Classifications

• • 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
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/20—Electrolytic after-treatment
  • C25D11/22—Electrolytic after-treatment for colouring layers

Definitions

• This invention relates to colored protective surface layers on aluminum or alloys of aluminum and methods and compositions for the preparation of same.
• Such coatings have been produced in various ways, one of which consists of forming a porous surface on the aluminum object by anodization, depositing metal pigments into the pores by alternating current electrolysis in an acid solution of metal salts with the object itself as one of the electrodes while the other electrode or counterelectrode is formed of stainless steel or more often of the metal of the salt dissolved in the electrolyte, and then sealing the colored layer by immersion in boiling water.
• the electrolysis bath is formulated to contain dissolved nickel chloride as a component thereof whereby crystallization in the electrolyte does not occur at ambient temperature and polarization of the counter-electrode does not take place.
• the process applies to aluminum and its alloys.
• the object can be subjected to a surface treatment beforehand, depending upon the final appearance required. For example, a mat or dull appearance is obtained by pickling the object for 10 minutes at 50 C. in a 50 g./liter soda solution. The object is rinsed, immersed in nitric acid at 36 Be and then re-rinsed. A bright appearance is obtained either by mechanical polishing or by chemical or electrolytic brightening. A porous layer of alumina 1 to 50 microns thick is then formed on the object by any known means, for example anodization in a 50 g./ liter sulphuric or chromic acid bath using direct or alternating current. This layer is then colored using alternating current.
• the operating conditions are as follows:
• C0unter-electrode Electrical conditions Alternating current; Either at a constant density of from 0.1 to 5 A. etildmfl, preferably 0.1 to 1 A.
• efiJdmfl at a constant voltage of from 5 to v., preferably 7 to 30 v.; duration from 5 seconds to 20 minutes, preferably 1 to 10 minutes.
• a sheet of 99.5% pure aluminum which has been chemically brightened and anodized to a layer thickness of 10 microns in a chromic acid bath is colored by treatment with alternating current in a bath containing: g./liter of nickel sulphate, 10 g./1iter of ammonium sulphate, 20 g./liter of boric acid, 30 g./liter of nickel chloride, with a pH value of 4.55, a resistivity of 21.5 ohms cmP/cm. and with crystals at the bottom of the cell, at 20 C.
• Treatment was carried out with a voltage of 10 volts at a temperature of 22 C. for a period of 5 minutes with a ratio of surface area of component to surface area of counter-electrode of 3.
• the stainless steel counter-electrodes retain a clean appearance and the current density varies from 0.35 to 0.4 a. eif/dm. during the treatment.
• the treatment was carried out at C. at a current density of 0.4 a. eif./dm. for a period of three minutes with a ratio of surface area of component to surface area of counter-electrode of 2.
• the nickel counter-electrodes retain a clear appearance and the electrolysis voltage varies from 9 to 9.6 volts during the treatment. It is possible in this Way to obtain a bronze color finish which, after minutes sealing in boiling distilled water, containing 1 g./1iter of nickel acetate, is resistant both to corrosion and to ultra-violet rays.
• EXAMPLE 3 A piece of aluminum alloy section containing 0.5% of silicon and 0.5 of magnesium, which has been mechanically polished and anodized to a layer thickness of 12 microns in a sulphuric acid bath, is colored by treatment with alternating current in a bath containing: 100 g./liter of nickel sulphate, 30 g./liter of ammonium sulphate, 25 g./liter of boric acid and 200 g./liter of nickel chloride, with a pH value of 3.99 and a resistivity of 15.2 ohms cmF/cm. At 20 C. there are no crystals at the bottom of the cell.
• the treatment was carried out at 30 C. at a current density of 0.4 a. e1T./dm. for a period of 10 minutes with a ratio of surface area of component to surface area of counter-electrode of 2.
• the nickel counter-electrodes retain a clear appearance and the electrolysis voltage varies from 9 to 9.7 volts during the treatment. It is possible in this way to obtain a very deep bronze color finish which, after 30 minutes sealing in boiling distilled water, is resistant both to corrosion and to ultra-violet rays.
• EXAMPLE 4 A piece of a section of aluminum alloy containing 1% of silicon, 1% of magnesium and 1% of manganese, which has been satinized and anodized to a layer thickness of 5 microns in an alternating current sulphuric acid bath, is colored by treatment with alternating current in a bath containing: 75 g./liter of nickel sulphate, 20 g./liter of ammonium sulphate, g./liter of boric acid and 350 g./liter of nickel chloride, with a pH value of 3.6 and a resistivity of 14.8 ohms cmF/cm. At 20 C., there are no crystals at the bottom of the cell.
• the treatment was carried out for 10 minutes at 22 C. with a current density of 0.4 a. elf./dm. and a ratio of surface area of component to surface area of counterelectrode of 4.
• the stainless steel counter-electrodes retain a clean appearance and the electrolysis voltage remains constant at 9.6 volts, during the treatment. It is possible in this way to obtain a very deep bronze color finish which, after 30 minutes sealing in boiling distilled water, is resistant both to corrosion and to ultra-violet rays.
• this invention provides a new and improved electrolysis bath for the production of uniform bronze colors on aluminum and alloys of aluminum in a simple, efficient and reproducible manner.
• a process for producing colored surfaces of aluminum and alloys of aluminum comprising contacting an anodized surface of aluminum or alloy of aluminum as one of the electrodes with an electrolysis bath comprising an acidic solution of 5 to grams per liter hydrated nickel sulfate, 10 to 50 grams per liter ammonium sulfate and 50 to 250 grams per liter hydrated nickel chloride, and passing an alternating current between the electrodes.
• a process as claimed in claim 1 which includes the step of sealing the colored surface by immersion in boiling water.

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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 And Plating Baths Therefor (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Electroplating Methods And Accessories (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=9037743

Family Applications (1)

Country Status (12)

Cited By (7)

Families Citing this family (1)

• 1969
  • 1969-07-21 FR FR6924728A patent/FR2052132A5/fr not_active Expired
• 1970
  • 1970-07-15 US US55295A patent/US3704210A/en not_active Expired - Lifetime
  • 1970-07-16 GB GB34473/70A patent/GB1292699A/en not_active Expired
  • 1970-07-16 NL NL7010552A patent/NL7010552A/xx unknown
  • 1970-07-17 DE DE2035599A patent/DE2035599C3/de not_active Expired
  • 1970-07-17 LU LU61358D patent/LU61358A1/xx unknown
  • 1970-07-17 ES ES381942A patent/ES381942A1/es not_active Expired
  • 1970-07-20 BE BE753706D patent/BE753706A/fr unknown
  • 1970-07-20 CA CA088629A patent/CA926337A/en not_active Expired
  • 1970-07-20 CH CH1100470A patent/CH515338A/fr not_active IP Right Cessation
  • 1970-07-20 JP JP45062918A patent/JPS5015216B1/ja active Pending
  • 1970-07-21 SE SE10074/70A patent/SE351441B/xx unknown

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