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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids

Definitions

• This invention relates to a method of anodising aluminium and its alloys, for example, in the form of wrought or cast articles.
• the anodising of aluminium. and its alloys in electrolytes including sulphuric acid solutions is well known.
• concentration of sulphuric acid employed ranges from 5% by volume up to over 20% by volume and the .anodic coatings produced range in thickness from 2 microns or less up to over 25 microns, the current densities ranging from to 60 amperes per square foot and the applied voltage varying between 12 and 20 volts.
• the temperature of the electrolyte must be maintained at between 15 C. and 25 C. for optimum results.
• Very hard anodic coatings have also been produced on aluminium alloys at temperatures below 5 C., usually 0 C., but the voltages required to produce the current densities of 10 to 60 amperes per square foot are higher than those just referred to and may rise to as high as 100 volts for the production of hard coatings of a thickness of over 25 microns on some alloys. The higher the voltage required to produce a given current density the greater the amount of cooling needed to maintain the electrolyte at the required temperature.
• aluminium alloys particularly those containing more than 1% of copper, nickel or silicon or admixtures of these elements, are very diflicult to anodise or hard anodise in a sulphuric acid electrolyte using conventional techniques to produce an anodic coating of sufficient thickness to have a commercial value.
• Such alloys include, for example, those known under the nomenclature of British Standards specifications 1470 and 1490 as LM6, HIS, RR250 and LM4.
• a further object of the invention is to enable acceptable anodic coatings to be formed upon aluminium alloys hitherto found difficult to anodise.
• a method of anodising aluminium and its alloys in an electrolyte comprising a sulphuric acid solution comprises adding nitric acid to the electrolyte before or during the carrying out of the anodising operation.
• the amount of nitric acid added may vary between 0.1% and 2% both being percentages by volume, but the preferred addition is in the region of 1% by volume of the electrolyte.
• the electrolyte may comprise 3% to 30% by volume of an aqueous solution of sulphuric acid and preferably comprises 7.5% by volume of such solution.
• a sample of the alloy HE9 was anodised at a current density of 60 amperes per square foot in an electrolyte consisting of a 7.5% by volume solution of sulphuric acid maintained at 20 C. After one hour the voltage had risen from 20 to over 50 volts and the average thickness of the anodic coating produced was microns.
• the sulphuric acid-nitric acid electrolyte is particularly useful for producing thick hard anodic coatings.
• the film thicknesses obtained on different alloys at the same voltages and temperatures (peak voltage of about 60 volts and temperature of 0 C.) and a current density of about 36 amperes per square foot, when using either a conventional hard anodising electrolyte (17.5% volume H 80 and 1.0% by weight oxalic acid) or an electrolyte according to this invention (7.5% by volume H 80; and 1.0% by volume HNO Film thickness (microns) Sulphuric Convenacid-nitric tional acid elecelectrolyte trolyte 1 British Standards nomenclature.
• the electrolyte had a sulphuric acid concentration of 7.5% by volume it has been found that this may vary between 3% and 30% by volume.
• nitric acid is added to the sulphuric acid solution before anodising commences it will be understood that nitric acid could be added to a sulphuric acid electrolyte during the anodising operation.
• a method of anodising aluminium and its alloys in an electrolyte comprising 3% to 30% by volume of an aqueous solution of sulphuric acid comprising adding between 0.1% and 2% by volume of nitric acid to the electrolyte before or during the carrying out of the anodising operation maintaining the electrolyte at a temperature between 0 C. and 25 C. and carrying out the anodising operation at an applied voltage between 10 and and at a current density between 60 and amperes per square foot.

Landscapes

• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
• Weting (AREA)
• Electrodes Of Semiconductors (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Printing Plates And Materials Therefor (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=10463568

Family Applications (1)

Country Status (5)

Cited By (2)

• 1965
  • 1965-12-09 GB GB52348/65A patent/GB1114463A/en not_active Expired
• 1966
  • 1966-12-03 DE DE19661496721 patent/DE1496721A1/de active Pending
  • 1966-12-05 US US598966A patent/US3563867A/en not_active Expired - Lifetime
  • 1966-12-08 FR FR86652A patent/FR1505680A/fr not_active Expired
  • 1966-12-09 CH CH1756866A patent/CH472506A/de not_active IP Right Cessation

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