Method for producing a coated sheet-metal unit, and coated sheet-metal unit

Abstract

The invention relates to a method for producing a sheet-metal unit and preferably for further processing the sheet-metal unit, comprising: a coating step (II) in which a first, preferably single-layer initial coating (7) is applied to a first surface (5) of a metal sheet (3) to form a sheet-metal unit (1) comprising the metal sheet (3) and at least the first initial coating (7); and a heating step (III) in which the sheet-metal unit (1) is heated to or above a heating temperature. According to the invention, the alloy of the first, preferably metal, initial coating (7) comprises titanium as a first alloying element, aluminum as a second alloying element, manganese as a third alloying element and zinc as a fourth alloying element.

Description

[0001] Description

[0002] Method for producing a coated sheet metal unit and a coated sheet metal unit

[0003] The invention relates to a method for producing a sheet metal unit according to the preamble of claim 1 and to a sheet metal unit according to claim 11.

[0004] A generic sheet metal unit comprises a metal sheet and an aluminum-silicon coating (AISi coating). The aluminum-silicon coating is applied to at least one surface of the metal sheet. The aluminum-silicon coating provides corrosion protection for the metal sheet by contributing to the formation of a passivation layer on the surface of the metal sheet. However, the corrosion protection effect of the passivation layer is limited, so that the passivation layer only offers sufficient corrosion protection for the metal sheet in dry areas, for example, in a vehicle body. The sheet metal unit therefore has the disadvantage, among other things, that it cannot be used in wet areas, for example in a vehicle body, without further additional measures.

[0005] DE 102016 102 504 A1 discloses an aluminum-based coating for steel sheets or steel strips and a method for producing the same. DE 10 2020 201 451 A1 discloses a steel sheet for hot forming, a method for producing a hot-formed steel sheet component, and a hot-formed steel sheet component. EP 2 848 709 B1 discloses a method for producing a steel component provided with a metallic, corrosion-protective coating and a steel component.

[0006] An object of the invention is to provide a sheet metal unit by means of which, in comparison with a known sheet metal unit, a wider range of applications can be covered.

[0007] This object is achieved by the features of the independent claims. Preferred developments of the invention are disclosed in the subclaims.

[0008] According to the invention, a method is proposed for producing a sheet metal unit and preferably for further processing the sheet metal unit, comprising a coating step in which a first, preferably single-layer, initial coating is applied to a first surface of a metal sheet, specifically to form a sheet metal unit comprising the metal sheet and at least the first initial coating, and a heating step in which the sheet metal unit is heated to or above a heating temperature. According to the invention, the alloy of the first, preferably metallic, initial coating comprises titanium as the first alloying element, aluminum as the second alloying element, manganese as the third alloying element, and zinc as the fourth alloying element. In combination, preferably only in combination, with these four alloying elements, the coating can meet the various requirements in the further processing and application of the sheet metal unit.The alloying element titanium prevents the coating from alloying with iron during the heating step. The alloying element aluminum prevents surface scaling during the heating step. The alloying element manganese increases the temperature resistance of the coating during the heating step. The alloying elements zinc and manganese achieve the desired corrosion resistance and weldability.

[0009] In a specific embodiment, it can be provided that the heating temperature is in a range from 300°C to 1100°C, preferably in a range from 450°C to 1000°C, particularly preferably in a range from 550°C to 1000°C, most preferably in a range from 700°C to 950°C, and / or that the heating temperature corresponds to the austenitizing temperature AC1 of the alloy of the metal sheet, and / or that the heating temperature corresponds to the austenitizing temperature AC3 of the alloy of the metal sheet. From a temperature of 300°C, the diffusion processes start and from 450°C the diffusion processes proceed at an accelerated rate, leading to demixing. Up to a temperature of 700°C, the sheet unit can be pre-diffused in a heating device, for example as a coil, without changing the sheet properties.From 550°C to 700°C, the diffusion processes are accelerated to such an extent that, for example, sheet metal blanks and / or cold-formed components can be produced using the process. From 700°C to 1100°C, the sheet metal unit can be further processed, for example, in a hot forming step. This requires temperatures of at least the austenitizing temperature. The austenitizing temperature AC1 begins at approximately 700°C, and complete austenitization of the structure is preferably completed at 950°C. For the application of rapid heating processes, it can be advantageous to briefly subject the sheet metal unit to higher temperatures up to 1100°C. In principle, the sheet metal unit can adopt ramp-like or step-like temperature profiles within these temperature ranges, for example.In an exemplary embodiment, it can be provided that the first initial coating is single-layered and / or has only a single layer after completion of the coating step and / or before the start of the heating step, and / or before the heating temperature is reached. Preferably, all alloying elements are evenly distributed and / or evenly mixed in the single layer. This simplifies the coating process and allows it to be carried out with shorter process times, for example, in a single pass during cold strip production.

[0010] In an exemplary embodiment, it can be provided that during the heating step, preferably upon reaching the heating temperature, the first, preferably single-layer, starting coating is converted into a first, preferably three-layer, coating system, and / or that the alloying elements in the single layer of the first starting coating demix to form the first coating system, wherein it is preferably provided that the first coating system, after the demixing of the alloying elements, has essentially, preferably exactly, three layers, namely a first bonding layer and a first, preferably graded, middle layer and a first surface layer. Only through the layer formation and arrangement can the diverse requirements for further processing of the sheet metal unit be met.The respective layer can meet a specific requirement in further processing, for example the surface layer can provide scale protection, the bonding layer can form a diffusion barrier and the middle layer can provide corrosion protection.

[0011] In a specific embodiment, it can be provided that the single layer of the first initial coating is converted into the first coating system during the heating step, preferably upon reaching the heating temperature, and / or the alloying elements are separated in such a way that the first bonding layer is arranged between the metal sheet and the first middle layer, and / or that the first middle layer is arranged between the first bonding layer and the first surface layer, and / or a surface of the first surface layer facing away from the middle layer is free of further coatings and / or is covered by a layer of lacquer. The arrangement of the first bonding layer ensures that the diffusion of, for example, iron from the metal sheet into the coating is impeded and an undesirable alloying of zinc with iron according to the invention is avoided.The arrangement of the first middle layer, for example, ensures that the alloying elements zinc and manganese can interact electrochemically with each other. The arrangement of the first surface layer prevents scaling of the layer during the heating step.

[0012] In an exemplary embodiment, it can be provided that the first bonding layer essentially comprises, preferably only, the first alloying element, i.e., titanium, and / or that the first middle layer essentially comprises, preferably only, the third alloying element, i.e., manganese, and the fourth alloying element, i.e., zinc, and / or that the first surface layer comprises the second alloying element, i.e., preferably essentially aluminum, and / or the fourth alloying element, i.e., zinc. This allows the requirements for further processing and application of the sheet metal unit to be met with particularly short processing times.

[0013] In a specific embodiment, it can be provided that the first alloying element, i.e. titanium, is present in the first bonding layer, preferably in the core of the first bonding layer, with a weight fraction in wt.% of at least 50% higher, preferably 100% higher than in the first starting coating, and / or that the third alloying element, i.e. manganese, and the fourth alloying element, i.e. zinc, are present in the first middle layer, preferably in the core of the first middle layer, in total with a weight fraction of at least 60 wt.%, preferably 70 wt.%, and / or that the second alloying element, i.e. aluminum, is present in the first surface layer, preferably in the core of the first surface layer, and / or the fourth alloying element, i.e. zinc, is present with a weight fraction in wt.% of at least 50% higher, preferably 100% higher than in the starting coating.Under these conditions, the requirements for further processing and application of the sheet metal unit can be met particularly cost-effectively. If the first surface layer contains the second alloying element, i.e., aluminum, and the fourth alloying element, i.e., zinc, the coating can also provide active corrosion protection and, for example, can be used without painting.

[0014] In an exemplary embodiment, it can be provided that the alloying elements in the alloy of the first starting coating have the following weight proportions in wt.%:

[0015] - Titanium: less than or equal to 10 wt.%, preferably 2.5 to 7.5 wt.%, particularly preferably 2.5 to 5 wt.%, and - Aluminium: less than or equal to 20 wt.%, preferably 5 to 15 wt.%, particularly preferably 5 to 10 wt.%, and

[0016] - Manganese: less than or equal to 55 wt.%, preferably 30 to 55 wt.%, particularly preferably 35 to 45 wt.%, and

[0017] - Zinc: less than or equal to 45 wt.%, preferably 25 to 45 wt.%, particularly preferably 35 to 42.5 wt.%, and preferably

[0018] - a residue of unavoidable impurities and / or accompanying elements.

[0019] Extensive in-house analyses have shown that only with these weight proportions can all requirements for further processing and application of the sheet unit be met.

[0020] In a specific embodiment, it can be provided that the alloying elements in the alloy of the first initial coating have the following weight ratios to one another:

[0021] - Titanium to aluminum in a weight ratio of 1 : 2, and / or

[0022] - zinc to manganese in a weight ratio of 1 : 2, and / or

[0023] - Titanium to aluminum to zinc to manganese in a weight ratio of 1 : 2 : 7 : 10.

[0024] Extensive in-house analyses have shown that the requirements of the invention can be met particularly well and efficiently with these weight ratios.

[0025] In a specific embodiment, it can be provided that, during the coating step, a second initial coating, identical to the first initial coating, is applied to a second surface of the metal sheet. Preferably, during the heating step, the alloying elements in the single layer of the second initial coating separate to form a second coating system identical to the first coating system. During further processing and application, it is particularly advantageous to provide a coating on both sides. This avoids the need for additional cleaning and protective measures for the uncoated metal sheet surface.

[0026] According to the invention, a sheet metal unit is also proposed, preferably a sheet metal unit as described above, with a metal sheet, preferably according to one of the preceding claims, and a first coating system arranged on the metal sheet and / or a second coating system arranged on the metal sheet, preferably according to one of the preceding claims, wherein it is preferably provided that the first coating system essentially comprises three layers, namely a first bonding layer and a first, preferably graded, middle layer and a first surface layer, and / or that the second coating system essentially comprises three layers, namely a second bonding layer and a second, preferably graded, middle layer and a second surface layer, wherein it is particularly preferably provided that the first bonding layer and / or the second bonding layer essentially, preferably only,the first alloying element, i.e., titanium, and / or that the first middle layer and / or the second middle layer essentially, preferably only, comprises the third alloying element, i.e., manganese, and the fourth alloying element, i.e., zinc, and / or that the first surface layer and / or the second surface layer essentially comprises the second alloying element, i.e., preferably essentially, aluminum, and / or the fourth alloying element, i.e., zinc. The sheet unit has the same advantages as already mentioned in connection with the method.

[0027] Embodiments of the invention are described below with reference to the accompanying figures.

[0028] They show:

[0029] Figure 1 shows a purely schematic flow diagram of a method for

[0030] Manufacturing a sheet metal unit with a first coating system, and

[0031] Figure 2 shows a side view of the sheet metal unit with the first

[0032] Conversion coating and a second coating system.

[0033] Figure 1 illustrates a method for producing a sheet metal unit 1. The method comprises a preparation step 1, in which a metal sheet 3 is prepared. The metal sheet 3 is formed, here merely by way of example, by a sheet metal blank.

[0034] Of course, in all embodiments of the sheet metal unit 1, the metal sheet 3 can also be formed, for example, by a long metal sheet strip or, for example, by a metal sheet coil. The material of the metal sheet 3 is, here merely by way of example, a hardenable steel material, which is preferably assigned to a material class for the production of ultra-high-strength sheet steel components. The hardenable steel has a preferably achievable strength RM of greater than 980 MPa, preferably greater than 1180 MPa, particularly preferably greater than 1650 MPa. The material of the metal sheet, preferably the alloy of the metal sheet, comprises, here merely by way of example, the following alloying elements in weight percent (wt%):

[0035] - carbon with a weight fraction in a range of 0.20 wt% to 0.42 wt%, preferably in a range of 0.30 wt% to 0.38 wt%, and

[0036] - silicon with a weight fraction of less than or equal to 2.2 wt.%, preferably with a weight fraction in a range of 1.0 wt.% to 1.8 wt.%, and

[0037] - manganese with a weight fraction in a range of 0.6 wt% to 3.5 wt%, preferably in a range of 0.8 wt% to 2.0 wt%, and

[0038] - boron in a weight fraction of 0.001 wt% to 0.1 wt%, preferably in a range of 0.003 wt% to 0.005 wt%, and

[0039] - nitrogen in a weight fraction of less than or equal to 0.01% by weight, and

[0040] - sulphur in a weight fraction of less than or equal to 0.01% by weight, and

[0041] - Phosphorus with a weight fraction of less than or equal to 0.02 wt.%, and preferably

[0042] - an alloy residue of iron and / or impurities.

[0043] After the preparation step I, a coating step II is carried out in the method. In coating step II, a coating material is applied to a first surface 5 of the metal sheet 3, forming a first, metallic, initial coating 7 arranged on the first surface. In coating step II, the coating material is deposited on the first surface by means of physical vapor deposition (PVD), here merely by way of example. The metal sheet 3 and the first initial coating 7 together form the sheet unit 1.

[0044] The alloy of the initial coating 7 comprises titanium as the first alloying element, aluminum as the second alloying element, manganese as the third alloying element, and zinc as the fourth alloying element. The alloying elements in the alloy of the first initial coating 7 can, by way of example only, have the following weight percentages in wt.%:

[0045] - Titanium: 5 wt%, and

[0046] - Aluminium: 10 wt%, and

[0047] - Manganese: 50 wt.%, and - Zinc: 35 wt.% and preferably

[0048] - a residue of unavoidable impurities and / or accompanying elements.

[0049] For the sake of completeness, it is explicitly pointed out again at this point that the alloying elements in the alloy of the first initial coating 7 can also have the following weight proportions in wt.%, here only as an example:

[0050] - Titanium: less than or equal to 10 wt.%, preferably 2.5 to 7.5 wt.%, particularly preferably 2.5 to 5 wt.%, and

[0051] - Aluminium: less than or equal to 20 wt.%, preferably 5 to 15 wt.%, particularly preferably 5 to 10 wt.%, and

[0052] - Manganese: less than or equal to 55 wt.%, preferably 30 to 55 wt.%, particularly preferably 35 to 45 wt.%, and

[0053] - Zinc: less than or equal to 45 wt.%, preferably 25 to 45 wt.%, particularly preferably 35 to 42.5 wt.% and preferably

[0054] - a residue of unavoidable impurities and / or accompanying elements.

[0055] In addition, the alloying elements in the alloy of the first starting coating 7 may preferably have the following weight ratios to one another:

[0056] - Titanium to aluminum in a weight ratio of 1 : 2, and / or

[0057] - zinc to manganese in a weight ratio of 1 : 2, and / or

[0058] - Titanium to aluminum to zinc to manganese in a weight ratio of 1 : 2 : 7 : 10.

[0059] After completion of the coating step II, the starting coating 7 is initially present in a single layer, i.e. the first starting coating 7 has only a single layer in which all alloying elements of the alloy of the starting coating 7 are evenly distributed and evenly mixed with one another.

[0060] After coating step II, a heating step III is carried out in the method. In heating step III, sheet metal unit 1 is heated by means of a heating device 8 to at least the austenitizing temperature AC1, preferably to the austenitizing temperature AC3, of the alloy of metal sheet 3. During heating step III, specifically upon reaching the austenitizing temperature AC1, preferably the austenitizing temperature AC3, of the alloy of metal sheet 3, the first, single-layer starting coating 7 is converted into a first, three-layer coating system 9. Specifically, during heating step III, the alloying elements in the single layer of the first starting coating 7 demix to form the first coating system, specifically in such a way that after demixing of the alloying elements, the first coating system essentially has exactly three layers and / or is three-layered.One of the three layers is a first bonding layer 11 and one of the three layers is a first graded middle layer 13 and one of the layers is a first surface layer 15.

[0061] The first bonding layer 11 is arranged between the metal sheet 3 and the first middle layer 13 and serves to improve the adhesion of the first middle layer to the metal sheet 3 and as a barrier for intermetallic phases, so that the diffusion of iron from the metal sheet 3 into the first middle layer 13 is hindered. The first middle layer 13 is arranged between the first bonding layer 11 and the first surface layer 15 and contributes to the formation of a passive layer, increases the melting point, improves weldability and hot formability. The first surface layer 15 serves as an anti-scale layer and / or as an oxide protection layer. A surface of the first surface layer 15 facing away from the first middle layer 13 can be covered with a lacquer layer (not shown).

[0062] The first bonding layer 11 can have a layer thickness in a range from 0.05 μm to 5 μm. The first middle layer 13 can have a layer thickness in a range from 0.1 μm to 10 μm. The first surface layer 15 can have a layer thickness in a range from 0.05 μm to 5 μm. The first middle layer 13 has a layer thickness that is at least 2 times greater, preferably at least 5 times greater, than the first bonding layer 11 or the first surface layer 15.

[0063] In the first bonding layer 11, the content of the first alloying element, i.e., titanium, in wt.% is at least 50% higher, preferably 100% higher, than in the first starting coating 7. In the first middle layer 11, all four alloying elements are present, with the third alloying element, i.e., manganese, and the fourth alloying element, i.e., zinc, being present in a total weight fraction of at least 60%, preferably 70%. In the first surface layer 15, the content of the second alloying element, i.e., aluminum in wt.% and / or the fourth alloying element in wt.%, i.e., zinc, is at least 50% higher, preferably 100%, than in the first starting coating 7.

[0064] In the event of mechanical damage, such as a scratch or stone chipping, the first coating system 9 locally forms a water-insoluble, passive corrosion protection layer under the influence of a corrosion medium, such as, for example, an alkali salt, preferably NaCl, and atmospheric oxygen, which blocks the corrosive attack of the corrosion medium. In other words: the first middle layer 13, comprising zinc and manganese, together with NaCl forms a so-called "galvanic cell" in which an electrochemical reaction can take place. The contact between the first middle layer 13 and the atmospheric oxygen and the corrosion medium, namely NaCl, is brought about by the damage. The atmospheric oxygen and / or the zinc advantageously support the formation of the corrosion protection layer.The corrosion protection top layer is a black solid layer and can contain at least manganese oxide and / or zinc oxide and / or zinc-manganese mixed oxide. Since the corrosion protection top layer is water-insoluble and stationary, no red rust corrosion products appear. A further advantageous development according to the invention involves the presence of the fourth alloying element, i.e., zinc, in the first surface layer 15, whereby, in the absence of a paint layer or in the case of surface paint damage, additional corrosion protection is provided by zinc and / or zinc oxide.

[0065] The method has been described above only with reference to the first coating system 9. Of course, a second coating system 17 can be applied to a second surface 16 of the metal sheet 3, said second coating system being obtained in the same way as the first coating system 9. The second coating system 17 has a second bonding layer 19, which is preferably identical to the first bonding layer 11 in terms of structure, material, layer thickness, arrangement, and function. The second coating system 17 has a second middle layer 21, which is preferably identical to the first middle layer 13 in terms of structure, material, layer thickness, arrangement, and function. The second coating system 17 has a second surface layer 23, which is preferably identical to the first surface layer 15 in terms of structure, material, layer thickness, arrangement, and function.Corresponding to the first coating system 9, the second bonding layer 19 in the second coating system 17 is also arranged between the metal sheet 3 and the second middle layer 21. Furthermore, the second middle layer 21 is arranged between the second bonding layer 21 and the second surface layer.

[0066] The method may further comprise a further processing step in which the sheet metal unit 1 comprising the metal sheet 3 and the first coating system 9 and / or the second coating system 17 is further processed into a hardened sheet steel component in a cold forming and / or hot forming and / or press hardening process. The sheet steel component can be used as a vehicle body component and / or as a structural component and / or as a vehicle chassis component. List of reference symbols

[0067] 1 Blechemheit

[0068] 3 metal sheet

[0069] 5 first surface

[0070] 7 first initial coating

[0071] 8 Heating device

[0072] 9 first coating system

[0073] 11 first connection layer

[0074] 13 first middle class

[0075] 15 first surface layer

[0076] 16 second surface

[0077] 17 second coating system

[0078] 19 second connection layer

[0079] 21 second middle class

[0080] 23 second surface layer

[0081] I Deployment step

[0082] II Coating step

[0083] III Heating step

Claims

Patent claims 1. A method for producing a sheet metal unit and preferably for further processing the sheet metal unit, comprising: a coating step (II) in which a first, preferably single-layer, starting coating (7) is applied to a first surface (5) of a metal sheet (3), specifically to form a sheet metal unit (1) comprising the metal sheet (3) and at least the first starting coating (7), and a heating step (III) in which the sheet metal unit (1) is heated to or above a heating temperature, characterized in that the alloy of the first, preferably metallic, starting coating (7) has titanium as the first alloying element, aluminum as the second alloying element, manganese as the third alloying element, and zinc as the fourth alloying element.

2. The method according to claim 1, characterized in that the heating temperature is in a range from 300°C to 1100°C, preferably in a range from 450°C to 1000°C, particularly preferably in a range from 550°C to 1000°C, most preferably in a range from 700°C to 950°C, and / or that the heating temperature corresponds to the austenitizing temperature AC1 of the alloy of the metal sheet (3), and / or that the heating temperature corresponds to the austenitizing temperature AC3 of the alloy of the metal sheet (3).

3. Method according to claim 1 or 2, characterized in that the first starting coating (7) after completion of the coating step (II) and / or before the start of the heating step (III), and / or before reaching the heating temperature is single-layered and / or has only a single layer, wherein it is preferably provided that in the single layer all alloying elements are evenly distributed and / or evenly mixed with one another.

4. Method according to one of the preceding claims, characterized in that during the heating step (III), preferably upon reaching the heating temperature, the first, preferably single-layer, starting coating (7) is converted into a first, preferably three-layer, coating system (9), and / or that the alloying elements in the single layer of the first starting coating (7) demixing to form the first coating system (9), wherein it is preferably provided that the first coating system (9) after demixing of the alloying elements has essentially, preferably exactly, three layers, namely a first bonding layer (11) and a first, preferably graded, middle layer (13) and a first surface layer (15).

5. The method according to claim 3 or 4, characterized in that the single layer of the first starting coating (7) is converted into the first coating system during the heating step (III), preferably when the heating temperature is reached, and / or the alloying elements are separated in such a way that the first bonding layer (11) is arranged between the metal sheet (3) and the first middle layer (13), and / or that the first middle layer (13) is arranged between the first bonding layer (11) and the first surface layer (15), and / or a surface of the first surface layer (15) facing away from the middle layer (13) is free of further coatings and / or is covered by a layer of lacquer.

6. The method according to claim 5, characterized in that the first bonding layer (11) essentially comprises, preferably only, the first alloying element, that is to say titanium, and / or that the first middle layer (13) essentially comprises, preferably only, the third alloying element, that is to say manganese, and the fourth alloying element, that is to say zinc, and / or that the first surface layer (15) comprises the second alloying element, that is to say aluminum, and / or the fourth alloying element, that is to say zinc.

7. The method according to claim 5 or 6, characterized in that the first alloying element, that is to say titanium, is present in the first bonding layer (11), preferably in the core of the first bonding layer (11), with a weight fraction in wt.% of at least 50% higher, preferably 100% higher than in the first starting coating (7), and / or that the third alloying element, that is to say manganese, and the fourth alloying element, that is to say zinc, are present in the first middle layer (13), preferably in the core of the first middle layer (13), in total with a weight fraction of at least 60 wt.%, preferably 70 wt.%, and / or that the second alloying element, that is to say aluminum, is present in the first surface layer (15), preferably in the core of the first surface layer (15), and / or the fourth alloying element, that is to say zinc, with a weight fraction in wt.% of at least 50% higher, preferably 100% higher than in the first starting coating (7).

8. Method according to one of the preceding claims, characterized in that the alloying elements in the alloy of the first starting coating (7) have the following weight proportions in wt.%: - Titanium: less than or equal to 10 wt.%, preferably 2.5 to 7.5 wt.%, particularly preferably 2.5 to 5 wt.%, and - Aluminium: less than or equal to 20 wt.%, preferably 5 to 15 wt.%, particularly preferably 5 to 10 wt.%, and - Manganese: less than or equal to 55 wt.%, preferably 30 to 55 wt.%, particularly preferably 35 to 45 wt.%, and - Zinc: less than or equal to 45 wt.%, preferably 25 to 45 wt.%, particularly preferably 35 to 42.5 wt.%, and preferably - a residue of unavoidable impurities and / or accompanying elements.

9. Method according to one of the preceding claims, characterized in that the alloying elements in the alloy of the first starting coating (7) have the following weight ratios to one another: - Titanium to aluminum in a weight ratio of 1 : 2, and / or - zinc to manganese in a weight ratio of 1 : 2, and / or - Titanium to aluminum to zinc to manganese in a weight ratio of 1 : 2 : 7 :

10.

10. Method according to one of the preceding claims, characterized in that in the coating step (II) a second starting coating, identical to the first starting coating (7), is applied to a second surface (16) of the metal sheet (3), wherein it is preferably provided that during the heating step (III) the alloying elements in the single layer of the second starting coating separate to form a second coating system (17) which is identical to the first coating system (9).

11. Sheet metal unit, preferably according to one of the preceding claims, comprising: a metal sheet (3), preferably according to one of the preceding claims, and a first coating system (9) arranged on the metal sheet (3) and / or a second coating system (17) arranged on the metal sheet (3), preferably according to one of the preceding claims, wherein it is preferably provided that the first coating system (9) essentially comprises three layers, namely a first bonding layer (11) and a first, preferably graded, middle layer (13) and a first surface layer (15), and / or that the second coating system essentially comprises three layers, namely a second bonding layer (19) and a second, preferably graded, middle layer (21) and a second surface layer (23), wherein it is particularly preferably provided that the first bonding layer (11) and / or the second bonding layer (19) essentially comprises, preferably only, the first alloying element, i.e., titanium, and / or that the first middle layer (13) and / or the second middle layer (21) essentially comprises, preferably only, the third alloying element, i.e., manganese, and the fourth alloying element, i.e., zinc,and / or that the first surface layer (15) and / or the second surface layer (23) comprises the second alloying element, that is, preferably substantially, aluminum, and / or the fourth alloying element, that is, zinc.,

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