WO2015124322A1 - Activation treatment of coated steel substrates - Google Patents

Activation treatment of coated steel substrates Download PDF

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Publication number
WO2015124322A1
WO2015124322A1 PCT/EP2015/025006 EP2015025006W WO2015124322A1 WO 2015124322 A1 WO2015124322 A1 WO 2015124322A1 EP 2015025006 W EP2015025006 W EP 2015025006W WO 2015124322 A1 WO2015124322 A1 WO 2015124322A1
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Prior art keywords
steel
phosphate
zinc
siloxane
coated
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PCT/EP2015/025006
Other languages
French (fr)
Inventor
Robert Bleeker
Jurgen Wilhelmus Vrenken
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Tata Steel Ijmuiden B.V.
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Publication of WO2015124322A1 publication Critical patent/WO2015124322A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
    • C09D183/14—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers in which at least two but not all the silicon atoms are connected by linkages other than oxygen atoms
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
    • C23C18/122—Inorganic polymers, e.g. silanes, polysilazanes, polysiloxanes
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/125—Process of deposition of the inorganic material
    • C23C18/1254—Sol or sol-gel processing
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/78—Pretreatment of the material to be coated
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/78—Pretreatment of the material to be coated
    • C23C22/80—Pretreatment of the material to be coated with solutions containing titanium or zirconium compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/22—Polysiloxanes containing silicon bound to organic groups containing atoms other than carbon, hydrogen and oxygen
    • C08G77/26—Polysiloxanes containing silicon bound to organic groups containing atoms other than carbon, hydrogen and oxygen nitrogen-containing groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/48—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule in which at least two but not all the silicon atoms are connected by linkages other than oxygen atoms
    • C08G77/50—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule in which at least two but not all the silicon atoms are connected by linkages other than oxygen atoms by carbon linkages
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
    • C23C2222/20—Use of solutions containing silanes

Definitions

  • the present invention relates to a zinc coated cold formable cold rolled steel substrate provided with an activating layer for phosphating.
  • the invention also relates to a method for producing a part made from the coated substrate, to a method for producing an article comprising a part made from the coated substrate and to the article thus produced.
  • Galvanised steel strips and sheets are well known, and in the automotive industry they are formed into parts and then assembled into automotive articles such as automotive bodies.
  • the automotive article is alkaline cleaned to remove oil and dirt resulting from the aforementioned forming and assembly processes.
  • the cleaned automotive article is then subjected to an activating treatment. This typically involves dipping the automotive article in a Ti phosphate containing activating solution. Alternatively, the automotive article may be sprayed with the activating solution.
  • the purpose of the activating treatment is to increase the number of sites on the galvanised surface where phosphate crystals can form during a phosphate treatment that follows the activating treatment.
  • the purpose of the phosphate coating is to provide additional corrosion protection and to prepare the automotive body for subsequent processing steps such as electro-coating and painting.
  • the performance of the phosphate coating largely depends on the size and orientation of the phosphate crystals that form on the galvanised surface, with a smaller crystal size generally leading to greater improvements in corrosion resistance and paint adhesion.
  • the size of the phosphate crystals may be controlled by selecting an appropriate zinc phosphate solution.
  • Nickel-containing zinc phosphate solutions are particularly suitable for obtaining phosphate layers that exhibit good corrosion resistance and paint adhesion.
  • a drawback of using nickel- containing zinc phosphate solutions is that nickel is carcinogenic and therefore harmful to human health. While nickel-free zinc phosphate solutions may be used, this generally results in larger phosphate crystals being formed at the galvanised surface. Consequently, only minor improvements in corrosion resistance and paint adhesion are observed.
  • a coated substrate for phosphating which comprises a strip or sheet made of cold formable cold rolled steel, a zinc coating provided on the strip or sheet, and an activating layer provided on the zinc coating, wherein the activating layer comprises a siloxane or a polysiloxane and has a thickness corresponding to 1-10 mg/m 2 Si.
  • siloxane or polysiloxane coated strip or sheet was very suitable for cold-forming. It was found that the siloxane or polysiloxane coated steel exhibited reduced friction during severe drawing conditions and consequently less galling compared to a bare zinc coated substrate. The siloxane or polysiloxane coated steel also exhibited improved adhesive bonding behaviour relative to a bare zinc coated substrate. It was also found that the siloxane or polysiloxane coated steel exhibited comparable weldability to that of a bare zinc coated steel substrate. Thus, the siloxane or polysiloxane coated steel can be used to manufacture automotive parts comprising two or more parts as well as automotive bodies formed from those parts.
  • the siloxane or polysiloxane coated strip or sheet was also very suitable for phosphating.
  • phosphate coatings exhibiting very good corrosion resistance and paint adhesion were obtained when provided on the siloxane or polysiloxane coated steel strips or sheets.
  • the zinc coating consists of zinc and unavoidable impurities.
  • the steel has a composition in weight% of:
  • Steel types having a composition within these ranges are generally used for cold forming operations.
  • the steel has a tensile strength of at most 600 MPa.
  • the steel is selected from an Interstitial Free steel (IF-steel), a bake hardenable steel or a dual phase steel (DP steel). These steel types are frequently used in the automotive industry for parts that are bonded to other parts.
  • IF-steel Interstitial Free steel
  • DP steel dual phase steel
  • the zinc coating on the steel has a thickness of 20 - 140 g/m 2 on each side. These zinc thicknesses are generally used in the automotive industry on steel and afford good corrosion protection top the steel sheet or strip.
  • the siloxane or polysiloxane activating layer has a layer thickness corresponding to 1 - 8 mg/m 2 Si, preferably 1 - 5 mg/m 2 Si. It has been found that with these reduced thicknesses, the advantages are retained, while it is preferred to use thin layers from an economic perspective.
  • the siloxane or polysiloxane is formed from a bis- tri(m)ethoxysilylalkane, preferably a bis-triethoxysilylethane (BTSE), and preferably in combination with another silane such as y-aminopropyltriethoxysilane (yAPS), bis- aminosilane (BAS), bis-diaminosilane (BDAS), vinyltriacetoxysilane (VTAS), y- ureidopropyl-trimethoxysilane (yUPS) and/or bis-trimethoxysilylpropylurea (BUPS).
  • silane chemicals can be used as a water based solution that is relatively easy to apply on a zinc coated steel strip or sheet. In water the silane chemicals will hydrolyze to form silanols.
  • the siloxane or polysiloxane layer is covered by an oil.
  • Zinc coated strip is usually provided with a thin layer of oil before it is supplied to the automotive industry.
  • the invention relates to a method for manufacturing a coated steel part. The method comprises the steps of applying a water based silane or silanol solution on a zinc coated cold formable cold rolled steel strip or sheet, drying and/or curing the applied solution to form a siloxane or polysiloxane activating layer having a thickness corresponding to 1-10 mg/m 2 Si on the zinc coating, cutting a blank from the coated strip or sheet and cold forming the blank into a part.
  • siloxane or polysiloxane activating layer exhibited good adhesion to the zinc coating and did not substantially adhere to the cold-forming apparatus. Thus, tool pollution was kept to a minimum.
  • the siloxane or polysiloxane coated steel strip or sheet also exhibited good galling behaviour.
  • the water based silane or silanol solution comprises a fluoride, preferably hydrogen fluoride, fluorosilicic acid, fluorozirconic acid and/or fluorotitanic acid.
  • fluorides are added to improve the adhesion of the siloxane or polysiloxane layer to the zinc coating.
  • the invention relates to a method for manufacturing an article that comprises one or more cold formed parts made from the coated steel strip or sheet according to the first aspect of the invention or produced according to the method of the second aspect of the invention, wherein the article is contacted with a zinc phosphate solution to form a phosphate coating on the article.
  • Immersing the article in a zinc phosphate solution is a very suitable means for providing a phosphate coating on the article.
  • Spraying is also a suitable means for providing a phosphate coating on the article since this typically results in a faster manufacturing process.
  • the zinc phosphate solution contains Fe, Mg, Mn,
  • the article is subjected to an activation treatment before contacting the article with a zinc phosphate solution.
  • Ti-containing activating solutions are particularly preferred.
  • the siloxane or polysiloxane coated article was treated with an activating solution prior to phosphating, it is understood that the siloxane or polysiloxane material enhanced the initiating effect of the activating solution on phosphate deposition and also contributed to reducing phosphate crystal size.
  • the article is cleaned with an alkaline solution before the activation treatment, preferably the pH of the alkaline solution is between pH 9 and pH 1 1. It was found that when the article comprising the siloxane or polysiloxane coating was cleaned prior to phosphating, that at least part of the siloxane or polysiloxane coating was removed from the zinc coated surface. Nevertheless, the remaining siloxane or polysiloxane material helps initiate the phosphate deposition reaction such that a phosphate coating is deposited on the remaining siloxane or polysiloxane material and the zinc coating.
  • the invention relates to a phosphate coated article, which comprises one or more cold formed steel parts made from the coated steel strip or sheet according to the first aspect of the invention or produced according to the method of the second aspect of the invention, a zinc coating provided on the steel part, a siloxane or polysiloxane material provided on the zinc coating and a phosphate coating provided on the siloxane or polysiloxane material and the zinc coating.
  • the siloxane or polysiloxane coated steel was very suitable for phosphating and exhibited good corrosion protection and paint adhesion after phosphating.
  • This improvement has been attributed to the reduction in phosphate crystal size that was obtained when phosphate coatings were provided on the siloxane or polysiloxane material.
  • the reduced crystal size has the effect of reducing porosity within the phosphate coating and improving the surface coverage of the coating on the article.
  • the siloxane or polysiloxane material contributes to a more epitaxial growth of the phosphate crystals. In this way the zinc coated steel surface is better protected against early corrosion.
  • a further effect of providing a phosphate coating on the siloxane or polysiloxane coated steel is that phosphate coatings with reduced coating weights can be obtained.
  • the reduced coating weight does not adversely affect the corrosion protective properties and the paint adhesion properties of the phosphate coating. This means that in order to obtain a certain phosphate performance, e.g. in terms of corrosion resistance, less phosphate is required when phosphating siloxane or polysiloxane coated steels compared to the amount of phosphate that is required when phosphating equivalent zinc coated steels without the siloxane or polysiloxane coating. This results in a less expensive manufacturing process.
  • the phosphate coating comprises phosphate crystals having a reduced size dimension.
  • the phosphate coating comprises phosphate crystals having a size dimension that is reduced by at least 50% relative to the size of phosphate crystals that were deposited onto zinc coated surfaces without the siloxane or polysiloxane material. It is preferred that such a phosphate coating comprises phosphate crystals having a size dimension of less than 3 pm, preferably a size dimension of 1-2 pm.
  • a paint layer is provided on the phosphate coating. It was found that the phosphate coated article exhibited good adhesion to a subsequently applied paint layer.
  • the paint layer is an electro-coating.
  • the article is an automotive article, preferably an automotive body.
  • Such phosphated articles are particularly suitable for use in motor vehicles such as cars and trucks.
  • Figure 1 shows the friction behaviour of zinc coated steels with and without a siloxane coating.
  • a cold rolled steel having a gauge of 0.7 mm was provided and then hot-dip galvanised to form a zinc coating on the steel.
  • the zinc coating was provided in a continuous hot-dip galvanising line where the zinc coating thickness was regulated by nitrogen wiping to about 70 mg/rn 2 per side (approximately 10 pm per side).
  • the zinc coated steel was then temper rolled with about 0.8 % elongation.
  • a water based solution was prepared by mixing bis-triethoxysilylethane (BTSE) and aminopropyltriethoxysilane (APS), and subsequently applying this mixture onto the zinc coated steel with a chem. Coater.
  • the (poly)siloxane layer had a thickness of 2 mg/m 2 Si after drying and/or curing.
  • the results of the linear friction test are shown in Figure 1.
  • the solid line relates to the bare zinc coated steel substrate, while the dashed line relates to a the zinc coated steel substrate provided with the siloxane coating.
  • the results show that it takes more time for the siloxane treated zinc coated steel samples to start galling (increased friction). After 6 passes the friction of the siloxane treated zinc coated steel is, on average, 0.05 pm less than that of the bare zinc coated steel. Consequently, less galling and less tool pollution is expected when siloxane treated zinc coated steel sheets are subjected to forming operations.
  • Zinc coated steel samples with and without siloxane (2mg/m 2 Si) were prepared and evaluated for their adhesive bonding behaviour.
  • the test was carried out in accordance with the StahlEisen SEP 1 160 Part 5 procedure:
  • Adhesive thickness 0.2 to 0.3 mm, controlled using glass beads
  • the adhesive used was Betamate 1496V of DOW Chemical. After tensile testing the samples were evaluated for their strength upon failure, energy absorption, as well as the amount and type of failure (adhesive/cohesive). The bond can break in the adhesive (cohesive failure), which is the preferred failure mode. It can also break between the adhesive and the metallic coating (adhesive failure), which is less favourable. Often, the broken bond shows a combination of both failure modes, and the amount of each is estimated visually (in % of the overlap area).
  • the results of the lap shear test are shown in Table 1.
  • the results show that the siloxane treated zinc coated sample (1 b) exhibits improved bond strength and energy absorption properties relative to the zinc coated steel (1 a). This means that more time is required in order to break the adhesive bond.
  • the results show that the failure mode for sample (1 b) is cohesive (100%), whereas the failure mode observed for sample (1a) was 40% cohesive and 60% cohesive. Having 100% cohesive failure is an important demand of some automotive manufacturers.
  • Zinc coated steel samples (100x200 mm), with and without the siloxane coating (2 mg/m 2 Si) were phosphated according to automotive standards.
  • the samples were cleaned with a standard automotive alkaline cleaner (GC S5176), rinsed with water, activated and then phosphated. The samples were rinsed again to remove excess phosphate and subsequently dried.
  • Two commercially available phosphate solutions were used, (1 ) GB 26S and (2) Granodine SX35.
  • the activating solution and phosphate solutions (1 ) and (2) were provided by Chemetall. Table 3 shows the type and amount of zinc phosphate that was deposited on zinc coated samples with and without siloxane.
  • the phosphate coating weight was measured by dissolving a phosphated zinc coated sample in hydrochloric acid. The phosphorous content in the acidic solution was then determined using Ion Conductive Plasma (ICP) analysis. The value obtained was then used to calculate the original zinc phosphate weight.
  • the amount of phosphate deposited on the siloxane coated samples (3b and 3d) is approximately 10% less than the amount of phosphate deposited on the corresponding bare zinc coated samples (3a and 3c). This means that less phosphate is required to manufacture phosphated zinc coated steel when the coated steel additionally comprises a siloxane coating.
  • the phosphate coatings were also analysed with a secondary electron microprobe (SEM) to determine phosphate crystal size and the morphology of the phosphate coating. It was found that the size of phosphate crystals on the siloxane coated samples (3b and 3d) were up to two times smaller than the size of phosphate crystals that were deposited onto the bare zinc coated sample (3a and 3c). Phosphate coatings having smaller phosphate crystals are attractive to automotive manufacturers since thin and less expensive phosphate coatings may be obtained. Furthermore, phosphate crystals that were deposited onto siloxane coated samples often exhibited improved epitaxial growth relative to those deposited onto bare zinc coated steel samples, resulting in better surface coverage and therefore improved corrosion resistance properties.
  • SEM secondary electron microprobe

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Abstract

The invention relates to a coated substrate for phosphating, which comprises a strip or sheet made of cold formable cold rolled steel, a zinc coating provided on the strip or sheet, and an activating layer provided on the zinc coating, wherein the activating layer comprises a siloxane or a polysiloxane and has a thickness corresponding to 1-10 mg/m2 Si.

Description

ACTIVATION TREATMENT OF COATED STEEL SUBSTRATES
The present invention relates to a zinc coated cold formable cold rolled steel substrate provided with an activating layer for phosphating. The invention also relates to a method for producing a part made from the coated substrate, to a method for producing an article comprising a part made from the coated substrate and to the article thus produced.
Galvanised steel strips and sheets are well known, and in the automotive industry they are formed into parts and then assembled into automotive articles such as automotive bodies. The automotive article is alkaline cleaned to remove oil and dirt resulting from the aforementioned forming and assembly processes. The cleaned automotive article is then subjected to an activating treatment. This typically involves dipping the automotive article in a Ti phosphate containing activating solution. Alternatively, the automotive article may be sprayed with the activating solution. The purpose of the activating treatment is to increase the number of sites on the galvanised surface where phosphate crystals can form during a phosphate treatment that follows the activating treatment. The purpose of the phosphate coating is to provide additional corrosion protection and to prepare the automotive body for subsequent processing steps such as electro-coating and painting.
The performance of the phosphate coating largely depends on the size and orientation of the phosphate crystals that form on the galvanised surface, with a smaller crystal size generally leading to greater improvements in corrosion resistance and paint adhesion. The size of the phosphate crystals may be controlled by selecting an appropriate zinc phosphate solution. Nickel-containing zinc phosphate solutions are particularly suitable for obtaining phosphate layers that exhibit good corrosion resistance and paint adhesion. However, a drawback of using nickel- containing zinc phosphate solutions is that nickel is carcinogenic and therefore harmful to human health. While nickel-free zinc phosphate solutions may be used, this generally results in larger phosphate crystals being formed at the galvanised surface. Consequently, only minor improvements in corrosion resistance and paint adhesion are observed. It is also known that reductions in phosphate crystal size can be obtained by immersing the automotive article in a zinc phosphate solution, i.e. by dipping. However, compared to treatments where the automotive article is sprayed with a zinc phosphate solution, such dip-treatments are more time consuming, leading to longer processing times and reduced production volumes. An additional drawback of current phosphating processes is that the design of certain automotive articles does not always allow critical areas of the article to be activated and phosphated. Thus, these areas often exhibit reduced corrosion protection properties with respect to other areas of the automotive article.
It is an object of the invention to provide a galvanised steel strip or sheet that is suitable for subsequent processing steps such as cold-forming.
It is an object of the invention to provide a means for reducing the size of phosphate crystals that form on galvanised steel surfaces during a phosphate treatment.
It is an object of the invention to provide a means for increasing the formation and surface coverage of phosphate crystals on galvanised steel surfaces during a phosphate treatment.
It is another object of the invention to improve the corrosion resistance of a phosphate coated galvanised steel substrate.
It is also an object of the invention to improve the adhesion between a phosphate coated galvanised steel substrate and a paint system provided thereon.
It is a further object of the invention to provide an environmentally acceptable and cost-effective method for manufacturing phosphate coated steel substrates.
One or more of the above objects is reached by providing a coated substrate for phosphating, which comprises a strip or sheet made of cold formable cold rolled steel, a zinc coating provided on the strip or sheet, and an activating layer provided on the zinc coating, wherein the activating layer comprises a siloxane or a polysiloxane and has a thickness corresponding to 1-10 mg/m2 Si.
It was found that the siloxane or polysiloxane coated strip or sheet was very suitable for cold-forming. It was found that the siloxane or polysiloxane coated steel exhibited reduced friction during severe drawing conditions and consequently less galling compared to a bare zinc coated substrate. The siloxane or polysiloxane coated steel also exhibited improved adhesive bonding behaviour relative to a bare zinc coated substrate. It was also found that the siloxane or polysiloxane coated steel exhibited comparable weldability to that of a bare zinc coated steel substrate. Thus, the siloxane or polysiloxane coated steel can be used to manufacture automotive parts comprising two or more parts as well as automotive bodies formed from those parts. The siloxane or polysiloxane coated strip or sheet was also very suitable for phosphating. In this respect, phosphate coatings exhibiting very good corrosion resistance and paint adhesion were obtained when provided on the siloxane or polysiloxane coated steel strips or sheets.
Preferably the zinc coating consists of zinc and unavoidable impurities.
In a preferred embodiment the steel has a composition in weight% of:
0.01 < C < 0.15 0.1 < Mn < 2.0
0.05 < Si < 0.5
Cr < 1.0
Al < 0.5
Mo < 0.2
Ti < 0.2
P < 0.1
N < 0.15
S < 0.05
B < 0.01
the remainder being Fe and unavoidable impurities.
Steel types having a composition within these ranges are generally used for cold forming operations.
In a preferred embodiment the steel has a tensile strength of at most 600 MPa. Preferably the steel is selected from an Interstitial Free steel (IF-steel), a bake hardenable steel or a dual phase steel (DP steel). These steel types are frequently used in the automotive industry for parts that are bonded to other parts.
In a preferred embodiment the zinc coating on the steel has a thickness of 20 - 140 g/m2 on each side. These zinc thicknesses are generally used in the automotive industry on steel and afford good corrosion protection top the steel sheet or strip.
In a preferred embodiment the siloxane or polysiloxane activating layer has a layer thickness corresponding to 1 - 8 mg/m2 Si, preferably 1 - 5 mg/m2 Si. It has been found that with these reduced thicknesses, the advantages are retained, while it is preferred to use thin layers from an economic perspective.
In a preferred embodiment the siloxane or polysiloxane is formed from a bis- tri(m)ethoxysilylalkane, preferably a bis-triethoxysilylethane (BTSE), and preferably in combination with another silane such as y-aminopropyltriethoxysilane (yAPS), bis- aminosilane (BAS), bis-diaminosilane (BDAS), vinyltriacetoxysilane (VTAS), y- ureidopropyl-trimethoxysilane (yUPS) and/or bis-trimethoxysilylpropylurea (BUPS). These silane chemicals can be used as a water based solution that is relatively easy to apply on a zinc coated steel strip or sheet. In water the silane chemicals will hydrolyze to form silanols.
Preferably the siloxane or polysiloxane layer is covered by an oil. Zinc coated strip is usually provided with a thin layer of oil before it is supplied to the automotive industry. According to a second aspect, the invention relates to a method for manufacturing a coated steel part. The method comprises the steps of applying a water based silane or silanol solution on a zinc coated cold formable cold rolled steel strip or sheet, drying and/or curing the applied solution to form a siloxane or polysiloxane activating layer having a thickness corresponding to 1-10 mg/m2 Si on the zinc coating, cutting a blank from the coated strip or sheet and cold forming the blank into a part. During cold forming it was found that the siloxane or polysiloxane activating layer exhibited good adhesion to the zinc coating and did not substantially adhere to the cold-forming apparatus. Thus, tool pollution was kept to a minimum. The siloxane or polysiloxane coated steel strip or sheet also exhibited good galling behaviour.
In a preferred embodiment the water based silane or silanol solution comprises a fluoride, preferably hydrogen fluoride, fluorosilicic acid, fluorozirconic acid and/or fluorotitanic acid. Such fluorides are added to improve the adhesion of the siloxane or polysiloxane layer to the zinc coating.
According to a third aspect, the invention relates to a method for manufacturing an article that comprises one or more cold formed parts made from the coated steel strip or sheet according to the first aspect of the invention or produced according to the method of the second aspect of the invention, wherein the article is contacted with a zinc phosphate solution to form a phosphate coating on the article. Immersing the article in a zinc phosphate solution is a very suitable means for providing a phosphate coating on the article. Spraying is also a suitable means for providing a phosphate coating on the article since this typically results in a faster manufacturing process.
In a preferred embodiment the zinc phosphate solution contains Fe, Mg, Mn,
Ca, Ti, Zr or Cu. These zinc phosphate solutions do not contain nickel and therefore the use of these phosphate solutions to coat the article results in an environmentally acceptable manufacturing process. It was found that very good corrosion resistance and paint adhesion could be obtained when the siloxane or polysiloxane coated steel was treated with a zinc phosphating solution that did not contain nickel. In this respect, the observed corrosion resistance and paint adhesion was comparable to that of uncoated galvanised steel substrates that were treated with nickel-containing zinc phosphate solutions.
In a preferred embodiment the article is subjected to an activation treatment before contacting the article with a zinc phosphate solution. Ti-containing activating solutions are particularly preferred. When the siloxane or polysiloxane coated article was treated with an activating solution prior to phosphating, it is understood that the siloxane or polysiloxane material enhanced the initiating effect of the activating solution on phosphate deposition and also contributed to reducing phosphate crystal size.
Preferably the article is cleaned with an alkaline solution before the activation treatment, preferably the pH of the alkaline solution is between pH 9 and pH 1 1. It was found that when the article comprising the siloxane or polysiloxane coating was cleaned prior to phosphating, that at least part of the siloxane or polysiloxane coating was removed from the zinc coated surface. Nevertheless, the remaining siloxane or polysiloxane material helps initiate the phosphate deposition reaction such that a phosphate coating is deposited on the remaining siloxane or polysiloxane material and the zinc coating. Advantageously, it was found that smaller phosphate crystals were obtained when the zinc phosphate solution was contacted with the siloxane or polysiloxane material on the zinc coated steel. It is preferred that at least 50 % of the siloxane or polysiloxane material remains on the zinc coated steel prior to phosphate deposition.
According to a fourth aspect, the invention relates to a phosphate coated article, which comprises one or more cold formed steel parts made from the coated steel strip or sheet according to the first aspect of the invention or produced according to the method of the second aspect of the invention, a zinc coating provided on the steel part, a siloxane or polysiloxane material provided on the zinc coating and a phosphate coating provided on the siloxane or polysiloxane material and the zinc coating. The siloxane or polysiloxane coated steel was very suitable for phosphating and exhibited good corrosion protection and paint adhesion after phosphating. This improvement has been attributed to the reduction in phosphate crystal size that was obtained when phosphate coatings were provided on the siloxane or polysiloxane material. The reduced crystal size has the effect of reducing porosity within the phosphate coating and improving the surface coverage of the coating on the article. It is also understood that the siloxane or polysiloxane material contributes to a more epitaxial growth of the phosphate crystals. In this way the zinc coated steel surface is better protected against early corrosion. A further effect of providing a phosphate coating on the siloxane or polysiloxane coated steel is that phosphate coatings with reduced coating weights can be obtained. Importantly, the reduced coating weight does not adversely affect the corrosion protective properties and the paint adhesion properties of the phosphate coating. This means that in order to obtain a certain phosphate performance, e.g. in terms of corrosion resistance, less phosphate is required when phosphating siloxane or polysiloxane coated steels compared to the amount of phosphate that is required when phosphating equivalent zinc coated steels without the siloxane or polysiloxane coating. This results in a less expensive manufacturing process.
In preferred embodiment the phosphate coating comprises phosphate crystals having a reduced size dimension. For instance, when the phosphate coating is provided on the article by a dipping process, the phosphate coating comprises phosphate crystals having a size dimension that is reduced by at least 50% relative to the size of phosphate crystals that were deposited onto zinc coated surfaces without the siloxane or polysiloxane material. It is preferred that such a phosphate coating comprises phosphate crystals having a size dimension of less than 3 pm, preferably a size dimension of 1-2 pm.
In a preferred embodiment a paint layer is provided on the phosphate coating. It was found that the phosphate coated article exhibited good adhesion to a subsequently applied paint layer. Preferably the paint layer is an electro-coating.
In a preferred embodiment the article is an automotive article, preferably an automotive body. Such phosphated articles are particularly suitable for use in motor vehicles such as cars and trucks.
The invention will now be elucidated with reference to the following non- limiting examples.
Figure 1 . shows the friction behaviour of zinc coated steels with and without a siloxane coating.
A cold rolled steel having a gauge of 0.7 mm was provided and then hot-dip galvanised to form a zinc coating on the steel. The zinc coating was provided in a continuous hot-dip galvanising line where the zinc coating thickness was regulated by nitrogen wiping to about 70 mg/rn2 per side (approximately 10 pm per side). The zinc coated steel was then temper rolled with about 0.8 % elongation.
To provide a (poly)siloxane coating on the zinc coated steel, a water based solution was prepared by mixing bis-triethoxysilylethane (BTSE) and aminopropyltriethoxysilane (APS), and subsequently applying this mixture onto the zinc coated steel with a chem. Coater. The (poly)siloxane layer had a thickness of 2 mg/m2 Si after drying and/or curing.
The following experiments were performed to determine certain performance characteristics of zinc coated steel substrates and zinc coated steel substrates that had been provided with the (poly)siloxane coating. Linear friction test
Linear friction tests were performed to investigate the friction and galling behaviour of zinc coated steel and zinc coated steel provided with the siloxane coating (2 mg/m2 Si). The tests were performed using one flat tool and one round tool to develop a high-pressure contact with the sample surface. The tool material used was DIN 1.3343. 1 g/m2 of Multidraw. PL61 of Zeller & Gmelin prelube oil was applied on the samples. For each material/lubrication system, strips of 50 mm width and 300 mm length were pulled at a speed 20 mm/min between a set of tools pushed together with a normal force of 5 kN. The strips were drawn through the tools six times (passes) along a testing distance of 55mm; after each stroke the tools were released and the strips returned to the original starting position in preparation for the next stroke. All tests were conducted at 20°C and performed in triplicate.
The results of the linear friction test are shown in Figure 1. The solid line relates to the bare zinc coated steel substrate, while the dashed line relates to a the zinc coated steel substrate provided with the siloxane coating. The results show that it takes more time for the siloxane treated zinc coated steel samples to start galling (increased friction). After 6 passes the friction of the siloxane treated zinc coated steel is, on average, 0.05 pm less than that of the bare zinc coated steel. Consequently, less galling and less tool pollution is expected when siloxane treated zinc coated steel sheets are subjected to forming operations.
Lap shear test
Zinc coated steel samples with and without siloxane (2mg/m2 Si) were prepared and evaluated for their adhesive bonding behaviour. The test was carried out in accordance with the StahlEisen SEP 1 160 Teil 5 procedure:
• Size of steel samples: 100 mm x 25 mm
• Cleaning: US degreased in heptane for 10 minutes
· Oil application (if applied): 2 g/m2 MULTIDRAW PL61 of Zeller&Gmelin
(standard automotive Prelube)
• Overlap: 10 mm
• Adhesive thickness: 0.2 to 0.3 mm, controlled using glass beads
• Excess adhesive removed before curing
· Cure: 15 minutes at 180°C object temperature
• Test length: 1 10 mm
• Test speed: 10 mm/min.
The adhesive used was Betamate 1496V of DOW Chemical. After tensile testing the samples were evaluated for their strength upon failure, energy absorption, as well as the amount and type of failure (adhesive/cohesive). The bond can break in the adhesive (cohesive failure), which is the preferred failure mode. It can also break between the adhesive and the metallic coating (adhesive failure), which is less favourable. Often, the broken bond shows a combination of both failure modes, and the amount of each is estimated visually (in % of the overlap area).
The results of the lap shear test are shown in Table 1. The results show that the siloxane treated zinc coated sample (1 b) exhibits improved bond strength and energy absorption properties relative to the zinc coated steel (1 a). This means that more time is required in order to break the adhesive bond. Moreover, the results show that the failure mode for sample (1 b) is cohesive (100%), whereas the failure mode observed for sample (1a) was 40% cohesive and 60% cohesive. Having 100% cohesive failure is an important demand of some automotive manufacturers.
Table 1
Figure imgf000009_0001
Weldability tests
The weldability of zinc coated steel with and without siloxane (2 mg/m2 Si) was checked according to test procedure SEP1220-2, i.e. only one growth curve has been established and CTS (cross tensile strength) and TSS (tensile shear strength) tests have been carried out. For the silane treated zinc coated steel sample, an electrode life test was additionally performed.
The results of the welding tests are shown in Table 2. The results show that the welding range (WR), CTS and TSS are largely the same for zinc coated steel (2a) and zinc coated steel provided with a siloxane coating (2b). Furthermore it has been found that sample (2b) exhibited about 1 150 welds (> 4 t = 3.5 mm), which is in the range of this type of zinc coated steel (ca. 1000 welds). Thus, the siloxane coating does not have a significant negative impact on weldability.
Table 2
Ref Sample WR (kA) TSS (kN) CTS (kN)
2a Gl 1.8 2.9 2.0
2b Gl + siloxane 1.5 2.7 2.0 Phosphatinq
Zinc coated steel samples (100x200 mm), with and without the siloxane coating (2 mg/m2 Si) were phosphated according to automotive standards. The samples were cleaned with a standard automotive alkaline cleaner (GC S5176), rinsed with water, activated and then phosphated. The samples were rinsed again to remove excess phosphate and subsequently dried. Two commercially available phosphate solutions were used, (1 ) GB 26S and (2) Granodine SX35. The activating solution and phosphate solutions (1 ) and (2) were provided by Chemetall. Table 3 shows the type and amount of zinc phosphate that was deposited on zinc coated samples with and without siloxane.
Table 3
Figure imgf000010_0001
The phosphate coating weight was measured by dissolving a phosphated zinc coated sample in hydrochloric acid. The phosphorous content in the acidic solution was then determined using Ion Conductive Plasma (ICP) analysis. The value obtained was then used to calculate the original zinc phosphate weight. The amount of phosphate deposited on the siloxane coated samples (3b and 3d) is approximately 10% less than the amount of phosphate deposited on the corresponding bare zinc coated samples (3a and 3c). This means that less phosphate is required to manufacture phosphated zinc coated steel when the coated steel additionally comprises a siloxane coating.
The phosphate coatings were also analysed with a secondary electron microprobe (SEM) to determine phosphate crystal size and the morphology of the phosphate coating. It was found that the size of phosphate crystals on the siloxane coated samples (3b and 3d) were up to two times smaller than the size of phosphate crystals that were deposited onto the bare zinc coated sample (3a and 3c). Phosphate coatings having smaller phosphate crystals are attractive to automotive manufacturers since thin and less expensive phosphate coatings may be obtained. Furthermore, phosphate crystals that were deposited onto siloxane coated samples often exhibited improved epitaxial growth relative to those deposited onto bare zinc coated steel samples, resulting in better surface coverage and therefore improved corrosion resistance properties.

Claims

A coated substrate for phosphating, which comprises a strip or sheet made of cold formable cold rolled steel, a zinc coating provided on the strip or sheet, and an activating layer provided on the zinc coating, wherein the activating layer comprises a siloxane or a polysiloxane and has a thickness corresponding to 1-10 mg/m2 Si.
Coated steel substrate according to claim 1 , wherein the steel has a composition in weight% of:
0.01 < C < 0.15
0.1 < Mn < 2.0
0.05 < Si < 0.5
Cr < 1.0
Al < 0.5
Mo < 0.2
Ti < 0.2
P < 0.1
N < 0.15
S < 0.05
B < 0.01
the remainder being Fe and unavoidable impurities.
Coated steel substrate according to claim 1 or claim 2, wherein the steel has a tensile strength of at most 600 MPa, such as an Interstitial Free steel (IF-steel), a bake hardenable steel or a dual phase steel (DP steel).
Coated steel substrate according to any one of claims 1-3, wherein the zinc coating on the steel has a thickness of 20 - 140 g/m2 on each side.
Coated steel substrate according to anyone of the preceding claims, wherein the siloxane or polysiloxane activating layer has a layer thickness corresponding to 1 - 8 mg/m2 Si, preferably 1 - 5 mg/m2 Si.
Coated steel substrate according to any one of the preceding claims, wherein the siloxane or polysiloxane activating layer is formed from a bis- tri(m)ethoxysilylalkane, preferably a bis-triethoxysilylethane (BTSE), and preferably in combination with another silane such as γ- aminopropyltriethoxysilane (yAPS), bis-aminosilane (BAS), bis-diaminosilane (BDAS), vinyltriacetoxysilane (VTAS), γ-ureidopropyl-trimethoxysilane (vUPS) and/or bis-trimethoxysilylpropylurea (BUPS).
7. Method for manufacturing a coated steel part according to any one of the preceding claims, which comprises the steps of applying a water based silane or silanol solution on a zinc coated cold formable cold rolled steel strip or sheet, drying and/or curing the applied solution to form a siloxane or polysiloxane activating layer having a thickness corresponding to 1-10 mg/m2 Si on the zinc coating, cutting a blank from the coated strip or sheet and cold forming the blank into a part.
8. Method according to any one of claim 7, wherein the water based silane or silanol solution comprises a fluoride, preferably hydrogen fluoride, fluorosilicic acid, fluorozirconic acid and/or fluorotitanic acid.
9. Method for manufacturing an article that comprises one or more cold formed parts made from the coated steel strip or sheet according to any one of claims 1-6, wherein the article is contacted with a zinc phosphate solution to form a phosphate coating on the article.
10. Method according to claim 9, wherein the zinc phosphate solution contains additional elements selected from the group consisting of Fe, Mg, Mn, Ca, Ti, Zr or Cu.
1 1. Method according to claim 9 or claim 10, wherein the article is subjected to an activating treatment before contacting the article with the zinc phosphate solution.
12. Phosphate coated article, which comprises one or more cold formed steel parts made from the coated steel strip or sheet according to any one of claims 1-6, a zinc coating provided on the steel part, a siloxane or polysiloxane material provided on the zinc coating and a phosphate coating provided on the siloxane or polysiloxane material and the zinc coating. Phosphated article according to claim 12, wherein a paint layer is provided on the phosphate coating.
Phosphate coated article according to claim 12 or 13, wherein the article is an automotive article, preferably an automotive body.
PCT/EP2015/025006 2014-02-20 2015-02-20 Activation treatment of coated steel substrates WO2015124322A1 (en)

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