Zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing and preparation method thereof

Abstract

The invention belongs to the technical field of metal materials, and particularly relates to a zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing and a preparation method thereof. The plating layer of the alloy plating layer steel plate comprises the following components in percentage by weight: 1-3% of aluminum, 1-2% of magnesium, 1.0-1.5% of aluminum / magnesium and the balance of zinc and inevitable impurities. The steel base of the alloy coating steel plate is ultra-low carbon steel, the structure of the alloy coating steel plate is ferrite, the grain size is 10-30 microns, and the inclusion size needs to be smaller than or equal to 15 microns. The reflective rate of the surface of the coating is reduced through Al / Mg content control and large finishing elongation control, and the requirements of television backboards, automobile panels and other very complex parts with the size smaller than 85 inches are met.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, specifically a zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing and a preparation method thereof. Background Art

[0002] Coated steel sheets are coated with zinc or zinc alloys on the surface of steel sheets and strips by hot-dip coating, electroplating, or vapor deposition. This treatment protects the steel substrate from corrosion and extends the material's service life. Annual production capacity for coated steel sheets has reached over 100 million tons. As the user market demands increasingly stringent corrosion resistance, hot-dip galvanized (GI) sheet was first developed, followed by the third generation of highly corrosion-resistant hot-dip 55% Al-Zn alloy-coated (GL) steel sheets and hot-dip galvanized aluminum sheet. In the past 20 years, the fourth generation of highly corrosion-resistant Zn-Al-Mg alloy-coated steel sheets has been developed.

[0003] Multimedia generally refers to equipment such as televisions and monitors. Multimedia back panels are generally made of electro-galvanized steel sheets or hot-dip galvanized steel sheets. In recent years, some have begun to use zinc-aluminum-magnesium alloy coated steel sheets.

[0004] The stamping process for multimedia backplanes is complex, requiring automatic rapid stamping on a punch press, followed by degreasing, cleaning, and spray coating. The main challenges in developing coated steel sheets for multimedia applications lie in the need for excellent stamping properties and a certain level of strength, currently only met by the highest-grade IF steel. Furthermore, due to the relatively thin material required, strict control of impurities in the steel is required to minimize the impact of small inclusions on the coating's formability. my country's research into Zn-Al-Mg alloy coatings is relatively late, and companies such as Jiugang, Baosteel, Shougang, Jiugang, and Panzhihua Iron and Steel have introduced hot-dip Zn-Al-Mg alloy-coated steel sheets, which are widely used in the photovoltaic field but have yet to be applied to multimedia backplanes. Patent CN 115491583 B discloses an ultra-deep-drawn cold-rolled hot-dip aluminum-zinc steel sheet and its manufacturing method, which mainly solves the technical problems of high manufacturing cost and poor stamping performance of existing cold-rolled hot-dip aluminum-zinc steel sheets with a yield strength of 140-175 MPa. The chemical composition of the substrate is as follows by weight: C: 0.0002%-0.0006%, Si: 0-0.03%, Mn: 0.02%-0.05%, P: 0-0.015%, S: 0.0020%-0.0040%, Ti: 0.010%-0.019%, N: 0.0010%-0.0018%, Al: 0.015%-0.030%, and satisfies 0.0008%≤[Ti-(4C+3.4N+1.5S)]≤0.0140%, with the remainder being Fe and unavoidable inclusion elements. It is used for ultra-deep drawing parts of home appliances, hardware, etc. Its A 80mm is 34-45%, plastic strain ratio r value is 1.9-2.5, and n value is 0.18-0.20. However, it is a hot-dip aluminum-zinc plate, and the aluminum-zinc coating has slightly poor formability. It has not yet been applied to multimedia back panels, and A80mm , r value and n value are all low and cannot meet the usage requirements of 55-75 inch TVs.

[0005] Patent CN 118703877 A discloses an ultra-deep drawing IF steel and its preparation method. The chemical composition of the ultra-deep drawing IF steel includes, by mass percentage: C: 0.0015-0.003%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.025%, S: 0-0.025%, Al: 0.02-0.1%, Ti: 0.02-0.10%, Nb: 0.015-0.025%, N: 0-0.005%, and the remainder is Fe and unavoidable inclusions. The ultra-deep drawing IF steel provided in this patent can be well applied to the oil tank shell of the two-flap forming process, can improve the deformation uniformity of the oil tank mouth, reduce the occurrence of weld cracking in the flanging process of the oil tank mouth, improve production efficiency, and reduce rework costs. As can be seen from its embodiment, the elongation A of this steel type is 80mm It is less than 40%, and it is a cold-rolled plate with poor corrosion resistance, so it cannot be used for parts with complex shapes and corrosion resistance such as multimedia backplanes.

[0006] Patent CN 116288035 A provides an extra-deep-drawing grade Nb-IF cold-rolled steel sheet, the chemical composition of which includes by weight the following: C: 0.001-0.002%, Si: 0.004-0.006%, Mn: 0.15-0.17%, P: ≤0.010%, S≤0.006%, Nb: 0.060-0.065%, and the remainder is Fe and unavoidable impurities. This patent provides an extra-deep-drawing grade Nb-IF cold-rolled steel sheet and its preparation method. The Nb-IF cold-rolled steel sheet has excellent extra-deep-drawing performance, low yield strength ratio, and good plasticity. It is suitable for automobile exterior panels and home appliance panels produced by complex stamping processes. The yield strength of the cold-rolled steel sheet is 136MPa-148MPa, the tensile strength is 292MPa-305MPa, and the elongation is A 80mm However, it is a cold-rolled steel with poor surface quality and corrosion resistance, and cannot be used for home appliances and automotive parts with high surface requirements such as multimedia backplanes.

[0007] This suggests that currently, zinc-aluminum-magnesium (ZnAl-Mg) steel sheets are not yet available for ultra-deep drawing applications that can meet the requirements of automated stamping and complex forming. Furthermore, most steel sheets still have shortcomings in surface quality, corrosion resistance, and formability. Based on characteristics such as reflectivity, ZnAl-Mg is more suitable for multimedia applications. To meet the higher stamping and forming requirements of multimedia, research is needed on ZnAl-Mg alloy-coated steel sheets for ultra-deep drawing. Summary of the Invention

[0008] In order to improve the formability of zinc-aluminum-magnesium coated steel sheets and meet the requirements of automated stamping and complex forming for home appliances and automobile users, the present invention provides a zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing and a preparation method thereof. The zinc-aluminum-magnesium sheet has excellent formability and can meet the requirements of complex components such as TV back panels below 85 inches and automobile panels.

[0009] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0010] The present invention provides a zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing with a reflectivity of less than 50%. The main components of the coating, calculated by weight percentage, are: aluminum 1-3%, magnesium 1-2%, aluminum / magnesium = 1.0-1.5, and the remainder is zinc and inevitable impurities; the steel base is an ultra-low carbon steel with a ferrite structure, a grain size of 10-30 μm, and an inclusion size of ≤15 μm.

[0011] Furthermore, the zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing of the present invention has a steel base composed of, by weight percentage, carbon ≤ 0.0030%, silicon ≤ 0.02%, manganese 0.05-0.5%, phosphorus ≤ 0.010%, sulfur ≤ 0.010%, aluminum 0.01-0.06%, titanium 0.04-0.10%, niobium 0.001-0.050%, and the balance being iron and unavoidable impurities.

[0012] Furthermore, the ultra-deep drawing zinc-aluminum-magnesium alloy coated steel sheet of the present invention has a reflectivity controlled at 35-50%, a yield strength of 130-170 MPa, a tensile strength of 260-350 MPa, and an elongation after fracture of A 80mm 43-50%, n 90 ≥0.20, r 90 ≥2.7.

[0013] Furthermore, the present invention provides a method for preparing the above-mentioned zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing, comprising processes such as steelmaking, hot rolling, pickling, and galvanizing. In the galvanizing process, the continuous annealing process controls the volume fraction of hydrogen in the furnace to be greater than 4.0%, the annealing temperature to be 780-890°C, and the annealing time to be ≥45s; the skin-clearing elongation is 0.7-1.5%, and the tensile elongation is ≤0.2%.

[0014] The chemical composition of the zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing provided by the present invention is as follows: carbon ≤ 0.0025%, silicon ≤ 0.02%, manganese 0.05-0.5%, phosphorus ≤ 0.010%, sulfur ≤ 0.010%, aluminum 0.01-0.06%, titanium 0.04-0.10%, niobium 0.001-0.050%, and the balance is iron and unavoidable impurities.

[0015] Furthermore, the key hot rolling process of the zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing provided by the present invention is: steel tapping temperature 1080-1300°C, final rolling temperature 880-980°C, coiling temperature 740-850°C, intermediate billet thickness 30-42mm, and steel plate thickness after hot rolling 3.0-6.0mm.

[0016] Furthermore, the cold rolling reduction rate of the zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing provided by the present invention is 70-90%.

[0017] The galvanizing process of the zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing provided by the present invention is as follows: in the continuous annealing process, the volume fraction of hydrogen in the furnace is controlled to be ≥6.0%, the annealing temperature is 780-890°C, and the annealing time is ≥45s; the skin-pass elongation is 0.7-1.5%, and the tensile elongation is ≤0.2%.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing described in the present invention has better stamping formability than ordinary hot-dip galvanized DC06 sheet for ultra-deep drawing. Its steel base structure adopts steel purity control, and the inclusion size is controlled below 15μm, which reduces steel base defects. The grain size is large and uniform, which reduces stress concentration points during complex continuous deformation. The surface reflectivity of the coating is reduced to below 50% by controlling the Al / Mg content and the large straightening elongation, meeting the requirements of very complex components such as TV back panels above 65 inches and automobile panels. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Cross-sectional morphology of Example 1. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0022] A zinc-aluminum-magnesium alloy-coated steel sheet for ultra-deep drawing is prepared. The steel base composition and the coating composition are shown in Table 1. The steel sheet is prepared through steelmaking, hot rolling, pickling, and galvanizing processes. The specific process parameters are shown in Table 2. During the hot rolling process, the tapping temperature is controlled at 1080-1300° C., the finishing temperature is controlled at 880-980° C., and the coiling temperature is controlled at 740-850° C. The intermediate billet thickness is controlled at 30-42 mm, and the thickness of the steel sheet after hot rolling is 3.0-6.0 mm. Subsequently, pickling and cold rolling are performed, and the reduction ratio is controlled at 70-90%. After the cold rolling is completed, a galvanizing process is performed, which includes a continuous annealing process, during which the volume fraction of hydrogen in the furnace is controlled to be ≥6.0%, the annealing temperature is controlled at 780-890° C., and the annealing time is controlled at least 45 seconds to ensure that a uniform zinc-aluminum-magnesium alloy coating is formed on the surface of the steel sheet. In addition, the skin-pass elongation is controlled at 0.7-1.5%, and the tension-leveling elongation is controlled at ≤0.2%. The properties of the prepared steel plates are shown in Table 3.

[0023] Table 1 Steel base and coating composition

[0024]

[0025]

[0026] Table 2 Process parameters

[0027]

[0028] Table 3 Microstructure and performance parameters of prepared steel plates

[0029]

[0030] The zinc-aluminum-magnesium alloy coated steel sheets for ultra-deep drawing in Examples 1-5 were punched into the most complexly deformed 65-inch or 75-inch TV back panels without any cracking.

[0031] In comparative example 1, the ultra-deep drawing zinc-aluminum-magnesium alloy coated steel plate was punched into a relatively simple deformation, but the back panel of a 40-43 inch TV still cracked.

[0032] In Comparative Example 2, the ultra-deep drawing zinc-aluminum-magnesium alloy coated steel sheets were punched into television back panels with a deformation of 50 inches or more, and cracks occurred.

[0033] It can be seen that the zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing with specific composition and content of the present invention has excellent stamping resistance and meets the needs of larger-sized multimedia back panels.

[0034] Although the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made herein without departing from the spirit and scope of the present invention as defined in the claims and their equivalents. The embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the present invention is defined not by the specific embodiments of the present invention, but by the claims, and all differences within the scope are to be construed as included in the present invention.

Claims

1. Zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing, characterized in that: The coating composition of the alloy-coated steel plate is, by weight percentage, 1-3% aluminum, 1-2% magnesium, aluminum / magnesium = 1.0-1.5, and the rest is zinc and inevitable impurities; the steel base of the alloy-coated steel plate is ultra-low carbon steel.

2. The zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing according to claim 1, characterized in that: The structure of the steel base is ferrite, the grain size is 10-30 μm, and the inclusion size is ≤15 μm.

3. The zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing according to claim 1, characterized in that: The steel base has the following components by weight percentage: carbon ≤ 0.0030%, silicon ≤ 0.02%, manganese 0.05-0.5%, phosphorus ≤ 0.010%, sulfur ≤ 0.010%, aluminum 0.01-0.06%, titanium 0.04-0.10%, niobium 0.001-0.050%, and the balance is iron and unavoidable impurities.

4. The zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing according to claim 1, characterized in that: The alloy-plated steel plate has a reflectivity of 35-50%, a yield strength of 130-170 MPa, a tensile strength of 260-350 MPa, and an elongation after fracture of A 80mm 43-50%, n 90 ≥0.20, r 90 ≥2.

7.

5. The method for preparing the zinc-aluminum-magnesium alloy coated steel sheet for ultra-deep drawing according to claim 1, characterized in that: The method includes steelmaking, hot rolling, pickling and galvanizing; The galvanizing process: in the continuous annealing process, the volume fraction of hydrogen in the furnace is controlled to be greater than 4.0%, the annealing temperature is 780-890° C., the annealing time is greater than or equal to 45 seconds, the skin-pass elongation is 0.7-1.5%, and the tensile elongation is less than or equal to 0.2%.

6. The preparation method according to claim 4, characterized in that The hot rolling process comprises: a tapping temperature of 1080-1300° C., a finishing rolling temperature of 880-980° C., a coiling temperature of 740-850° C., an intermediate billet thickness of 30-42 mm, and a steel plate thickness of 3.0-6.0 mm after hot rolling.

7. The preparation method according to claim 4, characterized in that The cold rolling reduction rate is 70-90%.

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