Flat metal product and component based thereon

Abstract

The invention relates to a flat metal product and a component made therefrom.

Description

[0001] Flat metal product and component thereof

[0002] The invention relates to a flat metal product and a component made therefrom.

[0003] Sheet materials made from steel, for example, for use in the automotive sector are usually provided with a zinc-containing coating, such as a zinc coating with particularly low aluminum contents from the melt (Z), a zinc-based coating with aluminum and magnesium contents from the melt (ZM), a zinc or zinc-based coating heat-treated after hot-dip coating (ZF), and an electrolytically applied zinc coating (ZE). The zinc acts as a sacrificial anode to protect the steel material from corrosion. The coatings applied to the flat metal product during production must withstand the stresses and strains encountered during forming into the component. Abrasion can cause scratches, pimples, and dents, even leading to component failure. The roughness of the sheet surface has a significant influence on the abrasion behavior, particularly of a zinc or zinc-containing coating.Typically, forming aids, such as forming oils, are used during forming to prevent direct metallic contact between the tool surface and the sheet metal surface. The surfaces slide against each other, with elevations in the surface of one contact partner rubbing against the surface of the other contact partner, thus creating groove-like depressions. The longer the distance the point loads travel without interruption on the surface, the more severe the grooves can be.

[0004] The roughness of the sheet metal surface can be changed, among other things, by choosing the coating system and by applying suitable textures.

[0005] The textures are usually applied to the surface of the flat metal products by skin passing. During skin passing, two skin passing rolls are used in a skin passing stand, between which the flat metal product is guided. So that the upper skin passing roll acts on the top side and the lower skin passing roll acts on the underside of the flat metal product, imprinting a corresponding texture on the top and underside of the flat metal product depending on the structure of the skin passing rolls. Convex structures on the surface of the skin passing rolls are imprinted concavely on the surface of the flat metal product, i.e. a raised area on the surface of the skin passing roll creates a depression on the surface of the flat metal product, particularly depending on the design of the structure and the degree of skin passing.

[0006] Skin-pass rolls can be manufactured using stochastic structuring processes, mostly using the so-called EDT process, see for example EP 2 006 037 Bl .

[0007] Roll surfaces can be provided with a structure in a targeted manner using microlithography. For example, US Pat. No. 5,532,051 discloses circular and square structures that are created in a recurring sequence in a square grid on a roll using lithography and can be transferred to the surface of the flat product during the rolling process to improve the forming properties.

[0008] In the document DE 689 10 866 T2, basin-like depressions in a rectangular or hexagonal arrangement are also described as advantageous in terms of forming technology, but not optimal in terms of paint appearance.

[0009] By means of laser beam bombardment, structures can be set in a deterministic arrangement on a skin-pass roll surface, see for example EP 2 892 663 B1, which are transferred to the flat product during skin-passing and such skin-passed flat products can contribute to an improvement in forming and varnish appearance.

[0010] Moire effects are to be avoided by means of pseudostochastic surfaces, see US 2019 / 0337032 Al with irregularly arranged circular elevations with a diameter of 50 - 150 pm, which overlap less than 10% and whose number per mm 2 by less than 20%.

[0011] Flat metal products can also be textured directly by laser bombardment, as described in WO 2017 / 125497 Al.

[0012] WO 2021 / 053088 A1 discloses surfaces in which the position of the depressions is varied using a random generator. Mathematical models are presented that are intended to be created either by laser-structured skin-pass rolling or by direct laser texturing of the sheet surface. WO 2021 / 013938 A1 discloses a texture that can be created by direct laser texturing, which is designed to reduce or even prevent abrasion on coated steel sheets to be formed and thus adhesion to the tool surfaces contacting the steel sheets. This requires that the material surfaces between the depressions on the flat sheet surface have the smallest possible radius.

[0013] Phenomena of surface failure with abrasion and adhesions occur not only in zinc-coated steel materials, but also in aluminum-coated steel materials, especially in the so-called indirect hot forming, and also in (uncoated) aluminum materials, since depending on the alloy the mechanical properties of aluminum differ only slightly from those of zinc, including in terms of strength.

[0014] In view of the state of the art, it is therefore desirable to provide a skin-passed metal flat product with a surface texture that produces essentially no or only low abrasion and less adhesion during forming.

[0015] A first teaching of the invention relates to a skin-passed metal flat product with a texture on the top and / or the bottom of the metal flat product. Metal flat product with a texture on the top and / or the bottom of the metal flat product with a mean height difference peak-to-valley d m-v and an average distance to the valley edge r v , where the product of d m-v and r v at least 6 pm 2 amounts.

[0016] The texture is preferably in the form of depressions with ridges arranged between the depressions, whereby the texture is based on a recurring pattern arranged in a grid. In addition to the average height difference, the texture includes the mountain-to-valley d m -v and the mean distance to the valley edge r v for example, further parameters selected from the group arithmetic mean roughness Ra, peak number RPc, material proportion Mr , mean distance to the mountain edge r v and the maximum values ​​of the inner radius of the mountain r m , max and the inner radius of the valley r v>max and optionally the arithmetic mean ripple Wsa.

[0017] Within the scope of the invention it was found that the tendency towards the formation of abrasion depends on the leveling behavior of the surface. Surfaces with a high resistance to leveling exhibit less abrasion. The roughness parameters such as the arithmetic mean roughness Ra and peak number RPc must be measured outside the principal texture directions in accordance with DIN EN 10049:2014.03 for deterministic surfaces. For a hexagonal grid with principal directions of 30° or 60°, a measuring direction of 45° ± 5° to the rolling direction is recommended. Since a hexagonal grid is invariant with rotations of 60° and measuring directions can be rotated by 90°, a measuring orientation of 15° + m ■ 30° is also permissible for integer numbers m (me Z).

[0018] The same considerations regarding the measurement direction apply to the waviness parameter Wsa according to SEP 1941. The profile parameters Ra, RPc, and Wsa can be determined using tactile or non-contact measuring systems. The height values ​​z(x) in a measuring length L must be centered:

[0019] The arithmetic mean roughness Ra is

[0020] The material proportion M r depends on the cutting plane c

[0021] The elevation values ​​z(x) above the intersection line c = 0 are considered mountains, and the values ​​below this line are considered valleys. The proportion of mountains in the surface topography is M r (0), short M r , the proportion of valleys is (1 — M r (0)), short (1 — M r ). The average height of the mountains h m is: h r L( z(x' for z(x' > 0 , , / r Lfl for z x') I L ,m = Jo t O otherwise dx / u O otherwise and the mean depth of the valleys t v is: r L( z(x') for z(x') < 0 , , / rLfl for z(x') <

[0022] Jot O otherwise dx l >« [ O otherwise

[0023] Due to the centering of the height values, h m M r = t v (l — M r ) and

[0024] The average altitude difference mountain-to-valley d m-v can be calculated from the parameters Ra and M as follows r calculate:

[0025] These parameters and their relationships to each other apply in the same way to area-measured height values ​​z(x,y). Area-measurement of the surface topography can be performed, for example, using a confocal microscope, particularly with a lateral resolution of approximately 1.56 pm. The preferred measurement area is at least 1 mm. 2. In the case of sheet metal curvature and larger measuring surfaces, shape components may need to be removed using standard filter methods, such as a Gaussian filter with a cut-off wavelength of X c = 1.0 mm. The topographical measurement data must be centered, i.e., their mean values ​​must be subtracted from the elevation values. A height value z(x,y) is referred to as a point on a mountain if z(x,y) > 0. A point is in a valley if z(x,y) < 0. The shortest distance from a point (x,y) on a mountain to a point in a valley is: for z(x,y) > 0.

[0026] The shortest distance from a point (x,y) in a valley to a point on a mountain is:

[0027] The (maximum) inner radius of the largest mountain area is

[0028] = max(r m (xy)), and the (maximum) inner radius of the largest valley area is r v _max = max(r r (x,y)).

[0029] The mean r m over the measuring area F is a measure of the fine shape of the mountains r M ", = J f J fFI n dx dy ff dx dy 0 otherwise 7 / JJ F(. 0 otherwise 7 and the mean r v a measure of the fine shape of the valleys r V " = ff JJ F fI (x ' y > fur z < x ' y) < °dx'dy'lN { 0 otherwise 7 / JJ FI 1 fur T 0 s X ' on V '' < °dx'dy' st 7

[0030] The sum of r m + r v is inversely proportional to the peak number RPc. The product has been found to be an essential measure to determine the resistance to abrasion A reSiSt of the surfaces. The higher A r e Sis t, the more favorable the surface behaves during forming.

[0031] The texture therefore has a resistance to abrasion A reSiSt from at least 6 pm 2 especially at least 8 pm 2 , preferably at least 10 pm 2 . A reSiSt can be set to a maximum of 200 pm 2 , especially maximum 150 pm 2 , preferably maximum 120 pm 2 , preferably maximum 100 pm 2 be limited.

[0032] "Flat metal product" refers to manufactured sheets or similarly constructed strips and other rolled products made of a metal material, which can be a metal or a metal alloy. The metal or metal alloy is preferably steel or a steel alloy, or alternatively, aluminum or an aluminum alloy.

[0033] Recurring depressions, separated from one another by webs, are embossed into the surface of the flat metal product using a skin-passing process. The depressions form fluid pockets for absorbing a forming aid that promotes the forming process, for example for absorbing forming oil. To ensure that the webs can be better wetted with a sufficient amount of the forming aid, excessively narrow web widths or even roughness peaks on the flat metal product surface must be avoided. The webs between the depressions, in conjunction with the geometry of the depressions, are designed in such a way that they are robust against leveling. The webs can preferably be present as a continuous area (plateau), thus connected as a continuous web area. In this respect, not only the surface area of ​​the webs, but also their geometry such as width and length plays a role in the friction behavior.This is primarily due to the fact that the stress is made up of two superimposed components. The normal compressive stress causes a deformation of the surface. In particular, the actual contact area between two rough surfaces is only a few percent of the total area. This can result in significantly higher pressure on the surface than initially assumed when taking the total area into account. This local pressure can then lead to plastic surface changes. The larger the local contact areas between the rough metal flat product surface and the tool surface, the lower the local pressures acting at the micro level, which can lead to plastic deformation of the surface. During forming, this static stress is superimposed on a relative movement in the sheet plane (dynamic stress), which can result in drawing marks.The longer the distances traveled, the more pronounced these marks can become, even leading to unwanted grooves on the surface. Therefore, the material areas, or mountain areas, should not be too wide.

[0034] The textures underlying the invention are based on recurring form elements arranged in a lattice. The underlying lattice has spacings in the range of 50 pm, in particular 70 pm, preferably 100 pm to 500 pm, in particular up to 450 pm, preferably up to 380 pm.

[0035] The shaped elements consist of individual recesses which, in plan view, are particularly polygonal in shape, for example in triangular, square or hexagonal shape, in particular in the form of an equilateral triangle or hexagon.

[0036] The pattern, comprising several adjacent individual depressions, is thus recurring on the flat metal product surface, particularly in the skin-pass direction, as well as perpendicular to it. The axes of symmetry can be in the skin-pass direction or perpendicular to it, but can also be rotated at a defined angle.

[0037] Skin-pass rolls (or pairs) are used which are appropriately structured and capable of producing flat metal products which have been skin-passed on one or both sides and have the aforementioned characteristics. Lasers, in particular short-pulse lasers, are therefore suitable for processing or structuring the surfaces of the skin-pass rolls. Corresponding laser structuring processes and devices for carrying out the laser structuring process are state of the art; see EP 2 892 663 B1, EP 3 172 006 B1 and EP 3 877 112 A1 in addition to the prior art. In this way, it is possible to create structures on the surface of the skin-pass roll which, when bombarded with lasers, cause ablation, i.e. material removal, on the surface in the area of ​​the impact. By careful adjustment, the laser shots can overlap or be spaced so far apart that an almost initial state remains between the laser shot areas.The areas not hit by the laser beam therefore form the elevation(s) on the skin-passing roll surface. A complete transfer of the surface structure of the skin-passing roll to the surface of the flat metal product to be skin-passed is practically impossible; instead, only the significant parts, such as the elevations of the surface profile of the skin-passing roll, will penetrate the surface of the flat metal product to be skin-passed, thus giving the surface of the flat metal product a new appearance or characteristic after skin-passing that is different from the state before skin-passing. The skin-pass surface with its elevations (positive shape) forms a surface texture due to the action of force on the surface of the optionally coated flat metal product, which is therefore only partially reflected in the surface of the steel sheet orSurface of the optionally coated flat metal product is embossed with corresponding depressions (negative form).

[0038] The texture on the surface of the metal flat product, whether uncoated or coated, meets the following criteria, for example:

[0039] - the arithmetic mean roughness Ra is at least 0.50 pm, in particular at least 0.60 pm, preferably at least 0.70 pm, and at most 5.0 pm, in particular at most 4.0 pm, preferably at most 3.0 pm; - the peak number RPc is at least 30 1 / cm, in particular at least 40 1 / cm, preferably at least 50 1 / cm, and at most 200 1 / cm, in particular at most 150 1 / cm, preferably at most 110 1 / cm, preferably at most 90 1 / cm;

[0040] - the material proportion M r is at least 30%, in particular at least 35%, preferably at least 40%, and at most 65%, in particular at most 60%, preferably at most 57%;

[0041] - the average height difference mountain-to-valley d m.v is at least 1.0 pm, in particular at least 1.5 pm, and a maximum of 8.0 pm, in particular a maximum of 7.0 pm, preferably a maximum of 5.5 pm;

[0042] - the maximum inner radius of the mountains r m>max is at least 14 pm, in particular at least 16 pm, preferably at least 18 pm, and at most 50 pm, in particular at most 40 pm, preferably at most 30 pm;

[0043] - the maximum inner radius of the valleys r v>max is at least 20 pm, in particular at least 25 pm, preferably at least 30 pm, and at most 100 pm, in particular at most 80 pm, preferably at most 70 pm;

[0044] - the mean distance to the mountain edge r m is at least 4 pm, in particular at least 5 pm, preferably at least 6 pm, and at most 40 pm, in particular at most 30 pm, preferably at most 20 pm;

[0045] - the mean distance to the valley edge r vis at least 4 pm, in particular at least 5 pm, preferably at least 6 pm, and at most 40 pm, in particular at most 30 pm, preferably at most 25 pm.

[0046] If the flat metal product according to the invention is intended, for example, for an outer skin application in vehicle construction, a further characteristic value can be taken into account: the arithmetic mean waviness Wsa is > 0 pm and in particular a maximum of 0.30 pm, preferably a maximum of 0.25 pm, preferably a maximum of 0.20 pm, further preferably a maximum of 0.15 pm, further preferably a maximum of 0.13 pm.

[0047] The waviness assumes small values, especially at higher roughness. The ratio of the arithmetic mean waviness Wsa to the arithmetic mean roughness Ra is preferably less than 0.3, preferably less than 0.25, and particularly preferably less than 0.2.

[0048] The characteristic values ​​are essentially to be understood as averages over the respective bottom and / or top side of the skin-passed (coated) flat metal product. The flat metal product according to the invention is a skin-passed and / or straightened flat metal product.

[0049] The flat metal product according to the invention can be a steel sheet, either uncoated or preferably coated. If the steel sheet is coated, the coating of the coated steel sheet comprises a metallic coating.

[0050] According to one embodiment, the steel sheet is coated with a zinc-based coating which is applied by hot-dip coating. In addition to zinc and unavoidable impurities, the coating can contain additional elements such as aluminum with a content of up to 8 wt.%, in particular up to 5 wt.% and / or magnesium with a content of up to 8 wt.%, in particular up to 5 wt.%. Steel sheets with a zinc-based coating have very good cathodic corrosion protection and have been used in automobile construction for years. If improved corrosion protection is required, the coating additionally contains magnesium with a content of at least 0.3 wt.%, in particular at least 0.6 wt.%, preferably at least 0.9 wt. Aluminum can be used alternatively or in addition to magnesium with a content of at least 0.1 wt.%, in particular at least 0.3 wt.-% in order to, for example, improve the bonding of the coating to the steel sheet and, in particular, to substantially prevent diffusion of iron from the steel sheet into the coating during heat treatment of the coated steel sheet, so that, for example, good adhesive suitability can be ensured. The thickness of the coating on each side can be between 1.5 and 30 pm, in particular between 2 and 20 pm, preferably between 3 and 15 pm. Below the minimum limit, sufficient cathodic corrosion protection cannot be guaranteed, and above the maximum limit, joining problems can arise when connecting the steel sheet according to the invention or a component made therefrom to another component. In particular, if the thickness of the coating exceeds the specified maximum limit, a stable process cannot be ensured during thermal joining or welding.

[0051] If the coating contains magnesium and aluminum in addition to zinc and unavoidable impurities, the coating or coating is known in the technical world as zinc-magnesium, ZM or Zn-Al-Mg.

[0052] In a preferred variant, the aluminum content of the melt is 1.1 to 8 wt.%, in particular 1.2 to 5 wt.%. In a preferred variant, the magnesium content of the melt is 1.1 to 8 wt.%, in particular 1.2 to 5 wt.%.

[0053] The coating may also contain only zinc with small amounts of aluminum in addition to unavoidable impurities, also known by the designation “Z” in technical circles.

[0054] As unavoidable impurities, for example, elements from the group silicon, antimony, lead, titanium, calcium, manganese, tin, lanthanum, cerium and chromium may be present individually or in combination with a total of up to 0.5 wt.%, in particular up to 0.3 wt.% in the coating.

[0055] The tempering process for providing a steel sheet with a metallic coating coated by hot-dip coating is usually carried out after coating, i.e. the embossing of a surface texture on the top and / or bottom of the steel sheet takes place on the coated steel sheet.

[0056] According to an alternative embodiment, the steel sheet is coated with a zinc-based coating applied by electrolytic plating. The thickness of the coating per side can be between 1.5 and 20 μm, in particular between 2 and 15 μm, preferably between 3 and 12 μm.

[0057] According to a further alternative embodiment, the steel sheet is coated with a zinc- or aluminum-based coating applied by PVD coating. The thickness of the coating per side can be between 1.5 and 20 μm, in particular between 2 and 15 μm, preferably between 3 and 12 μm.

[0058] When providing a steel sheet with a metallic coating coated by electrolytic coating or PVD coating, the skin passing process is usually carried out before coating, i.e. the embossing of a surface structure on the top and bottom of the steel sheet takes place on the uncoated steel sheet.

[0059] According to another alternative embodiment, the steel sheet is coated with an aluminum-based coating. In addition to aluminum and unavoidable impurities, the coating may contain up to 15 wt.% Si, optionally up to 4 wt.% Fe, and optionally up to 1.0 wt.% alkali or alkaline earth metals.

[0060] In a preferred variant, the silicon content is either 0.2 to 4.5 wt% or 7 to 13 wt%, in particular 8 to 11 wt%.

[0061] In a preferred variant, the optional iron content comprises 0.2 to 4.5 wt.%, in particular 1 to 4 wt.%, preferably 1.5 to 3.5 wt.%.

[0062] In a preferred variant, the optional content of alkali or alkaline earth metals comprises 0.01 to 1.0 wt.% magnesium, in particular 0.1 to 0.7 wt.% magnesium, preferably 0.1 to 0.5 wt.% magnesium. Furthermore, the optional content of alkali or alkaline earth metals can in particular comprise at least 0.0015 wt.% calcium.

[0063] According to another alternative embodiment, the steel sheet is coated with an aluminum-based coating. In addition to aluminum and unavoidable impurities, the coating may contain 2 to 24 wt.% zinc, 1 to 7 wt.% silicon, optionally 1 to 8 wt.% magnesium if the silicon content is between 1 and 4 wt.%, and optionally up to 0.3 wt.% lead, nickel, zirconium, or hafnium.

[0064] As unavoidable impurities, for example, elements from the group antimony, lead, titanium, manganese, tin, lanthanum, cerium and chromium may be present individually or in combination with a total of up to 0.5 wt.%, in particular up to 0.3 wt.% in the coating.

[0065] Sheet steel consists of a steel material that, in addition to iron and unavoidable impurities, contains alloying elements such as carbon, silicon, manganese, and aluminum. Other components, such as titanium, chromium, boron, and / or chromium, may also be included individually or in combination, depending on the application and strength class. Experts know which steel materials are suitable for the production of cold-formed and indirectly hot-formed components, depending on their application, particularly in automotive construction.

[0066] Alternatively, the (dressed) flat metal product can also be an aluminum sheet. According to a second teaching, the invention relates to a component produced by cold forming from a flat metal product according to the invention made of a steelZ alloy or aluminumZ alloy.

[0067] The component can be an outer skin part that can be used in automotive construction. Thus, the outer skin part is intended for moving parts such as doors and hatches, but also for vehicle roofs, fenders, etc. Alternatively, the component can also be a structural part for automotive construction. Use in the chassis area is also conceivable.

[0068] According to a third teaching, the invention relates to a component produced by indirect hot forming from a flat metal product according to the invention made of steelZ alloy.

[0069] The component can be a structural part that can be used in automotive construction. Thus, the structural part is part of the body, such as pillars (B-pillars), side members, and cross members (including bumpers).

[0070] According to one embodiment of the component according to the invention, the component is painted.

[0071] Skin-passed flat metal products according to the invention offer advantages for forming compared to the state of the art. This was demonstrated using the so-called multi-frottement test (MFT). Different steel sheets (interstitial free steel IF, bake-hardening steel BH, and dual-phase steel DP) with a thickness of 0.6 mm to 0.7 mm and different hot-dip coated coatings (Z and ZM) with a thickness of 7 μm per side were skin-passed on both sides using different skin-pass rolls (different structures), with the degree of skin-passing ranging between 1% and 1.5%. The surface textures produced on the coated steel sheet with the different skin-pass rolls exhibit, on average, the characteristic values ​​listed in Table 1.

[0072] The surfaces of samples 1 to 6 correspond to the state of the art. Sample 1 (IF with Z) and sample 2 (BH with Z) have a stochastic texture according to the teaching of EP 2 006 037 B1, whereby the surfaces of the skin-passing rolls were processed using an EDT texturing process followed by superfinishing (SF). For sample 3 (BH with ZM), an EDT skin-passing roll without SF was used. Samples 4 (IF with Z), 5 (DP with Z), and 6 (BH with ZM) have a deterministic texture in the form of a checkerboard pattern, whereby the surfaces of the skin-passing rolls were produced using pulsed laser texturing according to the teaching of EP 2 892 663 B1. Table

[0073] Samples 7 (IF with Z), 8 (DP with Z), and 9 (BH with Z) have a repeating pattern with the "triangle" texture according to the teaching of this invention. Samples 10 (IF with Z), 11 (DP with Z), and 12 (BH with Z) have a repeating pattern with the "trapezoid" texture according to the teaching of this invention. Samples 13 (IF with Z), 14 (DP with Z), 15 (BH with Z), and 16 (DP with ZM) have a repeating pattern with the "hexagon" texture according to the teaching of this invention.

[0074] The MFT, also known as the Renault test, is a common method for investigating the abrasion behavior of surfaces. Based on the test specification "Renault D31 1738 / C," a strip of the material to be tested is repeatedly pulled between a flat and a round friction jaw with a diameter of 20 mm. The tool sets are made of material 1.3342 with a hardness > 60HRC and a grinding roughness Ra of 0.1 μm. Due to the line contact, the round friction jaw leads to a higher surface pressure on the specimens. For the test, five test strips each of specimens 1 to 10, measuring 700 x 50 mm, were used. 2 cut, cleaned, degreased and coated with a lubricant PL 3802 S with 1.5 g / m 2 The strips were clamped one after the other in the clamping device and pulled by the two friction jaws over a measuring distance of 50 mm. The test speed was 5 mm / s, and the contact pressure or normal force FN was kept constant at 5 kN throughout the test. The required tensile forces F D The stroke and displacement were recorded during the test at a recording rate of 10 Hz. The process was repeated five times for each strip at the same location without cleaning the tool or strip. After the five strips had been drawn through the tool five times, the tool was inspected for abrasion and wear.

[0075] The coefficient of friction

[0076] _ F L(N) 2F Nwas determined as an average value for each strip in the nth pass. The friction coefficient Pi varied slightly between 0.11 and 0.14 in the first pass, regardless of the zinc coating from the melt (Z or ZM). For the same texture (EDT, double-I, etc.), the variants with higher roughness, cf. Ra value in Table 1, have a higher friction coefficient, see Table 2.

[0077] In the fifth pass, the friction coefficients p5 differ more significantly, with values ​​between 0.08 and 0.21. The higher the arithmetic mean roughness Ra, the lower the p-values ​​for the respective texture, see Table 2. For samples with state-of-the-art Z-coating (Double I or EDT), friction increases continuously after the second pass at the latest. The ZM coating alone leads to steadily decreasing p-values ​​for these textures. Table 2

[0078] The surfaces according to the invention can reduce the increase in friction. Especially with the "triangle" texture, friction decreases steadily with each pass, despite the zinc coating (Z) from the melt. The test shows that, in addition to the coating, the texture of the sheet surface can also have a significant influence on friction in coated flat metal products.

[0079] For this reason, sections of the surfaces of the examined strips in the MFT were recorded using confocal microscopy before the first and after the third and fifth pass in order to analyze the surface changes.

[0080] Figure 1 compares the surfaces with zinc coating (Z) from the melt after the third and fifth pass with the non-drawn surface. It is clearly visible that the original texture of the "Double-I" is no longer recognizable immediately after the third pass. In the "EDT" case, certain coarser depressions remain, which can serve as lubrication pockets and for the collection of abrasion particles. After further loading, deeper grooves or score lines formed in the surface.

[0081] In contrast, surfaces with a zinc-based coating from the melt with aluminum and magnesium additives (ZM) performed very robustly in the MFT. For all textures, even EDT and "double I," the structures did not completely disappear after the fifth pass, and no scoring was observed.

[0082] The inventive designs demonstrate significantly greater robustness and thus offer advantages for surfaces (coatings) that are otherwise highly prone to abrasion. This behavior was demonstrated on aluminum-coated steel sheet as well as aluminum sheet as a flat metal product, with the inventive surface textures also performing better than the "EDT" and "Double-I" textures.

[0083] The leveling of the essentially rough surface by contact with the smooth tool surface is delayed, so that a larger reservoir for the amount of lubricant is available, which leads to lower friction and fewer cold welds on the tool surfaces in contact with the sheet during forming.

[0084] It has been shown that textures with greater depth and whose recesses have a larger cross-section are more durable upon contact with the tool. From this, it can be concluded that the product ^resist T v ' -m—v should be as large as possible so that a surface is resistant to complete leveling and thus advantageous against adhesion or abrasion.

[0085] The texture pattern does not necessarily have to be a triangle or hexagon or equivalent contours such as a hexalobular socket or trefoil, but can also be a polygon with several corners, provided that the geometric specifications of the surface texture according to the invention are adhered to.

[0086] Figure 2 shows how the friction coefficient p5 in the fifth pass of the MFT changes depending on the parameter A reSiSt , the product of the mountain-to-valley height difference d m-vand mean distance to the valley edge r v , see characteristic values ​​in Tables 1 and 2, for Z and ZM. For the individual points in the shown coordinate system, a polygonal line for Z and a best-fit line for ZM were determined.

[0087] In Figures 3 and 4, two exemplary texture patterns, namely for the “triangle” A, see Figure 3, and for the “hexagon” A, see Figure 4, are shown the geometric relationships for determining the characteristic values ​​r m or r v and r mjmax or r v , max . The characteristic value r m , max is the inner radius of the largest mountain, so to speak the maximum inner radius of the mountains and corresponds to the largest distance between two depressions (A), as shown in Figures 3 and 4. The characteristic value r v>max is the inner radius of the largest valley, so to speak, the maximum inner radius of the valleys. The characteristic values ​​r m or r vcorrespond to the mean values ​​of all distances to the mountain edge or valley edge, particularly on the investigated measuring area. The texture is based on a recurring pattern, thus a deterministic pattern, arranged in a grid R. The underlying grid R consists of hexagonal shapes, Figure 3 and Figure 4, with a side length S in the range of 50 pm to 500 pm. M is the center of gravity / center of a depression A. Between the depressions A, webs are arranged, or the webs separate the individual depressions A from each other. The width of the webs, viewed in longitudinal extension, can vary between > 0 pm and r m>max The arrow shown symbolizes the dressing direction.

[0088] Figure 5 shows, as an example, a surface of a skin-passed metal flat product measured using confocal microscopy. The design essentially corresponds to a hexagonal depression A. However, due to the influence of the laser during structuring of the skin-pass roll, this cannot be created as a straight line, but rather from overlapping laser shots, resulting in a texture reminiscent of a hexagon socket or Torx texture, see also Figure 1, lower illustration. In this example, a texture depth of 3.89 pm, an arithmetic mean roughness Ra of 0.95 pm, a peak count RPc of 67 1 / cm, and an arithmetic mean waviness Wsa of 0.08 pm were determined. The material content M r was 40%. This resulted in a mountain-to-valley height difference of d m.v of 1.98 pm. The maximum inner radius of the mountain r m.max was 21.9 pm and the maximum inner radius of the valley r v , max was 51.2 pm. The mean distance to the mountain edge r m with 7.5 pm and the mean distance to the valley edge r v At 15.7 pm, the diameter was approximately one-third smaller than the maximum inner radii. The triangle texture would be more similar to a trefoil or tresfoil texture, see "triangle" in Figure 1.

Claims

Patent claims 1. Flat metal product with a texture on the top and / or bottom of the flat metal product having a mean height difference from peak to valley d m-v and a medium distance to the valley edge r VJ characterized by the fact that the product is made by d m.v and r v at least 18 pm 2 amounts.

2. Metal flat product according to claim 1, wherein the texture consists of depressions (A) and with ribs arranged between the depressions (A), wherein the texture is based on a repeating pattern which is arranged in a grid (R).

3. Metal flat product according to any of the preceding claims, wherein the texture has an arithmetic mean roughness Ra between at least 0.50 pm and at most 5.0 pm.

4. Metal flat product according to any of the preceding claims, wherein the texture has a peak count RPc between at least 30 1 / cm and at most 200 1 / cm.

5. Metal flat product according to one of the preceding claims, wherein the texture has a mean distance to the valley edge r v between at least 4 pm and at most 40 pm.

6. Metal flat product according to one of the preceding claims, wherein the texture has a mean distance to the mountain edge r m between at least 4 pm and at most 40 pm.

7. Metal flat product according to one of the preceding claims, wherein the metal flat product is a steel sheet and coated with a metallic coating.

8. Metal flat product according to any one of claims 1 to 6, wherein the metal flat product is an aluminum sheet.

9. Metal flat product according to claim 7, wherein the steel sheet is coated with a zinc-based coating applied by hot-dip coating. A flat metal product according to claim 7, wherein the steel sheet is coated with a zinc-based coating applied by electrolytic coating. A flat metal product according to claim 7, wherein the steel sheet is coated with a zinc-based or aluminum-based coating applied by PVD coating. A flat metal product according to claim 7, wherein the steel sheet is coated with an aluminum-based coating applied by hot-dip coating. A flat metal product according to any one of the preceding claims, wherein the arithmetic mean ripple Wsa with > 0 pm and a maximum of 0.30 pm is considered as a further characteristic value. A component manufactured by cold forming a flat metal product according to any one of claims 1 to 11. A component according to claim 14, wherein the component is an outer skin part. A component manufactured by hot forming a steel sheet according to claim 1, 7, or 12.Component according to claim 14, wherein the component is a structural part. Component according to any one of claims 14 to 17, wherein the component is painted.

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