CN110684379B

CN110684379B - Inorganic anti-corrosion coating for high-strength metal

Info

Publication number: CN110684379B
Application number: CN201910828418.4A
Authority: CN
Inventors: 闫东明; 刘毅; 钱昊
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2019-09-03
Filing date: 2019-09-03
Publication date: 2021-03-30
Anticipated expiration: 2039-09-03
Also published as: WO2021042561A1; CN110684379A

Abstract

The invention discloses an inorganic anti-corrosion coating for high-strength metal, which is formed on the surface of the high-strength metal by sintering coating at the high temperature of 800 ℃ under the action of 500-; the coating comprises 25-35 parts of silicon oxide, 10-25 parts of phosphorus pentoxide, 10-25 parts of aluminum oxide, 2-15 parts of fibers, 15-30 parts of a modifier and 1-3 parts of an anti-cracking agent; the fiber is one or a combination of two or three of aluminum silicate fiber, basalt fiber and calcium carbonate fiber; the coating is internally distributed with a plurality of closed holes with the diameter of 1/30-1/10 coating thickness, the number of the closed holes is reduced from inside to outside, the porosity of the inner layer of the multi-hole close to the surface of the high-strength metal is 2-15%, and the porosity of the compact outer layer far away from the surface of the high-strength metal is 0-2%. The invention has good toughness, does not generate cracks penetrating through the coating when the strain is 2800-3000 micro-strain, has high adhesive force with the base material, has excellent corrosion resistance, various construction modes and low use cost.

Description

Inorganic anti-corrosion coating for high-strength metal

Technical Field

The invention belongs to the field of engineering structures, and particularly relates to an inorganic anticorrosive coating for high-strength metal.

Background

The application of the high-strength steel bar can reduce the consumption of steel in unit area, reduce cost, save energy and reduce emission, and is gradually promoted to engineering application in recent years, the high-strength steel bar of 500MPa level is widely applied in engineering, and the high-strength steel bar of 600MPa level is formally written into national specifications (GB-T1499.2-2018) in 2018 and is gradually popularized. If the high-strength steel bar is corroded, the performance degradation of the high-strength steel bar is more serious than that of the common steel bar. Therefore, the corrosion prevention of the high-strength steel bar is the first problem to be solved when the high-strength steel bar is applied in a corrosive environment.

When the coating is deformed in cooperation with the reinforcing steel bar, cracking does not occur, which is the premise that the coating can exert the corrosion resistance. The high-strength steel bar puts higher requirements on the toughness of the coating due to larger yield strain. For the high-strength steel bars with 500MPa and 600MPa levels, the designed and used strength respectively reaches 435MPa and 540MPa, and the corresponding strain reaches more than 2175 and 2700 microstrain. Chinese patent CN105131660 "Rebar anticorrosion paint and coating method" discloses a fiber-containing coating mainly comprising glass powder and borax, but the cracking strain of the coating reaches 700 microstrain. Chinese patent CN105238105, a tough coating for steel bar corrosion prevention and a coating method thereof, improves the toughness of the coating by adding silicon carbide whiskers into a system mainly comprising mica powder and borax, but the coating is a compact structure, the maximum cracking strain reaches only 2000 microstrain, and the requirement of applying the coating to high-strength steel bars cannot be met. Meanwhile, the price of the silicon carbide whisker is high, so that the large-scale engineering application of the coating is limited. The above patents show that the existing coating system mainly comprising glass powder (or mica powder) and borax is not completely suitable for the requirement of high-strength steel bars on the cracking performance of the coating. The epoxy resin coating which is most widely applied at present essentially belongs to an organic material, the toughness of the epoxy resin coating is far greater than that of an inorganic coating, and the requirement of high-strength steel bars on the toughness of the coating can be met. However, epoxy coatings are susceptible to aging and are by themselves much less durable than inorganic coatings.

In conclusion, the development of an inorganic coating which is low in cost, good in corrosion resistance, high in toughness and suitable for high-strength steel bars is an urgent problem to be solved.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides the tough inorganic anticorrosive coating which is suitable for metal, particularly high-strength metal corrosion resistance and has the cracking strain of 2800-3000 microstrain.

The technical scheme adopted by the invention for solving the technical problems is as follows: an inorganic anti-corrosion coating for high-strength metal, which is formed on the surface of the high-strength metal by sintering the coating at the high temperature of 500-800 ℃; the coating comprises 25-35 parts of silicon oxide, 10-25 parts of phosphorus pentoxide, 10-25 parts of aluminum oxide, 2-15 parts of fibers, 15-30 parts of a modifier and 1-3 parts of an anti-cracking agent; the fiber is one or a combination of two or three of aluminum silicate fiber, basalt fiber and calcium carbonate fiber; the coating is internally distributed with a plurality of closed holes with the diameter of 1/30-1/10 coating thickness, the number of the closed holes is reduced from inside to outside, the porosity of the inner layer of the multi-hole close to the surface of the high-strength metal is 2-15%, and the porosity of the compact outer layer far away from the surface of the high-strength metal is 0-2%.

The tensile strength of the aluminum silicate fiber, the basalt fiber or the calcium carbonate fiber adopted by the invention is more than 1GPa, and the high temperature resistance is more than 850 ℃; the aluminum silicate fibers, the basalt fibers and the calcium carbonate fibers have high tensile strength, good oxidation resistance and excellent high-temperature resistance, are often used for fireproof materials, and can improve the brittleness of a coating, improve the cracking strain and the impact resistance of the coating and contribute to better exerting the corrosion resistance of the coating when added into the coating; secondly, the fibers have extremely high chemical stability in alkaline solutions and are suitable for use in concrete.

The fibers have an inhibiting effect on the diffusion of cracks through the effects of debonding, pulling out and bridging, when the bonding force between the fibers and the matrix is weak and the fibers are long, the cracks deviate and expand along the bonding surface between the fibers and the matrix, so that the debonding of the fiber-matrix interface is caused, and the expansion of the cracks is hindered; when the bonding force between the fiber and the matrix is weak and the fiber is short, the fiber is pulled out in the crack propagation process, so that the stress at the tip of the crack is relaxed, the crack propagation is slowed down, and the crack propagation energy is consumed; when the bonding force between the fiber and the matrix is strong and the length of the fiber is enough, the two crack surfaces can be pulled by the two ends of the fiber, and the further expansion of the crack is prevented. The binding force of the aluminum silicate fibers, the basalt fibers and the calcium carbonate fibers with the coating base material is strong, and when the fibers are short enough (10-20 micrometers), the fibers consume the energy of crack diffusion through pulling out; when the fibers are longer (20-80 microns), the fibers limit the further propagation of the crack by pulling the crack faces.

The high ductility of the coating of the present invention is achieved by dual toughening of the fiber and gradient pore structure. The holes of the coating are too large, so that communicating holes are easily formed, and the coating becomes a channel for corrosive media to permeate into the surface of the steel bar, so that the corrosion resistance is obviously reduced; the coating has small holes, compact and excellent corrosion resistance, but the brittleness of the coating is increased, and the damage resistance and the cracking resistance are reduced. The closed hole with the diameter of 1/30-1/10 coating thickness has little influence on corrosion resistance, but can block cracks when micro cracks spread, reduce the stress concentration phenomenon at the tip of the cracks and improve the integral crack resistance of the coating. Meanwhile, the gradual change structure consisting of the porous inner layer and the compact outer layer ensures that the stress inside the coating is redistributed under the action of tensile load of the coated product to form a strain distribution state gradually reduced from the metal base material to the surface of the coating, thereby being beneficial to delaying the cracking of the coating.

Preferably, the silicon oxide compound is one or a combination of two or three of silicon dioxide, quartz and silica.

Preferably, the fibers have a length of 10 to 80 microns and a diameter of 0.2 to 5 microns.

Preferably, the modifier is one or more of sodium carbonate, potassium carbonate, calcium fluoride, calcium oxide and boron oxide. Sodium carbonate, potassium carbonate, calcium fluoride, calcium oxide, boron oxide and the like have a fluxing function and can obviously reduce the sintering temperature of the coating; meanwhile, sodium carbonate, potassium carbonate, calcium fluoride, calcium oxide, boron oxide and the like have smaller surface tension, and proper doping can reduce the surface tension of the surface of the metal base material to the coating slurry, improve the fluidity of the slurry, ensure that the coating can be uniformly coated on the surface of the steel bar, particularly show better coating effect at the longitudinal ribs and the transverse ribs of the twisted steel bar and ensure that the coating has no defect or few defects. Further, in the high-temperature sintering process, the modifier, the anti-cracking agent and the phosphorus pentoxide have complex chemical reactions with the metal substrate in the range of the coating/substrate interface transition region, and gas generated by the reactions diffuses into the coating. The invention controls the dosage of the modifier, the anti-cracking agent and the phosphorus pentoxide, and adopts proper technological parameters to prepare the coating with uniform thickness and no defect on the surface. Meanwhile, a plurality of closed holes with the diameter of 1/30-1/10 are distributed in the coating, the number of the holes is reduced in a gradient manner from inside to outside, and a gradient structure consisting of a porous inner layer and a compact outer layer is formed. The porosity of the inner layer of the porous is 2-15%, and the porosity of the compact outer layer is 0-2%.

Preferably, the anti-cracking agent is one or more of nickel monoxide, nickel sesquioxide, cobalt monoxide and cobalt sesquioxide. During the firing process of the coating, iron in the steel bars reacts with water vapor to generate iron oxide and hydrogen. Hydrogen gas generated during the high temperature process is initially stored in the iron, and as the temperature decreases, the hydrogen storage capacity of the iron decreases and hydrogen gas accumulates on the surface of the coating and the steel bar. When the hydrogen pressure is sufficiently high, the coating will be cracked and fish-scale marks appear. The addition of the anti-cracking agent can fix hydrogen in the high-temperature process, and avoid the phenomenon of scale explosion. Meanwhile, the iron oxide layer and the coating generate phase migration in the generation process, and a sawtooth structure is formed at the interface of the oxide layer and the coating, so that the binding force between the coating and the metal base material is increased. Therefore, when the coating has fine cracks and corrosive media infiltrate, the surface of the steel bar can be slightly corroded, corrosion products are accumulated and compacted in the corrosion channel to block the corrosion channel and isolate the corrosive media, and therefore the purpose of delaying corrosion is achieved. Meanwhile, the corrosion area can not be diffused, and the situation of under-film corrosion like an epoxy coating is avoided.

Preferably, the coating is powder or gel formed by dissolving the powder coating in absolute ethyl alcohol, wherein the mass ratio of the coating to the absolute ethyl alcohol is 1.8-3: 1. The coating can be directly coated by a thermal spraying method, or can be formed by firstly attaching powder to the reinforcing steel bar by adopting the modes of electrostatic spraying, brush coating, dipping coating and the like, and then sintering by adopting a laser cladding or hot cladding method. The coating obtained by adopting the method combining electrostatic spraying and hot melt coating has the advantages of optimal effect, easy control of the thickness of the coating, uniform thickness, simple operation and easy industrial production.

Preferably, the powder coating is sieved by a 200-mesh sieve.

Preferably, the coating thickness is 50 to 500 microns.

Preferably, the coating has a coefficient of thermal expansion of 8.5 x 10^-6/℃-11.4×10^-6/℃。

Preferably, the high strength metal is a metal having a strain of less than or equal to 2800 microstrain when used.

The coating of the invention can be applied to the fields of construction steel bars, steel products, pipelines and the like, relates to metal corrosion prevention in the fields of reinforced concrete structures, steel structures, ocean platforms, industrial pipelines and the like, and is particularly suitable for the requirements of high-strength metal.

The coating of the invention can also be used for common metals, is suitable for various steel products, metal pipelines and the like, and can solve the problem of metal corrosion in the fields of reinforced concrete structures, steel structures, ocean platforms, industrial pipelines and the like.

The invention has the beneficial effects that (1) the toughness is good: cracks penetrating through the coating are not generated at 2800-3000 microstrain, and fine cracks are generated at the part of the coating at 3000-3100 microstrain, but corrosion is inhibited along with the accumulation of corrosion products; when 3100-; (2) high adhesion to the substrate: the adhesive force is more than 15 MPa; (3) excellent corrosion resistance: no obvious corrosion defect appears after 3000 hours of neutral salt spray test; (4) the construction mode is various: the appropriate coating method can be selected according to actual conditions; (5) the use cost is low.

Drawings

FIG. 1 is a partial SEM image of example 1 of the present invention.

FIG. 2 is a partial SEM image of comparative example 7 of the present invention.

FIG. 3 is an image of the appearance of the samples of examples 1, 2 and 3 of the present invention after a neutral salt spray test for 3000 hours.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Preparing a coating: taking 150 g of silicon dioxide, 100 g of phosphorus pentoxide, 75 g of aluminum oxide, 32.5 g of sodium carbonate, 6 g of potassium carbonate, 50 g of calcium fluoride, 25 g of boron oxide, 3 g of nickel monoxide and 8.5 g of cobalt monoxide, uniformly mixing, grinding, and sieving the powder material with a 200-mesh sieve; adding 25 g of basalt fiber (diameter of 1-2 microns and length of 20-50 microns) and 25 g of aluminum silicate fiber (diameter of 1-2 microns and length of 20-50 microns) into the sieved powder, and uniformly mixing for later use.

Treating a base material: removing rust and dirt on the surface of the steel bar in a sand blasting mode, and drying for later use; the steel bar is HRB600 threaded steel bar with strain less than or equal to 2800 microstrain when in use.

Coating: grounding the treated steel bar, uniformly coating the powder on the surface of the steel bar by using an electrostatic spray gun, wherein the electrostatic voltage is 60 kilovolts, the current is 40 microamperes, the gas output is 5 liters per minute, the distance between the gun mouth of the spray gun and the steel bar is 20 centimeters, and the thickness of the coating is controlled to be about 100 micrometers.

And (3) sintering: and (3) putting the sprayed steel bar into a high-temperature furnace, heating at the speed of 10 ℃ per minute, keeping the temperature for 40 minutes after the temperature reaches 500 ℃, and then cooling to room temperature along with the furnace.

And obtaining the high-toughness coating reinforcing steel bar.

Example 2

Preparing a coating: taking 50 g of silicon dioxide, 75 g of silica, 50 g of quartz, 75 g of phosphorus pentoxide, 100 g of alumina, 20 g of sodium carbonate, 32 g of potassium carbonate, 37 g of calcium fluoride, 6 g of nickel sesquioxide, 2 g of cobalt monoxide and 3 g of cobaltous trioxide, uniformly mixing, grinding, and sieving the powder material with a 200-mesh sieve; adding 50 g of aluminum silicate fiber (diameter is 1-2 microns, length is 20-50 microns) into the sieved powder, and uniformly mixing for later use.

Coating: mixing the powder with absolute ethyl alcohol according to a mass ratio of 1.8: 1, mixing, stirring into an emulsion, shaking uniformly, dipping the treated steel bar in the slurry for 5 seconds, and taking out, wherein the thickness is controlled to be about 60 microns.

And (3) sintering: and (3) putting the sprayed steel bar into a high-temperature furnace, heating at the speed of 10 ℃ per minute, keeping the temperature for 15 minutes after the temperature reaches 700 ℃, and then cooling to room temperature along with the furnace.

And obtaining the high-toughness coating reinforcing steel bar.

Example 3

Preparing a coating: taking 125 g of quartz, 100 g of phosphorus pentoxide, 100 g of alumina, 15.5 g of sodium carbonate, 35 g of calcium fluoride, 40 g of boron oxide, 5.5 g of nickel monoxide and 4 g of cobaltous oxide, uniformly mixing, grinding, and sieving the powder material with a 200-mesh sieve; adding 50 g of basalt fiber (diameter of 2-5 microns and length of 50-80 microns) and 25 g of calcium carbonate fiber (diameter of 0.2-1 micron and length of 10-20 microns) into the sieved powder, and uniformly mixing for later use.

Coating: grounding the treated steel bar, uniformly coating the powder on the surface of the steel bar by using an electrostatic spray gun, wherein the electrostatic voltage is 65 kilovolt, the current is 35 microamperes, the gas output is 6.5 liters per minute, the distance between the gun mouth of the spray gun and the steel bar is 20 centimeters, and the thickness of the coating is controlled to be about 150 micrometers.

And (3) sintering: and (3) putting the sprayed steel bar into a high-temperature furnace, heating at the speed of 10 ℃ per minute, keeping the temperature for 20 minutes after the temperature reaches 650 ℃, and then cooling to room temperature along with the furnace.

And obtaining the high-toughness coating reinforcing steel bar.

Example 4

Preparing a coating: taking 100 g of silica, 50 g of quartz, 50 g of phosphorus pentoxide, 125 g of alumina, 50 g of potassium carbonate, 50 g of calcium fluoride, 50 g of boron oxide, 9 g of nickel monoxide, 3 g of cobalt monoxide and 3 g of nickel sesquioxide, uniformly mixing, and grinding to enable powder to pass through a 200-mesh sieve; adding 20 g of aluminum silicate fiber (diameter of 1-2 microns and length of 20-50 microns) into the sieved powder, and uniformly mixing for later use.

Coating: mixing the powder with absolute ethyl alcohol according to a mass ratio of 2.5: 1, mixing, stirring into an opaque state, shaking uniformly, dipping the treated steel bar in the slurry for 5 seconds, and taking out, wherein the thickness is controlled to be about 300 microns.

And (3) sintering: and (3) putting the sprayed steel bar into a high-temperature furnace, heating at the speed of 10 ℃ per minute, keeping the temperature for 15 minutes after the temperature reaches 800 ℃, and then cooling to room temperature along with the furnace.

And obtaining the high-toughness coating reinforcing steel bar.

Example 5

Preparing a coating: taking 125 g of silicon dioxide, 50 g of silica, 125 g of phosphorus pentoxide, 50 g of alumina, 10 g of sodium carbonate, 10 g of potassium carbonate, 40 g of calcium fluoride, 25 g of calcium oxide, 20 g of boron oxide, 2.5 g of nickel monoxide and 2.5 g of nickel sesquioxide, uniformly mixing, grinding, and sieving the powder material with a 200-mesh sieve; 40 g of calcium carbonate fiber (the diameter is 0.2-1 micron, the length is 10-20 microns) is added into the sieved powder and evenly mixed for standby.

Coating: mixing the powder with absolute ethyl alcohol according to a mass ratio of 3:1, mixing, stirring into an emulsion, shaking uniformly, dipping the treated steel bar in the slurry for 5 seconds, and taking out, wherein the thickness is controlled to be about 500 microns.

And (3) sintering: and (3) putting the sprayed steel bar into a high-temperature furnace, heating at the speed of 10 ℃ per minute, keeping the temperature for 25 minutes after the temperature reaches 600 ℃, and then cooling to room temperature along with the furnace.

And obtaining the high-toughness coating reinforcing steel bar.

Comparative example 6

Preparing a coating: 150 g of silicon dioxide, 100 g of phosphorus pentoxide, 75 g of aluminum oxide, 32.5 g of sodium carbonate, 6 g of potassium carbonate, 50 g of calcium fluoride, 25 g of boron oxide, 3 g of nickel monoxide and 8.5 g of cobalt monoxide are uniformly mixed and ground, and the powder is sieved by a 200-mesh sieve for later use.

And obtaining the high-toughness coating reinforcing steel bar.

Comparative example 7

Preparing a coating: taking 150 g of silicon dioxide, 100 g of phosphorus pentoxide, 75 g of aluminum oxide, 3 g of nickel monoxide and 8.5 g of cobalt monoxide, uniformly mixing, and grinding to enable powder to pass through a 200-mesh sieve; after being uniformly mixed, the mixture is ground, and the powder is sieved by a 200-mesh sieve; adding 25 g of basalt fiber (diameter of 1-2 microns and length of 20-50 microns) and 25 g of aluminum silicate fiber (diameter of 1-2 microns and length of 20-50 microns) into the sieved powder, and uniformly mixing for later use.

And obtaining the high-toughness coating reinforcing steel bar.

In order to verify the effect of the present invention for metal corrosion prevention, the following test was performed.

(1) Coating microstructure

The results of examples 1-5 were similar when the coating was observed by Scanning Electron Microscopy (SEM), and are therefore described only with respect to the results of example 1 (shown in FIG. 1); an electron micrograph of comparative example 7 is shown in FIG. 2. As can be seen from FIGS. 1 and 2, in example 1, the inner layer had a large number of closed pores with a pore diameter of 1/30-1/10 coating thickness, and the outer layer was relatively dense and had few pores. In the coating of comparative example 7, the raw material was not completely melted, a large number of large diameter holes were formed, and the hole diameter reached 3/4 coating thickness, which directly affected the toughness and corrosion resistance of the coating.

The porosity calculated from the area of the planar pores according to the microstructure of the coating observed by a scanning electron microscope is shown in the following table.

Table 1: closed porosity of the coating

As can be seen from Table 1, the porosity of the porous inner layer and the porosity of the dense outer layer of examples 1-5 are between 2% and 15% and between 0% and 2%. From comparative example 6 it can be seen that the influence of the fibres on the porosity is insignificant. Comparative example 7 since the coating was not completely melted without the modifier, many large diameter pores were formed, and the porosity of both the inner layer and the outer layer was as high as 30% or more, the modifier plays a decisive role in the pore size and the gradient distribution of the pores.

(2) Coefficient of thermal expansion of coating

The measurement of the thermal expansion coefficient is carried out according to GB/T25144-.

Table 2: coefficient of thermal expansion of the coating (20 ℃ C.)

Table 3: coefficient of thermal expansion of commonly used metals (20 ℃ C.)

As can be seen from tables 2 and 3, the different components have an effect on the coefficient of thermal expansion of the coating, but no significant difference was found between comparative examples 6, 7 and examples 1 to 5. The thermal expansion coefficients of the coating of the invention are all 8.5 multiplied by 10^-6/℃-11.4×10^-6Between/° c, the coefficient of thermal expansion is slightly less than that of some commonly used metals, but not so much that the coating cracks during firing due to the difference in the coefficient of thermal expansion of the coating and the substrate. At the same time, a slightly smaller coefficient of thermal expansion may beThe coating is stressed after being cooled, and the tensile cracking resistance of the coating is further improved. Therefore, the coating has good thermal expansion coefficient matching with common metal, and can meet the requirements of the common metal.

(3) Cracking strain of coating

Because the coating has better toughness, the steel bars used in the cracking test are HRB600 threaded steel bars so as to have enough elastic sections until the coating cracks. It is anticipated that the experimental conclusions in this section apply equally to ordinary steel.

Tensile tests were performed on 7 coatings described in examples 1-5 and comparative examples 6-7. The total length of the sample was 300 mm, 70 mm each at both ends was used for clamping, and the coating area was 160 mm in the middle. Each group of 3 samples is slowly loaded by a universal mechanical testing machine, whether cracks are generated or not is checked by a microscope, and a strain value corresponding to the cracking is obtained by an extensometer.

Table 4: cracking strain value of coating

Table 5: design value of tensile strength and corresponding strain of common steel bar (wherein HRB500(E), HRBF500(E) and HRB600 are high-strength steel bars)

As can be seen from Table 4, the cracking strain of the coatings of examples 1-5 can reach 2800-3000 microstrain, which can satisfy the use requirements of the steel bars listed in Table 5 under the level of 600 MPa. As can be seen from comparative examples 6 and 7, the cracking strain was much smaller than that of examples 1 to 5, although the cracking strain was also about 2000 microstrain. The toughness of the coatings of examples 1-5 with a gradient pore structure and double fiber toughening is greatly better than that of comparative examples 6 and 7 with a gradient pore structure and single fiber. Therefore, in order to meet the use requirement of the 600 MPa-grade steel bar, the fiber and the modifier must exist simultaneously to generate a synergistic effect, the fiber can play a role in dissipating energy and limiting crack development, and the modifier can improve the pore structure and play a role in adjusting the pore distribution and the pore size.

(4) Adhesion of coatings

For the 7 coatings described in examples 1-5 and comparative examples 6 and 7, reference is made to GB/T5210-. Three test pieces per set. The calculation method of the adhesive force comprises the following steps: adhesion (MPa) is breaking force (N)/area of test column (mm)²)。

Table 6: bond strength of coated reinforcing bar

As can be seen from Table 6, the bonding strength between the coating and the base material reaches more than 15MPa, and the lack of the modifier (comparative example 7) causes the pores to be obviously increased, the strength of the coating to be reduced, and further causes the adhesion of the coating to be reduced. The adhesion of comparative example 6, which lacks fibers, is also significantly reduced because the fibers can simultaneously perform a reinforcing function, and the coating layer lacking fibers is liable to internal damage of the coating layer, thereby reducing the adhesion. It can be concluded that the coating adhesion of the coatings of examples 1-5, which are doubly toughened with a gradient pore structure and fibers, is better than that of comparative examples 6, 7, in which a gradient pore structure and fibers are present alone.

(5) Corrosion resistance of coating

The corrosion resistance of examples 1-3 of the present invention, as well as the uncoated samples, was tested. The test method is carried out according to the standard GB/T6458-86 neutral salt spray test (NSS) for metal coatings. The test temperature is 35 +/-2 ℃, and the used corrosion solution is 5% sodium chloride solution. After 3000 hours of etching, the results are shown in FIG. 3: the sample without the coating is seriously corroded, the height of a corrosion product can reach 2-8 mm, and the mass is increased by 13.9%; in the examples 1 to 3, no obvious corrosion phenomenon or only slight corrosion occurs, the quality is basically kept unchanged, and the phenomena of stripping, cracking and the like do not occur on the coating. It can be shown that the coating according to the invention has excellent corrosion resistance.

The foregoing detailed description is intended to illustrate and not limit the invention, which is intended to be within the spirit and scope of the appended claims, and any changes and modifications that fall within the true spirit and scope of the invention are intended to be covered by the following claims.

Claims

1. An inorganic anti-corrosion coating for high-strength metal, which is characterized in that: the coating is formed on the surface of the high-strength metal by sintering the coating at the high temperature of 500-800 ℃; the coating comprises 25-35 parts of silicon oxide, 10-25 parts of phosphorus pentoxide, 10-25 parts of aluminum oxide, 2-15 parts of fibers, 15-30 parts of a modifier and 1-3 parts of an anti-cracking agent; the fiber is one or a combination of two or three of aluminum silicate fiber, basalt fiber and calcium carbonate fiber; a plurality of closed holes with the diameter of 1/30-1/10 are distributed in the coating, the number of the closed holes is reduced from inside to outside, the porosity of the inner layer of the multi-hole close to the surface of the high-strength metal is 2-15%, and the porosity of the compact outer layer far away from the surface of the high-strength metal is 0-2%; the length of the fiber is 10-80 microns, and the diameter of the fiber is 0.2-5 microns; the modifier is one or more of sodium carbonate, potassium carbonate, calcium fluoride, calcium oxide and boron oxide.

2. The inorganic anticorrosive coating for high-strength metal according to claim 1, characterized in that: the silicon-oxygen compound is one or the combination of two or three of silicon dioxide, quartz and silica.

3. The inorganic anticorrosive coating for high-strength metal according to claim 1, characterized in that: the anti-cracking agent is one or more of nickel monoxide, nickel sesquioxide, cobalt monoxide and cobalt sesquioxide.

4. The inorganic anticorrosive coating for high-strength metal according to claim 1, characterized in that: the coating is powder or gel formed by dissolving the powder coating in absolute ethyl alcohol, wherein the mass ratio of the coating to the absolute ethyl alcohol is 1.8-3: 1.

5. The inorganic anticorrosive coating for high-strength metal according to claim 4, characterized in that: and sieving the powdery paint by a 200-mesh sieve.

6. The inorganic anticorrosive coating for high-strength metal according to claim 1, characterized in that: the coating thickness is 50-500 microns.

7. The inorganic anticorrosive coating for high-strength metal according to claim 1, characterized in that: the coefficient of thermal expansion of the coating is 8.5 x 10^-6/℃-11.4×10^-6/℃。

8. The inorganic anticorrosive coating for high-strength metal according to claim 1, characterized in that: the high-strength metal is a metal with the strain less than or equal to 2800 micro-strain in use.