Aluminum-zinc-silicon-magnesium plated steel sheet having excellent bending property and method for manufacturing the same

Abstract

The present application provides a kind of aluminium zinc silicon magnesium plated steel sheet with excellent bending performance and its manufacturing method, plating solution includes the following mass percentage components: Zn:45%~50%, Mg:1.5%~2.5%, Si:1.0~1.5%, Ti:0.002%~0.005%, La+Ce content 0.04%~0.06%, the rest is Al and inevitable impurity element element.Compared with prior art, by controlling the content of magnesium silicon alloy phase in the coating, the size of magnesium zinc phase, zinc-rich phase, silicon phase is controlled, by adding appropriate amount of titanium and mixed rare earth elements, the grain is refined, the wettability of plating solution is improved, and the implementation of cooling process control strategy is matched, so that the aluminium zinc silicon magnesium plated steel sheet with excellent bending deformation performance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically the field of hot-dip galvanizing of steel, and specifically relates to an aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties and its manufacturing method. Background Technology

[0002] Hot-dip galvanizing is of great significance for protecting steel plates, improving their durability, and reducing costs. To improve the corrosion resistance of traditional hot-dip galvanized steel plates and conserve zinc resources, aluminum is added to the pure zinc coating. At the same time, a certain amount of silicon is added to inhibit the violent reaction between aluminum and the steel substrate, thus forming an aluminum-zinc-silicon coating with superior corrosion resistance.

[0003] With the increasing demand for high corrosion resistance and high formability of steel plates in specific environments or long-term corrosive media such as construction and animal husbandry in recent years, the addition of magnesium to aluminum-zinc-silicon coatings has formed aluminum-zinc-silicon-magnesium coatings with excellent corrosion resistance. This coating is considered to be a promising next-generation protective coating material with a very broad development prospect in the field of color-coated steel sheets for engineering construction.

[0004] The application scenarios for aluminum-zinc-silicon-magnesium coated steel sheets require them to possess both high corrosion resistance and certain formability. However, because aluminum-zinc-silicon-magnesium coatings are aluminum-based multi-element alloy coatings, the coating forms a microstructure during solidification with aluminum dendrites as the structural framework and alloy and eutectic phases located between the dendrites as filling. This inhomogeneity of the coating microstructure makes it prone to cracking during forming. Compared with pure zinc and low-aluminum-content zinc-aluminum-magnesium coatings, its formability is poor, which to some extent restricts the application of aluminum-zinc-silicon-magnesium coated steel sheets and their color-coated sheets in the market.

[0005] Patent CN 101910444 A, published on December 8, 2010, discloses a metal-coated steel strip. The disclosed strip is coated with an Al-Zn-Si-Mg alloy, which comprises aluminum, zinc, silicon, and magnesium in the following weight percentage ranges: aluminum: 40-60%, zinc: 40-60%, silicon: 0.3-3%, and magnesium: 0.3-10%. The coating microstructure contains Mg2Si particles. The distribution of Mg2Si particles is such that only a small portion of Mg2Si particles are present on the surface of the coating, or at least there are virtually no Mg2Si particles. However, its formability does not meet current application requirements. Summary of the Invention

[0006] The purpose of this invention is to provide an aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending performance and its manufacturing method. By adjusting the morphology and proportion of the alloy phase in the coating, the crack incidence rate is reduced; by reducing the size of the aluminum flowers on the coating surface, the extension and propagation behavior of cracks in the coating is suppressed, and the proportion of long cracks after bending deformation of the coating is reduced, so that it meets the requirements of corrosion resistance while having better formability.

[0007] The specific technical solution of this invention is as follows:

[0008] An aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties includes a substrate, a restraining layer, and a coating.

[0009] In the cross-sectional microstructure of the aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties, the thickness deviation of the coating measured from the inhibition layer between the coating and the substrate to the coating surface within an arbitrarily selected 50μm length along the horizontal direction is no greater than 10%. The calculation method is as follows: under a microscope at 200x magnification, within an arbitrarily selected 50μm length along the horizontal direction, |the thickest or thinnest coating thickness - theoretical coating thickness| / theoretical thickness × 100%. The theoretical coating thickness is calculated as: single-sided coating weight / coating density.

[0010] The cross-sectional microstructure of the coating consists of at least three layers divided along the direction perpendicular to the coating thickness by an aluminum dendritic alloy phase (Mg-Si or Mg-Zn phase) or a eutectic structure.

[0011] The mass content of the Mg-Si phase in the interdendritic space of the coating is more than three times the mass content of the silicon phase in the interdendritic space.

[0012] In the cross-sectional microstructure of the coating, the distance between the single Si phase distributed between the dendrites and the inhibition layer between the coating and the substrate in the direction perpendicular to the coating thickness is no more than 1 / 3 of the total coating thickness, and the mass content of the single Si phase accounts for no more than 1% of the proportion of the interdendritic phase.

[0013] The cross-sectional microstructure of the coating contains Mg-Zn phases in the dendrites, which are irregularly distributed in blocky form and have a size of no more than 3 μm.

[0014] The zinc-rich phase contained between dendrites in the cross-sectional microstructure of the coating is distributed in granular or irregular blocky form with a size not exceeding 2 μm.

[0015] The present invention provides a method for manufacturing an aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties, comprising immersion coating;

[0016] The plating solution used for immersion plating contains the following components by mass percentage: Zn: 45%–50%, Mg: 1.5%–2.5%, Si: 1.0%–1.5%, Ti: 0.002%–0.005%, La+Ce content 0.04%–0.06%, with the balance being Al and unavoidable impurity elements;

[0017] The content of the unavoidable impurity elements is less than 1%.

[0018] The immersion coating control requirements include: after the strip exits the air knife, a front-stage fan cools it to 440°C, with a cooling rate controlled at 8°C / s to 15°C / s; when the strip temperature is between 390°C and 440°C, a mid-stage fan is used for cooling, with a cooling rate controlled at 15°C to 20°C / s; when the strip temperature is between 280°C and 390°C, a rear-stage fan is used for cooling, with a cooling rate controlled at 25°C to 35°C / s. The fans are segmented, and the strip cooling process is controlled in segments. Corresponding fans are used for cooling within specific temperature ranges, which can be easily achieved by adjusting the strip running speed in conjunction with the fan power.

[0019] During the immersion plating process, the zinc pot temperature is 590-600℃, with a zinc pot temperature deviation of ±1℃. The temperature of the strip steel outlet knife is 5-10℃ lower than the pot temperature, and the cooling device nozzle type is "straight seam".

[0020] The aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties uses cold-rolled steel sheet as its substrate.

[0021] The weight of the aluminum-zinc-silicon-magnesium coating after dip-plating is 150g / m. 2 ~200g / m 2 .

[0022] Compared with the prior art, the present invention obtains aluminum-zinc-silicon-magnesium coated steel sheets with excellent bending deformation performance by controlling the content of magnesium-silicon alloy phase and silicon phase in the coating, controlling the size of magnesium-zinc phase and zinc-rich phase, refining the grains and improving the wettability of the coating solution by adding appropriate amounts of titanium and mixed rare earth elements, and implementing a cooling process control strategy. Attached Figure Description

[0023] Figure 1 This section describes the cross-sectional microstructure of aluminum-zinc-silicon-magnesium coatings.

[0024] Figure 2 A schematic diagram of the bending deformation of an aluminum-zinc-magnesium-silicon coated steel plate.

[0025] Figure 3 The cross-section and surface morphology of the coating in Example 1 are shown.

[0026] Figure 4 The bending crack morphology of the coating in Example 1 is shown.

[0027] Figure 5 Comparative Example 1 shows the cross-section and surface morphology of the coating;

[0028] Figure 6 Comparative Example 1 shows the morphology of the coating bending cracks;

[0029] Figure 7 These are neutral salt spray photos of samples 1500h from Examples 1 and 2.

[0030] Figure 8 These are photos of neutral salt spray observed at 1500 hours for comparative samples 1 and 2. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The present invention provides an aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties, comprising a substrate, an inhibition layer, and a coating; the inhibition layer and the coating are sequentially arranged on the substrate, and the coating refers to an aluminum-zinc-silicon-magnesium coating. The microstructure of the aluminum-zinc-silicon-magnesium coating of the present invention mainly consists of an aluminum-rich dendritic phase and zinc-rich phases, binary alloy phases, and ternary eutectic phases located between the dendrites. Aluminum is the first precipitated phase, growing in a dendritic shape. As the solidification temperature decreases, the alloy phase and the eutectic phase gradually precipitate within the dendrite interstices, and the microstructure is as follows. Figure 1 As shown.

[0033] The inventors discovered that the characteristic microstructure of aluminum-zinc-silicon-magnesium (AZMS) coatings, with aluminum dendrites as the structural framework and alloy and eutectic phases filling the spaces between the dendrites, results in severe fragmentation of the coating and poor microstructure uniformity. During bending, the significant plasticity difference between the aluminum-rich phase and the alloy phases located between the dendrites prevents uniform deformation of the coating, making it prone to cracking. Selecting Zn-rich phases, Mg₂Si, MgZn₂, Al, and Si single crystals in the coating as research objects, the inventors calculated the Young's modulus of each single crystal phase in the coating to illustrate the differences in plastic deformation of the AZMS coating under stress.

[0034] The elastic modulus of a single crystal is E, S 11 S 33 S 13 S 44 Let E be the compliance coefficient acting in different crystallographic directions, and θ be the angle between a certain crystal plane (hkil) of the calculated HCP metal and the (0001) plane. Then E has the following relationship with the compliance coefficient:

[0035] 1 / E = S 11 (sin 4 θ)+S 33 (cos 4 θ)+(2S 13 +S 44 (cos) 2 θ)(sin 2 θ) (1)

[0036] The crystal plane angle is calculated using the following formula:

[0037] cosθ = 0.75 × (a / c) 2 ×l×{0.75(a / c) 2 ×(h 2 +k 2 +hk+0.75(a / c) 2 ×l 2 )}^(-1 / 2) (2)

[0038] The anisotropy coefficient is calculated using the following formula:

[0039] f E =S 11 / S 33 (3)

[0040] For cubic single crystals, the following relationship holds:

[0041] 1 / E = S 11 -2(S 11 -S 12 -1 / 2×S 44 )(L1^2×L2^2+L2^2×L3^2+L3^2×L1^2) (4)

[0042] Crystal plane angle:

[0043] cosθ=(h1h2+k1k2+l1l2) / {(h1 2 +k1 2 +l1 2 ) (1 / 2) ×(h2 2 +k2 2 +l2 2 ) (1 / 2)} (5)

[0044] Anisotropy coefficient:

[0045] f E =(2C 44 +C 12 ) / C 11

[0046] The calculated elastic modulus and anisotropy coefficients of each single crystal phase in the close-packed hexagonal and body-centered cubic structures are shown in Table 1.

[0047] Table 1. Young's modulus (GPa) and anisotropy coefficient of low-index crystal planes of HCP and FCC structured single crystals in aluminum-zinc-silicon-magnesium coatings.

[0048]

[0049] As shown in Table 1, the elastic moduli of MgZn2, Mg2Si, Si and aluminum-rich dendritic phases in the coating are significantly different. Therefore, when the alloy coating undergoes bending deformation, the plasticity difference between aluminum dendrites and interdendritic alloy phases can easily lead to cracking of the coating.

[0050] To address the aforementioned problems and without affecting the corrosion resistance of the alloy coating, this invention strictly controls the size or distribution of the aluminum interdendritic alloy phase in the alloy coating. Therefore, when the coating microstructure contains both Mg-Zn and Mg-Si phases, the size of the irregularly blocky Mg-Zn phase distributed between the dendrites in the cross-sectional microstructure of the coating should not exceed 3 μm. A certain amount of Mg-Si phase is formed to replace the single Si phase, thereby reducing the deformability difference between the Mg-Si phase and the aluminum-rich phase, and ensuring that a certain amount of magnesium-containing alloy phase provides Mg in the corrosive medium. 2+ Ions improve the corrosion resistance of the coating.

[0051] Furthermore, the size of the zinc-rich phase, which is granular or irregularly blocky and distributed between dendrites in the cross-sectional microstructure of the coating, should not exceed 2 μm. As shown in the calculations above, the zinc-rich phase in the coating exhibits the greatest elastic anisotropy. During bending, crack propagation is highly likely to occur in the zinc-rich phase. However, since the zinc-rich phase forms at the end of solidification, it is generally located within the eutectic phase and is beneficial for improving the corrosion resistance of the coating. When the size of the zinc-rich phase in the coating exceeds the range required by this invention, it indicates that significant component segregation occurs during solidification, which is detrimental to the refinement of the coating microstructure and reduces the content of the ternary alloy phase in the coating, resulting in a significant decrease in the corrosion resistance of the coating.

[0052] Furthermore, in the alloy coating process described in this invention, due to the high aluminum content in the plating solution, it is necessary to add more than 1% silicon to suppress the violent reaction between the plating solution and iron, ensuring the bonding force between the coating and the steel substrate. After the remaining silicon participates in the reaction between the iron substrate and the plating solution to form an alloy layer, it will react with magnesium in the aluminum-rich dendrites during the middle stage of solidification to form a Mg-Si phase. Due to the limitation of magnesium content, a certain amount of single silicon phase is usually also generated. As can be seen from the calculated value of elastic modulus, the single silicon phase has the largest elastic modulus, i.e. the worst plasticity. When the single silicon phase is arbitrarily distributed in the coating, it is very detrimental to the bending performance and corrosion resistance of the alloy coating described in this application. Therefore, the distance between the single Si phase distributed between the dendrites in the cross-sectional microstructure of the coating and the inhibition layer between the coating and the substrate in the direction perpendicular to the coating thickness is not greater than 1 / 3 of the total coating thickness, and the mass content of the single Si phase accounts for no more than 1% of the dendrite phase. This can effectively suppress the crack initiation and propagation caused by the distribution of silicon when the coating undergoes bending deformation.

[0053] The inventors also discovered that when the alloy coating is bent and deformed, the bending stress on the outer surface of the coating increases with the increase of the coating thickness. The uniformity of the coating thickness will seriously affect the cracking behavior of the coating during the bending process. Therefore, in the cross-sectional structure of the coating described in this application, the coating thickness deviation measured from the inhibition layer between the coating and the substrate to the coating surface within an arbitrarily selected 50μm length along the horizontal direction should not be greater than 10%, so as to ensure the uniformity of the coating thickness.

[0054] Furthermore, in order to control the uniformity of cracks generated during bending of the alloy coating described in this application, and to obtain high-quality color-coated steel sheets in subsequent painting or continuous coating processes, the microstructure of the alloy coating should be refined as much as possible. The more layers the microstructure of the coating cross section has, the higher the degree of refinement of the coating microstructure. Therefore, the coating structure divided by aluminum dendrite alloy phases or microstructures along the direction perpendicular to the coating thickness should be no less than 3 layers.

[0055] The magnesium content in the alloy coating is set to 1.5%–2.5%. The improved bending performance of the aluminum-zinc-silicon-magnesium (AZMS) coating should be achieved without sacrificing corrosion resistance. The coating contains a certain amount of Mg to ensure the formation of a certain amount of ternary eutectic phase and magnesium-zinc phase. During corrosion, the magnesium-zinc phase and eutectic phase readily undergo selective dissolution, generating high-density corrosion products that cover the coating surface, inhibiting further corrosion in the corrosive medium and thus significantly improving the corrosion resistance of the AZMS coating. Simultaneously, when the Mg content is maintained between 2.0% and 2.5%, the strong affinity between magnesium and silicon elements allows for the formation of a magnesium-silicon phase in the coating, effectively reducing the free silicon content. The coating also provides a certain amount of magnesium ion dissolution during corrosion, ensuring high corrosion resistance. However, excessively high magnesium content makes surface oxidation difficult to control, deteriorating the surface quality. Therefore, the magnesium content is controlled within the reasonable range described in this application.

[0056] Adding trace amounts of titanium to the coating: The Ti-Al phase formed after adding titanium has a low lattice mismatch with the aluminum-rich phase, promoting the nucleation of the aluminum-rich phase on the Ti-Al alloy phase particles. Furthermore, trace amounts of titanium can strongly inhibit the growth of aluminum dendrites, suppressing their growth after nucleation. Therefore, trace amounts of titanium in aluminum-zinc-silicon-magnesium coatings have a significant effect on refining aluminum dendrites during the coating solidification process. Excessive titanium in the alloy plating bath easily generates excessive high-melting-point Ti-Al phase, increasing the slag content in the zinc pot, which is detrimental to industrial production and the control of coating surface quality.

[0057] Adding 0.04%–0.06% of lanthanum-cerium mixed rare earth elements to the coating: Rare earth elements have a strong purifying effect on the alloy plating bath; as surfactants, they can reduce the wetting angle between the nucleating substrate and the aluminum-rich phase, thus refining the Al grains; simultaneously, trace amounts of mixed rare earth elements have a strong modifying effect on the pre-precipitated Si phase, significantly altering the morphology and distribution of the Si phase in the coating, which is beneficial for improving the bending performance of the coating. The effect of trace amounts of rare earth elements is very significant; excessive content is detrimental to the balance of the zinc pot slag system, and due to the low recovery rate of rare earth elements, excessively high rare earth content is also not conducive to reducing production costs.

[0058] The Zn content in the coating is controlled at 45%–50%: Due to the mutual solubility of aluminum and zinc, appropriately increasing the zinc content in the coating can produce a strong solid solution strengthening effect, improve the strength of the aluminum-rich phase, enhance the coordinated deformation ability of the aluminum-rich phase and the interdendritic phase of aluminum during bending, and improve the bending performance of the coating; the liquid phase with a higher zinc content has stronger wettability to the aluminum-rich phase in the later stage of solidification, which can strengthen the bonding force between the zinc-rich alloy phase and the ternary phase and the aluminum-rich phase interface, strengthen the interfacial bonding force during deformation, and improve the ability to resist cracks during bending.

[0059] The coating cooling process control requirements of this invention include: after the strip exits the air knife, a front-stage fan is used to cool it to 440°C, with a cooling rate controlled at 8°C / s to 15°C / s; when the strip temperature is between 390°C and 440°C, a mid-stage fan is used for cooling, with a cooling rate controlled at 15°C to 20°C / s; when the strip temperature is between 280°C and 390°C, a rear-stage fan is used for cooling, with a cooling rate controlled at 25°C to 35°C / s. The front-stage cooling refines the aluminum-rich dendrites while ensuring the cooling rate is not too high; the mid-stage cooling uses a higher cooling rate to suppress the size and content of magnesium-zinc phases during coating solidification, which is beneficial to improving the coating's bending performance; the rear-stage cooling uses the highest cooling rate to suppress further eutectoid reactions of the aluminum-rich phase in the coating, avoiding the formation of large-sized zinc-rich and aluminum-rich phases.

[0060] The zinc pot temperature and cooling device nozzle of this invention: precise control of zinc pot temperature helps to reduce the amount of slag in the pot, and the use of "straight seam" type air outlet nozzles can make the coating surface cool more evenly, effectively suppressing surface defects caused by uneven local cooling, which is conducive to producing products with high surface quality.

[0061] The present invention will now be described in detail with reference to embodiments, comparative examples and experimental data.

[0062] Examples 1-2, Comparative Examples 1-2

[0063] A method for manufacturing an aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties includes hot-dip galvanizing a substrate; using a cold-rolled sheet as the substrate, the substrate being a CQ grade steel sheet comprising the following components by mass percentage: C: 0.02%, Si: 0.03%, Mn: 0.2%, P: 0.015%, S: 0.008%, with the balance being Fe and unavoidable impurities. The chemical composition of the plating solution is shown in Table 2, with the balance being Al and unavoidable impurity elements at a content of less than 1%.

[0064] The immersion plating control requirements include: after the strip exits the air knife, a front-stage fan is used to cool it to 440°C, with a cooling rate controlled at 8°C / s to 15°C / s; when the strip temperature is between 390°C and 440°C, a middle-stage fan is used for cooling, with a cooling rate controlled at 15°C to 20°C / s; when the strip temperature is between 280°C and 390°C, a rear-stage fan is used for cooling, with a cooling rate controlled at 25°C to 35°C / s.

[0065] During the immersion plating process, the zinc pot temperature is 590-600℃, with a zinc pot temperature deviation of ±1℃. The temperature of the strip steel outlet knife is 5-10℃ lower than the pot temperature, and the cooling device nozzle type is "straight seam".

[0066] The weight of the aluminum-zinc-silicon-magnesium coating after dip-plating is 150g / m. 2 ~200g / m2 .

[0067] Comparative Example 1 - Comparative Example 2

[0068] A method for manufacturing an aluminum-zinc-silicon-magnesium coated steel sheet includes hot-dip galvanizing a substrate. The substrate steel sheet is of CQ grade and comprises the following components in the indicated mass ratios: C: 0.02%, Si: 0.03%, Mn: 0.2%, P: 0.015%, S: 0.008%, with the balance being Fe and unavoidable impurities. Plating solutions for Comparative Examples 1-2 are prepared, the chemical composition of which is shown in Table 2, with the balance being Al and unavoidable impurity elements at a content of less than 1%.

[0069] Examples 1-2 and Comparative Examples 1-2 were produced using the same process. The differences in the preparation process parameters are shown in Table 3. The phase composition of the coating and the bending properties of the coating are shown in Tables 4 and 5.

[0070] Table 2. Plating solution composition and coating weight of the examples and comparative examples.

[0071]

[0072] Table 3. Main process parameters for the preparation of each example and comparative example.

[0073]

[0074]

[0075] The coating structure and bending performance of the aluminum-zinc-silicon-magnesium coated steel sheets prepared according to the plating solution composition and process parameters in the above examples and comparative examples and according to the preparation method of the present invention were tested and analyzed. The evaluation methods adopted were as follows: (1) The coated steel sheets in the examples and comparative examples were subjected to 0T to 4T bending tests according to the bending test provisions in GB T 13448-2019 Test Methods for Color Coated Steel Sheets and Strips; (2) After T-bending, 3M transparent tape was tightly attached to the coated surface after bending, and then the tape was quickly lifted to observe whether there was any metal coating peeling off the tape; (3) The crack width was observed and measured under the same magnification of an electron microscope; (4) The distribution and size of characteristic phases in the coating structure were analyzed using ImageJ image processing software; (5) A neutral salt spray test was carried out according to ASTM B117. The sample size was 75mm×150mm. The edges of the sample were sealed with 3M tape. The sample was placed in a neutral salt spray test chamber for 1500°C to observe whether there was any red rust on the sample surface. The test evaluation results are shown in Tables 4 and 5.

[0076] Table 4. Microstructure characteristics and coating thickness of the coating cross-sections in the examples and comparative examples.

[0077]

[0078] Table 5. Test results of the bending performance and corrosion resistance of the coatings in the examples and comparative examples.

[0079]

[0080]

[0081] Based on the evaluation results in Table 5 and Figures 3-4 , Figures 5-6 , Figures 7-8 Compared with Comparative Examples 1-2, the zinc-aluminum-magnesium coated steel sheets prepared in Examples 1 and 2 of this invention exhibit smaller crack widths and better crack uniformity after bending deformation at 0T, 2T, and 4T. The coatings in these examples show more obvious layering morphology, indicating a significant refinement effect in the coating structure. Furthermore, the magnesium-silicon phase content in the coatings is higher than in the comparative examples, while the silicon phase content and the size of the zinc-rich phase and magnesium-zinc phase are lower, resulting in better crack propagation resistance and superior bending performance. Based on the comparison of surface dendrite morphology, it can be seen that the aluminum flower size on the surface of the coatings in these examples is smaller than that in the comparative examples, suppressing crack extension and propagation behavior in the coating and reducing the proportion of long cracks after bending deformation. No red rust was generated on the surface of the samples after 1500h neutral salt spray testing, demonstrating equivalent corrosion resistance.

[0082] The data underlined above do not meet the requirements of this invention.

[0083] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for manufacturing an aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties, characterized in that, The manufacturing method includes immersion plating, and the plating solution used includes the following components by mass percentage: Zn: 45%~50%, Mg: 1.5%~2.5%, Si: 1.0~1.5%, Ti: 0.002%~0.005%, La+Ce content 0.04%~0.06%, and the balance being Al and unavoidable impurity elements.

2. The manufacturing method according to claim 1, characterized in that, The immersion coating control is as follows: after the strip exits the air knife, a front-stage fan is used to cool it to 440℃, with a cooling rate controlled at 8℃ / s to 15℃ / s; when the strip temperature is between 390℃ and 440℃, a middle-stage fan is used for cooling, with a cooling rate controlled at 15℃ to 20℃ / s; when the strip temperature is between 280℃ and 390℃, a rear-stage fan is used for cooling, with a cooling rate controlled at 25℃ to 35℃ / s.

3. The manufacturing method according to claim 1 or 2, characterized in that, During the immersion plating process, the zinc pot temperature is 590~600℃, the zinc pot temperature deviation is ±1℃, and the strip outlet knife temperature is 5~10℃ lower than the pot temperature.

4. The manufacturing method according to claim 1 or 2, characterized in that, The weight of the aluminum-zinc-silicon-magnesium coating after dip-plating is 150g / m. 2 ~200g / m 2 .

5. An aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties manufactured by the manufacturing method according to any one of claims 1-4, comprising a substrate, an inhibition layer, and a coating; characterized in that, In the cross-sectional microstructure of the aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties, the thickness deviation of the coating measured from the inhibition layer between the coating and the substrate to the coating surface within a 50μm length arbitrarily selected along the horizontal direction is no greater than 10%.

6. The aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties according to claim 5, characterized in that, The cross-sectional microstructure of the coating consists of at least three layers divided by aluminum dendrite alloy phases or eutectic structures along the direction perpendicular to the coating thickness.

7. The aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties according to claim 5, characterized in that, The mass content of the Mg-Si phase in the interdendritic space of the coating is more than three times the mass content of the silicon phase in the interdendritic space.

8. The aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties according to claim 5, characterized in that, In the cross-sectional microstructure of the coating, the distance between the single Si phase distributed between the dendrites and the inhibition layer between the coating and the substrate in the direction perpendicular to the coating thickness is no more than 1 / 3 of the total coating thickness, and the mass content of the single Si phase accounts for no more than 1% of the proportion of the interdendritic phase.

9. The aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties according to claim 5, characterized in that, The cross-sectional microstructure of the coating contains Mg-Zn phases in irregular blocky distribution between dendrites, with a size not exceeding 3 μm.

10. The aluminum-zinc-silicon-magnesium coated steel sheet with excellent bending properties according to claim 5, characterized in that, The zinc-rich phase contained between dendrites in the cross-sectional microstructure of the coating is distributed in granular or irregular blocky form with a size not exceeding 2 μm.

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