EP4296399A1 - Method for producing hot-dip coated steel sheet, and hot-dip coated steel sheet - Google Patents

Abstract

The invention relates to a method for producing a hot-dip coated steel sheet, the method comprising the following steps: providing a steel sheet, hot-dip coating the steel sheet with a zinc-based coating, the steel sheet passing through a melt bath which contains aluminum between 0.1 and 4.0 wt. %, optionally magnesium between 0.1 and 4.0% by weight and the balance comprising zinc and unavoidable impurities, removing the steel sheet coated with liquid melt from the melt bath and stripping off part of the steel sheet still coated with liquid melt with a gaseous stripping medium a stripping environment, wherein the liquid melt remaining on the steel sheet solidifies completely after stripping and forms the coating on the steel sheet; and a hot-dip coated steel sheet.

Description

The invention relates to a method for producing a hot-dip coated steel sheet, the method comprising the following steps: providing a steel sheet; Hot-dip coating the steel sheet with a zinc-based coating, the steel sheet passing through a melt pool comprising aluminum between 0.5 and 4.0% by weight, magnesium between 0.5 and 4.0% by weight and the balance zinc and unavoidable impurities ; Removing the steel sheet coated with liquid melt from the melt bath and stripping off a part of the steel sheet still coated with liquid melt with a gaseous stripping medium in a stripping environment, the liquid melt remaining on the steel sheet completely solidifying after stripping and forming the coating on the steel sheet. Furthermore, the invention also relates to a hot-dip coated steel sheet. Such a Zn-Mg-Al coating is also referred to as a ZM coating.

In the conventional production of Zn-Mg-Al coatings on steel sheets, the coating cools down and thus crystallization occurs during and after the coating thickness is adjusted by stripping off the still molten coating. This primarily forms zinc crystals, which are surrounded by phases rich in magnesium and aluminum, cf. CN 110 983 224 A . During the solidification of Zn-Mg-Al melts, binary (zinc-magnesium) and/or ternary (zinc-aluminum-magnesium) eutectic phases occur locally to varying degrees between, above and below the primarily precipitated zinc grains. These eutectic phases are made of the eutectic and pure metals, ie these eutectic phases have, in addition to the eutectic, secondary zinc grains and possibly aluminum phases (aluminum grains). These secondary zinc grains should not be confused with the primary zinc grains since they have a volume that is several orders of magnitude smaller than the primary zinc grains. While the primary zinc grains can have a diameter of up to 30 µm and even more, the diameter of the secondary zinc grains in the eutectic phases is up to 2 µm. Furthermore, these secondary phases are precipitated before or after the eutectic. In the literature, the eutectic phases described above are referred to as hypo- or hyper-eutectic phases, depending on whether they are precipitated before or after the eutectic. The layer structure of a Zn-Mg-Al coating has an enrichment of eutectic phases that is not widespread but is distributed over the entire surface, which is above the zinc grains (and possibly also in the Zinc grains) are arranged. The eutectic and the eutectic phases are essentially magnesium-rich phases, optionally aluminum-rich phases, in particular in the form of mixed crystals. The enrichment of eutectic phases distributed over the entire area can be on average up to 100%, in particular up to 90%, for example up to 80%.

In general, the addition of magnesium to the melt results in an improvement in corrosion resistance as well as reduced tool wear during forming. During the formation of the binary eutectic in the ZM coating, the zinc-rich and the intermetallic MgZn2 phases are deposited from the melt in lamellar form, i.e. in alternating layers. In the case of the ternary eutectic, the aluminum-rich phase is also integrated into the lamellar layer structure. The zinc phases contained in the eutectic are also referred to as secondary zinc grains.

According to the prior art, the improved corrosion behavior is attributed to the microstructure of the eutectic phases in the coating. Essentially, dense eutectic structures consisting of zinc, zinc-magnesium (MgZn ₂ ) and optionally aluminum phases are crucial so that the magnesium-rich phases that initially arise form an equally dense barrier layer and thus slow down the further corrosion process. An increase in the surface area of the dense eutectic phases on the coating accordingly ensures an improvement in corrosion resistance. According to the prior art, the more efficient forming behavior of the Zn-Mg-Al coating is not yet fully understood, but it is assumed that it is based on the changed hardness properties of the phases that form on the coating surface. In comparison to the soft zinc grains, the intermetallic zinc-magnesium (MgZn ₂ ) phases in the eutectic are significantly harder and therefore more resistant to wear.

In order to ensure successful paint bonding to the steel sheets coated with Zn-Mg-Al coatings, chemical treatment and modification of the surface of the coating is also required. In the automotive sector, a great deal of effort goes into a phosphating process to ensure that phosphate crystals grow over the entire surface of a coating that is usually hot-dip coated, thereby achieving sufficient adhesion and a homogeneous appearance of the paint. Before crystals form, the surface of the hot-dip coated steel sheet is "pickled" by the phosphoric acid present in the phosphating solution. in order to at least partially remove/dissolve the non-reactive oxide layer on the surface of the coating that inevitably arises during the coating process. Only after this reaction barrier (oxide layer) has been removed can a successful conversion chemistry be formed, see for example DE 10 2019 204 224 A1 and EP 2 474 649 A1 .

In both the automotive and coil coating sectors, a certain contact time with the "pickling" medium is required, which ideally should be long enough for the oxide layer on the surface of the coating to be essentially completely removed. If this is not the case, spots can form during phosphating, which can be attributed to locally different crystal growth. The connection of bonding agents typical for automobiles or pretreatments from the coil coating sector, which have been designed for application to metallic coatings, cannot develop their effect fully and satisfactorily due to the existing, particularly thicker oxide layer. Incorrect connection of such systems generally results in poorer adhesive suitability and/or poorer paint adhesion. Areas where the oxide layer has not been completely stripped can, in the worst case scenario, represent predetermined breaking points. This problem occurs not only in the automotive sector, but also in other areas in which hot-dip coated steel sheets are used, which, in addition to excellent corrosion behavior, also have a sufficient surface that can be activated so that they can then be painted and/or coated with other materials (foils, etc.). can be done, for example in the so-called coil coating process.

The aging of the Zn-Al-Mg coatings when stored in air or in an oxygen-containing atmosphere can result in a change in the chemical composition of the layers near the surface, and thus also lead to the formation and growth of oxides and oxide layers in and on the metallic coating. The formation and growth of these oxides and oxide layers is associated with the penetration of oxygen into the eutectic phases of the protective layer and leads to additional deterioration in further processing. Surprisingly, there is a preferential penetration of oxygen from the surface into and along the magnesium-rich phases, so that these are preferentially oxidized. In this process, elementary metal atoms from the eutectic and the eutectic phases are oxidized to form oxides and/or hydroxides or similar compounds (metal oxides). In the corresponding or in the same period of time, phases rich in zinc and/or aluminum are hardly oxidized. The metal oxides are in layers close to the surface, i.e. in the upper layers of the Coating arranged, in particular at a depth of approximately 0.01 and 0.1 μm. This layer is also known as the oxide layer.

In order to be able to have a positive influence on improving the phosphatability and/or paint appearance of Zn-Mg-Al coatings, the DE 10 2020 208 991 A1 proposes to create a smaller oxide layer thickness compared to the prior art after the liquid coating has been applied to the steel sheet, which benefits the reduction of the contact time with "pickling" media by stripping off in an inert atmosphere containing hydrogen between 0. 1 and 10% by volume, the rest contains nitrogen and unavoidable impurities and has a dew point between -50 °C and +5 °C. This allows oxide layers of up to 10 nm to form on the coating, whereby in addition to the small oxide layer thickness, an essentially homogeneous thickness also results on the coating.

The object of the invention is to provide a method for producing a hot-dip coated steel sheet, with which the proportion of eutectic phases in the layer of the coating near the surface can be increased, and to provide a corresponding hot-dip coated steel sheet.

The object of the invention is also to provide a steel sheet which provides very good corrosion protection and an excellent surface for other applications.

The problem is solved in relation to the method with the features of patent claim 1 and in relation to the hot-dip coated steel sheet with the features of patent claim 10.

In the course of solidification and/or after solidification of the liquid melt remaining on the steel sheet after stripping, primary zinc grains and phases rich in magnesium and/or aluminum as well as eutectic phases, in particular at least intermetallic zinc-magnesium phases, form in the coating. If the melt consisting of aluminum and magnesium, the rest of zinc and unavoidable impurities is given sufficient time to cool down and thus solidify, the zinc crystals grow undisturbed in the coating into the layer near the surface and/or even locally up to the surface and do not push them or poorly soluble elements aluminum and magnesium aside, which, as cooling progresses, form phases rich in magnesium and aluminum solidify into eutectic phases, into which areas between the resulting primary zinc grains are displaced. The enrichment of eutectic phases, among other things, distributed in the zinc grain intermediate areas can therefore be up to 50 (area)% on average, especially when viewed below the oxide layer on the surface of the coating. Due to the high oxygen affinity of the magnesium in the coating, a magnesium-rich oxide layer inevitably forms on the coating, which can also contain aluminum and/or zinc-rich oxides. The oxide layer formed on the coating can be between 0.01 and 0.1 µm or more.

The inventors have surprisingly discovered that if the previously known solidification mechanism is not given enough time and therefore the primary zinc crystals cannot grow quickly enough, no significant shift of the magnesium- and aluminum-rich phases as well as the eutectic phases can take place.

As a result, a correspondingly higher surface area share of eutectic phases can form in the layer near the surface and/or on the surface of the coating and thus also above the primary zinc grains within the coating (i.e. below the oxide layer on the surface of the coating) if the stripping medium is with a Temperature below 15 °C is supplied for stripping and / or a temperature below 15 °C is set in the stripping environment. The higher surface area proportion of eutectic phases is present in comparison to a control that was produced analogously, but a stripping medium with a temperature above 15 ° C is supplied for stripping and / or there is a temperature above 15 ° C in the stripping environment. Due to the method according to the invention, after the coating has solidified, there is a surface area of eutectic phases in the layer near the surface and/or on the surface of the coating and thus also above the primary zinc grains within the coating (i.e. below the oxide layer on the surface of the coating) of at least 65%, in particular at least 70%, 75% or 80%, preferably at least 85% or 90%, preferably at least 95%, 96%, 97%, 98%, 99% or more, up to 100%.

In addition, the inventors have found that the method according to the invention reduces the thickness of the deposited lamellae, i.e. the phases in the lamellar layer structure of the eutectic, so that nanostructures are formed from zinc phases, preferably from the secondary zinc grains that are part of the eutectic and the other phases of the Eutectic, in particular the different mixed crystals form on the surface.

The secondary zinc grains, which are formed close to the surface in the eutectic in the process according to the invention, have an average diameter of a maximum of 1 μm, preferably a maximum of 800 nm, 700 nm or 600 nm, particularly preferably a maximum of 500 nm, 400 nm or 300 nm, in particular a maximum of 250 nm and at least 1 nm, preferably at least 10 nm, 20 nm or 30 nm, particularly preferably at least 50 nm, 60 nm or 75 nm, in particular at most 100 nm.

Due to the influence of temperature, the mechanism of primary zinc crystal growth will be reduced, advantageously in favor of the increased formation of eutectic phases in the area near the surface and/or on the surface of the coating. This is achieved by either a) supplying the stripping medium with a temperature below 15 °C for stripping, b) setting a temperature below 15 °C in the stripping environment or c) the stripping medium with a temperature below 15 °C is supplied for stripping and a temperature below 15 °C is set in the stripping environment. This increases the temperature difference between the acting medium and / or the acting environment and the still molten coating, so that a rapid in-situ "shock" cooling causes the formation or emergence of the eutectic phases in the area near the surface and / or on the Surface of the coating favored.

In a standard hot-dip coating system, the molten coating must be completely solidified on the steel sheet/strip passing from the melt pool and the stripping device before reaching a first deflection roller, for example in the cooling tower of the coating system, so that the process is not adversely affected. The hot-dip coated steel strip is thus (further) cooled in the cooling tower.

A layer close to the surface in the coating means a depth from the surface (including the oxide layer) up to at least 0.020 µm and in particular up to a maximum of 0.20 µm.

The formation of the oxide layer has little or no influence on the distribution and/or arrangement of the eutectic phases in the coating.

The temperature of the stripping medium and/or in the stripping atmosphere can in particular be below 10 °C, preferably below 5 °C, preferably below 0 °C. The temperature can be limited to -50 °C, in particular to -40 °C, preferably to -30 °C.

In particular, in order to set a predetermined thickness of the coating, which in the solid state can be between 2 µm and 60 µm, the melt that is still in the liquid state applied to the steel sheet is stripped off, in that after leaving the melt pool, the steel sheet coated with liquid melt passes through a stripping device is passed through, which has means, for example nozzles, in particular slot nozzles, which act on both sides of the steel sheet with a gaseous stripping medium for stripping off the liquid melt. In the area of impact or action of the gaseous stripping medium, a stripping environment is formed, which extends upwards and downwards in the direction of movement of the steel sheet and, depending on the intensity of the stripping (volume, speed, pressure, etc.), thus (passively) around the impact area of the gaseous stripping medium extends to the steel sheet coated with a molten coating. In a first approximation, this passive stripping environment can be described as a cuboid volume element. The stripping can also take place in a so-called enclosure, so that the stripping environment can essentially be (actively) predetermined by the enclosure. The stripping environment can therefore be passive or active, with the active version being adjustable in a more targeted manner, for example.

Suitable gaseous stripping mediums are (all) gases that are conventionally used in the stripping process, such as nitrogen, air, nitrogen-air mixture, etc., and can be cooled down to the desired temperature without changing their aggregate state and/or have a detrimental effect on the stripping process. In order to cool the gas down to the desired temperature, the gas can be treated accordingly, for example in a heat exchanger or through and/or in another device or process, before stripping and/or adjusting the temperature in the stripping environment, which occurs during use an enclosure would virtually correspond to flooding the enclosure. Either the gas can be provided at the appropriate temperature or it can be cooled down to the desired temperature using suitable and common devices and methods. Air, especially warm air, with any humidity is, for example, via an evaporator, e.g. B. a pipeline package with aluminum fins, guided and cooled, as a result of which the water vapor contained in the air condenses into water. The thus cooled or cold air (<15 ° C) can be used according to the invention.

The purpose of stripping is to return excess melt on the steel sheet to the melt pool and to set a predetermined thickness of the coating (in the solid state). After setting the specified thickness and thus after stripping, the melt that is still in the liquid state on the steel sheet is then converted into a solidified state by (further) cooling. Stripping devices and methods for stripping liquid melt on hot-dip coated steel sheets as well as supplying the gaseous stripping media for stripping and thus setting predetermined thicknesses of the coatings are state of the art. The use of an enclosure surrounding the stripping device is also state of the art.

Steel sheets with a zinc-based coating have very good cathodic corrosion protection, which has been used in automobile construction for years. If improved corrosion protection is provided, the coating additionally has magnesium with a content of at least 0.5% by weight, in particular at least 0.8% by weight, preferably at least 1.0% by weight. In addition to magnesium, aluminum is present in a content of at least 0.5% by weight, in particular at least 0.8% by weight, preferably at least 1.0% by weight. The zinc-based coating particularly preferably has aluminum and magnesium each with at least 1.0% by weight in order to be able to provide an improved cathodic protection effect. Depending on the requirements, the contents of aluminum and magnesium can in particular be a maximum of 3.5% by weight, each preferably a maximum of 3.0% by weight, each preferably a maximum of 2.7% by weight and particularly preferably in each case be limited to a maximum of 2.5% by weight. The aluminum with a content greater than 4.0% by weight in the coating can lead to a deterioration in desired processing properties, such as thermal joining. A magnesium content greater than 4.0% by weight in the coating and therefore also in the melt does not lead to improved corrosion protection and can lead to increased slag formation in the coating process. Furthermore, an increased use of aluminum and especially magnesium would significantly lower the solidus temperature of the eutectic, which could have a detrimental effect on the process control in the hot-dip coating system after stripping.

Elements such as bismuth, zirconium, nickel, chromium, lead, titanium, manganese, silicon, calcium, tin, lanthanum, cerium and iron can be present as impurities in the melt pool or in the coating in individual or cumulative amounts of up to 0.4% by weight be.

Sheet steel (substrate) is a flat steel product in strip form or sheet/plate form. It has a longitudinal extent (length), a transverse extent (width) and a height extent (thickness). The steel sheet can be a hot strip (hot-rolled steel strip) or cold strip (cold-rolled steel strip), or can be made from a hot strip or a cold strip. The flat steel product is preferably a cold strip.

The thickness of the steel sheet is, for example, 0.5 to 4.0 mm, in particular 0.6 to 3.0 mm, preferably 0.7 to 2.5 mm.

According to one embodiment of the method according to the invention, the zinc-based coating has a thickness between 2 and 60 μm, in particular between 4 and 58 μm, preferably between 5 and 55 μm. The thickness of the ZM coating can therefore be between at least 4 µm, preferably at least 5 µm and a maximum of 58 µm, preferably between 5 and a maximum of 55 µm, independently of each other on each side. This corresponds to the specified thickness, which can be specifically adjusted when stripping off the still liquid melt before solidification.

According to one embodiment, the hot-dip coated steel sheet is tempered. Through tempering, a surface structure is impressed into the hot-dip coated steel sheet, which can be, for example, a deterministic surface structure. Deterministic surface structure means, in particular, regularly recurring surface structures that have a defined shape and/or configuration or dimensioning. In particular, this also includes surface structures with a (quasi-) stochastic appearance, which are composed of stochastic form elements with a recurring structure. Alternatively, introducing a stochastic surface structure is also conceivable. In a further embodiment, the hot-dip coated steel sheet can be straightened and/or stretch-straightened. In a further embodiment, the hot-dip coated steel sheet is straightened and/or stretch-straightened after tempering.

According to one embodiment, the hot-dip coated steel sheet can be wetted with an aqueous cleaning solution. An acidic or alkaline solution can be used as an aqueous cleaning solution. The surface of the hot-dip coated steel sheet can be for a time of 1 to 60 s, in particular between 2 and 50 s, preferably between 3 and 40 s, preferably between 3 and 30 s, and at a temperature of 15 to 80 ° C, in particular from 20 to 80 ° C, preferably from 30 to 80 ° C, preferably from 40 to 80 ° C with an aqueous cleaning solution. The wetting can be ended with an aqueous cleaning solution by rinsing with water and/or an aqueous solution.

According to one embodiment, the hot-dip coated steel sheet can be conditioned with an aqueous solution of an inorganic acid. The aqueous solution of an inorganic acid has a pH value of less than 7, in particular less than 6, preferably less than 5, preferably less than 4. The pH value can be at least 0.5, in particular at least 1.0, preferably at least 1.5. An inorganic acid is selected from the group containing or consisting of: H ₂ SO ₄ , HCl, HNO ₃ , H ₃ PO ₄ , H ₂ SO ₃ , HNO ₂ , HF, or a mixture of 2 or more of these acids as an aqueous solution used. The determination of the pH value is known.

The conditioning of the surface of the hot-dip coated steel sheet is to be designed three-dimensionally in the sense of the present invention. Either defined areas of the surface or the surface are completely wetted with an aqueous solution of an inorganic acid. Although two-dimensional areas are wetted, the wetting acts in layers of the coating close to the surface, i.e. in depth and thus in the third dimension. Due to the wetting with an inorganic acid, deeper layers of the coating (including the oxide layer) are exposed, with the superficial removal to a depth of at least 50 nm, in particular at least 0.070 µm, 0.10 µm, 0.125 µm, 0.150 µm, 0 .20 µm, 0.250 µm, 0.30 µm, up to a maximum of 2 µm, in particular up to a maximum of 1.8 µm, 1.75 µm, 1.7 µm, preferably up to a maximum of 1.6 µm, 1.25 µm , preferably up to a maximum of 1 µm, with respect to the surface, i.e. in particular the phase boundary/atmosphere of an original, unconditioned coating.

The surface of the hot-dip coated steel sheet can be wetted with the aqueous solution of an inorganic acid for a time of 0.1 to 5 s and at a temperature of 10 ° C to 90 ° C. The coating is preferably applied for a time of at least 0.1 s, in particular at least 0.2 s, preferably at least 0.3 s, 0.4 s, preferably at least 0.5 s, and a maximum of 5 s, in particular a maximum of 4 s wetted with an aqueous solution of an inorganic acid for a maximum of 3 s, 2 s, 1.8 s, preferably a maximum of 1.5 s, 1.2 s, 1.0 s. The coating is wetted with an aqueous solution of an inorganic acid at a temperature of 10 °C to 90 °C, in particular 20 °C to 70 °C, preferably 20 °C to 50 °C, preferably 20 °C to 40 °C , particularly preferably 20 ° C to 30 ° C.

The wetting can be stopped by rinsing with water and/or an aqueous solution. For this purpose, the wetting with an aqueous solution of an inorganic acid is interrupted by rinsing with water and/or an alcohol, for example selected from the group containing or consisting of methanol, ethanol, propanol, isopropanol, ethanol, in particular isopropanol, or an aqueous solution. In an alternative, rinsing takes place in 2 steps, in a first step with water; in a second sub-step with an alcohol or an aqueous solution of an alcohol as stated above. In another alternative, rinsing is carried out with water and an alcohol in one step, preferably as a mixture of water with one of the alcohols specified above. The rinsing is preferably carried out continuously, and in particular a process selected from the group or consisting of spraying, spraying, dipping and application (coil coating process) can be used. After wetting, drying is preferably carried out by rinsing, with the “rinsed” coating preferably being dried by increasing the temperature (up to a maximum of 100 ° C) or by using a fan.

In an alternative, the “rinsed” coating is air-dried, for example without any additional aids.

According to one embodiment, the hot-dip coated steel sheet can be wetted with an aqueous activation solution. The one aqueous activation solution can contain or consist of: 0.8 to 1.5 g / l of a titanium salt, which in particular from the group titanium dioxide, potassium titanium fluoride, dipotassium hexafluorotitanate, titanyl sulfate, titanium tetrachloride, titanium tetrafluoride, titanium trichloride, titanium hydroxide, titanium nitrite, titanium nitrate, potassium titanium oxide oxalate, Titanium carbide is selected, residual water and unavoidable impurities.

Alternatively or additionally, an aqueous activation solution can contain or consist of: at least one compound from the group oxalic acid, nickel phosphate, manganese phosphate, calcium phosphate, iron phosphate, aluminum phosphate, cobalt (II, III) phosphate, copper, copper sulfate, copper nitrate, copper chloride, copper carbonate, copper oxide, Silver, cobalt, nickel, Jernstedt salt, lead acetate, tin (tertra)chloride, arsenic oxide, zirconium chloride, zirconium sulfate, zirconium, iron, lithium, Zn ₃ (PO ₄ ) ₂ , Zn ₂ Fe(PO ₄ ) ₂ , Zn ₂ Ni(PO ₄ ) ₂ , Zn ₂ Mn(PO ₄ ) ₂ , Zn ₂ Ca(PO ₄ ) ₂ .

The surface of the hot-dip coated steel sheet can be treated for a time of 1 to 60 s, in particular between 2 and 50 s, preferably between 3 and 40 s, preferably between 3 and 30 s, and at a temperature of 15 to 80 ° C, in particular from 20 to 80 ° C, preferably from 30 to 80 ° C, preferably from 40 to 80 ° C, with an aqueous activation solution.

Alternatively, activation can be dispensed with, whereby a step in the overall process can be saved and thus, according to a preferred embodiment, the surface of the hot-dip coated steel sheet is not wetted with an aqueous activation solution.

According to a preferred embodiment, the hot-dip coated steel sheet can be wetted with an aqueous silane-based solution. The aqueous silane-based solution may contain or consist of one or two or more compounds selected from the group (3,4-epoxyalkyl)trialkoxysilane, (3,4-epoxycycloalkyl)alkyltrialkoxysilane, 3-acryloxyalkyltrialkoxysilane, 3-glycidoxyalkyltrialkoxysilane, 3 -Methacryloxyalkyltrialkoxysilane, 3-(tri-alkoxysilyl)alkylsuccinic silane, 4-amino-dialkylalkyltrialkoxysilane, 4-amino-dialkylalkylalkyl-dialkoxysilane, aminoalkylaminoalkyltrialkoxysilane, aminoalkylaminoalkylalkyldialkoxysilane, amino-alkyltrialkoxysilane, bis-(trialkoxy silylalkyl)amine, bis-(trialkoxysilyl)ethane, gamma- Acryloxyalkyltrialkoxysilane, gamma-aminoalkyltrialkoxysilane, gamma-methacryloxyalkyl-trialkoxysilane, (gamma-trialkoxysilylalkyl)dialkylenetriamine, gamma-ureidoalkyltrialkoxysilane, N-2-aminoalkyl-3-aminoproplyltrialkoxysilane, N-(3-trialkoxysilylalkyl)alkylenediamine, N- Alkylaminoisoalkyltrialkoxysilane, N-(aminoalkyl )aminoalkylalkyldialkoxysilane, N-beta-(aminoalkyl)-gamma-aminoalkyltrialkoxysilane, N-(gamma-trialkoxysilylalkyl)dialkylentriamine, N-phenyl-aminoalkyl-trialkoxysilane, poly(aminoalkyl)alkyldialkoxysilane, tris(3-trialkoxysilyl)alkylisocyanurate, ureidoalk yltrialkoxysilane and vinylacetoxysilane, Residual water and unavoidable impurities. The surface of the hot-dip coated steel sheet can be for a time of 1 to 200 s, in particular between 2 and 150 s, preferably between 3 and 100 s, preferably between 3 and 40 s, and at a temperature of 15 to 40 ° C, in particular 20 up to 35 ° C, preferably from 25 to 30 ° C, with an aqueous solution based on silane.

• C bis 0,1 %, insbesondere zwischen 0,0002 % und 0,1 %,
• Mn bis 2,0 %, insbesondere zwischen 0,01 % und 2,0 %,
• Si bis 0,3 %, insbesondere zwischen 0,0002 % und 0,3 %,
• P bis 0,1 %, insbesondere bis 0,05 %,
• S bis 0,1 %, insbesondere bis 0,05 %,
• N bis 0,1 %, insbesondere bis 0,01 %,
• sowie optional eines oder mehrerer Legierungselemente aus der Gruppe (Al, Cr, Cu, Nb, Mo, Ti, V, Ni, B, Sn, Ca):
• Al bis 0,2 %, insbesondere zwischen 0,001 % und 0,1 %,
• Cr bis 1,0 %, insbesondere bis 0,8 %,
• Cu bis 0,2 %, insbesondere bis 0,18 %,
• Nb bis 0,1 %, insbesondere bis 0,05 %,
• Mo bis 0,2 %, insbesondere bis 0,1 %,
• Ti bis 0,2 %, insbesondere bis 0,15 %,
• V bis 0,2 %, insbesondere bis 0,1 %,
• Ni bis 0,2 %, insbesondere bis 0,18 %,
• B bis 0,005 %, insbesondere bis 0,004 %,
• Sn bis 0,1 %, insbesondere bis 0,05 %,
• Ca bis 0,1 %, insbesondere bis 0,01 %,
• Rest Fe und unvermeidbare Verunreinigungen.

According to one embodiment, the steel sheet, i.e. the substrate, consists of a steel material with the following chemical composition in% by weight:

• C up to 0.1%, in particular between 0.0002% and 0.1%,
• Mn up to 2.0%, in particular between 0.01% and 2.0%,
• Si up to 0.3%, in particular between 0.0002% and 0.3%,
• P up to 0.1%, in particular up to 0.05%,
• S up to 0.1%, in particular up to 0.05%,
• N up to 0.1%, in particular up to 0.01%,
• and optionally one or more alloying elements from the group (Al, Cr, Cu, Nb, Mo, Ti, V, Ni, B, Sn, Ca):
• Al up to 0.2%, in particular between 0.001% and 0.1%,
• Cr up to 1.0%, especially up to 0.8%,
• Cu up to 0.2%, in particular up to 0.18%,
• Nb up to 0.1%, in particular up to 0.05%,
• Mo up to 0.2%, especially up to 0.1%,
• Ti up to 0.2%, in particular up to 0.15%,
• V up to 0.2%, in particular up to 0.1%,
• Ni up to 0.2%, especially up to 0.18%,
• B up to 0.005%, in particular up to 0.004%,
• Sn up to 0.1%, in particular up to 0.05%,
• Approximately up to 0.1%, in particular up to 0.01%,
• Rest Fe and unavoidable impurities.

According to a second teaching, the invention relates to a hot-dip coated steel sheet with a zinc-based coating which has aluminum between 0.5 and 4.0% by weight, magnesium between 0.5 and 4.0% by weight and the balance zinc and unavoidable impurities , wherein the coating contains zinc grains, magnesium-rich and/or aluminum-rich phases and eutectic phases, and a magnesium- and/or aluminum- and/or zinc-rich oxide layer is formed on the coating. According to the invention, the eutectic phases are in the layer near the surface and/or on the surface of the coating and thus also above the primary zinc grains within the coating (i.e. below the oxide layer on the surface of the coating) in an area proportion of at least 65%, in particular at least 70% , 75% or 80%, preferably at least 85% or 90%, preferably at least 95%, 96%, 97%, 98%, 99% or more, up to 100% present, determined based on an SEM image viewed in cross section, where Starting from the surface of the oxide layer, a measuring depth of 1 µm and a measuring length of 80 µm, a rectangular spanned measuring surface is placed in the holder and the surface area of the eutectic phases is determined in relation to the spanned measuring surface.

SEM images are common and are part of the state of the art. The recording of surface areas in a defined measuring area, here 80 µm × 1 µm, is also part of the process

State of the art and can be achieved in particular using image software, for example ImageAccess, by creating lines within the measuring area and thus creating a grid so that the individual grid elements show a eutectic phase or not. The larger and finer the grid chosen, the more precise the determination. It is decided that if the eutectic phase in a grid element occupies more than 50% of the grid element area, the grid element receives a 1, if it is less then a 0. The ratio of all the summed up grid elements with 1 to all existing grid elements (sum of the grid elements 0 and 1) x 100 therefore gives the surface area of the eutectic phases in the measuring area in %.

1. 1.) das Magnesium in den intermetallischen Zink-Magnesium-Phasen opfert sich aufgrund seiner im Vergleich zum Zink unedleren Eigenschaften,
2. 2.) durch den erhöhten Flächenanteil der intermetallischen Zink-Magnesium-Phasen bildet sich eine Korrosionsbarriere, welche die fortschreitende Korrosion verlangsamt.

The improved or positive corrosion behavior of the coating according to the invention can be attributed to two phenomena:

1. 1.) the magnesium in the intermetallic zinc-magnesium phases is sacrificed due to its less noble properties compared to zinc,
2. 2.) Due to the increased surface area of the intermetallic zinc-magnesium phases, a corrosion barrier is formed, which slows down the progressive corrosion.

The measurement of the oxide layer thickness can be carried out, for example, by means of X-ray photoelectron spectroscopy through a depth profile measurement, the removal rate underlying the calculation of the oxide layer thickness corresponding, for example, to that of silicon dioxide on a silicon wafer.

The hot-dip coated steel sheet according to the invention as described above, preferably produced using the method according to the invention, has nanostructures made of zinc phases, preferably of the secondary zinc grains as part of the eutectic and the further phases of the eutectic, in particular the different mixed crystals on the surface.

The secondary zinc grains, which are arranged close to the surface in the eutectic, have an average diameter of a maximum of 1 μm, preferably a maximum of 800 nm, 700 nm or 600 nm, particularly preferably a maximum of 500 nm, 400 nm or 300 nm, in particular a maximum of 250 nm and at least 1 nm , preferably at least 10 nm, 20 nm or 30 nm, particularly preferably at least 50 nm, 60 nm or 75 nm, in particular at most 100 nm.

A nanostructure is arranged on the surface of the ZM coating, ie the ZM coating has a fissured surface, which is covered by the oxide layer and which the Nanostructure is essentially retained, since the oxide layer essentially follows the course of the nanostructure. Due to the high oxygen affinity of the magnesium in the ZM coating, a magnesium-rich oxide layer inevitably forms on the ZM coating, which can also contain aluminum-rich oxides. The oxide layer formed on the ZM coating can be between 5 and 50 nm or more. Due to solidification, the other phases of the eutectic, in particular the mixed crystal phases of the eutectic, are lower than the zinc phases, i.e. the secondary zinc grains. The nanostructure thus serves as an optimal starting point for anchoring at least one layer applied to the oxide layer.

A future trend that could emerge is that the use of phosphate-free, nanoscale pretreatments will continue to increase and displace the previously common phosphating process in the post-treatment of hot-dip coated coatings. Corresponding nanoscale pretreatments usually contain zirconium and/or organic silicon compounds and can be applied via spraying, dipping or coil coating processes. The target layer thicknesses are between 5 to approx. 100 nm and are therefore smaller than zinc phosphate crystals in the range between 0.5 to 10 µm.

Phosphating is a conversion process, i.e. the zinc surface is pickled and the crystals precipitate on the roughened surface. When applying the nanoscale pretreatments, there is no recognizable conversion chemistry. Because of the relatively thin target layer thickness, it is even more important that the pretreatment can be applied over the entire area and remains on the surface accordingly. This means that, on the one hand, the wettability and, on the other hand, the possibility of (further) post-treatment to adhere to the surface are given much greater importance than in the usual phosphating process.

A nanostructure on the surface of the coating can preferably be produced when the method described above is used. This increases the temperature difference between the acting medium and / or the acting environment and the still molten coating, so that a rapid in-situ "shock" cooling causes the formation or emergence of the eutectic phases in the area near the surface and / or on the Surface of the coating with the nanostructure is favored.

In a (standard) hot-dip coating system, the molten coating must be completely applied to the steel sheet/plate passing through the melt pool and the stripping device. band must be solidified before reaching a first deflection roller, for example in the cooling tower of the coating system, so that the process is not adversely affected. The hot-dip coated steel sheet/strip is thus (further) cooled in the cooling tower.

The oxide layer formation has little or no influence on the distribution and/or arrangement of the nanostructure in the coating.

The temperature of the stripping medium and/or in the stripping atmosphere can in particular be below 10 °C, preferably below 5 °C, preferably below 0 °C. The temperature can be limited to -50 °C, in particular to -40 °C, preferably to -30 °C. Alternatively or cumulatively, the nanostructure can also be influenced by alloying aluminum in the melt or in the coating, whereby the maximum content must be limited to 4.0% by weight.

A further subject of the invention is a hot-dip coated steel sheet, as described above, preferably produced using the method according to the invention, which has the nanostructure described above with a native oxide layer arranged thereon, which essentially follows the course of the nanostructure and thereon a layer containing or consisting of zirconium compounds and/or organic silicon compounds.

The layer containing or consisting of zirconium compounds and/or organic silicon compounds is bound to the metallic coating by chemisorption, i.e. H. through chemical bonding. In the broadest sense, the chemical bond is an ionic bond, covalent bond, coordination bond or weak bond via electro-static attraction or van der Waals forces.

In one embodiment, the at least one layer has an Si content of at least 1.0 mg/m2, in particular at least 2.5 mg/m2, preferably at least 5.0 mg/m2, preferably at least 7.5 mg/m2 and a maximum of 100.0 mg/m2 or 75.0 mg/m2, in particular a maximum of 50.0 mg/m2 or 40.0 mg/m2, preferably a maximum of 30.0 mg/m2 or 20.0 mg/m2 , preferably a maximum of 15.0 mg/m2 or 12.5 mg/m2. A quantitative determination of the applied layer weight follows, for example, using X-ray fluorescence analysis (XRF) or GDOES (Glow Discharge Optical Emission Spectroscopy). The expression that the layer has a layer weight with a layer of a certain element in a specified mass per unit area means that the layer has the contains the corresponding element (regardless of the form, i.e. elementary, atomic, ionic or oxidic) in the specified mass per unit area. In the event that the Si concentration of the steel sheet, i.e. the steel substrate, should interfere with the Si determination in the layer, i.e. could possibly lead to incorrect results, the expert carries out reference or difference measurements at points on the steel sheet where no layer is present or has been removed for measurement purposes. The information concerns the occurrence of the element Si (silicon), regardless of the form in which it is present, so it does not matter whether this element is present as neutral atoms, as ions or in compounds such as organic compounds, such as alcohols, Esters, polymers or complexes, oxides, salts, hydroxides or the like are present.

In one embodiment, this contains or consists of at least one layer of organic silicon compounds, preferably one or more compounds selected from the group comprising or consisting of: silanes, silanols, siloxanes, alkoxysilanes, derivatives of silanes, siloxanes and/or alkoxysilanes as well as polymers and derivatives thereof. Preferred derivatives are one or more compounds selected from the group comprising or consisting of: silanes, siloxanes, alkoxysilanes with functional groups such as -OR with R as H or alkyl, preferably C1 to C7, vinyl, phenyl, benzyl; -NR2 with R as H or alkyl, preferably C1 to C7, vinyl, phenyl, benzyl; Condensation products of hydrolyzed alkoxysilanes with elimination of water, i.e. silanols or alkoxysilanes with hydroxyl groups; at least one silane, silanol and/or siloxane with at least one alkoxy group, with at least one amido group, with at least one amino group, with at least one urea group, as well as condensation products, copolymers and polymers, from at least 2 of the above-mentioned compounds.

In an alternative or in addition, the above-mentioned silanes, silanols, siloxanes, alkoxysilanes and derivatives thereof are selected from the group comprising or consisting of: Bistri(m)ethoxysilylalkane, for example bis-triethoxysilylethanes, methyltrimethoxysilane, tetraethoxysilane, aminopropyltriethoxysilane, 4-amino-dialkylalkyldialkoxysilane , 2-aminoethyl-3-amino-propyltrimethoxysilane, 2-aminoethyl-3-amino-propyltriethoxysilane, gamma-aminoalkyltrialkoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-alkylaminoisoalkyltrialkoxysilane, poly(aminoalkyl)alkyldialkoxysilane, aminoalkylaminoalkyltrialkoxysil an, N-(gamma- trialkoxysilylalkyl)dialkylentriamine; Aminoalkylaminoalkyldialkoxysilane, aminoalkyltrialkoxysilane, bis-aminosilane, bis-diaminosilane, bis-(trialkoxysilylalkyl)amine, such as bis(trimethoxysilylpropyl)amine and/or bis(triethoxysilylpropyl)amine, bis-(trialkoxysilyl)ethane, N-(aminoalkyl)aminoalkyldialkoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, ureidopropyltrimethoxysilane, gamma-uridoalkyltrialkoxysilane, bis-trimethoxysilylpropylurea; 3-[2-(2-Aminoalkylamino)alkylamino]alkyltrialkoxysilane, 3-(2-Aminoethylamino)propyldimethoxymethylsilane, N-(3-(Trialkoxysilyl)alkyl)alkylenediamine, N-beta-(aminoalkyl)-gamma-aminoalkyltrialkoxysilane, 4-Amino -dialkylalkyltrialkoxysilane, 3-(trimethoxysilyl)propyl methacrylate, gamma-(trialkoxysilylalkyl) dialkylenetriamine, 3-glycidoxypropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N,N- Bis[3-(trimethoxysilyl)propyl]ethylenediamine and/or N-2-aminoalkyl-3-aminopropylltrialkoxysilane with alkyl preferably selected from the group comprising or consisting of: methyl, ethyl or/and propyl, such as N-2(aminoethyl )-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, combinations of at least two of the above-mentioned compounds and/or polymers thereof.

For the purposes of the invention, siloxane is used to describe compounds of the formula: R3Si-[O-SiR2]n-O-SiR3, with R as H or alkyl, preferably C1 to C7 and n=0 to 20. Polymers thereof with R=alkyl are called silicones designated. Alkoxysilanes have the general formula (RO)4-Si, R as alkyl, preferably C1 to C7.

In a cumulative or alternative embodiment, the at least one layer has a Zr content of at least 1.0 mg/m2, in particular at least 2.5 mg/m2, preferably at least 5.0 mg/m2, preferably at least 7.5 mg/m2 and a maximum of 100.0 mg/m2 or 75.0 mg/m2, in particular a maximum of 50.0 mg/m2 or 40.0 mg/m2, preferably a maximum of 30.0 mg/m2 or 20.0 mg/m2, preferably a maximum of 15.0 mg/m2 or 12.5 mg/m2. A quantitative determination of the applied layer weight is carried out, for example, via X-ray fluorescence analysis (XRF) or GDOES (Glow Discharge Optical Emission Spectroscopy) analogous to Si as described above.

In a cumulative or alternative embodiment, this contains or consists of at least one layer of organic zirconium compounds, one or more compounds selected from the group ZrO2 and zirconate.

• C: bis 0,20 %,
• Mn: bis 2,0 %,
• Si: bis 0,30 %,
• P: bis 0,10 %,
• S: bis 0,10 %,
• N: bis 0,10 %,
• sowie optional eines oder mehrerer Legierungselemente aus der Gruppe (Al, Cr, Cu, Nb, Mo,
• Ti, V, Ni, B, Sn, Ca):
  • Al: bis 0,20 %,
  • Cr: bis 1,0 %,
  • Cu: bis 0,20 %,
  • Nb: bis 0,10 %,
  • Mo: bis 0,20 %,
  • Ti: bis 0,20 %,
  • V: bis 0,20 %,
  • Ni: bis 0,20 %,
  • B: bis 0,005 %,
  • Sn: bis 0,10 %,
  • Ca: bis 0,10 %,
  • Rest Fe und unvermeidbare Verunreinigungen.

One embodiment relates to a hot-dip coated steel sheet, as described above, preferably produced using the method according to the invention, wherein the steel substrate consists of a steel material with the following chemical composition in% by weight:

• C: up to 0.20%,
• Mn: up to 2.0%,
• Si: up to 0.30%,
• P: up to 0.10%,
• S: up to 0.10%,
• N: up to 0.10%,
• and optionally one or more alloying elements from the group (Al, Cr, Cu, Nb, Mo,
• Ti, V, Ni, B, Sn, Ca):
  • Al: up to 0.20%,
  • Cr: up to 1.0%,
  • Cu: up to 0.20%,
  • Nb: up to 0.10%,
  • Mon: up to 0.20%,
  • Ti: up to 0.20%,
  • V: up to 0.20%,
  • Ni: up to 0.20%,
  • B: up to 0.005%,
  • Sn: up to 0.10%,
  • Approximately: up to 0.10%,
  • Rest Fe and unavoidable impurities.

One embodiment relates to a hot-dip coated steel sheet, as described above, where the steel sheet is tempered.

One embodiment relates to a hot-dip coated steel sheet, as described above, with a temporary corrosion protection containing or consisting of a corrosion protection oil being applied to one layer.

Specific embodiments of the invention are explained in more detail below.

Figure 1 shows a scanning electron microscope (SEM for short) (partial) image of a sample recorded in cross section, which has been separated from a hot-dip coated steel sheet (10) produced according to the invention. The SEM image was taken in a device from Tescan Vega. The corresponding resolution and parameters used are in the Figure 1 stated. With (1) is a steel sheet (substrate) and with (2) is on the steel sheet (1) Zn-Al-Mg coating applied by hot-dip coating including the oxide layer shown. The primary zinc grains (Zn) can be clearly seen in the coating (2) and the eutectic phases, which essentially comprise a combination of Zn and Mg, are shown with (E). Figure 2 shows an enlargement of the in Figure 1 marked rectangular area. Figure 3a is a schematic (not true to scale) reproduction of the facts as in Figure 1 and Figure 2 shown. In addition, the oxide layer (3) is shown with the nanostructure (4) arranged underneath. Figure 3b is a schematic (not to scale) enlargement of the area marked with the dash-dot line Figure 3a . In Figure 3b The nanostructure (4) can be seen with the fissured surface of the ZM coating, which is formed from the different height during the solidification of the secondary zinc grains (Zn-sec) and the further phases of the eutectic (E'). The nanostructure is covered by the oxide layer (3), the shape or the course of the surface of the nanostructure (4) being essentially maintained, since the oxide layer (3) essentially follows the course of the nanostructure (4). Additionally is in Figure 3b the layer (5) of the nanoscale pretreatments containing zirconium and/or organic silicon compounds is shown.

Using a hot-dipping simulator, hot-dipping processes used on an industrial scale can be simulated on a laboratory scale. In the hot-dipping simulator lwatani HDPS V, grade DC04 with a thickness of 0.7 mm was used as steel sheet, with 18 tests with different parameters, as shown in Table 1, being carried out. Zn-Al-Mg coatings with different aluminum [in wt.%] and magnesium contents [in wt.%] were examined. The stripping was carried out in an air atmosphere and a nitrogen-air mixture with a volume ratio of 30:70 was used as the gaseous stripping gas for stripping at different temperatures T [in °C]. The thickness of the coating in the solidified state was set at 12 μm. Samples were cut off from 18 experiments and, using SEM images, the eutectic phases (E), see Table 1, were shown in dashed lines in the defined measuring area (M) mentioned above, using a line grid in the ImageAccess image processing system with individual grid elements Dimension 10 nm x 10 nm can be determined. The embodiments (erf) according to the invention are marked accordingly in Table 1. Using X-ray photoelectron spectroscopy, thicknesses between 0.025 and 0.037 µm were measured on all samples. Before testing, the samples were treated as follows:
- Clean by immersing in an aqueous cleaning solution, Ridoline 124 N with a batch concentration of 12ml/l, remaining water and unavoidable impurities, pH value = 1; and a temperature of 55 °C, wetting time 5 s;
- Rinse with demineralised water by immersion at a temperature of 20 °C, wetting time 5 s. Table 1 Ongoing No. Zn [%] Mg [%] Al [%] T[°C] E [%] req 1 97.77 1.06 1.17 40 30 n 2 97.76 1.05 1.19 25 45 n 3 97.6 1 1.4 15 50 n 4 97.76 1.07 1.16 10 65 j 5 97.61 1.06 1.33 5 85 j 6 97.77 1.11 1.12 0 90 j 7 97.65 1.15 1.2 5 85 j 8th 97.29 1.31 1.4 30 50 n 9 97.07 1.41 1.52 -10 95 j 10 96.96 1.61 1.43 -15 100 j 11 96.58 1.78 1.64 -5 90 j 12 96.54 1.89 1.57 0 85 j 13 96.15 2.01 1.84 5 85 j 14 96.28 2.1 1.62 25 45 n 15 95.9 2.26 1.84 20 50 n 16 95.87 2.24 1.89 5 90 j 17 95.65 2.38 1.97 -10 95 j 18 95.57 2.42 2.01 30 55 n

• Aktivieren durch Tauchen in einer wässrigen Aktivierungslösung, Gardolene ZL 6 mit einer Ansatzkonzentration 6 g/l, Rest Wasser und unvermeidbare Verunreinigungen, pH-Wert=8,2; und einer Temperatur von 20 °C, Benetzungsdauer 15 s;
• Phosphatieren durch Eintauchen in einer wässrigen Phosphatierungslösung, mit 2,5 g/l Gardobond-Additive H 7200, mit 4,8 g/l Gardobond 24 T, mit 6,3 g/l Gardobond-Additive H 7256 und mit 17 g/l Gardobond-Additive H 7101, Rest Wasser und unvermeidbare Verunreinigungen, pH-Wert=2,5; und einer Temperatur von 55 °C, Benetzungsdauer 150 s, wobei die angesetzte Phosphatierungslösung einer Konzentration von etwa 25 Gesamtsäure-Punkten, 1,2 Freie-Säure-Punkten, 5 Beschleuniger-Punkten und einem Zink-Gehalt von 1,3 g/l entsprach;
• Spülen mit vollentsalztem Wasser durch Eintauchen und einer Temperatur von 20 °C, Benetzungsdauer 5 s; - Trocknen.

The samples were cleaned and rinsed again for further examination as described above, and for samples 1 to 9 the following steps were carried out:

• Activate by immersing in an aqueous activation solution, Gardolene ZL 6 with a batch concentration of 6 g/l, remainder water and unavoidable impurities, pH value = 8.2; and a temperature of 20 °C, wetting time 15 s;
• Phosphating by immersion in an aqueous phosphating solution, with 2.5 g/l Gardobond additives H 7200, with 4.8 g/l Gardobond 24 T, with 6.3 g/l Gardobond additives H 7256 and with 17 g/l Gardobond additives H 7101, remainder water and unavoidable impurities, pH value=2.5; and a temperature of 55 ° C, wetting time 150 s, the phosphating solution prepared having a concentration of approximately 25 total acid points, 1.2 free acid points, 5 accelerator points and a zinc content of 1.3 g/l corresponded;
• Rinse with deionized water by immersion and a temperature of 20 °C, wetting time 5 s; - Dry.

• Benetzen durch Eintauchen in einer wässrigen Lösung auf Silanbasis, wobei Oxsilan 9831 in einer Konzentration zugegeben wurde, dass sich in der wässrigen Lösung eine Leitfähigkeit in Höhe von 3 mS/cm einstellte, Rest Wasser und unvermeidbare Verunreinigungen, pH-Wert=4,1; und einer Temperatur von 25 °C, Benetzungsdauer 90 s;
• Spülen mit vollentsalztem Wasser durch Eintauchen und einer Temperatur von 20 °C, Benetzungsdauer 5 s; - Trocknen.

Samples 10 to 18 followed the steps:

• Wetting by immersion in a silane-based aqueous solution, where Oxsilan 9831 was added in a concentration such that a conductivity of 3 mS/cm was achieved in the aqueous solution, the remainder was water and unavoidable impurities, pH value = 4.1; and a temperature of 25 °C, wetting time 90 s;
• Rinse with deionized water by immersion and a temperature of 20 °C, wetting time 5 s; - Dry.

In samples 1 to 9, the oxide layer was essentially removed as well as some of the underlying eutectic phases, revealing a new surface chemistry.

In samples 10 to 18, the oxide layer was essentially retained, which benefited corrosion resistance and also, and as an alternative to phosphating, resulted in a new surface chemistry.

The corresponding (new) surfaces of samples 1 to 18 with a new surface chemistry were subjected to a wetting test. To determine the wettability or surface energy, a static contact angle measurement was carried out. The surface energy was measured using the contact angles of three different test liquids. The results (average of 3 contact angle measurements per test liquid) were determined to be an average of 65° for samples 1 to 9 and an average of 75° for samples 10 to 18. The higher the wettability, the better the bonding of other layers, such as lacquer layers.

Not investigated, but conceivably, the area where the steel sheet emerges from the melt pool up to the stripping device can also be provided with an enclosure and flooded with a gas, as described above, in a stripping environment with a temperature below 15 ° C can.

Claims (15)

A method for producing a hot-dip coated steel sheet, the method comprising the following steps: - providing a steel sheet, - Hot-dip coating of the steel sheet with a zinc-based coating, the steel sheet passing through a melt pool containing aluminum between 0.5 and 4.0% by weight, magnesium between 0.5 and 4.0% by weight, the balance zinc and unavoidable impurities includes, - removing the steel sheet coated with liquid melt from the melt bath and stripping off a part of the steel sheet still coated with liquid melt with a gaseous stripping medium in a stripping environment, the liquid melt remaining on the steel sheet completely solidifying after stripping and forming the coating on the steel sheet , characterized in that the stripping medium is supplied for stripping at a temperature below 15 °C and/or a temperature below 15 °C is set in the stripping environment. Method according to claim 1, wherein the stripping medium is supplied for stripping at a temperature below 0 °C and/or a temperature below 0 °C is set in the stripping environment. Method according to one of the preceding claims, wherein the melt pool has Al and Mg each with at least 0.8% by weight. Method according to one of the preceding claims, wherein the melt pool comprises Al and Mg each with at least 1.0% by weight. Method according to one of the preceding claims, wherein the stripping is carried out in such a way that a predetermined thickness of the coating in the solid state is set between 2 and 60 µm. Method according to one of the preceding claims, wherein the hot-dip coated steel sheet is tempered. Method according to one of the preceding claims, wherein the hot-dip coated steel sheet is wetted with an aqueous cleaning solution. Method according to one of the preceding claims, wherein the hot-dip coated steel sheet is conditioned with an aqueous solution of an inorganic acid. Method according to one of the preceding claims, wherein the hot-dip coated steel sheet is wetted with an aqueous activation solution. Method according to one of the preceding claims, wherein the hot-dip coated steel sheet is wetted with an aqueous silane-based solution. Hot-dip coated steel sheet with a zinc-based coating, which has aluminum between 0.5 and 4.0% by weight, magnesium between 0.5 and 4.0% by weight, the balance zinc and unavoidable impurities, the coating containing zinc grains, magnesium-rich and / or contains aluminum-rich phases and eutectic phases, and a magnesium and / or aluminum and / or zinc-rich oxide layer is formed on the coating, characterized in that the eutectic phases in the layer near the surface and / or on the surface of the coating and thus are also present above the zinc grains within the coating in an area proportion of at least 65% to 100%, determined using an SEM image viewed in cross section, with a measuring depth of 1 µm and a measuring length of 80 µm starting from the surface of the oxide layer spanned measuring surface is placed in the holder and the surface area of the eutectic phases is determined in relation to the spanned measuring surface. Hot-dip coated steel sheet according to claim 11, characterized in that it has a nanostructure of zinc phases, preferably of the secondary zinc grains as part of the eutectic and the further phases of the eutectic, in particular the different mixed crystals, on the surface. Hot-dip coated steel sheet according to claim 11 or 12, characterized in that a native oxide layer is arranged on the nanostructure, which essentially follows the course of the nanostructure. Hot-dip coated steel sheet according to one of claims 11 to 13, characterized in that a layer containing or consisting of zirconium compounds and / or organic silicon compounds is arranged on the oxide layer. Hot-dip coated steel sheet according to one of claims 11 to 14, characterized in that the layer containing or consisting of zirconium compounds and / or organic silicon compounds has a layer weight with a layer of at least 1.0 mg / m2 and a maximum of 100 mg / m2 Si and / or Zr having.

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