Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/36—Phosphatising

Definitions

• the invention relates generally to an electrolytic method for phosphating metal surfaces according to the preamble of claim 1. It also relates to a phosphated metal layer produced using this method.
• Zinc phosphating is a widely used process for the corrosion protection of low-alloy steels.
• zinc phosphate crystals Hopeit
• Hopeit zinc phosphate crystals
• the solubility product of the zinc phosphate must be exceeded. This is done by attacking (pickling) the base metal (eg Fe -> Fe 2+ +2 e " ). The electrons released in the process serve to reduce protons. The pH is shifted towards neutral to basic and the solubility product is exceeded. They form Usually layers with a thickness of 2-3 ⁇ m are formed, which have a degree of coverage of approximately 90 to 95% The corrosion protection is limited by the thin and porous layer that forms and is therefore usually combined with other coatings, for example corrosion protection oil or KTL Further developments aim to increase corrosion protection without such additional coatings.
• JP-A-85/211080 relates to a method for producing corrosion protection layers Metal surfaces with the help of zinc phosphating solutions with temporary use of a cathodic current.
• a corrosion-resistant protective layer is also produced on the edges of the metal surfaces to be treated.
• DE-41 11 186 AI discloses a method for phosphating metal surfaces, preferably electrolytically or hot-dip galvanized steel strip surfaces, by treating in immersion or spray-immersion with acidic, aqueous phosphating solutions, the workpieces being simultaneously treated cathodically with a direct current.
• phosphating solutions which contain the following components: Zn 2+ cations in the range from 0.1 to 5 g / 1; PO 3 " anions in the range from 5 to 50 g / 1; NO 3 ⁇ anions in the range from 0.1 to 50 g / 1; and Ni 2+ cations in the range from 0.1 to 5 g / 1, and / or Co 2+ cations in the range from 0.1 to 5 g 1.
• the pH of the phosphating solutions is in the range from 1.5 to 4.5, and the temperature of the phosphating solutions is in the range from 10 to 80 ° C.
• the current density of the direct current with which the workpieces are treated cathodically during phosphating is between 0.01 and 100 mA / cm 2 .
• a disadvantage of the conventional phosphating processes is that they are limited to low-alloy steels, as well as Zn and Al, and that the layers produced do not have cathodic corrosion protection due to the fact that they consist of zinc phosphate crystals. In addition, an upstream activation is necessary in most cases.
• the method according to the invention for phosphating metal surfaces has the advantage over the prior art that compact layers are formed whose thicknesses can be adjusted almost as desired.
• Another advantage is that the layers produced have a significantly higher corrosion resistance.
• the phosphating can be carried out without activation.
• the electrolysis can be carried out either potentiostatically or galvanostatically, or with a mixture of the two.
• FIG. 1 An exemplary embodiment of the invention is shown in the drawing and explained in more detail in the following description.
• the figure shows a schematic diagram of the manufacturing method according to the invention.
• the aim of the present invention is to develop an electrolytic coating method for phosphating metal surfaces, in which the pores in the phosphate layer are filled with metallic zinc or zinc alloys.
• the electrolytic zinc or zinc alloy deposition takes place simultaneously with the zinc phosphate crystal formation in the same electrolyte.
• the process according to the invention comes in contrast to conventional phosphating, in which after cleaning or pickling the workpiece was immersed in a titanium phosphate suspension (approx. 60 s at pH ⁇ 9) without an upstream activation process.
• the described process can also be used to directly coat stainless steels and other noble and base materials such as Al, Al alloys, Cu, Cu alloys, Ni, Ni alloys, etc.
• deposition can only be carried out on materials which permit a corrosive pickling attack, since otherwise the required pH shift described above cannot occur.
• the electrolysis can be controlled both potentiostatically and galvanostatically, or can be carried out with a mixture of the two parts.
• compact layers are formed, which are distinguished in that the spaces between the zinc phosphate crystals are filled up by a network of metallically deposited zinc or zinc alloy. Due to the simultaneous formation of the electrically conductive zinc or the zinc alloy, a pH shift induced by electrolysis can take place, i.e. the electrons are supplied from the outside, and an almost arbitrary layer thickness increase
• Zinc (zinc alloy) / zinc phosphate layer can be achieved by reducing H * on the zinc surface.
• the figure shows a schematic diagram of the coating method according to the invention.
• the zinc / zinc phosphate layer 14 is deposited on the base metal 11 in a conventional electrolysis cell 10 with a working electrode 11 made of the corresponding base metal and a counter electrode 12 through the electrolyte 13.
• the electrons required for pH shifting do not come from iron corrosion from the low-alloy steels (pickling attack on the base metal), but from an external power source 15. This protective current ensures, among other things, that the Base metal 11 is not attacked.
• the coating method according to the present invention can be carried out in commonly used electrolytic cells.
• the counter electrode can consist of noble sheets such as platinum, Pt / Ti or gold, as well as less noble sacrificial anodes such as Zn, Ni, Fe, which ensure continuous transport of metal ions.
• the electrolyte is essentially an electrolyte of the kind used in phosphating without external current.
• the electrolyte contains, for example: Zn 2+ : 5-50 g / 1 H 2 PO 4 " : 5-80 g / 1
• the electrolyte can contain ions from elements which can form an alloy with zinc, so that when the phosphating layer is deposited, zinc alloys are deposited simultaneously.
• ions from elements which can form an alloy with zinc so that when the phosphating layer is deposited, zinc alloys are deposited simultaneously.
• the addition of nanoparticles and organic molecules is also conceivable.
• Other possible bath additives for modifying the layers are polyphosphates, borates, organic polyhydroxy compounds, glycerophosphates and fluorides.
• the additional ions can be, for example, ions of a divalent metal M, the further divalent metal M being selected from the group consisting of Ni, Fe, Co, Cu, Mn and the like.
• the reaction can be carried out with or without the addition of an accelerator.
• Suitable accelerators are urea, nitrates, nitrites, chlorates, bromates, hydrogen peroxide, ozone, organic nitro bodies, peroxy compounds, hydroxylamine or mixtures thereof.
• Nitrate ions in the range of 0-20 g / l are advantageous as accelerators.
• the pH of the bath is between 1.5 and 4, preferably between 2.5 and 3.5.
• Binary, ternary or even higher alloys can be deposited by adding Zn, Ni, Co, Fe or Mn salts.
• the metal ions can also be supplied to the electrolyte by anodic dissolution.
• the electrolyte can either rest or be moved during the process.
• Current densities in the range from -5 to -50 A / dm 2 are particularly preferred.
• the temperature of the electrolyte is> 40 ° C and is preferably in the range between 40 and 80 ° C, particularly preferably between 60 and 70 ° C.
• the electrolysis process can be controlled both potentiostatically and galvanostatically, whereby either direct current or pulsed direct current can be used.
• the layer thickness distribution can be regulated by controlling the local current density, i.e. by shaping and / or current orifices between the anode and the workpiece. In this way, geometrically more demanding parts can also be coated.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating Methods And Accessories (AREA)
• Chemical Treatment Of Metals (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrolytic Production Of Metals (AREA)

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• 2003
  • 2003-10-16 DE DE10348251A patent/DE10348251A1/de not_active Withdrawn
• 2004
  • 2004-09-22 EP EP04787187A patent/EP1675975A2/de not_active Withdrawn
  • 2004-09-22 BR BRPI0415520-3A patent/BRPI0415520A/pt not_active Application Discontinuation
  • 2004-09-22 WO PCT/EP2004/052269 patent/WO2005038095A2/de active Application Filing
  • 2004-09-22 JP JP2006534745A patent/JP2007508457A/ja not_active Withdrawn
  • 2004-09-22 TR TR2006/01814T patent/TR200601814T1/xx unknown
  • 2004-09-22 CN CN200480030171.3A patent/CN1867704B/zh not_active Expired - Fee Related
  • 2004-09-22 US US10/575,907 patent/US20070295608A1/en not_active Abandoned

Non-Patent Citations (1)

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