JPS59116392A - Electroplated steel sheet having double layer - Google Patents

Abstract

PURPOSE:To improve the adhesive strength of a film on a steel sheet without deteriorating the corrosion resistance of the sheet by coating the sheet with zinc or zinc plating of a specified thickness and by electroplating the sheet having the zinc layer with a zinc alloy. CONSTITUTION:A steel sheet is coated with zinc or zinc plating contg. eta phase by about 0.1-5g/m<2>. Little shrinkage stress remains in the zinc layer, and the layer has superior adhesive strength and high corrosion resistance. The zinc layer is electroplated with a zinc alloy such as Fe-Zn or Ni-Zn. The zinc alloy layer is tough, and the relatively soft zinc layer is present under the zinc alloy layer, so cracking is not caused, and the coated film is not stripped off.

Description

[Detailed Description of the Invention] This invention relates to multi-layer electroplated steel sheets with excellent plating adhesion, and Z
It is an n-plated steel plate. Well-known path, Zn-plated steel plate (・
Is it possible that the sacrificial corrosion protection effect of the Zn plating layer can improve the corrosion resistance?Recently, as coated steel sheets are increasingly being applied to severe corrosion protection applications such as automobiles, it has been pointed out that Zn plating steel sheets lack corrosion resistance. There has been a growing strong demand for kaika.

In response to this, various research and development efforts were carried out at the manufacturer 1ull, first of all Zn alloys such as Fe-Zn alloys and Ni-Zn alloys.
With the advent of n-based alloy plating, advances in corrosion resistance have been obtained, and in addition to F-Zn alloyed copper sheets, which are manufactured through hot-dip Zn plating, alloy-plated steel sheets are also produced directly by electroplating. Further improvements in corrosion resistance and workability can be obtained by the kHz manufacturing method, and these Zn-based alloy plated steel sheets are in wide demand as corrosion-resistant materials in the field of painted steel sheets.

More recently, especially for automobile exterior materials, cationic electrodeposition coating is suitable for harsh corrosive environments as a secondary coating after chemical conversion treatment such as phosphate treatment is applied to plated steel plates used for painting materials. It has come to be mainly adopted as @. However, the adhesion of this cationic electrodeposition coating to the Zn-based alloy-plated steel sheet is poor (hereinafter referred to as secondary adhesion of the coating), and the so-called "electrification gun J" is produced by energization during the coating process. It has the disadvantage of being prone to rare film defects called δ.In order to solve this disadvantage, recently, the plating layer has been made into multiple layers to improve the secondary adhesion of the upper M. or low Zn fp FB
, a Zn-based alloy plating layer, and a 1zn-rich anti-corrosion plating layer as the lower layer to improve the secondary adhesion of the paint and the 1i
ii) The development of so-called multi-layer TQ-plated steel sheets that are excellent in both erodibility and corrosion resistance is progressing, and many inventions regarding various alloy compositions, layer constraints, etc. to achieve this objective have been published.

As described above, considerable improvements have been made in the secondary paint adhesion and corrosion resistance of Zh-based alloy plated steel sheets, but recently, the following improvements have been made in particular for automobile exterior materials: 'jJ The has woken up. in addition,
As mentioned above, Zn-based alloy plated steel (automobile exterior material manufactured by molding and painting using plates) has been improved with the aim of improving the secondary adhesion of paint and corrosion resistance. When a strong impact is received from sand grains, etc., the plating layer at the impact location becomes PA <H because the plating adhesion is weak.
This is a gap where the material peels off from the interface.

In the first place, if Zn-plated steel sheets are thoroughly pre-treated, such as degreasing and pickling, during the manufacturing process, the adhesion of the plating will generally be extremely strong, and this will prevent the problem of the plating layer peeling off in some products after the molding process. Almost never occurred. However, as mentioned above, the Zn-based alloy electroplated steel sheet that has been produced in recent years has potentially weak adhesion between the material steel sheet and the plating layer.
Even if pre-treatment is performed completely during the manufacturing process, the plating adhesion is still inferior to that of Zn-plated steel sheets. Therefore, when used as an automobile exterior material as described above, even if no signs of peeling of the plating layer are observed during the molding and painting stages,
If the vehicle receives a strong impact from a pebble or the like while driving, the fragile nature of the plating adhesion is lost by 1 exposure δ, causing a situation in which the plating layer peels off from the copper plate interface.

As described above, there are natural differences in the adhesion of Oker plating to Zn-based alloy electroplated steel sheets, secondary adhesion of paint, and corrosion resistance, and this is a new problem that needs to be solved, especially for automobile exterior materials! I've been given a lot.

The present invention has been made to solve the above problems, and aims to improve plating adhesion in Znn-based alloy air-plated steel sheets without reducing corrosion resistance or secondary density M property of coating. This is an attempt to propose a multi-layer electroplated steel sheet.

The inventors of the present invention have conducted extensive experimental research in order to develop an effective means for improving the plating density of Zn-based alloy electroplated steel sheets, which has not been developed so far. As a result, a thin layer of Zn plating or Zn-based alloy plating containing η phase is applied as a lower layer directly on the copper plate base, and on top of that, conventional single-layer or multi-layer Zn-based alloy plating is performed. We have obtained new knowledge that by adopting this method, the plating adhesion of Z+]-based alloy plating can be significantly improved.

Akina Himi and his colleagues first began by investigating the cause of the fact that the plating adhesion of Zn-based alloy plating was extremely weak, as in the case of l'lil j-ho. As a result, I discovered a number of things. That is, Fe-Zn system, Nj--Zn
When plating alloys, etc., plating solution 11 is used during plating.
- Expansion stress is generated under '8, but it remains as high contraction stress when plating is completed. On the other hand, in Zn plating, expansion stress is generated due to hydrogen absorption during plating, but upon completion of plating, the stress becomes almost zero and no contraction stress remains. It has been found that the residual shrinkage stress at the end of plating is the main cause of deterioration of plating adhesion. Therefore, it was thought that if the residual shrinkage stress at the end of plating in the Zn-based alloy plating could be alleviated, the plating adhesion would be improved.

On the other hand, the plating adhesion of "Fj" air-plated steel sheets is generally evaluated based on the results of the cello tape on the plating surface without post-plating processing or after Erichsen overhang processing. However, this In the case of Zn-based alloy electroplated steel sheets manufactured with complete pre-treatment for plating using the above test method, good results were obtained in all cases. There is no evaluation that can determine whether or not plating will peel off at certain locations on the material. Therefore, the present inventors conducted a more severe test method, for example, by testing Zn-based alloy plating coated as an automobile exterior material. A new method was devised when a test piece of steel plate was inserted with one cross cut in the shape of a cross that reached the substrate, and then Erichsen overhang was applied to the plated surface. As a result of the above-mentioned new method, we confirmed that it is possible to effectively determine the presence or absence of plating peeling in the case of strong impact as described above. The general method for plating adhesion is 1, and the new method is called the weighted test method for plating adhesion.) The above-mentioned z1'1 alloy plating layer is able to alleviate the shrinkage stress that it receives at the same time as plating is completed. We conducted further research on methods to improve plating adhesion to withstand the strong impact described above.As a result, we added a soft Zn plating layer between the Zn-based alloy plating layer and the copper plate base, and a similar 1tlt. By interposing a Zn-based alloy layer containing a soft η-phase, the contraction force exerted on the upper Zn-based alloy plating layer is absorbed by the intervening layer, and the natural KWII plate and alloy plating layer are It was discovered that if the stress at the interface between the plate and the plate was small, the adhesion of the plating could be improved by the strong impact described above.

The present invention has been made based on the above findings, and the lower layer is directly above the copper plate base, with O, ], g/m' or more, 5 g/m' or more.
A Zn-based alloy plating film containing a Z, n-based alloy plating film or a Zn-based alloy plating film containing an η phase with a plating date amount of 5 or more, and a multi-layered Zn-based alloy plating film extending over the Zn-based alloy plating film. This article focuses on the characteristics of multi-layer electroplated steel sheets.

Next, the structure of the plating skin directly above the steel plate in the non-inventive steel plate will be explained.

The plating layer provided as a lower layer directly above the copper plate is subjected to a known acidic Zn plating bath or a Zn-based alloy plating bath to remove stains. In other words, the film composition is Z
n alone (excluding unavoidable components contained as impurities) or including η phase, for example, Fe-Zn 1Nj--Zn, etc.
It is made of Zn-based alloy. U as a plating method
, When performing Zn single plating, the plating bath composition is, for example, mainly Zn5Op, and inorganic supporting salts (Na, Z
For example, in the case of Fe-Zn alloy plating, the above-mentioned Z
plating bath (a plating bath to which CFeSO2 is added may be used, and the plating bath is not particularly limited. Also, the plating conditions may be, for example, pH 1 to 4 and bath temperature 40 to 60°C to obtain the required basis weight. It may be carried out by a known method such as setting the required plating current density, and there are no particular conditions that should be restricted.Also, when performing Zn-based alloy plating, it is important to include the η phase in the plating film due to the manufacturing process in the plating production line. This can be easily done by setting the conditions such that the plating film contains the η phase, and does not require any new method.

In addition, regarding the Zn-based alloy plating layer overlaid on the above-mentioned lower layer, for example, the lower layer is made of
If the layer structure is such that it has a Zn-Fe alloy plating layer rich in Zn, and the surface layer has a pB-based or Fe-Zn-based alloy plating layer with a low Zn content, which has excellent secondary adhesion to the paint. A Zn-based alloy plating with excellent corrosion resistance, secondary coating adhesion, and plating adhesion can be obtained, but other layer configurations may be used depending on the purpose of use, and there are no particular limitations. Not in.

Next, in the present invention, the reason why the plating weight of the lower plating film directly above the steel plate is limited to 0.1 g/m' or more and less than 5 g/m'' will be explained.

This is because if the basis weight is less than 0.1 g/n12, it is insufficient to cover the surface of the forceps 11 and it is difficult to sufficiently relax the internal stress of the Zn-based alloy plating layer on the mesh. 5g again
/m' or more does not affect the plating adhesion, but if the feeding amount is thicker than 5 g//m2, the corrosion resistance especially after coating will deteriorate. In addition, from a practical point of view, the most preferable range of plating area weight is 05 to 8.
0 g/m2.

δAs mentioned above, regarding Zn-based alloy electroplating,
Conventionally, many inventions have been published to improve the alloy composition, layer structure, etc. regarding rigid corrosion, secondary adhesion of coatings, etc. For example, in JP-A-55-78888, Z
It has a composite Zn plating layer containing a small amount of bran metal across the n plating layer, and on top of that is a second layer containing Zn plating! There are % inventions in Zeng's history. However, the present invention aims to improve the edibility by limiting the number of main buttons to 5 to 120 g/m'. In line with this, the present invention &1ii aims to achieve the same plating adhesion by limiting the coating weight of the lower layer 'K to 0.1 g/m2 or more and less than 5 g/m2 as described above on the l plate. This is a new invention that is distinctly different from the conventional inventions described above.

Next, the effects of non-invention will be explained with reference to Examples.

Example 1 In a normal electroplated fin, 08-thickness x 900
If zinc sulfate is generated in a steel strip of Nm rlj)
Commonly used Z containing νIL acid soda and acetic acid soda
n plating bath was used, pH 3, bath temperature 50°C, plating current density 40 A/(March 12 plating condition, plating condition: 0.2
g//m2 of Zn military air plating and iron sulfate in the above Zn coating bath? In addition, the ratio of Zn and Fe content was varied.
c Fe-Znn manufactured using a Fe-Zn plating bath and varying the plating current density to have the Zn date stones 2 shown in Table 1 and to contain ηa't'k.
f) Cans were plated using air plating. Thereafter, F6-Zn alloy plating with a Fe5Q-Zn composition was applied as an upper layer on top of this, and a two-layer plated steel plate having a total basis weight of 25 g/+1]2 was produced and used as a test material of a non-inventive example. .

For comparison, a similar copper strip containing no η phase outside the non-inventive range was prepared using the same bath composition and plating conditions.
A lower layer was plated with -Zn alloy plating, and then an upper layer was similarly plated with Fe--Zn alloy plating to produce a two-layer electroplated steel sheet, which was used as a comparative sample material.

In addition, a Fe-Znn air-plated steel sheet was produced in which the lower Zn plating layer did not have a Zn alloy plating layer, but only Fe-Zr1 alloy plating was applied in the same manner, and the test material of the conventional example was manufactured. And so.

The plating adhesion of each sample material of the above-mentioned examples of the present invention, comparative examples, and conventional examples was evaluated by the following method.

First, the presence or absence of the η phase in the lower layer was investigated by X-ray diffraction. Next, the Erichsen overhanging process was performed using a plating machine, and after that, the plating surface was evaluated using the Cerotef test method (the normal test method described above), and each sample was subjected to phosphate treatment ( After dirough treatment using BT3080 manufactured by Nippon Berkafizing at a liquid temperature of 50'C) - cationic coating (20μ), a goblin-like cut was made on the surface, and then an Erichsen overhang (5M') process was applied.
After that, the plating adhesion was evaluated by the method of performing cello-tabe tenuto on the surface (the above-mentioned weighted test method).

The amount of Zn in the lower layer, the amount of grain in the lower layer, the presence or absence of η phase in the lower layer, and the evaluation of plating adhesion are summarized in Table 1.

The ○ mark in the plating adhesion evaluation column in Table 1 means that there is no plating peeling off due to cello tape, and ×
Fold with a symbol indicating a defect if the marking plating removal stain 11 is raised)
Ru.

Table 1 As shown in Table 1, the amount of the lower layer in Comparative Example 5 was within the range of the present invention, and Comparative Examples 6 and 7 were outside the range of the present invention, but both contained the η phase in the lower layer. Because of this, in the normal test method, the test results were good with a mark of ○, but in the weighted test method, the test results were poor with a mark of X. Similarly, Conventional Example 8 failed in the normal test method and failed in the weighted test method.

On the other hand, in Examples 1 to 4 of the present invention, the ordinary method was used, and 7JI
: Shows good results in both the gravity method, and has greater plating adhesion [1] f! compared to the comparative example and conventional example. , an improvement was obtained.

Central Strip Example 2 After plating the same copper strip as in Example 1 using the same Zn plating bath as the lower layer and applying various Z and N platings within the range of the present invention as shown in Table 2, Ni 18X
``We performed Ni-Zn alloy plating with the composition ``'' and achieved a gold medal.''
A double-layer plated steel plate having an amount of 25 g/m' was manufactured and used as a test material for the present invention example.

As shown in Table 2, various Zn platings with a basis weight outside the range of the present invention were applied to a similar copper strip using the same Zn plating bath as the lower layer due to the small specific gravity, and then the above-mentioned A similar 1'Ji-Zn alloy plating was performed to obtain a sample material of a comparative example. In addition, a Ni--Zn electroplated steel sheet was produced in which only the Ni--Zn alloy plating was applied in the same manner as above without performing the lower layer Zn plating 2, and it was used as a sample of the conventional example.

The plating adhesion of each of the above-mentioned test materials was evaluated using the ordinary tenuto method and the weighted test method in the same manner as in Example 1. In addition, each test material was treated with phosphate in the same manner as in Example 1, and then subjected to cationic electrodeposition coating, and cross-cuts were made in this coating film to reach the substrate, and after a 500-hour salt water spray test, Maximum bulge at cross-cut section "1"
The corrosion resistance of each sample material was evaluated by the method of measuring .

Table 2 summarizes the evaluation results of the amount of Znn used in the lower layer, plating adhesion, and corrosion resistance.

In Table 2, ○ and × in the plating adhesion evaluation column indicate the same evaluation contents as in Example 1.

As shown in Table 2, in both Comparative Examples 12 and 12, the Zn density of the lower layer exceeds the range of the present invention, so the plating adhesion is praised as good, but the maximum swelling RB
was as large as 42 mm and 65 πm, indicating a deterioration in corrosion resistance. Furthermore, since there was no lower Zn plating layer in Conventional Example 14, there was no deterioration in corrosion resistance, but the evaluation of plating adhesion by the weighted test method was poor. In line with this, all of Examples 9 to 11 of the present invention showed good results using both the normal tenuto method and the weighted tenuto method, and the maximum bulge width ranged from 1.9 to 2.8 in terms of corrosion resistance. The results were very good, with only a small drop.

As is clear from the above explanation, the tree is a trivial multilayer N,
The copper plate has a plating layer with excellent plating adhesion to the lower layer without deterioration of corrosion resistance, and on top of that, a single layer or multiple layers of Zn-based alloy plating of desired 1 and 1: No.
: 4, so it has corrosion resistance: 21.
Since it is possible to improve adhesion at a low cost by eliminating the two-dimensional density β'ff, it can have a remarkable effect on improving plating quality, especially in the field of automobile exterior materials.

Claims (1)

[Claims] (1) Immediately on the base steel sheet, there is a Zn plating film or a Zn plating film containing η phase with a plating pattern of 0.1 g/m2 or more and less than 5 Vm2 (-1 amount kl = i) as a lower layer, and A multilayer electroplated steel sheet characterized by having a multilayer Zn-based alloy plating film.