Method for producing a steel sheet with a zinc-aluminum-magnesium coating, corresponding coated steel sheet, component and vehicle

Abstract

This invention relates to a method for manufacturing a coated steel sheet, the coating comprising 0.80 wt% to 1.40 wt% Al, 0.80 wt% to 1.40 wt% Mg, unavoidable impurities, and one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr, or Bi, wherein the weight content of each additional element in the coating is less than 0.3%, with the remainder being Zn, and the outer surface of the coated steel sheet having a waviness Wa of less than or equal to 0.5 μm prior to finishing and cold rolling. 0.8 ; and coated steel sheet obtained by the method; components obtained by deformation of the steel sheet; and land motor vehicles including a body, the body including the component.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a coated steel sheet and the coated steel sheet obtained by the method, the coating comprising from 0.80 wt% to 1.40 wt% Al, from 0.80 wt% to 1.40 wt% Mg, unavoidable impurities, and one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr, or Bi, wherein the weight content of each additional element in the coating is less than 0.3%, with the remainder being Zn. This steel sheet is more specifically intended for manufacturing body parts for land-based motor-driven vehicles, such as automobiles. Background Technology

[0002] Typically, steel sheets are cut and deformed to form body parts or the body itself. The body is then coated with a paint film (or paint system) that ensures a good appearance and, together with a zinc-based coating, provides corrosion protection.

[0003] The zinc-based coating on the steel sheet has a waviness known as its outer surface, which can currently only be compensated for by significant paint thickness, at the cost of a so-called "orange peel" appearance, which is unacceptable for body parts.

[0004] The waviness W of the outer surface of the coating is a smooth pseudo-periodic geometric irregularity with a relatively long wavelength (0.8 mm to 10 mm), which is different from the roughness R with a short wavelength.

[0005] The arithmetic mean Wa of the waviness profile, expressed in μm, is commonly used to characterize the waviness of the outer surface of a steel sheet coating, and according to standard SEP1941, waviness is measured with a cutoff threshold of 0.8 mm and is expressed by Wa. 0.8 express.

[0006] Waviness Wa 0.8 The reduction in thickness can allow for a reduction in the thickness of the paint film used to achieve a given characteristic of the paint appearance, or, for a constant thickness of the paint film, can allow for an improvement in the quality of the paint appearance.

[0007] Some methods are known for reducing the waviness of zinc-coated steel sheets.

[0008] In fact, patent application WO 2014 / 135999 discloses a method for manufacturing a steel sheet with a zinc coating comprising 0.2% to 0.7% aluminum. The method includes the following steps: providing a steel sheet; depositing a coating on at least one surface of the steel sheet by immersing it in a bath; wiping the coating with a wiping gas from at least one nozzle that is sprayed through at least one outlet, the steel sheet traveling in front of the at least one nozzle, the wiping gas being ejected from the nozzle along the main spray direction E; and, after curing and before any finishing cold rolling operation, having an outer surface of the coating with a waviness Wa less than or equal to 0.55 μm. 0.8 And at least one of the following formulas must be satisfied:

[0009]

[0010]

[0011] in:

[0012] Z is the distance between the steel plate and the nozzle along the main injection direction E, expressed in mm; d is the average height of the outlet of at least one nozzle in front of the nozzle along the travel direction S of the steel plate, expressed in mm; V is the travel velocity of the steel plate in front of at least one nozzle, expressed in m·s. -1 P represents the pressure of the wiping gas in at least one nozzle, expressed in N·m. -2 It indicates that fO2 is the volume fraction of oxygen in the wiping gas.

[0013] The patent application also discloses the obtained coated steel sheet, wherein the outer surface of the coating has a waviness Wa of less than or equal to 0.35 μm prior to an optional light-finish cold rolling operation. 0.8 Finally, the patent discloses a component obtained by deforming the steel plate, wherein the outer surface of the coating has a waviness Wa of less than or equal to 0.43 μm. 0.8 .

[0014] However, this method is only applicable to controlling the waviness of coatings containing zinc and a small amount of aluminum. In reality, the waviness of the outer surface of a known coating can vary significantly depending on its properties.

[0015] Recently, new zinc-based coatings have been developed. These coatings, often referred to as "ZnAlMg coatings," consist of aluminum and magnesium, with the balance being zinc. They are used to further improve the corrosion resistance of steel sheets.

[0016] Patent application WO 2009 / 147309 discloses a method for manufacturing a steel strip with a corrosion-protective coating, the method comprising: passing the steel strip through a molten steel bath comprising between 2% and 8% by weight of aluminum, between 0% and 5% by weight of magnesium, and up to 0.3% by weight of additional elements, with the balance being zinc and unavoidable impurities, and said bath being maintained at a temperature between 350°C and 700°C to obtain a coated steel strip; wiping the coated steel strip with a nozzle that sprays gas on either side of the steel strip; and then cooling the coating in a controlled manner until the coating has been fully cured, said cooling being carried out at a rate of less than 15°C / s between the temperature at which the wiping occurs and the start of curing, and then at a rate of greater than or equal to 15°C / s between the start and end of coating curing.

[0017] The patent also discloses a hot-dip coated but unfinished cold-rolled steel strip, wherein the coating comprises 2% to 8% aluminum, 0% to 5% magnesium, and up to 0.3% additional elements, with the balance including zinc and unavoidable impurities, and the coating has a waviness Wa of 0.5 μm or less. 0.8 .

[0018] Finally, the patent application discloses a steel component obtained by deformation, wherein the coating of the steel component has a waviness Wa of 0.48 μm or less. 0.8 And a steel component that has undergone a separate cold rolling operation prior to deformation and is obtained by deformation, wherein the coating of the steel component has a waviness Wa of 0.35 μm or less. 0.8 .

[0019] However, in this application, the ZnAlMg coating includes a high amount of aluminum. As shown in the example, when the amount of aluminum is less than 2%, the corrugation leveling effect cannot be obtained by applying this method. Summary of the Invention

[0020] Therefore, the object of the present invention is to provide a method for manufacturing a ZnAlMg coated steel sheet having a small amount of Al and Mg, wherein the outer surface of the coating has a reduced waviness Wa. 0.8 .

[0021] For this purpose, the object of the present invention is the method according to claim 1.

[0022] The method may also include the features of claims 2 to 7, used alone or in combination.

[0023] The purpose of this invention is still the steel plate according to claim 8.

[0024] The steel plate may also include the features of claim 9.

[0025] The object of the present invention is still the component according to claim 10.

[0026] The component may also include the features of claims 11 to 13, used alone or in combination.

[0027] The object of this invention is still the vehicle according to claim 14. Attached Figure Description

[0028] The present invention will be described by way of example given by way of indication and not limitation, and with reference to the accompanying drawings, in which:

[0029] - Figure 1 A schematic side view illustrating the method according to the present invention is shown, and

[0030] - Figure 2 yes Figure 1 A partial, schematic, and enlarged view of the circled portion I.

[0031] - Figure 3 It is along Figure 2 The diagram is shown by arrow II, and it illustrates... Figure 2 The shape of the nozzle output. Detailed Implementation

[0032] The present invention relates to a method for manufacturing a coated steel sheet comprising a steel sheet coated with a coating comprising from 0.80 wt% to 1.40 wt% Al, from 0.80 wt% to 1.40 wt% Mg, unavoidable impurities, and one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr, or Bi, wherein the weight content of each additional element in the coating is less than 0.3%, and the remainder is Zn. The method comprises the following sequential steps:

[0033] A. Provide steel plates,

[0034] B. The steel sheet is cold-rolled, with at least the final pass performed using calibrated and unetched work rolls, wherein the work surface has a roughness Ra of less than or equal to 0.5 μm. 2.5 ,

[0035] C. Anneal the steel sheet in a continuous annealing line.

[0036] D. The coating is deposited by immersing the steel plate in a molten steel bath.

[0037] E. The coated steel sheet is moved through a restricted area including wiping nozzles, which spray wiping gas onto each side of the sheet through at least one outlet along the main spray direction (E), the wiping satisfying at least one of the following formulas:

[0038]

[0039]

[0040] in:

[0041] V is the speed at which the steel plate travels in front of the nozzle, expressed in m·s. -1 express,

[0042] P is the pressure of the wiping gas in the nozzle, expressed in Pa.

[0043] Z is the distance between the steel plate and the nozzle along the main injection direction (E), expressed in mm.

[0044] d is the average height of the nozzle outlet along the travel direction (S) of the steel plate in front of the nozzle, expressed in mm.

[0045] p O2 It is the partial pressure of oxygen in the restricted area.

[0046] F. Curing the coating.

[0047] Not wishing to be bound by any theory, it is believed that the method according to the invention allows steel sheets to be coated with a mixture comprising 0.80 wt% to 1.40 wt% Al, 0.80 wt% to 1.40 wt% Mg, and the balance Zn, to obtain a waviness Wa that is low enough to result in a highly improved surface appearance, and particularly a painted appearance. 0.8 The outer surface of the ZnAlMg coated steel sheet. In fact, conventional methods of the prior art do not appear to produce such low waviness for these ZnAlMg coated steel sheets. The inventors have discovered that not only the chemical elements of the coating and the amount of those elements, but also the method applied affects the waviness. To achieve the lowest possible waviness for ZnAlMg coated steel sheets with the specific amounts of Al and Mg described above, it seems necessary to control the surface of the ZnAlMg coating according to the method of the invention and obtain waviness values ​​never before achieved in the prior art.

[0048] In a preferred embodiment, the wiping step of the method according to the invention further satisfies at least one of the following formulas:

[0049]

[0050]

[0051] in:

[0052] V is the speed at which the steel plate travels in front of the nozzle, expressed in m·s. -1 express,

[0053] P is the pressure of the wiping gas in the nozzle, expressed in Pa.

[0054] Z is the distance between the steel plate and the nozzle along the main injection direction (E), expressed in mm.

[0055] d is the average height of the nozzle outlet along the travel direction (S) of the steel plate in front of the nozzle, expressed in mm.

[0056] p O2 It is the partial pressure of oxygen in the restricted area.

[0057] It has been observed that, in addition to satisfying at least one of formulas (1) or (2), satisfying at least one of formulas (3) or (4) allows for a further reduction in the waviness of the coated steel sheet.

[0058] Figure 1 The steel plate 1 comprises a steel plate coated with the aforementioned ZnAlMg coating on each of its two sides. Preferably, the steel plate is low-carbon steel, such as gapless steel (IF steel), bake-hardening steel, or aluminum-deoxidized steel.

[0059] The coating typically has a thickness of 25 μm or less and is designed to protect the steel plate 1 from corrosion.

[0060] To manufacture steel plate 1, for example, the following steps can be taken.

[0061] Use, for example, sheet materials obtained by hot rolling followed by cold rolling, such as steel plates.

[0062] Preferably, for cold rolling, it begins by cold rolling the sheet at a reduction rate generally between 30% and 85% to obtain a sheet 1 having a thickness, for example, between 0.2 mm and 2 mm. It is necessary to ensure that at least the final cold rolling pass is performed using so-called smooth or bright work rolls, i.e., calibrated and unetched rolls, wherein the work surface has a roughness Ra of less than or equal to 0.5 μm. 2.5 Roughness is measured using a cutoff threshold at 2.5 mm.

[0063] The work roll is the roll of the rolling mill that comes into direct contact with the sheet material 1 to ensure its deformation. The term "work surface" refers to the surface of the work roll that contacts the sheet material 1.

[0064] When considering the direction of travel of the sheet metal in the mill, the smooth work rolls will be present at least in the last stand of the mill.

[0065] The smooth work rolls are used at least in the final rolling pass to better control the waviness Wa of the steel sheet 1 subsequently obtained through coating. 0.8Furthermore, on the other hand, it allows for better control over components that can be produced by deforming the steel plate 1.

[0066] In particular, compared to rolling that relies solely on rolls with high surface roughness (so-called electrical discharge machining (EDT) rolls) etched by means such as shot peening or electrical discharge machining, this cold rolling allows for a higher degree of waviness Wa. 0.8 of the reduction.

[0067] In step C), the cold-rolled sheet 1 is annealed in a continuous annealing line. Preferably, the annealing is carried out in a reducing atmosphere to allow recrystallization of the cold-rolled sheet 1 after it has undergone work hardening during the cold rolling operation.

[0068] Recrystallization annealing can also activate the surface of the sheet material to promote the chemical reactions required for subsequent dip coating operations.

[0069] Depending on the grade of steel, recrystallization annealing can be carried out at a temperature between 650°C and 1200°C, preferably between 650°C and 900°C, for a time required for recrystallization of the steel and activation of the surface.

[0070] The plate is then cooled to a temperature close to that of the molten bath 2 contained in crucible 3.

[0071] In step D), the steel sheet is coated by hot-dip coating in a bath 2. Bath 2 is zinc-based and contains 0.8 wt% to 1.4 wt% aluminum and 0.8 wt% to 1.4 wt% magnesium. Preferably, the coating comprises 1.0 wt% to 1.40 wt% Al and 1.0 wt% to 1.40 wt% Mg. In practice, without wishing to be bound by any theory, it is believed that these amounts of Al and Mg in the coating, compared to Zn coatings, further improve the waviness of the ZnAlMg coating while maintaining improved corrosion resistance.

[0072] Bath 2 may also contain up to 0.3% by weight of optional additional elements, such as Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr, or Bi.

[0073] For example, these different elements can allow for improvements in the coating's corrosion resistance, its brittleness, or its adhesion.

[0074] Those skilled in the art, aware of the influence of different elements on coating properties, will know how to use them for the desired additional purpose. It was also examined that these elements do not interfere with the control of waviness obtained by the method according to the invention.

[0075] Finally, bath 2 may contain unavoidable impurities from the ingots used to supply the bath or other channels from the plates 1 in bath 2. Therefore, it can be specifically mentioned that the weight of the iron can be, for example, up to 5% by weight.

[0076] During hot-dip coating, aluminum present in the bath first reacts with the steel to produce a so-called inhibition layer, which comprises intermetallic elements made of aluminum and iron. This inhibition layer typically comprises FeAl3 and has a thickness varying from 20 nm to 80 nm. As described above, a coating comprising 0.8 wt% to 1.4 wt% aluminum and 0.8 wt% to 1.4 wt% magnesium is formed on this inhibition layer.

[0077] If passed Figure 1 and Figure 2 As illustrated, in step E), after leaving bath 2, steel plate 1 enters a confined area including wiping nozzles 4, which are positioned on either side of steel plate 1 and spray wiping gas, such as air or inert gas, toward the outer surface of the coating. The confined area can be constructed, for example, according to WO 2010 / 130883 and defined in the following manner:

[0078] - At the bottom, through the wiping line (in Figure 2 (represented by dashed lines)

[0079] -and the upper outer surface of the wiping nozzle 4,

[0080] - At the top, the upper portions of two limiting boxes 5 are positioned on each side of the plate, directly above the nozzle 4, and at a height of at least 10 cm relative to the wiping line.

[0081] - On the side, through the lateral portion of the limiting box 5.

[0082] Wiping gas is ejected from each nozzle 4 along the main injection direction E.

[0083] In the illustrated example, direction E is horizontal and orthogonal to steel plate 1, and follows the wiping line. In other embodiments, direction E may have other inclinations relative to steel plate 1.

[0084] The travel speed V of the sheet material 1 on the production line typically includes between 60 m / min and 200 m / min, and is preferably between 80 m / min and 120 m / min.

[0085] Alternatively, the nozzle 4 can have different structures, different positions, and / or be operated with different adjustments. It is also possible to have the nozzle only on one side of the steel plate 1.

[0086] Nozzle 4 has an outlet 6 through which wiping gas is sprayed toward the outer surface of the coating, which is placed opposite it. Various external shapes can be conceived for nozzle 4.

[0087] The outlet 6 of nozzle 4 is positioned at a distance Z from steel plate 1 along the main injection direction E. (If...) Figure 3 As illustrated, exit 6 typically appears as a slot, which is perpendicular to the direction of travel S and Figure 3 The plane extends to a width L that is at least equal to the width of the steel plate 1.

[0088] Preferably, the height of the outlet 6, i.e., its dimension in front of the nozzle 4 and parallel to the traveling direction S of the steel plate 1, is constant, such as through Figure 3 As illustrated, in some alternatives, the height can vary along the width of the outlet 6. Therefore, the outlet 6 can have, for example, a shape that flares slightly outward toward its ends (a bow shape).

[0089] To account for these possible height variations and different possible implementations, the average height d of the outlet 6 over its width L will then be considered.

[0090] Nozzle 4 sprays gas onto each side of the steel plate, the gas preferably having a lower oxidizing power than an atmosphere comprising 4% by volume oxygen and 96% by volume nitrogen. In particular, pure nitrogen or pure argon, or a mixture of nitrogen or argon with an oxidizing gas, such as, for example, oxygen, a CO / CO2 mixture, or an H2 / H2O mixture, can be advantageously used. A CO / CO2 mixture or an H2 / H2O mixture can also be used without adding an inert gas. Preferably, the wiping gas comprises nitrogen.

[0091] Then, in step F), the coating is cooled in a controlled manner to cure it.

[0092] In addition to the curing step, step G) can be performed, which includes a finishing cold rolling operation to give texture to the outer surface 23 of the coating 7, thereby facilitating the subsequent forming process of the steel sheet 1.

[0093] In practice, the finishing cold rolling operation provides the possibility of transferring sufficient roughness to the outer surface of the coating on the steel sheet 1, allowing the forming process of the steel sheet to proceed properly, while promoting good retention of the oil applied to the steel sheet 1 before the steel sheet is formed. During the finishing cold rolling operation, the elongation of the steel sheet 1 typically includes between 0.5% and 2%.

[0094] Because the work rolls have a working surface roughness of less than 5μm, the finishing cold rolling operation can maintain a low waviness Wa. 0.8 .

[0095] The finishing cold rolling operation will preferably be performed using EDT work rolls, wherein the working surface has a roughness Ra ranging from 1.70 μm to 2.95 μm. 2.5 If the elongation is less than or equal to 1.1% during the finishing cold rolling operation, then the surface roughness Ra of the working surface of the EDT work rolls... 2.5 The surface roughness Ra of the EDT work rolls will preferably be between 2.50 μm and 2.95 μm. If the elongation is greater than or equal to 1.1% during the finishing cold rolling operation, the surface roughness Ra of the EDT work rolls will be... 2.5 Preferably, it will be between 1.70 μm and 2.50 μm.

[0096] Steel sheet 1, intended for use in manufacturing body parts for automobiles, is typically subjected to a smoothing cold rolling operation.

[0097] When steel sheet 1 is intended for use in the manufacture of household appliances, this additional operation is not performed, for example. In the case of components used in household appliances, a baking operation may also be performed on the paint film using physical and / or chemical methods known per se.

[0098] For this purpose, the painted parts can also be passed through hot air or an induction oven, or further under a UV lamp or a device for diffused electron beams.

[0099] Using the method according to the invention, a steel sheet having an outer surface with a waviness Wa less than or equal to 0.50 μm before light finishing and cold rolling, and preferably less than or equal to 0.45 μm or even better less than or equal to 0.40 μm or less than or equal to 0.35 μm. 0.8 .

[0100] The already finished cold-rolled steel sheet 1 can then be cut and then undergo a forming process, such as by stretching, bending or shaping, to form a component, which can then be painted to obtain a paint film (or paint system) on each side.

[0101] After deformation, the outer surface of the component has a waviness Wa of less than or equal to 0.50 μm, or even less than or equal to 0.45 μm or 0.40 μm, or even less than or equal to 0.38 μm. 0.8。

[0102] The waviness can be measured using a Marciniak tool after 5% isoaxial stretch. In the conventional method, waviness can be measured after 3.5% isoaxial stretch. A difference of 0.03 waviness values ​​is generally considered to be between 3.5% and 5% stretch.

[0103] For automotive applications, after phosphate coating, each component is immersed in an electrophoretic bath and then a primer layer, base coat layer, and optional clear coat layer are applied in sequence.

[0104] Before applying the electrophoretic layer to the component, the component is first degreased and then coated with phosphate to ensure the adhesion of the electrophoretic layer.

[0105] The electrophoretic coating provides additional corrosion protection to the component. A primer layer, typically applied by a spray gun, prepares the component for its final appearance and protects it from stone chips and UV rays. The base coat gives the component its color and final look. The clear coat provides the component with good mechanical strength, resistance to corrosive chemicals, and a good surface finish.

[0106] Typically, the weight of a phosphate coating includes 1.5 g / m³. 2 With 5g / m 2 between.

[0107] The coatings applied to protect and ensure the best surface appearance of components include, for example, an electrophoretic layer with a thickness of 15 μm to 25 μm, a primer coating with a thickness of 35 μm to 45 μm, and a base coat coating with a thickness of 40 μm to 50 μm.

[0108] When the paint film also includes a clear coat layer, the thicknesses of different paint layers are typically as follows:

[0109] Electrophoretic layer: between 15 μm and 25 μm, preferably less than 20 μm.

[0110] Primer coating: less than 45μm

[0111] Base coat: less than 20μm.

[0112] Clear coat: less than 55μm.

[0113] Preferably, the total thickness of the paint film will be less than 120 μm, or even 100 μm.

[0114] Finally, the object of the present invention relates to a land motor vehicle comprising a body including components according to the present invention.

[0115] The invention will now be described by means of experiments given as indications rather than limitations.

[0116] Example

[0117] For all samples, conventional IF steel was cold-rolled, with the final rolling pass achieved using straightened and unetched work rolls, where the work surface had a roughness Ra of 0.35 μm. 2.5The samples were then annealed at 765°C and hot-dip coated with a molten bath containing 1.2 wt% Al, 1.2 wt% Mg (samples 2 to 38) or 1.5 wt% Al, 1.5 wt% Mg (sample 1), with the balance being Zn. The samples were then transferred to a confined area and wiped with nitrogen. After the coating cured, the coated steel sheet was cold-rolled to a smooth finish using rolls with a working surface having a roughness Ra of 2.1 μm. 2.5 .

[0118] All samples were deformed using a Marciniak tool. The samples were stretched in a 5% isoaxial stretch mode. Waviness was measured for each sample before final cold rolling (SKP), after final cold rolling, and after final cold rolling and deformation (DEF).

[0119] Used to measure ripple Wa 0.8 The process follows the protocol of standard SEP1941 and includes obtaining a steel sheet profile with a length of 50 mm in the rolling direction by mechanical probing (without slippage). An approximation of its general shape, having a fifth-order polynomial, is subtracted from the signal obtained by probing. The waviness Wa and arithmetic mean roughness Ra are then separated by a Gaussian filter with a cutoff value of 0.8 mm. In the case of deformed steel sheets, this process is applied to both the deformed and undeformed areas of the sheet.

[0120] The process parameters and ripple values ​​for experiments 1 to 15 are summarized in Table 1. All experiments according to the present invention satisfy formula (1) or formula (2).

[0121] Then, additional tests 16 to 38 with improved waviness values ​​were conducted, and the corresponding process parameters and waviness values ​​are summarized in Table 2. Such tests satisfy not only formula (1) but also formula (3) or formula (4).

[0122]

[0123]

Claims

1. A method for manufacturing a coated steel sheet, said coating comprising from 0.80 wt% to 1.40 wt% Al, from 0.80 wt% to 1.40 wt% Mg, unavoidable impurities, and one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr, or Bi, wherein the weight content of each additional element in said coating is less than 0.3%, and the remainder is Zn, said method comprising the following sequential steps: A. Provide the steel plate. B. The steel plate is cold-rolled, with at least the final rolling pass performed using straightened and unetched work rolls, wherein... The working surface has a roughness Ra of less than or equal to 0.5 μm. C. Anneal the steel plate in a continuous annealing line. D. The coating is deposited by immersing the steel plate in a molten bath. E. The coated steel sheet is moved through a restricted area including wiping nozzles, which spray wiping gas onto each side of the sheet through at least one outlet along the main spray direction (E), the wiping satisfying at least one of the following formulas: in: V is the speed at which the steel plate travels in front of the nozzle, expressed in m·s. -1 express, P is the pressure of the wiping gas in the nozzle, expressed in Pa. Z is the distance between the steel plate and the nozzle along the main injection direction (E), expressed in mm. d is the average height of the nozzle outlet along the travel direction (S) of the steel plate in front of the nozzle, d is expressed in mm. p O2 It is the partial pressure of oxygen in the restricted region. F. Curing the coating. G. The coated steel sheet is subjected to light-finish cold rolling using work rolls with a roughness Ra of less than 5 μm.

2. The method according to claim 1, wherein, The finishing cold rolling of the coated steel sheet is performed using EDT work rolls with a roughness Ra ranging from 1.70 μm to 2.95 μm.

3. The method according to claim 1, wherein, The coating comprises from 1.0 wt% to 1.40 wt% Al and from 1.0 wt% to 1.40 wt% Mg.

4. The method according to claim 1, wherein, The wiping gas includes nitrogen.

5. A coated steel sheet obtained by the method according to any one of the preceding claims, the steel sheet being provided with a coating comprising from 0.80% to 1.40% Al, from 0.80% to 1.40% Mg, unavoidable impurities, and one or more additional elements optionally selected from Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr, or Bi, wherein the weight content of each additional element in the coating is less than 0.3%, the remainder being Zn, and the outer surface of the coated steel sheet having a waviness Wa of less than or equal to 0.50 μm prior to light finishing and cold rolling. 0.8 This waviness is measured in the Marciniak tool in a 5% biaxial stretch mode.

6. The steel plate according to claim 5, wherein, Prior to the light-finishing cold rolling, the outer surface of the coated steel sheet has a waviness Wa of less than or equal to 0.40 μm. 0.8 This waviness is measured in the Marciniak tool in a 5% biaxial stretch mode.

7. The steel plate according to claim 5 or 6, wherein, The coating comprises from 1.0 wt% to 1.40 wt% Al and from 1.0 wt% to 1.40 wt% Mg.

8. A component obtained by deformation of a coated steel sheet according to any one of claims 5 to 7, wherein, The outer surface of the coated steel sheet has a waviness Wa of less than or equal to 0.50 μm. 0.8 This waviness is measured in the Marciniak tool in a 5% biaxial stretch mode.

9. A component according to claim 8, wherein, The outer surface of the coated steel sheet has a waviness Wa of less than or equal to 0.45 μm. 0.8 This waviness is measured in the Marciniak tool in a 5% biaxial stretch mode.

10. The component according to claim 9, further comprising a paint film on the coated steel plate.

11. The component according to claim 10, wherein, The thickness of the paint film is less than or equal to 120 μm.

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