EP2851452B1 - Inorganic functional coating on hot-dip galvanised steel - Google Patents

Description

The present invention relates to a galvanized steel sheet having an inorganic functional layer and a method for producing the coated galvanized steel sheet. Furthermore, the invention relates to the use of the steel sheet for the production of motor vehicle components.

Electrolytically galvanized and hot-dip galvanized sheet steel has been established from the mid-1980s until today as an essential pillar of corrosion protection for high-quality car bodies. Zinc-protected surfaces today ensure such high corrosion resistance that the useful life of the entire vehicle is no longer decisively limited by corrosion.

Electrolytically galvanized steel has been used for years in the automotive body shop. The surface finish is applied before galvanizing ("temper rolling"). The softer zinc layer is subsequently uniformly deposited by electrolysis on the hard base metal. To improve the formability, the elo-galvanized strip can be phosphated. This so-called Vorphosphatierung acts as a solid lubricant, reduces friction and prevents welding of the zinc on the tool. For pre-phosphated sheet metal, mainly Prelube oils are used. Ribbons and sinkers are often washed with low viscosity Prelube oils. A relubrication with drawing oils is only exceptionally necessary. Another possibility for improving the formability is the coating with dry lubricant (Drylube, Hotmelt) instead of the Prelubeöle.

In recent years, the proportion of hot-dip galvanized sheets in the automotive industry has risen sharply. In hot dip galvanizing, the band can only be trained after galvanizing. The texture is thus embossed in contrast to the electrolytically galvanized strip in the soft zinc layer. Due to the process, the zinc immersion bath contains a certain amount of aluminum, which accumulates on the surface as aluminum oxide. Hot-dip galvanized sheets tend to deform during forming Material transfer of the soft zinc to the tool. Friction and wear increase. This effect is also called job wear or galling. Unlike elo-galvanized steel, drawing oils and hotmelts can not sufficiently reduce this phenomenon in hot-dip galvanized steel. A phosphating similar to the Vorphosphatierung when elo-galvanized steel is due to the process not applied economically to Feuerzinkblechen.

Since the zinc surfaces, which are very ductile compared to steel, lead to increased abrasion in pressing tools, which can easily lead to visually perceptible surface defects, initially one-sided galvanized sheet was used for visible parts, whereby the lacquered visible side itself was not galvanized. Continuous improvements in the process chain now make it possible to produce outer skin parts with a galvanized surface on both sides.

In their production as well as in difficult forming parts - in addition to lubrication with liquid or semi-solid media - anchored on the surface of the metallic workpiece or tool separating layers of advantage. In addition to the tribological effect, which is based at least on a sufficiently strong mechanical separation of the metal surfaces of the tool and workpiece, a comprehensive compatibility with the process chain in the body shell is sought.

Release layers or tribo layers applied to the surface of galvanized steel must be compatible with the raw building adhesives used for automotive use. Out WO 2005/071140 A1 For example, the use of an aqueous treating solution containing sulfate ions in a concentration of at least 0.01 mol / l is known to treat the surface of a galvanized steel sheet to reduce damage to the coating during forming and for temporarily improved corrosion protection.

ArcelorMittal has developed such a tribolayer for fire zinc sheets and launched it under the name "NIT". This layer is characterized by a very good friction reduction with good adhesive adhesion.

For the production-related rougher, often used in the outer skin, electrolytically galvanized sheet has been proven in addition to oiling a tri-cation tape phosphating. This is similar to the later applied in the Lackierlinie tri-cation phosphating.

Art-equivalent tri-cation tape phosphatizations on hot-dip galvanized sheet have so far not been able to establish themselves in the automotive industry as artlike, non-crystalline "no-rinse" phosphating, as z. B. offered by Salzgitter AG under the brand name μPhos®. It is an inorganic conversion layer with a thickness of about 300 nm as a forming aid for hot-dip galvanized sheet.

DE 102008016050 A1 describes a primer for forming a forming layer, metal substrates coated with this primer and the use of the primer and the coated substrates. The primers contain binders, additives, anticorrosive pigments, crosslinking agents and solvents. Branched polyester resins or other resins may be used as the binder, and anticorrosive pigments may be calcium modified silica, zinc phosphates, aluminum phosphates, aluminum triphosphates, silica-magnesium pigments and mixtures.

These layers offer a good reduction in friction, but in some cases have adhesive incompatibilities, so that the usability for the automotive body is limited.

WO 2004/050808 A1 discloses a lubricant coated sheet metal having improved forming properties. The coating lubricant is a corrosion protection oil, a so-called Prelube oil and / or a dry lubricant (Drylube, Dry Film Lubricant), wherein the metal sheet comprises a layer by applying a solution containing an organic phosphoric acid ester, on the Surface of the sheet is formed. For the preparation of the lubricant-coated metal sheet, a solution which is the organic Contains phosphoric acid ester, applied to the top and / or bottom of the sheet and then the lubricant to the thus coated sheet. The solution can be applied by dipping, spraying, brushing or knife coating. However, insufficient process compatibility in automotive engineering still limits the use.

Out EP 2 570 515 A2 discloses a chromate-free treatment method for aluminum substrates for forming a conversion layer using an aqueous alkaline treatment solution containing Li ions, phosphate, hydroxide ions and carbonate ions and having a pH greater than 10. The treatment solution is applied to the metal substrate to produce a wet film of any thickness, depending on the application requirements. Without performing a rinse step, the wet film is dried, wherein the exposure time varies based on the type and thickness of the desired conversion layer.

US Pat. No. 5,660,707 describes a method of improving the formability and weldability of a galvanized steel sheet by producing a zinc oxide layer on the surface of the steel sheet as a forming auxiliary layer. For this purpose, an aqueous, alkaline treatment solution with hydrogen peroxide is used as the oxidizing agent. The treatment solution is buffered with NaOH and NaHCO ₃ to a pH in a range of 7 to 11 and applied to the galvanized steel sheet to form a wet film which is allowed to act for a predetermined period of time at a predetermined temperature and then rinsed to remove a wet film Zinc oxide layer with at least 150 mg / m ² to obtain.

US Pat. No. 6,231,686 B1 describes a method of treating a galvanized steel sheet to improve formability. Here, a forming auxiliary layer is produced on the surface of the steel sheet, which comprises a conversion layer of zinc carbonates. The aqueous treatment solution used has 1 to 150 g / l of ammonium hydrogencarbonate or alkali metal hydrogencarbonate, resulting in a pH of the solution in a range of 6 to 9. The aqueous processing solution is applied to the galvanized steel sheet and a wet film is produced which is at a predetermined time for a predetermined period of time Temperature is allowed to act in dependence of the concentration of the solution. Thereafter, the wet film is rinsed off and the resulting conversion layer has a coating weight of 10 to 100 mg / m ² surface, which is determined by the contact time and the concentration of the solution.

Based on this prior art, the present invention based on the object to produce a conversion layer on the surface of a galvanized steel sheet in a simplified and accelerated work process without affecting subsequent process steps. In particular, the time-economic and in existing manufacturing processes, especially in automotive integrable production of a galvanized steel sheet with a functional layer is to be made possible, which is significantly improved in terms of formability compared to only oiled surfaces, especially at high contact pressures and high temperatures, and large-scale Apply economically and is safe in terms of environment, health and safety.

This object is achieved by a method having the features of independent claim 1.

Another object is to provide the galvanized steel sheet with functional layer, which is significantly improved in terms of formability compared to only oiled surfaces, especially at high contact pressures and high temperatures. In addition, the functional layer should be insoluble or compatible with subsequently sprayed on lubricating oil. The functional layer should also show a good adhesion of structural adhesive and suitable for body pretreatment (phosphating and phosphate-free process) and KTL-compatible.

This object is achieved by a coated steel sheet having the features of independent claim 8.

Claim 12 discloses the use of the coated galvanized steel sheet in automobile construction.

Further developments of the objects are described by the respective subclaims.

A method according to the invention for the time-economic production of a galvanized steel sheet having an inorganic functional layer on the surface forming a Umformhilfsschicht or part of a Umformhilfsschicht begins with the preparation of an aqueous, silane-free (silane-free) solution or suspension containing at least one carbonate Supplier or at least one carbonate supplier and at least one hydroxide supplier.

In the present case, "carbonate" or "hydroxide supplier" refers to salts which are at least partially soluble in aqueous medium and dissociate, so that the desired zinc salts are formed on the galvanized surface by chemical reaction in the aqueous treatment solution or suspension become. The carbonate supplier (s) are selected from ammonium bicarbonate, ammonium carbonate, alkali metal hydrogencarbonates, alkali metal carbonates, and alkali metal carboxylates, and the hydroxide source (s) are selected from alkali metal hydroxides, alkali metal oxides, alkali metal alcoholates, and magnesium hydroxide or magnesium oxide.

Thus, it is conceivable, depending on the nature of the carbonate supplier, that an additional hydroxide supplier can advantageously be dispensed with if the carbonate supplier goes into solution with the formation of hydroxide ions in an aqueous medium, as described, for example, in US Pat. B. with alkali metal bicarbonates and alkali metal carbonates is the case.

A concentration of the carbonate supplier (s) required in the solution or suspension to form the conversion layer is in a range from 1 to 5% by weight, preferably from 3 to 5% by weight.

The pH of the aqueous solution or suspension is in the range of 8 to 12. It has been found that a pH of (9 ± 0.5) leads to particularly suitable conversion layers. Depending on the type of carbonate or hydroxide suppliers selected, the pH of the treatment solution or suspension may already be in the range mentioned area; however, if desired or required, addition of sodium hydroxide and / or potassium hydroxide may be made to adjust the pH.

The aqueous solution or suspension is applied to at least one side of the galvanized steel sheet, and thus a wet film having a predetermined thickness is produced, which is adjusted in accordance with the concentration of the treating solution of 1 to 20 μm, so that a chemical reaction of the metallic coating with the at least partially dissolved in the aqueous medium and dissociated carbonate suppliers or hydroxide suppliers to form zinc salts. After the wet film has dried without a rinsing step being carried out, a conversion layer of zinc salts, which are at least partially carbonates, is then obtained as the inorganic functional layer. The layer weight of the dry substance after drying the wet film is determined by the thickness of the wet film and the concentration and is advantageously in a range of 25 to 200 mg / m ² surface, preferably from 40 to 90 mg / m ² and is thus the desired further processing suitable.

Thus, for example, for a surface to be treated containing only zinc and zinc oxide with a treatment solution containing as carbonate supplier sodium bicarbonate, a deposited dry matter of 40 to 90 mg / m ² surface is obtained, which converts to hydrozincite. Under these conditions, the coating weight of the conversion layer is in a range of 190 to 340 mg / m ² and thus has a favorable and suitable strength for the intended purpose.

With this no-rinse process, the hot-dip galvanized or elo-galvanized steel sheets with the functional layer can be economically produced with a small amount of time and equipment.

This treatment solution or suspension advantageously contains neither heavy metals nor organic compounds or solvents. The risks associated with the use of alkaline solutions are known and can be well managed; necessary protective measures against chemical burns are limited. Further this conversion layer is oil-resistant and only soluble in acids. The conversion layer shows good adhesion of raw building adhesives and is suitable for car body pretreatment and KTL-compatible.

Of course, any alkali element can generally be used as a cation of the carbonate and hydroxide suppliers, but mainly for cost and availability reasons, sodium and / or potassium will preferably be used. Particularly preferred as carbonate suppliers are sodium and / or potassium bicarbonate and / or carbonate and used as hydroxide suppliers sodium or potassium hydroxide. A treatment solution or suspension with these components achieves conversion layers with an optimum combination of friction behavior and bondability.

• Natrium- und/oder Kalium-Phosphat oder Natrium- und/oder Kalium- Di- und/oder Tri-Phosphate, oder
• Kalium-Hydrogencarbonat, oder
• Natrium- und/oder Kalium-Sulfat, oder
• Natrium- und/oder Kalium-Silikate, Natrium- und/oder Kalium-Metasilikate, oder eine Natrium-haltige SiO₂-Dispersion
• eine Zinn- oder Titan-Verbindung

aufweist. Für das Tracersystem kann eine Konzentration im Bereich von 1 bis 30 Gew.-%, bevorzugt 10 bis 20 Gew.-%, besonders bevorzugt 15 Gew.-%, bezogen auf den Gehalt an Carbonat- und Hydroxid-Lieferanten, gewählt werden.In order to be able to check the thickness of the conversion layer produced, in one embodiment of the method, a tracer system which can be detected in the X-ray fluorescence analysis can be added during the preparation of the treatment solution or suspension

• Sodium and / or potassium phosphate or sodium and / or potassium di- and / or tri-phosphates, or
• Potassium bicarbonate, or
• Sodium and / or potassium sulfate, or
• Sodium and / or potassium silicates, sodium and / or potassium metasilicates, or a sodium-containing SiO ₂ dispersion
• a tin or titanium compound

having. For the tracer system, a concentration in the range of 1 to 30 wt .-%, preferably 10 to 20 wt .-%, particularly preferably 15 wt .-%, based on the content of carbonate and hydroxide suppliers, are selected.

The application of the aqueous solution or suspension to the galvanized steel sheet can generally be done by spraying without squeezing or jetting and stripping with non-driven squeeze rolls. Preferably, however, the aqueous solution or suspension is applied by rolling continuously on a strip of galvanized steel sheet. For this purpose, a Rollcoater, usually per Coating side with two or three rollers (scoop roller, application roller and possibly regulating roller) works, whereby the band is deflected at the counter-pressure roller.

Surprisingly, it has been shown that the aqueous solution or suspension can be rolled up in a time-economical manner by means of two squeeze rolls, between which the hot-dip galvanized steel sheet or steel strip is guided, in a simple and thus preferred manner.

In this case, the aqueous solution or suspension is sprayed in excess onto the squeezing rollers arranged on both sides of the galvanized steel sheet and excess solution or suspension, which drips off the sheet or the rollers, is collected and guided into a feed tank. The squeeze rolls are pressurized to the surfaces of the galvanized steel sheet, thereby stripping the aqueous solution or suspension onto the surfaces of the galvanized steel sheet. The thickness of the wet film is set in a range of 1 to 20 μm by selecting the setting pressure, a hardness of rubberizing the squeezing rollers, a speed of the squeezing rollers and a speed of the steel sheet and thus a relative speed of the squeezing rollers to the steel sheet.

In a further method step, the application of a corrosion protection oil and / or a Prelubeöls or a dry lubricant (Hotmelt, Dry Film Lubricant, Drylube) carried on the conversion layer, so that a lubricating oil layer having a basis weight of 0.2 to 3.0 g / m ^{2 is} obtained.

An inventive hot-dip galvanized steel sheet has on the surface an inorganic functional layer which forms a forming auxiliary layer or is part of a forming auxiliary layer. The inorganic functional layer according to the invention is based on an alternative chemical basis. It is a conversion layer formed of zinc and zinc salts, at least part of which belongs to the carbonates. The conversion layer is obtained by applying a treatment medium to the galvanized sheet steel surface which is an aqueous, silicic acid-free solution or suspension which contains at least one carbonate supplier, but preferably at least one carbonate supplier and additionally at least one hydroxide supplier.

The zinc salts of the conversion layer may further include zinc hydroxides and zinc oxides; The conversion layer may thus preferably have a hydrozincite-like mineral structure which is formed from the dry substance deposited by the method according to the invention by application and drying of a wet film with a coating weight of 25 to 200 mg / m ² surface.

Advantageously, the conversion layer with a method according to the invention can be displayed time-economically.

If the layer weight of the dry substance which leads to the formation of the conversion layer is from 25 to 200 mg / m ² surface, preferably from 40 to 90 mg / m ² , a sufficiently good formability is ensured. In order to be able to detect the thickness of the conversion layer, a tracer system can be provided in the conversion layer, which can be detected by X-ray fluorescence analysis and is selected from potassium, phosphorus, silicon or even tin or titanium compounds.

In order to achieve optimum forming results, the Umformhilfsschicht the hot-dip galvanized steel sheet also has a lubricating oil layer, which is applied to the conversion layer, which in itself shows only limited anti-corrosion and lubricating effect. This lubricating oil layer has a basis weight of 0.2 to 3.0 g / m ² , typically 1.0 -1.5 g / m ² , and thus meets the current delivery instructions for oiled steel strip.

It has been shown that the conversion layer is compatible with subsequently sprayed on corrosion protection oil or Prelube oil or dry lubricants and their suitability for subsequent process steps such as adhesive bonding or removability in automotive shell construction does not affect. The application of corrosion protection or prelube oil or dry lubricant is for corrosion protection and lubrication necessary during forming. By combining the oil layer with the inorganic functional layer, a significant improvement in the lubrication properties can be achieved. In the present case, the terms "conversion layer" and "functional layer" are used synonymously. While the term "conversion layer" is used more in the context of chemical composition and formation process, the term "functional layer" is more likely to be associated with the effect of this layer (in subsequent process steps).

A coated galvanized steel sheet according to the invention can be used for the production of a motor vehicle component, wherein the steel sheet is subjected to one or more forming steps. The conversion layer applied to the galvanized sheet steel as a tribo layer is suitable for use in the automotive industry; and also the application of the treatment solution can be industrially implemented in mass production.

• Fig. 1 zeigt eine lediglich schematische Darstellung als Seitenansicht auf eine Anlage zur Herstellung des erfindungsgemäßen beschichteten Stahlblechs,
• Fig. 2 zeigt in einem Diagramm Ergebnisse von Flachbahn-Streifenziehversuchen an erfindungsgemäß behandelten Blechen im Vergleich mit unbehandeltem Blech,
• Fig. 3 zeigt in einem Diagramm Ergebnisse von Napfziehversuchen an verschiedenen erfindungsgemäß behandelten Blechen im Vergleich mit unbehandeltem Blech,
• Fig. 4 zeigt in einem Diagramm Ergebnisse von Napfziehversuchen an erfindungsgemäß bei unterschiedlichem pH-Wert behandelten Blechen im Vergleich mit unbehandeltem Blech.

Further advantages will be set forth by the following description with reference to the accompanying drawings. The reference to the figures in the description is to aid in the description and understanding of the subject matter. It shows:

• Fig. 1 shows a merely schematic representation as a side view of a plant for producing the coated steel sheet according to the invention,
• Fig. 2 shows in a diagram results of flat strip stripping tests on sheets treated according to the invention in comparison with untreated sheet,
• Fig. 3 shows in a diagram results of Napfziehversuchen on various inventively treated sheets compared with untreated sheet,
• Fig. 4 shows in a diagram results of Napfziehversuchen inventively treated at different pH sheets compared with untreated sheet.

In general, solids with layer lattice structure should be particularly suitable for reducing the solid friction in which the linking of the structure-forming Layers with one another in a spatial direction is much weaker than in the layer plane. This property is found z. As in graphite, molybdenum disulfide (MoS ₂ ) or hexagonal boron nitride (h-BN). However, such solids are generally not suitable for use on sheet metal surfaces for automobile bodies, since they exert a separating effect on the adhesives used in the shell. Furthermore, the above-mentioned substances have low surface energies and are insoluble in the treatment baths used for cleaning and pretreating the body panels, which would lead to poor results in the structure of the paint job.

In contrast, compounds with a similar structural composition and a chemical composition that does not cause any negative interactions in the later process chain would be suitable. A suitable mineral is brucite, which consists of magnesium hydroxide, Mg (OH) ₂ . It forms a layer grid of the Cdl2 type (where the iodide ions form a hexagonal close-packed spherical packing, the octahedral gaps of every second interlayer space are completely filled with cadmium ions) with pronounced cleavage in one spatial direction, but in contrast to graphite, molybdenum disulfide or hexagonal boron nitride has no pronounced low surface energies and is soluble in treatment baths because of its predominantly ionic bonding character. The solubility in water is low, which makes the continuous application of a drying wet film difficult.

Investigations show that weathered surfaces of galvanized sheet have significantly lower coefficients of friction than non-weathered surfaces. Under atmospheric weathering, hydrozincite, Zn ₅ [(OH) ₆ | (CO ₃ ) ₂ ], is formed on zinc surfaces, which has structural similarities to brucite, due to the action of water and carbon dioxide.

However, the representation of weathered surfaces in the context of a stretched from the continuous galvanizing process time window few seconds alone by the action of water and CO ₂ can not be achieved or would not be economically and sustainably feasible due to the required plant length. In short, weathering is not considered time-economic.

However, it has been found that the action of aqueous solutions of alkali metal hydrogencarbonates (AHCO ₃ ), alkali metal carbonates (A ₂ CO ₃ ), alkali metal hydroxides (AOH), alkali metal oxides (A ₂ O), alkali metal alcoholates (AO-R) and alkali metal carboxylates (AOOC). R) and magnesium oxide and / or magnesium hydroxide on galvanized surfaces conversion layers can be formed with comparable effect.

The functional or conversion layer to be produced on the galvanized steel surface ensures the reduction of the friction during forming of the steel sheet. The conversion layer is formed by the reaction of the surface-dried solution described above with the metal surface. The thickness of the conversion layer thus results from the concentration of the treatment solution and the thickness of the applied wet film. The basis weight of the dry substance is 25 to 200 mg / m ² , preferably 40 to 90 mg / m ² .

The pH of the treatment solution or suspension should be 8 to 12. In general, the solutions or suspensions of the carbonate or hydroxide suppliers may contain cations of the elements lithium, sodium, potassium, rubidium, cesium, but preferably sodium and potassium, and magnesium hydroxide or oxide.

Furthermore, the treatment solution may contain as an additive a tracer system which, although not required to obtain the tribological effect, serves as an indicator for the quantitative detection of the applied amount and does not hinder the formation of the conversion layer. For this purpose, substances of the following elements can be used: potassium, phosphorus, silicon, tin or titanium. These elements can be detected more easily than the element sodium by X-ray fluorescence analysis (RFA). Preferably, the compounds potassium carbonate / bicarbonate, Na / K phosphate or Na / K di- / tri-phosphates, alkali silicate (especially sodium silicate, potassium silicate) tin carbonate / bicarbonate can be used for this purpose. The treatment solution can be 0.01 to 1.5 wt .-% of the respective tracer system, preferably 0.05 to 1 wt .-%.

The application of the solution or suspension can generally be done by dipping, spraying, spraying / squeezing, roller coater or combinations of these methods with subsequent drying - of course, or thermally assisted. In combination with a lubrication of 0.2 to 3.0 g / m ² per side, the galvanized sheet steel coated according to the invention has a reduced coefficient of friction, wherein in addition the stick-slip behavior is avoided or at least reduced. Furthermore, the transfer of material from the workpiece to the tool and the formation of metal abrasion is reduced. On the other hand, the paintability and adhesiveness of the surface is retained. The galvanized sheet steel coated according to the invention is wash-resistant to wash oils, while the conversion layer is very readily wettable with water.

The Fig. 1 shows a preferred simple method for producing a friction-reducing coated steel sheet according to the invention. The sketched for carrying out the process plant can be roughly divided into three steps, jetting, squeezing and drying.

The galvanized steel strip 1 is moved in accordance with the feed direction a and guided between the rubberized squeezing rollers 10, which are located above and below the steel strip 1. By means of suitable application devices 12, the treatment solution L (or suspension) is sprayed in excess onto the rubber coating 11 of the squeeze rollers 10. The excess of the processing solution L at the squeegee 10 above the steel strip 1 flows first onto the steel strip 1, then over the strip edge in the receiver 13, while the excess of the treatment solution L at the squeegee 10 below the steel strip 1 directly from the roller 10 back into the storage container 13 passes. From the storage tank 13, the treatment solution L is supplied to the application devices 12 via corresponding feed lines 14.

The self-propelled squeeze rolls 10 are placed on the surfaces of the steel strip 1 with pneumatic or hydraulic pressure and strip the excess processing solution L thereon. The upper roller serves as an abutment for the lower roller and vice versa. By selecting the Anstelldrucks, the hardness of the rubber coating 11, the relative speed of the squeeze rolls 10, which rotate at speed b, the steel strip 1 and the speed a of the steel strip 1 wet films 2 'of 1 to 20 microns, but preferably 2 to 3 microns produced become. Thinner wet films may be preferred as they allow shorter dryer runs, lower belt temperatures, or faster belt speeds.

The wet film 2 'is dried in a circulating air dryer 15, so that the functional layer 2 is obtained on the hot-dip galvanized steel strip surface. Between outlet squeeze rollers 10 and outlet circulating air dryer 15, the steel strip 1 is tensioned without support.

In general, the wet film can also be air-dried.

Construction and arrangement of the application device may well differ from the example shown.

Thus, as an alternative to the example illustrated, the application is conceivable by means of a roller coater equipped with two or three rollers, which allow greater freedom in the design of the wet film independently of the belt speed. Rollcoaters are also part of the standard equipment for many systems, especially for the inline coating of antifinger printing. However, since roller coater cause significantly higher investment, maintenance and operating costs, they are used for simple post-treatments, as it represents the application of the treatment solution according to the invention, less frequently.

Furthermore, the spraying of a wet film without squeezing (for example in a cloud chamber) or spraying and stripping with non-driven squeezing rollers and pulling through an immersion bath is also conceivable.

• feuerverzinktes Blech, hot dip galvanized (Blech "Z"), gemäß Stahlinformationszentrum Charakteristische Merkmale CM095 Ausgabe 2010, ISSN 0175-2006, wobei es sich um ein kontinuierlich schmelztauchveredeltes Stahlfeinblech mit Zinküberzug "Z" einer Zinkauflage von 50 bis 600 g/m² - vorzugsweise 50 bis 140 g/m² - kalt nachgewalzt und texturiert mit einer mittleren Rauheit Ra = 0,7 bis 1,6 µm und einer Spitzenzahl RPc = 60 bis 140/cm und einem Dressiergrad von 0,2% bis 2,5% handelt,
• feuerverzinktes Blech, hot dip galvanized (Blech "ZM"), gemäß Stahlinformationszentrum Charakteristische Merkmale CM095 Ausgabe 2010, ISSN 0175-2006, wobei es sich um kontinuierlich schmelztauchveredeltes Stahlfeinblech mit Zink/Magnesium-Überzug "ZM" einer Zink/Magnesium-Auflage von 40 bis 350 g/m² - vorzugsweise 50 bis 140 g/m² - kalt nachgewalzt und texturiert mit einer mittleren Rauheit Ra = 0,7 bis 1,6µm und einer Spitzenzahl RPc = 60 bis 140/cm und einem Dressiergrad von 0,2% bis 2,5% handelt.
• elektrolytisch verzinktes Blech, electro-galvanized (Blech "ZE"), gemäß Stahlinformationszentrum Charakteristische Merkmale CM092, Ausgabe 2008, ISSN 0175-2006, wobei es sich um kaltgewalztes Stahlfeinblech, kalt nachgewalzt und texturiert mit einer mittleren Rauheit Ra = 0,7 bis 1,6 µm und einer Spitzenzahl RPc = 60 bis 140/cm, kontinuierlich elektrolytisch veredelt mit Zinküberzug "ZE" und einer Zinkschichtdicke von 2,5 bis 10 µm je Seite, vorzugsweise 5 bis 7,5 µm je Seite handelt.

As a substrate, for example, the following sheets can be used:

• hot-dip galvanized sheet, according to the Steel Information Center Characteristic features CM095 Edition 2010, ISSN 0175-2006, which is a continuously hot-dip coated steel sheet with zinc coating "Z" of a zinc coating of 50 to 600 g / m ² . preferably 50 to 140 g / m ² cold-rolled and textured with a mean roughness Ra = 0.7 to 1.6 μm and a peak number RPc = 60 to 140 / cm and a degree of skin pass of 0.2% to 2.5% These,
• hot dip galvanized (ZM), according to Steel Information Center Characteristic features CM095 Edition 2010, ISSN 0175-2006, which is a continuously hot dip coated steel sheet with zinc / magnesium coating "ZM" of a zinc / magnesium overlay of 40 to 350 g / m ² - preferably 50 to 140 g / m ² - cold-rolled and textured with an average roughness Ra = 0.7 to 1.6μm and a peak number RPc = 60 to 140 / cm and a degree of tempering of 0.2 % to 2.5%.
• electrolytically galvanized sheet metal, electro-galvanized (sheet "ZE"), according to Steel Information Center Characteristic features CM092, Edition 2008, ISSN 0175-2006, which is cold rolled steel sheet, cold rolled and textured with an average roughness Ra = 0.7 to 1 , 6 microns and a peak number RPc = 60 to 140 / cm, continuously electrolytically finished with zinc coating "ZE" and a zinc layer thickness of 2.5 to 10 microns per side, preferably 5 to 7.5 microns per page is.

As active ingredients in the exemplary treatment solutions preferably sodium and potassium carbonate and bicarbonate or sodium and potassium bicarbonate and hydroxide are selected with a total concentration in the treatment solution of 3 to 5 wt .-% and the pH in a range of 7 to 13, preferably 8 to 12, more preferably set to 9.

• Na/K-Phosphat bzw. Na/K- Di-/Tri-Phosphate,
• K-Hydrogencarbonat,
• Na/K-Sulfat,
• Na/K-Silikate, Na/K-Metasilikate, SiO₂-Dispersion Na-haltig.
• Zinn- oder Titan-Verbindungen

If a tracer system is used to detect the layer thickness, its concentration is in a range from 1 to 30% by weight, preferably 10 to 20% by weight and particularly preferably 15% by weight, based on the active ingredient content, if the tracer system is aus the following is selected:

• Na / K phosphate or Na / K di- / tri-phosphates,
• K-hydrogen carbonate,
• Na / K-sulfate,
• Na / K silicates, Na / K metasilicates, SiO ₂ dispersion Na-containing.
• Tin or titanium compounds

Even with a tracer system, the pH of the treatment solution should be in a range from 8 to 12, more preferably about 9, and is optionally adjusted, preferably with NaOH or KOH.

The exemplary process described here of forming conversion layers by the action of basic alkali metal carbonates on galvanized steel surfaces provides for the formation of structures which resemble the hydrozincite Zn ₅ [(OH) ₆ | (CO ₃ ) ₂ ] pure zinc by corrosion in the presence of airborne CO ₂ as the basic zinc carbonate, along with other hydroxides, carbonates and oxides.

In contrast to pure zinc surfaces, surfaces of hot-dip galvanized steel strips contain not only zinc but also a smaller proportion of aluminum (Z-plates and ZM-plates) or magnesium (ZM-plates). In these surfaces, the conversion layer resulting from corrosion also contains aluminum or magnesium compounds (hydroxides, carbonates, oxides). The formed corrosion layer is amorphous, an exact chemical composition or crystal structure is not given. The layers of basic zinc-aluminum carbonate / hydroxide (sheet "Z"), basic zinc / magnesium-aluminum carbonate / hydroxide (sheet "ZM") or basic zinc carbonate / hydroxide (sheet "ZE") are referred to below as the conversion layer or Functional layer described.

The wet film applied to the metal surface according to the invention is dried and subsequently not rinsed with water. Therefore, all non-volatile components remain on the surface. The layer weight of the dry substance is in a range from 25 to 200 mg / m ² surface, preferably 40 to 90 mg / m ² . The coating weight of the forming conversion layer is due to corrosion and incorporation of the zinc, aluminum or magnesium from the sheet surface accordingly greater.

The coating weight of the dry substance can be determined by the thickness of the wet film as a function of the concentration of the treatment solution. For example, a wet film of a 3% solution is to be applied 1.3 to 3.0 μm thick in order to achieve the preferred basis weight of the dry matter of 40 to 90 mg / m ² . The layer thickness can be checked by X-ray fluorescence analysis of the added to the solution and present in the dry substance tracer elements potassium, phosphorus, sulfur or silicon, tin, titanium.

The friction-reducing effect of the conversion layer can be detected, for example, by strip drawing experiments based on VDA 230-213 and by cup draw tests, as described below with reference to FIGS FIGS. 2 to 4 will be shown.

The treatment solutions used to treat the sheets for strip pulling tests and cupping tests are listed in the table below. Table 1: Examples of treatment solutions: designation Treatment or aqueous treatment solution FG TS [mg / m ² ] EMERGENCY untreated - NC 5% by weight NaHCO ₃ / NaOH, pH 9 70 KC 5% by weight KHCO ₃ / KOH, pH 9 70 NC + KC 4.25% NaHCO ₃ + 0.75% KHCO ₃ / NaOH, pH 9 70 NC + PH 4.25% NaHCO ₃ + 0.75% Na tripolyphosphate / NaOH, pH 9 70 NC + S 4.25% NaHCO ₃ + 0.75% Na ₂ SO ₄ / NaOH, pH 9 70 NC + Si 4.25% NaHCO ₃ + 0.75% Na metasilicate / NaOH, pH 9 70 NC + SiO ₂ 4.25% NaHCO ₃ + 0.75% SiO ₂ dispersion Aerodisp W 7520 N (Evonik, Hanau) / NaOH, pH 9 70 H ₂ O Steam - NC pH 11.5 5% by weight of Na ₂ CO ₃ 70 NC pH 8.6 5% by weight of NaHCO ₃ 70 FG TS: basis weight dry substance

Thus, for example NC, the 5% strength by weight treatment solution having a pH of 9 is obtained by dissolving 50 g of NaHCO ₃ in 950 g of demineralized water and then the solution with sodium hydroxide solution (eg with 50% by weight of NaOH) pH 9 is adjusted.

Fig. 2 shows in a graph in which the friction coefficient is plotted against the contact pressure, results for flat-strip stripping experiments, on a treated with 5 wt .-% NaHCO ₃ / NaOH aqueous solution (pH 9) NC sheet and a 5 wt. % KHCO ₃ / KOH aqueous solution (pH 9) treated sheet KC (see Table 1) and for comparison on an untreated sheet NOT according to VDA 230-213 were performed. (Tool material GJS-700-2 (GGG 70L), tool temperature 40 ° C, tool dimension 74 x 144 mm ² , sheet type = DX54D + Z100, sheet width 100 mm, sheet length 1500 mm, sheet thickness = 1 mm, drawing speed 10 mm / s.) All test panels were oiled after the conversion treatment before the strip pulling test with 1.1 to 1.3 g / m ² Prelube oil Anticorit PL 3802-39S from Fuchs Europe GmbH, Mannheim. The sheets NC, KC treated according to the invention have significantly reduced coefficients of friction compared with the untreated sheet metal NOT, and in addition the stick-slip behavior (adhesion-slip behavior) which occurs in the untreated sheet metal NOT is avoided. In addition, it can be seen that the conversion layers of the sheet NC produced with NaHCO ₃ / NaOH tend to lead to lower coefficients of friction than the conversion layers of the sheet KC produced with KHCO ₃ / KOH.

Fig. 3 shows the results of Napfziehversuchen with 0.8 mm thick HDG sheet (press BUP 200 from Zwick Roell, Ulm, tool material punch and drawing ring = 1.2510, tool material downholder = 1.0503, mold temperature 25 ° C, cylindrical cup, punch diameter = 50 mm , Punch radius = 5 mm, ring diameter = 100 mm, radius draw rounding = 5 mm, drawing gap = 1.3 mm, drawing ratio = 2.0, holding force = 30 kN, sheet metal = DX54D + Z100, sheet thickness = 0.8 mm, pulling speed 10 mm / s). In the bar graph, the maximum punch force on the untreated sheet NOT is plotted against the differently pretreated sheet according to Table 1. Again, after the conversion treatment, all test panels were oiled with 1.1 to 1.3 g / m ² Prelube oil Anticorit PL 3802-39S. The treated with the NaHCO ₃ -containing treatment solutions sheets (NC, NC + KC, NC + PH, NC + S, NC + Si, NC + SiO ₂ ) allow a significantly lower maximum punch force than the untreated sheet NOT. It turns out that even a conversion layer, which is obtained from a reaction of a galvanized surface with water vapor (H ₂ O test plate), has a reduced maximum punching force in Napfziehversuch result and thus shows improved tribological behavior.

However, hitherto treatment with steam, which leads to an effective conversion layer, can not be realized in terms of process technology with the installations of the steel industry which are usually used, since considerably longer treatment times are required for steam treatment than is possible in the fully continuous process. Thus, effective conversion layers form at a temperature of 40 ° C only after 1 hour and even at a temperature of 95 ° C are still 2 minutes required. At a typical strip speed in the mill of 200 meters per minute treatment times of z. B. 2 minutes require a treatment line on the production line of 400 meters. Therefore, treatment times of seconds required by the manufacturing process to achieve the necessary productivity of the plants can not be achieved with steam so far.

For the effectiveness of a functional layer according to the invention in terms of friction reduction, the presence of tracers is not required. However, the examples given show that the different tracer systems have some influence on the overall layer friction, albeit to a lesser extent. Thus, the conversion layers of treatment solutions with the tracer systems, in particular with phosphate (NC + PH) and silicon dioxide (NC + SiO 2), allow the lowest stamping forces. This suggests that either the presence of certain tracer components is more effective Promotes conversion layer or contribute certain tracer components for better tribological effectiveness and, for example, be installed even in the conversion layer. Thus, phosphates are known as lubricating components, and the SiO ₂ dispersion is attributed to lubricating effect. Optionally, both effects come into consideration.

In the bar chart in Fig. 4 the results of Napfziehversuchen with HDG sheet thickness of 1.0 mm are applied, wherein the untreated sheet NOT with a at pH 11.5 with Na ₂ CO ₃ and at pH 8.6 with NaHCO ₃ treated sheet (NC pH 11 5 and NC pH 8.6, see Table 1). Tool material die and drawing ring = 1.2510, tool material hold down = 1.0503, tool temperature 25 ° C, cylindrical cup, diameter = 50 mm, diameter = 100 mm, drawing ratio = 2.0, holding force = 30 kN, type of sheet = DX54D + Z100, sheet thickness = 1.0 mm, pulling rate 10 mm / s) the test panels were oiled after treatment with 1.1 to 1.3 g / m ² prelube oil Anticorit PL 3802-39S.

Both treated sheets NC pH 11.5 and NC pH 8.6 surprisingly require a significantly reduced maximum punch force in the cup drawing test compared with the untreated sheet NOT, with the sheet treated at pH 8.6 cutting NC pH 8.6 even better than this At pH 11.5 treated sheet NC pH 11.5, resulting from the fact that at pH 8.6, the formation of the tribologically particularly effective hydrozincite Zn ₅ [(OH) ₆ (CO ₃ ) ₂ ] thermodynamically preferred, while at pH 11.5 the formation of the less effective zinc oxide and hydroxide takes place.

Furthermore, it has surprisingly been found that the conversion layer is compatible with a subsequent manufacturing process of a car body shell: In practice, the temporary corrosion protection of the steel sheet is indispensable for the storage and transport of steel coils and still unpainted pressed parts. This is usually achieved by applying anti-corrosive or Prelube oils or waxy hotmelt dry lubricants in the rolling mill. The proof of the anti-corrosion properties can be exemplified by a condensed water climate test be carried out as described in the test specification VDA 230-213.

For the condensed water climate test, five plates were pretreated according to Table 1 (NOT, NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SiO ₂ ), with 1.1 to 1.3 g / m ² Anticorit PL 3802-39 S oiled and exposed to a corrosive atmosphere in accordance with VDA 230-213 (5.4.8) for 30 cycles. It has been shown that the protective effect of the treated sheets (NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SiO ₂ ) corresponds to that of the only oiled reference sheets without conversion layer (NOT). The Prelube Anticorit PL 3802-39 S used for lubrication has been used for years for coil lubrication in the German steel and automotive industry. It can therefore be assumed that the conversion coatings are suitable for the temporary corrosion protection of coils and pressed parts.

Furthermore, a good adhesion of the adhesives used is essential for the carcass shell. The compatibility of the conversion layer with such structural adhesives can be investigated by way of example with an adhesive bead test. Here, a strand (bead) of the still liquid adhesive is applied to the pretreated and with 2.8 to 3.2 g / m ² Anticorit PL 3802-39 S oiled test sheet and subsequently thermally cured. After cooling, the adhesive bead is mechanically peeled off and the surfaces of the sheet and the removed bead are examined. A retention of adhesive residues on the metal surface indicates good adhesion of adhesive metal. Such good adhesion is accompanied by a rough, and thus whitish surface of the adhesive bead. The adhesives used were, for example, the products Betamate ™ 1496 F and Betamate ™ 1040 from Dow Automotive.

It could be shown that the adhesion properties of the test sheets with conversion layer (NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SiO ₂ ) advantageously correspond to those without such pretreatment (NOT). A cohesive (CF) or near-surface cohesive (SCF) fracture pattern was achieved in all cases.

In a further experiment, the adhesive beads cured on the sheets were subjected to corrosion before peeling. For this purpose, for example, moisture loads were carried out over a period of 504 h at 50 ° C and 95% relative humidity. It was found that the fracture pattern after the corrosion load is also cohesive (CF) or near-surface cohesive (SCF). These results suggest the suitability of the conversion layers according to the invention for the adhesive methods in the manufacture of car bodies.

Before the painting of car bodies, the removal of oily and the paint adhesion of negatively influencing layers is required. This is done by an aqueous alkaline cleaning. The complete removal of such layers is indicated by complete water wettability of the surface. Proof of removability can be provided, for example, by the removability test according to VDA 230-213 (5.10).

It has been found that both sheets without (NOT) and with conversion layer (NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SiO ₂ ) are advantageously completely water-wettable after such a removability test , Therefore, the suitability of the conversion layers for pretreatment or painting of car bodies is postulated.

Claims (12)

1. A method for time-saving production of a galvanised steel sheet (1) comprising a forming aid layer of at least one inorganic functional layer (2),
   comprising the steps of:

   - producing an aqueous, silane-free solution (L) or suspension of at least one carbonate supplier or an aqueous, silane-free solution (L) or suspension of at least one carbonate supplier and at least one hydroxide supplier, wherein the at least one carbonate supplier is selected from ammonium hydrocarbonate, ammonium carbonate, alkali metal hydrocarbonates, alkaline metal carbonates and alkaline metal carboxylates, and the at least one hydroxide supplier is selected from alkaline metal hydroxides, alkaline metal oxides, alkaline metal alcoholates, magnesium hydroxides and magnesium oxide,
   wherein a concentration of the at least one carbonate supplier lies in a range of between 1 and 5% by weight, based on the total weight of the solution (L) or suspension,

   - setting the pH value of the solution (L) or suspension in a range of between 8 and 12,

   - applying the aqueous solution (L) or suspension to at least one side of the galvanised steel sheet (1) and generating a wet film (2') comprising a predetermined thickness, which is set as a function of the concentration of the treatment solution of between 1 and 20 µm,

   - drying the wet film (2') without carrying out a rinsing step by maintaining a layer weight of a dry substance of between 25 and 200 mg/m² surface, wherein the layer weight of the dry substance is determined by the thickness of the wet film (2') and the concentration, and wherein a conversion layer of zinc and zinc salts (2), which are at least partially carbonates, is obtained as inorganic functional layer (2).
2. The method according to claim 1,
   wherein
   the concentration of the at least one carbonate supplier lies in a range of between 3 and 5% by weight, based on the total weight of the solution (L) or suspension,
   and/or
   the layer weight of the dry substance from the wet film (2') is between 40 and 90 mg/m², and/or

   - the pH value of the solution (L) or suspension is set to 9 ± 0.5, if necessary by adding sodium hydroxide and/or potassium hydroxide.
3. The method according to claim 1 or 2,
   wherein
   the alkaline metal is sodium or potassium, wherein the at least one carbonate supplier is preferably sodium and/or potassium hydrocarbonate and/or carbonate and the at least one hydroxide supplier is sodium and/or potassium hydroxide.
4. The method according to at least any one of claims 1 to 3,
   comprising the step of:

   - adding a tracer system, which can be detected in the X-ray fluorescence analysis, to detect the layer thickness by means of X-ray fluorescence analysis in response to producing the aqueous, silane-free solution (L) or suspension, said tracer system having

   - sodium and/or potassium phosphate or sodium and/or potassium diphosphate and/or triphosphate or

   - sodium hydrocarbonate, potassium carbonate or

   - sodium and/or potassium sulphate or

   - sodium and/or potassium silicates, sodium and/or potassium metasilicates or a sodium-containing SiO₂ dispersion and/or tin or titanium compounds comprising a concentration in a range of between 1 and 30% by weight, preferably between 10 and 20% by weight, particularly preferably 15% by weight, based on the content of carbonate and hydroxide suppliers.
5. The method according to at least any one of claims 1 to 4,
   wherein the application takes place by

   - dipping

   - spraying without squeezing or

   - spraying and wiping off by means of non-driven squeezing rollers or

   - rolling on by means of a rollcoater or preferably by means of two squeezing rollers (10), between which the galvanised steel sheet (1) is guided.
6. The method according to claim 5,
   wherein the rolling on by means of two squeezing rollers (10) comprises the steps of:

   - spraying an excess of the aqueous solution (L) or suspension onto the squeezing rollers (10) arranged on both sides of the galvanised steel sheet (1), wherein excess solution of suspension is caught and is guided into a storage container (13),

   - setting the squeezing rollers (10) against the surfaces of the galvanised steel sheet (1) under pressure and wiping off the aqueous solution (L) or suspension to the surfaces of the galvanised steel sheet (1) and

   - setting the thickness of the wet film (2') in a range of between 1 and 20 µm by selecting the surface pressure, a hardness of a rubber coating (11) of the squeezing rollers (10), a speed (b) of the squeezing rollers (10), and a speed (a) of the steel sheet.
7. The method according to at least any one of claims 1 to 6,
   comprising the steps of:

   - applying an anticorrosive oil and/or a prelube oil and/or a dry lubricant to the conversion layer (2), so that a lubricating oil layer comprising a surface weight of between 0.2 and 3.0 g/m² is obtained.
8. A coated galvanised steel sheet (1), the surface of which has a forming aid layer of at least one inorganic functional layer (2),
   characterised in that
   the inorganic functional layer (2) is a conversion layer of zinc and zinc salts comprising a hydrozincite-like mineral structure, which is formed from a dry substance separated by means of the method according to at least any one of claims 1 to 7 by application and drying a wet film (2') comprising a layer weight of between 25 and 200 mg/m² surface.
9. The galvanised steel sheet (1) according to claim 8,
   characterised in that
   the galvanised steel sheet (1) is a hot-dip galvanised steel sheet (1).
10. The galvanised steel sheet (1) according to claim 8 or 9,
    characterised in that
    the conversion layer (2) has a tracer system for detecting the layer thickness, which can be detected by means of X-ray fluorescence analysis and which is selected from potassium, phosphor, sulphur, silicon, zinc or titanium compounds.
11. The galvanised steel sheet (1) according to at least any one of claims 8 to 10,
    characterised in that
    the forming aid layer comprises a lubricating oil layer, which is applied to the conversion layer (2), wherein the lubricating oil layer preferably

    - comprises an anticorrosive oil and/or a prelube oil and/or a dry lubricant, and

    - has a surface weight of between 0.2 and 3.0 g/m², preferably between 1.0 and 1.5 g/m².
12. A use of a coated, galvanised steel sheet (1) according to at least any one of claims 8 to 11 for producing a motor vehicle component by carrying out at least one forming step.

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