WO2026001677A1 - Highly corrosion-resistant coated steel plate and preparation method therefor - Google Patents

Abstract

A highly corrosion-resistant coated steel plate and a preparation method therefor. The steel plate is composed of a steel base and a coating layer. The microstructure of the coating layer is a Zn-MgZn2-Al ternary eutectic phase, a Zn-Al binary eutectoid phase, a Zn-MgZn2 binary eutectic phase, an Mg2Si-Zn ternary eutectic phase, and an Al-Zn-Fe-Si alloy layer, and the chemical composition of the coating layer comprises 10-20% of Al, 2.2-6% of Mg, 0.08-0.4% of Si, and 0.05-0.6% of RE. The medium-aluminum-zinc-aluminum-magnesium coated steel prepared by the method has better corrosion resistance than a traditional zinc-aluminum-magnesium coating layer. The microstructure of the coating layer is controlled by means of a composition system and a cooling process. Thus, the microstructure of grains is refined, the occurrence of a pure zinc phase as a weak phase is avoided, the corrosion resistance is improved, the occurrence of brittle phases such as a rare earth phase and a silicon-rich phase is eliminated, and the formability of the coating layer is optimized; moreover, the coating layer, after being bent, shows reduced cracks and still has good corrosion resistance, and thus the use requirements of photovoltaic steel for 30 years can be met.

Description

A high corrosion-resistant coated steel sheet and its preparation method

This application claims priority to Chinese Patent Application No. 202410848359.8, filed on June 27, 2024, entitled "A High Corrosion-Resistant Coated Steel Sheet and Its Preparation Method", the entire contents of which are incorporated herein by reference.

Technical Field

This invention belongs to the field of metal materials technology, specifically relating to a high corrosion-resistant coated steel sheet and its preparation method.

Background Technology

Zn-Al-Mg alloy coatings attracted widespread attention abroad in the 1980s, becoming a key research focus in the fields of hot-dip galvanizing and zinc alloy coatings. Research from domestic and international peers indicates that, under the same Zn and Al content conditions, hot-dip Zn-Al-Mg alloy coated steel sheets with added Mg exhibit superior corrosion resistance and excellent processing and application properties (formability, weldability, and paintability). They can replace existing hot-dip galvanized or zinc alloy coated steel sheets, indicating a very broad market demand prospect. Research on Zn-Al-Mg alloy coatings in my country started relatively late. Currently, companies such as Jiuquan Iron & Steel, Baosteel, Shougang Group, Jiuquan Iron & Steel, and Panzhihua Iron & Steel have launched hot-dip Zn-Al-Mg alloy coated steel sheets, with the most widespread application in the photovoltaic field. The Southwest region alone requires approximately 550,000 tons of zinc, aluminum, and magnesium products annually.

In the prior art, patent CN 116288097 A discloses a zinc-aluminum-magnesium alloy coated steel plate for photovoltaic applications and its preparation method. The chemical composition and mass percentage of the zinc-aluminum-magnesium alloy coating of the zinc-aluminum-magnesium coated steel plate are: Al 5-9%, Mg 2.5-4.5%, Ni 0-0.15%, Ti 0-0.2%. This patent contains a small amount of pure zinc phase, which affects the overall corrosion resistance of the coating.

Patent CN 115305386 A provides a high corrosion-resistant hot-dip zinc-aluminum-magnesium alloy, a material with a ZAM coating, and a method for preparing the same. The high corrosion-resistant hot-dip zinc-aluminum-magnesium alloy is composed of the following components: Mg 0.3%–3.9%, Al 1.2%–9.8%, RE 0.08%–3.2%, and Ge 1.0%–3.0%. The preparation method includes: heating and melting Mg, Al, and Zn raw materials at a first temperature, then adding RE and Ge, and heating at a second temperature until completely dissolved to obtain a liquid alloy; placing the preheated substrate into the liquid alloy, and then cooling to obtain the material with a ZAM coating. The material exhibits significant microstructure variations and contains a pure zinc phase with poor corrosion resistance, and may also contain acicular rare earth phases with poor formability.

The existing research on aluminum, zinc, aluminum, and magnesium alloys mainly focuses on composition, but there are still shortcomings in terms of the composition and relationship between each phase and the coordination of the component systems. Since the coating microstructure determines the coating performance, and the coating microstructure is determined by composition and process, it is necessary to develop a high-corrosion-resistant coated steel sheet and its preparation method based on compositional coordination control to eliminate weak phases, in order to further optimize the corrosion resistance and formability of the coating.

Summary of the Invention

To overcome the shortcomings of the existing technology, this invention optimizes the composition system, refines the grain structure, avoids the appearance of the weak pure zinc phase, and thus improves corrosion resistance; eliminates the appearance of brittle phases such as rare earth phase, silicon-rich phase, and intermediate alloy layer, optimizes the formability of the coating, and reduces cracks after bending while still maintaining good corrosion resistance, so as to meet the 30-year service requirements of photovoltaic steel.

To achieve the above-mentioned objectives, this invention provides a high corrosion-resistant coated steel sheet, comprising a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 2–50 μm. The microstructure of the coating consists of a Zn- _MgZn2 -Al ternary eutectic phase, a Zn-Al binary eutectoid phase, a Zn- _MgZn2 binary eutectic phase, a _Mg2Si -Zn ternary eutectic phase, and an Al-Zn-Fe-Si alloy layer. The chemical composition of the coating, by mass percentage, is Al: 10%–20%, Mg: 2.2%–6%, Si: 0.08%–0.40%, RE: 0.05%–0.60%, with the balance being Zn and other unavoidable impurities.

Furthermore, the coating structure of the high corrosion-resistant coated steel sheet does not contain pure zinc phase, rare earth phase, or silicon-rich phase. The rare earth is a mixture of lanthanum and cerium, which is uniformly distributed in the coating and does not exhibit needle-like accumulation.

Furthermore, to ensure that the coating consists of Zn- _MgZn2 -Al phase, Zn-Al phase, Zn-MgZn2 _binary phase, or _Mg2Si -Zn phase, the coating composition of the high corrosion-resistant coated steel sheet, in terms of atomic number, is 5.5Mg+2.5Al＞Zn+0.5Si, and Zn≥Al+2Mg.

Furthermore, based on the good fluidity of the plating solution, the control of the alloy layer thickness, and the good surface quality, the coating composition of the high corrosion-resistant coated steel sheet, by mass percentage, is 0.3% ≤ RE + Si ≤ 0.8%.

Furthermore, the steel base of the high corrosion-resistant coated steel sheet can be one of the following: low carbon aluminum killed steel, IF steel, P-containing high-strength IF steel, bake-hardening steel, SPCC, structural steel, QP steel, etc., either cold-rolled strip steel or hot-based strip steel.

A method for preparing the above-mentioned high corrosion-resistant coated steel sheet, the method comprising the following steps: pickling, rolling (or light pressing), degreasing and cleaning, continuous annealing, hot-dip galvanizing, air knife blowing, cooling, and finishing; wherein, the rolling is performed using a rough roll, and the surface roughness of the strip after rolling is controlled at 1.2 to 3.5 μm;

The continuous annealing process controls the hydrogen content in the furnace to be ≥2.5% by volume percentage;

The temperature of the steel plate entering the zinc pot is 420-620℃, the temperature of the plating solution during the hot-dip galvanizing process is 420-600℃, the temperature of the strip steel entering the zinc pot is not lower than the temperature of the zinc pot, and the hot-dip galvanizing time is 1-3 seconds.

Furthermore, in the method for preparing the high corrosion-resistant coated steel sheet, the degreasing and cleaning process involves rinsing thoroughly after degreasing; the air knife purging medium is at least one of _N2 and inert gas, with a _CO2 content ≤50ppm and an _O2 content ≤50ppm; rapid cooling is required after coating, with a cooling rate of 5–30℃/s, and the temperature of the strip reaching the top guide roller is ≤270℃; the surface roughness Ra of the finishing roller is controlled to be 2.0–4.5μm, and the finishing elongation is 0.5–1.5%.

Furthermore, the chemical composition of the plating solution is as follows: Al: 10.0%–20.0%, Mg: 2.2%–6.0%, Si: 0.08%–0.40%, RE: 0.05%–0.60%, with the balance being Zn and other unavoidable impurities.

Compared with the prior art, the beneficial effects of the present invention are as follows:

The aluminum-zinc-aluminum-magnesium coated steel prepared by this invention exhibits superior corrosion resistance compared to traditional zinc-aluminum-magnesium coatings. Through compositional design and cooling process control, the coating's microstructure is refined, preventing the formation of the weak pure zinc phase and improving corrosion resistance. It also eliminates the presence of brittle phases such as rare earth and silicon-rich phases, reduces the thickness of the brittle phases in the intermediate alloy layer, and optimizes the coating's formability. This results in reduced cracking after bending while maintaining good corrosion resistance, meeting the 30-year service life requirements for photovoltaic steel.

Attached Figure Description

Figure 1 shows the cross-sectional microstructure of the high corrosion-resistant coated steel sheet prepared in Example 1.

Detailed Implementation

The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

A high corrosion-resistant coated steel sheet is composed of a steel base and a coating. The coating structure consists of a Zn- _MgZn2 -Al ternary eutectic phase, a Zn-Al binary eutectoid phase, a Zn- _MgZn2 binary eutectic phase, a _Mg2Si -Zn ternary eutectic phase, and an Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is as follows (mass percentage): Al: 10.0%–20.0%, Mg: 2.2%–6.0%, Si: 0.08%–0.40%, RE: 0.05%–0.60%, with the balance being Zn and other unavoidable impurities.

The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 2–50 μm. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase; the rare earth element is a mixture of lanthanum and cerium. In the coating composition, by atomic number, 5.5Mg + 2.5Al > Zn + 0.5Si, Zn ≥ Al + 2Mg. In the coating composition, by mass percentage, 0.3% ≤ RE + Si ≤ 0.8%. The steel base is one of the following: low-carbon aluminum-killed steel, IF steel, high-strength IF steel containing phosphorus, bake-hardening steel, SPCC, structural steel, QP steel, or other cold-rolled or hot-rolled strip steel.

A method for preparing the above-mentioned high corrosion-resistant coated steel sheet includes the following steps: pickling, rolling, degreasing and cleaning, continuous annealing, hot-dip galvanizing, air knife blowing, cooling, and finishing; wherein,

The rolling process employs a rough roll rolling technique, and the surface roughness of the strip after rolling is controlled within the range of 1.2–3.5 μm.

The continuous annealing process controls the hydrogen content in the furnace to be ≥2.5% by volume percentage;

The temperature of the steel plate entering the zinc pot is 420-620℃, the temperature of the plating solution during the hot-dip galvanizing process is 420-600℃, the temperature of the strip steel entering the zinc pot is not lower than the temperature of the zinc pot, and the hot-dip galvanizing time is 1-3 seconds.

Degreasing and cleaning involves rinsing thoroughly after degreasing treatment; the air knife purging medium is at least one of _N2 and inert gas, with _CO2 content ≤50ppm and _O2 content ≤50ppm; rapid cooling is required after plating, with a cooling rate of 5～30℃/s, and the temperature of the strip reaching the top guide roller is ≤270℃; the surface roughness Ra of the finishing roller is controlled at 2.0～4.5μm, and the finishing elongation is 0.5～1.5%. The chemical composition of the plating solution is as follows (mass percentage): Al: 10%～20%, Mg: 2.2%～6%, Si: 0.08%～0.40%, RE: 0.05%～0.60%, with the balance being Zn and other unavoidable impurities.

Example 1

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base is low-carbon aluminum-killed steel DX52D. During cold rolling, the surface roughness of the strip after rolling is controlled at 1.2μm. The chemical composition of the plating solution is: Al 10%, Mg 3.0%, Si 0.10%, RE 0.20%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at ≥3.5% by volume percentage. The temperature of the steel plate entering the zinc pot is 420℃. The temperature of the plating solution during hot-dip galvanizing is 420℃, and the hot-dip galvanizing time is 1s. The air knife blowing medium is _N2 . The cooling rate after plating is 10℃/s, and the temperature of the strip reaching the top turning roll is 270℃. The surface roughness Ra of the finishing roll is controlled at 2.0μm, and the finishing elongation is 0.6%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 5 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is: Al 10%, Mg 3.0%, Si 0.10%, RE 0.20%, with the balance being Zn and other unavoidable impurities. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Example 1 are shown in Table 1.

Example 2

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base is low-carbon aluminum-killed Ti-IF steel. During cold rolling, the surface roughness of the strip after rolling is controlled at 1.5μm. The chemical composition of the plating solution is: Al 12%, Mg 2.5%, Si 0.15%, RE 0.10%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 4.0% by volume. The temperature of the steel plate entering the zinc pot is 480℃. The temperature of the plating solution during hot-dip galvanizing is 460℃, and the hot-dip galvanizing time is 2s. The air knife blowing medium is _N2 . The cooling rate after plating is 20℃/s, and the temperature of the strip reaching the top turning roll is 240℃. The surface roughness Ra of the finishing roll is controlled at 3.5μm, and the finishing elongation is 0.8%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 10 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is: Al 12%, Mg 2.5%, Si 0.15%, RE 0.10%, with the balance being Zn and other unavoidable impurities. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Example 2 are shown in Table 1.

Example 3

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base is structural steel S320GD. During cold rolling, the surface roughness of the strip after rolling is controlled at 1.5μm. The chemical composition of the plating solution is: Al 14%, Mg 3.5%, Si 0.30%, RE 0.20%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 5.0% by volume. The temperature of the steel plate entering the zinc pot is 480℃. The temperature of the plating solution during hot-dip galvanizing is 470℃, and the hot-dip galvanizing time is 3s. The air knife blowing medium is _N2 . The cooling rate after plating is 30℃/s, and the temperature of the strip reaching the top turning roll is 220℃. The surface roughness Ra of the finishing roll is controlled at 4.0μm, and the finishing elongation is 1.0%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 20 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is: Al 14%, Mg 3.5%, Si 0.30%, RE 0.20%, with the balance being Zn and other unavoidable impurities. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Example 3 are shown in Table 1.

Example 4

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base grade is SPCC. During cold rolling, the surface roughness of the strip after rolling is controlled at 3.0 μm. The chemical composition of the plating solution is: Al 16%, Mg 5.0%, Si 0.40%, RE 0.05%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 5.0% by volume. The temperature of the steel plate entering the zinc pot is 500℃. The temperature of the plating solution during hot-dip galvanizing is 480℃, and the hot-dip galvanizing time is 2s. The air knife blowing medium is _N2 . The cooling rate after plating is 25℃/s, and the temperature of the strip reaching the top turning roll is 245℃. The surface roughness Ra of the finishing roll is controlled at 4.5 μm, and the finishing elongation is 0.7%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 25 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is: Al 16%, Mg 5.0%, Si 0.40%, RE 0.05%, with the balance being Zn and other unavoidable impurities. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Example 4 are shown in Table 1.

Example 5

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base grade is 250P1. During cold rolling, the surface roughness of the strip after rolling is controlled at 3.5μm. The chemical composition of the plating solution is: Al 15%, Mg 6.0%, Si 0.20%, RE 0.15%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 6.0% by volume. The temperature of the steel plate entering the zinc pot is 520℃. The temperature of the plating solution during hot-dip galvanizing is 520℃, and the hot-dip galvanizing time is 1s. The air knife blowing medium is _N2 . The cooling rate after plating is 30℃/s, and the temperature of the strip reaching the top turning roll is 255℃. The surface roughness Ra of the finishing roll is controlled at 3.0μm, and the finishing elongation is 1.5%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 50 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is: Al 15%, Mg 6.0%, Si 0.20%, RE 0.15%, with the balance being Zn and other unavoidable impurities. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Example 5 are shown in Table 1.

Example 6

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base grade is S550GD. During cold rolling, the surface roughness of the strip after rolling is controlled at 2.5μm. The chemical composition of the plating bath is: Al 20%, Mg 4.0%, Si 0.35%, RE 0.25%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 3.5% by volume. The temperature of the steel plate entering the zinc pot is 550℃. The temperature of the plating bath during hot-dip galvanizing is 540℃, and the hot-dip galvanizing time is 2s. The air knife blowing medium is _N2 . The cooling rate after plating is 25℃/s, and the temperature of the strip reaching the top guide roll is 245℃. The surface roughness Ra of the finishing roll is controlled at 4.5μm, and the finishing elongation is 0.9%.

The microstructure of the zinc-aluminum-magnesium coated steel sheet prepared in Example 6 is shown in Figure 1. The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 30 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn- _MgZn2 binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and Al-Zn-Fe-Si alloy layer. The chemical composition of the coating is: Al 20%, Mg 4.0%, Si 0.35%, RE 0.25%, with the balance being Zn and other unavoidable impurities. The coating microstructure does not contain pure zinc phase, rare earth phase, or silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Example 6 are shown in Table 1.

Comparative Example 1

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base grade is low-carbon aluminum killed steel DX51D. During cold rolling, the strip is rolled without roughening the rolls, and the surface roughness is 1.0μm. The chemical composition of the plating bath is: Al 6%, Mg 3%, Si 0.20%, RE 0.10%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 4.0% by volume. The temperature of the steel plate entering the zinc pot is 480℃. The temperature of the plating bath during hot-dip galvanizing is 460℃, and the hot-dip galvanizing time is 1s. The air knife blowing medium is _N2 . The cooling rate after plating is 20℃/s, and the temperature of the strip reaching the top turning roll is 240℃. The surface roughness Ra of the finishing roll is controlled at 3.5μm, and the finishing elongation is 0.8%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 10 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, Al-Zn-Fe-Si alloy layer and pure zinc phase. A large number of zinc blowing defects appear on the surface.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Comparative Example 1 are shown in Table 1.

Comparative Example 2

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base grade is Ti-IF steel. During cold rolling, the surface roughness of the strip after rolling is controlled at 1.5μm. The chemical composition of the plating bath is: Al 14%, Mg 3.5%, Si 1.0%, RE 0.5%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 5.0% by volume. The temperature of the steel plate entering the zinc pot is 480℃. The temperature of the plating bath during hot-dip galvanizing is 470℃, and the hot-dip galvanizing time is 3s. The air knife blowing medium is _N2 . The cooling rate after plating is 30℃/s, and the temperature of the strip reaching the top turning roll is 220℃. The surface roughness Ra of the finishing roll is controlled at 4.0μm, and the finishing elongation is 1.0%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 20 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al _binary eutectoid phase, Zn-MgZn2 binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, Al-Zn-Fe-Si alloy layer, and silicon-rich phase.

The performance test results of the zinc-aluminum-magnesium coated steel prepared in Comparative Example 2 are shown in Table 1.

Comparative Example 3

A high corrosion-resistant coated steel sheet and its preparation method, the specific process flow is as follows:

The steel base is S350GD. During cold rolling, the surface roughness of the strip after rolling is controlled at 2.0μm. The chemical composition of the plating solution is: Al 10%, Mg 3.0%, Si 0.10%, RE 0.20%, with the balance being Zn and other unavoidable impurities. Degreasing and cleaning are performed by rinsing after degreasing treatment. During continuous annealing, the hydrogen content in the furnace is controlled at 2.0% by volume. The temperature of the steel plate entering the zinc pot is 420℃. The temperature of the plating solution during hot-dip galvanizing is 420℃, and the hot-dip galvanizing time is 1s. The air knife blowing medium is _N2 . The cooling rate after plating is 3℃/s. The temperature of the strip reaching the top turning roll is 350℃. The surface roughness Ra of the finishing roll is controlled at 1.5μm, and the finishing elongation is 0.3%.

The prepared high corrosion-resistant coated steel sheet consists of a steel base and a coating. The coating is a zinc-aluminum-magnesium alloy coating with a thickness of 10 μm. The microstructure of the coating consists of Zn- _MgZn2 -Al ternary eutectic phase, Zn-Al binary eutectoid phase, Zn-MgZn2 _binary eutectic phase, _Mg2Si -Zn ternary eutectic phase, and an Al-Zn-Fe-Si alloy layer. The coating microstructure is coarse and uneven. The coating surface exhibits defects such as incomplete coating, poor adhesion, and black spots. The performance test results of the zinc-aluminum-magnesium coated steel prepared in Comparative Example 3 are shown in Table 1.

The quality performance of zinc-aluminum-magnesium coated steel was evaluated by comparing the coating microstructure, surface quality, corrosion resistance, and formability of the zinc-aluminum-magnesium coated steel obtained in Examples 1-6 and Comparative Examples 1-3.

Corrosion resistance: A neutral salt spray accelerated corrosion test was conducted. The test conditions and methods followed GB/T 10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The test instrument was a salt spray corrosion test chamber. A 50 g/L NaCl deionized water solution with a pH of 6.5 was used as the corrosive medium. The test temperature was 35 ± 2℃. The sample dimensions were 75 mm * 150 mm × 0.8 mm, and the edges were sealed with 5 mm of transparent tape to prevent end corrosion from affecting the results. The samples were placed at an angle of 15° to 25° to the vertical direction. The time it took for red rust to appear on the sample surface was observed.

Formability: The sample is bent at 0T (180° bend, bending radius is 0), and the presence of cracks is observed visually. The maximum crack width ≤ 50μm is grade 0, the maximum crack width 51-100μm is grade 1, 101～200μm is grade 2, and > 200μm is grade 3. The time for red rust to appear on the bent part is also tested under neutral salt spray test conditions. The neutral salt spray test conditions and methods are performed in accordance with GB/T 10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test".

Table 1. Performance test results of zinc-aluminum-magnesium coated steels prepared in the examples and comparative examples.

As shown in Table 1, by controlling the composition system and cooling process, the aluminum-zinc-aluminum-magnesium coating eliminates unfavorable phases, achieves full coverage of beneficial phases, and further refines the grain size, thus improving corrosion resistance and formability.

For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims (10)

A high corrosion-resistant coated steel sheet, comprising a steel base and a coating, characterized in that the coating structure comprises a Zn- _MgZn2 -Al ternary eutectic phase, a Zn-Al binary eutectoid phase, a Zn-MgZn2 _binary eutectic phase, a _Mg2Si -Zn ternary eutectic phase, and an Al-Zn-Fe-Si alloy layer; the chemical composition of the coating, by mass percentage, is Al: 10%–20%, Mg: 2.2%–6%, Si: 0.08%–0.40%, RE: 0.05%–0.60%, with the balance being Zn and other unavoidable impurities. The high corrosion-resistant coated steel sheet according to claim 1 is characterized in that the coating is a zinc-aluminum-magnesium alloy coating with a thickness of 2-50 μm. According to claim 1, the high corrosion-resistant coated steel sheet is characterized in that the coating structure does not contain pure zinc phase, rare earth phase, or silicon-rich phase, and the rare earth is a mixture of lanthanum and cerium. According to claim 1, the high corrosion-resistant coated steel sheet is characterized in that, in terms of atomic number, the coating composition is 5.5Mg+2.5Al＞Zn+0.5Si, Zn≥Al+2Mg. According to claim 1, the high corrosion-resistant coated steel sheet is characterized in that, in the coating composition, by mass percentage, 0.3% ≤ RE + Si ≤ 0.8%. According to claim 1, the high corrosion-resistant coated steel sheet is characterized in that the steel base is one of cold-rolled strip steel or hot-rolled strip steel, including low-carbon aluminum killed steel, IF steel, P-containing high-strength IF steel, bake-hardening steel, SPCC, structural steel, and QP steel. A method for preparing a high corrosion-resistant coated steel sheet as described in claim 1, characterized in that the preparation method includes the following steps: pickling, rolling, degreasing and cleaning, continuous annealing, hot-dip galvanizing, air knife blowing, cooling, and finishing; wherein, The rolling process employs a rough roll rolling technique, and the surface roughness of the strip after rolling is controlled within the range of 1.2–3.5 μm. The continuous annealing process controls the hydrogen content in the furnace to be ≥2.5% by volume percentage; The temperature of the steel plate entering the zinc pot is 420℃～620℃, the temperature of the plating solution during the hot-dip galvanizing process is 420℃～600℃, the temperature of the strip steel entering the zinc pot is not lower than the temperature of the zinc pot, and the hot-dip galvanizing time is 1～3s. According to the preparation method of claim 7, the air knife purging medium is at least one of _N2 and inert gas, and its _CO2 content is ≤50ppm and _O2 content is ≤50ppm. According to the preparation method of claim 7, the cooling rate is controlled at 5-30℃/s, and the temperature of the strip reaching the top turning roller is ≤270℃; the surface roughness Ra of the finishing roller is controlled at 2.0-4.5μm, and the finishing elongation is 0.5-1.5%. According to the preparation method of claim 7, the chemical composition of the plating solution is as follows: Al: 10%–20%, Mg: 2.2%–6%, Si: 0.08%–0.40%, RE: 0.05%–0.60%, with the balance being Zn and other unavoidable impurities.