JPH01127683A - Plating material deposited with zn-mg alloy by evaporation having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a corrosion-resistant Zn alloy plated steel sheet having an excellent rust preventive effect by plating a Zn-Mg alloy contg. a specific ratio of Mg by a vacuum deposition method on the surface of a steel sheet, etc. CONSTITUTION:Various metallic materials such as steel material, alloy steels and Al are put into a vacuum vessel provided with two pieces of crucibles contg. Zn and Mg. The inside of the vessel is evacuated to a vacuum and both the crucibles are heated to evaporated the Zn and Mg and to deposit the Zn-Mg alloy contg. 3-30wt.% Mg by evaporation on the surface of the metallic materials, by which the plating films are formed. The vapor deposited plating layer of the Zn-Mg alloy contg. 3-30wt.% Mg is obtd. by controlling the heating temp. of both the crucibles contg. the Zn and Mg. This plating layer consists of the Mg and basic zinc chloride formed on the surface thereof by the reaction of the Mg with the Cl ions in a corrosive atmosphere where the Cl ions exist; in addition, the hexagonal crystal bodies of the basic zinc chloride are arranged in the thickness direction of the plating. The plating layer having the high corrosion resistance and excellent adhesion is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a Zn-Mg alloy vapor-deposited plating material having higher corrosion resistance.

Metal materials to which the present invention is applicable include various metal materials such as iron, steel, various alloy steels, and aluminum.
Although various shapes such as plates, rods, tubes, corrugated plates, or irregularly shaped rods with an L-shaped or H-shaped cross section are applicable, in this specification, the most typical steel plate, that is, a steel plate. I will mainly explain.

[Prior Art] Until now, Zn-plated steel sheets have been mainly used as rust-proof steel sheets used for body materials of automobiles and vehicles, outer panels of household electrical appliances, various building materials, and the like. However, as the level of rust prevention required for the above applications increases, conventional Zn-plated steel sheets are no longer able to meet the requirements, and various Zn alloy platings are being considered to improve the rust prevention effect. .

Among these, Zn-Mg alloy plating is said to have an excellent antirust effect.

[Problems to be Solved by the Invention] The Zn-Mg alloy plating method conventionally used for boat fishing is hot-dip plating. However, the melting point of Zn (419
Since the melting point of Mg (651°C) is too high compared to
In the case of hot-dip bonding, there is a limit to the amount of Mg that can be added to the Zn melt, and the Zn--Mg alloy plating composition cannot be freely adjusted. Therefore, the effect of Mg addition cannot be fully demonstrated, and since hot-dip plating is performed in a high-temperature environment, an oxide layer and an intermetallic compound layer are formed at the interface between the plating layer and the steel sheet, resulting in poor plating adhesion and workability. It became something that
Furthermore, there was a problem in that the steel plate itself deteriorated due to the heat treatment effect.

Further, even if an attempt is made to employ an ordinary electroplating method using an aqueous solution, it is impossible to form an optimal Zn--Mg alloy plating layer because the unipolar potentials of Zn and Mg are too different.

In view of this situation, in the present invention, the conventional Zn-
Zn- has higher corrosion resistance than Mg alloy plating materials and also has excellent plating adhesion (and therefore workability).
We investigated Mg alloy vapor deposition plating materials.

[Means for solving the problems] The present invention that can solve the above problems is a Zn-Mg alloy vapor deposition plating containing 3 to 30% (weight %) of Mg on a base metal. The surface of the Zn-Mg alloy vapor deposited layer is made of Mg and basic zinc chloride, and the hexagonal crystals of the basic zinc chloride are oriented in the plating thickness direction. The gist of the structure is that the

[Function] In order to solve the above-mentioned problems observed in Zn-based plated steel sheets, the present inventors conducted research on various Zn-based alloys and plating methods, and found that Mg formed by vapor deposition It has been found that Zn-Mg alloy vapor deposition plating containing 3 to 30% of Zn-Mg alloy has excellent corrosion resistance and excellent moldability.

Furthermore, according to the study results of the present inventors, simply Zn and Mg
Not only is the mixed vapor attached to the surface of the steel sheet, but if the plated layer is then placed in a corrosive atmosphere containing chlorine ions, the Mg in the plating layer will react with the chlorine ions and elute to a certain limit, causing the plating to deteriorate. It was found that a special layer consisting of Mg and basic zinc chloride and hexagonal crystals of basic zinc chloride arranged in the thickness direction is formed on the surface of the layer, which exhibits excellent corrosion resistance. . In places like countries where the dots are surrounded by the sea (especially near the coast), the air contains a lot of NaCl, and in such an environment, Zn-Mg alloy evaporation plating is It has been found that the surface of the coating layer is composed of Mg and basic zinc chloride layers as described above, and has a structure in which hexagonal crystals of basic zinc chloride are densely plated and oriented in the thickness direction. - In the corrosive environment of boat fishing, Mg in the plating layer is
It was also found that the progression of n-hZnO was inhibited. Since the production of ZnO is correlated with the corrosion loss of the plating layer, suppressing the production of ZnO means that the corrosion resistance is improved. In addition, the hexagonal crystals of basic zinc chloride are densely oriented on the surface of the plating layer and are oriented in the direction of the plating thickness, which prevents the diffusion of dissolved oxygen and prevents ZnO from penetrating deep into the plating layer. It can be said that the Zn-Mg alloy plating material having such a structure is very suitable for exhibiting corrosion resistance. Furthermore, since the present invention employs a vapor deposition plating method as described below, it is easy to control the plating composition, and Mg
The addition effect can be fully exhibited.

Next, regarding the composition of the Zn-Mg alloy constituting the plating layer, in order for the Mg in the plating layer to have the above-mentioned effect, the Mg in the composition should be 3 to 30%, preferably 5 to 30%. 25%, and the remainder must be vapor-deposited plating such that it consists essentially of Zn (see Table 1). However, if the amount of Mg is less than 3%, the effect of adding Mg is not substantially exhibited, and in particular, no particular difference in corrosion resistance from a surface layer made of Zn alone will be observed. On the other hand, the amount of Mg is 30%
If it exceeds this, corrosion resistance will deteriorate when further coating is applied on top of the plating layer. The reason for this can be considered as follows. In other words, when a scratch occurs on the Zn-Mg plating layer, the uneven part becomes the anode part and the area under the coating becomes the cathode part, so the anode part becomes 4M-4M"+4e-, and the cathode part becomes 2H20+4e-- As the 408- reaction progresses, the pH under the coating film increases, resulting in poor alkali resistance, and if the Mg content exceeds 30%, it can be said that the corrosion resistance after coating film formation deteriorates. .

On the other hand, a Zn-Mg alloy plating layer with an Mg content of 3 to 30% exhibits superior corrosion resistance compared to a pure Zn plating layer, and also has the sacrificial anticorrosion effect inherent to Zn-based plating. Furthermore, combined with the property of extremely excellent adhesion to steel plates, etc., it is possible not only to significantly improve the corrosion resistance of the entire plated steel plate, but also to ensure excellent formability. Although the thickness of the plating layer is not particularly limited, generally the thickness of the plating layer is about 1 g/m' or more, so that the purpose of corrosion prevention can be sufficiently achieved.

As a plating method, Zn and Mg are heated and evaporated in separate crucibles in a vacuum atmosphere, and a heated steel plate is placed or run on top of the crucible, and Zn and Mg are mixed and evaporated onto the base steel plate. By appropriately controlling the heating temperature of the crucible, the amount of Zn and Mg evaporated can be adjusted as desired, and the composition of the plating alloy can be changed as desired. In order to prevent oxidation of the deposited metal, vapor deposition is usually carried out under vacuum conditions as described above, and the present invention is no exception, and is usually carried out under vacuum conditions at a pressure of about 10-2 Torr or less.

Any means may be used to heat Zn and Mg; in particular, since Zn has a low melting point (419° C.) and low vapor pressure, general electric resistance heating can sufficiently achieve the purpose. - On the other hand, Mg has a low melting point (651° C.) but has a high vapor pressure, so it is necessary to use a high-energy beam such as an electron beam with good heat convergence to carry out heating evaporation. In any case, by controlling the heating temperatures of Zn and Mg, the ratio of the amount of evaporation of both metals can be freely adjusted.
The composition ratio of Mg, etc. can be changed freely. Moreover, as vapor deposition plating is performed under high vacuum conditions as mentioned above, there is no risk of an oxide film being formed on the plating surface of the steel sheet and reducing adhesion, and there is also no risk of a weak alloy layer forming on the interface of the steel sheet. There is no fear that the bonding strength between the layers will decrease due to the formation of the like. The specific method for performing vapor deposition plating is not particularly special; for example, Zn' and Mg are simultaneously heated and evaporated from separate crucibles in a vacuum chamber, and a moderately heated steel plate is run over the crucible. It is possible to adopt a method in which vapor deposition plating is performed continuously, or a method in which the above operations are carried out in a batch method. Furthermore, the present invention also includes an ion blating method in which metal vapor is ionized and attached to the base metal surface. It can be applied as one type of vapor deposition plating method.

In addition, demand for Al plates and A1 alloy plates has recently increased rapidly in the automobile industry and the building materials industry, mainly for weight reduction.
Not only is it difficult to form a phosphate film on these Al plates and A1 alloy plates, which is performed as a chemical conversion treatment to improve corrosion resistance or adhesion with paint, but also the A13+ phosphate is removed during the treatment process. There is a problem that the life of the treatment liquid is significantly shortened due to elution, but if the A1 or A1 alloy plate is subjected to the Zn-Mg alloy plating treatment according to the present invention, such a problem will not occur.

[Example] A cold-rolled steel sheet with a thickness of O, f3 nm was used as the base metal, and after its surface was cleaned by electrolytic degreasing, Zn-Mg alloy plating with different Mg contents was applied by a vacuum evaporation buffing method. I did this. In addition, when performing vacuum evaporation plating, to-2
Two crucibles are placed next to each other in a device whose pressure is reduced to a pressure below Torr, and each crucible is charged with Zn and Mg,
While heating Zn and Mg to evaporate, 2
Zn-Mg alloy vapor deposition plating was applied to the lower surface of the cold-rolled steel plate preheated to 00° C. while running the steel plate. The obtained Zn--Mg alloy vapor-deposited steel sheet was subjected to salt water jetting and the red rust generation time was investigated. The results are shown in FIG.

As is clear from Figure 1, the Mg content is 3 to 30%, especially 5.
It can be seen that those with a content of ~25% have excellent corrosion resistance.

Example 2 A Zn-10% Mg alloy vapor-deposited steel plate was produced in the same manner as in Example 1. Tests (1) to (6) as described below were conducted on the obtained Zn-10% Mg alloy vapor-deposited steel sheet. For comparison, the same test was conducted on the same degreased steel sheet as above, which was electrolytically plated with Zn, and on which the Zn-12%Ni alloy vapor deposition plating obtained in the same manner as in Example 1 was applied. . As a result of research conducted by the present inventors, the Zn-12%Ni alloy vapor-deposited plating material is one of the Zn alloy vapor-deposited plating materials with excellent corrosion resistance.

(1) Red rust generation time In order to evaluate the corrosion resistance of various sewn steel plates, the red rust generation time was measured by a salt spray test.

Table 1 As is clear from Table 1, the Zn-10% Mg alloy vapor-deposited steel sheet has a much longer red rust generation time than other steel sheets and is superior in corrosion resistance. This is also supported by the results of tests (2), (3), (4), (5) and (6) described below.

(2) Corrosion current after salt water spray Salt water was sprayed on the plated steel sheets obtained as described above and shown in Table 1, and the relationship between the corrosion current after salt water spray and the salt water spray time is shown in Figure 2. . The polarization measurement conditions were as follows: Polarization was measured in an open state at 35° C. in a 5% NaCl solution to determine the corrosion current.

As is clear from FIG. 2, the corrosion current is large in the Zn electroplated steel sheet, and red rust occurs in about 50 hours in the salt spray test. In the Zn-10% Mg alloy vapor-deposited steel sheet of the present invention, the corrosion current is smaller and the rise is slower and the curve is gentler than the Zn electroplated steel sheet or the Zn-12% Ni alloy vapor-deposited steel sheet. This means that the plating layer is stable and has excellent corrosion resistance.

(3) X-ray diffraction of the rust layer after salt water spray Salt water was sprayed on the plated steel sheets shown in Table 1, and the X-ray diffraction results of the rust layer formed are shown in Figures 3 (b) and (c).
, shown in (d). In addition, Fig. 3(a) shows ZnCl2.4
Z n (OH) 2 [ASTM 5 standard
d] Diffraction peak of the standard product.

Figure 3(b) shows the X-ray diffraction results of the rust layer after 48 hours of salt spraying (sometimes referred to as SST) for Zn electroplating.
The O peak appears.

Figure 3(c) shows Zn-12%Ni alloy vapor deposition plating 5ST.
After 192 hours, ZnCO3・3Zn(OH
)2 peak appears and ZnC1□ ・4Zn(OH)
The peak of z does not appear.

Figure 3 (C) shows 5S of Zn-10%Mg alloy vapor deposition plating.
The X-ray diffraction results of the rust layer after 7192 hours show the peaks ((003),
(006) is displayed. This peak is only for basic zinc chloride, and clearly shows the tendency of preferential orientation, which is not scattered as shown in FIG. 3(a), but neatly oriented in one direction.

(4) Composition of coating layer after salt spraying The various plated steel sheets listed in Table 1 above were subjected to salt spraying to investigate the content of alloying elements in the coating layer and the content of alloying elements in the surface layer of the coating. The results are shown in Figure 4.

As is clear from FIG. 4, Zn-10% which is an example of the present invention
It can be seen that in Mg vapor deposition plating, the Mg content in the surface layer portion decreases and Mg is eluted. Also, Zn-12%N
In the i-alloy plating layer, the amount of Ni in the surface layer portion is decreasing, and the content in the plating layer is increasing. This means that Ni becomes concentrated as the plating layer corrodes, and as Ni becomes concentrated, the potential reverses that of the base steel (see Figure 5), eliminating the sacrificial corrosion protection effect. On the other hand, as mentioned above, although the Mg in the Zn-10%Mg combined all-Mg next layer is slightly reduced, there is almost no change and it has a sacrificial corrosion protection effect.

(5) Natural potential after salt water spraying Salt water was sprayed on various plated steel plates and the natural potential was measured. The results are shown in Figure 5. As is clear from FIG. 5 (and also inferred from the change in the composition of the plating layer after salt water spraying), in the Zn-12%Ni alloy vapor deposition plating, Zn
-The natural potential is higher than that of 10% Mg alloy vapor deposited mating and Zn electroplating, and the rise in potential is rapid. This also indicates that the sacrificial corrosion protection ability of Zn-12%Ni alloy plating decreases relative to the base steel, and the Zn-12%Ni alloy plating according to the present invention
This shows that -10% Mg vapor deposition plating has excellent corrosion resistance.

(6) Corrosion loss after salt water spraying Figure 6 shows the results of investigating the corrosion loss by spraying salt water on various coated steel plates. Also Z n-0,34%
Items with Mg combined and total Mg plating are also listed.

As is clear from FIG. 6, Zn-10%M according to the present invention
It can be seen that those subjected to vapor deposition plating have less corrosion loss and excellent corrosion resistance compared to those subjected to other plating. Although it is scaled out in Figure 6, the results of a longer salt spray test show that Z n -0,
With 34% Mg and total Mg plating, the plating weight loss increased rapidly.

[Effect of the invention] Since the present invention is configured as described above, the Z of the present invention
The n-Mg alloy vapor-deposited plating material fully exhibits the effect of Mg addition, and hexagonal crystals of basic zinc chloride that are densely oriented in the direction of the plating thickness are formed on the surface of the plating layer, resulting in higher corrosion resistance. show. Furthermore, since it is a vapor deposition plating, no intermetallic compounds or oxide film layers are formed at the interface between the plating layer and the base metal, and the plating adhesion (workability) is excellent.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the Mg content in the Zn-Mg alloy vapor-deposited plating layer and red rust generation time, and Fig. 2 is a diagram showing the relationship between salt water spray time and corrosion current in salt water spraying of various plated steel sheets. Figure 3 is an X-ray diffraction diagram, Figure 4 is a diagram showing the relationship between salt water spray time and alloying element content in the plating layer in salt water spraying of various plated steel sheets, and Figure 5 is the salt water spray time and self-potential. FIG. 6 is a diagram showing the relationship between salt water spray time and plating layer weight loss.

Claims (1)

[Claims] Zn-Mg containing 3 to 30% by weight of Mg on base metal
An alloy vapor-deposited plating layer is applied, and the surface of the Zn-Mg alloy vapor-deposited layer is made of Mg and basic zinc chloride, and hexagonal crystals of the basic zinc chloride are oriented in the plating thickness direction. Z with excellent corrosion resistance
n-Mg alloy vapor deposition plating material.