A method for controlling the microstructure of hot-dip galvannealed aluminum-magnesium alloy by directional solidification

Abstract

The application provides a method for regulating microstructure of hot-dip galvanizing zinc-aluminum-magnesium alloy through directional solidification technology, and belongs to the technical field of hot-dip plating. The technical problem solved by the application is that, in the actual production process, the accurate control of the cooling process cannot be realized, which leads to serious deficiencies in the accurate regulation of the solidification behavior and the alloy structure of the zinc-aluminum-magnesium coating. The technical scheme adopted by the application is that the coating surface temperature in each cooling process in the actual production process is measured, and the corresponding simulation results are combined to obtain the coating cooling parameters in the actual production process, and on this basis, the directional solidification test parameters are designed, so that the regulation of the microstructure of the hot-dip galvanizing zinc-aluminum-magnesium alloy through the directional solidification technology is realized. The method provided by the application can regulate the phase composition and the area fraction of the eutectic structure of the hot-dip galvanizing zinc-aluminum-magnesium alloy under different cooling processes through the directional solidification technology, so as to provide important theoretical guidance for improving the hot-dip galvanizing zinc-aluminum-magnesium process in the actual production process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot-dip galvanizing zinc-aluminum-magnesium process, and particularly relates to a method for regulating microstructure of hot-dip galvanizing zinc-aluminum-magnesium alloy through directional solidification technology. BACKGROUND

[0002] Steel is widely used in the fields of construction, energy, transportation, aerospace and so on due to its excellent mechanical properties and outstanding material formability. However, steel material is prone to oxidation and corrosion in service environment, which causes serious environmental pollution and a large amount of resource waste. The protection of steel material is a major problem to be solved. Hot-dip galvanizing is an important method for protecting steel. In order to further optimize the corrosion resistance of the coating, a large number of researchers have carried out alloying treatment on the hot-dip galvanizing coating. Studies have shown that Al, Mg, Si and RE (rare earth) elements are effective alloying elements for improving the corrosion resistance of hot-dip galvanizing coating. Compared with the traditional hot-dip galvanizing coating, the hot-dip galvanizing zinc-aluminum-magnesium coating has higher strength and more excellent corrosion resistance, and is widely used in the surface coating protection of steel material.

[0003] Alloy microstructure regulation is the key factor to improve its performance. The current research direction of hot-dip galvanizing zinc-aluminum-magnesium mainly focuses on composition design and performance. There is still a lack of research on the solidification behavior-microstructure-performance of hot-dip galvanizing zinc-aluminum-magnesium alloy. In 2023, the patent number CN116426793A "High-corrosion-resistant zinc-aluminum-magnesium plated steel plate and its preparation method" was published on China Patent Network. By adding elements such as Mg, Al, and Si in the zinc-aluminum-magnesium alloy coating and controlling their content in the coating, the zinc-aluminum-magnesium plated steel plate has good corrosion resistance and excellent surface quality. In 2023, the patent number CN116426856A "Hot-based zinc-aluminum-magnesium steel plate and its preparation method" was published on China Patent Network. The preparation method effectively controls the uniformity of the coating thickness by changing the composition of the zinc-aluminum-magnesium plating solution and related process parameters. In 2023, the patent number CN116426792A "Alloy and its preparation method and application" was published on China Patent Network. By regulating the element content of hot-dip galvanizing zinc-aluminum-magnesium alloy and adding a certain amount of rare earth elements Ce and La, a eutectic structure of Zn, Al, and Mg-Zn compounds is obtained, and at least 80% of the eutectic structure exists in the form of grains with a size not greater than 100 μm. However, in addition to composition design, the cooling stage also has a decisive influence on the microstructure of hot-dip galvanizing zinc-aluminum-magnesium. The article "Correlative characterization of Zn-Al-Mg coatings by electron microscopy and FIB tomography" published in Materials Characterization in 2020, vol. 166, points out that the equilibrium eutectic reaction of zinc-aluminum-magnesium alloy is L→Zn+Al+Mg2Zn 11 , however, in actual production process, cooling often deviates from equilibrium cooling, under faster cooling conditions, Mg2Zn 11 in the ternary eutectic is replaced by MgZn2 phase, and the corrosion resistance of zinc-aluminum-magnesium alloy also changes.

[0004] From the current research status of hot-dip galvanizing zinc-aluminum-magnesium alloy, the following problems can be found, (1) Currently, there is less research on the effect of cooling speed on the solidification behavior of zinc-aluminum-magnesium. Mg-Zn in the ternary eutectic exists in two different organizations, Mg2Zn 11 and MgZn2, under different cooling conditions, the mechanism of phase transition, and the critical cooling speed are not further clear. (2) The effect of Zn-Al-Mg2Zn 11 and Zn-Al-MgZn2 two ternary eutectic organizations on corrosion performance is not clear. (3) The solidification process of zinc-aluminum-magnesium alloy requires cooling fan control, the equipment is complex, and precise control of the cooling process cannot be achieved.

[0005] In the process of hot-dip galvanizing zinc-aluminum-magnesium alloy coating, the thickness of the steel plate is very small, which is three orders of magnitude different from the width of the steel plate, and the lateral heat dissipation can be ignored, so it can be considered that the plating solution is unidirectional heat dissipation along the direction perpendicular to the steel plate, which is consistent with the process of directional solidification. In the process of directional solidification cooling, the middle of the furnace body is an alumina heat insulation baffle, the upper part of the baffle is a heating area, the alloy test rod sample is placed in a high-purity alumina ceramic tube with appropriate size (3-10 mm), the ceramic tube is coated with a heating graphite body, and the graphite body is outside an induction heating coil. The cooling area below the alumina baffle is a cooling liquid Ga-In-Sn ternary alloy (Ga 62 In 25 Sn 13 room temperature liquid), which has the best heat conduction capacity under laboratory conditions, can ensure unidirectional heat transfer, and realize directional solidification. Two temperature measuring thermocouples measure the temperature difference ΔT of the positions apart by ΔX, and the temperature gradient G can be obtained according to G = ΔT / ΔX. The stretching rod controlled by the stepping motor penetrates the cooling area, and the pulling speed V is controlled. The cooling speed R = G x V in the directional solidification, so different cooling speeds can be obtained by selecting the temperature gradient and the pulling speed. Through the directional solidification technology, the cooling speed can be accurately controlled, so as to establish the relationship between the microstructure of zinc-aluminum-magnesium alloy and the cooling speed.

[0006] In summary, for hot-dip galvanizing zinc-aluminum-magnesium alloy, it is hoped to develop a method which is simple to operate and can accurately predict the microstructure of hot-dip galvanizing zinc-aluminum-magnesium coating. And by adjusting the parameters of directional solidification technology, the microstructure of zinc-aluminum-magnesium alloy can be controlled, which provides theoretical guidance for the actual production of hot-dip galvanizing zinc-aluminum-magnesium coating cooling process, and further improves the comprehensive performance of zinc-aluminum-magnesium coating. SUMMARY

[0007] In order to solve the above problems, the present application provides a method for controlling the microstructure of hot-dip galvanizing zinc-aluminum-magnesium alloy by directional solidification technology. The method provided by the present application can judge the final solidification structure of the alloy, and in the process of directional solidification of zinc-aluminum-magnesium, the cooling parameters can be adjusted to obtain a variety of different microstructures, which provides theoretical guidance for the control of the actual production cooling process.

[0008] In order to achieve the above purpose, the present application provides the following technical scheme:

[0009] The present application provides a method for controlling the microstructure of hot-dip galvanizing zinc-aluminum-magnesium alloy by directional solidification technology, which comprises the following steps:

[0010] 1) Determination of cooling parameters of hot-dip galvanizing zinc-aluminum-magnesium in actual production process: the actual temperature of the zinc-aluminum-magnesium steel plate coating out of the ladle and the coating surface in each cooling process is measured by an infrared thermometer; the cooling stage of zinc-aluminum-magnesium is simulated by Ansys, and the cooling speed of hot-dip galvanizing zinc-aluminum-magnesium is 6-10.5℃ / s and the temperature gradient is 60K / mm according to the simulation results and the actual temperature measurement results;

[0011] 2) Design of directional solidification test parameters: according to the cooling speed and temperature gradient of hot-dip galvanizing zinc-aluminum-magnesium in the actual production process determined in step 1), and combining the relationship between cooling speed R and temperature gradient G and pulling speed V in the directional solidification process R=G×V, the temperature gradient is 60K / mm and the pulling speed range is 20-300μm / s in the directional solidification test, and the corresponding cooling speed range is 1.2℃ / s-18℃ / s, which includes the cooling speed in step 1) required in the actual production process;

[0012] 3) Heat treatment of zinc-aluminum-magnesium alloy in a directional solidification furnace to obtain a heat-treated zinc-aluminum-magnesium alloy;

[0013] The component of the zinc-aluminum-magnesium alloy is Zn-11Al-3Mg;

[0014] 4) Drawing of the heat-treated zinc-aluminum-magnesium alloy obtained in step 3) and quenching in a cooling liquid after drawing;

[0015] When the temperature gradient of the heat treatment is 60K / mm and the pulling speed of the drawing is 20μm / s, the solidification structure of the zinc-aluminum-magnesium alloy is composed of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-Mg2Zn 11 ternary eutectic structure, and the area fraction of Zn-Al-Mg2Zn 11 ternary eutectic is 89%;

[0016] When the temperature gradient of the heat treatment is 60K / mm and the pulling speed of the drawing is 50μm / s, the solidification structure of the zinc-aluminum-magnesium alloy is composed of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-Mg2Zn 11 ternary eutectic structure, and the area fraction of Zn-Al-Mg2Zn 11 ternary eutectic is 76%;

[0017] When the temperature gradient of the heat treatment is 60K / mm and the pulling speed of the drawing is 100μm / s, the solidification structure of the zinc-aluminum-magnesium alloy is composed of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structure, and the area fraction of Zn-Al-MgZn2 ternary eutectic is 59%;

[0018] When the temperature gradient of the heat treatment is 60K / mm, and the pulling speed of the pulling is 200μm / s, the solidification structure of the zinc-aluminum-magnesium alloy is composed of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic, and the area fraction of the Zn-Al-MgZn2 ternary eutectic is 56%.

[0019] When the temperature gradient of the heat treatment is 60K / mm, and the pulling speed of the pulling is 300μm / s, the solidification structure of the zinc-aluminum-magnesium alloy is composed of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic, and the area fraction of the Zn-Al-MgZn2 ternary eutectic is 49%.

[0020] Preferably, the diameter of the zinc-aluminum-magnesium alloy in the step 3) is 7mm, and the length is 110mm.

[0021] Preferably, the zinc-aluminum-magnesium alloy in the step 3) is placed in the directional solidification furnace, and then vacuumized to a pressure of 10 -2 Pa, and then argon is introduced to a pressure of 300Pa.

[0022] Preferably, the heat treatment in the step 3) is performed under the following conditions: the sample is heated from room temperature (25℃) to 550℃ at a heating rate of 25℃ / min, and after the temperature of the sample reaches 550℃, the sample is subjected to a heat preservation treatment, and the heat preservation time is 30min.

[0023] Preferably, the pulling distance of the pulling in the step 4) is 60mm.

[0024] The principle of the present application is as follows:

[0025] In the process of hot-dip galvanizing zinc-aluminum-magnesium alloy coating, the thickness of the steel plate is very small, which is three orders of magnitude smaller than the width and length of the steel plate, and the lateral heat dissipation can be ignored, so it can be considered that the plating solution is unidirectionally cooled along the direction perpendicular to the steel plate. A high-precision infrared thermometer is used to measure the actual temperature of the zinc-aluminum-magnesium steel plate coating out of the pot and the coating surface in each cooling process, and the cooling speed of the plate strip is calculated.

[0026] The cooling speed is simulated by the cooling parameters of the hot-dip galvanizing zinc-aluminum-magnesium coating. There are three basic ways of heat transfer: heat conduction, convection and heat radiation. Heat conduction is the transfer of heat energy by the thermal motion of microscopic particles such as molecules, atoms and free electrons. According to the heat transfer law formula shown in formula (1), the heat Q transferred by heat conduction per unit time is proportional to the thermal conductivity k, the cross-sectional area A perpendicular to the heat flow, and the temperature gradient Proportional. Convection is the relative displacement between different parts of the fluid caused by the macroscopic motion of the fluid, and the heat transfer caused by the mixing of hot and cold fluids. Its influencing factors can be obtained from the cooling formula shown in equation (2), where ΔT is the temperature difference between the solid surface and the fluid, and h is the convection coefficient, which represents the heat flow rate through a unit area under a unit temperature difference. Under forced air convection conditions, the air convection coefficient can reach 20-100 W / m. 2 The thermal conductivity of air is only 0.023 W / m·℃ under unsteady, enclosed conditions, and its temperature gradient is much lower than that of the coating and the base steel. Therefore, the heat transferred by conduction is much less than that transferred by convection. Thermal radiation is the transfer of energy from an object in the form of electromagnetic waves; the radiated energy is relatively low and depends on the type and state of the object. Clearly, during the cooling process of hot-dip galvanized aluminum-magnesium coatings, convection heat transfer dominates.

[0027]

[0028] Q=AhΔT (2)

[0029] In actual production, the cooling rate is generally controlled by adjusting the convection coefficient between the coating surface and the outside air by changing the pressure of the bellows. The derivation process of the relationship between the bellows pressure and the convection coefficient is as follows: As can be seen from formula (3), the convection coefficient h is a function of the wind speed v; when the airflow of a certain cross section with pressure P impacts a structure with a large area, due to the obstruction, the airflow changes to diffuse to the surrounding periphery, forming a pressure curtain. Assuming that the airflow remains uniform and stable, and taking the pressure in the direction of flow as positive, according to Newton's second law, the resultant force of the airflow should be equal to the product of the mass of the airflow and the acceleration in the direction of flow (formula (4)); Solving the differential equation (4) yields the relationship between wind pressure and wind speed, as shown in formula (5). Combining formulas (3)-(5), the relationship between the bellows pressure and the convection coefficient can be obtained, as shown in formula (6).

[0030]

[0031]

[0032]

[0033]

[0034] In formulas (3)-(6), P is pressure, v is wind speed, A is unit cross-sectional area, dl is a small segment of the streamline, M is the mass of the airflow within the segment, a is the acceleration in the downstream direction, ρ is air density, g is gravitational acceleration, γ is the gravity per unit volume of air, C is a dimensionless constant, k is the thermal conductivity of air, μ is the viscosity of air, and C p It is a specific heat at constant pressure.

[0035] As can be seen from formulas (1)-(6), convective heat transfer dominates during the cooling process of hot-dip galvanized aluminum-magnesium coating. By changing the air box pressure and convective heat transfer coefficient, the cooling rate of the coating, the surface of the steel substrate, and the core of the steel can be effectively controlled under different processes.

[0036] The heat transfer process between the steel plate core and surface (coating) was calculated and simulated based on Fourier's law of heat transfer and the law of conservation of energy. Thermal properties such as thermal conductivity and specific heat capacity of the steel substrate and zinc-aluminum-magnesium coating were obtained using Jmatpro software. A finite element model was then established using Ansys software. The model is shown below. Figure 2 As shown. The temperature of the zinc-aluminum-magnesium plating bath and the temperature of the base steel plate in the zinc crucible are approximately 470℃, the ambient air temperature is 28℃, and the thermal resistance at the interface between the zinc-aluminum-magnesium plating layer and the steel substrate is 4×10⁻⁶. -4 K·m 2 / W, the thermal emissivity of the coating is 0.93. By adjusting the cooling box pressure and convection coefficient, the temperature distribution of the coating, the surface of the steel, and the core of the steel, as well as the corresponding temperature gradient G, can be obtained.

[0037] During the cooling process of hot-dip galvanized aluminum-magnesium alloy coating, the steel plate thickness is very small, and its length differs from the plate width by three orders of magnitude. Lateral heat dissipation is negligible, and the plating solution dissipates heat unidirectionally along a direction perpendicular to the steel plate, which is consistent with the directional solidification process. During directional solidification, the cooling rate R satisfies the relationship between the temperature gradient G and the pulling speed V, where R = G × V. The temperature gradient G can be obtained by measuring the temperature difference ΔT at a distance ΔX using two thermocouples, according to G = ΔT / ΔX. A tension rod controlled by a stepper motor penetrates the cooling zone, controlling the pulling speed V. The cooling rate of the strip is calculated by measuring the actual temperature of the zinc-aluminum-magnesium steel plate surface after it leaves the crucible and at each cooling stage. Furthermore, the temperature distribution and corresponding temperature gradients of the hot-dip galvanized aluminum-magnesium coating, the steel surface, and the steel core are obtained through finite element simulation. Based on the strip cooling rate R and the temperature gradient G obtained from finite element simulation, by selecting the appropriate temperature gradient G and pulling speed V for the directional solidification experiment, a cooling rate corresponding to that in the actual hot-dip galvanized aluminum-magnesium coating cooling process can be achieved during directional solidification. Furthermore, directional solidification technology allows for precise control of the cooling rate, thereby establishing the relationship between the microstructure of the zinc-aluminum-magnesium alloy and the cooling rate.

[0038] Directional solidification ensures a unidirectional temperature gradient and growth direction during alloy solidification. This technology allows for the manipulation of the cooling rate's influence on the solidification microstructure of hot-dip galvanized aluminum-magnesium alloy sheets and strips. For Zn-11Al-3Mg ternary hypereutectic alloys deviating from the eutectic composition, the final solidified microstructure generally consists of primary dendritic phases and eutectic structures. Studies show that zinc-aluminum-magnesium alloys form different eutectic structures under different cooling conditions. This is due to the competitive growth of phases within the ternary eutectic structure during cooling. In actual production, the cooling rate of hot-dip galvanized aluminum-magnesium alloy sheets and strips is often relatively fast, causing the solidification process to deviate from equilibrium. Consequently, the solidified microstructure of the alloy also deviates from equilibrium, making phase diagrams less instructive for understanding the solidification microstructure of hot-dip galvanized aluminum-magnesium alloys. Only alloys with eutectic composition can achieve a completely eutectic structure. For alloys with composition deviating from the eutectic composition, since the liquidus temperature is always higher than the eutectic temperature, the primary phase has greater undercooling, which is more conducive to the nucleation of the primary phase. Primary Al dendrites and Al-MgZn2 binary eutectic are formed at different cooling rates. Mg2Zn exists in the ternary eutectic nucleation stage. 11 The competitive growth of MgZn2 will determine the final solidification morphology of the alloy.

[0039] In this invention, the microstructure of the air-cooled cast zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure was determined based on actual temperature measurements. The cooling rate of hot-dip galvanized aluminum-magnesium alloy was 6-10.5℃ / s, with a temperature gradient of 60K / mm. The corresponding drawing speed was 100μm / s-175μm / s. To further investigate the microstructure changes of the zinc-aluminum-magnesium alloy under a wider range of cooling rates, a drawing speed range of 20-300μm / s and a temperature gradient of 60K / mm were selected in this experiment. The corresponding cooling rate range was 1.2℃ / s-18℃ / s, which includes the cooling rate required for actual production processes.

[0040] In directional solidification experiments at different pulling speeds of 20-300 μm / s, the alloy microstructure still consisted of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn, Al, Mg-Zn compound ternary eutectic, with the ternary eutectic being Zn-Al-Mg2Zn. 11 The alloy exhibits two distinct microstructures: Zn-Al-MgZn2. EDS analysis results of the ternary eutectic microstructure at different pulling speeds are shown in Table 1. When the pulling speed is 20-50 μm / s, the microstructure is consistent with the as-cast state, consisting of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn... 11It consists of a ternary eutectic structure. As the pulling speed increases to 100 μm / s, its constituent phases change from Zn-Al-Mg2Zn. 11 The eutectic structure transforms into Zn-Al-MgZn2. By adjusting the directional solidification parameters, the eutectic structure can be transformed from Zn-Al-Mg2Zn. 11 The transition to Zn-Al-MgZn2 provides guidance for cooling control in actual production processes.

[0041] Table 1. EDS analysis results of ternary eutectic structures at different pulling speeds

[0042] Point 1 Point 2 Point 3 As-cast Al Mg2Zn 11 ]]> Zn 20 μm / s Al Mg2Zn 11 ]]> Zn 50 μm / s Al Mg2Zn 11 ]]> Zn 100 μm / s Al MgZn2 Zn 200 μm / s Al MgZn2 Zn 300 μm / s Al MgZn2 Zn

[0043] During the corrosion process of zinc-aluminum-magnesium alloy coatings, the ternary eutectic structure preferentially corrodes. The area fraction of the eutectic structure significantly affects the coating performance, making the control of the eutectic structure area fraction crucial in actual production. Directional solidification experiments effectively demonstrate that the area fraction of the eutectic structure in zinc-aluminum-magnesium alloys decreases continuously with increasing drawing speed, as shown in the attached figure. Figure 9 As shown, with increasing pulling speed, the distance between primary and secondary dendrite arms decreases significantly, and the eutectic structure becomes significantly refined and more uniformly distributed. The increased pulling speed disrupts the equilibrium diffusion of solute at the solid-liquid interface. Dendrites must reduce their tip radius to establish a new equilibrium, accelerating solute expulsion and thus promoting the nucleation of primary dendrites and reducing the eutectic structure.

[0044] This invention improves the hot-dip galvanizing aluminum-magnesium process in the following ways:

[0045] (1) The phase composition of hot-dip galvanized aluminum-magnesium alloys under different cooling processes can be controlled by directional solidification technology.

[0046] (2) The area fraction of the eutectic structure of hot-dip galvanized aluminum-magnesium alloy can be controlled by directional solidification technology under different cooling processes. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0048] Figure 1 Temperature and cooling rate measurements were taken during the cooling process of hot-dip galvanized aluminum-magnesium plating.

[0049] Figure 2 A finite element model of the hot-dip galvanizing process for aluminum-magnesium alloys;

[0050] Figure 3 The temperature distribution of the coating, the surface layer of the steel, and the core of the steel is simulated under different cooling times, where (ae) represents the temperature distribution at 0s, 5s, 10s, 15s, and 20s, respectively.

[0051] Figure 4 Simulation results of coating cooling rate at different cooling times;

[0052] Figure 5 The microstructure of the as-cast Zn-11Al-3Mg alloy;

[0053] Figure 6 XRD patterns of directionally solidified Zn-11Al-3Mg alloys at different pulling speeds;

[0054] Figure 7 The microstructures of directional solidified Zn-11Al-3Mg alloys at different drawing speeds are shown, where (ae) are 20 μm / s, 50 μm / s, 100 μm / s, 200 μm / s, and 300 μm / s, respectively.

[0055] Figure 8 The microstructure of the directional solidified Zn-11Al-3Mg alloy under different pulling speeds and the EDS test locations are shown in the magnified images. (ae) represents 20 μm / s, 50 μm / s, 100 μm / s, 200 μm / s, and 300 μm / s, respectively.

[0056] Figure 9 The area fraction of the eutectic structure of directional solidified Zn-11Al-3Mg alloy under different drawing speeds. Detailed Implementation

[0057] This invention provides a method for controlling the microstructure of hot-dip galvanized aluminum-magnesium alloys using directional solidification technology, comprising the following steps:

[0058] 1) Determination of cooling parameters for hot-dip galvanized aluminum-magnesium steel in actual production: The actual surface temperature of the zinc-aluminum-magnesium steel plate coating after leaving the crucible and during each cooling process was measured on-site using an infrared thermometer; the cooling stage of zinc-aluminum-magnesium steel was simulated using Ansys, and the cooling rate of hot-dip galvanized aluminum-magnesium steel was 6-10.5℃ / s, and the temperature gradient was 60K / mm.

[0059] 2) Design of directional solidification test parameters: Based on the cooling rate and temperature gradient of hot-dip galvanized aluminum-magnesium alloy in the actual production process determined in step 1), and combined with the relationship between cooling rate R, temperature gradient G, and pulling speed V in the directional solidification process, R = G × V, the temperature gradient in the directional solidification test is determined to be 60 K / mm, and the pulling speed range is 20-300 μm / s. The corresponding cooling rate range is 1.2℃ / s-18℃ / s, which includes the cooling rate in step 1) required in the actual production process.

[0060] 3) The zinc-aluminum-magnesium alloy is placed in a directional solidification furnace for heat treatment to obtain a heat-treated zinc-aluminum-magnesium alloy;

[0061] The composition of the zinc-aluminum-magnesium alloy is Zn-11Al-3Mg;

[0062] 4) The heat-treated zinc-aluminum-magnesium alloy obtained in step 3) is drawn out and then quenched in a cooling liquid.

[0063] When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed is 20 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure consists of Zn-Al-Mg2Zn. 11 The area fraction of the ternary eutectic is 89%;

[0064] When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed is 50 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure consists of Zn-Al-MgZn2 ternary eutectic with an area fraction of 76%.

[0065] When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed of the pulling is 100 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structures, and the area fraction of Zn-Al-MgZn2 ternary eutectic is 59%.

[0066] When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed of the pulling is 200 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structures, and the area fraction of Zn-Al-MgZn2 ternary eutectic is 56%.

[0067] When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed of the pulling is 300 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structures, with the area fraction of Zn-Al-MgZn2 ternary eutectic being 49%.

[0068] This invention involves heat-treating a zinc-aluminum-magnesium alloy in a directional solidification furnace to obtain a heat-treated zinc-aluminum-magnesium alloy; the composition of the zinc-aluminum-magnesium alloy is Zn-11Al-3Mg. In this invention, the diameter of the zinc-aluminum-magnesium alloy is preferably 7 mm, and the length is preferably 110 mm. Preferably, the zinc-aluminum-magnesium alloy is placed in an alumina crucible, and then the alumina crucible is placed in a directional solidification furnace and evacuated to a pressure of 10... -2 Pa, then high-purity argon gas is introduced until the pressure reaches 300 Pa. Preferably, one end of the alumina crucible is fixed in the heat preservation zone of the directional solidification furnace, and the other end is placed in the coolant.

[0069] This invention involves drawing the obtained heat-treated zinc-aluminum-magnesium alloy, followed by quenching in a cooling liquid. Preferably, the heat treatment conditions include heating the sample from room temperature (25°C) to 550°C at a heating rate of 25°C / min, and then holding the sample at 550°C for 30 minutes. Preferably, the drawing distance is 60 mm.

[0070] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0071] Example 1

[0072] Step 1: Using a UNI-T (UT302) high-precision infrared thermometer, the actual surface temperature of the zinc-aluminum-magnesium steel plate coating after removal from the crucible and during each cooling process was measured. Positions 1, 2, 3, 4, and 5 correspond to the positions of the air knife, air box 1, air box 2, air box 4, and air box 5, respectively. The temperatures and cooling rates at different positions are as follows: Figure 1 As shown. The cooling stage of zinc-aluminum-magnesium alloy was simulated using Ansys, and the model is as follows. Figure 2 As shown, the temperature distribution and cooling rate are as follows: Figure 3 , Figure 4 As shown, the actual temperature measurement results are basically consistent with the simulation calculation results.

[0073] Step 2: Based on the measurement results from Step 1, the cooling rate during the cooling stage of hot-dip galvanized aluminum-magnesium is 5-10.5℃ / s. Based on this, the experimental parameters for directional solidification are designed: the directional solidification temperature gradient is selected as 60K / mm, the pulling speed is selected as 20μm / s, and the sample cooling rate is 1.2℃ / s.

[0074] Step three: Conduct the directional solidification experiment using the experimental parameters from step two. A zinc-aluminum-magnesium alloy with a composition of Zn-11Al-3Mg is cut into metal rods with a diameter of 7 mm and a length of 110 mm. These rods are placed inside an alumina crucible and fixed within the directional solidification furnace, with the upper end in the heat preservation zone and the lower end submerged in the coolant. The directional solidification furnace is then evacuated to a pressure of 10... -2 Pa, then high-purity argon gas was introduced to 300 Pa to reduce the oxidation and volatilization of alloying elements during the experiment.

[0075] Step four: Heat the sample above the melting point of the Zn-11Al-3Mg alloy to completely melt it and hold it at that temperature for a certain period of time to make the elements more homogeneous. Specifically, turn on the heating power supply and heat the sample from room temperature (25℃) to 550℃ at a heating rate of 25℃ / min. After the sample temperature reaches 550℃, hold the sample at that temperature for 30 minutes, with a temperature gradient of 60K / mm.

[0076] Step 5: After the heat preservation treatment is completed, the sample is pulled at a speed of 20 μm / s for a distance of 60 mm. During the cooling process, the temperature of the upper heating zone remains constant, and the sample is immersed in the coolant at a specific speed. When the growth distance reaches the set distance, the sample is quickly immersed in the coolant for quenching.

[0077] Based on the results of scanning electron microscopy and X-ray energy dispersive spectroscopy ( Figure 6 , Figure 7 a, Figure 8 In case a), when the zinc-aluminum-magnesium alloy is cooled with a temperature gradient of 60 K / mm and a pulling speed of 20 μm / s, the solidification structure of the alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure consists of Zn-Al-Mg2Zn. 11 The area fraction of the ternary eutectic is 89% ( Figure 9 ).

[0078] Example 2

[0079] Step 1: Using a UNI-T (UT302) high-precision infrared thermometer, the actual surface temperature of the zinc-aluminum-magnesium steel plate coating after removal from the crucible and during each cooling process was measured. Positions 1, 2, 3, 4, and 5 correspond to the positions of the air knife, air box 1, air box 2, air box 4, and air box 5, respectively. The temperatures and cooling rates at different positions are as follows: Figure 1 As shown. The cooling stage of zinc-aluminum-magnesium alloy was simulated using Ansys, and the model is as follows. Figure 2 As shown, the temperature distribution and cooling rate are as follows: Figure 3 , Figure 4 As shown, the actual temperature measurement results are basically consistent with the simulation calculation results.

[0080] Step 2: Based on the measurement results from Step 1, the cooling rate during the cooling stage of hot-dip galvanized aluminum-magnesium is 5-10.5℃ / s. Based on this, the experimental parameters for directional solidification are designed as follows: the directional solidification temperature gradient is selected as 60K / mm, the pulling speed is selected as 50μm / s, and the cooling rate is 3℃ / s.

[0081] Step three: Conduct the directional solidification experiment using the experimental parameters from step two. A zinc-aluminum-magnesium alloy with a composition of Zn-11Al-3Mg is cut into metal rods with a diameter of 7 mm and a length of 110 mm. These rods are placed inside an alumina crucible and fixed within the directional solidification furnace, with the upper end in the heat preservation zone and the lower end submerged in the coolant. The directional solidification furnace is then evacuated to a pressure of 10... -2 Pa, then high-purity argon gas was introduced to 300 Pa to reduce the oxidation and volatilization of alloying elements during the experiment.

[0082] Step four: Heat the sample above the melting point of the Zn-11Al-3Mg alloy to completely melt it and hold it at that temperature for a certain period of time to make the elements more homogeneous. Specifically, turn on the heating power supply and heat the sample from room temperature (25℃) to 550℃ at a heating rate of 25℃ / min. After the sample temperature reaches 550℃, hold the sample at that temperature for 30 minutes, with a temperature gradient of 60K / mm.

[0083] Step 5: After the heat treatment is completed, the sample is pulled at a speed of 50 μm / s for a distance of 60 mm. During the cooling process, the temperature of the upper heating zone remains constant, and the sample is immersed in the coolant at a specific speed. When the growth distance reaches the set distance, the sample is quickly immersed in the coolant for quenching.

[0084] Based on the results of scanning electron microscopy and X-ray energy dispersive spectroscopy ( Figure 6 , Figure 7 b, Figure 8 In section b, when the zinc-aluminum-magnesium alloy is cooled with a temperature gradient of 60 K / mm and a pulling speed of 50 μm / s, the solidification structure of the alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure consists of Zn-Al-MgZn. 11 The area fraction of the ternary eutectic is 76% ( Figure 9 ).

[0085] Example 3

[0086] Step 1: Using a UNI-T (UT302) high-precision infrared thermometer, the actual surface temperature of the zinc-aluminum-magnesium steel plate coating after removal from the crucible and during each cooling process was measured. Positions 1, 2, 3, 4, and 5 correspond to the positions of the air knife, air box 1, air box 2, air box 4, and air box 5, respectively. The temperatures and cooling rates at different positions are as follows: Figure 1 As shown. The cooling stage of zinc-aluminum-magnesium alloy was simulated using Ansys, and the model is as follows. Figure 2 As shown, the temperature distribution and cooling rate are as follows: Figure 3 , Figure 4 As shown, the actual temperature measurement results are basically consistent with the simulation calculation results.

[0087] Step 2: Based on the measurement results from Step 1, the cooling rate during the cooling stage of hot-dip galvanized aluminum-magnesium is 5-10.5℃ / s. Based on this, the experimental parameters for directional solidification are designed as follows: the directional solidification temperature gradient is selected as 60K / mm, the pulling speed is selected as 100μm / s, and the cooling rate is 6℃ / s.

[0088] Step three: Conduct the directional solidification experiment using the experimental parameters from step two. A zinc-aluminum-magnesium alloy with a composition of Zn-11Al-3Mg is cut into metal rods with a diameter of 7 mm and a length of 110 mm. These rods are placed inside an alumina crucible and fixed within the directional solidification furnace, with the upper end in the heat preservation zone and the lower end submerged in the coolant. The directional solidification furnace is then evacuated to a pressure of 10... -2 Pa, then high-purity argon gas was introduced to 300 Pa to reduce the oxidation and volatilization of alloying elements during the experiment.

[0089] Step four: Heat the sample above the melting point of the Zn-11Al-3Mg alloy to completely melt it and hold it at that temperature for a certain period of time to make the elements more homogeneous. Specifically, turn on the heating power supply and heat the sample from room temperature (25℃) to 550℃ at a heating rate of 25℃ / min. After the sample temperature reaches 550℃, hold the sample at that temperature for 30 minutes, with a temperature gradient of 60K / mm.

[0090] Step 5: After a certain holding time, the sample is pulled at a speed of 100 μm / s for a distance of 60 mm. During the cooling process, the temperature of the upper heating zone remains constant, and the sample is immersed in the coolant at a specific speed. Once the growth distance reaches the set distance, the sample is quickly immersed in the coolant for quenching.

[0091] Based on the results of scanning electron microscopy and X-ray energy dispersive spectroscopy ( Figure 6 , Figure 7 c, Figure 8In the case of zinc-aluminum-magnesium alloy, when cooled with a temperature gradient of 60 K / mm and a pulling speed of 100 μm / s, the solidification structure of the alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-MgZn2 ternary eutectic, with the Zn-Al-MgZn2 ternary eutectic having an area fraction of 59%. Figure 9 ).

[0092] Example 4

[0093] Step 1: Using a UNI-T (UT302) high-precision infrared thermometer, the actual surface temperature of the zinc-aluminum-magnesium steel plate coating after removal from the crucible and during each cooling process was measured. Positions 1, 2, 3, 4, and 5 correspond to the positions of the air knife, air box 1, air box 2, air box 4, and air box 5, respectively. The temperatures and cooling rates at different positions are as follows: Figure 1 As shown. The cooling stage of zinc-aluminum-magnesium alloy was simulated using Ansys, and the model is as follows. Figure 2 As shown, the temperature distribution and cooling rate are as follows: Figure 3 , Figure 4 As shown, the actual temperature measurement results are basically consistent with the simulation calculation results.

[0094] Step 2: Based on the measurement results from Step 1, the cooling rate during the cooling stage of hot-dip galvanized aluminum-magnesium is 5-10.5℃ / s. On this basis, the experimental parameters for directional solidification are designed: the directional solidification temperature gradient is selected as 60K / mm, the pulling speed is selected as 200μm / s, and the cooling rate is 12℃ / s.

[0095] Step three: Conduct the directional solidification experiment using the experimental parameters from step two. A zinc-aluminum-magnesium alloy with a composition of Zn-11Al-3Mg is cut into metal rods with a diameter of 7 mm and a length of 110 mm. These rods are placed inside an alumina crucible and fixed within the directional solidification furnace, with the upper end in the heat preservation zone and the lower end submerged in the coolant. The directional solidification furnace is then evacuated to a pressure of 10... -2 Pa, then high-purity argon gas was introduced to 300 Pa to reduce the oxidation and volatilization of alloying elements during the experiment.

[0096] Step four: Heat the sample above the melting point of the Zn-11Al-3Mg alloy to completely melt it and hold it at that temperature for a certain period of time to make the elements more homogeneous. Specifically, turn on the heating power supply and heat the sample from room temperature (25℃) to 550℃ at a heating rate of 25℃ / min. After the sample temperature reaches 550℃, hold the sample at that temperature for 30 minutes, with a temperature gradient of 60K / mm.

[0097] Step 5: After a certain holding time, the sample is pulled at a speed of 200 μm / s for a distance of 60 mm. During the cooling process, the temperature of the upper heating zone remains constant, and the sample is immersed in the coolant at a specific speed. Once the growth distance reaches the set distance, the sample is quickly immersed in the coolant for quenching.

[0098] Based on the results of scanning electron microscopy and X-ray energy dispersive spectroscopy ( Figure 6 , Figure 7 d, Figure 8 In the case of zinc-aluminum-magnesium alloy, when cooled with a temperature gradient of 60 K / mm and a pulling speed of 200 μm / s, the solidification structure of the alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-MgZn2 ternary eutectic, with the Zn-Al-MgZn2 ternary eutectic having an area fraction of 56%. Figure 9 ).

[0099] Example 5

[0100] Step 1: Using a UNI-T (UT302) high-precision infrared thermometer, the actual surface temperature of the zinc-aluminum-magnesium steel plate coating after removal from the crucible and during each cooling process was measured. Positions 1, 2, 3, 4, and 5 correspond to the positions of the air knife, air box 1, air box 2, air box 4, and air box 5, respectively. The temperatures and cooling rates at different positions are as follows: Figure 1 As shown. The cooling stage of zinc-aluminum-magnesium alloy was simulated using Ansys, and the model is as follows. Figure 2 As shown, the temperature distribution and cooling rate are as follows: Figure 3 , Figure 4 As shown, the actual temperature measurement results are basically consistent with the simulation calculation results.

[0101] Step 2: Based on the measurement results from Step 1, the cooling rate during the cooling stage of hot-dip galvanized aluminum-magnesium is 5-10.5℃ / s. On this basis, the experimental parameters for directional solidification are designed: the directional solidification temperature gradient is selected as 60K / mm, the pulling speed is selected as 300μm / s, and the cooling rate is 18℃ / s.

[0102] Step three: Conduct the directional solidification experiment using the experimental parameters from step two. A zinc-aluminum-magnesium alloy with a composition of Zn-11Al-3Mg is cut into metal rods with a diameter of 7 mm and a length of 110 mm. These rods are placed inside an alumina crucible and fixed within the directional solidification furnace, with the upper end in the heat preservation zone and the lower end submerged in the coolant. The directional solidification furnace is then evacuated to a pressure of 10... -2 Pa, then high-purity argon gas was introduced to 300 Pa to reduce the oxidation and volatilization of alloying elements during the experiment.

[0103] Step four: Heat the sample above the melting point of the Zn-11Al-3Mg alloy to completely melt it and hold it at that temperature for a certain time to make the elements more homogeneous. Specifically, turn on the heating power supply and heat the sample from room temperature to 550℃ at a heating rate of 25℃ / min. After the sample temperature reaches 550℃, hold the sample at that temperature for 30 minutes, with a temperature gradient of 60K / mm.

[0104] Step 5: After a certain holding time, the sample is pulled at a speed of 300 μm / s for a distance of 60 mm. During the cooling process, the temperature of the upper heating zone remains constant, and the sample is immersed in the coolant at a specific speed. Once the growth distance reaches the set distance, the sample is quickly immersed in the coolant for quenching.

[0105] Based on the results of scanning electron microscopy and X-ray energy dispersive spectroscopy ( Figure 6 , Figure 7 e, Figure 8 In the case of zinc-aluminum-magnesium alloy, when cooled with a temperature gradient of 60 K / mm and a pulling speed of 300 μm / s, the solidification structure of the alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-MgZn2 ternary eutectic, with the Zn-Al-MgZn2 ternary eutectic having an area fraction of 49%. Figure 9 Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Figure 7 Figure 8 Figure 9 Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Figure 7 Figure 8 Figure 9 ).

[0106] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for controlling the microstructure of hot-dip galvanized aluminum-magnesium alloys using directional solidification technology, characterized in that, Includes the following steps: 1) Determination of cooling parameters for hot-dip galvanized aluminum-magnesium steel in actual production: The actual surface temperature of the zinc-aluminum-magnesium steel plate coating after leaving the crucible and during each cooling process was measured on-site using an infrared thermometer; the cooling stage of zinc-aluminum-magnesium steel was simulated using Ansys, and the cooling rate of hot-dip galvanized aluminum-magnesium steel was 6-10.5℃ / s, and the temperature gradient was 60K / mm. 2) Design of directional solidification test parameters: Based on the cooling rate and temperature gradient of hot-dip galvanized aluminum-magnesium alloy in the actual production process determined in step 1), and combined with the relationship between cooling rate R, temperature gradient G, and pulling speed V in the directional solidification process, R=G×V, the temperature gradient in the directional solidification test is determined to be 60K / mm, and the pulling speed range is 20-300μm / s. The corresponding cooling rate range is 1.2℃ / s-18℃ / s, which includes the cooling rate in step 1) required in the actual production process. 3) The zinc-aluminum-magnesium alloy is placed in a directional solidification furnace for heat treatment to obtain a heat-treated zinc-aluminum-magnesium alloy; The composition of the zinc-aluminum-magnesium alloy is Zn-11Al-3Mg; 4) The heat-treated zinc-aluminum-magnesium alloy obtained in step 3) is drawn out and then quenched in a cooling liquid. When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed is 20 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure consists of Zn-Al-Mg2Zn. 11 The area fraction of the ternary eutectic is 89%; When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed is 50 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic, and Zn-Al-Mg2Zn. 11 The ternary eutectic structure consists of Zn-Al-Mg2Zn. 11 The area fraction of the ternary eutectic is 76%; When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed of the pulling is 100 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structures, and the area fraction of Zn-Al-MgZn2 ternary eutectic is 59%. When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed of the pulling is 200 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structures, and the area fraction of Zn-Al-MgZn2 ternary eutectic is 56%. When the temperature gradient of the heat treatment is 60 K / mm and the pulling speed of the pulling is 300 μm / s, the solidification structure of the zinc-aluminum-magnesium alloy consists of primary Al dendrites, Al-MgZn2 binary eutectic and Zn-Al-MgZn2 ternary eutectic structures, and the area fraction of Zn-Al-MgZn2 ternary eutectic is 49%. In step 3), after the zinc-aluminum-magnesium alloy is placed in the directional solidification furnace, a vacuum is drawn to a pressure of 10⁻² Pa, and then argon gas is introduced to a pressure of 300 Pa. The conditions for heat treatment in step 3) include: heating the sample from 25°C to 550°C at a heating rate of 25°C / min; after the sample temperature reaches 550°C, the sample is kept at the temperature for 30 minutes. The pulling distance in step 4) is 60mm.

2. The method according to claim 1, characterized in that, The zinc-aluminum-magnesium alloy in step 3) has a diameter of 7 mm and a length of 110 mm.

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