JPH04282239A - Laminated steel sheet excellent in end surface corrosion resistance and weldability - Google Patents

Abstract

PURPOSE:To make the end surface corrosion resistance of a laminated steel sheet having a resin layer in which a conductive powder is dispersed excellent without damaging the spot weldability of said laminated steel sheet by appling Zn-Cr alloy plating to at least the bonding surface of the resin layer of the steel sheets being the skin materials of the laminated steel sheet. CONSTITUTION:Zn-Cr alloy plating 1 with Cr-content of 1-70wt.% is applied to the surfaces coming in contact with a resin layer 3 in which a conductive powder is dispersed of steel plates 2, 2. By this method, the end surface corrosion resistance of the bonding surfaces of the steel plates 2 and the resin layer 3 is enhanced without damaging the spot weldability of the laminated steel sheet.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated steel plate formed by sandwiching a resin between two steel plates and joining them together, and more particularly to a laminated steel plate having excellent end face corrosion resistance and spot weldability.

0002

BACKGROUND OF THE INVENTION In recent years, laminated steel sheets have been attracting attention as steel sheets for measures against automobile noise regulations or for measures to reduce the weight of automobiles. A laminated steel plate is a composite steel plate made by sandwiching and bonding both sides of a resin core material with two steel plates serving as a skin material, and is used in automobiles due to its excellent vibration damping properties, light weight, and deep drawing workability. It is widely used for industrial equipment parts (dash lowers, roofs, oil pans, etc.), home appliance parts, general building materials, covers for industrial equipment, etc. For example, when the material is used as an automobile component, it is often assembled by spot welding and then subjected to phosphate treatment and cationic electrodeposition coating to impart anti-corrosion properties.

[0003] By the way, the resin which is the intermediate layer of the laminated steel plates is an insulating material and has no conductivity, so spot welding cannot be performed by directly applying current to the laminated steel plates as it is. The fact that spot welding is not possible is due to the use of this laminated steel plate,
In particular, this greatly limits its use in automobiles.

[0004] Various proposals have thus far been made to enable spot welding by direct energization. For example, a method of spot welding a cold-rolled steel plate as a skin material by dispersing various conductive materials in a resin as a core material (Japanese Unexamined Patent Publication No. 5
No. 0-79920, No. 57-146649,
Japanese Patent No. 58-16041, Japanese Patent No. 62-90236, etc.), and a method of spot welding electrogalvanized steel sheets as a skin material by dispersing metal powder in a resin as a core material (Patent No. 1279253). There is. Spot welding of laminated steel plates is certainly possible using these methods. However, when these laminated steel sheets are used for automobiles, for example, and subjected to phosphate treatment and cationic electrodeposition coating as described above, corrosion resistance can only be imparted to the outer surface of the steel material (not in contact with the resin layer), which is the skin material. (face) only. Therefore, the corrosion resistance of the steel plate serving as the skin material from the cut surface of the bonding interface with the resin (hereinafter referred to as "end face corrosion resistance") becomes insufficient.

[0005] As a result of studies on steel plates sandwiching resin in which conductive powder is dispersed, a method was also proposed in which the joint surface of the steel plate with the resin is subjected to chromate treatment to improve the end face corrosion resistance. JP-A-61-123537 discloses applying a coating type chromate treatment to the non-plated surface of a cold-rolled steel sheet or a single-sided plated steel sheet, which is a skin material. Additionally, JP-A-1-263043 discloses that the edge corrosion resistance and spot weldability of a steel plate can be improved by applying zinc plating and chromate treatment to at least the surface of the steel plate that is the skin material in contact with the resin layer. has been done. However, since chromate film is originally an insulator, chromate treatment tends to reduce spot weldability.
Spot welding may be inhibited by an increase in the amount of chromate deposited or by the type of underlying plating.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated steel plate that has both end face corrosion resistance and spot weldability.

[0007]

[Means for Solving the Problems] The present inventors have investigated the corrosion resistance of steel plates in multilayer steel plates in which a resin in which conductive powder is dispersed is sandwiched between steel plates. It has been found that by applying zinc-based plating that can form chromate in a corrosive environment, that is, Zn-Cr alloy plating, to the joint surface with the resin layer, the end face corrosion resistance can be improved without impairing spot weldability. That is, Zn-Cr
Alloy plating has good electrical conductivity, and also has good spot weldability because it does not form chromates that can reduce electrical conductivity when spot welding steel plates. In a corrosive environment during use, chromate is formed and contributes to improving end face corrosion resistance, so a laminated steel plate with excellent both spot weldability and end face corrosion resistance can be obtained.

Furthermore, if a zinc-based plated steel sheet is selected as the base steel sheet to which Zn-Cr alloy plating is applied, Zn-C
R-alloy plating can be applied thinly (flash plating), which further improves spot weldability. It has also been found that among galvanized steel sheets, when an alloyed hot-dip galvanized steel sheet is used, it also has corrosion resistance of its own and has excellent end face corrosion resistance.

Here, the gist of the present invention is to provide a laminated steel plate comprising a resin layer in which conductive powder is dispersed and steel plate layers sandwiching the resin layer from both sides. Zn-C with Cr content of 1 to 70% by weight
A laminated steel plate with excellent end face corrosion resistance and weldability, characterized by using a steel plate coated with r-alloy. Also, Zn
-If a zinc-based plated steel sheet is used as the base steel plate to which Cr alloy plating is applied, spot weldability is further improved, and in particular, when an alloyed hot-dip galvanized steel sheet is used, not only spot weldability but also end face corrosion resistance is further improved. A laminated steel plate is obtained.

0010

[Function] In the laminated steel plate of the present invention, the resin layer sandwiched between the steel plates and having conductive powder dispersed therein may be any conventional resin layer and is not particularly limited. Examples of usable resins include various resins such as polyolefin, polyester, polyurethane, and polyvinyl, with polyolefin resins such as polyethylene being representative. The thickness of the resin layer varies depending on the purpose and use, but is usually 10 to 100 μm.

Since these resins are insulators, as is already known, conductive powder such as metal particles (eg, iron, stainless steel, nickel) is dispersed in the resin to ensure conductivity. The particle size of the conductive powder may be selected from an appropriate particle size distribution in consideration of adhesive strength, vibration damping properties, etc., and is preferably about 0.5 to 1.5 times the thickness of the resin layer. The amount of conductive powder added is 0.1 from the viewpoint of vibration damping properties, electrical conductivity, and adhesive properties of the laminated steel plate.
~10% by volume is preferred. The present invention is characterized by steel plate layers sandwiching the resin layer from both sides. That is, a steel plate is used in which at least the surface of the steel plate that contacts the resin layer is plated with a Zn-Cr alloy.

[0012] As the base steel plate to which Zn--Cr alloy plating is applied, a cold-rolled steel plate, a zinc-based plated steel plate, an Al-based plated steel plate, etc. are used. Galvanized steel sheets include electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-based alloy coated steel sheets,
An example is an alloyed hot-dip galvanized steel sheet. In zinc-based alloy plating, alloy components include Fe, Ni, Al, and M.
At least one selected from n, Mg, Co, etc. may be used. Examples of Al-based plated steel sheets include 55Al-Zn plating and Al-plated steel sheets. The amount of plating applied when applying these platings is not particularly limited, but is usually 10 to 1
00g/m2 is preferred. In addition, the thickness of the base material is set to 0.
．． Approximately 2 to 0.8 mm is desirable.

[0013] In order to apply Zn--Cr alloy plating to the above-mentioned base steel plate, for example, electroplating using an acid bath, vapor deposition plating, etc. can be employed. Further, although this plating is always performed on the surface of the steel plate that is bonded to the resin layer, the type of plating is not limited to the surface that is not bonded to the resin, that is, the outer surface of the laminated steel plate. It may be determined by considering corrosion resistance, workability, spot weldability, paintability, etc., but it is preferable to apply Zn-Cr alloy plating to both surfaces because these points are satisfied.

[0014] If the basis weight of Zn--Cr plating is too small, sufficient corrosion resistance cannot be obtained, and if it is too large, the corrosion resistance does not improve much, which is disadvantageous in terms of the scale of the production line and economic efficiency. The specific weight varies depending on the type of base steel plate. When the base material steel plate is a cold-rolled steel plate, it is usually 10 to 40 g/m2.
For practical purposes, about 20 g/m2 is sufficient. When a zinc-based or Al-based plated steel sheet is used as the base material, a plating layer already exists, so a thin plating (flash plating) of about 0.5 to 10 g/m2 is usually sufficient. From the viewpoint of corrosion resistance and economic efficiency, it is preferably 1 to 5 g/m2.

[0015] If the Cr content in the Zn-Cr plating is too low, the chromate forming ability will decrease and the end face corrosion resistance will deteriorate.
On the other hand, if it is too high, the adhesion of this plating will decrease;
-70% by weight. The desirable range for commercialization is about 10 to 30% by weight. FIG. 1 shows a cross-sectional view of a laminated steel plate of the present invention in which the base steel plate is a cold-rolled steel plate and Zn-Cr plating layers are provided on both sides thereof. Further, FIG. 2 shows a cross-sectional view of a similar laminated steel plate in which the base steel plate is a zinc-based plated steel plate. In the figure, 1 is a Zn-Cr alloy plating layer, 2 is a cold-rolled steel plate, 3 is a resin film, 4 is a stainless steel ball deformed by pressure bonding, and 5 is a zinc-based plating layer.

The reason why spot weldability and end face corrosion resistance are improved by applying Zn--Cr alloy plating to the base steel plate in the present invention is as follows. While chromate is an insulator, Zn-Cr alloy plating is an alloy, so it has high electrical conductivity and excellent spot weldability. Furthermore, when exposed to a corrosive environment where water or oxygen is present after spot welding, it is assumed that chromate is formed on the contact surface between the steel sheet layer and the resin layer, so that the end face corrosion resistance is not impaired. Therefore, sufficient corrosion resistance can be ensured without further chromate treatment of the steel plate serving as the skin material.

Furthermore, when a zinc-based or Al-based plated steel sheet is used as the base material, the Zn--Cr alloy plating applied to this steel sheet has sufficient corrosion resistance even if it is a thin film formed by flash plating. According to this flash plating, the plating surface, that is, the bonding surface with the resin layer becomes smoother, and the possibility of contact between the plating layer and the conductive powder in the resin layer increases, so the conductivity increases. Spot weldability is further improved. In addition, among galvanized steel sheets, when alloyed hot-dip galvanized steel sheets are used, the steel sheet itself has high corrosion resistance,
The corrosion resistance is further improved due to the particularly high porosity resistance.

If Zn--Cr alloy plating is applied to the joint surface of the steel plate with the resin, sufficient corrosion resistance can be ensured as described above even without further chromate treatment. A conventional method may be used to manufacture a laminated steel plate by joining the resin layer and the Zn-Cr alloy plated steel plate. In order to sandwich and laminate a resin layer between two steel plates, it is necessary to use a film-shaped resin with conductive powder dispersed in advance, or to apply liquid resin to the steel plate using a roll coater or the like and then scatter the conductive powder. After supplying resin between the steel plates, heating, crimping,
This can be done by cooling. Next, examples of the present invention will be shown,
This is an illustration of the present invention, and the present invention is not limited thereby.

[0019]

[Example] Zn-Cr alloy plating with the Cr content shown in Table 2 was applied to both sides of a cold-rolled steel sheet and a zinc-based plated steel sheet with a thickness of 0.5 mm using an electroplating method at the basis weight shown in Table 2. A steel plate was fabricated as a skin material. On the other hand, a 45-μm film was prepared using a resin in which 2% by volume of stainless steel spheres (SUS304) with a diameter of 60 μm were dispersed in maleic anhydride-modified polyethylene as conductive powder. This film was sandwiched between the two steel plates from both sides and bonded under heat and pressure. Heat compression bonding was carried out using a hot press at a compression temperature, compression force, and compression time of 150° C., 30 kgf, and 15 minutes, respectively.

[0020] The produced laminated steel plate is 30 mm x 150 mm.
It was cut to size and subjected to an end face corrosion resistance test and a spot weldability test. The end face corrosion resistance test is a salt spray test (JIS
Z2371), and after 500 and 2000 hours, the surface steel plate was peeled off from the test piece and the length of corrosion progression was measured. Evaluation was performed based on the criteria shown in Table 1.

[0021]

[Table 1]

[0022] The spot weldability test was conducted by stacking the same type of materials at a current of 10,000 A and a current application time of 15 cycles. Also, the pressing force is 100kgf and 300kgf.
The test was conducted at two levels of f, and the number of test pieces was 100 for each level.
And so. The evaluation was ◎ if spark bulges did not occur in all tests, ○ if spark bulges did not occur at 300 kgf but occurred at 100 kgf, and × when spark bulges occurred at both 300 and 100 kgf. The results are shown in Table 2.

[0023]

[Comparative Example] As a comparative example, the influence of presence or absence of chromate treatment, Cr content, and Zn-Cr alloy plating weight on end face corrosion resistance and weldability was investigated. The results are shown in Table 2.

[0024]

[Table 2]

As is clear from Table 2, when the Cr content is 1
In the example of the present invention in which Zn-Cr alloy plating was applied to ~70% by weight, both the end face corrosion resistance and spot weldability were good, and the end face corrosion resistance was particularly excellent when the base material was an alloyed hot-dip galvanized steel sheet. There is.

[0026]

As described in detail above, according to the present invention, by applying Zn-Cr alloy plating to at least the joint surface with the resin layer of the steel plate that is the skin material of the laminated steel plate,
Excellent end face corrosion resistance can be achieved without impairing the spot weldability of a laminated steel plate having a resin layer in which conductive powder is dispersed. In addition, if a zinc-based plated steel plate is used as the base steel plate to which Zn-Cr alloy plating is applied, spot weldability will be further improved.In particular, if alloyed hot-dip galvanized steel plate is used, not only spot weldability but also extreme edge corrosion resistance will be achieved. It is possible to obtain laminated steel sheets with excellent properties.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of a laminated steel plate of the present invention using a cold-rolled steel plate as a base material.

FIG. 2 shows a cross-sectional view of a laminated steel sheet of the present invention using a zinc-based plated steel sheet as a base material.

[Explanation of symbols]

1 Zn-Cr alloy plating layer 2 Cold rolled steel plate 3 Resin film 4 Stainless steel ball deformed by pressure bonding 5 Zinc-based plating layer

Claims (1)

[Claims] 1. A laminated steel plate comprising a resin layer in which conductive powder is dispersed and a steel plate layer sandwiching the resin layer from both sides, wherein the steel plate layer is made of Cr at least on the surface in contact with the resin layer.
A laminated steel plate with excellent end face corrosion resistance and weldability, characterized by using a steel plate plated with a Zn-Cr alloy having a content of 1 to 70% by weight.