JPS61159590A - Pretreatment before electroplating - Google Patents

Abstract

PURPOSE:To reduce the occurrence of plating defects during the production of a zinc alloy electroplated steel sheet by carrying out brushing in a pickling stage. CONSTITUTION:When the surfaces of a steel sheet are cleaned by pickling and electroplated with a zinc alloy, brushing is carried out with an acid-resistant brush during the pickling. It is preferable that the brush contains abrasive grains. Slightly soluble rust and inclusions which exist on the surfaces of the steel sheet are mechanically removed by the brushing, and at the same time, the surfaces are activated. Accordingly, the occurrence of plating defects is reduced during the electroplating, thereby improving the quality of plating.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a pretreatment method for preventing the occurrence of plating defects when electroplating a zinc alloy on a steel plate using a pretreatment including a pickling process. . (Prior art) Electroplated steel sheets whose plating metal is zinc-based include electrogalvanized steel sheets whose plating layer is almost pure zinc or something close to it, and zinc-based alloys such as Zn-Ni and Zn-Fe. There is electrolytic zinc alloy plating #1JIi, but the former has a high sacrificial corrosion resistance of the plating layer, so even if there is a plating defect such as a pinhole, the corrosion resistance will hardly decrease. However, in the latter case, the sacrificial corrosion protection of the plating layer is low, so if there is a plating defect such as a pinhole, the steel base is likely to corrode and red rust occurs based on this defect. Therefore, in the latter case, compared to the former, it is required that there be no plating defects such as pinholes.

In general, the occurrence of plating defects in electroplating (in addition to the above-mentioned pinholes, localized areas with insufficient plating coverage, dark areas where no plating has been applied, etc.) varies depending on the plating conditions, but it depends on the surface condition of the original plate and pretreatment. Since this is largely related to the force method, it is preferable to change the pretreatment method immediately depending on the surface condition of the plating original plate in order to reduce the occurrence of plating defects. However, since there is no suitable pretreatment method according to the surface condition of the original plated plate, electrolytic lipophilic resin → water washing (combined with brushing) is applied regardless of whether the product is an electrogalvanized steel sheet or an electrolytic zinc alloy plated steel sheet. → Pickling (usually just immersing in acid) → Water washing was the pretreatment process.

(Problem to be Solved by the Invention) According to this method, even if some pinholes occur during plating, in the case of electrogalvanized steel sheets, the corrosion resistance is almost the same as that of sheets without plating defects for the above reasons. However, electrolytic zinc alloy coated steel sheets have poor corrosion resistance,
In particular, minute rust and inclusions [e.g. alumina, silica, titanium compounds (carbides, oxides, nitrides)] are present on the surface of the plating original plate.
If 1 is present, plating defects will occur in the area where it exists, resulting in poor corrosion resistance. For example, titanium killed steel (Ti content 0.05~
This is because when a titanium-killed steel sheet (0.15 wt%) is used, titanium is concentrated on the surface, forming hardly soluble carbides, oxides, and nitrides. Similarly, in the case of a silicon-based high-tensile steel sheet, silicon is concentrated on the surface of the steel sheet to form hardly soluble 5iOz.

(Means for solving the problem) In general, in the electroplating pretreatment method that cleans the steel plate surface mainly by pickling, acid concentration and pickling temperature are changed to thoroughly remove slight rust and inclusions on the steel plate surface. It would be fine to make it higher, but if this is done, the normal parts of the steel plate will be over-pickled, resulting in a large amount of smut, and the over-pickling area will become rough and turn gray, causing the plating to deteriorate. However, that part does not disappear and appears as uneven color tone.

Therefore, the present inventors investigated a pretreatment method that would reduce the occurrence of plating defects even if there was minute rust or poorly soluble inclusions on the surface of the steel sheet during the production of electrolytic zinc alloy plated steel sheets. It has been found that brushing during pickling in the washing process is very effective.

Conventionally, steel sheets are sometimes pickled or brushed during pre-plating treatment that includes a pickling process, but in this case, the steel sheet is temporarily lifted from the acid solution after pickling or during pickling. In the case of the present invention, which is a method of carrying out pickling, brushing using such a method has no effect, and brushing must be carried out at the time of pickling.

In the present invention, an acid-resistant brush such as a nylon brush is sufficient for brushing. However, if the plated original plate is titanium killed steel or silicon-based high-strength steel plate, there will be insoluble inclusions on the surface.
It is preferable to use a brush containing abrasive grains. The grain size of the abrasive grains used in this base alloy is preferably #240 to @1ooo. If it is rougher than 240, large scratches will occur on the original plate due to polishing, and will remain as an appearance even after plating. On the other hand #1000
If the abrasive grains are finer, the polishing effect of the abrasive grains will hardly be seen, and it will be no different from polishing with a normal brush that does not contain abrasive grains.

(Function) In the present invention, brushing the steel plate during pickling reduces the occurrence of plating defects during electroplating. It is presumed that the surface is subjected to abrasion corrosion (erosion), becomes easier to dissolve, and the surface is activated.

The present invention will be explained below with reference to Examples.

(Example) ^1 killed steel (^1
Ti killed steel (Ti content 0.085 wt%), Si-based high tensile strength steel (Si content 0.065 wt%), Ti killed steel (Ti content 0.085 wt%),
27 wt%, Mn content 0.55 wt%) and rimmed steel were electrolytically degreased with IOA/da'' in a sodium orthosilicate solution with a concentration of 5 wt% and a temperature of 60°C, and then washed with water while brushing. Afterwards, it was pickled under the conditions shown in Table 1. After pickling, it was washed with water, and each copper strip was electroplated with Zn-former alloy [plating weight 209/ah2 (one side), old content 12wt%1]. For brushing when washing with water after electrolytic degreasing, use a nylon brush (outer diameter 320 mm).
, thread diameter 0.6 mm) and rotated at l 800 rpm for one pass. 1 from each copper strip after plating
10 samples (dimensions 100 mm) from the center of the belt at m intervals
X150-■) and JIS Z 237
Corrosion resistance was investigated by subjecting the sample to a salt spray test based on 1. Table 2 shows the results.

As is clear from Table 2, the electrolytic zinc alloy coated steel sheet obtained by pre-treating the steel plate using the pre-treatment method of the present invention and then plating it has better corrosion resistance than that of the steel sheet pre-treating using the conventional method and then plating it. is also almost constant.

(Effects) As described above, according to the pretreatment method of the present invention, it is possible to reduce the occurrence of plating defects in electroplating of zinc-based alloys where plating defects are likely to occur depending on the surface condition of the steel sheet, thereby improving quality. You can make improvements.

Claims (1)

[Claims] An electroplating pretreatment method including a pickling process, which comprises picking a steel plate while brushing it during the pickling process when electroplating a zinc-based alloy onto a steel plate.