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
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
• • 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

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.
• Direct galvanic coating with aluminum proves to be particularly problematic in the case of those metallic materials which corrode quickly, form a covering layer or become brittle through hydrogen. This is because an adherent, non-porous deposition of aluminum is not guaranteed.
• the adhesive galvanic aluminization (from an aprotic electrolyte system) of oxide-forming metallic materials can be carried out in such a way that a so-called adhesion promoter, i.e. an intermediate layer, for example made of nickel, is applied.
• adhesion promoter i.e. an intermediate layer, for example made of nickel
• the medium used consists of an anhydrous alcohol, in particular methanol, with a content of 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 metal 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 measures for the pretreatment of metallic materials which allow high-strength steels without hydrogen embrittlement and reactive materials which already form or corrode surface layers when rinsed with water to be directly adhesive and non-porous - in an industrially usable process to coat non-aqueous solutions or electrolyte systems with metal, in particular aluminum.
• the metallic substrate surface is first pre-cleaned to suit the material. This is done according to methods known per se, for example by dry blasting or by means of economy pickling solutions, i.e. Pickling solutions containing inhibitor in the form of aqueous inorganic acids. In certain cases, however, it may already be sufficient to degrease the workpieces with conventional organic solvents.
• the metallic material is treated with an activating solution; this takes place under an inert gas atmosphere, for which argon is preferably used.
• the treatment with the activating solution is generally carried out at room temperature, the treatment time being approximately between 2 and 5 minutes.
• the activating solution is a solution of a water-containing inorganic acid, preferably sulfuric acid, hydrochloric acid, hydrofluoric acid or nitric acid or mixtures of these acids, in an aliphatic mono- or dihydric alcohol, preferably methanol.
• the alcohol can advantageously be present in a mixture with an aromatic hydrocarbon, in particular toluene.
• the inorganic acid is generally used in a commercially available concentration (for example 32% hydrochloric acid or 98% sulfuric acid) and with the organic solvent to approx. Diluted 1 to 5% by volume.
• the activation solution is a solution of an anhydrous inorganic acid, preferably hydrogen chloride , Hydrogen fluoride or sulfuric acid, in an aliphatic, aromatic or cyclic ether, preferably in an ethylene glycol or diethylene glycol ether, such as diethylene glycol dimethyl ether.
• the ether can advantageously be present in a mixture with an aromatic hydrocarbon, in particular toluene.
• the acid concentration is generally in the range from 0.1 to 5% by weight.
• An activating solution in the form of a solution of an anhydrous aliphatic carboxylic acid, preferably acetic acid, in an aliphatic alcohol or ether, preferably isopropanol, can also be used for the pretreatment of high-strength steels.
• Alcohol and ether can advantageously be present in a mixture with an aromatic hydrocarbon, in particular toluene.
• the aliphatic carboxylic acid which is a saturated mono-, di- or tricarboxylic acid, can advantageously be used together with the corresponding carboxylic anhydride, an acetic acid / acetic anhydride mixture being preferred.
• the preferred solvent is a mixture of alcohol or ether and toluene in a proportion of 50 to 75% toluene.
• the residues of the activation solution must be removed, since the material cannot be coated directly with the metal because of the lack of adhesion of the coating and, especially with aluminum, because of the risk of decomposition of the electrolyte.
• This is done by thoroughly rinsing the material with inert liquids in the form of aromatic hydrocarbons, especially toluene.
• inert liquids in the form of aromatic hydrocarbons, especially toluene.
• Methanol or isopropanol is preferably used as the alcohol.
• the galvanic metal deposition then follows the rinsing processes.
• 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 for the electrolytic deposition of other metals from non-aqueous organic electrolytes Find use.
• 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 titanium sheets are first subjected to an aqueous preliminary cleaning.
• the sheets are treated with a commercially available pickling agent (1 min), rinsed with water (30 s), degreased cathodically using a commercially available degreasing agent (90 s), rinsed with water and dried, in a mixture (volume ratio 5: 1) of 50% hydrofluoric acid and 65% nitric acid immersed (15 s), rinsed with water and then dried with acetone and in air.
• the activation is then carried out (with the exclusion of oxygen) in an argon atmosphere (5 min), a solution of 50% hydrofluoric acid (2% by volume) in methanol serving as the activation solution.
• the sheets are first rinsed twice with methanol (15 s each) and then twice with toluene (30 s each), and then coated with aluminum.
• the doped silicon wafers are first subjected to an aqueous preliminary cleaning.
• the wafers are treated with a commercially available pickling agent (30 s), rinsed with water (30 s), cathodically degreased using a commercially available degreasing agent (1 min), rinsed with water and dried, in a mixture (volume ratio 10: 1) of 50% hydrofluoric acid and 65% nitric acid immersed (30 s), rinsed with water and degreased again cathodically (1 min), rinsed with water and then dried with acetone and toluene.
• the activation is then carried out (with the exclusion of oxygen) in an argon atmosphere (5 min), a mixture of methanol, 50% hydrofluoric acid and 65% nitric acid (volume ratio 7: 3: 1) serving as the activation solution.
• the wafers are first rinsed twice with methanol (15 s each) and then twice with toluene (15 s each) and then coated with aluminum.
• the high-strength iron materials are first subjected to pre-cleaning.
• the materials are blasted dry with electro corundum (particle size: 70 to 90 ⁇ m) and then cleaned with toluene under the influence of ultrasound.
• the activation is then carried out (with the exclusion of oxygen) in an argon atmosphere (2 min), a solution of hydrogen chloride (3% by weight) in diethylene glycol dimethyl ether serving as the activation solution.
• the materials are rinsed twice with toluene (30 s each) and then coated with aluminum.
• the super magnets for example vacodymium magnets, are first subjected to pre-cleaning.
• the magnets are blasted dry with electro corundum (particle size: 70 to 90 ⁇ m) and then cleaned with toluene under the influence of ultrasound.
• the activation is then carried out (with the exclusion of oxygen) in an argon atmosphere (2 min), a solution of hydrogen chloride (1% by weight) in ethylene glycol dimethyl ether serving as the activation solution.
• the magnets are rinsed twice with toluene (30 s each) and then coated with aluminum.
• the iron materials are first subjected to an aqueous preliminary cleaning.
• the materials are treated with a commercial pickling agent (2 to 5 s), rinsed with water, cathodically degreased using a commercially available degreasing agent (90 s), rinsed with water (30 s) and then dried with isopropanol and in air.
• the activation is then carried out (with the exclusion of oxygen) in an argon atmosphere (2 min), a mixture of acetic acid and acetic anhydride (volume ratio 9: 1) serving as the activation solution.
• the materials are first rinsed twice with isopropanol (30 s each) and then twice with toluene (30 s each) and then coated with aluminum.
• the steel leaf springs (size: 50 mm x 5 mm) are first subjected to an aqueous preliminary cleaning.
• the leaf springs are treated with a commercially available saving stain (approx. 10 s), rinsed with water and dehydrated with chlorofluorocarbon vapor and dried.
• the activation is then carried out (with the exclusion of oxygen) in an argon atmosphere (about 2 to 3 min), a solution of hydrogen chloride (about 0.5% by weight) in diethylene glycol dimethyl ether serving as the activation solution.
• the leaf springs are rinsed with diethylene glycol dimethyl ether and toluene (each about 1 to 2 minutes), and then coated with aluminum.
• the pretreated leaf springs are placed in an aluminizing cell under inert gas and coated with approx. 20 ⁇ m aluminum.
• the test of hydrogen embrittlement by tension tests showed no reduction in tensile strength.

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• Chemical Kinetics & Catalysis (AREA)
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• 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 EP92104033A patent/EP0504705A1/fr not_active Withdrawn

Patent Citations (7)

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