JPS62211397A - Production of zinc alloy plated steel sheet having excellent adhesiveness - Google Patents

Abstract

PURPOSE:To remarkably improve the adhesiveness of zinc alloy plating by subjecting a strip to a surface treatment consisting in forming extra-thin plating then remelting the same at the time of subjecting a strip to zinc alloy plating. CONSTITUTION:An electroplating installation for the strip 1 is constituted of a plating cell 2 consisting of plural acidic baths of sulfuric acids and the strip 1 is continuously moved and is subjected to the zinc alloy plating. This plating stage is constituted of an extra-thin plating 3 by the initial plating cell 2, a remelting stage 4 to allow the extra-thin plating to melt naturally and an alloy plating stage 5 for applying the prescribed plating layer to the strip. The strip is subjected to about 0.5-5g/m<2> alloy plating in the extra-thin plating 3 in the case of producing, for example, a steel sheet plated with a Zn-Ni alloy contg. 12% Ni, then about 60-600mg/m<2> remains in the remelting stage 4. The adhesiveness of the Zn-Ni alloy plating in the alloy plating stage 5 is thereby remarkably improved.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is a surface-treated steel sheet with excellent corrosion resistance, which has particularly excellent rust prevention performance and is suitable not only as an inner plate of an automobile body but also as an outer plate. The present invention relates to a method for manufacturing a Zn-based alloy plated steel sheet with excellent plating adhesion.

(Prior art and its problems) Requirements for rust prevention of automobile bodies have become more and more severe in recent years, and as so-called 10-5-2 rust prevention targets have been set, countermeasures have become even more serious. In particular, emphasis has been placed on guaranteeing 10 years against perforation and 5 years against surface rust, and many surface-treated steel sheets have been developed and proposed to meet these requirements.

Zn-based alloy plated steel sheets of this width, typified by Zn-Fe and Zn-Ni, have excellent overall rust prevention performance such as paintability and corrosion resistance, and have already been put into practical use.

These plated steel plates have traditionally been used for interior purposes as a countermeasure against pitting and corrosion. On the other hand, cold-rolled surfaces have been used for the exterior surfaces of automobiles from the perspective of emphasizing paintability (in the case of plated steel sheets, single-sided plated steel sheets are used), but recently, as a measure against external rust, plated surfaces are also used on the outside surfaces. There is a growing trend to use double-sided plated steel sheets.

However, when applying Zn-based alloy plating, particularly plating having an intermetallic compound with Zn, to the outer surface, chipping resistance becomes a major problem.

That is, unlike the inner surface, the outer surface receives chipping impact from stones, sand, etc. when the vehicle is running. Many Zn-based alloy platings have intermetallic compound coatings that have higher hardness than pure Zn plating and are quite brittle, so the plating tends to peel off from the underlying steel plate when subjected to this impact. Particularly in cold regions such as North America and Canada, the coating hardens due to the low temperatures (-20 to -40°C), increasing the binding force to the plating film, and also causing the plating to peel off due to chipping of rock salt sprinkled on roads to prevent freezing. Very likely. Although a certain degree of sacrificial anticorrosion effect is exerted by the surrounding plating film on the part where the plating has peeled off, there is a limit, and as a result, the purpose of using plating on the outer surface is lost.

Known techniques to solve this problem include: 1. A method of specifying plating bath conditions (pH 1 temperature, composition) and electrolytic conditions (current density, etc.) (U.S. Pat. (No. 3,558,442) ■ There are methods such as adding stress relievers to the plating bath, but each has the following drawbacks, and at present no satisfactory solution has yet been found.

■Productivity improvements such as the inability to operate at high speed and high current density
In the case of (2), the original corrosion resistance performance may be impaired, and operational management such as controlling the concentration of additives is difficult.

(Means for Solving the Problems) The present invention solves the above problems by performing surface treatment using a plating solution at the initial stage of passing the plate through the plating bath.The gist of the present invention is as follows. It is as expected.

Using continuous electroplating equipment with multiple plating baths,
In the method of applying Zn-based alloy plating to a strip using an acid bath, the plating process consists of an ultra-thin plating process in an initial plating bath, a re-melting process in which the ultra-thin plating is naturally dissolved in a plating solution, and a predetermined plating layer. A method for manufacturing a zinc-based alloy plated steel sheet with excellent adhesion, which is characterized by comprising a gold plating process.

(Embodiments and operations) The present invention will be explained with reference to the accompanying drawings. The electroplating equipment used in the present invention consists of plating tanks (2) (2) consisting of a plurality of sulfuric acid acid baths. The strip (1) is continuously moved through the plating equipment and is coated with a Zn-based alloy (Zn-Ni, Zn-Fe, etc.).

At that time, the plating process includes an ultra-thin plating process (3) in an initial plating bath, a re-melting process (4) in which the ultra-thin plating is naturally dissolved in the acidic bath solution of the plating bath, and an alloy plating process in which a predetermined plating layer is applied. It consists of (5).

The ultra-thin plating process consists of an initial plating bath, for example a first bath, in which ultra-thin alloy plating is applied. The amount of ultra-thin plating depends on the line speed (remelting time) and plating bath conditions (temperature, pH, etc.), but is 0.05 to 5 g/m', especially 0.
．． 5 to 5 g/m'' is preferred.

Next, the subsequent plating baths, for example, several plating baths, are turned off and the ultra-thin plating layer is naturally dissolved in an acidic plating solution. After the initial plating tank is used to prepare the base for plating, normal plating is performed in the subsequent plating tank to obtain a predetermined plated steel plate.

For example, in the case of manufacturing a Zn-Ni alloy plated steel sheet with 12% Ni, an extremely thin coating amount of 0.5 to 5 g/rn'
i is deposited at 80-600 mg/rrI2.

Since this Ni is electrochemically more sensitive than Zn, it is hardly dissolved even in the subsequent remelting process and remains as it is on the steel plate. On the other hand, according to experiments conducted by the present inventors, when the residual amount of Ni is less than 50 mg/m', the effect of improving plating adhesion is weakened, and on the contrary, when the residual amount of Ni is less than 600 mg/m' (particularly 1 g/m'),
m' or more), residual Ni after remelting causes Zn to
It was found that the bare corrosion resistance of the -Ni alloy itself was impaired. Considering the residual amount of Ni and productivity, the amount of extremely thin plating is preferably 0.5 to 5 g/rrf.

In addition, when the amount of re-dissolution is small (<0.1 g/m'), no improvement in adhesion is observed, and the amount of dissolution is equivalent to the amount of Zn contained in ultra-thin plating. It is preferable to set the immersion time so that the immersion time (non-energized) occurs, and it is possible to perform the surface treatment based on the same idea for alloy systems other than the Zn-Ni alloy.

In the present invention, it is not clear why the adhesion is improved by the surface treatment in the initial plating bath, but due to the thin plating → remelting process, it is much more suitable as a base for plating than the conventional base (cold rolled steel plate). This is thought to be due to the fact that it has many microscopic irregularities and has a substantially large surface area. In addition, residual elements Ni,
It is also expected that elements such as Fe may have some relationship with adhesion. Even in existing alloy electroplating equipment with multiple plating tanks, by changing the initial cell selection,
Can be used in the present invention. Furthermore, since the amount of natural dissolution in the re-dissolution step is at most about 5 g/rn', there is no fear that the ion balance in the bath will vary greatly due to plating dissolution.

The present invention provides Zn-F including Zn-Ni alloy plating.
It can be applied to the production of Zn-based alloy plating that forms intermetallic compounds such as e, Zn-Mn, etc. in an acid bath.
The Ni alloy showed a significant improvement in plating adhesion. Examples of two Zn--Fe alloy platings will be shown below.

(Example 1) Using an ordinary electroplating line with multiple plating baths, a copper strip 0.8 mm thick x 900 mm wide was plated with Zn-Ni alloy using the plating bath shown in Table 1. After washing, the initial plating bath was used to perform ultra-thin plating and then remelting.

The amount of ultra-thin metal + was basically adjusted by the current density, and the amount of re-dissolution was adjusted by the plating solution immersion time, bath temperature, bath pH, etc. Table 3 shows the evaluation results of the plating adhesion and corrosion resistance of the obtained steel plate.

Surface Zn-NE alloy plating bath (Example 2) Using the plating bath shown in Table 2, Z
N-Fe alloy plating was performed. Table 3 shows the evaluation results of the obtained steel plates.

The evaluation method is as follows.

(1) Plating adhesion A plated steel plate was painted with the usual 3 coats (cationic electrodeposition + 10 intermediate coats), and 500 g of granite was coated with 4 kg at a low temperature of -20°C on a test panel with a total film thickness of 90 tiles.
/crn' pressure. 150X70mm
'Evaluation was based on the number of peeled platings with a diameter of 0.5 mm in the panel.

5 points 10 points Δ10 to 20 points (2) After painting, make a cross cut with a cutter knife on the 1-coat material (20 tons) before corrosion-resistant cationic electrodeposition coating, and apply 5ST (FP water spray test) for 600 hours. Evaluate the bulge from the later crosscut.

(Example 3) Using the plating bath shown in Table 4, Z
n-M n alloy plating was applied. Table 5 shows the results of varying the amount of ultra-thin plating and the amount of re-melting.

Surface Zn-Mn alloy plating bath (hereinafter referred to as blank space) (Effects of the invention) According to the present invention, Z
It is possible to significantly improve the plating adhesion of alloy plating such as n-Ni and Zn-Fe.

[Brief explanation of drawings]

The accompanying drawings are schematic diagrams showing the plating process of the present invention. 1. Strip 2. Plating tank 3. Ultra-thin plating process 4. Re-melting process 5. Alloy plating process

Claims (1)

[Claims] Using continuous electroplating equipment with multiple plating layers,
In the method of applying Zn-based alloy plating to a strip using an acid bath, the plating process consists of an ultra-thin plating process in an initial plating bath, a re-melting process in which the ultra-thin plating is naturally dissolved in a plating solution, and a predetermined plating layer. A method for manufacturing a zinc-based alloy plated steel sheet with excellent adhesion, which is characterized by comprising a gold plating process.