JPS61110791A - Zn-ni-ti alloy plating method superior in chemical conversion treatability - Google Patents

Abstract

PURPOSE:To provide a superior chemical conversion treatability, by applying Zn-Ni alloy electroplating previously as the first layer, then applying Zn-Ni-Ti alloy electroplating to a specified thickness as the second layer. CONSTITUTION:Zn-Ni-Ti alloy electroplating is applied to steel sheet or strip. Thereat, Zn-Ni alloy electroplating is applied previously as the first layer. Then, Zn-Ni-Ti alloy electroplating is applied at 1-15g/m<2> per one side as the second layer. In such a way, Zn-Ni-Ti alloy plated steel sheet or strip superior in phosphate treatability is obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides Zn with excellent chemical conversion treatment properties, particularly phosphate treatment properties.
-Regarding a Ni-Ti alloy plating method.

(Prior art) Zn-Ni-Ti alloy plating! I steel plate has a coating weight of Z
Exhibits excellent corrosion resistance even with less n-Ni alloy plated steel sheet. Zn-Ni-Ti alloy plated steel sheets are also widely used as base plates for painting.

When painting Zn-Ni-Ti alloy plated steel sheets, use the normal method! ! As with the case of steel plates, pretreatment is performed before painting, but phosphate-based and chromate-based pretreatments have conventionally been mainly used.

(Problem to be solved by the invention) However, when a Zn-Ni-Ti alloy plated W4 plate is subjected to phosphate treatment, there are cases where the phosphate treatment is good and cases where it is not. No membrane performance was obtained.

(Means for solving the problem) The inventors of the present invention conducted various studies to investigate the cause, and as a result, they discovered that the cause was the amount of precipitation of T1 compounds present on the plating surface layer. .

As shown in Fig. 1, the corrosion resistance of Zn-Ni alloy coated steel sheets improves almost in proportion to the increase in coating weight;
- In the case of a Ni-Ti alloy plated steel sheet, it increases sharply from 15 g/so2. Therefore, in order to find out what caused this sudden improvement in corrosion resistance, we investigated the element distribution in the thickness direction of plating %/i. It turned out that this was due to phase 4. Figure 2 shows Ohnoe analysis of the surface N part of the plating layer of Zn-Ni-Ti alloy plated flange plates with different amounts of plating. When we investigated the element distribution in the thickness direction of the layer, we found that in the case of (a) with a coating weight of 21) g/m2 per side, the amount of Tl is 10 g/m2 in (b). This suggests that Zn-Ni-Ti alloy plating is a unique plating.
In the case of alloy plating, unlike ordinary alloy plating in which alloy elements are precipitated at a constant rate, a hydrolyzate of Ti is formed in the form of Wl and Ni on the surface layer of the plating layer during plating. Therefore, most of the Ti in the plating layer is not dispersed in the plating layer but is present in the plating surface layer.

On the other hand, when Zn-Ni-Ti alloy coated steel sheets with different coating weights are subjected to phosphate treatment, the amount of phosphate crystal precipitation decreases as the coating weight increases. ! :rS
[31] shows the state of precipitation of phosphate crystals when a Zn-Ni-Ti alloy plated IIF plate and a Zn-Ni alloy plated plate with different coating weights were subjected to phosphate treatment. -In the case of Ni-Ti alloy plated steel sheet, if the coating weight per side is 20g/2, the state of precipitation of phosphate crystals will be small, but if the coating weight is 15g/+
m'', it increases considerably, and when it becomes 10 [1/l112, it becomes more than in the case of Zn-Ni alloy plated steel sheet.

In this way, the Zn-Ni-Ti alloy plated steel sheet has the characteristic that corrosion resistance and phosphate treatability are opposite depending on the amount of plating deposited. This is because the amount of plating deposited is large. ! Dense TiN is formed on the surface layer, improving corrosion resistance, but the reactivity with the phosphate treatment solution decreases, resulting in poor phosphate treatment properties.On the other hand, when the coating weight decreases, the plating layer This is thought to be because Ti is dispersed in the surface layer, and Ti becomes a nucleus for phosphate crystal formation, thereby improving phosphate treatment properties. Therefore, Zn-Ni-T
In order to improve the phosphatability of i-alloy coated steel sheets, it is necessary to reduce the coating weight to 15 g/m2 or less per side, and in particular, to make the coating weight better than that of Zn-Ni alloy plated steel sheets, it is necessary to reduce the coating weight to 10 g/m2 or less per side. It is preferable to make it less than /m2. However, when the coating weight is reduced to 15 g/+*" or less, deterioration in corrosion resistance is unavoidable even on Zn-Ni-Ti alloy plated steel sheets, which have excellent corrosion resistance. Therefore, in the present invention, this deterioration in corrosion resistance is Zn-Ni before Ti alloy plating
This can be prevented by alloy plating. That is, in the present invention, when performing Z-row Ni-Ti alloy electroplating on a steel plate or steel strip, the first layer is
n-N: Zn-Ni-Ti alloy electroplating is applied as a second layer, and then Zn-Ni-Ti alloy electroplating is applied on one side.
It was designed to run at a rate of 15H/m2.

Here, the lower limit of the plating deposition amount during Zn-Ni-Ti alloy electroplating was set to Ig/U2 per side.
This is because if the amount is less than 1 g/2, there is almost no Ti present in the surface layer of P scraps, and no improvement in phosphate treatability and corrosion resistance is observed due to Ti.

The coating weight ratio of the 1st M and tjS2 layers during plating of the present invention should be determined depending on the usage environment of the plated steel sheet, but since the 27th layer contains '1'1, Plating cost is higher than 171it. For this reason, depending on the usage environment, instead of making the second tear thinner, it may be changed to 1/Rainbow! By increasing the thickness of F and making the total plating amount a certain amount,
It is also possible to reduce plating costs.

The plating of the 1st/I and 12th layers is carried out using a known plating bath, for example f
In the case of JSlffi, the composition is as shown in JP-A No. 58-207389! T1, ^1 (or Mg) from the bath,
Or a plating bath excluding Co and each ion (P 111
, 5 to 2.5), and in the case of the second layer, eight days from the plating bath of JP-A-58-207389 or Mg)
, or remove each ion of CO! This can be done using an I bath. In addition, when plating the 1@1 layer and the 2nd layer, one or more highly corrosion-resistant metals such as ^1, M[+, 8g, Cr, etc. are added to the plating bath so that they are incorporated into the plating layer in small amounts. fi may be included.

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

(Example) After degreasing and pickling a cold-rolled steel plate with a thickness of 0.8+ am by a conventional method, Zn-Ni alloy was applied to the first layer and Zn-Ni- alloy was applied to the second layer under the conditions shown in Table Pr51. Ti alloy was sequentially electroplated. After that, this steel plate was subjected to phosphate treatment (BT-103, manufactured by Nippon Parinong Co., Ltd., treated at 65°C for 8 seconds), and 2-foot, 2-bake coating (undercoat: commercially available epoxy paint 5 μl, topcoat: commercially available melamine liquid) Dull paint 2
The first adhesion test of the coating film was carried out on the coated VC steel plate obtained here (0μ ring) and the 2
Next adhesion test (2 hour immersion → peel off the goblin tape @
) was conducted to investigate phosphate treatment properties based on paint film adhesion.

The results are shown on the right side of No. 1 &, and the coating plated according to the present invention has good primary adhesion and secondary adhesion of the coating film. On the other hand, Zn-Ni alloy and Zn
-N i -T i alloy has a plating weight of 20 g
/va'' is poor in both primary adhesion and secondary adhesion.Generally, the quality of phosphate treatment depends on the secondary adhesion of the coating film, so those plated according to the present invention are inferior in both primary and secondary adhesion. It can be said that the processability is excellent.

(Effects) As explained above, by plating according to the present invention, a Zn-Ni-Ti alloy plated steel sheet with excellent phosphate treatment properties can be obtained, making it suitable for general painting and automobile exterior panels.
! Steel plates can be manufactured.

[Brief explanation of drawings]

Figure 1 shows Zn-Ni-Ti alloy plated steel sheet and Z++
Fig. 27 shows the relationship between the amount of plating on a -Ni alloy plated steel sheet and the time until red rust occurs. P142 figure is Zn-
It is a graph showing the element distribution in the thickness direction when the plating layer surface M&IS of the Ni-Ti alloy plated Pw4 plate is subjected to an optical analysis. Figure 3 shows a Zn-Ni-Ti alloy plated steel plate and a Zn-Ni alloy plated plate! It is a photograph showing the state of precipitation of phosphate crystals when a steel plate is subjected to phosphate treatment.

Claims (1)

[Claims] When performing Zn-Ni-Ti alloy electroplating on a steel plate or steel strip, Zn-Ni alloy electroplating is first performed as a first layer, and then Zn-N is applied as a second layer.
i-Ti alloy electroplating 1~15g/m^ per side
2 Zn-Ni with excellent chemical conversion treatment properties
-Ti alloy plating method.