JPH04116179A - Production of steel sheet electroplated with zn-ni alloy having excellent chipping resistance - Google Patents

Abstract

PURPOSE:To shorten the treatment time required for the dissolution of a preplating layer by subjecting the plating surface under an immersion treatment to roll squeezing at the time of subjecting the steel sheet to electroless immersion into the plating liquid after preplating, then applying ordinary plating of Zn-Ni thereon. CONSTITUTION:The steel sheet is subjected to the preplating at 0.1 to 2g/m<2> with the plating liquid made of the same compsn. as the compsn. of the plating liquid used for the electroplating of the Zn-Ni alloy. The steel sheet is subjected to the electroless treatment in the plating which has the same compsn. as the compsn. of the above-mentioned plating liquid. The plating surface under the treatment is simultaneously subjected to the roll squeezing; thereafter, the steel sheet is thereafter subjected to a prescribed amt. of the Zn-Ni alloy plating in the above-mentioned plating liquid. The plating is dislodged in nearly the entire amt. by the electroless immersion treatment when the steel sheet is subjected to the roll squeezing if the deposition of the plating is below 0.1g/m<2>. Fine cracks do not enter the entire surface of the preplating layer and the stress relief at the boundary between the preplating layer and the base sheet is insufficient in spite of the roll squeezing if the adhesion exceeds 2g/m<2>. The dissolving power decreases and the longer immersion time is required if the roll squeezing is not executed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a Zn-Ni alloy electroplated steel sheet, and particularly to a method for producing a Zn-Ni alloy electroplated steel sheet, which has excellent chipping resistance and is particularly suitable for use in the exterior material (body) of an automobile. The present invention relates to a method of manufacturing an excellent Zn-Ni alloy plated steel sheet.

<Prior art> In recent years, high corrosion resistance has been required mainly for automobile steel plates in order to prevent corrosion of automobile bodies caused by antifreeze agents sprayed on roads. Steel plates have been developed and their use is increasing.

Conventionally, Zn-based alloy electroplated steel sheets used as steel sheets for automobiles are often plated on only one side. Three coats were applied to the steel plate: chemical conversion treatment, electrodeposition coating, intermediate coating, and top coating, but recently, Zn-based alloy electroplating has been applied to the exterior of the car body in order to improve the rust prevention properties of the exterior of the car body. Steel plates that have undergone this process are beginning to be used.

However, the Zn-based alloy plating film is hard and brittle, so when it is used on the outer surface of an automobile body, there is a problem that the plating film is likely to peel off due to so-called chipping, which occurs when small stones on the road fly off and collide with the outer surface of the automobile body. was there.

As a means to solve this problem advantageously,
Publication No. 39 discloses that high N is applied to the base of normal Zn-Ni plating.
It is disclosed to apply Zn-Ni pre-plating with l content.

However, this technology required a plating solution different from that used for normal plating for pre-plating, which led to the problem of complicated management of the plating solution. After that, a technology has been developed that gives plating adhesion equivalent to high Ni pre-plating by melting the plating layer anodically or electrolessly dipping it in a plating solution to elute the base phase in the plating layer. (The anodic dissolution of the plating layer is disclosed in JP-A-63-11690, and the electroless immersion treatment is disclosed in JP-A-62-211397).

However, anodic melting requires a power supply and a counter electrode, which increases equipment costs and running costs.On the other hand, in electroless immersion, the elution rate of the plating layer is low, so the plating layer is In order to achieve sufficient dissolution, the line speed must be lowered or the length of the immersion cell must be increased, which again poses problems such as increased equipment costs and hindered productivity.

<Problems to be Solved by the Invention> The present invention advantageously solves the above-mentioned problems of the prior art. The purpose of this invention is to shorten the processing time required for sufficient dissolution of a plating layer in a technique in which Zn-Ni is conventionally plated after the plating layer is spontaneously dissolved by immersion.

<Means for Solving the Problems> In the present invention, when applying Zn-Ni alloy electroplating to a steel plate, a plating solution having the same composition as the plating solution used for Zn-Ni alloy electroplating is applied to the steel plate by 0.1%. ~2g/m2 Z
Pre-plating with n-Ni alloy was applied, and then the pre-plated W4 plate was subjected to electroless immersion treatment in a plating solution having the same composition as the above-mentioned plating solution, and the plated surface during the electroless immersion treatment was This method of manufacturing a Zn--Ni alloy electroplated steel sheet with excellent chipping resistance is characterized in that after performing roll drawing, a predetermined amount of ZnNi alloy electroplating is performed using the plating solution.

<Function> Hereinafter, the method for producing a Zn-Ni alloy electroplated steel sheet having excellent chipping resistance according to the present invention will be described in detail.

Normally, in order to industrially manufacture Zn-Ni alloy electroplated steel sheets, after performing pre-treatments such as electrolytic degreasing → water washing → pickling → water washing, an electrolytic solution of a predetermined composition is used, and several or Cathode treatment is performed sequentially in a plating bath consisting of several cells, and electroplating is performed with a predetermined alloy content and a predetermined deposition amount.

In the present invention, after performing the above-mentioned normal pretreatment, first, a plating solution having the same composition as that used for Zn-Ni alloy electroplating is applied to the steel plate to coat the steel plate with 0.1 to 2 g/m2 of Zn-
Pre-plating with Ni-based alloy (hereinafter referred to as pre-plating) is applied, and then the pre-plated steel sheet is subjected to electroless immersion treatment in a plating solution having the same composition as the above-mentioned plating solution. After performing roll drawing on the surface, a predetermined amount of Zn-Ni alloy electroplating (hereinafter referred to as main plating) is applied using the plating solution.

The amount of pre-plating applied is 0.1 to 2 g/rrf.

The reason is as follows. If the amount of adhesion is less than 0.1 g/rrf, when the plated surface is subjected to roll squeezing during electroless immersion in a plating solution, almost all of the attached plating falls off, so there is no effect of improving chipping resistance. Also, 2g/
If rd is exceeded, even if the roll is squeezed during the subsequent electroless immersion treatment in the plating solution, the fine racks will not enter the entire surface of the pre-plated layer, and the stress relaxation at the interface between the pre-plated layer and the substrate will be insufficient. This is because the effect of improving chipping resistance is reduced.

The plating conditions for pre-plating are not particularly limited as long as the amount of pre-plating is within the range of 0.1 to 2 g/rrr.

The electroless immersion treatment time is preferably a time suitable for forming a pre-plating layer with good adhesion to the base steel sheet in relation to the above-mentioned pre-plating deposition amount, and specifically, 0.
The time is preferably 5 seconds or more and less than 3 seconds. If the electroless immersion treatment time is less than 0.5 seconds, cranks will not reach the entire surface of the pre-plated layer, and the chimping resistance will not be improved. Further, even if the electroless immersion treatment is performed for 3 seconds or more, the effect of improving the chipping resistance remains unchanged, and it is not a good idea to make the time longer than necessary because it will reduce the production capacity.

Next, a description will be given of the roll squeezing performed on the plated surface during the electroless dipping treatment.

When Zn in the pre-plating layer is dissolved by the free acid in the plating solution, the free acid near the pre-plating layer is consumed. Therefore, at the interface between the pre-plating layer and the plating solution, the pH of the liquid film increases and the dissolution of the pre-plating layer becomes slow. When a steel plate is immersed in a plating solution and then rolled, the free acid at the interface between the pre-plating layer and the plating solution is consumed and the pl
This is to wipe away the liquid film with a high + content and make the interface a liquid film with a high free acid content, and the number of times the roll is squeezed is one or more times.

The reason for this is that if roll squeezing is not used, the melting power will be reduced, requiring a longer soaking time, which will reduce production capacity, which is not a good idea. The upper limit of the number of times the roll is squeezed is not particularly limited, but from the viewpoint of line operation and maintenance, it is preferably 5 times or less.

Note that a normal linger roll may be used for the roll squeezing.

The types of Zn-Ni alloy electroplating to which the present invention can be applied include any two-element, three-element, or more-element electroplating, including P, Co, Cr, Sn, and Sb.
, V, Fe, Ti, Mn, Si, TI, B1
XPb, A! Applicable to the formation of any Zn-Ni alloy or composite plating film containing one or more of these oxides, carbides, nitrides, etc. intentionally added or unavoidably mixed. I can do it.

Further, as the plating method for pre-plating and main plating, any conventionally used method such as horizontal type, vertical type, radial type, etc. can be applied.

Furthermore, the plating bath used in the present invention includes a sulfate bath,
A chloride bath or a mixed bath thereof may be used.

<Example> Examples of the present invention will be described below.

A 5 pcc steel plate with a plate thickness of 0.8 was degreased → washed with water → pickled → washed with water according to the conventional method, and then Zn-Ni alloy electroplating was performed on this steel plate using the plating solution used for the main plating. Next, the steel plate was subjected to electroless immersion treatment in the same plating solution as this plating solution, and the plated surface during this electroless immersion treatment was subjected to roll drawing. Immediately after that, main plating was performed using the same plating solution, and the plating amount was 30.
A Zn-Ni-based alloy electroplated steel sheet with a Zn-Ni content of 12% and a Ni content of 12% was obtained.

The amount of pre-plating applied, the number of roll squeezes during the dipping treatment, and the dipping time are as shown in Table 1.

Further, a normal ringer roll was used for the roll drawing.

The plating bath and plating conditions are as follows.

Plating bath composition N15O,・6H, 0250g/
lZn5Oa ・7 Hz 130 g /
lNa2SO440g/1 Plating conditions pH 1,6 Bath temperature 55°C Current density 50A/dJ The thus obtained steel plate was coated with Nippon Paint's phosphate treatment liquid Surfdyne S D2500M Z (Dip
A chemical conversion treatment was performed using a cationic electrodeposition coating (30 mm thick), an intermediate coat (351 thick), and a top coat (35 fm thick), followed by the frozen chipping test (stepping stone test) was conducted. The result is the first
Shown in the table.

Note that comparative samples Nα12, 13, and 14 in Table 1 are conventional samples that were subjected to long-time electroless immersion without roll drawing.

(Frozen chipping test) The 3-coated painted board was cooled to -20°C, and 15 pebbles (0.3 g/piece of marble) were placed one by one at an air pressure of 4 kg.
The chipping resistance of the plating film was examined by spraying it with / CD and colliding it with a painted plate, and peeling it off with cellophane tape.

The evaluation method is as follows.

5...The average value of the maximum peeling diameter of 5 points is less than 411ff14
...The average value of the maximum peeling diameter of 5 points is 4■ or more and less than 6mm3
...The average value of the maximum peeling diameter of 5 points is 6 or more and less than 8 2.
...The average value of the maximum peeling diameter of 5 points is 8ffl [11 or more 10
Less than 1...The average value of the maximum peeling diameter at 5 points is 10 or more.As is clear from the results in Table 1, the plated steel sheets obtained by the method of the present invention have Excellent chipping resistance under freezing.

<Effects of the Invention> As explained above, according to the manufacturing method of the present invention, Zn
- In the manufacturing method of Ni-based alloy electroplated steel sheet, Zn
- It is possible to easily produce Zn-Ni alloy electroplated steel sheets that have chipping resistance equivalent to that of cold-rolled steel sheets, especially extremely excellent chipping resistance in freezing regions, without changing the 84-series alloy plating solution. can.

Claims (1)

[Claims] When applying Zn-Ni alloy electroplating to a steel plate, Z
Zn-N of 0.1 to 2 g/m^2 was applied to the steel plate using a plating solution with the same composition as that used for n-Ni alloy electroplating.
Pre-plating with i-based alloy is applied, and then the pre-plated steel sheet is subjected to electroless immersion treatment in a plating solution having the same composition as the above-mentioned plating solution, and the plated surface during the electroless immersion treatment is subjected to roll drawing. After that, a predetermined amount of Zn-Ni alloy electroplating is performed using the plating solution.