JPH0243394A - Surface-treated steel sheet for automobile having excellent chipping resistance - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and chipping resistance especially in a low-temp. region by forming the electroplating layer of a Zn-Ni based alloy having specified contents of Tl and Ni on the surface of a steel sheet, and relieving the internal stress in the plating film. CONSTITUTION:The electroplating layer of a Zn-Ni based alloy contg. Tl is formed on at least one side of the title surface-treated steel sheet for an automobile. The alloy contains, by weight, 0.005-5% Tl and >=10% Ni. Consequently, the internal stress in the plating film is relieved, the adhesive strength to the base steel is improved, and the corrosion resistance and chipping resistance especially in a low-temp. region are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a Zn-Ni alloy plated steel sheet, and particularly to a surface-treated steel sheet for automobiles with excellent chipping resistance.

<Prior art> In recent years, high corrosion resistance has been required mainly for automobile steel plates in order to prevent corrosion of automobile bodies caused by antifreeze agents sprayed on roads. Steel plates have been developed and their use is increasing.

Conventionally, Zn-based alloy electroplated steel sheets used as steel sheets for automobiles are often plated on only one side; - For boat fishing, the non-plated side (cold rolled steel sheet) is used on the outside of the car body. Chemical conversion treatment on the steel plate → Electrodeposition coating → Intermediate coating → Top coating 3
However, recently, in order to improve the rust prevention properties of the outer surface of automobile bodies, steel sheets coated with Zn-based alloy electroplating are also being used on the outer surface of automobile bodies.

However, the Zn-based alloy plating film is hard and brittle, so when used on the outer surface of an automobile body, the plating film tends to peel off due to so-called chipping, which occurs when pebbles on the road splash and collide with the outer surface of the automobile body. There is.

As a solution to this problem, the present inventors have previously proposed Zn-N in Japanese Patent Application Laid-Open No. 63-7393.
A method for improving the adhesion of plating was proposed.
In the production of Zn-Ni electroplated steel sheets, this technology applies ZnNi pre-plating on the steel plate with a Zn-Ni plating solution, immerses it in the same Zn-Ni plating solution without applying electricity, and then coats the steel plate with the same Zn-Ni electroplated steel sheet. A predetermined amount of Zn- is applied using a Ni-based plating solution.
This is a method of performing Ni-based alloy plating. However, in this method, the plating cells must be used for non-current immersion, which reduces the number of effective plating cells and lowers productivity. In addition, since it requires non-current immersion for a predetermined time,
The line speed is determined by the immersion time, resulting in poor production efficiency.

Furthermore, for example, in Japanese Patent Application Laid-open No. 6C1-128286, Fe, Ni, Cu, Sn, Cd, and P, which are more harmful than Zn, are added to a steel plate.
Type b or 2f! Z
A steel plate electroplated with an n-Ni alloy, and JP-A-61-019794 discloses that Fe in a metallic state with a Vickers hardness of 300 or more is applied as a lower layer on a steel plate from 1.5 to 20.
A steel plate coated with a coating of at least g/m 2 and then subjected to Zn-Ni alloy electroplating is indicated as a steel plate with excellent chipping resistance. However, Ni, Cu,
The base plating for Sn, Cd, and Pb is a Zn-Ni alloy.
) It has an adverse effect on the corrosion resistance of the coating layer, and the Fe plating does not contribute to the corrosion resistance, and plating of 1.5 to 20 g/m2 is wasteful from the viewpoint of corrosion resistance.

<Problems to be Solved by the Invention> Therefore, the present invention solves the above-mentioned problems of the prior art, and provides a Zn-Ni alloy that has good corrosion resistance while also having good corrosion resistance while having good corrosion resistance in a low temperature range. The purpose is to provide electroplated steel sheets.

Means for Solving the Problems> As a result of repeated studies on the development of a Zn-Ni alloy electroplated steel sheet that has chipping resistance in a low temperature range and excellent corrosion resistance, the present inventors found that the lower layer It has been discovered that by forming a plating layer containing Tl, the internal stress of the plating film is relaxed and the adhesion to the base steel interface is improved, and the present invention has been achieved.

That is, the present invention provides T on at least one surface of the steel plate.
Provided is a surface-treated steel sheet for automobiles having excellent chipping resistance, characterized by having a Zn-Ni alloy electrical layer containing 0005 to 5 wt% of IL and 10 wt% or more of Ni.

In addition, at least one surface of the steel plate is coated with T as a lower layer plating.
It has a Zn-Ni alloy electroplating layer containing 0.005 to 5 wt% of l2 and 10 wt% or more of Ni, and a ZnNi alloy electroplating layer containing 10 to 20 wt% of Ni as an upper layer on the top surface. Provided is a surface-treated steel sheet for automobiles having excellent chipping resistance.

Preferably, the amount of the lower Zn--Ni alloy electroplated layer is 0.1 g/m2 or more.

The present invention will be explained in detail below.

In the present invention, the lower Zn-Ni electroplating layer is
0005-5wt% of Tl on at least one side of the steel plate
, it is necessary to contain 10 wt% or more of Ni.

When the content of Tfl is less than 0.005 wt%, the effect of improving chipping resistance is small, and when it exceeds 5 wt%, corrosion resistance is reduced.

Further, the Ni content in the lower layer is desirably 10 wt% or more, and this is for improving corrosion resistance.

The amount of the lower layer Zn--Ni alloy electroplated film is preferably 01 g/m2 or more. Adhesion amount is 0.
If it is less than 1 g/m2, chipping resistance will be insufficient.
Further, there is no upper limit to the amount of adhesion, and a single layer of the above-mentioned Tu-containing Z-Ni alloy film may be used.

However, since peeling of the plating layer due to chipping occurs from the interface between the base steel and the plating layer, the base plating has a large effect on chipping resistance.

However, increasing the amount of adhesion is expensive TfL.
Since a large amount of T is required, it is economically disadvantageous.
The upper limit of the adhesion amount of the l-containing Zn-Ni alloy plating film is 3
Approximately 0 g/m2 is preferable.

As a source of Tu ions, Tl2 (so4ks, TIL202, TLCρ3,)
ICOOTρ, Ti 2 (OOCCH2C00), Tl
Examples include 1NO3, (CF3COO)3Tρ, and the like.

The Tj2 content in the Zn-Ni alloy electric pottery film is reduced to 0.
In order to control the content within the range of 0.005 to 5 wt%, it is best to control T, 9 ion concentration, Ni molar concentration, current density, etc.

The upper layer Zn-Ni alloy electroplating performed on the upper surface of the lower layer TJZ-containing Zn-Ni alloy electroplating layer is 1
This is a range in which a Zn-Ni alloy electroplated film containing 0 to 20 wt% Ni has a sacrificial corrosion prevention effect and is excellent in corrosion resistance. Further, the amount of the upper plating film deposited may be - the amount of licking, and there is no particular upper or lower limit.

This upper layer Zn-Ni alloy electroplating can be carried out according to conventional methods, and the current density and pH should be adjusted in the same manner as the lower layer plating.
1. Plating conditions such as temperature are not particularly limited.

Note that C01Cr and Sn are contained in the Zn--Ni alloy plating layer containing Tl2 applied to the lower layer and the normal ZnNi-based alloy plating layer applied to the upper layer.

Sb, V, Fe, Ti, P, Mn, A sBi,
There is no problem even if In, Cd, Ir, etc. are unavoidably mixed in or intentionally added.

The type and dimensions of the steel material used in the present invention are not particularly limited, and cold-rolled steel sheets suitable for the intended automobile body,
There are high-tensile strength cold-rolled steel sheets, deep-drawn cold-rolled steel sheets, and their bake-hardened cold-rolled steel sheets.

Further, as pretreatment, degreasing, pickling, water washing, etc. may be performed according to general methods.

As the plating method, conventionally known methods such as a horizontal method, a vertical method, and a radial cell method can be applied.

As the polishing bath, a sulfate bath, a chloride bath, a mixed bath thereof, etc. may be used.

<Example> Hereinafter, the present invention will be specifically explained based on examples.

(Example) Using a cold-rolled steel plate equivalent to 5PCE with a plate thickness of 0.7 mm,
Plating was carried out under the following plating conditions.

(Plating conditions) <Lower layer plating> (1) ZnSO4・HI20 120-240 g
/j2(2) NiSO4・6820 210~33
0 g/ρ(3) Na2SO440g/ It (4) Tit 2 (504130~100 g/
42(5) p8 1.2-1.8(6)
Bath temperature 50-60℃ (7) Current density 10-100 A/dm2 (upper layer wipe) (1) ZnSO4.61 (20150g/u (2)
Ni5Oa・7H20300g/It(3) Na2S
0440 g/j2 (4) pH 1,6 (5) Bath temperature 60°C (6) Current density 50 A/dm' For the above plating, the contents of Tρ and Ni in the lower layer plating and their adhesion amounts are shown in Table 1. Then, electroplating was applied. Then, on this Tu-containing Zn-Ni alloy plating layer, the Ni content of the upper layer plating was changed to 12.5% Zn so that the total adhesion amount with the lower layer plating was 30 g/m2.
-Ni alloy electroplating was performed. Table 1 also shows the cases in which the upper layer of Zn--Ni alloy is not covered.

The thus obtained surface-treated steel sheet of the present invention and its comparative example were compared in various tests.

The results are shown in Table 1.

(1) Corrosion resistance without painting A salt water spray test was conducted, and visual judgment was made based on the following criteria.

○... Red rust occurrence rate after 300 hours is less than 5% △...
Red rust occurrence rate after 300 hours is 5-10% x 300
Red rust occurrence rate after hours is 10% or more (2) Low-temperature chipping property Dip method After phosphate treatment, a low-temperature gravel test was performed on a sample that was coated with 3 coats of cationic electrodeposition, intermediate coat, and top coat to a total thickness of 90 μm. went. The Gravelo test here refers to a 3-coat test piece in which 20 pieces of granite weighing Ig/piece were dropped into a 50 mm diameter cylinder and cooled to -20°C with air at a pressure of 4 kg/cm' introduced into the cylinder. After the plating is applied, the tape is peeled off and the degree of peeling of the plating is observed. Low-temperature chipping property evaluation is for those with large peeling diameter 5
The points were actually measured and the criteria for judgment were as follows.

○...The average value of peeling diameter is 4 mm or less and the maximum peeling diameter is 5mm or less.△...The average value of peeling diameter is 4mm or less and the maximum peeling diameter is 5mm or more ×...The average value of peeling diameter is 5mm or less Fruit surface of 4 mm or more <Effects of the Invention> As detailed above, according to the present invention, a Zn-Ni alloy that has excellent corrosion resistance and good chipping resistance at low temperatures without reducing productivity can be obtained. An electroplated steel sheet is obtained.

Claims (3)

[Claims] (1) Tl of 0.005 on at least one side of the steel plate
~5 wt%, and Zn containing 10 wt% or more of Ni
- A surface-treated steel sheet for automobiles with excellent chipping resistance, characterized by having a Ni-based alloy electrical layer. (2) T as a lower layer plating on at least one side of the steel plate
A Zn-Ni alloy electroplating layer containing 0.005 to 5 wt% of L and 10 to 20 wt% of Ni as an upper layer plating on the upper surface thereof. A surface-treated steel sheet for automobiles having excellent chipping resistance. (3) The surface-treated steel sheet for automobiles with excellent chipping resistance according to claim 1 or 2, wherein the deposited amount of the lower Zn-Ni alloy electroplated layer is 0.1 g/m^2 or more.