Preparation method of energy-saving zinc-aluminum-magnesium alloy coating

Abstract

The invention relates to a preparation method of an energy-saving zinc-aluminum-magnesium alloy coating, which comprises the following steps: sequentially depositing a pure magnesium coating with the average thickness of 10-50 microns, a pure zinc coating with the average thickness of 200-300 microns and a pure aluminum coating with the average thickness of 50-100 microns on the surface of a pretreated cold-roll steel plate by adopting a cold spraying technology to obtain a coated steel plate; and then the coated steel plate is subjected to heat treatment at the temperature of 250-450 DEG C, zinc powder particles in the middle zinc coating start to diffuse at the interface after reaching the recrystallization temperature, crystal grains at the interface are nucleated and grown again, and finally zinc-magnesium, zinc-aluminum and zinc-aluminum-magnesium alloy coatings are formed. The technological process is simple and efficient, and the interface bonding strength of the prepared zinc-aluminum-magnesium alloy coating is good.

Description

Technical Field

[0001] The invention relates to the field of metal material processing, and in particular to a method for preparing an energy-saving zinc-aluminum-magnesium alloy coating. Background Art

[0002] In recent years, the research on zinc-aluminum-magnesium alloy coatings has continued to grow due to the good anti-scratch and anti-corrosion performance, corrosion resistance, notch corrosion resistance and electric welding performance of galvanized aluminum-magnesium steel sheets. At the same time, the demand for galvanized aluminum-magnesium steel sheets is also on the rise. Due to its good corrosion resistance and edge protection performance, it is widely used in photovoltaics, automobiles, home appliances and equipment manufacturing.

[0003] The traditional preparation of zinc-aluminum-magnesium alloy coatings generally adopts the hot-dip coating method. The process generally first casts zinc, aluminum, magnesium and other metals into alloy ingots through alloy melting, then melts the alloy ingots into alloy liquid again, and prepares the hot-dip zinc-aluminum-magnesium alloy coating on the surface of the steel. Relatively speaking, this coating preparation method has complicated procedures, not only has high requirements on the quality of upstream alloy ingots, but also requires the alloy ingots to be melted again in the downstream coating preparation process, which consumes a lot of energy and increases carbon emissions. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a simple, efficient and energy-saving method for preparing a zinc-aluminum-magnesium alloy coating.

[0005] In order to solve the above problems, the present invention discloses a method for preparing an energy-saving zinc-aluminum-magnesium alloy coating, which is characterized in that: the method refers to first using cold spraying technology to deposit a pure magnesium coating with an average thickness of 10-50um, a pure zinc coating with an average thickness of 200-300um and a pure aluminum coating with an average thickness of 50-100um on the surface of a pretreated cold-rolled steel plate in sequence to obtain a coated steel plate; then heat-treating the coated steel plate at 250°C-450°C so that the zinc powder particles in the middle zinc coating layer reach the recrystallization temperature and begin to diffuse at the interface, and the grains re-nucleate and grow at the interface to finally form zinc-magnesium, zinc-aluminum and zinc-aluminum-magnesium alloy coatings.

[0006] The pre-treated cold-rolled steel sheet refers to the cold-rolled steel sheet surface being pre-treated by sandblasting.

[0007] The pure magnesium coating is formed by deformation and accumulation of magnesium spherical powder particles with an average particle size of 5 to 15 μm, wherein the spherical magnesium powder is embedded in the surface layer of the pretreated cold-rolled steel plate.

[0008] The pure zinc coating is formed by deformation and accumulation of zinc spherical powder particles with an average particle size of 10-15 μm, wherein the spherical zinc powder is embedded in the surface layer of the pure magnesium coating.

[0009] The pure aluminum coating is formed by deformation and accumulation of aluminum spherical powder particles with an average particle size of 5 to 15 μm, wherein the spherical aluminum powder is embedded in the surface layer of the pure zinc coating.

[0010] The cold spraying conditions refer to the use of low-pressure cold spraying equipment, a preheating temperature of 100~300°C, a spraying distance of 12~20mm, a spraying pressure of 0.8~1.2MPa, and a spraying gas of high-purity nitrogen. The content ratio of the cold-sprayed magnesium, zinc and aluminum coatings is controlled by the amount of magnesium, zinc and aluminum powder particles.

[0011] During the cold spraying, the preheating temperature is 200-300° C., the spraying distance is 12-15 mm, and the spraying pressure is 1-1.2 MPa.

[0012] The heat treatment process includes heating, heat preservation and cooling processes, wherein: the heating rate is 5-10°C / min, and the heat preservation time is 20-40min.

[0013] Compared with the prior art, the present invention has the following advantages: 1. The traditional zinc-aluminum-magnesium alloy ingot smelting process, due to the high alloy smelting temperature, causes a certain degree of burning and oxidation of easily oxidized aluminum and magnesium elements, accompanied by the generation of slag, and the whole process is difficult to control the element content in the zinc-aluminum-magnesium alloy. The present invention uses cold spraying technology to prepare magnesium, zinc and aluminum coatings in the early stage, where the element content of magnesium, zinc and aluminum can be accurately controlled by the quality of each powder particle, and the working temperature of the entire cold spraying process is 100~300℃, which only softens and accelerates the metal powder particles, and can avoid the oxidation of the metal powder particles.

[0014] 2. The present invention adopts a metal heat treatment method to replace the process of melting zinc-aluminum-magnesium alloy ingots in the traditional hot-dip plating process. Since the heat treatment temperature is relatively low, it can greatly reduce energy consumption and carbon emissions. At the same time, during the heat treatment, the powder particles in the intermediate zinc coating have a relatively low melting point, and preferentially reach the recrystallization temperature in the multi-layer coating, and diffuse and nucleate at the interface of the zinc-magnesium and zinc-aluminum coatings. When the temperature reaches a certain critical point, the interface of the zinc-magnesium and zinc-aluminum coatings begins to alloy, and finally form zinc-aluminum, zinc-magnesium and zinc-aluminum-magnesium alloy coatings through metallurgical bonding.

[0015] 3. The process flow of the present invention is simple and efficient, and the zinc-aluminum-magnesium alloy coating prepared by the method of the present invention has good interface bonding strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0017] Figure 1 This is a schematic diagram of cold spraying zinc, aluminum and magnesium in the present invention.

[0018] Figure 2 Schematic diagram of the coating interface after heat treatment in the present invention (left: aluminum-magnesium interface; right: aluminum-zinc interface).

[0019] In the figure: 1—spray nozzle; 2—cold spray powder particles; 3—pure aluminum coating; 4—pure zinc coating; 5—pure magnesium coating; 6—pretreated cold rolled steel sheet. DETAILED DESCRIPTION

[0020] A method for preparing an energy-saving zinc-aluminum-magnesium alloy coating, the method first uses a cold spraying technology to sequentially deposit a pure magnesium coating 5 with an average thickness of 10-50 um, a pure zinc coating 4 with an average thickness of 200-300 um, and a pure aluminum coating 3 with an average thickness of 50-100 um on the surface of a pre-treated cold-rolled steel plate 6 to obtain a coated steel plate, such as Figure 1 As shown. The cold spray powder particles 2 reach supersonic speed under the acceleration of the nozzle 1. After the high-speed cold spray powder particles hit the substrate surface, "adiabatic shear instability" is formed under high stress and high strain rate, and mechanical bite and metallurgical bonding are formed at the coating interface, and the coating interface is well bonded. Then the coated steel plate is placed in a muffle furnace for heat treatment at 250℃~450℃. The heat treatment process includes heating, insulation and cooling processes, wherein: the heating rate is 5~10℃ / min, and the insulation time is 20~40min. After the heat treatment, the zinc powder particles in the intermediate zinc coating layer reach the recrystallization temperature and begin to diffuse at the interface. The grains re-nucleate and grow at the interface, and finally form zinc-magnesium, zinc-aluminum and zinc-aluminum-magnesium alloy coatings.

[0021] The pre-treated cold-rolled steel plate 6 refers to the cold-rolled steel plate surface being pre-treated by sandblasting to remove oxide scale and stains on the surface of the steel plate.

[0022] The pure magnesium coating 5 is formed by deformation and accumulation of magnesium spherical powder particles with an average particle size of 5 to 15 μm, wherein the spherical magnesium powder is embedded in the surface layer of the pre-treated cold-rolled steel plate 6 .

[0023] The pure zinc coating 4 is formed by deformation and accumulation of zinc spherical powder particles with an average particle size of 10-15 um, wherein the spherical zinc powder is embedded in the surface layer of the pure magnesium coating 5 .

[0024] The pure aluminum coating 3 is formed by deformation and accumulation of aluminum spherical powder particles with an average particle size of 5 to 15 μm, wherein the spherical aluminum powder is embedded in the surface layer of the pure zinc coating 4 .

[0025] The conditions for cold spraying refer to the use of a low-pressure cold spraying equipment including a nozzle 1 and a nozzle; before cold spraying, the cold spraying equipment is preheated, and the preheating temperature is 100~300℃, preferably 200~300℃; during cold spraying, the metal powder particles are preheated in the nozzle and continuously accelerated through the nozzle; the spraying distance is 12~20mm, preferably 12~15mm; the spraying pressure is 0.8~1.2MPa, preferably 1~1.2MPa; the spraying gas is high-purity nitrogen, and the content ratio of the cold-sprayed magnesium, zinc and aluminum coatings is controlled by the amount of magnesium, zinc and aluminum powder particles. Example

[0027] Spherical zinc powder particles (average particle size 10um), spherical magnesium powder particles (5um), and spherical aluminum powder particles (average particle size 5um) were selected as raw materials for cold spraying. Cold-rolled steel plates were used as substrate materials. The surface of the cold-rolled steel plates was sandblasted to remove oil stains and oxide scale on the surface of the steel plates. Low-pressure cold spray equipment was used for spraying, with a spraying distance of 12mm, a spraying pressure of 1.2MPa, a spraying gas of high-purity nitrogen, and a spraying temperature of 300℃. Magnesium, zinc, and aluminum coatings were prepared on the surface of the cold-rolled steel plates in sequence, with an average thickness of 50um for the magnesium coating, 300um for the zinc coating, and 100um for the aluminum coating. The deposited coated steel plates were then placed at 350℃ for heat treatment. After keeping warm for 30 minutes, they were taken out of the furnace and cooled with air.

[0028] Since zinc has the lowest melting point among the three elements of zinc, aluminum and magnesium, it reaches the recrystallization temperature first during the heat treatment process. When the critical nucleation and crystallization temperature is reached, the zinc metal particles in the intermediate zinc coating begin to diffuse along the interface to the pure aluminum and pure magnesium coatings, and gradually form zinc-aluminum and zinc-magnesium diffusion layers at the interface. After 30 minutes of heat preservation, as the thickness of the diffusion layer increases, a zinc-aluminum-magnesium alloy coating is formed. Figure 2 As shown, it can be found that the zinc powder particles in the middle coating diffuse into the aluminum and magnesium coatings to different degrees, forming an alloy diffusion layer.

Claims

1. A method for preparing an energy-saving zinc-aluminum-magnesium alloy coating, characterized in that: The method comprises firstly using cold spraying technology to sequentially deposit a pure magnesium coating (5) with an average thickness of 10 to 50 um, a pure zinc coating (4) with an average thickness of 200 to 300 um, and a pure aluminum coating (3) with an average thickness of 50 to 100 um on the surface of a pre-treated cold-rolled steel sheet (6) to obtain a coated steel sheet; and then heat treating the coated steel sheet at 250° C. to 450° C. so that the zinc powder particles in the intermediate zinc coating layer reach the recrystallization temperature and begin to diffuse at the interface, and the grains at the interface re-nucleate and grow, and finally form a zinc-magnesium, zinc-aluminum, and zinc-aluminum-magnesium alloy coating.

2. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that: The pre-treated cold-rolled steel sheet (6) refers to the cold-rolled steel sheet surface being pre-treated by sandblasting.

3. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that: The pure magnesium coating (5) is formed by deformation and accumulation of magnesium spherical powder particles with an average particle size of 5 to 15 μm, wherein the spherical magnesium powder is embedded in the surface layer of the pre-treated cold-rolled steel plate (6).

4. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that: The pure zinc coating (4) is formed by deformation and accumulation of zinc spherical powder particles with an average particle size of 10 to 15 μm, wherein the spherical zinc powder is embedded in the surface layer of the pure magnesium coating (5).

5. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that: The pure aluminum coating (3) is formed by deformation and accumulation of aluminum spherical powder particles with an average particle size of 5 to 15 μm, wherein the spherical aluminum powder is embedded in the surface layer of the pure zinc coating (5).

6. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that: The cold spraying conditions refer to the use of low-pressure cold spraying equipment, a preheating temperature of 100~300°C, a spraying distance of 12~20mm, a spraying pressure of 0.8~1.2MPa, and a spraying gas of high-purity nitrogen. The content ratio of the cold-sprayed magnesium, zinc and aluminum coatings is controlled by the amount of magnesium, zinc and aluminum powder particles.

7. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 6, characterized in that: During the cold spraying, the preheating temperature is 200-300° C., the spraying distance is 12-15 mm, and the spraying pressure is 1-1.2 MPa.

8. The method for preparing an energy-saving zinc-aluminum-magnesium alloy coating according to claim 1, characterized in that: The heat treatment process includes heating, heat preservation and cooling processes, wherein: the heating rate is 5-10°C / min, and the heat preservation time is 20-40min.

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