JP2833380B2 - Zn-Ni-based alloy-plated steel excellent in corrosion resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a Zn alloy having excellent corrosion resistance.
The present invention relates to a Ni-based alloy plated steel material, and more particularly to a plated steel sheet suitable as a rust-preventive steel sheet for automobiles.

[0002]

2. Description of the Related Art Conventionally, Zn-plated steel sheets have been used as surface-treated steel sheets for automobiles.
If the corrosion rate is relatively high and long-term rust prevention is expected, a larger amount of plating is required. So, Z
In order to suppress the activity of the n-plated layer, Zn or Ni or F
A surface-treated steel sheet having a Zn-Ni alloy plating layer or a surface-treated steel sheet having a Zn-Fe alloy plating layer alloyed by adding e has been put to practical use and is widely used. In particular, Zn-Ni alloy electroplated steel sheets are widely used because they have very good corrosion resistance when coated with an organic composite film.

[0003] Generally, when industrially producing a Zn-Ni alloy electroplated steel sheet, a plating solution is an acid bath. Therefore, the steel sheet dissolves in the plating solution, and a small amount of Fe ions inevitably mix into the plating solution. Conventionally, it has been considered that when Fe is mixed in the Zn—Ni alloy electroplating, the corrosion resistance of the Zn—Ni alloy electroplating is reduced, and the upper limit of the ion concentration of Fe mixed into the plating solution is set to a certain amount (for example, (1 to 1.5 g / l). In this case, F in the Zn—Ni alloy plating layer
The e content is 0.3% by weight (3000 ppm) or less. However, even if the upper limit of the concentration of Fe ions is controlled to be low and the Fe content of the Zn—Ni alloy plating layer is suppressed as much as possible, a sufficiently satisfactory corrosion resistance has not always been obtained. In addition, when only the upper limit of the Fe ion concentration in the plating bath is controlled, the Fe concentration fluctuates by about 0.1 g / l, and as a result, the Fe content in the Zn—Ni alloy electroplated layer is a few. It fluctuated on the order of 100 ppm or more, and due to this fluctuation, the corrosion resistance was remarkably different.
Therefore, the corrosion resistance of the Zn-Ni alloy electroplated steel sheet is as follows:
There was a problem that the corrosion resistance performance was unstable due to a change depending on the lot.

[0004] In recent years, surface-treated steel sheets used for rust-preventive steel sheets for automobiles have been used as deicing agents (rock salt,
What can withstand red rust and perforation for a predetermined time even under a severe corrosive environment due to calcium chloride or the like is desired. For this reason, improvement of corrosion resistance by increasing the basis weight of Zn—Ni alloy electroplating has been attempted. However, if the plating weight is too large, spot weldability, workability and the like deteriorate, so that there is a limit to the improvement in corrosion resistance due to the increase in plating weight. In particular, in the conventional Zn-Ni alloy electroplating, as described above, the corrosion resistance is not sufficient, and the variation in the corrosion resistance is large, so that the weldability, even if the basis weight of the plating is increased within a range that does not deteriorate the workability, The desired corrosion resistance could not be obtained.

Japanese Patent Application Laid-Open No. 58-84990 discloses a method of forming a Zn—Ni alloy layer on one side of a steel sheet, wherein the Ni content of the alloy layer is 8.5% or more and less than 10%. One or two kinds containing 30% or less in total with Ni (specifically, the composition of the alloy layer is Zn-13% Ni-
20g with 6% Fe or Zn-12.5% Ni-5% Fe
/ M ² (For example, the amount of plating). Then, by adding Fe, Co, and Cr,
The corrosion rate is reduced and red rust is hardly generated. However, according to the experiments performed by the present inventors, this alloy also has insufficient corrosion resistance (the Fe content in FIG. 1 is 50,000).
See red rust incidence in ppm).

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to provide:
Zn-Ni with improved corrosion resistance with less plating weight
It is to provide a base alloy plated steel material.

[0007]

An alloy-plated steel material according to the present invention comprises a steel material and an alloy plating layer formed on at least one surface of the steel material, wherein the alloy plating layer comprises:
11.8 to 20% by weight of Ni and 0.35 to 0.65 of Fe
Wt% and the total amount of Fe and Co (including Co = 0 wt%).
) Is 0.65% by weight or less, and the balance consists of Zn and unavoidable impurities, and the basis weight is 10 g / m ^{2 to} 60 g / m ^2.
This is a Zn—Ni-based alloy-plated steel excellent in corrosion resistance by suppressing the formation of non-uniform corrosion products . In addition, the method for producing an alloy-plated steel material of the present invention is characterized in that Ni is 11.8 to 20% by weight and Fe is 0.35 to 0.65% by weight on at least one surface of the steel material by electroplating. Fe and C
The total amount of o (including Co = 0% by weight) is 0.65% by weight
In the following, an alloy plating layer having a composition consisting of the balance Zn and unavoidable impurities is formed, and its basis weight is 10 g / m ^{2 to} 60 g / m ^2.
g / m ² to prevent the formation of non-uniform corrosion products
This is a method for producing a Zn—Ni-based alloy plated steel material having excellent corrosion resistance .

[0008]

The type of the steel material applied to the present invention is preferably a cold rolled steel plate, a hot rolled steel plate or the like, but is not particularly limited thereto. The Zn—Ni-based alloy plating layer on the steel sheet is formed on one side or both sides of the steel sheet according to its use. In particular, those formed by alloy electroplating are preferred. The Ni composition of this plating layer is 11.8 to 20% by weight, preferably 11.8 to 15% by weight. The reason is as follows.

The corrosion resistance of the Zn—Ni-based alloy plating layer mainly depends on the Ni content. In addition, Zn-Ni
The relationship between the base alloy phase and corrosion resistance has been known, and Zn
-When the Ni-based alloy is mainly in the γ phase, the corrosion resistance is good. The Ni content at this time is about 10 to 20% by weight, but 11.8 in order to suppress the generation of non-uniform corrosion products.
-20%, and especially 12-14% has a region with the best corrosion resistance.

[0010] The alloy plating layer contains 0.35 Fe.
0.65% by weight (3500ppm-6500ppm)
And This was determined based on the following findings.

In view of the fact that Zn-Ni-plated steel sheets have an element capable of realizing a higher corrosion resistance than the current state, but the characteristics thereof are not sufficiently exhibited, the present inventor has proposed that the Ni—
A 0 wt% Zn-Ni alloy electroplated steel sheet was corroded in an unpainted state in a corrosion promotion test, and its corrosion resistance was examined.
Then, a stable corrosion product was generated in the corrosion process, and when a predetermined time was reached, red rust was generated from a part of the product by corrosion of the base iron. The state of occurrence of this red rust indicates that there is a portion where corrosion locally progresses. Zn-N
Since the i-plated steel sheet has such a slight non-uniformity in the corrosion process, it has been found that the characteristic that the time until the occurrence of red rust is extremely long is not sufficiently exhibited.

The mechanism by which the Zn—Ni alloy electroplated steel sheet has good corrosion resistance is that Zn forms a corrosion product consisting of insulating basic zinc chloride in a corrosive environment in the presence of chloride ions, and this forms a Zn—Niγ. It is attributed to the relatively stable existence in the grain boundaries of the phase. However, depending on the environment at the initial stage of corrosion, there is a possibility that the formation of corrosion products is not always uniform. At this time,
It is presumed that the non-uniformity becomes apparent with the passage of time of the corrosion and that local corrosion progresses.

By the way, if an active site acting as a starting point of the formation of corrosion products is present in the coating in an appropriate amount, the formation of non-uniform corrosion products is suppressed, and it is presumed that the corrosion products are uniformly and densely formed. You. Based on the above presumption, the present inventor has found that Fe is required as a third element inevitably mixed in order to act as an active site in Zn-Ni alloy electroplating.
Was added in a small amount, and the relationship between the amount added and the corrosion resistance was investigated.
As a result, 0.35% of Fe was contained in the Zn—Ni alloy plating layer.
め っ き 0.65% by weight (3500 to 6500 ppm) of a plated steel sheet is compared with a Zn—Ni alloy coated steel sheet containing Fe at a lower content and a Zn—Ni alloy coated steel sheet containing Fe exceeding 6500 ppm. And showed good corrosion resistance. The value showing this good corrosion resistance is higher than the upper limit of the Fe content controlled by the conventional manufacturing method, and is completely opposite to the conventional knowledge that the corrosion resistance is improved if the Fe concentration is kept as low as possible. The result. The reason why the corrosion resistance is improved when the Fe content is 0.35 to 0.65% by weight is not clear, but the present inventor promoted non-uniformity by adding Fe out of the range of the present invention, and as a result, Guess it has the opposite effect.

In addition, when the same effect as that of Fe was aimed at, Co was examined. As a result, the corrosion resistance also changed depending on the Co content. That is, the corrosion resistance depends on the total content of Fe and Co, and therefore, in the present invention.
Has a Fe + Co content of 0.65% or less.

The present inventor has set the Ni content in the plating layer to 1
3 ± 0.2% by weight, the Fe content was changed within and outside the range of the present invention, and the adhesion amount was 20 g / m ² ± 1.0 g / m ^2.
, Zn-Ni alloy electroplated steel sheets in the range of were prepared, and these steel sheets were subjected to a salt spray test, and the occurrence rate of red rust was measured at 500 hours. The result is shown in FIG. As is clear from FIG. 1, the Fe content in the plating layer was 3500 to 650.
It can be seen that the corrosion resistance of the plated steel sheet in the region of 0 ppm is good. In addition, the effect of adding Fe was not observed for those whose Ni content deviated from the present invention.

In the present invention, if the coating amount is too small, sufficient corrosion resistance cannot be obtained, and if it is too large, press formability (workability) and weldability are deteriorated. 10 to 60 g / m ² per side It is preferable to set it in the range.

Further, a chromate film (chromate layer) may be formed on the plating layer of the present invention by a chromate treatment. The chromate treatment may be of any known type. The amount of the chromate film attached is 5 to 10 as chromium.
0 mg / m ² Is preferred. Further, an organic resin film (organic resin layer) of 0.5 to 2.5 μm may be further formed on the chromate film. The organic resin film in this case is
Any of those conventionally used can be used, but those containing a rust preventive additive such as SiO ₂ are particularly effective.

The Zn— of the present invention having these films formed thereon
The Ni alloy electroplating exhibited its effect more remarkably, and showed better corrosion resistance than a similar coating applied to a Zn-Ni alloy electroplated steel sheet outside the scope of the present invention.

The Zn—Ni alloy electroplated layer of the present invention is manufactured as follows. Predetermined amount of Ni ²⁺ ion, Z
Using an acidic plating solution containing n ²⁺ ions and Fe ²⁺ ions or Co ²⁺ ions, an alloy plating layer according to the present invention is formed on at least one surface of a steel sheet by a normal electroplating method. .

In the above plating bath, the plating solution is electrically conductive.
In order to confer properties, K⁺ , Na⁺ , NH_Four ⁺ Mosquitoes
Thion may be added. Further, as the anion, S
O_Four ^2-, Cl^- , BF_Four ^- Use any of these
Can be. The pH of the plating solution is in the range of 0.5 to 3.0.
It is desirable to do. The plating current density is specified
Although it is not something, 30-200A / dm^Two Is desirable
No. The relative flow velocity between the plating solution and the steel sheet is 0.5 to 5.0 m
/ S is desirable, and the plating solution temperature is preferably 30 to 70 ° C.
No.

[0021]

Next, an embodiment of the present invention will be described. Example 1

An alloy plating layer was formed on a cold-rolled steel sheet by electroplating to prepare a Zn-Ni alloy electroplated steel sheet. In this case, the Ni content in the alloy plating layer was 13 ±
0.2 wt%, Fe content was changed and the amount of adhesion was 20 g
/ M ² ± 1.0 g / m ² Within the range. These steel sheets were subjected to a salt spray test, and the rate of occurrence of red rust after 500 hours was measured. The result is shown in FIG. As is clear from FIG. 1, the Fe content in the alloy layer is 3500 to 6500 p.
Those in the pm range have good corrosion resistance, and
It can be seen that the corrosion resistance is stable without fluctuating. For this effect, a similar experiment was performed by adding Co instead of Fe, and the same tendency was observed in this case. In addition, when the Ni content was out of the range of the present invention, the effect of adding Fe and Co was not observed. Example 2

For a cold-rolled steel sheet having a thickness of 0.7 mm,
Electroplate under the conditions shown, and place Fe on the surface of the steel sheet.
A quantitatively contained Zn-Ni electroplating layer was formed. What
In addition, the composition of the plating layer is Ni in the plating solution.²⁺Ion, Z
n²⁺Ions, and Fe²⁺Ion or Co²⁺Ion
Adjusted by changing. Plating solution composition ZnSO_Four7H_TwoO: 130-200 g / l NiSO_Four6H_TwoO: 300 to 450 g / l Fe²⁺, Co²⁺ : 0.5 to 1.5 g / l Na in total_TwoSO_Four : 60 g / l Plating conditions pH: 1.3 Temperature: 50 ° C Plating current density: 50 to 150 A / dm^Two  Plating time: Adhesion amount 20g / m^Two Adjusted to be

In the corrosion resistance test, an unpainted Zn—Ni alloy electroplated steel sheet prepared by the method described above was subjected to a salt spray test, and the time at which the area ratio of occurrence of red rust became 5% was compared. Table 1 shows the results together with the composition of the alloy plating layer.
(Examples 1 to 6 of the present invention) and Table 2 (Comparative Examples 13 to 2)
It is shown in 5). As shown in Examples and Comparative Examples, all of the test samples of the present invention had better corrosion resistance than those of Comparative Examples. Further, the corrosion resistance after coating with the organic anastomotic film was also compared (Sample No. 7 and Sample Nos. 26 to 29). The processing conditions for the organic composite film are shown below. Treatment conditions Chromate: reactive type, adhesion amount 50 mg / m ² as chromic acid Treatment liquid Chromic anhydride: 20 g / l, phosphate ion: 4 g / l zirconium fluoride ion: 1 g / l zinc ion: 1 g / l, Cr ^{6 +} / Cr3 ⁺ : 3/3 Chromic anhydride / zirconium fluoride ion: 20 / l Organic bark film: Resin: Block urethane modified epoxy resin Silica: AEROSIL200 (dry silica) manufactured by Nippon Aerosil Co., Ltd. Chromate: Kikuchi Barium chromate resin manufactured by Dyeing Industry Co., Ltd./(silica+Cr acid salt): 60/40 Silica / Cr acid salt: 75/25 As shown in Examples and Comparative Examples, the specimen of the present invention after coating with an organic composite film Showed good corrosion resistance as compared with the comparative specimen after the organic composite film.

[0025]

As described above, according to the present invention, F
By setting the e content in a predetermined range, a Zn—Ni alloy-plated steel sheet having excellent corrosion resistance can be obtained with a small amount of plating, and the corrosion resistance, spot weldability, and workability can be improved. Further, when the Fe content in the plating layer is within the range of the present invention, the rate of occurrence of red rust can be suppressed to almost the same low rate, so that products can be stably manufactured with good reproducibility.

[0026]

[Table 1]

[0027]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Fe content in a plating layer (within and outside the range of the present invention) and corrosion resistance (the occurrence rate of red rust) after 500 hours of a salt spray test.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-14891 (JP, A) JP-A-63-11692 (JP, A) JP-A-62-116796 (JP, A) JP-A-62-116796 56594 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C25D 3/00-5/56

Claims (4)

(57) [Claims] 1. A steel material and an alloy plating layer formed on at least one surface of the steel material, wherein the alloy plating layer contains 11.8 to 20% by weight of Ni and 0.35% of Fe. ~
0.65% by weight, and the total amount of Fe and Co (Co = 0 weight)
%) Is 0.65% by weight or less, and the balance is composed of Zn and unavoidable impurities to suppress the formation of non-uniform corrosion products.
It won excellent corrosion resistance Zn- Ni-based alloy plated steel. 2. The alloy plating layer has a basis weight of 10 g / m 2.
² to 60 g / m ² a highly corrosion resistant Zn- Ni based alloy plated steel material according to claim 1. 3. The method according to claim 1, wherein at least one surface of the steel material is composed of 11.8 to 20% by weight of Ni and 0.3% of Fe by electroplating.
5 to 0.65% by weight, and the total amount of Fe and Co (Co =
0% by weight or less) and 0.65% by weight or less, which forms an alloy plating layer having a composition consisting of the balance of Zn and unavoidable impurities , suppresses the formation of non-uniform corrosion products, and has excellent corrosion resistance. A method for producing a Ni-based alloy plated steel material. 4. The alloy plating layer has a basis weight of 10 g / m 2.
² to 60 g / m ² a method for producing superior Zn- Ni based alloy plated steel in corrosion resistance according to claim 3.