Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/625—Discontinuous layers, e.g. microcracked layers
• • 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
  • C25D3/22—Electroplating: Baths therefor from solutions 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
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/615—Microstructure of the layers, e.g. mixed structure
  • C25D5/617—Crystalline layers

Definitions

• the invention relates to a corrosion protection coating with zinc.
• Zinc layers as corrosion protection of metallic objects are well known in the art, as well as methods for depositing such a zinc layer from a galvanic bath.
• the invention is based on the problem of specifying an improved corrosion protection coating.
• the invention solves the problem with a process for anticorrosive coating in which a first zinc layer with a thickness of at least 4 microns in an acidic plating bath and immediately on the first a second zinc layer is deposited with a thickness of at least 5 microns in an alkaline galvanic bath ,
• the invention is directed to an article that can be produced in this way.
• the invention is based on the idea to improve the corrosion protection with a well-adhering and durable zinc coating by directly two successive zinc layers of an acidic and an alkaline galvanic bath each of at least a certain thickness are deposited.
• the anticorrosion coating according to the invention has two directly successive zinc layers, of which the first zinc layer is deposited from an aqueous acidic and the second zinc layer from an aqueous alkaline galvanic bath.
• These two galvanic bath types for the deposition of zinc layers are known in principle from the prior art, the invention being significantly in the specified combination and thickness of the layers deposited from each different baths.
• the zinc layer deposited from an aqueous acidic bath has a very good surface adhesion, in particular also on steel, at least in comparison with the layer deposited from an alkaline bath, but may show a cracked, columnar surface.
• a zinc layer deposited from an alkaline bath has a quasi-amorphous closed surface of comparatively high hardness but lower ductility, which can be torn comparatively easily under mechanical stress or else detached from the coated material. Only through the combination according to the invention of the first zinc layer with the immediately following second zinc layer can a significantly improved corrosion protection be achieved in the layer thicknesses according to the invention.
• the first (ductile) zinc layer in particular ensures a very good adhesion to the coated article, can absorb mechanical compression or strain and serves as a primer for the second zinc layer, which has a closed surface of the entire coating of larger Hardship creates.
• the thickness of the first zinc layer is at least 4 .mu.m, 5 .mu.m or 6 .mu.m and the thickness of the second zinc layer in this order is increasingly preferably at least 5 .mu.m, 7 .mu.m, 9 .mu.m or 10 .mu.m.
• the layer thickness of the first zinc layer can be increasingly preferred in this order at most 15 microns, 12 microns, 10 microns or 8 microns and the thickness of the second zinc layer in this order increasingly preferably be at most 25 microns, 22 microns, 20 microns or 18 microns.
• the aqueous acid plating bath preferably has a pH of in these orders increasingly preferably at least 4.5, 4.8 or 4.9 and at most 5.8, 5.5 or 5.3.
• the aqueous alkaline galvanic bath preferably has a pH of at least 12 and at most 14, with a pH above 13 being particularly preferred here.
• the galvanic treatment time for depositing the first zinc layer may be in these sequences increasingly preferably at least 4 min, 6 min, 8 min or 10 min and at most 30 min, 27 min, 24 min or 20 min.
• a bath temperature of at least 12 ° C or 20 ° C and at most 35 ° C or 30 ° C is preferred.
• the treatment time for depositing the second zinc layer from the alkaline bath may be increasingly preferably at least 15 minutes, 18 minutes or 20 minutes and at most 45 minutes, 42 minutes or 40 minutes in these orders.
• the alkaline bath preferably has a temperature of at least 15 ° C or 20 ° C and at most 40 ° C or 30 ° C.
• the current density in the electrodeposition of the first zinc layer in the acid bath is preferably at least 0.3 A / dm 2 and at most 2.5 A / dm 2 , preferably at a voltage between 1.5 V and 5 V.
• the current density in the alkaline bath is preferably at least 0.5 A / dm 2 and at most 5 A / dm 2 , preferably at a voltage of at least 3 V and at most 8 V.
• the acid plating bath is preferably increasingly preferred in these orders at least 10 g / l, 20 g / l, 25 g / l or 30 g / l and at most 60 g / l, 45 g / l or 40 g / l zinc, at least 80 g / l, 100 g / l or 120 g / l and not more than 200 g / l, 180 g / l or 160 g / l chloride and at least 10 g / l, 15 g / l, 20 g / l or 25 g / l and at most 40 g / l or 35 g / l boric acid.
• the acid plating bath may additionally be increasingly preferred in the respective orders at least 0.5 ml / l or 0.8 ml / l and not more than 2 ml / l or 1.5 ml / l organic brightener additive and / or at least 30 ml / l and not more than 80 ml / l or 50 ml / l of organic surfactants.
• the acidic bath may be an aqueous solution which, with particular preference to all possible impurities, has exclusively the abovementioned components.
• the alkaline plating bath may be increasingly preferred in these orders at least 5 g / l or 10 g / l and not more than 20 g / l or 14 g / l zinc, at least 50 g / l or 100 g / l and at most 200 g / l or 140 g / l of an alkaline additive, wherein the alkaline additive may be, for example, NaOH.
• the alkaline bath in these orders may be increasingly preferred in addition at least 8 ml / l or 10 ml / l and not more than 20 ml / l or 15 ml / l of an organic luster carrier and / or at least 0.5 ml / l and at most 3 ml / l or 2 ml / l of an organic gloss enhancer.
• the alkaline galvanic bath is preferably in the form of an aqueous solution and, in a particularly preferred embodiment, may contain, in addition to possible impurities, at most the abovementioned components in aqueous solution.
• the object to be coated is rinsed, conveniently at least with water.
• rinsing can take place after the deposition of the second galvanic zinc layer.
• a cleaning of the article to be coated prior to the deposition of the first zinc layer is advantageous, in which case, in particular, depending on the material of the article to be coated, from the prior art, numerous cleaning methods are known.
• the galvanic bath and / or also the object to be coated can be moved in the bath.
• a thick-layer passivation can follow (in particular directly) onto the second zinc layer, wherein it can be applied in a further process in a chemical bath in a further bath.
• Such an additional thick-film passivation can additionally increase the mechanical resistance of the entire coating.
• an additional protection against chemical influences can be achieved.
• a lacquer can also be applied directly to the second zinc layer or also directly following the thick-layer passivation.
• the mechanical resistance and / or the protection against chemical influences can likewise be improved in a known manner.
• the paint can be applied by electrochemical dip coating, preferably by cathodic dip coating, which is also referred to as KTL coating and is known from the prior art.
• An article which has at least the two galvanic zinc layers according to the invention can be used as a component of a motor vehicle, particularly preferably as a component that is freely accessible from below the vehicle. It may be a vehicle part made of stainless steel and be protected according to the invention from moisture, corrosive substances such as salt, but also mechanical effects on its surface. Particularly preferred may be a component of a motor vehicle floor, in particular a part of a drive system or a suspension, for example a subframe, have a coating according to the invention.
• a subframe made of a non-stainless steel sheet is cleaned in a first treatment, in particular degreased and freed from surface oxides. After rinsing in water, it is galvanized in an acid plating bath at 28 ° C with a current of 0.6 A / dm 2 under a voltage of 2.7 V at a treatment time of 15 min.
• the bath with a pH of 5.0 consists here of an aqueous solution of 35 g / l zinc, 140 g / l chloride, 30 g / l boric acid, 1.2 ml / l organic brightener and 40 ml / l organic surfactants.
• a first ductile well-adhering zinc layer of surface-cracked structure of about 7 microns is applied and then rinsed the steering column in water.
• a further galvanic treatment takes place in an alkaline bath with a pH of about 14 and at a temperature of 26 ° C.
• a second zinc layer is deposited during a treatment period of 30 minutes at a current density of 1 A / dm 2 at an applied voltage of 5.5 V.
• This second galvanic bath in this case has an aqueous solution of 12 g / l zinc, 120 g / l NaOH, 12 ml / l organic gloss and 1.2 ml / l organic gloss enhancer on.
• a layer thickness of about 16 microns of a quasi-amorphous zinc structure is deposited here, wherein after the galvanic coating of the subframe is rinsed again with water.
• a thick film passivation is chemically deposited on a coated subframe in a further bath directly on the second zinc layer, and then the article is rinsed again in a water bath.
• the subframe produced in this way has a corrosion protection coating with two directly successive zinc layers and an outer thick-film passivation.
• Another embodiment resides in the anti-corrosion coating of a subframe which differs from that previously described by a cathodic dip-coating rather than the thick-film passivation.
• a fourth embodiment corresponds to the first, thus has two successive zinc layers according to the invention.
• a thick-film passivation is applied directly to the second zinc layer and directly to this one KTL coating.
• This embodiment thus has a corrosion protection coating with these four successive layers.

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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)
• Crystallography & Structural Chemistry (AREA)
• Electroplating Methods And Accessories (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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Citations (4)

• 2008
  • 2008-08-08 EP EP08014206A patent/EP2157213B1/fr not_active Expired - Fee Related

Patent Citations (4)

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