KR20060121716A - Shot material for mechanical plating, and high corrosion resistant coating using same - Google Patents

Abstract

A zinc-based coating film formed by mechanical plating that itself has significantly improved corrosion resistance without depending on formation treatment of a protective coating film such as chromate treatment and the like is provided. A shot material for mechanical plating comprises steel particles as a core, and an alloy for covering the periphery of the steel particles, wherein the alloy comprises 1 to 5 mass % of Al, 3 to 15 mass % of Mg, and the balance of Zn and impurities. A shot material for mechanical plating comprises steel particles as a core, and an alloy for covering the periphery of the steel particles, wherein the alloy comprises 1 to 5 mass % of Al, 5 to 15 mass % of Mg, and the balance of Zn and impurities. The alloy has an Fe-Zn alloy layer interposed between the alloy and the steel particles. The shot material contains 3 to 80 mass % of Fe. The shot material has an average particle diameter of 100 to 600 mum. As a high corrosion resistant coating film formed on the surface of the metal material by impacting the surface of a metal material with the shot material, the high corrosion resistant coating film has a thickness of 2 to 15 mum and comprises 1 to 5 mass % of Al, 3 to 15 mass % of Mg, 20 mass % or less of Fe, and the balance of Zn and impurities.

Description

Shot material for mechanical plating, and high corrosion resistant coating using same

The present invention relates to a projection material for mechanical plating for forming a high 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 iron-based metal materials, a method of forming zinc or zinc alloy coatings (hereinafter referred to as zinc coatings) is widely used. Specifically, hot dip plating, phosphate plating, electroplating, and mechanical play are used. Techniques such as Ting have been industrially used.

When a material forming a general zinc-based coating such as zinc plating is exposed to the atmospheric environment as it is, white rust of zinc occurs in a relatively short period of time, and the film may be quickly consumed. In particular, it is remarkable in an outdoor environment. Therefore, a treatment (for example, chromate treatment) is performed on the zinc-based coating to form a protective coating again.

Since the zinc coating formed by mechanical plating has a structure in which flakes are laminated (so-called "pie crust phase"), when chromate treatment is performed thereon, the chromate treatment liquid sufficiently penetrates into the coating. As a result, a remarkable corrosion resistance improvement effect is exhibited. For example, when a zinc coating having a time of about 24 hours until the occurrence of red rust by the salt spray test (hereinafter referred to as test according to JIS Z2371) is formed by mechanical plating, chromate treatment is performed. As a result, the corrosion resistance is remarkably improved up to 3000 hours.

The chromate treatment is relatively inexpensive and can be easily formed with a high protective effect. Therefore, the chromate treatment is widely used for practical purposes. However, a solution containing toxic hexavalent chromium is used for this treatment. As a protective film forming process without using hexavalent chromium, there are also methods of forming a film made of trivalent chromium, a polymer chelate film, a silicate inorganic film, and the like, but the protective effect of these films is higher than that of a hexavalent chromate film. I can't seem. As a cause of this, these coatings do not have self-healing properties as seen in hexavalent chromate coatings. In other words, it causes a significant decrease in corrosion resistance at the place of injury. Moreover, in the method which does not use hexavalent chromium, the management of a process liquid is complicated, a nonuniformity arises easily in the characteristic after a process, and a process cost becomes high compared with hexavalent chromate.

The method of improving the corrosion resistance of the zinc-based film itself formed by mechanical plating is also examined. Japanese Unexamined Patent Application Publication No. 55-119101, Japanese Unexamined Patent Application Publication No. 56-93801, and Japanese Unexamined Patent Application Publication No. 57-110601 include alloying elements such as Al and Mg. The use of powders consisting of Zn alloys is disclosed.

On the other hand, in order to improve the durability of the zinc-based coating by mechanical plating, it is also important to improve the adhesion of the coating to the base metal. JP-A-56-45372 and JP-A-62-140768 use iron or iron alloy particles as nuclei and particles coated with zinc or zinc alloy thereon as projection materials. Use is described. It is thought that a large projection energy is obtained by colliding the particle having the nucleus of hard and heavy iron-based particles with the surface of the material to be treated, and as a result, the compressive effect of the adherend is increased and the film adhesion is improved.

As described above, the zinc-based coating by mechanical plating can greatly improve the corrosion resistance by chromate treatment. However, environmental regulations are now tightening, which severely limits the use of toxic hexavalent chromium. In addition, no treatment method for forming an effective protective film has been established.

On the other hand, there is a limit in terms of corrosion resistance to using these parts in the state of the film formed by mechanical plating. That is, the zinc alloy which improved the corrosion resistance as described in Unexamined-Japanese-Patent No. 55-119101, 56-93801, and Japan Unexamined-Japanese-Patent No. 57-110601. Even by the method using powder, the time from salt spray test to red rust generation is increased to around 1500 hours by the composition of Zn-Al-Mg, which is added around 500 hours and the composition containing special elements such as Na and Be. Is the limit. For parts used outdoors, it is desirable to exhibit corrosion resistance such that the time from salt spray test to red rust generation is about 1800 hours or more. In addition, in an environment where salts such as automobile parts are susceptible to corrosion, corrosion resistance of 3000 hours or more until red rust occurs is desired. It is difficult to meet these demands simply by depositing a zinc alloy having high corrosion resistance.

In addition, even in the method using a projection material having a nucleus of iron-based particles as disclosed in JP-A-56-45372 and JP-A-62-140768, there is a fundamental improvement in corrosion resistance. It is not reaching.

In view of such a phenomenon, an object of the present invention is to remarkably improve the corrosion resistance of the zinc-based coating film itself formed in mechanical plating without requesting a protective film formation treatment such as chromate treatment.

The object is to use steel particles as nuclei, and to coat around them an alloy composed of 1 to 5% by mass of Al, 3 to 15% by mass of Mg, preferably 5 to 15% by mass, balance Zn and impurities. Achieved by a projection material for mechanical plating. Impurities in the alloy are generally allowed to be mixed up to about 1% by mass in total. The Fe-Zn alloy layer is interposed between the coating alloy and the steel in the center portion.

Content of Fe contained in such a 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 formed on the surface of this metal material by making such a projection material collide with the surface of metal materials, such as steel, and is 1-5 mass% of Al, 3-15 mass% of Mg, 20 mass% or less of Fe, remainder Zn And a highly corrosion resistant film having a thickness of 2 to 15 µm composed of impurities. Impurities in this case are generally allowed to be mixed up to about 1% by mass in total.

Effects of the Invention

According to the present invention, the corrosion resistance of the part can be remarkably improved in the coating state while being formed by mechanical plating. Therefore, it can be applied to various conventional parts use without performing chromate treatment, and can reduce the part manufacturing cost and respond appropriately to environmental regulation. In particular, when the Mg content in the zinc-based alloy coating layer constituting the projection material is increased, an iron-based component exhibiting very high corrosion resistance is obtained so that the time from salt spray test to red rust generation exceeds 4000 hours. In addition, even if the film thickness is as thin as 15 μm or less or 2 to 5 μm, a sufficient effect is obtained, so that a high corrosion resistance can be obtained even for parts such as “screws” which cannot be applied to the hot dip coating, which becomes a weight per thick unit area. You can give it. Thus, for example, a large cost reduction effect is obtained by replacing parts of the outdoor structure, which must be used with expensive stainless steel, with those having the coating of the present invention.

Best Mode for Carrying Out the Invention

As a result of various examinations, the inventors found that when the following two points are combined, a very remarkable corrosion resistance improvement effect is obtained.

(i) The deposited substance to be deposited by mechanical plating is a Zn-Al-Mg-based alloy, and its Mg content is 3% by mass or more, preferably 5% by mass or more.

(ii) The deposited material to be deposited by mechanical plating is incorporated into the projection material having the nuclei of the steel particles to collide with the surface of the material to be treated.

None of these (i) and (ii) alone has a significant corrosion resistance improvement effect confirmed, and in the present invention, a novel corrosion resistance improvement effect by synergy of (i) and (ii) is used. The mechanisms causing the synergies of these (i) and (ii) are not necessarily clear at the present time.

[Zn-Al-Mg type deposition material]

In the film formed by mechanical plating, very dense corrosion products are produced between Zn and Al, thereby establishing a stable film with holes sealed. In order to fully exhibit such an effect, it is preferable that 1 mass% or more Al is contained in the formed film. However, even if it exceeds 5 mass%, the effect suitable for addition increase cannot be expected. Since the composition of the alloy coating layer constituting the periphery of the steel particle nucleus of the projection material is generally reflected in the film composition formed on the surface of the part as it is, in the present invention, the Al content is defined as 1 to 5% by mass in the alloy coating layer of the projection material.

Mg forms oxides or hydroxides in the film formed by mechanical plating. Since oxides and hydroxides of Mg have high electrical insulating properties, corrosion currents are suppressed when Zn in the film corrodes. In addition, since it prevents the permeation of oxygen, it shows a protective action against corrosion of Zn. Mg is potentially lower than Zn, but under the corrosive environment produces a stable corrosion product and at the same time mitigates the galvanic action of Zn. It is thought that the elution of Zn in a film by this is suppressed and a corrosion prevention effect becomes high. According to the detailed examination by the inventor etc., when the Mg content in a film is made into 3 mass% or more, it turned out that such an effect of Mg exists. It is preferable to set it as 5 mass% or more. In addition, when a high Mg concentration of 7% by mass or more is achieved, in combination with the effect of ii) (the effect of colliding the projection material having the nucleus of the steel particles), a very remarkable corrosion resistance improvement effect is exerted than that of the chromate treatment. Will be. However, since Mg is easy to be oxidized in Zn alloy molten metal, when it is going to ensure too high Mg content, it becomes difficult to manufacture the projection material using the molten metal of Zn alloy as mentioned below. Therefore, Mg content in a film needs to be 15 mass% or less. Usually, a good result is obtained in the range of 12 mass% or less.

In view of the above, in this invention, Mg content is prescribed | regulated to 3-15 mass% in the alloy coating layer of a projection material. The range of more preferable Mg content in an alloy coating layer is 5-15 mass%, and a further preferable range is 7-12 mass%.

The film obtained by mechanical plating usually contains Fe derived from a projection material or a part. A good result is obtained in the range of 20 mass% or less (for example, 0.1-20 mass%) in Fe content in a film.

It is preferable to suppress impurity elements except Zn, Al, Mg, and Fe in the range of 1 mass% or less in total.

[Projection material]

In this invention, what has the nucleus of a steel particle is employ | adopted as a projection material particle. That is, the particles of the present invention are composite particles composed of steel particles and zinc-based alloys. Impingement of a conventionally known film adhesion property is obtained by impinging such a composite structure particle on the surface of the material to be treated. However, when the material to be deposited is composed of an Al-Mg composite addition having a high Mg content, further improvement in corrosion resistance is also achieved. This is to be achieved. Eventually, synergy by (i) + (ii) is expressed. This is a phenomenon not previously predicted. By colliding the projection material having the steel particles as the nucleus, the film is firmly deposited on the underlying metal, and the film itself is further strengthened, and the resistance to film damage is considered to be improved. And it is estimated that the hole sealing effect by Al of an adherend substance and the elution prevention effect of Zn by raising Mg content are suitable, and, as a result, a significant corrosion resistance improvement effect arises.

In order to sufficiently exhibit such effects peculiar to the present invention, the ratio of the amount of the steel particles serving as nuclei and the zinc-based alloy layer (adhesive material) coated thereon so that the Fe content contained in the projection material becomes 3 to 80% by mass. It is desirable to adjust. If the Fe content is less than this, it is difficult to obtain sufficient projection energy, and if it is more than that, the amount of the deposited material is relatively small, and the life of the projection material ends at an early stage in the blasting process of mechanical plating and is not efficient.

It is preferable to use the thing of hardness 200-700HV as steel particle used as a core. Moreover, it is preferable that 95 mass% or more of all the particle | grains of the projection material are in the range of 10-800 micrometers, and, as for an average particle diameter, 100-600 micrometers is preferable.

[Film thickness]

The film thickness formed on the surface of the to-be-processed metal material needs to ensure 2 micrometers or more. However, it is not economical to perform a weight per thick unit area exceeding 15 μm by mechanical plating. Usually, by adjusting to the film thickness of about 2-15 micrometers, a remarkable corrosion resistance improvement effect is acquired.

[Production Method of Projection Material]

In the projection material of the present invention, the steel particles serving as nuclei are added to a zinc alloy molten metal having a composition equivalent to the substance to be deposited and stirred, and withdrawn from the point where it reaches a reaction state according to the drop of the molten metal temperature, followed by pulverization and sieving. It can manufacture by the process of making. At this time, it is preferable to adjust the amount of molten zinc alloy and the amount of steel particles so that the Fe content occupied in the particles of the projection material becomes 3 to 80% by mass. By adhering a zinc alloy around the steel particles by this method, a Fe—Zn alloy layer is formed in the vicinity of both interfaces. Since the Fe-Zn alloy layer is relatively fragile, when the projection material collides with the surface of the material to be treated during blasting, fine particles of zinc alloy finely sheared into the Fe-Zn alloy layer portion are pressed onto the surface of the material to be treated. The uniformity of the film is improved.

As steel particles, commercially available steel shots can be used. It is preferable that the particle | grains (after alloy coating) which comprise a projection material exist in the range of 10-800 micrometers of particle diameters as mentioned above. It is preferable that the average particle diameter is 100-600 micrometers, and it can be especially 100-400 micrometers or the range of 150-300 micrometers. Since the Fe content in the projection material particles is preferably about 3 to 80% by mass, it is preferable to set the size and amount of the steel particles to be used in accordance with these target values.

Example 1

Invention Example 1

50 kg of a zinc alloy molten metal having a composition of Zn-3.5% by mass Al-8.0% by mass Mg (less than 1% by mass of impurities) was kept at 570 ° C, homogenized, and the burner burned for the purpose of maintaining at 570 ° C was turned off. Immediately afterwards, 65 kg of steel shot was added while stirring in the molten metal. The steel shot used is a commercial item which has an average particle diameter of 237 micrometers, and an average hardness of 312 HV. At the time when the molten metal reaches a solid state with temperature drop, the mixture of zinc alloy and steel shot is taken out and transferred to the grinder while it is not completely solidified and grinding is started. Then, the grinding is continued until the individual steel shots are separated and become generally spherical surface properties, thereby obtaining a projection material.

The average particle diameter of such a projection material is 218 micrometers. In addition, observation of the cross section of the particles of the projection material by the EDS method (energy dispersive X-ray spectroscopy) revealed that the core had a nucleus of steel particles derived from the steel shot and formed by the reaction of the steel shot and the molten metal around the core. It has a zinc alloy coating layer through an alloy layer. In addition, the cross section was analyzed and it was found that the alloy layer formed by the reaction between the steel shot and the molten metal was a Fe-Zn alloy layer, and the zinc alloy coating layer constituting the surroundings generally had a composition reflecting the initial molten metal composition. The content of Fe in the projection material was 49.9% by mass as a result of compositional analysis of the samples of the projection material by the method for quantitating all iron in the JIS M8212-1958 iron ore and the appropriate capacity of potassium permanganate.

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

Invention Example 2

The molten metal composition of the zinc alloy is Zn-3.5% by mass, Al-6.0% by mass and Mg (less than 1% by mass of other impurities), and the projection material is obtained under the same conditions as in Example 1 except that the molten metal holding temperature is 535 ° C. .

The average particle diameter of such a projection material is 217 micrometers, and has a zinc alloy coating layer through the nucleus of the steel particle originating in a steel shot in the center part, and interposing the alloy layer formed by reaction of a steel shot and a molten metal around it. 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 a Fe-Zn alloy layer, and the zinc alloy coating layer constituting the surroundings generally had a composition reflecting the initial molten metal composition as it was. In addition, content of Fe in a projection material is 54.8 mass%.

Using such a projection material, a zinc alloy film is formed on the surface of a commercially available 4T bolt (steel) under the same conditions as in Inventive Example 1. The obtained film was about 4.5 micrometers in thickness, a film composition is about 3.3 mass% of Al, about 5.6 mass% of Mg, about 6.2 mass% of Fe, and remainder is Zn substantially. The total amount of other elements (impurity) is less than 1 mass%.

Comparative Example 1

A projection material is obtained under the same conditions as in Inventive Example 1 except that Zn molten metal (less than 1% by mass of other impurities) is used and the molten metal holding temperature is 480 ° C.

The average particle diameter of such a projection material is 235 micrometers, and has the zinc layer through the core of the steel particle derived from a steel shot in the center part, and interposing the alloy layer formed by reaction of a steel shot and a molten metal around it. The content of Fe in the projection material is 55.7 mass%.

Using such a projection material, a zinc alloy film is formed on the surface of a commercially available 4T bolt (steel) under the same conditions as in Inventive Example 1. The obtained film was about 4.6 micrometers in thickness, and a film composition contains about 13.7 mass% of Fe other than Zn.

Comparative Example 2

On the film formed in the comparative example 1, the bolt which chromate-processed by the conventional general method is produced.

[Salt spray test]

About the bolt obtained by each invention example and the comparative example, the salt spray test is performed by the method according to JISZ2371, and time until red rust generate | occur | produces is investigated. As a result,

Invention example 1: 5160 hours,

Inventive Example 2: 1920 hours,

Comparative Example 1: <24 hours,

Comparative Example 2 (chromate treatment): 3000 hours.

According to the present invention, it is possible to give high corrosion resistance in which salt rust occurs in salt spraying exceeds 1800 hours. In particular, when the Mg content in the coating is increased (invention example 1), it greatly exceeds the chromate treatment material. It was found that excellent corrosion resistance could be imparted.

Example 2

In each of the invention examples and the comparative examples described in Example 1, a cold rolled steel sheet (SPCC) having a thickness of 0.8 mm instead of bolts was used as a material to be treated, and mechanical plating was carried out on the surface thereof under the same conditions. Investigate. That is as follows.

Invention Example 3 The same conditions as in Inventive Example 1.

Invention Example 4 The same conditions as in Inventive Example 2.

Comparative Example 3 The same conditions as in Comparative Example 1.

Comparative Example 4 The same conditions as in Comparative Example 2 (chromate treatment).

About the sample of each case, the following characteristic is investigated.

Coating adhesiveness: It evaluates by the baking test by the plating adhesion test of JISH8504, and the checkerboard graduation tape test of JISK5400.

Self-repairing property (preventing sacrificial corrosion): The cross cut is injected into the salt spray test of JIS Z2371 to evaluate the time until the occurrence of red rust.

Weatherability: The days until the occurrence of red rust are investigated and evaluated by the outdoor exposure test (direct exposure test) of JIS Z2381-1987.

The results are shown in Table 1.

division Film adhesion Self-healing property (preventing sacrificial corrosion) Corrosion Resistance (Outdoor Exposure Test) Baking test Checkerboard tick tape test Inventive Example 3 Good Good 1140 hours ≥6 months Inventive Example 4 Good Good 312 hours ≥6 months Comparative Example 3 Good Good <24 hours <1 month Comparative Example 4 (Chromate Treatment) Good Good 1080 hours ≥6 months

As can be seen from Table 1, according to the present invention, a significant improvement in self repair and weather resistance is realized while maintaining good film adhesion. In particular, in increasing the Mg content in the film (Invention Example 3), it is noted that it exhibits self-healing properties equivalent to or greater than that of the chromate treatment material.

According to the present invention, the corrosion resistance of the part can be remarkably improved in the coating state while being formed by mechanical plating. Therefore, it can be applied to various conventional parts use without performing chromate treatment, and can reduce the part manufacturing cost and respond appropriately to environmental regulation.

Claims (6)

A projection material for mechanical plating in which steel particles are used as a nucleus, and an alloy composed of 1 to 5% by mass of Al, 3 to 15% by mass of Mg, balance Zn, and impurities is coated thereon. A projection material for mechanical plating, wherein steel particles are used as a nucleus, and an alloy composed of 1 to 5% by mass of Al, 5 to 15% by mass of Mg, balance Zn, and impurities is coated thereon. The projection material for mechanical plating according to claim 1 or 2, wherein the alloy is coated around the steel particles via the Fe—Zn alloy layer. The projection material for mechanical plating as described in any one of Claims 1-3 whose content of Fe is 3-80 mass%. The projection material for mechanical plating according to any one of claims 1 to 4, wherein the average particle diameter is 100 to 600 µm. As a film formed on the surface of the metal material by colliding the projection material according to any one of claims 1 to 5 with the surface of the metal material, A highly corrosion resistant film having a thickness of 2 to 15 µm composed of 1 to 5 mass% of Al, 3 to 15 mass% of Mg, 20 mass% or less of Fe, the balance Zn and impurities.