JPS6393888A - Zinc alloy electroplated steel sheet having superior resistance to exfoliation by shock after coating - Google Patents

Abstract

PURPOSE:To improve the resistance of a plated steel sheet to exfoliating by shock after coating by pretreating the surface of a base steel sheet so as to control the concn. of an alloy in the vicinity of the interface between a plated layer and the base steel sheet. CONSTITUTION:When a steel sheet is electroplated with a Zn alloy, it is pretreated by pickling and polishing, electrolytic oxidation or short-time annealing with a gas having a low dew point so that an Mn and/or Al enriched layer is not formed by the electroplating in the steel in the vicinity of the interface between a plated layer and the base steel sheet. A pretreated and Zn alloy electroplated steel sheet has superior resistance to stripping by shock after coating and can be widely used as a rustproof steel sheet for an automobile, a base sheet for a precoated steel sheet or the like.

Description

[Detailed Description of the Invention] [Industrial Application Field] Regarding the zinc-based alloy electroplated steel sheet with excellent impact peeling resistance after painting according to the present invention, more specifically, Zn-Ni alloy plating, Zn-Fe Zinc-based alloy electroplating that is highly resistant to impact peeling after painting with other platings such as alloy plating! 4 Concerning provisional.

[Prior art] Zn alloy electroplated steel sheets such as Zn-Ni alloy plating and Zn-Fe alloy plating have better corrosion resistance, corrosion resistance after painting, spot weldability, etc. than conventional electrogalvanized steel sheets and hot-dip galvanized steel sheets. Because it is superior to galvanized steel sheets, it has recently been widely used for other purposes, including automotive rust prevention.

The characteristics of these Zn-based alloy electroplated steel sheets, such as their corrosion resistance, corrosion resistance after painting, and spot weldability, vary depending on their alloy composition and alloy layer.

These properties are good because Zn-Ni alloy electroplating has γ phase, which is an intermetallic compound of Zn-Ni, as the main component, whereas Zn-Fe alloy electroplating has the same <Zn-
This is the case where the intermetallic compound of Fe, ζ, δ1, and F phases, is the main component, and the case where the intermetallic compound is the main component of the plated layer in any alloy system.

Therefore, these zinc-based alloy electroplated layers are harder and more brittle than conventionally widely used zinc plating. Therefore, it has been found that when an impact force is applied to these zinc-based alloy coated steel sheets after coating, a problem arises in that the coating film peels off from the interface between the plating layer and the base steel sheet.

This phenomenon does not occur even when an impact force is applied to a Zn-Ni alloy electroplated steel sheet that is not coated, but only occurs when it is coated. The thicker the coating film, the harder the coating film, and the lower the ambient temperature, the more this phenomenon occurs.

A typical example of this phenomenon is the chipping phenomenon caused by flying stones in winter when a Zn--Ni alloy electroplated steel sheet is used for the hood of an automobile.

In this case, since the coating film will be used on the exterior of the car, 10
It is thick, about 0 μm, and the coating film is hardened due to the low temperature, so if the impact energy of a flying stone is large, the coating film will peel off from the interface between the plating layer and the underlying steel plate. Since no Zn-N1 alloy electroplating layer remains on this peeled surface, there is a problem in that scab corrosion and pitting corrosion easily occur from this peeled surface.

As described above, the following techniques have been proposed as measures to improve the impact peelability after coating.

For example, in JP-A-60-128286, Fe5Ni, Cu, Sn, and Cd, which are nobler than Zn, are deposited on a steel plate.

Zn-Ni
Steel sheets electroplated with alloys, and JP-A-61-0
No. 19794 discloses that a steel plate is coated with 1.5 to 20 g of Fe in a metallic state with a Vickers hardness of 300 or more as a base layer, and then electroplated with a Zn-Ni alloy. It is shown as a steel plate with excellent peelability.

However, in order to manufacture these W4 boards, Zn-N
In addition to the i-series alloy electroplating bath, equipment for these base platings is required, and this cannot be implemented immediately. In addition, the base plating of Cu, Sn, Cd, and Pb is Zn-Ni.
It has a negative effect on the corrosion resistance of the electroplated layer of the Fe plating, and does not contribute to the corrosion resistance of the Fe plating.
' plating is useless from the point of view of corrosion resistance.

In addition, Zn-Ni alloy electroplated steel sheets have problems related to the processing of Zn-Ni alloy electroplated plates, such as the corrosion resistance of the beuda ring processing part during press working, in addition to the impact peeling resistance of the coating layer after painting. Countermeasures for these problems have also been proposed.

For example, in JP-A-58-130299, using the same plating solution, Z
After performing n-Ni alloy electroplating, Zn-Ni alloy electroplating is further performed at a current density of 20 A/dm" or more to produce a Zn-Ni alloy electroplated steel sheet with excellent corrosion resistance in processed parts. A method is shown.
Publication No. 204196 discloses that a Zn-Ni alloy with a higher Ni content than a Zn-Ni alloy with a predetermined Ni content is coated on a steel plate in advance.
A method for manufacturing an electrolytic zinc alloy coated steel sheet characterized by electroplating a zinc alloy to a thickness of 0.05 to 08 .mu.m and exhibiting corrosion resistance in processed parts is disclosed.

However, in the method of plating in advance at a current density of 2 to 20 A/dm'', the current density is 1/2 to 1/2 of the flow rate.
20, which causes a problem of reduced productivity.Also, if the Z
In the method of electroplating n Ni-based alloys, it is necessary to use two plating solutions with different compositions or temperatures, which requires measures in terms of equipment.

As described above, the conventional and proposed Zn-based alloy electroplated steel sheet and its manufacturing method that improve the workability of the plating layer are improvements to the plating layer and the plating method, and therefore, the plating layer is improved. There is a risk that properties such as corrosion resistance may change, and there are problems such as changes in manufacturing equipment.Furthermore, there is a demand for Zn-based alloy electroplated steel sheets that have excellent impact peeling resistance after coating.

[Problems to be Solved by the Invention] In view of the problems of the prior art described above, the present inventor has conducted extensive research, and as a result, the present invention has been developed to control the alloy concentration near the interface between the substrate preparation and the plating layer. By doing so, we developed a Zn-based alloy electroplated steel sheet that has excellent impact peeling resistance after coating.

[Means for Solving the Problems] The zinc-based alloy electroplated steel sheet with excellent impact peeling resistance after coating according to the present invention is characterized by the presence of Mn or Al type 1 or 2
The reason is that the zinc-based alloy plating is applied without the presence of a concentrated layer of N.

The zinc-based alloy electroplated steel sheet having excellent impact peeling resistance after painting according to the present invention will be described in detail below.

Zn-based alloy electroplated steel sheets, that is, Zn-Ni-based alloy electroplated steel sheets, and Zn-Fe-based alloy electroplated steel sheets, are mainly used in applications that require a beautiful surface such as automobiles, so they are used as base steel sheets. Generally, cold-rolled steel sheets are used.

It is known that during annealing performed after cold working, this cold rolled steel sheet has a so-called surface enriched layer in which alloy components such as C5Mn, Al, St, and P are concentrated. The degree of concentration and thickness of this surface concentrated layer vary depending on the annealing method.

Although these surface concentration layers can be partially removed by degreasing and pickling, which are pre-treatments for zinc-based alloy electroplating, and the accompanying surface scrubbing, they cannot necessarily be completely removed; Even after Ni-based alloy electroplating, these concentrated layers generally exist near the interface between the plated and base steel sheets. This concentrated layer is formed by the recently developed G
It can be measured by surface analysis methods such as DS (glow discharge emission spectroscopy), AES (Auger electron spectroscopy), and ESCA (photoelectron spectroscopy).

The present inventor has developed Zn-Ni using a base steel plate with various changes in the base annealing method, degreasing, pickling conditions, surface polishing conditions, etc.
After applying the 3-coat coating for automobiles, stones were pounded onto the coating film of electroplated steel sheets using alloys based on the electroplating method. When we investigated the presence or absence of a concentrated layer of Mn and Al and their relationship, we found that coatings with a concentrated layer of Mn and Al near the interface had poor impact peeling resistance, and ~1n,
It was found that the coating film in which no concentrated Al layer was observed had good impact peeling resistance.

In this case, the element concentration near the plating-substrate interface can be defined as described below.

Figure 1 is a schematic diagram of the luminescence intensity vs. discharge time curve when a Zn-Ni alloy electroplated steel sheet was analyzed by GDS. Light emission appears, and when the base steel sheet appears, the light emission of ZnSNi decreases, the light emission of Fe increases, and then becomes constant.

If the alloying element in the alloy is uniformly contained and is not concentrated near the plating-steel plate interface, the luminescence intensity of that element will be similar to the luminescence profile of Fe, as shown by 1 in Figure 1. It should be.

On the other hand, when a certain element forms a concentrated layer near the interface between the plated steel sheets, the emission intensity of that element once reaches a peak and then decreases to a certain level, as shown in 2 in Figure 1. It should be the value. Therefore, the presence or absence of a concentrated layer in the vicinity of the plated steel plate interface can be determined depending on whether the profile of the emission intensity-discharge time curve by GDS is type 1 or type 2. Note that the determination of the concentrated layer can be similarly performed using surface analysis methods other than GDS.

Figure 2 is a diagram showing an example of the concentration distribution of various elements in the depth direction by GDS of a Zn-Ni alloy electroplated steel sheet with good impact peeling resistance of the coating film. No enrichment of Mn5Al is observed.

Figure 3 is a diagram showing an example of the concentration distribution of various elements in the depth direction by GDS of a Zn-Ni alloy electroplated steel sheet with poor impact peeling resistance of the coating film. , concentration of Al is observed.

When a concentrated layer of MnsAl exists in this way, Zn-N
The reason for the deterioration of the impact peeling resistance after painting of I-based alloy electroplated steel sheets is that Mn and Al concentrated on the surface of cold-rolled steel sheets after annealing are not in a metal state but are iron oxides. Zn--Ni alloy electroplating and Zn-- When hard alloy plating such as Fe-based alloy electroplating is deposited, it becomes a factor that inhibits the metal bond between the plating layer and the base steel, and if an impact force is applied after painting, the base steel -
It is thought that the bond at the plating interface is destroyed.

There are several methods for producing an alloy electroplated steel sheet in which this Mn5Al concentrated layer does not remain near the plating-substrate interface, as described below.

l) A concentrated layer of Mn and Al formed on the surface of the base steel sheet is polished by means of a puff or a belt polisher.

2) Chemically, that is, pickling is usually carried out as a pretreatment for plating, but under normal conditions, the thick Mn and Al concentrated layer produced by annealing cannot be completely removed and some parts remain. Therefore, it is desirable to increase the pickling capacity by increasing the acid concentration, increasing the pickling temperature, etc.

3) Furthermore, the effect can be further enhanced by polishing with a puff or the like during, before and after the pickling process.

4) Electrolytic oxidation in which the steel plate is polarized to the anode side in the 71i solution is effective.

5) By using an annealing method that reduces the thickness of the concentrated Mn and Al layer formed on the surface of the base steel sheet, for example, using a gas with a low dew point, short-time annealing, etc., in combination with the above method,
You can increase the effect.

With the above method, the concentrated layer can be removed in the in-line pickling process, even if the concentrated layer cannot be removed with a hot rolled steel sheet produced by the normal annealing process, and therefore, alloy plating can be performed on it. In this case, the impact peeling resistance after coating is improved.

As described above, Zn-Ni alloy electroplating, Zn-Fe alloy electroplating, which improves the impact peeling resistance after coating by removing the Mn and At concentrated layer near the plating-steel plate interface, Examples include alloy plating of zinc and iron group, such as Zn-Co alloy electroplating and Zn-Co alloy electroplating.

In the case of Zn-Ni alloy electroplating, Ni-containing
If it is 7 to 20 wt%, the impact peeling resistance after coating is particularly poor, and therefore Mn and A near the plating-steel plate interface are
The presence or absence of the 1a4+c layer has a large influence, and the N content is within a range that provides good corrosion resistance.

In the case of Zn--Fe alloy electroplating, the presence or absence of a Mn and Al enriched layer has a large effect when the Fe content is 7 to 70 wt%.

In addition to these zinc and iron group alloy electroplating, Zn-C
r-based alloy electroplating, Zn-Mo-based alloy electroplating, Z
n-W alloy electroplating, Zn-V alloy electroplating,
There are Zn-Ti alloy electroplating, Zn-Pb alloy electroplating, Zn-5n alloy electroplating, etc., and this alloy plating is also affected by the presence or absence of Mn and At enriched layers near the interface between the plated and steel sheets. .

In addition, on the above-described zinc-based alloy electroplated steel sheet, a multilayer alloy-plated steel sheet is further plated, for example, a lower layer Zn-Ni alloy electroplated, an upper layer Zn-80wt%.
Even in the case of Fe-based alloy electroplating, the effect of the presence or absence of an enriched layer of ~(n, Al) is the same as in the case of a single layer.

ε Example] An example of a zinc-based alloy electroplated steel sheet having excellent impact peeling resistance after coating according to the present invention will be described.

Example 1 After degreasing an aluminum killed cold-rolled steel plate, its surface was polished with #600 sandpaper, and then after pickling with sulfuric acid, Z
An n-Ni alloy electroplating (Ni content Q12 wt%, adhesion m 30 g/m'') was performed.

As a comparative example, polishing was omitted and the other treatments were the same as above.

These specimens were subjected to dipping phosphate treatment, cationic electrodeposition coating, intermediate coating, and top coating according to the automotive coating process.

The total thickness of the three coats was 100 μm.

After cooling these painted specimens to -20°C, scratches were made on the painted surfaces using a gravelometer.

The conditions of the gravelometer are as follows.

Air pressure: 4kgf/c Stone type: Granite stone diameter: 7.7-11.1mm Amount of stone:
100 g After this test, the paint film released from the steel plate was removed using adhesive tape, and the maximum diameter of the part where the paint film was peeled off from the interface between the plate and the base steel plate was measured.

Measurements were made at 10 points starting from the largest diameter, and the average diameter is shown.

In addition, presence or absence of concentration of Mn and Al near the interface between the plated steel sheets was analyzed by GDS.

Table 1 shows the results.

In the examples without the concentrated Mn and Al layers in Table 1, the peeled diameter of the coating film was small.

Example 2 A cold rolled aluminum killed steel plate was soaked in 5% sulfuric acid at room temperature for 10 minutes.
A/dm'X After 5 seconds of electrolytic pickling, Zn-Ni
based alloy electroplating (Ni content 112 wt%, deposition amount 30
g/m”) was applied.

As a comparative example, 1 in 5% sulfuric acid at room temperature instead of electrolytic pickling.
Pickling was performed by immersion for 0 seconds.

These specimens were tested under the same conditions as in Example 1.

Table 2 shows the results.

Table 2 In the examples in which the Mn and Al concentrated layers were dissolved by electrolytic pickling, the peeled diameter of the coating film was small.

Example 3 After degreasing a cold-rolled aluminum-killed steel sheet, it was pickled with 5% sulfuric acid while being polished with #600 sandpaper. After that, Zn-Fe alloy electroplating (Fe-containing ff115w
t%, adhesion ff 120 g/m'').

As a comparative example, the same steel plate as above was not polished, but was pickled with 5% sulfuric acid, and then electroplated with the same Zn-Fe alloy as in the example.

These specimens were tested under the same conditions as in Example 1, and the results are shown in Table 3.

Table 3 Examples without Mn and Al concentrated layers have smaller peeling diameters than comparative examples.

[Effects of the Invention] As explained above, since the zinc-based alloy electroplated steel sheet of the present invention which has excellent impact peeling resistance after painting is purchased as described above, it has excellent impact peeling resistance after painting. It has the effect that it can be widely applied to rust-proof steel sheets for automobiles, pre-coated steel sheets, and rust-proof steel sheets that are painted and used for electrical appliances, furniture, etc.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the luminescence intensity-discharge time curve obtained by GDS analysis of a Zn-Ni alloy electroplated steel sheet, and Figure 2 is a GDS diagram of a Zn-Ni alloy electroplated steel sheet with good impact peeling resistance of the coating film. Figure 3 is a diagram showing the analysis results of the GD of a Zn-Ni alloy electroplated steel sheet with poor impact peeling resistance of the coating film.
It is a figure showing a S analysis result. Spear 1 - Mosquito 1 To Ginma Sai 2 Diagrams

Claims (1)

[Claims] Mn or Al is added to the steel base near the interface between the plating and the base steel plate.
1. A zinc-based alloy electroplated steel sheet having excellent impact peeling resistance after coating, characterized in that the zinc-based alloy plating is applied without the presence of one or two types of concentrated layers.