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
  • C25D11/14—Producing integrally coloured layers

Definitions

• This invention relates to an electrolyte composition and process for self-coloring aluminum and alloys of aluminum by anodization and to articles produced thereby.
• a coating of naturally colored aluminum on articles made of aluminum or alloys of aluminum can be produced without coloring agents by a process called self-colored anodization.
• the process comprises anodizing the articles in an electrolyte formed of an aqueous solution of a mixture of organic acids of the family of sulphonated aromatic acids, sulphonated or unsulphonated aliphatic acids and possibly sulphuric acid.
• electrolyte compositions such as an aqueous solution of chromotropic acid and sulphomaleic acid or an aqueous solution of 2- naphthol-3,6-disulphonic acid, suphomaleic acid and sulphuric acid.
• Electrolytes containing sulphonated aromatic acids are relatively expensive. It has been found by applicants that good results can be obtained without such sulphonated aromatic acids when use is made of a properly selected sulphonated aliphatic acid.
• the present invention concerns an electrolyte containing a sulphonated aliphatic acid which permits the aluminum or alloy of aluminum to be produced with a layer of self-colored alumina with shades ranging from pale bronze to black and passing through deeper and deeper bronze and brown shades therebetween.
• the invention also includes articles treated in accordance with the process.
• the electrolyte comprises an aqueous solution of sulphomaleic acid:
• the electrolyte is composed of a solution of from to 300 g./l. and preferably 50 to 200 g./l. of sulphomaleic acid and from 0 to 15 g./l. and preferably 0.5 to 8 g./l. of sulphuric acid in de-ionized water.
• the articles can be subjected to various surface treatments in order to prepare the surface with a matt or shiny finish.
• Matt surfaces can be obtained by chemical or electro-chemical pickling, such, for example, as in a solution containing 50 g./l. of sodium hydroxide at 50 C. for 10 minutes, followed by rinsing in 3,565,772 Patented Feb. 23, 1971 running Water, immersion in 36 B. nitric acid and then further rinsing with water.
• a shiny surface can be produced by mechanical polishing or by chemical or electrolytic polishing.
• selfcolored anodization of the aluminum or alloy of aluminum in the electrolyte can be effected either with alternating current or with an undulating current resulting from the super-position of a direct current and alternating current, but preferably with direct current, the voltage at the terminals of the anodization tank being regulated such that the current density is from 0.5 to 10 amperes per sq. dm. of anodized surface and preferably within the range of 1 to 4 a./sq. dm.
• the electrolyte is maintained at a temperature within the range of 10 C. to +50 C. and preferably within the range of 15 C. to 30 C.
• the current has been passed for approximately /2 to 1 hour, there is obtained generally a 10 to 50 micron thick layer of uniformly colored alumina with more or less dark bronze or even brown tints.
• the layer is characterized by being very hard and having remarkable light and weather resistance. Sealing of the layer of alumina is effected by immersion for about 30 minutes in boiling water preferably with a salt, such as nickel acetate, dissolved therein in an amount within the range of 0.5 to 2 g./l.
• the tint of the oxide layer by fixing the two main regulating parameters, which are current density and temperature of the electrolyte.
• the tint becomes lighter as the current density decreases and as the temperature increases.
• the shiny surface can be retained when anodization is initiated at low current density, such as 1 ./sq. dm. for about 10 minutes, after which the density may be increased to terminate the anodization reaction at a current density greater than 1.5 a./sq. dm.
• composition of the aluminum or alloy of aluminum has noticeable influence on the tint of the resulting layer of alumina.
• an alloy containing manganese should be used.
• variation of the aforementioned parameters of temperature and current density makes it possible to promote the appearance of dark tints, such as brown or even black, when use is made of aluminum alloys which do not contain manganese.
• the same results are not secured with other organic electrolytes or similar composition, such as with sulphosuccinic acid.
• EXAMPLE 1 ing layer of alumina which is 18 microns thick, is of a light bronze, uniform color which is resistant to ultraviolet rays.
• EXAMPLE 2 A shaped part made of A-GS alloy having the same composition as the alloy of Example 1 is anodized in an aqueous solution containing 150 g./l. of sulphomaleic acid and 3 g./l. of sulphuric acid and maintained at 20 C. With a direct current density of 2.5 a./sq. dm. for 30 minutes. After sealing, the layer of alumina, which is 20 microns thick, is of a dark bronze, uniform color which is resistant to ultra-violet rays.
• EXAMPLE 3 A sheet made of A-GO 6 alloy containing, by weight, 0.6% Of magnesium, the remainder being 99.7% pure aluminum, is anodized in an aqueous solution containing 80 g./l. of sulphomaleic acid and 6 g./l. of sulphuric acid and maintained at 21 C., with a current density of 1.5 a./sq. dm. for 40 minutes. After sealing, the layer of alumina, which is 18 microns thick, is of a light bronze, uniform color which is resistant to ultra-violet rays.
• EXAMPLE 4 A shaped part made of A-SGM alloy containing, by weight, 1% of silicon, 1% of magnesium, 1% of manganese, the remainder being 99.5% pure aluminum, is anodized in an aqueous solution containing 120 g./l. of sulphomaleic acid and 4 g./l. of sulphuric acid, at a temperature of 20 C., with a current density of 2.5 a./sq. dm. for 60 minutes.
• the resulting layer of alumina which is 30 microns thick, is of a black, uniform color which is resistant to ultra-violet rays.
• a process for surface anodization of articles of aluminum and alloys of aluminum comprising suspending the article as an anode in an electrolytic bath formed of an aqueous solution containing 10 to 300 g./l. of sulphomaleic acid and to 15 g./l. of sulphuric acid, maintaining the bath at a temperature within the range of to +50 C. during anodization, passing a current therethrough at a current density within the range of 0.5 to 10 amperes per sq. drn. of anodized surface.
• a process as claimed in claim 1 in which the anodized layer that is formed has a thickness within the range of 10 to microns.
• a process as claimed in claim 1 which includes the step of pre-treating the surface prior to anodization to provide a matt or shiny surface.
• a process as claimed in claim 1 in which, in order to retain a shiny surface during anodization, the anodization is carried out at a current density Which is less than 1 ampere per sq. dm. for about the first 10 minutes and then is raised for the remainder of the anodization.
• a process as claimed in claim 1 which includes the step of sealing the anodized layer by immersing in boiling water containing a metal salt dissolved therein in an amount within the range of 0.5 to 2 g./l.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Electroplating Methods And Accessories (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Printing Plates And Materials Therefor (AREA)
• Hybrid Cells (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8645753

Family Applications (1)

Country Status (18)

Cited By (1)

Families Citing this family (1)

• 1968
  • 1968-02-09 FR FR139222A patent/FR1573033A/fr not_active Expired
• 1969
  • 1969-02-03 BG BG011577A patent/BG17636A3/xx unknown
  • 1969-02-04 OA OA53497A patent/OA02989A/xx unknown
  • 1969-02-06 AT AT120569A patent/AT281532B/de not_active IP Right Cessation
  • 1969-02-07 PL PL1969131621A patent/PL76036B1/pl unknown
  • 1969-02-07 NO NO0472/69A patent/NO121986B/no unknown
  • 1969-02-07 GB GB6765/69A patent/GB1213114A/en not_active Expired
  • 1969-02-07 BE BE728059D patent/BE728059A/xx not_active IP Right Cessation
  • 1969-02-07 NL NL6902003A patent/NL6902003A/xx unknown
  • 1969-02-07 CH CH192169A patent/CH506631A/fr not_active IP Right Cessation
  • 1969-02-07 CA CA042348A patent/CA921425A/en not_active Expired
  • 1969-02-07 ES ES363358A patent/ES363358A1/es not_active Expired
  • 1969-02-07 IL IL31572A patent/IL31572A/en unknown
  • 1969-02-07 DE DE19691906225 patent/DE1906225B2/de not_active Withdrawn
  • 1969-02-07 SE SE1707/69A patent/SE343091B/xx unknown
  • 1969-02-07 LU LU57941D patent/LU57941A1/xx unknown
  • 1969-02-10 CS CS865A patent/CS163756B2/cs unknown
  • 1969-02-10 US US798122A patent/US3565772A/en not_active Expired - Lifetime

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