JPH01111864A - Zn-cr alloy-plated metallic material having high corrosion resistance - Google Patents

Abstract

PURPOSE:To improve adhesive strength and formability and also to provide excellent corrosion resistance by providing a specific composition to a plating layer and also providing two or more diffraction peaks other than the main peak of a Zn (002) phase within a specific diffraction-angle range in the X-ray diffraction pattern of the plating layer. CONSTITUTION:This metallic material is coated with a Zn-Cr alloy plating layer, and this plating layer has a composition consisting of 1-70wt.% and the balance essentially Zn. Further, two or more diffraction peaks are provided other than the main peak of a Zn (002) phase within the range of diffraction angle of 30-50degrees in the X-ray diffraction pattern of the alloy plating layer. By this method, superior corrosion resistance and firm adhesive state can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a Zn-Cr alloy plated metal material having excellent corrosion resistance. It is extremely useful as a building material, etc. The metal substrates to be plated according to the present invention include Fe and Fe-based alloys, as well as nonferrous metals such as Cu and AI, and their alloys, and their shapes include plate materials, corrugated sheet materials, and tube materials. , bars, etc., but the following explanation will focus on the most typical steel plate.

[Prior Art] Zn plating has conventionally been widely used as a means for anticorrosion processing of steel plates and the like. However, the demand for improving the corrosion resistance of steel sheets and the like is increasing, and conventional Zn-plated steel sheets are no longer able to sufficiently meet the demands of customers.

Against this background, Zn-
Zn such as Ni, Zn-Fe, Zn-Mn, Zn-Co, etc.
Alloy coated steel sheets have been developed, and Zn-Al-Mitshu metal, Zn-Al-5t, Z
Zn-Al based multi-component alloy plated steel sheets such as n-Al-Mg and Zn-Al-3n have also been developed. However, even with these plated steel sheets, it cannot be said that they fully meet the needs of users, and as there is a demand for extension of service life under harsh usage environments, plating with superior corrosion resistance has been developed. The appearance of steel plates is awaited.

On the other hand, since Cr has excellent corrosion resistance under various corrosive environments, research has been conducted for quite some time to improve the corrosion resistance of 2n-Cr alloy plating materials by incorporating an appropriate amount of Cr into Zn-based plating materials. It has been carried out since.

[Problems to be Solved by the Invention] However, when attempting to form a Zn-Cr alloy plating, it is difficult to incorporate a large amount of Cr into the plating layer, regardless of whether electroplating or hot-dip plating is employed. Therefore, the expected corrosion resistance improvement effect was not obtained. In other words, if an electroplating method is used to incorporate a large amount of Cr, not only will the gloss of the plating layer decrease and the commercial value will be significantly impaired, but also the current efficiency will decrease and the plating efficiency will become extremely poor. . In addition, if hot-dip plating is used to incorporate a large amount of Cr, the temperature of the plating bath must be raised considerably, resulting in the formation of a fragile alloy layer at the bonding boundary between the base steel sheet and the plating material. In addition, this alloy layer is relatively easily cracked and destroyed during the subsequent forming process, resulting in problems such as the plating layer easily peeling off after the forming process. .

For this reason, the Cr content of Zn-Cr alloy plated materials is limited to about 0.8% at most, and the effect of improving corrosion resistance by adding Cr is extremely small.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to improve adhesion and improve adhesion by eliminating the formation of a fragile alloy layer at the boundary between the metal base material and the plated layer. The object of the present invention is to provide a Zn--Cr alloy plated metal material that has good formability and can exhibit excellent corrosion resistance even in a highly corrosive environment.

[Means for solving the problems] The configuration of the present invention that can achieve the above object is based on Z
A metal material coated with an n-Cr alloy plating layer, the plating layer having Cr: 1 to 70% by weight, balance: substantially Zn.
and Z n (00
2) The gist is that it shows two or more diffraction peaks in addition to the main peak of the phase.

[Function] The present inventors focused on Zn-Cr alloy plated steel sheets and conducted various studies mainly on improving the plating method in order to improve the various defects of the plated steel sheets. As a result, we adopted a vacuum evaporation method and heated and heated Zn and Cr from separate containers.
If a method of evaporating and depositing it on the surface of the base steel plate is adopted, the Cr content in the vapor-deposited plating components can be increased without any problems, and Zn-Cr has excellent corrosion resistance.
It has been found that an alloy plating layer can be formed on the surface of a base steel plate with good adhesion. Moreover, when we examined the X-ray diffraction pattern of the coating layer obtained in this way, we found that, as will be explained in detail later, it was found that it was difficult to see in Zn-Cr alloy plating formed by conventional electroplating or hot-dip plating. It has become clear that this shows a unique peak that cannot be observed.

That is, in manufacturing the Zn-Cr alloy coated steel sheet of the present invention, two crucibles are arranged in a vacuum evaporation plating apparatus, Zn and Cr are charged into each crucible, and the inside of the evaporation plating apparatus is reduced in pressure (10 −'Torr or less, more preferably 10'''Torr or less) in each crucible.
Zn and Cr are heated and evaporated, and Zn and Cr are simultaneously deposited on a base steel plate (usually preheated to 100 to 350°C) placed above these crucibles. In this case, the amount of evaporation of each of Zn and Cr can be adjusted individually by adjusting the heating temperature, so the amount of evaporation of each of Zn and Cr constituting the plating layer can be arbitrarily controlled. In other words, with conventional electroplating and hot-dip plating methods, it has not been possible to increase the Cr content in Zn-Cr alloy plating to about 0.8% or more for the reasons mentioned above. By changing the heating temperature of each
The evaporation amount of n and Cr can be adjusted freely, and Zn
The Zn/Cr content ratio constituting the -Cr alloy plating layer can be easily adjusted over a wide range. In this case, since Cr has a high melting point and a very low vapor pressure, high energy is required to evaporate it, requiring a high-energy heating source such as an electron beam or laser beam, but Zn has a low Since it has a high melting point and high vapor pressure, it can be sufficiently evaporated by electric resistance heating. By adjusting the output of these heating sources and controlling the amount of evaporation of Zn and Cr, the contents of Zn and Cr constituting the Zn-Cr alloy plating layer can be freely adjusted. In order to achieve the desired corrosion resistance improvement effect, the deposition conditions must be set so that the Cr content in the alloy plating layer is 1% or more; below this, the corrosion resistance improvement effect of Cr will be negligible. It doesn't show its full potential. However, if the Cr content becomes too large, the potential of the Zn-Cr alloy plating layer will become nobler than that of the steel sheet, and the sacrificial anodic corrosion protection effect unique to Zn alloy plating will no longer be exhibited, so the Cr content must be kept below 70%. be.

By the way, in the case of a conventional Zn-Cr alloy plated steel sheet (with a Cr content of about 0.8%), the only peak that can be confirmed by the X-ray diffraction pattern is the peak indicating the pure Zn phase [see Section 1 below]. see figure (A)], but the Cr content is 1
In the case of the Zn-Cr alloy vapor-deposited steel sheet of the present invention, which has a Zn-Cr alloy vapor deposition of 70%, the Z angle (002) is in the range of 30 to 50 degrees.
In addition to the main peak of the phase, there are two or more diffraction peaks [see Figures 1 (C) to (G) below]. The origin of these diffraction peaks is determined by the Zn-Cr alloy. Although it cannot be confirmed because the phase diagram has not been clarified, it is presumed that it originates from a Zn-Cr-based intermetallic compound (hereinafter sometimes referred to as "theta phase"). That is, the Zn-Cr alloy plated steel sheet of the present invention has Zn within a diffraction angle of 30 to 50 degrees in X-ray diffraction analysis.
It can be clearly distinguished from conventional Zn-Cr alloy plated steel sheets etc. in that it shows two or more diffraction peaks in addition to the main peak of the (002) phase, and Zn-Cr having such diffraction peak characteristics. Alloy-plated steel sheets not only have extremely superior corrosion resistance compared to conventional materials, but also have no fragile alloy layer formed at the boundary between the base steel sheet and the plating layer, and exhibit a strong adhesion. Therefore, there is no fear that the plating layer will peel off during the molding process.

As already mentioned, the Zn-Cr alloy plating material of the present invention is obtained by a vacuum evaporation method,
If the conditions at this time exceed 10-" Torr, the base material and the plating metal may be locally oxidized and the adhesion may be insufficient.
It is desirable to employ high vacuum conditions of 2 Torr or less, more preferably 10-'Torr or less. In addition, in this vapor deposition process, it is also possible to employ the so-called ion blating method in which the evaporated metal is ionized using a high-frequency induction device and deposited on the base metal. This includes the following methods.

[Example] Two crucibles were placed in a vacuum evaporation apparatus, Zn and Cr were charged into each crucible, and the pressure inside the apparatus was reduced to 2x10-3 Torr.
A steel plate (electrolytic polished steel plate, thickness: 0.6 mm, preheating temperature: 250°C) was placed above the crucible by heating and evaporating Zn and Cr with an electron beam while maintaining the temperature below r.
A Zn-Cr alloy was deposited on the surface. At this time, Zn and C
By controlling the output of the electron beam irradiated to r, the amount of evaporation of each is adjusted, and the content of Cr in the Zn-Cr alloy plating layer is varied in the range of O to 91.0%,
Corrosion resistance and adhesion were measured for each, and X-ray diffraction analysis was conducted to investigate the number of peaks in the θ phase.

Corrosion resistance test method: Salt spray test (25℃) of each plated steel plate
The time required for red rust to appear on the surface of the plating layer was investigated.

Adhesion test method: Each plated steel plate (0.6X20X50mm
) was bent at 180 degrees, an adhesive tape was attached to the bent portion, and the peeling state of the plating layer was evaluated.

O... Plating layer does not separate ×... Plating layer is partially peeled off X-ray diffraction The second-order X-ray source is CuKa ray, Ni filter,
Table 1 shows the results at an acceleration voltage of 35 KV and a recording paper full scale of 1000 counts/sec. For comparison, test results for conventional electrolytic Zn-Cr plated steel sheets are also shown.

Further, the X-ray diffraction patterns of typical ones shown in Table 1 are shown in FIGS. 1(A) to (G).

As is clear from Table 1 and Figures 1 (A) to (G),
The Zn-Cr alloy plating formed by the conventional electroplating method [Experiment No. 12, Figure 1 (^)] only showed a peak indicating the Zn phase, and even when the vapor deposition plating method was adopted, the amount of Cr was small. In the case of less than 1% Zn-Cr alloy plating [Experiment Nos. 1 and 2, Figure 1 (B)], only a peak indicating the Zn phase could be confirmed, and both of these had poor corrosion resistance.

On the other hand, those that adopted the vapor deposition plating method and secured a Cr content of 1 to 70% [Experiments N003 to 9, Figure 1 (C)
~(G)], Z n in the diffraction angle range of 30 to 50 degrees
In addition to the main peak of the (002) phase, two to three peaks that are thought to be Zn-Cr intermetallic compounds (θ phase) can be confirmed, and all of these indicate excellent corrosion resistance and adhesion. .

However, even if the vapor deposition plating method is adopted, if the Cr content in the Zn-Cr alloy plating layer exceeds 0% (Experiment No.
, 10.11), the sacrificial anode effect of the Zn--Cr alloy plating layer is lost, and the corrosion resistance begins to show a sharp decreasing tendency.

Next, vapor deposition plating was performed according to the above method while varying the degree of vacuum in the vapor deposition apparatus (base steel plate thickness: 0.6 m).
m, plating composition: Zn-10%Cr.

Plating thickness: 3.1 to 3.2 μm), and the adhesion of the plating layer was examined in the same manner as above.

The results are shown in Table 2, and the internal pressure is 10'''
When the vacuum level exceeded Torr, poor adhesion was observed, which was thought to be caused by oxidation of the base material and plating metal vapor during the vapor deposition process, whereas when the vacuum level was lower than 1O-2 Torr, no such problem occurred. , a strong adhesion was obtained.

Table 2 [Effects of the Invention] The present invention is constructed as described above, and by carrying out the Zn-Cr alloy plating treatment using the vacuum evaporation method, the content ratio of Cr can be increased without any problem. can be increased,
In addition, it has become possible to provide a Zn-Cr alloy plated steel sheet with excellent corrosion resistance, which can be identified by the presence of a unique X-ray diffraction peak that has not been seen in conventional Zn-Cr alloy plating. Furthermore, the plating adhesion of this mated steel sheet is very excellent, and there is no fear that the plating layer will peel off during subsequent forming processes. Furthermore, the greatest feature of the present invention is that it enables Zn-Cr alloy plating with a high Cr content by utilizing a vapor deposition method, so the base metal is not limited to steel plate.
The present invention can be similarly applied to various alloy steels, non-ferrous metals such as copper, aluminum, and alloys thereof, and can be used in a wide variety of shapes such as plates, tubes, and rods.

[Brief explanation of the drawing]

FIGS. 1(^) to (G) are diagrams showing X-ray diffraction patterns of Z, n-Cr alloy plated steel sheets obtained in experimental examples. Procedural amendment (written November 28, 1988 1, case description 1988 Patent Application No. 82069 2, title of the invention Highly corrosion resistant Zn-Cr alloy plated metal material 3, person making the amendment Relationship with the case) Patent applicant 5 3-18 Wakihama-cho-chome, Chuo-ku, Kobe (119) Kobe Steel, Ltd. Representative Sokichi Kametaka 4, Agent 6 Shinko Building, 2-3-7 Dojima, Kita-ku, Osaka 530, amended (1) "Brief explanation of drawings" section of the specification (2) Drawing 7, content of amendments (1) "Figures 1 (8) to (G)" on page 16 of the specification have been changed to "
Figure 1” is corrected.

Claims (1)

[Claims] A metal material coated with a Zn-Cr alloy plating layer,
The plating layer contains Cr: 1 to 70% by weight, remainder: substantially Z.
Zn(002
) A highly corrosion-resistant Zn-Cr alloy plated metal material exhibiting two or more diffraction peaks in addition to the main peak of the phase.