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
  • C25D3/42—Electroplating: Baths therefor from solutions of light metals
  • C25D3/44—Aluminium
• • 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
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated

Definitions

• the invention relates to a method for the pretreatment of metallic materials for the direct galvanic coating with metal from non-aqueous solutions, in particular with aluminum from aprotic electrolyte media.
• the direct galvanic coating with aluminum proves to be particularly problematic with materials that corrode quickly; These are, for example, aluminum, iron and zinc and their alloys. This is because an adherent deposition of aluminum is not guaranteed.
• metallic materials can only be galvanically adhered if their surface is completely metallic, i.e. is free of oxide and fat layers.
• nobler metals such as copper, silver and gold
• this can be achieved with regard to the galvanic aluminization, as known from electroplating, for example by pickling or cathodic degreasing.
• less noble metals, in particular aluminum, iron and zinc materials have so far only been able to be applied by applying a so-called adhesion promoter, i.e. an intermediate layer, for example made of nickel or copper, are securely aluminized. Otherwise, when rinsed with water - in the presence of air - the materials form such a thick oxide layer that they cannot be coated with adhesive.
• EP-OS 0 054 743 discloses a process for the chemical removal of oxide layers from objects made of metals, in particular titanium and nickel and their alloys as well as chromium-nickel steels, for subsequent coating with metals, in particular in an organic electrolyte, which has an adhesive strength Coating of the materials mentioned should enable.
• a treatment is carried out in an anhydrous organic medium with a mixture of hydrogen fluoride (HF) and one or more alkali fluorides and / or ammonium fluoride.
• HF hydrogen fluoride
• the medium used consists of an anhydrous alcohol, in particular Methanol, containing 3 to 8% by weight of hydrogen fluoride, 5 to 8% by weight of ammonium fluoride and 5 to 10% by weight of an alkali fluoride, in particular sodium fluoride; the treatment temperature is between 10 and 50 ° C.
• the removal of the oxide layer can be supported electrochemically, the workpieces being alternately anodically and cathodically switched with the addition of a conductive salt.
• a disadvantage of this process is that the treatment is carried out in a relatively aggressive medium and that the process is carried out exclusively without water.
• the electrochemically assisted pickling process can lead to deposits on the substrates and to gas evolution (hydrogen or oxygen), and moreover the necessary conductive salts, such as sodium sulfate, are poorly soluble or can crystallize out.
• the object of the invention is to provide a method for the pretreatment of metallic materials, which allows in particular iron materials - from non-aqueous solutions or electrolyte systems - directly, i.e. without an intermediate layer, to be adherently coated with metal, especially aluminum.
• the metallic substrate surface is first pre-cleaned to suit the material. This is done in a manner known per se by an aqueous treatment; the material is degreased and pickled and then rinsed with water. Degreasing is carried out, for example, by boiling degreasing or electrical degreasing; conventional economy pickling solutions are used for pickling, i.e. Pickling solutions containing inhibitor in the form of aqueous inorganic acids.
• the pre-cleaning itself is carried out - in a conventional way - in air.
• the method according to the invention enables an adherent coating of the material with metal. This is surprising and could not have been foreseen because, as is well known, it is not possible to coat with adhesive if there is a cover layer. In the method according to the invention, however, it is rinsed with water, i.e. the activation or pickling solution is removed with water, specifically with oxygen-free water. However, it is known that, for example, iron - with exclusion of oxygen - is dissolved from distilled water, a layer of iron (II) hydroxide being formed.
• the metal is adequately adhered to the material in the subsequent galvanic coating.
• this is working under an inert gas atmosphere and, on the other hand, the use of oxygen-free activation or pickling solutions and rinsing baths; argon or nitrogen is preferably used as the inert gas.
• oxygen-free means that the agents are saturated with an inert gas, but traces of oxygen may still be present.
• the hydrogen generated by pickling or cathodic degreasing does not interfere because an overall reducing inert gas atmosphere is created, which reduces the oxidation of the material surface, for example from iron.
• the oxygen generated during electrical degreasing must be removed separately.
• the duration of the individual rinsing processes i.e. the period from the start of one rinsing process to the beginning of the next or to the aluminizing, generally in each case up to 10 min; this period is preferably up to 5 minutes.
• the treatment with the activating solution serves to remove the thin oxide layers which form in air during the aqueous preliminary cleaning.
• the activation itself takes place with an aqueous solution of an inorganic or organic acid, for which purpose preferably sulfuric acid is used; In addition, hydrochloric acid can also be used, for example.
• Treatment with the pickling solution ie an aqueous solution of an inorganic acid, also serves to remove oxide layers. Otherwise, the activation solution - like the pickling solution - can be an inhibitor contain.
• the mixture is either flushed with an aromatic hydrocarbon, preferably toluene, or dried with a preferably hot inert gas or in vacuo. It is advantageous if the rinsing processes take place under the influence of ultrasound, because this ensures complete removal of the activation or pickling solution.
• the galvanic metal deposition then follows the rinsing processes. In the case of aluminum, an oxygen-free aprotic electrolyte system such as is known, for example, from EP-PS 0 084 816 is used for this.
• the method according to the invention can also be used in the electrolytic deposition of other metals from non-aqueous organic electrolytes.
• metals are, in particular, titanium, chromium, iron, cobalt, nickel, copper, zinc and tin, alcohols and ethers as well as dimethylformamide and dimethyl sulfoxide being able to serve as non-aqueous solvents (see, for example: "Yearbook of Surface Technology", vol. 46 (1990), Metall-Verlag GmbH Berlin / Heidelberg, Pages 163 to 174).
• the process according to the invention gives aluminum layers which are particularly adhesive to iron materials. Scratch and filing tests and heating to temperatures up to 250 ° C are used to assess the adhesive strength. When tensile tests are carried out using epoxy adhesive, the adhesive tears.
• the steel sheet is first subjected to an aqueous preliminary cleaning (in air).
• the sheet is degreased in trichlorethylene, cleaned with a commercially available pickling agent (1 to 2 min), degreased cathodically using a commercially available degreasing agent (1 to 2 min at 5 to 10 A / dm2) and then rinsed with water (0.5 to 1 min).
• This is followed by activation under inert gas (2 min) with an aqueous solution of sulfuric acid (5% by volume).
• the sheet is rinsed twice with water (0.5 to 1 min each) and then twice with isopropanol and toluene (0.5 to 1 min each) under inert gas, and then coated with aluminum .
• the liquid adhering to the substrate to be coated is allowed to drip between the individual work steps - activation, rinsing with water, rinsing with isopropanol, rinsing with toluene and aluminizing.
• the draining time is per work step approx. 1 min.
• the workpieces are first degreased in air in trichlorethylene and then rinsed with water (0.5 to 1 min). This is followed by pickling under inert gas (approx. 2 min) with an aqueous solution of hydrochloric acid (approx. 18.5% by volume) which contains small amounts of an inhibitor and a wetting agent. After pickling, the workpieces - under inert gas - are rinsed at least once with water, with isopropanol and with toluene (approx. 1 min each) and then coated with aluminum. Draining time (per work step): 2 min; Charging time: 0.5 to 1 min.
• the steel sheet is first pre-cleaned according to Example 1 and then activated in a corresponding manner with aqueous sulfuric acid (4 min). After activation, it is rinsed twice with water (0.5 min each) and then once each with commercially available dewatering fluid and with toluene (each 1 min), and then coated with aluminum. Draining time (per work step): approx. 0.5 min; Charging time: 0.5 to 1 min.
• the steel sheet is first pre-cleaned according to Example 1 and then activated in a corresponding manner with aqueous sulfuric acid (4 min). After activation, it is first rinsed twice with water (0.5 min each), then it is blown dry with hot nitrogen (60 ° C.) (0.5 to 1 min), and then it is coated with aluminum. Draining time (per work step): approx. 0.5 min; Charging time: 0.5 to 1 min.
• the die-cast part which consists of aluminum, silicon and copper, is first subjected to a preliminary cleaning.
• the workpiece is blasted with glass beads, degreased in perchlorethylene, pickled in an aqueous solution of nitric acid (HN03) and hydrofluoric acid (HF) (60 vol .-% 65% HN03, 3 vol .-% 50% HF, the rest water ), degreased cathodically using a commercially available degreasing agent and then rinsed with water. It is then activated in accordance with Example 1 (4 min).
• HN03 nitric acid
• HF hydrofluoric acid
• the workpiece After activation, the workpiece is rinsed twice with water (0.5 min each) and then twice with isopropanol and toluene (0.5 min each), and then coated with aluminum. Draining time (per work step): approx. 0.5 min; Charging time: 0.5 to 1 min.

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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)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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Citations (7)

• 1992
  • 1992-03-09 EP EP92104032A patent/EP0504704A1/fr not_active Withdrawn

Patent Citations (7)

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