JPH0273932A - Highly corrosion resistant zn-mg alloy powder - Google Patents

Abstract

PURPOSE:To allow the title alloy powder to display sacrificial corrosive property to a base steel sheet at the time of using the above alloy powder as rust preventive paint by constituting the above alloy powder of an alloy consisting of Zn2Mg phase and Zn phase. CONSTITUTION:The above high corrosion resistant Zn-Mg alloy powder is constituted of Zn2Mg phase and Zn phase. Since the alloy having the above metallic phases is reduced in dissolution velocity, this alloy can protect a base steel sheet over a long period when used as a rust preventive paint. Further, white rust represented by ZnCl2.4Zn(OH)2 is formed under an environment containing Cl ions. Since the above white rust is dense and excellent in adhesive strength of rust layer, the progress of rust can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a Zn-Mg alloy powder that exhibits excellent anticorrosion ability when used, for example, as an anticorrosive paint.

[Prior Art] Corrosion countermeasures for steel materials used in industrial machinery, vehicles, buildings, chemical industry facilities, power facilities, and other various structures are based on alloy compositions or metals depending on the environment in which they are used. Although structural corrosion countermeasures have been taken, a simple surface protection measure is to apply paint to the surface of steel materials.

However, simply forming a coating layer mainly made of organic resin on the surface of the steel material and physically shielding the surface of the iron t14trA material from the usage environment does not allow the coating film itself to be Since it does not have any sacrificial corrosion protection ability, if the paint film itself deteriorates or is damaged, the underlying steel material will immediately corrode, resulting in the formation of red rust, blistering of the paint film, or Peeling occurs.

For this reason, chemical conversion treatments such as chromate treatment are applied to the surface of steel materials, or zinc plating is applied and then painted, but this is not always sufficient depending on the usage environment.

In response to this, recently, zinc-rich paints have been developed whose coating components are composed of zinc powder and organic resin. This zinc-rich paint has many features, such as suppressing corrosion of steel materials through the sacrificial anticorrosive action of zinc powder in the coating film, and enabling electrodeposition coating and spot welding by utilizing the conductivity of zinc powder. It is an anti-rust paint.

However, the paint film applied with zinc-rich paint,
As mentioned above, since the sacrificial anticorrosion ability of zinc is used to exhibit corrosion protection, depending on the usage environment, the rate of loss of zinc due to corrosion is high and the protective effect on steel materials does not last long. Therefore, by increasing the content of zinc powder in the coating film,
The coating film is made thicker to maintain its protective effect on steel materials. However, these methods are non-wood solutions that simply increase costs, and they also worsen the adhesion of the coating film to steel materials, worsen the powdering properties of the coating film itself, and impair workability. There is. Further, depending on the product, there may be restrictions on the coating thickness, so the above-mentioned means cannot be said to be industrially perfect.

Due to this situation, conventional zinc rich vein]
There is a growing need for zinc-rich paints that have even higher anti-corrosion ability while retaining the advantages of ・and can exhibit sacrificial anti-corrosion ability for steel materials over a long period of time. In addition to zinc powder, Z
A zinc-rich paint containing n-Mg alloy powder or Mn powder has been proposed, and Japanese Patent Application Laid-Open No. 159334/1983 discloses a technique regarding a paint containing a rust-preventing pigment and ZnMg alloy powder. It is true that when these mixed paints are applied, the corrosion resistance and processability are improved compared to those using only Zn powder or only antirust pigments.

However, even if the above paint is applied, it can be said that the rust prevention property and workability are sufficient, and the above publication also describes the effect of the Zn-Mg alloy powder on the corrosion resistance, especially the effect of Zn-Mg alloy powder on the corrosion resistance. In the only Japanese Patent Application Laid-open No. 1981-142, which discloses nothing about the correlation between Mg content and corrosion resistance, Z n − It only mentions regulating the Mg content in the Mg alloy.

[Problems to be Solved by the Invention] Therefore, the inventors of the present invention investigated the preferable amount of Mg to be added.

Now suppose that high Mg Zn-
If Mg alloy powder is used, Mg that is not alloyed with Zn will exist in the system. This Mg has a sacrificial corrosion protection ability for steel materials, but since it is an electrochemically less base metal than Zn, it disappears at a much faster rate due to corrosion than pure Zn, and when viewed as a whole Zn-Mg alloy powder, The period during which the sacrificial anticorrosion effect is exhibited is not much different from that when pure Zn powder is used, and in some cases, it is shorter than when pure Zn powder is used. Furthermore, when the Mg phase exceeds a certain level, a H2 generation reaction (cathode reaction) occurs in response to the Mg dissolution reaction (anode reaction) in a corrosive environment, and this H2 causes paint film blistering and peeling. Furthermore, since Mg is more expensive than Zn, using a Zn-Mg alloy powder with an excessively large Mg content is disadvantageous in terms of cost.

In view of the above circumstances, the present invention has conducted extensive research on the influence of Mg on the anticorrosion properties of Zn-Mg alloy powder, and aims to impart superior corrosion resistance to steel materials than before when used as an anticorrosive paint. We investigated the Zn-Mg alloy powder that can be used in this study.

[Means for solving the problem] Highly corrosion resistant Zn of the present invention that can solve the above problem
-Mg-based alloy powder is Zn-Mg-based alloy powder consisting of Zn1Mg and inevitable impurities, and the Zn-M
The gist is that the g-based alloy is substantially composed of a Zn2Mg phase and a Zn phase.

"Function" The present inventors created pure Zn powder, pure Mg powder, and Zn-Mg alloy powder of various compositions, and after drying, the coating film components were pure Z.
Various paints were prepared, including a paint made of n powder and an epoxy resin, a paint made of pure Mg powder and an epoxy resin, and a paint made of WiZ n -Mg alloy powders with different Mg contents and an epoxy resin. These paints were degreased so that the film thickness after drying was 5 μm, and the content of Zn powder, Mg powder, or Zn-Mg alloy powder in the paint film was 80% by weight (hereinafter simply referred to as %). It was applied to the surface of a steel plate by a roll coating method. Furthermore, JIS 22371
Based on this, a salt water spray test was conducted to investigate the time required for red rust to develop due to corrosion of steel plates. The results are shown in Table 1. In addition, X-ray diffraction analysis was performed on each of the metal powders to investigate the phase structure constituting each metal powder. The results are shown in Table 1.

Condolences 1 table The following things became clear from Table 1.

(2) Those using pure Zn powder and pure Mg powder have a short red rust generation time and have a low ability to maintain sacrificial corrosion protection. Furthermore, in the case where pure Mg powder was used, the paint film blistered or peeled off shortly after the start of the corrosion test, and the base steel sheet and the paint film were separated.

■Those using Zn-M & alloy powder are pure Zn powder and pure M.
Compared to those using g powder, the time to develop red rust was longer, and among them, the one using Zn-Mg alloy, which is composed of Zn2Mg phase and Zn phase, had a longer time to develop red rust and had the best corrosion resistance. . Also, Zn-Mg with Mg phase
In the case where alloy powder was used, as in the case where pure Mg powder was used, the paint film blistered or peeled, and red rust occurred on the base steel plate.

From the above, Zn2 in Zn-Mg alloy powder
It can be seen that when a Zn-Mg alloy powder composed of an Mg phase and a Zn phase is used in a rust-preventing paint, it exhibits sacrificial anti-corrosion ability against the base steel plate for a long time, providing an excellent anti-corrosion paint.

Next, the present inventors investigated the reason why a Zn-Mg alloy powder composed of a Zn2Mg phase and a Zn phase has the most remarkable anticorrosion ability. As a result, it became clear that the rejection was based on three points.

(2) A ZnMg alloy powder consisting essentially of a Zn2Mg phase and a Zn phase has a sacrificial anticorrosion ability against a base steel plate in a corrosive environment, similar to Zn-Mg alloy powders having other metal phases. Moreover, since the dissolution rate is lower than that of those having a metal phase, it takes a longer time for the alloy powder to disappear, and as a result, the base steel sheet is protected for a long time. Such an effect can be achieved by an appropriate balance distribution between the Zn2Mg phase and the Zn phase, and the effect is small in intermetallic compound phases such as Zn11Mg2 with a high Zn content and ZnMg containing Mg.

(2) When pure Zn powder and Zn-Mg alloy powder are compared in a corrosive environment where chlorine ions are present, the chemical structure of the rust (white rust) that is formed is different. That is, from pure Zn powder, Z
White rust indicated by nO occurs, and since this ZnO has poor adhesion to the paint film, is porous, and has high electrical conductivity, it has little effect in protecting the Zn powder in the paint film in a corrosive environment. On the other hand, from Zn-Mg alloy powder, ZnC12.4
Forms white rust represented by Zn(OH)2. This rust forms a dense rust layer in which hexagonal crystals are arranged in the thickness direction of the coating film, and the adhesion of the rust layer is also superior to that of a white rust layer made of ZnO, and the electrical conductivity is also low. Therefore, not only the effect of protecting the coating film layer is increased, but also the elution rate of the Zn-Mg alloy powder is further reduced. In addition, Mg in the Zn-Mg alloy powder becomes Mg ions and elutes in a corrosive environment, and some of it remains in the rust layer and forms ZnCl2.4Zn(
OH)2 is inhibited from progressing to ZnO.

It has thus been found that Mg ions eluted from the Zn-Mg alloy powder are an essential component for maintaining ZnC12.4Zn(OH)2 with excellent corrosion resistance. Although the optimum amount of Mg ions that exist in the rust layer and have this function is not certain, according to the results of the study by the present inventors, a Zn-Mg alloy consisting of a Zn2 Mg phase and a Zn phase. It has been found that the optimum amount of Mg ions is such that it is eluted from the powder and remains in the rust layer.

■Pure Mg alloy powder or Zn-Mg with Mg phase
As described above, the alloy powder has a high elution rate in a corrosive environment, and also generates H2 gas by the cathode reaction in response to the anode reaction due to the dissolution of Mg, causing paint blistering or peeling. On the other hand, Zn--Mg based alloy powder consisting of Zn2Mg phase and Zn phase does not contain Mg phase, and thus such a phenomenon does not occur.

As mentioned above, the Zn-Mg alloy powder does not have to have any composition;
The one composed of 2Mg phase and Zn phase exhibits the highest corrosion resistance.

Next, the inventors studied how the content of Zn-Mg alloy powder in the coating film affects corrosion resistance. As a result, as the content of this powder in the coating film increases, the sacrificial anticorrosion ability against the base steel sheet improves, but the content remains almost constant at about 80%, and when the content exceeds 90%, On the contrary, it was found that the adhesion of the coating film decreased and had an adverse effect on processability. Therefore, it is desirable that the content of the Zn-Mg alloy powder in the coating film be 90% or less. The lower limit of the content is not particularly limited, but it is desirable to set it to 60% or more, which provides high sacrificial corrosion protection.

Furthermore, as a result of examining the particle size of the Zn-Mg alloy powder, it was found that when the average particle diameter of the Zn-Mg alloy powder exceeds 15 μm, the corrosion resistance slightly decreases even if it is contained in the same weight ratio in the coating film. A tendency to decrease was observed, and the surface became noticeably uneven after painting, which was unfavorable in terms of appearance. Therefore, the average particle size of the Zn-Mg alloy powder is preferably 15 μm or less, preferably 5 μm or less.

In addition, when manufacturing anti-corrosion paints, resins used as binders include epoxy resins, urethane resins, acrylic resins, phenoxy fruit resins, polyester resins, and other resins used as binders for general paints. . The type of paint may be either emulsion type or solvent type, and Mg-
Dispersants and other additives can also be added as long as they do not impair the rust prevention properties of the Zn-based alloy powder.

The anticorrosive paint obtained as described above is generally applied directly to steel plates, but if applied to steel plates that have been subjected to phosphate treatment, chromate treatment, etc., it is possible to obtain coated steel plates with better corrosion resistance. can. In addition, each fli coated with this anti-rust paint
The anticorrosion function can be further enhanced by forming a coating film on the steel plate by cationic electrodeposition coating or ordinary spray coating.

[Example] Example 1 A 0.7 mm thick cold-rolled steel plate was degreased with alkaline, washed with water, and dried.
After performing phosphate treatment to form a phosphate film, each coated steel plate was coated with a paint consisting of various metal powders consisting of the coating film components shown in Table 2 and a general-purpose epoxy resin.
It was cut into 150mm x 150mm. The unpainted back and cut surfaces were sealed with tape and subjected to a salt water spray test (5%
The red rust generation time of the steel plate was investigated using a NaCl solution (35°C).

The results are shown in Table 2.

As is clear from Table 2, Z n 2 M g phase and Z
Steel sheets on which a coating film is formed using Zn-Mg alloy powder, which is composed of n-phase, have a longer red rust generation time than those using other metal powders, and the coating film has a longer time to form. It can be seen that the corrosion resistance is excellent because there is no blistering or peeling.

Example 2 Zn-based plating (Zn plating, Zn
-12%N1 alloy plating) was subjected to chromate treatment to form a chromate film (chromium content: 50 mg/m2), and the coating film components were various metal powders and urethane shown in Table 3. A coating film was formed by applying a paint made of a resin based resin. The anticorrosive coated steel sheet thus obtained was subjected to a corrosion test for 200 cycles, with one cycle ranging from salt spray to wetness as shown below.

Saltwater DJ Dew (35℃ x 4hr) - Drying (60℃ x 2hr)
) → Moisture (50° C. x 2 hr) Furthermore, after the test piece after the corrosion test was rust-proofed with an ammonium citrate solution, the corrosion depth in the steel plate was measured. The results are shown in Table 3. The size of the test piece is 70mm x 150
The corrosion test was carried out by tape-sealing the unpainted surface and the cut surface, and the corrosion depth was measured at the deepest perforated part of the test piece.

As is clear from Table 3, the absolute erosion depth varies depending on the composition of the underlying Zn-based plating, but a coating film containing the Zn-Mg-based alloy powder consisting of the Zn2Mg phase and Zn phase of the present invention was formed. It can be seen that the rust-proof steel plate has the smallest perforation depth compared to other types.

[Effects of the Invention] Since the present invention is configured as described above, the Zn-
Anticorrosion paints using Mg-based alloy powder exhibit excellent anticorrosion ability on steel materials.

Claims (1)

[Claims] A Zn-Mg alloy powder consisting of Zn, Mg and inevitable impurities, the Zn-Mg alloy containing substantially Zn_
A highly corrosion-resistant Zn-Mg alloy powder characterized by being composed of a 2Mg phase and a Zn phase.