention, the alloyed hot-dip galvanized layer as the lower layer and the electroplated layer as the upper layer are formed only on the surfaces of the upper and lower two steel sheets facing the polymer resin layer. Is formed. The reason why the electroplating layer 4 is formed on the upper layer is mainly to prevent melting and scattering due to resistance heating of the plating layer. That is, the iron content in the lower layer galvannealed layer 5 is 4 to 17%.
The melting point is within the range of wt.%, and 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. As the type of electroplating, alloy electroplating of iron-zinc, zinc-nickel, zinc-manganese, or the like, or iron electroplating, nickel electroplating, etc., can be used. It is desirable to use iron electroplating or iron-zinc alloy electroplating with an iron content in the range of 50 to 100 wt.%.

The effect of forming the electroplating layer 4 on the surface on the side facing the polymer resin layer 2 is not only the effect of improving the spot weldability described above, but also the following effects. That is, the electroplating layer 4 has less surface oxide film, has a smooth surface, and has an effect of improving the electrical contact state with the conductive metal powder 3 as compared with the alloyed hot-dip galvanized layer 5. Further, since the iron content of the electroplating layer 4 is high, the wettability is improved, and there is also an effect of increasing the adhesive force with the polymer resin. It also has the effect of preventing peeling due to rust penetration. The iron content of the electroplating layer 4 needs to be higher than the iron content of the underlying galvannealed layer 5. The iron content of the electroplating layer 4 is 50 wt. % Or more is preferable. The iron content of the electroplating layer 4 is 50 wt. %, The weldability decreases.

On the other hand, the reason why the alloyed hot-dip galvanized layer 5 is formed on the surface that is not in contact with the polymer resin layer 2 is that the alloyed hot-dip galvanized layer 5 is used in the above-described continuous spot welding to prevent electrode wear. This is because it has the effect of preventing the occurrence of an electrode and extending the life of the electrode. Conventional veneers have an iron content of 10
wt. % Compared to galvannealed steel sheet
The content is 80 wt. % Galvanized steel sheet
Has better continuous spot weldability (longer electrode life)
It is said that in such laminated steel sheets, the opposite is true.
Showed a trend. That is, compared to the electroplating layer 4, the alloyed hot-dip galvanized layer 5 has an effect of preventing an alloying reaction between copper and zinc of the electrode at the time of continuous spot welding because a large number of oxide films are formed on the surface layer. There is. The adhesion amount of the electroplating layer 4 is 1 to 10 g / m ² , preferably 2 to 5 g / m ² .
in the range of m ^2. The amount of the galvannealed steel sheet 5 is 20 to 300 g / m ² , preferably 3 g / m ² .
It is in the range of 0 to 120 g / m ² . Other range
In this case, the balance between corrosion resistance and weldability is reduced.

As the conductive metal powder 3, a powder whose original size before crushing is larger than the thickness of the polymer resin layer 2 is used. The reason is that the conductive metal powder 3 is brought into contact with the upper and lower steel plates by crushing to the thickness of the polymer resin layer 2 at the time of lamination, and as a result, a low resistance can be obtained. As the size of the conductive metal powder 3, the average particle diameter D
However, with respect to the thickness T of the polymer resin layer 2, one having a range of T ≦ D ≦ 2T is used. For D> 2T, conductive metal powder 3
Is difficult to crush. The conductive metal powder 3 has a substantially spherical shape before being crushed. The reason 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 obtained. On the other hand, when D <T, sufficient contact cannot be obtained. Also, conductive metal
The amount of powder added is 10 to 30 wt. %, Preferably 10 to 2
0 wt. % Is preferred. 10 wt. %, The weldability is low.
30 wt. %, The conductive metal powder is crushed.
It will be difficult.

The conductive metal powder 3 has a Vickers hardness of Hv
Use the one with 180 or less. The reason is that the conductive metal powder 3 can be easily crushed. That is, the Vickers hardness of the electroplating layer 4 is about Hv300 in iron-zinc alloy plating having an iron content of about 10 wt.%, For example. Therefore, when the hard conductive metal powder 3 is used, the conductive metal powder 3 cannot easily penetrate into the plating layer even when the rolling force is increased during lamination, and the rolling force is increased when crushing. In this case, the skin steel plate 6 is rather deformed, and as a result, the conductive metal powder and the plating layer are in point contact with each other, the contact becomes insufficient, and the spot weldability tends to be reduced. Further, since the conductive metal powder 3 is not crushed, air bubbles enter into a bonding surface with the polymer resin layer 2 and adverse effects such as a decrease in adhesion force occur. As described above, by using the conductive metal powder 3 having a Vickers hardness of Hv180 or less, not only good conductivity can be obtained, but also air bubbles enter the bonding surface between the polymer resin layer 2 and the skin steel plate 6. No good adhesion can be obtained.

The melting point of the conductive metal powder 3 is desirably higher than the melting point of the electroplating layer 4. That is, the purpose of forming the electroplating layer 4 on the upper layer is mainly to increase the melting point of the electroplating layer 4 and improve the spot weldability, and the melting point of the conductive metal powder 3 is higher than that of the electroplating layer 4. is required. As the conductive metal powder 3, nickel powder, iron powder, stainless steel powder, copper powder and the like are used.

As the polymer resin layer, for example, thermoplastic resins such as polyolefins and polyamides represented by ethylene-based copolymers, propylene-based copolymers and butene-1 polymers, or acrylic resins and polyester resins Use a thermosetting resin such as Further, in the case of a polyolefin, the polyolefin is used as a vibration-damping resin layer, and two layers of modified polyolefin such as modified polyethylene and modified polypropylene are used as an adhesion layer in order to enhance the adhesion to a steel sheet. It is preferable to use a film composed of three layers sandwiching layers. In the case of only one damping layer, the adhesive strength to the steel sheet is inferior.

[0018]

Next, examples of the present invention will be described together with comparative examples. The laminated steel sheet of the present invention and a single steel sheet (material to be welded) shown in Table 1 were welded by simple spot welding or continuous spot welding. Further, for comparison, a laminated steel sheet and a single steel sheet (material to be welded) outside the scope of the present invention were welded by the same simple spot welding or continuous spot welding as in the examples. The following shows the single steel plate, polymer resin, conductive metal powder, lamination conditions and spot welding conditions. Then, in Examples and Comparative Examples, the number of occurrences of welding defects in simple spot welding, the number of continuous hitting points (ie, electrode life) until the tensile shear strength of the nugget portion in continuous spot welding does not decrease, and Table 1 summarizes the evaluation results of the shear adhesion between the molecular resin and the skin steel sheet. Further, the corrosion resistance of the laminated steel sheet was evaluated by the salt spray test shown below, and the results are shown in Table 1.

[0019]

[Table 1]

. [0020] (1) steel sheet iron - zinc molten alloy plated steel sheet "duplex plating" (material cold-rolled steel sheet, below): iron content 10.0 wt%, the coating weight per side 45 g / m ² or 60 g / m ² , 0.4 mm thick, with or without chromate treatment, Chromium (Cr) adhesion 40-50 mg
/ M ² . An iron-zinc alloy electroplating layer is formed on the iron-zinc hot-dip alloy plating layer. The above steel sheet (the upper layer plating is single-sided or double-sided only on the side facing the polymer resin) (Rolled steel sheet): The iron content of the electroplated iron-zinc alloy layer is 80.4 wt.%, And the adhesion amount is 4.0 g / m ² per side. Cold rolled steel sheet (aluminum-killed steel sheet, 0.4 mm thick).

(2) Polymer resin  Ethylene-acrylate copolymer resin
Lum-shaped one. Modified polyethylene / ethylene acrylic
3 layers of acrylate copolymer / modified polyethylene. thickness
Is 50 μm.Modified acrylic resin. The thickness is 50 μm.

(3) Conductive metal powder Kind: An approximately spherical nickel powder produced by a precipitation method is used. Average particle size: 82 μm (distribution 74 to 90 μm), 68 μm (distribution 63 to 74 μm), 59 μm (distribution 44 to 74 μm) and 48 μm (distribution
44 ~ 53μm) is used. Hardness: Hv100, Hv180 and Hv28 in Vickers hardness
Use 0. Addition amount: selected within the range of 10 to 30 wt.%. The conductive metal powder was added at the time of forming the film.

(4) Lamination Conditions In Examples 1 to 5, lamination was performed by the following method. That is,
Using a laminator, attach a polymer resin film containing nickel powder to one side of a preheated steel plate (about 120 ° C).
C.) and separately heated and heated in a heating furnace at a temperature of at least 10 Kgf / cm ² with a pair of pinch rolls lined with a heat-resistant resin. After lamination, it was gradually cooled in the air to room temperature. Example 6 was laminated by the following method. That is, using an acrylic resin as a polymer resin, an acrylic resin with nickel powder added to the surface of a steel sheet is applied by a coater,
Thereafter, the steel sheets are laminated by applying a surface pressure of 10 kgf / cm ² or more with a pair of pinch rolls lined with resin,
Bonding was performed at a temperature of 170 ° C. for 10 minutes. After bonding, the resultant was gradually cooled to room temperature in air.

(5) Simple spot welding conditions Electrode; dome type, copper-chrome electrode (tip diameter, 6 mm
φ). Pressure: 180 Kgf. Current: 10 kA. Energizing time: 12 cycles (60 Hz). Control method: Constant current control (0.5 cycle control). Welding: 30mm x 100mm sample and 0.8mm thick single steel plate (If the laminated steel plate is a galvanized steel plate, use a galvannealed steel plate. If the laminated steel plate is a cold rolled steel plate, use a cold rolled steel plate. Used) were overlapped and welded.

(6) Continuous spot welding conditions Electrode, pressing force, current, conduction time,
The control method is the same as the simple spot welding condition described above. Welding: A 30 mm wide sample and a 0.8 mm thick single steel plate (separately used in the above-mentioned simple spot welding) were overlapped and continuously welded at a pitch of 26 mm. In addition, welding was performed 20 times continuously at a pace of 1 hit point / 1 second, and a pause of 40 seconds was defined as one cycle, and this cycle was repeated.

(7) Salt Spray Test To evaluate the corrosion resistance, a sample was subjected to a salt spray test (JIS Z 2371) for 1000 hours, the upper and lower steel plates were peeled off, and the rust on the joint surface of the polymer resin was removed. The amount of penetration was examined visually.

[Evaluation method] With respect to simple spot weldability, one spot was welded to one sample per 500 pieces, and a total of 500 pieces were welded.
The number of occurrences of defects such as non-energization and fusing around the electrodes was determined. ○: good, Δ: slightly poor,
X: Evaluated as defective. In addition, for continuous spot welding, a 30 mm x 100 mm sample prepared separately and a single steel plate were welded every 2000 spots, and the tensile shear strength of the nugget was measured, and the strength of the nugget decreased. The total number of hitting points before the application was determined, and this was determined as the electrode life.
◎: best, 打: good, Δ: slightly poor, according to the total number of hit points. Corrosion resistance was evaluated by the amount of rust penetration from the end face.
More than 1 mm to less than 5 mm was defined as O, and more than 5 mm was defined as X.

As is evident from Table 1, Examples Nos. 1 to 6 within the scope of the present invention were all good in simple spot welding, continuous spot welding, corrosion resistance and shear adhesion.

On the other hand, Comparative Example No. 1 and N
o. Sample No. 2 had an electroplating layer (upper layer) on the side not in contact with the polymer resin layer, and the continuous spot weldability was slightly inferior. Comparative Example No. In No. 3, there was no electroplating layer on the side facing the polymer resin layer, the simple spot weldability was somewhat poor, and the conductive breaking adhesion was inferior. Comparative Example No. In No. 4, the average particle size of the conductive metal powder was D <T, and the simple spot weldability was poor.
Comparative Example No. 5 is the Vickers hardness of the conductive metal powder is Hv
It exceeded 180, and the simple spot weldability was poor. Comparative Example No. Sample No. 6 had no electroplating layer and had a chromate treatment, so that the simple spot weldability was poor. Comparative Example No. Sample No. 7 had no electroplating layer, had a chromate treatment, and had a Vickers hardness exceeding Hv180, so that the weldability was somewhat poor. Comparative Example No. 8, N
o. Reference numeral 9 denotes a cold-rolled steel sheet. 8 is corrosion resistant,
No. No. 9 was inferior in simple spot weldability. Comparative Example N
o. 10, the average particle diameter of the conductive metal powder is D>2T;
The simple spot weldability was slightly inferior, and the shear adhesion was also inferior. Comparative Example No. 11 means that the amount of conductive metal powder added is 10
wt. %, Poor continuous spot weldability
Was.

[0030]

As described above, according to the present invention , a special treatment is applied to the surface of a galvanized steel sheet.
Without being excellent in corrosion resistance, it is possible to obtain a laminated steel sheet having excellent weldability, particularly excellent in simple spot weldability and continuous spot weldability, and also excellent in adhesive strength, and can be obtained in conventional automobiles, home appliances and building materials. Significant application expansion to applications that could not be applied due to corrosion resistance and spot weldability problems, and thus,
An industrially useful effect is provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a front view showing a spot welding procedure.

[Explanation of symbols]

 Reference Signs List 1 laminated steel sheet 2 polymer resin layer 3 conductive metal powder 4 electroplating layer 5 galvannealed layer 6 skinned steel sheet 7 electrode 8 single steel sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location F16F 15/02 8917-3J F16F 15/02 Q

Claims (3)

(57) [Claims] 1. A laminated steel sheet having a polymer resin layer sandwiched between two upper and lower steel sheets, wherein each of the steel sheets is an alloy as a lower layer only on a surface facing the polymer resin layer. A two-layer plating formed by a galvannealed layer and an electroplating layer as an upper layer is formed, and an alloyed galvanized layer is formed on the other surface not in contact with the polymer resin layer. In the polymer resin layer, the shape before being crushed and sandwiched between the steel plates is substantially spherical, and the average particle diameter D is T with respect to the thickness T of the polymer resin layer. ≤
A laminated steel sheet excellent in corrosion resistance and weldability, wherein D ≦ 2T, a Vickers hardness is Hv180 or less, and a conductive metal powder having a melting point higher than that of the electroplated layer is added. 2. The electroplating layer has an iron content of 50 to
The laminated steel sheet having excellent corrosion resistance and weldability according to claim 1, wherein the laminated steel sheet is made of iron or iron-zinc alloy plating within a range of 100 wt.%. 3. The polymer resin layer includes two adhesive layers,
The laminated steel sheet having excellent corrosion resistance and weldability according to claim 1 or 2, which is a film composed of three layers of a vibration damping resin layer sandwiched between the two adhesive layers.