JPS6026838B2 - Electrolytic zinc alloy plated steel sheet and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic zinc alloy coated steel sheet with excellent bare corrosion resistance and post-coating corrosion resistance, and a method for manufacturing the same.

As a zinc alloy plated steel sheet, the entire plating layer is Zn-F.
The Zn-Fe alloy plated steel sheet, which has become an e-alloy, has better pre-painting treatment (chemical conversion treatment properties) and coating adhesion than galvanized steel sheets in which the entire plating layer is made of pure zinc. It is widely used in fields such as building materials.

In recent years, the characteristics of this Zn-Fe alloy plated steel sheet have been widely recognized in the automobile and home appliance industries, and it has become important as a base plate for painting, but conventional Zn-Fe alloy plated steel sheets are mostly The entire plated layer is made into a Zn-Fe alloy by melt-plating zinc onto a steel plate and then heat-treating it, so when using it in place of the conventionally used electrogalvanized steel plate, the following steps are required: There was a problem like this.

○} The workability of the Zn-Fe alloy of the plating layer is inferior to that of pure zinc, and it is difficult to thin it with hot-dip plating, so it becomes thick, so the plating layer is easy to break even with light processing, and processing is difficult. Lacks sex.

[2} AI, which is an additive element, becomes enriched on the surface of the Zn-Fe alloyed plating layer and becomes inactive A03, so that the chemical conversion treatment of that part is not necessarily sufficient. '3' The plated original sheet undergoes thermal distortion during alloying treatment, and its workability is inferior to that of cold rolled steel sheet.

Therefore, as a Zn-Fe alloy plated steel sheet without the above-mentioned problems, Zn-Fe alloy is coated directly on the steel sheet by glaze plating.
Electric Zn-Fe alloy plated steel sheets that have been subjected to alloy plating are attracting attention.

However, this electric Zn--Fe alloy plated steel sheet is essentially no different from the conventional Zn--Fe alloy plated steel sheet in terms of bare corrosion resistance, corrosion resistance after coating, etc.

Therefore, if the coating layer is partially exposed due to processing habits after painting, corrosion will progress more easily from that area, and even if the coating layer is not exposed, if the coating is thin, there will be a large number of pins. There is still the problem that corrosion progresses from the hole and the paint film peels off in a short period of time. Regarding the improvement of this problem, various studies have been made in the past in the range of Zn-Fe binary alloys for the composition of the plating layer, and the Fe content is 15 to 45% by weight.
It is known that the bare corrosion resistance is the best when

The inventors of the present invention have conducted various studies to solve the above problems, and have found that if titanium is included in the Zn-Fe alloy plating layer, the corrosion resistance of the plating layer will be significantly improved even when the Fe content is 8 to 70%. I found that it could be improved. That is, the present invention uses Z containing 8 to 70% by weight of Fe based on the total weight of the plating layer.
By uniformly containing 0.001 to 2% titanium in the n-Fe alloy plating layer, a chemically stable titanium film is formed on the surface of the plating layer, and this film prevents corrosion of the plating layer. The present invention provides a suppressed electrolytic zinc alloy coated steel sheet.

In the case of the present invention, if the titanium content is less than 0.001% by weight, the surface of the plating layer cannot be uniformly and densely covered with a titanium film.

On the other hand, the corrosion resistance of the plated layer improves as the titanium content increases, but when the titanium content exceeds 2% by weight, the effect on corrosion resistance is almost saturated, and the plated layer also becomes brittle and its workability deteriorates. . As mentioned above, titanium contributes to improving the corrosion resistance of the plated layer, but in the case of the present invention, the content is small, so it is difficult to clarify the compound composition.

However, it is presumed that its composition is close to that of the titanium compound added to the metallurgy, or that it is a hydrolyzate. When the plating layer contains titanium in the above amount, the corrosion resistance of the plating layer is twice that of the conventional Zn-Fe alloy plating layer with an Fe content of 15 to 45% by weight, which has the best corrosion resistance. Furthermore, the Fe content of 8 to 7% by weight is equivalent to that of the conventional method or 1. Improves sound sealing.

However, when the Fe content exceeds 7% by weight based on the total weight of the plated layer, the corrosion inhibiting effect of titanium and titanium compounds on the plated layer decreases, and its corrosion resistance is lower than that of conventional Zn-
With the Fe alloy plating layer, the corrosion resistance is comparable to that of the same amount of Fe content, and when the content reaches 8% by weight, the corrosion inhibiting effect of titanium and titanium compounds is recognized, but the coating pretreatment method is As a result, the coating film adhesion and the corrosion resistance after coating become the same as those of a galvanized steel plate, resulting in a disadvantage that the original properties of the Zn-Fe alloy plating layer are lost. The plating layer of the electrolytic zinc alloy plated steel sheet of the present invention is based on Zn, and contains Fe and Ti as described above. There is no problem even if the electrolyte contains inevitable impurities contained in the electrolyte.

To manufacture the electrolytic zinc alloy plated steel sheet of the present invention, acidity is used to dissolve Zn, Fe, and Ti as ions as ions, and the steel sheet is thereby subjected to dew plating.

In this case, if the metsuki case is acidic, chloride bath, sulfuric case,
Alternatively, a mixture of these may be used. In the formation of titanium ions, soluble titanium compounds tend to be hydrolyzed to become elutriation-soluble titanium hydroxide, so in order to stabilize the ions for a long time, it is preferable to add a complexing agent such as fluoride or tartaric acid.

These galvanizing agents act more effectively than a sulfuric acid bath at the above chloride level and form extremely stable titanium ions. In the case of zinc ions and iron ions, it is necessary that the ion concentrations in the Metsuki Yunaka be 5 or more and 20 or more in the case of zinc ions and iron ions, respectively.

If the concentration is below this level, the cracking efficiency of Zn and Fe will be significantly lowered, and productivity will be lowered. Further, for titanium ions, it is necessary to be in the range of 1 to 10 days/day.
If it is less than 1 hour, the concentration of titanium ions in the coating will change significantly due to the removal of the plating solution by the steel plate during electroplating operation, and the amount of titanium or titanium compound required for the present invention cannot be stabilized. cannot be secured.

On the other hand, after 10 days/day, titanium ions are susceptible to hydrolysis even if a locking agent is added, and when hydrolyzed, they turn into powdered titanium hydroxide and form a plating layer. This makes the plating layer brittle and reduces its adhesion. In the case of the present invention, in order to set the composition of the plating layer to the above composition, it is necessary to further control the ratio of each ion concentration.

That is, in order to make the Fe content in the plating layer 8 to 7% by weight based on the total weight of the plating layer, the weight ratio of iron ions to zinc ions (Fe20/Zn20) should be 0.7 to 4. 0
and 0.001 per total weight of the titanium plated layer.
To make it ~2% by weight, the weight ratio of titanium ions to zinc ions and iron ions [Ti ions/(Zn20 Fe2
(10)] must be between 0.004 and 0.06. As mentioned above, the acidity is used for the metallization rating, but in order to stably electrolyze titanium and increase the hazy folding efficiency of Zn and Fe, the pH needs to be 1.0 to 3.0. , when the pH is in this range, the electrical folding efficiency of Zn and Fe can be as high as 70% or more.

Plating liquid PH is 1. In the case of Bo*man, the cracking of titanium becomes extremely difficult, and the elutriation efficiency of Zn and Fe is 20 to 40.
%. On the other hand, when Yutaka Metsuki PH exceeds 3.0,
Ferrous ions (Fe20) become extremely susceptible to oxidation, and the formation of ferric ions (Fe30) and ferric hydroxide precipitates becomes inevitable, which impedes normal Zn-Fe-Ti alloy plating. become unable to do so. In the case of the present invention, the plating conditions other than the plating bath are conventional methods (for example, current density 10~
It can be carried out at a temperature of 6 sails/d〆 and a temperature of 40 to 70 qo), and no special conditions are required.

Example 1 A cold-rolled steel plate having a thickness of 0.8 mm was degreased and pickled using a conventional method, and then electroplated with a zinc alloy having a composition according to a conventional method using the plating grades shown in Table 1.

Table 2 shows the plating composition and corrosion resistance of the obtained electrolytic zinc alloy plated steel sheet. For corrosion resistance, the salt water light fog test (JIS Z 2371) was performed in the still-plated state.
The test was carried out for 8 hours, and the increase in corrosion weight of each steel plate was investigated. Table 2 shows the composition and corrosion weight increase of the formed sagging layer. Table 1 Table 2 Example 2 Each electrolytic zinc alloy coated steel sheet obtained in Example 1 was coated with an undercoat (epoxy paint, film thickness 5 cm) and a top coat (polyester paint, film thickness 10 cm). After applying 2 coats of bake, a 4-fold bending process was applied, and the resulting product was subjected to a salt water mist test for 24 hours.

Table 3 shows the corrosion resistance of the 42 loaf bending section. Table 3 However, the evaluation of corrosion resistance was based on the following criteria.

◎ No paint blisters or rust.

○ Items with slight blistering or rust on the paint film.

Claims (1)

[Claims] 1. 8 to 70% iron based on the total weight of the plating layer on the steel plate, and 0
．． An electrolytic zinc alloy plated steel sheet, characterized in that a zinc alloy plated layer containing 0.001 to 2% titanium is electroplated. 2 Contains 5 g/l of zinc ions, 20 g/l or more of iron ions, 1 to 10 g/l of titanium ions, and has a weight ratio of iron ions to zinc ions (Fe^2^+/Zn^2
^+) is 0.7 to 4.0, and the weight ratio of titanium ions to zinc ions and iron ions [Ti ion/(Zn^2
A plating layer is formed on the steel plate by electroplating the steel plate in an acidic electrogalvanizing bath with a pH of 1.0 to 3.0 and a pH of 0.004 to 0.06. A method for producing an electrolytic zinc alloy plated steel sheet, which comprises producing a zinc alloy plated layer containing 8 to 70% iron and 0.001 to 2% titanium based on the total weight.