Method for sealing a steel strip having a magnesium-containing zinc layer, steel strip and motor vehicle

Abstract

The invention relates to a method for coating a steel strip (12) for a sheet metal component of a motor vehicle, in which the steel strip (12) is introduced into a treatment chamber (14) in which a negative pressure is present. In the treatment chamber (14), a first material layer is applied to at least one side (22, 24) of the steel strip (12), and a cover layer is applied to the first material layer. A magnesium-containing zinc layer is applied as the first material layer to at least one side (22, 24) of the steel strip (12). The cover layer is formed from a second material which has a lower tendency to form oxides than the magnesium-containing zinc layer. Furthermore, the invention relates to a steel strip (12) for a sheet metal component of a motor vehicle and to a motor vehicle.

Description

The invention relates to a method for coating a steel strip for a sheet metal component of a motor vehicle, in which the steel strip is introduced into a treatment space in which a reduced pressure is present. In the treatment space, a first layer of material is applied to at least one side of the steel strip. A cover layer is applied to the first material layer. Furthermore, the invention relates to a steel strip produced according to such a method for a sheet metal component of a motor vehicle and to a motor vehicle.In particular for use in motor vehicle construction, steel sheets or steel strips, which are also referred to as coils in wound form, are coated, for example galvanized. This ensures that components produced from the steel strip or steel sheet are more corrosion-resistant. Different methods can be used for applying a zinc-containing coating to the steel strip. For example, the steel strip can be introduced into a dip bath in order to apply a coating which increases corrosion resistance to the steel strip electrophoretically or by hot-dip galvanizing.Furthermore, a method of physical vapor deposition can be used for applying a coating which increases corrosion resistance. In this case, the steel strip is sprayed with liquefied coating material under vacuum or in the presence of a reduced pressure.When the coated steel strip enters the free environment in which oxygen of the ambient air is contained, the surface of the coating can react with the oxygen depending on a chemical composition of the coating material. In this case, oxide formation can occur in particular, which can be disadvantageous or unfavourable for further processing steps of the coated steel strip or subsequent processes. This is because if a component formed from the steel strip, which has the coating with oxides that are detrimental to subsequent processes, is to be subjected, for example, to a subsequent process such as, for example, adhesive bonding or soldering or pickling, the oxides can impair such subsequent processes.For example, a solder material usable for soldering holds less well on an oxide-containing surface than would be the case for a surface of the same type, but not containing oxides that are detrimental to such a subsequent process. The same applies analogously to an adhesion of an adhesive on the oxide-containing coating or the coating with oxides that are detrimental to the adhesion of the adhesive. Here too, the oxides can provide poorer adhesion of the adhesive to the surface.EP 0 627 496 A2 describes a method for coating metal substrates such as steel sheets or aluminum sheets in strip form, in which an adhesion promoter layer made of aluminum is first applied to the substrate under vacuum. Subsequently, in a coating section, under vacuum, a cover layer is applied to the adhesion promoter layer.Furthermore, DE 10 2021 101 383 A1 and DE 10 2018 215 102 A1 describe respective methods for coating a strip or a strip-shaped material.It is an object of the present invention to provide a method of the type mentioned at the beginning, by means of which a particularly resistant coating of the steel strip is provided, and to specify a steel strip produced accordingly, and a motor vehicle having a component formed from the steel strip.This object is achieved by a method having the features of claim 1, a steel strip having the features of claim 9 and a motor vehicle having the features of claim 10. Advantageous embodiments with expedient refinements are specified in the dependent patent claims and in the following description.In the method according to the invention for coating a steel strip for a sheet metal component of a motor vehicle, the steel strip is introduced into a treatment space in which a reduced pressure is present. In the treatment space, a first layer of material is applied to at least one side of the steel strip. A cover layer is then applied to the first material layer. As the first material layer, a zinc layer containing magnesium is applied to the at least one side of the steel strip. The overcoat is formed of a second material having a lower tendency to form oxides than the magnesium-containing zinc layer.This is based on the finding that it is favorable for providing a particularly resistant coating of the steel strip to apply the magnesium-containing zinc layer as the first material layer to the steel strip. This is because the material of the first material layer, which contains zinc as a major proportion and magnesium in a small proportion-for example in a proportion of about one percent by weight to about three percent by weight-results in the formation of zinc-magnesium phases or zinc-magnesium mixed crystals. These mixed crystals containing zinc-magnesium phases or magnesium and zinc, for example in the form of MgZn 2, ensure, on the one hand, an advantageously high hardness of the coating of the steel strip. In addition, a coating formed as a zinc layer containing magnesium is more corrosion resistant than a zinc layer containing no magnesium. Therefore, it is particularly advantageous if the steel strip is coated with the magnesium-containing zinc layer as the first material layer.The presence of magnesium in the magnesium-containing zinc layer, however, in principle carries the possibility that undesired magnesium oxides form. However, this is particularly largely prevented in the present case because the magnesium-containing zinc layer is applied to the steel strip in the treatment space in which the reduced pressure is present or prevails. The negative pressure can be generated in the treatment chamber, for example, by air being conveyed out of the treatment chamber by means of vacuum pumps, that is to say at least the negative pressure, in particular a vacuum, being set in the treatment chamber. Because oxygen-containing air is not present in the treatment chamber or is at most present in traces, it is very largely avoided that an undesired formation of magnesium oxides occurs.The disadvantages associated with forming magnesium oxides on a steel strip with regard to further subsequent processes such as, for example, adhesive bonding and / or soldering and / or pickling, are thereby advantageously very largely avoided.In addition, the covering layer applied to the first material layer ensures that even when the steel strip coated with the first material layer and the covering layer is exposed to the ambient air, atmospheric oxygen cannot reach the magnesium contained in the first material layer. In other words, the covering layer provides for sealing the magnesium-containing zinc layer which is applied as the first material layer to the at least one side of the steel strip.Because the second material from which the covering layer is formed has a lower tendency to form oxides than the magnesium-containing zinc layer, oxide formation of the covering layer is advantageously particularly largely prevented.In particular, the lower tendency of the covering layer to form oxides may further be manifested in the covering layer tending to form oxides to a lesser extent, which are detrimental to subsequent processes such as bonding and / or soldering and / or pickling than is the case for the magnesium-containing zinc layer. In other words, the zinc layer containing magnesium can have a greater tendency to form oxides that are detrimental to these subsequent processes than the covering layer. The lower tendency of the cover layer to form oxides can thus be provided in particular by the fact that oxides formed by the cover layer are less detrimental to the subsequent processes than would be observed for oxides formed by the first material layer.By carrying out the respective subsequent process or further processing step on a test basis for a steel strip having only the first material layer on the one hand and for a steel strip having the first material layer and the covering layer on the other hand, it is very easily possible to establish to what extent oxides are present which are detrimental or disadvantageous for the subsequent process.Overall, the first material layer and the covering layer applied to the first material layer result in a particularly resistant coating of the steel strip. This is because the magnesium-containing zinc layer ensures the high hardness and good corrosion resistance of the coating. And the covering layer further improves corrosion resistance and protects the underlying first material layer. This is advantageous.In order to provide the covering layer, a second material can be used in particular, which is less noble than magnesium, i.e. has a higher standard potential in the electrochemical series than magnesium.Preferably, a zinc layer is applied as the covering layer to the first material layer. This is based on the finding that passivation of components can be achieved very well by means of a coating containing essentially pure zinc. The passivating zinc layer thus advantageously ensures sealing of the first material layer lying underneath. And the very thin passivation layer which forms on a surface of the zinc layer or covering layer under the influence of atmospheric air is not detrimental to subsequent processes during the further use of the coated steel strip. This is particularly due to the fact that a passivating oxide layer, which can form on the surface of the covering layer in the form of the zinc layer, is preferably very thin.In particular, the passivating oxide layer of the top layer is much thinner than would be the case if magnesium oxides were formed due to oxidation of the magnesium-containing zinc layer. The lower tendency of the second material to form oxides, in particular to form oxides that are detrimental to subsequent processes in the form of soldering, adhesive bonding or pickling, can therefore be expressed, for example, in the fact that the first material layer would form more oxides when in contact with oxygen and thus a thicker oxide layer than the second material from which the covering layer is formed.Preferably, the cover layer is applied to the first material layer in the treatment space in which the negative pressure is present. As a result, the same treatment space can be used for applying the first material layer to the steel strip and for applying the covering layer to the first material layer. This is advantageous. In addition, by applying the cover layer under the prevailing reduced pressure, in particular under vacuum, a very uniform and at the same time very thin cover layer can be formed. This is advantageous.For example, a first coating station can be formed in the treatment space, which is used for applying the first material layer to the at least one side of the steel strip. At this first processing station, physical vapor deposition, in particular, can be used for applying the magnesium-containing zinc layer to the steel strip.Furthermore, at a second coating station in the treatment space, the covering layer can be applied to the first material layer. Physical vapor deposition is also preferably used for applying the cover layer to the first material layer.This is because, with a comparatively small use of material, very reliably continuous layers in the form of the first material layer and the covering layer can be provided by means of physical vapor deposition. As a result, the need for the first material for providing the first material layer and for the second material for providing the covering layer can be advantageously kept low.Preferably, the covering layer is applied to the magnesium-containing zinc layer following an at least partial solidification of the magnesium-containing zinc layer. This is based on the finding that the at least partial solidification of the first material layer particularly largely prevents magnesium from reaching an outer surface of the first material layer. As a result, even in the event of contact of the outer surface of the first material layer with atmospheric oxygen, it is very largely avoided that undesired magnesium oxides are formed.This applies in particular if, as a result of the solidification of the magnesium-containing zinc layer, complete transfer of the material of the first material layer into the solid state, i.e. curing of the first material layer, occurs.Preferably, the at least partial solidification of the magnesium-containing zinc layer is effected by means of at least one cooling unit, wherein the at least one cooling unit absorbs heat released from the magnesium-containing zinc layer. Thus, the at least partial solidification, in particular the curing, of the magnesium-containing zinc layer can be achieved very quickly. This is advantageous in particular in order to prevent a mixing of the second material with the first material, from which the first material layer is formed, when the cover layer is applied to the first material layer. This also makes it possible to prevent magnesium from reaching a surface of the covering layer facing the environment to a particularly great extent. Both are advantageous in order to prevent magnesium oxides from forming on this surface of the covering layer.The first material layer and / or the cover layer may be formed in a plurality of layers. In this way, it can be ensured that the respective layer adheres particularly well to the previously formed layer. This is advantageous for a compact and dense construction of the coating of the steel strip.Preferably, the first material layer is formed to a thickness of less than 10 μm. As a result, the material requirement for providing the first material from which the magnesium-containing zinc layer is formed is advantageously very low. Nevertheless, with the first material layer, which has the thickness of a few micrometers, a very stable, in particular corrosion-resistant and at the same time hard coating of the steel strip can be provided, which well shields the steel material lying underneath from the environment. For example, the first material layer may be formed in a thickness of about 3 μm to 9 μm, in particular in a thickness of about 5 μm to about 7 μm.Additionally or alternatively, the cover layer may be formed in a thickness of, for example, about 1 μm to about 2 μm. This is based on the finding that it is sufficient for the cover layer if the cover layer primarily effects the sealing of the underlying first material layer. In contrast, the first material layer contributes the main contribution to the corrosion resistance of the coated steel strip.Forming the cover layer with the thickness that is less than the thickness of the first material layer advantageously ensures that particularly little of the second material needs to be used to form the cover layer. This is advantageous.Preferably, all sides of the steel strip are provided with the first material layer and with the covering layer. For example, for this purpose, the mutually opposite sides of the steel strip can be acted upon in the treatment space by means of respective stressing devices with the first material, i.e. with the magnesium-containing zinc, and subsequently with the second material. By coating all sides of the steel strip with the first material layer and with the covering layer arranged on the first material layer, a particularly good protection of the steel material of the steel strip by the coating is provided. This is advantageous.The steel strip according to the invention, which is provided for providing a sheet metal component or sheet steel component of a motor vehicle, is produced in the method according to the invention. Consequently, the steel strip advantageously has the particularly resistant coating.The sheet metal component of the motor vehicle formed from the steel strip can form, for example, a partial region of an outer skin of the motor vehicle and / or be formed as a structural component of the motor vehicle. In particular for providing sheet metal components which are exposed to environmental influences during operation of the motor vehicle, the use of the steel strip with the covering layer on the magnesium-containing zinc layer is advantageous. This is because the steel strip having the covering layer on the magnesium-containing zinc layer is particularly corrosion-resistant.In order to provide the sheet metal component of the motor vehicle, the coated steel strip, i.e. provided with the first material layer and the covering layer, can be provided with at least one further layer, in particular a lacquer layer, in further processing steps. For example, after forming and / or joining molded parts formed from the steel strip, a plurality of lacquer layers can be applied to the covering layer.Such lacquer layers may comprise a primer applied by dip-coating, a filler applied thereto, a base lacquer applied to the filler as a colouring layer and a clear lacquer as a protective outer protective layer. In particular, if, in order to provide a partial region of an outer skin of the motor vehicle, the steel strip having the covering layer is provided with such a multilayer finish, the finish advantageously ensures further protection of the steel strip from corrosion.However, even when using the sheet metal component for providing a structural component of the motor vehicle, such as a side sill and / or a door of the motor vehicle, the use of the steel strip having the first material layer and the covering layer is advantageous. Such structural components or body components of the motor vehicle are also preferably provided at least with a primer applied, for example, by dip-coating. Furthermore, further sealing measures can be carried out on such dip-coated structural components or body components, for example by at least local application of sealing materials.The motor vehicle according to the invention has at least one sheet metal component. In this case, at least one partial region of the sheet metal component is produced from a steel strip according to the invention. For example, the steel strip can be used for providing body panels of the motor vehicle, by means of which, in particular in a painted state of the body panels, partial regions of an outer skin of the motor vehicle and / or of at least one structural component of the motor vehicle are formed.The advantages and preferred embodiments described for the method according to the invention apply analogously to the steel strip according to the invention and to the motor vehicle according to the invention and vice versa.Accordingly, the invention also includes developments of the steel strip according to the invention and of the motor vehicle according to the invention, which have features as have already been described in connection with the developments of the method according to the invention. For this reason, the corresponding developments of the steel strip according to the invention and of the motor vehicle according to the invention are not described again here.The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.The invention also includes the combinations of the features of the described embodiments. The invention therefore also comprises implementations which each have a combination of the features of a plurality of the described embodiments, provided that the embodiments have not been described as mutually exclusive.Exemplary embodiments of the invention are described below. The following shows: FIG. 1 schematically shows a treatment space in which a first material layer in the form of a magnesium-containing zinc layer is applied under vacuum to a steel strip passing through the treatment space, wherein a covering layer is applied to the first material layer in a further processing step before the steel strip leaves the treatment space again; FIG. 2 is a schematic sectional view of the steel strip with the first material layer and the covering layer applied to the first material layer; and FIG. 3 schematically shows a motor vehicle, wherein at least one partial region of a sheet metal component of the motor vehicle is produced using the steel strip shown in FIG. 2.The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another and that also develop the invention independently of one another. Therefore, the disclosure is intended to include combinations of the features of the embodiments other than those illustrated. Furthermore, the described embodiments can also be supplemented by further features of the invention that have already been described.In the figures, identical reference numerals designate functionally identical elements.FIG. 1 schematically shows a treatment plant 10 for coating a steel strip 12. The treatment plant 10 comprises a treatment chamber 14 in which a reduced pressure is present. Preferably, the negative pressure is generated in the treatment chamber 14 by atmospheric air being discharged from the treatment chamber 14 by means of at least one pump (not shown). By this at least partial vacuuming, the reduced pressure can be set in the treatment space 14.At an inlet 16, the steel strip 12 enters the treatment space 14 and at an outlet 18, the steel strip 12 exits the treatment space 14 again. A first processing station or coating station 20 is arranged in the treatment space 14, by means of which a first material layer 26 is applied to at least one side of the steel strip 12, preferably to mutually opposite sides 22, 24 of the steel strip 12 (compare FIG. 2 ). As the first material layer 26, a zinc layer containing magnesium is applied to the two mutually opposite sides 22, 24 of the steel strip 12 at the first coating station 20 according to FIG. 1.The magnesium-containing zinc layer may comprise, in addition to the major proportion of zinc, for example about 1 percent by weight to 3 percent by weight of magnesium. In addition, the magnesium-containing zinc layer may include, in particular, about 1 weight percent to about 4 weight percent aluminum. As a remainder, the first material from which the first material layer 26 is formed contains zinc as well as inevitable impurities.Such a zinc-magnesium coating is advantageous in order to provide a very hard coating on the one hand and a very corrosion-resistant coating on the other hand for the steel strip 12. Namely, the formation of zinc-magnesium phases such as MgZn 2- phases in the first material layer 26 provides the high hardness and the very high corrosion resistance of the coated steel strip 12.However, if the magnesium from the first material layer 26 comes into contact with oxygen, for example in the form of atmospheric oxygen, an undesired formation of magnesium oxides may occur on the surface of the first material layer 26. This is particularly largely prevented in the present case. On the one hand, the first material layer 26 tending to form oxides is namely applied to the steel strip 12 in a vacuum or within the treatment chamber 14, wherein at least the reduced pressure prevails in the treatment chamber 14.Additionally, a cover layer 28 is applied to the first material layer 26 (see FIG. 2 ). The cover layer 28 is formed in the present case from a second material which has a lower tendency to form oxides than the magnesium-containing zinc layer or first material layer 26.Furthermore, the second material forming the cover layer 28 may have a lower tendency to form oxides that are detrimental to subsequent processes or further processing steps such as adhesive bonding and / or soldering and / or pickling than the zinc layer or first material layer 26 containing magnesium.According to FIG. 1, a second coating station 30 is arranged in the treatment space 14, which second coating station ensures the formation of the covering layer 28 on the first material layer 26 (compare FIG. 2 ).Both the first coating station 20 and the second coating station 30 preferably operate on the principle of physical vapor deposition. Accordingly, the first material, from which the first material layer 26 is formed, is first vaporized at the first coating station 20 and then applied as material vapor or as aerosol to the steel strip 12 to be coated. In an analogous manner, this takes place at the second coating station 30, at which the second material evaporates and is then moved as material vapor or as aerosol toward the steel strip 12 already having the first material layer 26, in order to form the covering layer 28 on the first material layer 26.In particular, by means of physical vapor deposition, the coatings in the form of the first material layer 26 and the covering layer 28 can be provided with a particularly small thickness and thus very saving material. In this regard, it is indicated in the schematic sectional view in FIG. 2 that the cover layer 28 preferably has a thickness that is less than the thickness of the first material layer 26. for example, the first material layer 26 can have a thickness of a few micrometers, in particular of less than 10 μm, and the cover layer 28 can have a thickness of, for example, approximately 1 μm to approximately 2 μm.According to FIG. 1, by means of respective application devices 32 which are associated with the first coating station 20, the two sides 22, 24 of the steel strip 12 can be simultaneously provided with the first material layer 26. However, it is also possible to carry out these processing steps successively in time. Analogously, the first material layers 26 can be provided with the respective cover layer 28 by means of respective application devices 34 which are associated with the second coating station 30.Preferably, a zinc layer is applied as the cover layer 28 to the first material layer 26. This is because the second material in the form of pure zinc advantageously acts as a passivating coating of the steel strip 12 comprising the magnesium-containing zinc layer or of the first material layer 26.In the case of the multilayer coating of the steel strip 12, preferably in vacuum, the layer more prone to oxidation in the form of the first material layer 26, which can in particular have a more proneness to the formation of oxides that are detrimental to subsequent processes, is therefore firstly applied to the steel strip 12 and the more passivating covering layer 28 is subsequently applied to the first material layer 26. In particular, the cover layer 28 forms, to a lesser extent, reaction products on contact with air, which are disadvantageous or disadvantageous for the subsequent processes such as adhesive bonding and / or soldering and / or pickling. Since the covering layer 28 does not contain magnesium but is preferably provided from pure zinc, magnesium oxides do not form on an outer surface of the covering layer 28.Preferably, the cover layer 28 is applied to the first material layer 26 after a treatment, in particular in the form of a curing. For this purpose, at least one cooling unit 36 can be arranged in the treatment space 14, for example in the conveying direction of the steel strip 12 between the first coating station 20 and the second coating station 30.In particular, two cooling units 36 shown schematically in FIG. 1 can absorb heat which is released from the zinc layer containing magnesium during the solidification thereof or curing thereof. Between the two cooling units 36, an intermediate space can be formed through which the steel strip 12 having the first material layer 26 is conveyed further to the second coating station 30.Due to the at least partial solidification, in particular curing, of the first material layer 26, it is possible to prevent magnesium contained in the first material layer 26 from reaching the surface of the cover layer 28 to a particularly great extent before the cover layer 28 is applied.In addition, the at least partial solidification of the magnesium-containing zinc layer or first material layer 26 ensures that the passivating covering layer 28 adheres particularly well to the underlying first material layer 26. Furthermore, the at least partial solidification of the first material layer 26 entails that mixing of the first material, by which the first material layer 26 is formed, and of the second material, by which the covering layer 28 is formed, is particularly largely prevented. This is also advantageous.By applying the first material layer 26 more prone to the formation of oxides in a vacuum or under the presence of a reduced pressure in the treatment chamber 14, the formation of oxides is minimized or at least greatly restricted. And by applying the passivating covering layer, the first material layer 26 which is more prone to the formation of oxides is sealed. If, at the outlet 18, the steel strip 12 provided with the first material layer 26 and the covering layer 28 is then exposed again to the ambient air, the covering layer 28 prevents oxidation of the first material layer 26 from occurring.Subsequent processes, such as, for example, adhesive bonding and / or soldering and / or pickling of the steel strip 12 provided with the first material layer 26 and the covering layer 28, are therefore not hindered by oxides, in particular in the form of magnesium oxides.A treatment, in particular in the form of cooling of the covering layer 28, can be provided before the coated steel strip 12 leaves the treatment space 14 again at the outlet 18. For this purpose, in particular at least one further cooling unit (not shown in FIG. 1 ) can be used.The coated steel strip 12 shown in FIG. 2 can be used for producing sheet metal components 40, such as can be used, for example, in the region of an outer skin and / or a structural component of a motor vehicle 38 shown schematically in FIG. 3. For example, body panels can be produced from the steel strip 12 provided with the first material layer 26 and the covering layer 28, which body panels can be painted and can form partial regions of the outer skin and / or of the structure of the motor vehicle 38 in the painted state.In particular, if partial regions of the outer skin and / or of the structure of the motor vehicle 38 are formed by such painted body panels, it is expedient to provide thin coatings in the form of the first material layer 26 and the covering layer 28 on the steel strip 12 or steel sheet used to form these partial regions of the outer skin and / or of the structure. This is because the at least one layer additionally applied to the covering layer 28 during the painting of the coated steel strip 12 or steel sheet ensures a further protection of the coated steel strip 12 or steel sheet against corrosion.The at least one layer additionally applied to the top layer 28 can comprise, in particular, a primer produced by cathodic dip coating. In particular, if at least a partial area of an outer skin of the motor vehicle 38 and / or of a structural component of the motor vehicle 38 is to be provided by the sheet metal component 40, a filler, a basecoat material and a clearcoat material can be applied to the outer layer 28 as further layers in addition to the primer.Overall, the examples show how sealing of the coating or first material layer 26 of the steel sheet or steel strip 12 which is prone to oxidation or has oxides which are detrimental to subsequent processes can be provided under vacuum.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 0 627 496 A2

[0006] DE 10 2021 101 383 A1

[0007] DE 10 2018 215 102 A1

[0007]

Claims

Method for coating a steel strip (12) for a sheet metal component (40) of a motor vehicle (38), in which the steel strip (12) is introduced into a treatment space (14) in which a reduced pressure is present, wherein a first material layer (26) is applied in the treatment space (14) to at least one side (22, 24) of the steel strip (12), and wherein a covering layer (28) is applied to the first material layer (26), characterized in that a zinc layer containing magnesium is applied as the first material layer (26) to the at least one side (22, 24) of the steel strip (12), wherein the covering layer (28) is formed from a second material which has a lower tendency to form oxides than the zinc layer containing magnesium.Method according to Claim 1, characterized in that a zinc layer is applied to the first material layer (26) as the covering layer (28).Method according to one of the preceding claims, characterized in that the covering layer (28) is applied to the first material layer (26) in the treatment space (14) in which the reduced pressure is present.Method according to one of the preceding claims, characterized in that the covering layer (28) is applied to the magnesium-containing zinc layer after the magnesium-containing zinc layer has at least partially solidified.Method according to Claim 4, characterized in that the at least partial solidification of the magnesium-containing zinc layer is effected by means of at least one cooling unit (36) which absorbs heat released by the magnesium-containing zinc layer.Method according to one of the preceding claims, characterized in that the first material layer (26) and / or the covering layer (28) are formed in a plurality of layers.Method according to one of the preceding claims, characterized in that the first material layer (26) is formed in a thickness of less than 10 μm and / or the covering layer (28) is formed in a thickness less than the first material layer.Method according to one of the preceding claims, characterized in that all sides (22, 24) of the steel strip (12) are provided with the first material layer (26) and with the covering layer (28).Steel strip (12) for a sheet metal component (40) of a motor vehicle (38), wherein the steel strip (12) is produced in a method according to one of Claims 1 to 8.Motor vehicle (38) having at least one sheet metal component (40), wherein at least a partial region of the at least one sheet metal component (40) is formed from a steel strip (12) according to Claim 9.

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