Plated member

Abstract

To provide a plated member having a plating layer capable of imparting high corrosion resistance to a steel material.SOLUTION: A plated member having a plating layer according to the present invention comprises a member made of a metallic material or steel material and a plating layer formed on a surface of the member, wherein the plating layer is essentially composed of a metal such as zinc and a compound of an alkaline earth metal. In the plated member, the plating layer may contain at least one metal selected from the group consisting of zinc and zinc alloys. The plating layer may contain a sulfate. The present invention makes it possible to provide a member having a plating layer capable of imparting high corrosion resistance.SELECTED DRAWING: Figure 1

Description

Detailed Description of the Invention [Technical Field]

[0001] The present invention relates to plated members and plated steel materials having high corrosion resistance. [Background technology]

[0002] In the field of corrosion protection for metal materials and steel materials (hereinafter collectively referred to as steel materials), as disclosed in Patent Documents 1 and 2, it is known that a film containing various components is formed on the steel material, and a corrosion-protective oxide layer is formed in the film or at the interface between the film and the steel material, and this oxide layer enhances the corrosion resistance of the steel material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5681332 [Patent Document 2] Japanese Patent Application Publication No. 2020-169380 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the idea of ​​forming such a corrosion-resistant oxide layer involves a certain degree of corrosion of the steel material, and further improvement in corrosion resistance is desired. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plated member having a plating layer that can impart high corrosion resistance to the steel material. [Means for solving the problem]

[0005] The plated member having a plating layer of the present invention comprises a steel material and a plating layer formed on the surface of the steel material, and the plating layer is basically composed of a metal plating layer such as zinc and particles of an alkaline earth metal compound contained in the metal plating layer.

[0006] In the plated member, the plated layer may contain at least one metal selected from the group consisting of zinc and zinc alloys.

[0007] The plating layer may also contain a sulfate. [Effects of the Invention]

[0008] (Steel) The type of steel used in the present invention is not particularly limited, and may be ordinary steel, low-alloy steel, or high-alloy steel. Since the corrosion resistance of the plating layer contributes to the corrosion resistance of the plated member, similar effects are also exhibited with metals other than steel, but most of the objects for which society requires the application of advanced corrosion prevention technology are steel materials.

[0009] (Alkaline earth metal compounds and sulfates) According to the present invention, when the plating layer covering the steel material dissolves due to corrosion, the alkaline earth metal compound particles in the plating layer also dissolve, thereby maintaining the pH of the plating layer surface slightly above neutral, thereby providing a plated member with high corrosion resistance. Furthermore, adding sulfate particles with a solubility of 0.1 g or more in 100 g of water at 20°C slightly lowers the elevated pH and brings it closer to neutral, causing the various ions dissolved on the plating layer surface to precipitate as dense oxides, forming a corrosion-resistant oxide layer on the plating layer surface. Furthermore, the alkaline earth metal cations and sulfate ions react to form new, sparingly soluble substances, thereby filling defects in the corrosion-resistant oxide layer on the plating layer surface and further improving corrosion resistance. To further enhance this effect, adding a sulfate with a solubility of 0.5 g or more in 100 g of water at 20°C is recommended. The inclusion of alkaline earth metal compounds and sulfates in the plating layer allows their effects to be maintained even after the plating layer has worn off, providing longer-lasting corrosion protection compared to methods that apply these compounds or sulfates only to the surface, such as painting. The effective amount of alkaline earth metal compounds and sulfates in the plating layer is 0.01 to 30 mass%, but 0.03 mass% or more, preferably 0.1 mass% or more, is more effective. To avoid deterioration of the mechanical properties of the plating layer, a concentration of 20 mass% or less is preferable, and 10 mass% or less is even better. To efficiently generate a sparingly soluble substance by reacting alkaline earth metal cations and sulfate ions, the mass ratio of alkaline earth metal compounds to sulfates is preferably adjusted to 2±1, more preferably 2±0.5. In addition, when the plating layer does not contain alkaline earth metals but only sulfates, the surface of the plating layer shifts to an acidic state due to the hydrolysis reaction of metal cations released when the sulfates dissolve, and the release of sulfate ions, which has a negative effect on corrosion resistance.

[0010] Among alkaline earth metal compounds, calcium oxide, calcium hydroxide, strontium oxide, strontium hydroxide, and barium oxide are particularly effective. Considering market prices and availability, calcium oxide and calcium hydroxide are practical. Furthermore, particularly effective sulfates are aluminum sulfate and magnesium sulfate, which act as cations and easily substitute for the crystal lattice of the oxide in the process in which the metal that makes up the plating layer electrochemically dissolves in a corrosive environment and precipitates as a corrosion-resistant oxide.

[0011] (metal plating layer) Although there are no particular limitations on the metal that constitutes the plating layer, it is effective to include at least one metal selected from the group consisting of zinc and zinc alloys, which exhibit sacrificial corrosion protection. It is also effective to include a metal such as aluminum, which has sacrificial corrosion protection. Note that there is no problem if the metal that constitutes the plating layer reacts with the atmospheric corrosive environment and its surface becomes partially converted into a compound such as an oxide.

[0012] (Method of manufacturing a member having a plated layer) While there are no particular limitations on the method for manufacturing a member having a plating layer, one example is a method in which alkaline earth metal compounds or sulfates are added to molten zinc in a plating bath during a hot-dip galvanizing process, thereby dispersing particles of the alkaline earth metal compounds or sulfates in a zinc plating layer or alloy zinc plating layer. In this case, to ensure that the alkaline earth metal compounds or sulfates act effectively, the average particle size of the alkaline earth metal compounds or sulfates present in the plating layer is preferably 1 / 2 or less of the plating layer thickness, more preferably 1 / 4 or less, and even more effectively 1 / 8 or less. Note that greater effects are achieved when the alkaline earth metal compounds or sulfates are dispersed as fine particles as uniformly as possible. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a member having a plating layer according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] As shown in FIG. 1, the member having a plating layer comprises a member 101 made of a metal or alloy, and a metal plating layer 102 formed on the surface of the member and having a different composition from the member, and the metal plating layer 102 contains an alkaline earth metal compound and, if necessary, a sulfate 103.

[0015] The members having the plating layer of the present invention are effective not only in general corrosive environments but also in severe corrosive environments containing chlorides and environments with a low pH because they contain alkaline earth metal compounds. [Example]

[0016] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples and various modifications are possible within the scope of the technical idea of ​​the present invention.

[0017] <Preparing steel materials> Steel A, measuring 70 × 150 × 3 mm, was prepared. In addition to iron, it contained 0.05% carbon, 0.02% silicon, 0.35% manganese, 0.005% phosphorus, and 0.003% sulfur. The surface of the steel was polished to remove black scale, dirt, rust, etc., resulting in a clean metal surface. The surface of Steel A was then heated to 470°C and brought into contact with molten zinc and a molten zinc alloy containing 5% aluminum, both of which contained dispersed alkaline earth metal compound and sulfate particles. The thickness of the coating was then adjusted by machining to produce Zn test specimens plated with zinc containing alkaline earth metal compound and sulfate, and ZnAl test specimens plated with zinc alloy containing alkaline earth metal compound and sulfate. The average particle size of the alkaline earth metal compounds and sulfates, defined as the arithmetic mean value of the maximum diameter in a specific direction of 200 particles observed through cross-sectional observation of the plating layer, was adjusted to 1 / 8±1 / 16 of the plating layer thickness.

[0018] <Corrosion test> The obtained test specimens were subjected to a neutral salt spray cyclic corrosion test for 80 days according to JIS K 5621, which consisted of the following consecutive steps (a), (b), (c), and (d) (returning to (a) after (d)). (a) A 5% by mass aqueous solution of sodium chloride at a pH of 7 and a temperature of 30°C is sprayed for 0.5 hours. (b) Leave the sample in an environment with a temperature of 30°C and a relative humidity of 98% for 1.5 hours. (c) Leave the sample in an environment with a temperature of 50°C and a relative humidity of 25% for 2 hours. (d) Leave the sample in an environment with a temperature of 30°C and a relative humidity of 25% for 2 hours.

[0019] <Corrosion resistance evaluation> After the corrosion test, the test pieces were immersed in a 10% by mass aqueous solution of ammonium acetate heated to 70°C for 5 minutes, and then lightly rubbed with a brush to remove the corrosion products that had formed on the surface of the test pieces. The weight of the test pieces after the corrosion products had been removed was compared with the weight of the test pieces before the corrosion test began to calculate the average amount of corrosion of the plating layer, and the corrosion resistance was evaluated.

[0020] <Corrosion test results> The corrosion test results are shown in Tables 1 and 2. In the comparative examples, Test Nos. 1 to 3 and 19 to 21, some iron rust was observed after the test, and it is presumed that corrosion had progressed partially to the base steel A. A large average amount of corrosion was observed in these comparative examples. In particular, in Test Nos. 2 to 3 and 20 to 21, in which only sulfate was added without adding an alkaline earth metal compound, the pH decreased due to the hydrolysis of the metal cations released by the dissolved sulfate, and the corrosive environment on the coating layer surface became even more severe, and a larger average amount of corrosion was observed than in the case in which neither an alkaline earth metal compound nor sulfate was added.

[0021] On the other hand, in test numbers 4 to 18 and 22 to 36, which are examples of the present invention, no iron rust was observed on the surface and anticorrosive corrosion products were present, and the average corrosion amount was small, and in particular, the average corrosion amount was extremely low when sulfate was added simultaneously with an alkaline earth metal compound.

[0022] For the test specimens in the examples where alkaline earth metal compounds and sulfates were simultaneously added, the surfaces were dried immediately after the test, and low-angle incidence X-ray diffraction measurements were performed using an X-ray diffractometer (Rigaku Corporation RINT-Ultima III) with a Cu target at 40 kV and 40 mA. The results showed the presence of sparingly soluble alkaline earth metal sulfates, which enhance corrosion protection. In other words, when alkaline earth metal compounds and sulfates are simultaneously added, the alkaline earth metal cations released when the alkaline earth metal compounds dissolve react with the sulfate ions released when the sulfates dissolve, generating newly formed sparingly soluble alkaline earth metal sulfates, which contribute to the formation of corrosion products with high corrosion protection properties.

[0023] As described above, the present invention can provide a member having a plating layer that can impart high corrosion resistance to a steel material.

[0024] [Table 1]

[0025] [Table 2]

Claims

1. A member having a plating layer, comprising a member made of a metal or alloy and a metal plating layer formed on the surface of the member, characterized in that the metal plating layer contains a compound of an alkaline earth metal.

2. The member having a plating layer according to claim 1 , wherein the metal plating layer contains at least one metal selected from the group consisting of zinc and zinc alloys.

3. 3. The member having a plating layer according to claim 1 or 2, wherein the alkaline earth metal compound comprises at least one compound selected from the group consisting of calcium oxide, calcium hydroxide, strontium oxide, strontium hydroxide, barium hydroxide, and barium oxide.

4. The member having a plating layer according to any one of claims 1 to 3, wherein the content of the alkaline earth metal compound in the metal plating layer is 0.01 to 30 mass %.

5. The member having a plating layer according to any one of claims 1 to 4, wherein the metal plating layer further contains a sulfate having a solubility of 0.1 g or more in 100 g of water at 20°C.

6. 6. The member having a plating layer according to claim 5, wherein the sulfate in the metal plating layer includes at least one sulfate selected from the group consisting of aluminum sulfate and magnesium sulfate.

7. The member having a plating layer according to claims 5 and 6, wherein the content of sulfate in the metal plating layer is 0.01 to 30 mass%.

8. The member having a plating layer according to any one of claims 1 to 7, wherein the member made of a metal or alloy is a member made of steel.

Images