JPS6318678B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminated Zn-based alloy coated steel sheet with excellent corrosion resistance. In recent years, there has been a demand for surface-treated steel sheets for automobiles that can withstand red rust and pitting for a specified period of time even under harsh environments such as rock salt and calcium chloride, which are used as antifreeze agents in cold winter regions. There is. Various studies have been conducted to give automotive steel sheets high corrosion resistance that can withstand the harsh environments mentioned above, but at the same time, workability and weldability are also required, so we developed laminated steel sheets that are thin but have excellent corrosion resistance. Zn-based alloy electroplated steel sheets are attracting attention. Zn-based alloy plating refers to Zn-Fe, Zn-Ni, Zn
-Means alloy plating such as Co, Zn-Fe-Ni, Zn-Ni-Co. Furthermore, the following have been proposed as laminated Zn-based alloy plated steel sheets that combine such Zn-based alloy plating, but as a result of experiments, it has been found that each of them has drawbacks. In addition, in recent years, there has been a strong demand from automobile manufacturers for surface-treated steel sheets for car body rust prevention that are excellent in bare corrosion resistance in the plate joints or bag structure parts, as well as in suppressing paint film blistering and red rust in areas with paint film defects. Therefore, it is desired to develop a surface-treated steel sheet that satisfies all of these corrosion resistance properties. Various types of corrosion-resistant surface-treated steel sheets have been developed. Typical examples are as follows, but as mentioned above and as shown in the comparative examples, they do not exhibit sufficient corrosion resistance. (1) JP-A-51-112436 (2) JP-A-51-112437 ●Both of the above two patents are
A solid layer containing Zn ^as the main component and one or more of oxides and/or hydroxides of Cr, In, Zr, and Co;
This is a two-layer plated steel sheet with a plated layer consisting only of Zn. ●After electrodeposition coating, in a corrosion test on a test material in which a cross cut was made to reach the base steel, it was found that the cross cut part was prone to blistering of the paint film. ●Note that Zn-Co alloy plating is not shown in the second layer. -The present invention uses a Zn-Co alloy plating layer as the second layer, and is clearly different from the present invention. (3) JP-A No. 52-85030 ●The first layer is a solid layer mainly composed of Zn and containing Co oxide and/or hydroxide, and the second layer is mainly composed of Zn and contains Cr, Cr, Sn,
This is a two-layer plated steel sheet with a blind layer containing one or more of In oxides and hydroxides. ●After electrodeposition coating, in a corrosion test on a test material in which a cross cut was made to reach the base steel, it was found that the cross cut part was prone to blistering of the paint film. ●Note that Zn-Co alloy plating is not shown in the second layer. ●The present invention uses a Zn-Co based plating layer as the second layer, which is clearly different from the present invention. (4) Special Publication No. 57-28754 ●5 to 120g/ ^m2 of Zn or composite as the first layer
It is a two-layer plated steel sheet with a Zn plated layer and a Zn-Fe plated layer (Fe content 1 to 60 wt%) as the second layer. ●After electrodeposition coating, in a corrosion test on a test material in which a cross cut was made to reach the base steel, it was found that the cross cut part was prone to blistering of the paint film. ●In addition, in the examples, Zn-Co alloy plating is not shown in the second layer. ●The present invention uses a Zn-Co based plating layer as the second layer, which is clearly different from the present invention. (5) JP-A No. 56-142885 ●Anti-corrosion metal coating layer as the first layer (inner layer), second layer
2 with Fe-based continuous coating layer as layer (surface)
It is a layered steel plate. ●After electrodeposition coating, in a corrosion test of the test material with crosscuts that reached the base steel, significant red rust was observed at the crosscuts. ●In addition, in the examples, Zn-Co alloy plating is not shown for either the first layer or the second layer. ●In the present invention, both the first layer and the second layer are made of Zn-
This is a Co-based plating layer, which is clearly different from the present invention. (6) JP-A-56-166390 ●Ni, Co, with a thickness of 0.03 to 1.50 μm as the first layer.
Single coating layer of Sn, Cu, Co as second layer,
Zn with a total content of Fe, Sn and Mn of 10-95%
-It is a two-layer plated steel plate with a Co-based alloy plated layer. ●After electrodeposition coating, in a corrosion test on a test material with crosscuts that reached the base steel, it was found that the crosscuts were susceptible to red rust. ●Please note that the first layer is not Zn-Co based plating, and in the examples, the Co content of the second layer is
The Co content of the present invention is as high as 10% or more, from 0.1 to
It is clearly different from 6wt%. In the present invention, the first layer has a coating amount of 1 to 10 g/
m ² , Zn-Co alloy plating with a Co content of 6 to 30 wt%, second layer plating with a coating weight of 3 to 30 g/m ² , a Co content of 0.1 to 6 wt%, and chromium, alumina, silica, and titania. The present invention provides a highly corrosion-resistant surface-treated steel sheet having a Zn--Co alloy plating containing 0.01 to 3 wt% of one or more selected from the group consisting of: The present invention also provides that the first layer has a plating amount of 1 to 10
g/m ² , Co content 6-30wt%, further chromium,
Zn-Co containing 0.01 to 3 wt% of one or more selected from the group consisting of alumina, silica, and titania
Based alloy plating, second layer plating amount 3-30g/
The ^present invention provides a highly corrosion-resistant surface-treated steel sheet having a Zn-Co alloy plating with a Co content of 0.1 to 6 wt% and a Co content of 0.1 to 6 wt% on at least one surface. The present invention further provides that the first layer has a plating amount of 1 to 10
g/m ² , Co content 6-30wt%, further chromium,
Zn-Co containing 0.01 to 3 wt% of one or more selected from the group consisting of alumina, silica, and titania
Based alloy plating, second layer plating amount 3-30g/
^m2 , Co content 0.1~6wt%, and 0.01~3wt of one or more of chromium, alumina, silica, and titania.
The present invention provides a highly corrosion-resistant surface-treated steel sheet formed on at least one surface of a Zn--Co alloy plating containing Zn--Co alloy. The present invention will be explained in detail below. The Co content of the first layer Zn-Co alloy plating is 6~
30wt% is desirable. If it is less than 6 wt%, no effect of improving corrosion resistance will be observed, and if it exceeds 30 wt%, the plating layer will become hard and the plating adhesion will decrease, which is not desirable. The amount of Zn-Co alloy plating is 1~
10g/ ^m2 is desirable. If it is less than 1 g/m ² , no improvement in corrosion resistance will be observed, and if it exceeds 10 g/m ² , workability will decrease and it will also become undesirable from a cost standpoint. When Zn-Co alloy plating further contained 0.01 to 3 wt% of one or more selected from the group consisting of chromium, alumina, silica, and titania, corrosion resistance was further improved, but less than 0.01 wt% had an effect on improving corrosion resistance. is not observed, and if it exceeds 3 wt%, it is undesirable because it causes a decrease in plating adhesion. The Co content of the second layer Zn-Co alloy plating is 0.1~
6wt% is desirable. If it is less than 0.1wt%, no improvement in corrosion resistance is observed, and if it exceeds 6wt%, the Zn−
This is undesirable because it is affected by Co-based alloy plating and reduces plating adhesion. The amount of Zn--Co alloy plating is preferably 3 to 30 g/ ^m2 . 3
If less than 30g/ ^m2 , no corrosion resistance improvement effect is observed.
If it exceeds g/m ² , weldability and workability deteriorate, and it is also undesirable from a cost standpoint. For Zn-Co alloy plating, one or more selected from the group consisting of chromium, alumina, silica, and titania is added from 0.01 to
When the content is 3 wt%, the corrosion resistance is further improved, but when it is less than 0.01 wt%, no corrosion resistance improvement effect is observed, and when it is more than 3 wt%, the mating adhesion deteriorates, which is not desirable. The laminated steel sheet of the present invention has a first layer of Zn-Co alloy plating with a relatively high Co content and a second layer of Zn-Co alloy plating with a relatively low Co content. Although the reason for this superiority is not necessarily clear, it is thought to be as follows. The second layer (upper layer) Zn-Co alloy plating is Co
Since the content is 0.1 to 6wt% and the layer is Zn-rich, it has excellent sacrificial corrosion protection. Therefore, it has a remarkable effect in preventing the occurrence of red rust due to corrosion of the base steel plate. Additionally, Co in the plating layer increases the stability of the corrosion product Zn(OH) ₂ , which has an excellent protective effect, thereby suppressing the progress of corrosion. Furthermore, if a small amount of one or more selected from the group consisting of chromium, alumina, silica and titania is contained, corrosion products Zn
In addition to further increasing the stability of (OH) ₂ , due to the steric effect of these fine particulate oxides or hydroxides present in the plating layer or the corrosion process,
Corrosion resistance is thought to be significantly improved by retaining and inactivating corrosion products on the surface. Since the Zn-Co alloy plating of the first layer (lower layer) has a relatively high Co content of 6 to 30 wt%, the sacrificial anticorrosion ability is somewhat suppressed. Since the first layer plating is in direct contact with the base steel plate, it is desirable that the potential difference with the steel plate be small. In addition, salt water tends to accumulate in the cracked parts damaged by cross-cuts, etc., and furthermore, when corrosion progresses from there, corrosion products are generated, and the corrosion products retain moisture, so they cannot be used in wet environments. The time spent in the room will be longer. This tendency is particularly strong in the deep part of the plating defect, so as in the present invention, the first layer is
Zn-Co alloy plating containing 30 wt% Co is preferred. In addition, as mentioned above, Co in the plating layer is
It is also effective in increasing the stability of Zn(OH) ₂ , a corrosion product with excellent protective properties. Furthermore, if a small amount of one or more selected from the group consisting of chromium, alumina, silica, and titania is contained, the above-mentioned effects will be obtained, and the corrosion resistance will be significantly improved. The present invention provides a first layer and a second layer each having characteristics.
Due to the synergistic effect of laminated plating that combines layers, it has excellent corrosion resistance even though it is thin, and has good weldability and workability.
The present invention provides Zn-based surface-treated steel sheets. By changing the plating thickness of the first layer and the second layer, the laminated plated steel sheet based on the Zn-based alloy plating of the present invention can relatively easily cope with the corrosive environment of the inner and outer surfaces of the vehicle body. That is, the plating thickness can be easily changed by changing the current density and line speed, which is advantageous in actual production. Zn-Co alloy plating baths include chloride bath, sulfate bath,
A sulfamate salt bath or the like or a mixture of these baths can be used, and the bath composition is not limited to a particular one. Next, the present invention will be explained based on examples. Alkaline electrolytic degreasing of cold rolled steel plate (SPCC), 5
After pickling with % hydrochloric acid and washing with water, the first layer of Zn-Co alloy is plated under the following conditions, and then the second layer of Zn-Co alloy is plated on the first layer. Summer. Stirring is performed by a pump, and the liquid flow rate is approximately
60m/min, current density 75A/ ^dm2 , liquid temperature 50℃
And so. (1) Zn-Co alloy plating conditions Bath composition Zinc chloride 200g / Potassium chloride 300g / Cobalt chloride 10-200g / PH2.5 For Zn-Co alloy plated steel sheets with different Co contents, the cobalt chloride concentration in the bath should be adjusted. It was made by changing. Further, the following chromium, alumina, silica, and titania to be eutectoided in the Zn-Co alloy plating layer were used, and a predetermined content was obtained by changing the additive concentration. Chromium: Chromium chloride as chromium metal
0.1-15g/addition. Alumina: 5-100% of alumina sol #520 (Al ₂ O ₃ , 20wt%) manufactured by Nissan Chemical Industries, Ltd.
ml/added. Silica: manufactured by Nissan Chemical Industries, Ltd., Snowtex-O (SiO ₂ , 20wt%), Snowtex-AK (SiO ₂ , 18wt%, Al ₂ O ₃ ,
Add 5-100ml/2wt%). Titania: Titania sol (TiO ₂ , 9wt%) 5
~50ml/addition. (2) Zn-Co alloy plating conditions Bath composition Zinc chloride 200g / Potassium chloride 300g / Cobalt chloride 0.1-100g / PH2.5 Zn-Co alloy plated steel sheets with different Co contents have different cobalt chloride concentrations in the bath. It was made by changing. Further, the same chromium, alumina, silica, and titania as described above were used to be eutectoid in the Zn-Co alloy plating layer. The test materials, which were plated steel plates, were subjected to a salt spray test (SST) in accordance with JIS Z 2371 to examine their corrosion resistance. The processing conditions and corrosion resistance evaluation method for SST specimen materials were as follows. [Corrosion resistance] Bare material Treatment: As is Evaluation: Red rust occurrence area rate after 21 days of SST Coating material Treatment Bonderite #3030 (Dip type) →
Cationic electrodeposition coating 20 μm (Nippon Paint Power Top U-30) → Cross cut (scratches until it reaches the base steel plate) Evaluation: Rate of red rust occurrence and coating film swell width on cross cut portion after 7 days of SST. Red rust occurrence rate ◎... Red rust occurrence rate 10% or less〇... 〃 10~30% △... 〃 30~50% ×... 〃 50% or more Paint film blistering width◎...Paint film blistering width 1.5mm or less〇... 〃 1.5~3mm △... 〃 3 ~ 6mm ×... 〃 6mm or more [Plating adhesion] Dupont impact test: Center of impact 1/2 inch diameter, load 1Kg,
Height: 50cm. 〇…No plating peeling △…Slight plating peeling Table 1 shows reference examples of the present invention that do not contain chromium, alumina, silica, or titania, and Tables 2 to 4 show the scope of each claim. The corresponding test results are shown. As is clear from this, it is clearly seen that the steel plate of the present invention has superior corrosion resistance compared to the conventional steel plate shown in the comparative example.

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Claims (1)

[Claims] 1. The first layer has a Zn-Co alloy plating with a coating weight of 1 to 10 g/m ² and a Co content of 6 to 30 wt%;
Layer adhesion: 3~30g/ ^m2 , Co content: 0.1~
6wt%, and 0.01% of one or more selected from the group consisting of chromium, alumina, silica, and titania.
A highly corrosion-resistant surface-treated steel sheet formed with a Zn-Co alloy plating containing ~3wt% on at least one surface. 2. The first layer has a plating weight of 1 to 10 g/m ² , a Co content of 6 to 30 wt%, and further contains 0.01 to 3 wt% of one or more selected from the group consisting of chromium, alumina, silica, and titania. Co-based alloy plating, second layer coated with a Zn-Co alloy plating with a coating weight of 3 to 30 g/m ² and a Co content of 0.1 to 6 wt% on at least one surface. Highly corrosion resistant surface treated steel sheet. . 3. The first layer has a plating weight of 1 to 10 g/m ² , a Co content of 6 to 30 wt%, and further contains 0.01 to 3 wt% of one or more selected from the group consisting of chromium, alumina, silica, and titania. Co-based alloy plating, the second layer has a plating weight of 3 to 30 g/ ^m2 , a Co content of 0.1 to 6 wt%, and further contains 0.01 to 3 wt% of one or more of chromium, alumina, silica, and titania.
A highly corrosion-resistant surface-treated steel sheet formed with Zn-Co alloy plating on at least one surface.