CN109023197A - A kind of preparation method of the zinc-aluminium Mg Alloy Coating steel plate of environmental protection - Google Patents

Abstract

The present invention is a kind of preparation method of the zinc-aluminium Mg Alloy Coating steel plate of environmental protection.This method pre-processes hot-rolled mild steel sheet using mechanical derusting and electrolytic degreasing, is heated by HF induction heating apparatus to steel plate, in N₂‑H₂The steel plate pre-processed is restored to obtain the surface state of suitable hot-dip in mixed atmosphere.In N₂Cooling metal sheets in atmosphere control immersion plating front spring temperature, the immersion plating in zinc-aluminum-magnesium alloy electroplating bath.Subsequent cooling metal sheets in air.Harm the invention avoids acid pickling and rust removing during conventional hot-dip and the polluter for helping plating process to generate to human body and environment, meets increasingly harsh environmental requirement, and improve quality of coating, has broad application prospects.

Description

A kind of preparation method of environment-friendly zinc-aluminum-magnesium alloy coated steel plate

technical field

The invention relates to the technical field of hot-dip galvanizing, in particular to an environment-friendly production method of a zinc-aluminum-magnesium alloy coated steel plate.

Background technique

Iron and steel materials are the metal materials with the largest output and widest uses in the world. They have many advantages such as good toughness, high strength, high hardness, and high production economy. However, during use, steel materials are exposed to humid air and seawater for a long time, or are often exposed to complex working conditions such as strong corrosiveness and industrial high temperature, so corrosion is prone to occur. Anodic protection, cathodic protection, addition of inhibitors, protective coatings and metallic coatings are all commonly used methods of protection. Zinc coatings are widely used for the protection of steel. In this case, the reactive zinc metal corrodes preferentially over the steel substrate through cathodic reactions, preventing anodic corrosion of the steel. The different types of zinc coatings include: hot-dip galvanizing (batch or continuous), electroplating, metallization (zinc spraying), mechanical electroplating, and zinc-rich coatings. Among them, the hot-dip galvanizing process provides a unique combination of excellent properties such as high strength, excellent formability, light weight, good corrosion resistance, low cost and recyclability.

For hot-dip galvanizing, different industries have different needs. For example, the automotive industry needs zinc coatings with light weight and high surface quality, the home appliance industry needs zinc coatings that can shield electromagnetic noise and heat radiation, and the construction industry needs corrosion-resistant zinc coatings. Different needs have prompted the development of different types of zinc layers. In addition to traditional galvanized steel sheets (Zn-0.2% Al), other products include galvannealed (Zn-～10% Fe), galvalume (55% Al-43.5% Zn-1.5 %Si) and galfan (Zn-5%Al) and so on. Adding Al and Mg to the zinc solution can further improve the corrosion resistance of the alloy. Japanese researchers have developed different zinc-aluminum-magnesium alloy systems, such as ZAM (Zn-6%Al-3%Mg), DymaZinc (Zn-0.5%Mg ), SuperDyma (Zn-11%Al-3%Mg-0.2%Si), etc. have been widely used in Japan.

Due to the lag in basic theory and application, there is a big gap between domestic products and the international advanced level in terms of quality control, etc., and the country mainly relies on imports, and the price is expensive. Even if the zinc, aluminum and magnesium coating has excellent performance, it cannot be obtained. Widely promote and apply.

The hot-dip galvanizing process is mainly divided into the solvent method and the reduction method. The solvent method is a traditional hot-dip galvanizing method. Its process flow is simple, it has low requirements on the workpiece, and the strength loss is small, but the solvent method is used to hot-dip galvanized aluminum-magnesium alloys. , high energy consumption, and a series of problems such as unstable coating quality, while the reduction method hot-dip galvanized aluminum-magnesium alloy has the characteristics of closed production, continuous, and high efficiency compared with the solvent method, and it has relatively good control over the coating quality and has a high It has market advantages, but it has high requirements on technology, and it is only widely used in a few countries such as Japan, with a great market prospect.

At present, there are many studies on zinc-aluminum-magnesium alloys, but most of them are basic discussions on the microstructure and corrosion resistance of zinc-aluminum-magnesium alloys. There are few studies on the effect of reduction process on hot-dip galvanized aluminum-magnesium alloys. Therefore, it is of great theoretical and practical significance to study the reduction hot-dip galvanized aluminum-magnesium alloy process, formulate efficient, environmentally friendly and reasonable process parameters, and improve the quality of the alloy coating.

CN104711502A "A corrosion-resistant zinc-aluminum-magnesium rare earth alloy coating and its preparation and hot-dip plating method" discloses that the steel plate is washed with alkali, pickled, and water, and the plating flux composition is ZnCl2 with a concentration of 250-280g/L. 40-60g/L NH4Cl, 40-60g/L AlCl3, 30-50g/L LiCl, 4-8g/L emulsifier OP-10 and solvent water solution After 1-2min, at 600-620°C, the composition is 3-9wt% of Al content, 0.03-0.09wt% of Mg content, 0.01-0.15wt% of rare earth content, and immersion plating in a plating solution with the balance of zinc for 10 ~20s to obtain a corrosion-resistant zinc-aluminum-magnesium rare earth alloy coating.

CN1632157A "Production method of zinc-aluminum-magnesium alloy coated steel with good corrosion resistance and zinc-aluminum-magnesium alloy coated steel" discloses that the steel plate is degreased, washed, pickled, coated with solvent, dried, hot dipped, and air cooled. Galvanized aluminum magnesium alloy. The solvent is an aqueous solution, the chemical composition is ZnCl2 with a concentration of 200-1000g/L, NH4Cl with a concentration of 0-200g/L, KCl with a concentration of 0-100g/L, NaCl with a concentration of 0-100g/L, and a concentration of 0-100g/L rare earth chloride, the pH of the solvent is 3-4. At 450-580°C, the composition is Al content of 2.5-20wt%, Mg content of 1.5-4.5wt%, rare earth content of 0.01-0.3wt%, and the balance is zinc in the plating solution for 2-300s, and the resistance is obtained. Zinc-aluminum-magnesium alloy coating with good corrosion resistance.

The above patents all use the solvent method in the process of hot-dip galvanizing aluminum-magnesium alloys, that is, the steel plate is pickled, derusted and galvanized before hot-dip. During the treatment process, waste acid and other harmful substances will be produced, which is harmful to the human body and the environment. cause harm. Therefore, it is necessary to find an environmentally friendly, efficient and stable process method for hot-dip galvanizing aluminum-magnesium alloys, and obtain high-quality alloy coatings, which meet the requirements of sustainable development and environmental protection.

Contents of the invention

The object of the present invention is to provide an environment-friendly preparation method of zinc-aluminum-magnesium alloy coated steel sheet to address the shortcomings in the current technology. In the steps of mechanical derusting, electrolytic degreasing, N ₂ -H ₂ mixed atmosphere reduction of steel plate, etc., the method realizes the replacement of traditional polluted pickling and flux fluxing process through ingenious production sequence and related parameters. The invention can avoid the generation of polluting substances such as waste acid and waste gas which are harmful to the human body and the environment during the production process, and obtain an alloy coating with a smooth surface, few defects, and good bonding force with the steel plate.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A method for preparing an environmentally friendly zinc-aluminum-magnesium alloy coated steel plate comprises the following steps:

(1) Alloy melting: one of the following two methods:

Method 1: Take zinc ingots, magnesium ingots, aluminum ingots and aluminum foil according to the ratio of Al: 6wt%, Mg: 3wt%, and the balance is Zn; heat the zinc to 500°C to 550°C to completely melt, and then add aluminum in sequence Put the block into the zinc liquid until it melts, stir and then add the magnesium block wrapped in aluminum foil until it melts; then raise the temperature of the alloy liquid to 560 ° C ~ 600 ° C, stir once every 30 minutes, keep it warm for 5 ~ 10 hours, and set aside;

Or, method 2: Melt the ZAM alloy, then heat it to 560°C-600°C, stir once every 30min, keep it warm for 5-10h, and set aside;

(2) Mechanical rust removal: the hot-rolled steel plate is polished and derusted by a continuous derusting machine;

(3) Electrolytic degreasing: prepare a NaOH solution with a mass fraction of 5-10wt%, the solution temperature is 40-80°C, a DC stabilized power supply is used to output the voltage and current, the steel plate to be cleaned is used as the cathode, graphite is used as the anode material, and the current density is adjusted to 3A/dm2～6A/dm2, cleaning time 5～20min, after cleaning, wash with water and dry;

(4) Steel plate reduction: place the steel plate in a N ₂ -H ₂ mixed atmosphere, where the H ₂ content is 1vol% to 40vol%, and heat the steel plate to 800-850°C by high-frequency induction heating equipment, and perform reduction in the atmosphere ;The frequency of high-frequency induction heating is 220kHz, the heating power is 1.4-1.7kW, and the reduction time in the atmosphere is 10-60s;

(5) Adjust the temperature of the steel plate before plating: cool the steel plate after reduction in _N2 atmosphere, so that the temperature of the steel plate is reduced to 400-700 °C;

(6) Hot-dip galvanized aluminum-magnesium alloy: immerse the steel plate obtained in the previous step into the alloy solution in step (1), the dipping time is 5-60s, the temperature of the plating solution is 380-550°C, and air-cool after plating. Finally, an environmentally friendly zinc-aluminum-magnesium alloy coated steel plate is obtained.

The hot-rolled steel plate is preferably Q235 steel plate.

The beneficial effects of the present invention are:

At present, most of the hot-dip plating uses pickling to remove rust. Among other methods, not only the process is complicated, but also the requirements for equipment are high, and the requirements for steel plates are also very strict. The invention adopts the steps of mechanical derusting, electrolytic degreasing, N ₂ -H ₂ mixed atmosphere to reduce the steel plate, etc., instead of the traditional polluted pickling and fluxing process, avoiding the pollution caused by the generation of waste acid and waste gas, reducing the The harm to the human body and the environment during the production process is avoided, and the quality of the coating obtained after hot-dip plating is good. As shown in Figure 1, Example 3, the coating has a smooth surface, no missing plating, and no obvious zinc tumors. The structure of the coating is uniform and dense, and it is well combined with the steel substrate. As shown in Example 3 of Figure 3, the cross section of the coating is uniform and straight, and the structure is stable, which ensures the stable combination of the coating and the substrate.

Description of drawings

Fig. 1 is a macroscopic photo of the hot-dip galvanized aluminum-magnesium alloy coating in Example 3 of the present invention.

Fig. 2 is the surface XRD spectrum of the hot-dip galvanized aluminum-magnesium alloy coating in Example 3 of the present invention.

Fig. 3 is a cross-sectional SEM picture of the hot-dip galvanized aluminum-magnesium alloy coating in Example 3 of the present invention.

Fig. 4 is a cross-sectional SEM picture of the hot-dip galvanized aluminum-magnesium alloy coating in Example 5 of the present invention.

Detailed ways

The preparation method of an environment-friendly zinc-aluminum-magnesium alloy coated steel sheet according to the present invention will be further described below in conjunction with the accompanying drawings and specific examples.

The ZAM zinc-magnesium-aluminum alloy involved in the present invention is a known material, which can be obtained commercially or through preparation.

The purity of the zinc ingot, magnesium ingot, aluminum ingot and aluminum foil involved in the present invention are respectively 99.97%, 99.94%, 99.65% and 99.72%.

Example 1

The invention discloses a preparation method of an environment-friendly zinc-aluminum-magnesium alloy coated steel plate.

Take zinc ingot, magnesium ingot, aluminum ingot and aluminum foil according to the ratio of Al: 6wt%, Mg: 3wt%, and the balance is Zn (the quality of aluminum foil is included in the content of aluminum). Heat the zinc to 500°C to completely melt, weigh the aluminum block, press the aluminum block into the molten zinc solution with a graphite rod until it is completely melted, and stir. Weigh the magnesium block, wrap it with aluminum foil, and press it into the molten zinc solution with a graphite rod until it is completely melted to reduce oxidation and ablation loss. Raise the temperature of the alloy solution to 560°C, stir once every 30 minutes, keep warm for 5 hours, and set aside.

Mechanical derusting: adopt continuous derusting machine to hot-rolled Q235 steel plate (the specific material of Q235 steel plate is C: 0.12～0.2wt%, Mn: 0.3～0.65wt%, Si: 0.17～0.3wt%, S: ≤0.045wt%) , P: ≤ 0.035wt%, Cr: ≤ 0.25wt%, Ni: ≤ 0.25wt%, and the balance is Fe. The following examples are the same) for grinding and derusting to clean up the surface corrosion of the steel plate, improve subsequent reduction, and hot-dip plating Productivity.

Perform electrolytic degreasing on the Q235 steel plate after mechanical derusting, prepare 5wt% NaOH solution, the solution temperature is 60°C, and use a DC stabilized power supply with a model of WYJ-0-15V5A to output voltage and current. The steel plate to be cleaned is used as the cathode, and the graphite is used as the anode material, the current density is adjusted to 3A/dm2, the cleaning time is 5min, and then washed with water and dried.

The steel plate is heated to 800°C by the high-frequency induction heating equipment model SPG-06A-II, and the reduction is carried out in the atmosphere. The frequency of high-frequency induction heating is 220kHz, and the heating power is 1.4kW. The reduction atmosphere is 0.1vol% H ₂ -N ₂ , and the reduction time is 40s; the reduced steel plate is cooled in the N ₂ atmosphere, and the temperature change of the steel plate is detected in real time by an infrared thermometer, so that the temperature of the steel plate before hot-dip galvanizing is 400°C. Set the temperature of the plating solution to 380°C, immerse the steel plate obtained above into the alloy plating solution for 5 seconds, air-cool after plating, and finally obtain an environmentally friendly zinc-aluminum-magnesium alloy coated steel plate.

The surface of the coating is smooth, with a small amount of missing plating. After the bending test, the coating has a small amount of peeling off, and the coating is poorly bonded to the steel plate. It shows that the _H2 content in the atmosphere is low, and the residual oxides on the surface of the Q235 steel plate cannot be effectively reduced, resulting in poor bonding between the coating and the steel plate, and a small amount of missing plating.

Example 2

The invention discloses a preparation method of an environment-friendly zinc-aluminum-magnesium alloy coated steel plate.

Zinc ingots, magnesium ingots, aluminum ingots and aluminum foils are taken according to the ratio of Al: 6wt%, Mg: 3wt%, and the balance is Zn. Heat the zinc to 520°C to completely melt, weigh the aluminum block, press the aluminum block into the molten zinc solution with a graphite rod until it is completely melted, and stir. Weigh the magnesium block, wrap it with aluminum foil, and press it into the molten zinc solution with a graphite rod until it is completely melted to reduce oxidation and ablation loss. Raise the temperature of the alloy solution to 580°C, stir once every 30 minutes, keep warm for 8 hours, and set aside.

Mechanical descaling: The hot-rolled Q235 steel plate is polished and derusted by a continuous descaling machine to clean the surface rust of the steel plate and improve the production efficiency of subsequent reduction and hot-dip plating.

Perform electrolytic degreasing on the Q235 steel plate after mechanical derusting, prepare 5wt% NaOH solution, the temperature of the solution is 40°C, and the output voltage and current of the DC stabilized power supply with the model WYJ-0～15V5A are used. The steel plate to be cleaned is used as the cathode, and the graphite is used as the anode material, the current density is adjusted to 3A/dm2, the cleaning time is 10min, and then washed with water and dried.

The steel plate is heated to 830°C by the high-frequency induction heating equipment model SPG-06A-II, and the reduction is carried out in the atmosphere. The frequency of high-frequency induction heating is 220kHz, and the heating power is 1.5kW. The reduction atmosphere is 10vol% H ₂ -N ₂ , the reduction time is 20s, the steel plate after reduction is cooled in the N ₂ atmosphere, and the temperature change of the steel plate is detected in real time by an infrared thermometer, so that the temperature of the steel plate before hot-dip galvanizing is 500°C, set Set the bath temperature to 460°C, immerse the steel plate obtained above into the alloy bath for 60 seconds, air-cool after plating, and finally obtain an environmentally friendly zinc-aluminum-magnesium alloy-coated steel plate.

The surface of the coating is smooth, without missing plating, and there are a small amount of zinc nodules. After the bending test, the coating has no obvious peeling off, and the coating is well bonded to the steel plate.

Example 3

The invention discloses a preparation method of an environment-friendly zinc-aluminum-magnesium alloy coated steel plate.

Zinc ingots, magnesium ingots, aluminum ingots and aluminum foils are taken according to the ratio of Al: 6wt%, Mg: 3wt%, and the balance is Zn. Heat the zinc to 520°C to completely melt, weigh the aluminum block, press the aluminum block into the molten zinc solution with a graphite rod until it is completely melted, and stir. Weigh the magnesium block, wrap it with aluminum foil, and press it into the molten zinc solution with a graphite rod until it is completely melted to reduce oxidation and ablation loss. Raise the temperature of the alloy solution to 560°C, stir once every 30 minutes, keep warm for 5 hours, and set aside.

Mechanical descaling: The hot-rolled Q235 steel plate is polished and derusted by a continuous descaling machine to clean the surface rust of the steel plate and improve the production efficiency of subsequent reduction and hot-dip plating.

Perform electrolytic degreasing on the Q235 steel plate after mechanical derusting, prepare 8wt% NaOH solution, the temperature of the solution is 80°C, and the output voltage and current of the DC stabilized power supply with the model WYJ-0～15V5A are used. The steel plate to be cleaned is used as the cathode, and the graphite is used as the anode material, the current density is adjusted to 5A/dm2, the cleaning time is 5min, and then washed with water and dried.

The steel plate is heated to 840°C by the high-frequency induction heating equipment model SPG-06A-II, and the reduction is carried out in the atmosphere. The frequency of high-frequency induction heating is 220kHz, and the heating power is 1.5kW. The reduction atmosphere is 10vol% H ₂ -N ₂ , the reduction time is 40s, the steel plate after reduction is cooled in the N ₂ atmosphere, and the temperature change of the steel plate is detected in real time by an infrared thermometer, so that the temperature of the steel plate before hot-dip galvanizing is 600°C, set Set the temperature of the plating solution to 460°C, immerse the steel plate obtained above into the alloy plating solution for 40 seconds, air-cool after plating, and finally obtain an environmentally friendly zinc-aluminum-magnesium alloy coated steel plate.

Fig. 1 is the macroscopic appearance figure of the Zn-6wt%Al-3wt%Mg alloy coating of embodiment 3 hot-dip coating, and three groups of coating samples in the figure are the coating obtained from three repeated experiments carried out under the conditions of embodiment 3. The surfaces of the three groups of coatings are all smooth and smooth, and there is no missing coating on the surface. The lower part of the coating is caused by the accumulation of zinc liquid during the flow process, which does not affect the actual production and use. There is no obvious zinc tumor, and the three groups of coated steel plates are tested by bending test by CMT6104 electronic universal testing machine. The coating has no obvious peeling off, and the coating is well combined with the steel plate.

Fig. 2 is the XRD spectrum of embodiment 3 hot-dip plating Zn-6wt%Al-3wt%Mg alloy coating surface, as can be seen from the spectrum, coating surface is made up of Zn, Al, MgZn ₂ three phases, and the tiny MgZn of coating surface ₂ pair to improve The corrosion resistance of the coating has an important influence.

Fig. 3 is embodiment 3 hot-dip plating Zn-6wt%Al-3wt%Mg alloy coating cross-section scanning picture, can find out that coating solidification layer is made up of Zn _- MgZn binary eutectic structure by the figure, near the strip shape at matrix place The structure is Fe ₂ Al ₅ alloy layer, and the coating is closely combined with the substrate.

Example 4

The invention discloses a preparation method of an environment-friendly zinc-aluminum-magnesium alloy coated steel plate.

Zinc ingots, magnesium ingots, aluminum ingots and aluminum foils are taken according to the ratio of Al: 6wt%, Mg: 3wt%, and the balance is Zn. Heat the zinc to 530°C to completely melt, weigh the aluminum block, press the aluminum block into the molten zinc solution with a graphite rod until it is completely melted, and stir. Weigh the magnesium block, wrap it with aluminum foil, and press it into the molten zinc solution with a graphite rod until it is completely melted to reduce oxidation and ablation loss. Raise the temperature of the alloy solution to 580°C, stir once every 30 minutes, keep warm for 10 hours, and set aside.

Mechanical descaling: The hot-rolled Q235 steel plate is polished and derusted by a continuous descaling machine to clean the surface rust of the steel plate and improve the production efficiency of subsequent reduction and hot-dip plating.

Perform electrolytic degreasing on the Q235 steel plate after mechanical derusting, prepare 8wt% NaOH solution, the temperature of the solution is 40°C, and the output voltage and current of the DC stabilized power supply with the model WYJ-0～15V5A are used. The steel plate to be cleaned is used as the cathode, and the graphite is used as the anode material. The current density is adjusted to 6A/dm2, the cleaning time is 20min, and then washed with water and dried.

The steel plate is heated to 850°C by the high-frequency induction heating equipment model SPG-06A-II, and the reduction is carried out in the atmosphere. The frequency of high-frequency induction heating is 220kHz, and the heating power is 1.7kW. The reduction atmosphere is 20vol% H ₂ -N ₂ , the reduction time is 60s, the steel plate after reduction is cooled in the N ₂ atmosphere, and the temperature change of the steel plate is detected in real time by an infrared thermometer, so that the temperature of the steel plate before hot-dip galvanizing is 600°C, set The temperature of the plating solution was set at 550°C, and the steel plate obtained above was immersed in the alloy plating solution for 10 seconds, and air-cooled after plating to obtain an environmentally friendly zinc-aluminum-magnesium alloy coated steel sheet.

The surface of the coating is smooth, without missing plating, and without obvious zinc bumps. After the bending test, the coating has no obvious peeling off, and the coating is well bonded to the steel plate.

Example 5

The invention discloses a preparation method of an environment-friendly zinc-aluminum-magnesium alloy coated steel plate.

Zinc ingots, magnesium ingots, aluminum ingots and aluminum foils are taken according to the ratio of Al: 6wt%, Mg: 3wt%, and the balance is Zn. Heat the zinc to 550°C to completely melt, weigh the aluminum block, press the aluminum block into the molten zinc solution with a graphite rod until it is completely melted, and stir. Weigh the magnesium block, wrap it with aluminum foil, and press it into the molten zinc solution with a graphite rod until it is completely melted to reduce oxidation and ablation loss. Raise the temperature of the alloy solution to 600°C, stir once every 30 minutes, keep it warm for 8 hours, and set aside.

Mechanical descaling: The hot-rolled Q235 steel plate is polished and derusted by a continuous descaling machine to clean the surface rust of the steel plate and improve the production efficiency of subsequent reduction and hot-dip plating.

Perform electrolytic degreasing on the Q235 steel plate after mechanical derusting, prepare 10wt% NaOH solution, the temperature of the solution is 60°C, and the output voltage and current of the DC stabilized power supply with the model WYJ-0～15V5A are used. The steel plate to be cleaned is used as the cathode, and the graphite is used as the anode material, the current density is adjusted to 5A/dm2, the cleaning time is 10min, and then washed with water and dried.

The steel plate is heated to 820°C by the high-frequency induction heating equipment model SPG-06A-II, and the reduction is carried out in the atmosphere. The frequency of high-frequency induction heating is 220kHz, and the heating power is 1.4kW. The reduction atmosphere is 40vol% H ₂ -N ₂ , the reduction time is 10s, the steel plate after reduction is cooled in the N ₂ atmosphere, and the temperature change of the steel plate is detected in real time by an infrared thermometer, so that the temperature of the steel plate before hot-dip galvanizing is 750°C, set The temperature of the plating solution was fixed at 580°C, and the steel plate obtained above was immersed in the alloy plating solution for 10 seconds, and air-cooled after plating to obtain an environmentally friendly zinc-aluminum-magnesium alloy coated steel sheet. There is no missing coating on the surface of the coating, and there are many zinc nodules. After the bending test, the coating has a small amount of peeling off, and the bonding between the coating and the steel plate is poor.

Fig. 4 is the scanning picture of the cross section of the Zn-6wt%Al-3wt%Mg alloy coating of embodiment 5, it can be seen from the figure that the thickness of the coating increases, and the thickness of the Fe ₂ Al ₅ alloy layer near the substrate in the coating increases, and there are many Porosity, this is because the temperature of the steel plate and the temperature of the zinc solution before immersion plating are relatively high, resulting in a violent reaction between Fe and Al, which produces a thick and unstable alloy layer, resulting in a decrease in the bonding force between the coating and the steel plate.

From the above examples, we can see that,

(1) Most of the rust and scale can be removed by mechanical derusting on the surface of the steel plate, but there is still a certain amount of iron oxide residue after derusting, which is easy to cause defects such as missing plating and zinc tumors, so hydrogen is needed Reduction, reducing iron oxides into porous and loose sponge iron, which is beneficial to the combination of plating solution and steel matrix. When the _H2 content in the reducing atmosphere is lower than 0.1vol%, the reduction is insufficient, and iron oxides still exist at the interface, resulting in a decrease in the bonding force of the coating. When the _H2 content in the reducing atmosphere is higher than 40vol%, the production cost increases.

(2) The alloy plating solution adopted in the present invention contains Al: 6wt%, Mg: 3wt%, the addition of aluminum element can suppress the generation of brittle iron-zinc alloy layer, and generate iron-aluminum alloy layer, which improves the binding force of the coating , the addition of magnesium element can refine the coating structure, significantly improve the corrosion resistance of the coating, make the coating have cutting edge protection performance, form a fine MgZn ₂ structure on the surface of the coating, improve the corrosion resistance and the anti-powdering performance of the coating. When the magnesium content exceeds 3wt%, the corrosion resistance of the coating does not improve significantly, and the zinc dross in the bath increases.

(3) The temperature of the steel plate before plating is one of the important factors affecting the quality of the coating. If the temperature of the steel plate before plating is too high, the aluminum in the plating solution reacts violently with the iron in the steel plate, resulting in many zinc bumps on the surface and poor quality of the coating. If the temperature of the steel plate before plating is too low, the heat loss of the plating solution will be serious, and the temperature of the plating solution will be unstable, resulting in unstable coating quality and prone to missing plating.

(4) The dipping time and bath temperature also have an important influence on the coating. In order to obtain the ideal coating quality, the immersion plating time should be controlled at 5-60s, and the bath temperature should be 380-550°C. If the immersion plating time is too short, the reaction between the plating solution and the steel plate will be uneven, metallurgical bonding cannot be formed, and missing plating will easily occur. If the immersion plating time is too long, the excessive reaction of iron and aluminum will cause the iron and aluminum alloy layer to be too thick, which will affect the bonding force and corrosion resistance of the coating. If the temperature of the plating solution is too low, the fluidity of the plating solution will be poor, which will affect the surface quality of the coating. If the temperature of the bath is too high, the iron loss of the steel plate will increase, and the zinc slag in the bath will increase, which will cause a large loss of equipment and increase the production cost.

Matters not covered in the present invention are known technologies.

Claims (2)

1. the preparation method of the zinc-aluminium Mg Alloy Coating steel plate of a kind of environmental protection, it is characterized in that including the following steps:

(1) alloy molten: for one of following two method:

Method one: according to Al:6wt%, Mg:3wt%, surplus is that the proportion of Zn takes zinc ingot metal, magnesium ingot, aluminium ingot and aluminium foil；Zinc is heated It is completely melt to 500 DEG C ~ 550 DEG C, then sequentially adds aluminium block into zinc liquid to melting, add after stirring and wrapped up with aluminium foil Good MAG block, until fusing；Aluminium alloy is warming up to 560 DEG C ~ 600 DEG C again, every 30min stirring is primary, keeps the temperature 5 ~ 10h, for use；

Alternatively, method two: by ZAM alloy melting, then to 560 DEG C ~ 600 DEG C, every 30min stirring is primary, keeps the temperature 5 ~ 10h, to With；

(2) polishing derusting mechanical derusting: is carried out to hot rolled steel plate using continuous rust remover；

(3) electrolytic degreasing: the NaOH solution that mass fraction is 5 ~ 10wt% is prepared, solution temperature is 40 ~ 80 DEG C, steady using direct current Voltage source output voltage electric current, steel plate to be cleaned of cylinder as cathode, graphite as anode material, adjusting current density be 3A/dm2 ~ 6A/dm2,5 ~ 20min of scavenging period are washed after cleaning, drying；

(4) steel plate restores: steel plate is placed in N₂-H₂In mixed atmosphere, wherein H₂Content is 1vol% ~ 40vol%, passes through high frequency sense It answers heating equipment that steel plate is heated to 800 ~ 850 DEG C, is restored in atmosphere；High-frequency induction heating frequency is 220kHz, is added Thermal power is 1.4 ~ 1.7kW, and the recovery time in atmosphere is 10 ~ 60s；

(5) adjustment plating front spring temperature: by the steel plate after reduction in N₂Cool down in atmosphere, steel billet temperature is made to be reduced to 400 ~ 700 DEG C；

(6) hot-dip aluminum zinc magnesium alloy: the steel plate that upper step obtains is immersed into the aluminium alloy in (1) step, and the immersion plating time 5 ~ 60s, bath temperature is 380 ~ 550 DEG C, air-cooled after plating, finally obtains the zinc-aluminium Mg Alloy Coating steel plate of environmental protection.

2. the preparation method of the zinc-aluminium Mg Alloy Coating steel plate of environmental protection as described in claim 1, it is characterized in that the hot rolling Steel plate is Q235 steel plate.