JP5007424B2 - Projection material for mechanical plating and highly corrosion-resistant coating - Google Patents

Abstract

Shot material for mechanical plating is provided, comprising steel core particles clad with an alloy comprising 1 to 5% by weight of aluminum, 3 to 15% by weight of magnesium, preferably 5 to 15% by weight of magnesium, and the balance of zinc and unavoidable impurities. The alloy may contain a total of 1% by weight of impurities. An Fe-Zn alloy layer may be provided between the alloy cladding and the steel core. The shot material may contain 3 to 80% by weight of iron. The preferable average diameter of the shot particles is 100 to 600 µm.

Description

  The present invention relates to a projection material used for mechanical plating for forming a highly corrosion-resistant film on the surface of a metal material and a high corrosion-resistant film formed using the same.

  As a method for improving the corrosion resistance of ferrous metal materials, a method of forming a zinc or zinc alloy film (hereinafter referred to as a “zinc-based film”) is widely employed. Specifically, hot-dip plating, phosphate plating, electroplating In addition, techniques such as mechanical plating have been put into practical use industrially.

  If a material on which a general zinc-based film such as galvanizing is formed is exposed to the atmospheric environment as it is, white rust of zinc is generated in a relatively short period of time, and the consumption of the film may be accelerated. This is particularly noticeable in outdoor environments. For this reason, the process (for example, chromate process) which forms a protective film further on a zinc-type film | membrane is performed.

  The zinc-based film formed by mechanical plating has a structure in which flakes are stacked (so-called “pie dough-like”). Therefore, when chromate treatment is applied from above, the chromate treatment solution penetrates sufficiently into the film. As a result, a remarkable effect of improving corrosion resistance is exhibited. For example, when a zinc coating with a time of about 24 h until the occurrence of red rust by a salt spray test (referring to a test according to JIS Z2371) is formed by mechanical plating, it jumps to about 3000 h by applying chromate treatment. Corrosion resistance is improved.

  Since chromate treatment is relatively inexpensive and can easily form a highly protective film, it is widely used in practice. However, a solution containing toxic hexavalent chromium is used for this treatment. There are methods to form a film with trivalent chromium, a polymer chelate film, a silicate inorganic film, etc. as a protective film forming treatment that does not use hexavalent chromium. To do. The reason for this is that these films do not have the self-repairing property found in hexavalent chromate films. That is, the corrosion resistance is remarkably lowered at the scratched portion. In addition, these techniques that do not use hexavalent chromium have the disadvantages that the management of the treatment liquid is complicated and the characteristics after treatment tend to vary, and the treatment cost is considerably higher than that of hexavalent chromate.

  A method for improving the corrosion resistance of the zinc-based coating itself formed by mechanical plating has been studied. Patent Documents 1 to 3 disclose the use of a powder made of a Zn alloy to which an alloy element such as Al or Mg is added.

  On the other hand, in order to improve the durability of the zinc-based film by mechanical plating, it is also important to improve the adhesion of the film to the underlying metal substrate. Patent Documents 4 and 5 describe that iron or iron alloy particles are used as a nucleus, and particles coated with zinc or zinc alloy are used as a projection material. It is considered that a large projection energy is obtained by colliding particles having nuclei of hard and heavy iron-based particles against the surface of the material to be treated, and as a result, the pressure-bonding effect of the adherend is increased and the film adhesion is improved.

JP-A-55-119101 JP 56-93801 A Japanese Unexamined Patent Publication No. 57-110601 JP 56-45372 A Japanese Patent Laid-Open No. 62-140768

  As described above, the corrosion resistance of the zinc-based film by mechanical plating can be greatly improved by the chromate treatment. However, recently, regulations on the environment have been strengthened, and the use of toxic hexavalent chromium is being severely restricted. Moreover, the processing method which forms the effective protective film which replaces this is not established.

On the other hand, there is a limit in terms of corrosion resistance in using the part in the state of the film formed by mechanical plating. That is, even by the method using the zinc alloy powder having improved corrosion resistance as shown in Patent Documents 1 to 3, the time until the occurrence of red rust in the salt spray test is around 500 h with a simple alloy composition of Zn—Al—Mg. The upper limit is about 1500 h with a composition added with special elements such as Na and Be. In the use of parts used outdoors, it is desired to exhibit corrosion resistance such that the time until the occurrence of red rust in the salt spray test is about 1800 h or more. Further, in an environment where salt damage is likely to occur, such as automobile parts, corrosion resistance of 3000 h or more is desired. It is difficult to meet such needs simply by depositing a zinc alloy having high corrosion resistance.
Further, even a method using a projection material having iron-based particle nuclei as disclosed in Patent Documents 4 and 5 has not led to a drastic improvement in corrosion resistance.

  In view of such a current situation, an object of the present invention is to significantly improve the corrosion resistance of a zinc-based film itself formed in mechanical plating without depending on a protective film forming process such as a chromate process.

  The above-mentioned purpose is for mechanical plating in which steel particles are used as a core, and the periphery thereof is coated with an alloy of Al: 1 to 5% by mass, Mg: 3 to 15% by mass, preferably 5 to 15% by mass, the remainder Zn and impurities. This is achieved with a projectile. The impurities in the alloy are allowed to be mixed up to about 1% by mass in total. An Fe—Zn alloy layer may be interposed between the coated alloy and the central steel.

  Content of Fe contained in this projection material can be 3-80 mass%. Moreover, the projection material whose average particle diameter is 100-600 micrometers becomes a suitable object.

  Moreover, in this invention, it is a film | membrane formed in the said metal material surface by making such a projection material collide with the surface of metal materials, such as steel materials, Comprising: Al: 1-5 mass%, Mg: 3-15 mass %, Fe: 20% by mass or less, the remaining Zn and impurities, and a high corrosion resistance film having a thickness of 2 to 15 μm is provided. The impurities in this case are allowed to be mixed up to about 1% by mass in total.

  According to the present invention, the corrosion resistance of the component can be dramatically improved in the state of the film as formed by mechanical plating. For this reason, it can be applied to various conventional parts applications without performing chromate treatment, and it becomes possible to reduce parts manufacturing costs and appropriately respond to environmental regulations. In particular, when the Mg content in the zinc-based alloy coating layer constituting the projection material is increased, an iron-based component exhibiting extremely high corrosion resistance such that the time until occurrence of red rust in the salt spray test exceeds 4000 h is obtained. It is done. Also, even if the film thickness is 15 μm or less, or even as thin as 2 to 5 μm, a sufficient effect can be obtained, so that high corrosion resistance can be obtained even for parts that cannot be applied with hot dip plating, such as screws. Can be granted. For this reason, for example, a large cost reduction effect can be obtained by substituting parts of the outdoor structure for which expensive stainless steel had to be used with those having the coating of the present invention.

As a result of various studies, the inventors have found that when the following two points are combined, an extremely remarkable corrosion resistance improvement effect can be obtained.
i) The deposition material to be deposited by mechanical plating is a Zn—Al—Mg alloy, and the Mg content is at least 3 mass%, preferably at least 5 mass%.
ii) The material to be deposited by mechanical plating is incorporated into a projection material having a core of steel particles and collides with the surface of the material to be treated.
None of these i) and ii) alone have been found to have a significant effect on improving corrosion resistance, and the present invention utilizes a new effect of improving corrosion resistance due to the synergistic action of i) and ii). The mechanism causing the synergistic action of i) ii) is not necessarily clarified at present.

[Zn-Al-Mg-based adherent]
In the film formed by mechanical plating, a very dense corrosion product is generated between Zn and Al, and thereby a stable film sealed is constructed. In order to sufficiently exhibit such an action, it is preferable that 1% by mass or more of Al is contained in the formed film. However, even if it exceeds 5% by mass, an effect commensurate with the added amount cannot be expected. Since the composition of the alloy coating layer that forms the periphery of the steel particle core of the projection material is almost directly reflected in the coating composition formed on the surface of the component, in the present invention, the Al content in the alloy coating layer of the projection material is 1 It is prescribed to ˜5% by mass.

Mg forms an oxide or hydroxide in a film formed by mechanical plating. Mg oxides and hydroxides have high electrical insulation, and therefore suppress the corrosion current when Zn in the film corrodes. In addition, since it prevents oxygen permeation, it exhibits a protective action against Zn corrosion. Although Mg is lower in potential than Zn in terms of potential, it produces a stable corrosion product in a corrosive environment and relaxes the galvanic action of Zn. This is considered to suppress the elution of Zn in the film and increase the anticorrosion effect. According to detailed investigations by the inventors, it has been found that when the Mg content in the film is 3% by mass or more, such an effect of Mg becomes apparent. It is preferable to set it as 5 mass% or more. Furthermore, when a high Mg concentration of 7% by mass or more is realized, in combination with the effect of the above ii) (the effect of colliding a projection material having a core of steel particles), extremely remarkable corrosion resistance exceeding that when chromate treatment is performed. The improvement effect comes to be demonstrated. However, since Mg is easily oxidized in the molten Zn alloy, it is difficult to produce a projection material using a molten Zn alloy as will be described later if an excessively high Mg content is to be secured. For this reason, Mg content in a film needs to be 15 mass% or less. Usually, good results are obtained in the range of 12% by mass or less.
From the above, in the present invention, the Mg content in the alloy coating layer of the projection material is regulated to 3 to 15% by mass. A more preferable range of the Mg content in the alloy coating layer is 5 to 15% by mass, and a more preferable range is 7 to 12% by mass.

The film obtained by mechanical plating usually contains Fe derived from the projection material and parts. Good results are obtained when the Fe content in the film is 20% by mass or less (for example, 0.1 to 20% by mass).
It is desirable to keep the impurity elements other than Zn, Al, Mg, and Fe within a total range of 1% by mass or less.

[Projection material]
In the present invention, a projection material particle having a core of steel particles is employed. That is, the particles of the present invention are composite particles composed of steel particles and the zinc-based alloy. By colliding the particles having such a composite structure with the surface of the material to be treated, the conventionally known effect of improving the film adhesion can be obtained. In the case of the composition, a dramatic improvement in the corrosion resistance is achieved. That is, the synergistic effect of i) + ii) is expressed. This is a phenomenon that has not been predicted in the past. It is considered that the collision of the projecting material having the steel particles as nuclei firmly adheres the coating to the base metal and further strengthens the coating itself, thereby improving the resistance to coating damage. And it is guessed that the sealing effect by Al of the adherend and the elution prevention effect of Zn by increasing the Mg content may result in a significant improvement in corrosion resistance.

In order to sufficiently exhibit such effects peculiar to the present invention, the steel particles that serve as nuclei and the zinc-based coating around them are made so that the Fe content contained in the projection material is 3 to 80% by mass. It is desirable to control the amount ratio of the alloy layer (deposited material). If the Fe content is less than this, it will be difficult to obtain sufficient projection energy, and if it is more than this, the amount of the deposited material will be relatively small, and the life of the projection material will be early during the blasting process for mechanical plating. It is exhausted and is not efficient.
It is desirable to use steel particles having a hardness of about 200 to 700 HV as the core. Further, the particle size of the projection material is desirably 95% by mass or more of all particles in the range of 10 to 800 μm, and the average particle size is preferably 100 to 600 μm.

[Film thickness]
The film thickness formed on the surface of the metal material to be processed needs to ensure at least 2 μm. However, it is not economical to apply a weight per unit area exceeding 15 μm by mechanical plating. Usually, a remarkable corrosion resistance improvement effect is obtained by controlling the film thickness to about 2 to 15 μm.

[Production method of projection material]
The projection material of the present invention, the steel particles that serve as nuclei are charged into a zinc alloy molten metal having a composition corresponding to the adherend, and stirred, and this is taken out when it becomes a semi-solidified state as the molten metal temperature decreases, Then, it can manufacture in the process of grind | pulverizing and sieving. At that time, it is preferable to control the amount of molten zinc alloy and the amount of steel particles charged so that the Fe content in the particles of the projection material is 3 to 80% by mass. When a zinc alloy is deposited around the steel particles by such a technique, an Fe—Zn alloy layer is formed in the vicinity of the interface between the two. Since the Fe-Zn alloy layer is relatively brittle, when the projection material collides with the surface of the material to be treated during the blasting process, finely-sheared zinc alloy fine particles are pressed onto the surface of the material to be treated. As a result, the uniformity of the film is improved.

  Commercial steel shots can be used as the steel particles. The particles constituting the projection material (after alloy coating) are preferably in the range of 10 to 800 μm in particle size as described above. The average particle diameter is preferably 100 to 600 μm, and in particular, can be in the range of 100 to 400 μm, or 150 to 300 μm. Further, since the Fe content in the projection material particles is preferably about 3 to 80% by mass, it is desirable to set the size and amount of the steel particles to be used according to these target values.

[Invention Example 1]
50 kg of molten zinc alloy having a composition of Zn-3.5 mass% Al-8.0 mass% Mg (less than 1 mass% of other impurities) is kept at 570 ° C. and homogenized, and then kept at 570 ° C. The burner scooping for the purpose was turned off, and immediately after that, 65 kg of steel shot was put into the molten metal with stirring. The steel shot used is a commercial product having an average particle diameter of 237 μm and an average hardness of 312 HV. When the molten metal became a semi-solid state as the temperature dropped, the mixture of zinc alloy and steel shot was taken out and transferred to a pulverizer before it completely solidified to start pulverization. Then, the individual steel shots were separated, and pulverization was continued until the surface properties were almost spherical, thereby obtaining a projection material.

  The average particle diameter of this projection material was 218 μm. Moreover, as a result of observing the cross section of the particles of the projecting material by the EDS method (energy dispersive X-ray spectroscopy), the core has a core of steel particles derived from the steel shot, and the periphery of the steel shot and the molten metal. It had a zinc alloy coating layer through an alloy layer formed by the reaction. Further, when this cross section was analyzed, the alloy layer formed by the reaction between the steel shot and the molten metal was an Fe-Zn alloy layer, and the surrounding zinc alloy coating layer had a composition reflecting the initial molten metal composition as it was. I understood. In addition, as a result of analyzing the composition of the sample of the projection material by the total iron determination method in JIS M8212-1958 iron ore and the potassium permanganate titration volume method, the Fe content in the projection material was 49.9% by mass. It was.

  Using this projection material, a zinc alloy film was formed on the surface of a commercially available 4T bolt (made of steel) by a mechanical plating apparatus. The projection conditions were: projection amount: 60 kg / min, projection particle velocity: initial velocity of about 51 m / sec, and projection time: 80 min. As a result of observing the cross section of the bolt after film formation by the EDS method, the film thickness was about 4.4 μm. Further, as a result of examining the composition of the formed film, Al: about 3.3 mass%, Mg: about 7.5 mass%, Fe: about 5.5 mass%, and the balance was substantially Zn. The total amount of other elements (impurities) is less than 1% by mass.

[Invention Example 2]
The same conditions as in Invention Example 1 except that the molten metal composition of the zinc alloy was Zn-3.5 mass% Al-6.0 mass% Mg (other impurities less than 1 mass%) and the molten metal holding temperature was 535 ° C. A projectile was obtained.
This projection material has an average particle diameter of 217 μm, has a core of steel particles derived from steel shot in the center, and has a zinc alloy coating layer around the alloy layer formed by the reaction of steel shot and molten metal. Was. As a result of the measurement, it was found that the alloy layer formed by the reaction between the steel shot and the molten metal was an Fe—Zn alloy layer, and the surrounding zinc alloy coating layer had a composition reflecting the initial molten metal composition as it was. The content of Fe in the projection material was 54.8% by mass.

  Using this projection material, a zinc alloy film was formed on the surface of a commercially available 4T bolt (made of steel) under the same conditions as in Invention Example 1. The obtained film was about 4.5 μm thick, and the film composition was Al: about 3.3% by mass, Mg: about 5.6% by mass, Fe: about 6.2% by mass, and the balance being substantially the same. Zn. The total amount of other elements (impurities) is less than 1% by mass.

[Comparative Example 1]
A projection material was obtained under the same conditions as in Invention Example 1 except that a molten metal of Zn (less than 1% by mass of other impurities) was used and the molten metal retention temperature was 480 ° C.
This projection material has an average particle size of 235 μm, has a core of steel particles derived from steel shot in the center, and has a zinc layer around the alloy layer formed by the reaction of steel shot and molten metal around it. It was. The Fe content in the projection material was 55.7% by mass.

  Using this projection material, a zinc alloy film was formed on the surface of a commercially available 4T bolt (made of steel) under the same conditions as in Invention Example 1. The obtained film had a thickness of about 4.6 μm, and the film composition contained about 13.7% by mass of Fe in addition to Zn.

[Comparative Example 2]
On the film formed in Comparative Example 1, a bolt subjected to chromate treatment by a conventional general method was produced.

[Salt spray test]
About the bolt obtained by each invention example and the comparative example, the salt spray test was done by the method according to JISZ2371, and time until red rust generate | occur | produced was investigated. as a result,
Invention Example 1: 5160h,
Invention Example 2: 1920h,
Comparative Example 1: <24h,
Comparative Example 2 (chromate treatment): 3000 h
Met.
According to the present invention, high corrosion resistance exceeding 1800 h can be imparted until the occurrence of red rust by salt water spraying, and in particular, the one with an increased Mg content in the coating (Invention Example 1) is extremely superior to the chromate treatment material. It can be seen that corrosion resistance can be imparted.

In each invention example and comparative example shown in Example 1, using a cold-rolled steel plate (SPCC) having a thickness of 0.8 mm instead of a bolt as the material to be treated, mechanical plating was performed on the surface under the same conditions. And various characteristics were examined. That is, it is as follows.
[Invention Example 3] The same conditions as in Invention Example 1.
[Invention Example 4] The same conditions as in Invention Example 2.
[Comparative Example 3] Same conditions as in Comparative Example 1.
[Comparative Example 4] The same conditions as in Comparative Example 2 (chromate treatment).
The following characteristics were examined for the samples of each example.
-Film adhesion: evaluated by a bending test by plating adhesion test of JIS H8504 and a cross-cut tape test of JIS K5400.
-Self-healing property (sacrificial anticorrosive property): A cross-cut was inserted, and the time until red rust occurred was evaluated by a salt spray test of JIS Z2371.
-Weather resistance: JIS Z2381-1987 outdoor exposure test (direct exposure test) was used to examine and evaluate the number of days until red rust occurred.
The results are shown in Table 1.

  As can be seen from Table 1, those according to the present invention can achieve significant improvements in self-repairability and weather resistance while maintaining good film adhesion. Of particular note is the fact that the Mg content in the film is increased (Invention Example 3) and exhibits a self-repairing property equal to or higher than that of the chromate treatment material.

Claims (6)

  Steel particles are used as cores, and the surrounding particles are coated with a zinc alloy composed of Al: 1 to 5% by mass, Mg: 5.5 to 15% by mass, the balance Zn and impurities, and the zinc alloy is an Fe—Zn alloy layer. The projecting material for mechanical plating, wherein the steel particles are coated around the steel particles, and the Fe content is 3 to 80% by mass.   The steel particles are cores, and the periphery is coated with a zinc alloy composed of Al: 1 to 5 mass%, Mg: 7 to 15 mass%, the balance Zn and impurities, and the zinc alloy is interposed through the Fe-Zn alloy layer. A projection material for mechanical plating, which is coated around the steel particles and has a Fe content of 3 to 80% by mass.   The projection material for mechanical plating according to claim 1 or 2, wherein the average particle size is 100 to 600 µm. It is a film | membrane formed in the said metal material surface by making the projection material of Claim 1 or 3 collide with the metal material surface, Comprising: Al: 1-5 mass%, Mg: 5.5-15 mass%, Fe: 0.1 to 20% by mass , balance 2 and 15 μm thick highly corrosion-resistant film composed of impurities and impurities. It is a film | membrane formed in the said metal material surface by making the projection material of Claim 2 or 3 collide with the metal material surface, Comprising: Al: 1-5 mass%, Mg: 7-15 mass%, Fe: A highly corrosion-resistant film having a thickness of 2 to 15 μm composed of 0.1 to 20% by mass , the balance Zn and impurities.   The high corrosion-resistant film according to claim 4 or 5, wherein the metal material is a bolt.