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
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers

Definitions

• a number of processes are known for the production of anodic oxide coatings on aluminum.
• the production of the oxide coatings takes place for example by direct current in solutions of sulfuric acid (Direct current-sulfuric acid process).
• solutions of organic acids such as in particular sulfophthalic acid or sulfanilic acid or mixtures of these acids with sulfuric acid are used.
• the last mentioned processes are known in particular as hard anodizing processes.
• An object of the present invention is the development in the process for treating aluminum surfaces which comprises subjecting aluminum and aluminum alloy surfaces to an anodic oxidation and subsequent sealing with hot water or steam, the improvement selected from the group consisting essentially of (A) applying a solution containing from 0.1 gm to 50 gm per liter of dextrin to the anodic oxidized surfaces at temperatures of from C to 100 C prior to said sealing and (B) applying said solution to the anodic oxidized surfaces simultaneously with said sealing with hot water.
• the present invention provides a process for the treatment of aluminum or aluminum alloy surfaces by anodic oxidation with a subsequent sealing by water or steam, in which, prior to the sealing, the said surfaces are treated at a temperature of from 15 C to 100 C with a solution containing dextrin.
• the dextrin solution preferably contains from 0.1 to 50 gm/l of dextrin.
• the commercial dextrins may be used.
• the intermediate treatment is carried out with solutions containing dextrins of a viscosity of 50 to 400 c? in 50 percent solution at C.
• the viscosity is measured with a Brookfield rotary viscometer.
• the solution for the intermediate treatment contains 0.1 to 50 gm/l of the said dextrins, which may be used singly or in mixtures. It is also possible, of course, to use larger quantities, but this offers no further advantages.
• the above-mentioned solutions for the intermediate treat ment have a pH value situated between 5 and 7. This pH value has proved appropriate and is the natural pH of said solutions, so that additional pH adjustment is not required.
• For the preparation of the solutions it is advantageous if fully demineralized, or distilled or condensed water is used.
• the intermediate treatment is carried out at temperatures between 15 C and 100 C, preferably at temperatures above 50' C.
• the anodized articles of aluminum or aluminum alloys are dipped into the solutions or are sprayed with the same.
• the duration of treatment is from 0.5 to 60 minutes, generally less than 15 minutes. Longer treatments have no detrimental effect.
• a rinsing with water may take place to avoid an entrainment of substances removable by rinsing into the subsequent sealing stage. This rinsing is not essential however. No disadvantages result if the aluminum parts are transferred, immediately after the intermediate treatment to the after-sealing stage.
• the after-sealin g with water and the intermediate treatment are carried out in one operating stage.
• the water provided for the after-sealing is mixed with the said dextrins in the specified quantities and the scaling is carried out in the customary manner. It is appropriate subsequently to rinse with fully demineralized water or distilled or condensed water.
• the after-sealing solutions may also contain additives known for such purposes, such as nickel acetate, in small quantities. It is possible by the new process to prevent the formation of sealing films without impairing the anodic oxide coating or diminishing the quality of the after-sealing. The appearance of the surface is not affected by the process in accordance with the invention. The effects, as achieved by the pretreatment and anodizing, remain unchanged.
• the quality of the oxide coatings is determined by the so-called Testal value according to DIN 50,949. Furthermore, the quality of the sealing was tested by the Griin test according to DIN 50,146.
• the designation of the aluminum alloys used in the examples is in accordance with DIN 1,725. Testal values above 15 are technically not satisfactory. DIN is the abreviation for Irish Industrie-Norm representing a series of standard German published test procedures.
• EXAMPLE 1 Aluminum shaped specimens (A1 Mg Si 0.5), alkaline degreased and pickled in the customary manner, which had been anodically oxidized by the direct current-sulfuric acid process (thickness of coating 20 [.L), were treated for 10 minutes with a solution of 5 gm/] of dextrin having a viscosity of cP (measured in 50 percent solution at 20 C with the Brookfield rotary viscometer), in fully demineralized water at C. After subsequent sealing in fully demineralized hot water C, 60 minutes) the sections showed no sealing film. The thickness of layer after sealing was 20 [.L, the Testal value had dropped from over 300 to 6.5. The Grt'in" test showed a perfect sealing.
• EXAMPLE 2 Aluminum sheets (Al Si 5), degreased in the customary manner, which had been anodically oxidized by the direct current sulfuric acid-oxalic acid process (thickness of coating 10 10 t), were treated with a solution of 10 gm/l of dextrin having a viscosity of 275 c? (measured in 50 percent solution at 20 C with the Brookfield rotary viscometer) in distilled water at 50 C for 15 minutes. After intermediate rinsing, the aluminum parts were sealed in steam for 60 minutes. After this, the sheets showed no sealing film. The thickness of layer after sealing was 10 p. and the Testal value had dropped from over 300 to 16.0. The Gn'in"test indicated a perfect sealing.
• EXAMPLE 3 Aluminum shaped specimens (Al Mg 3), 3), alkaline degreased and pickled in the customary manner, which had been anodically oxidized by the hard anodizing process (thickness of coating 29 [.L), were sealed for 60 minutes in a solution of l gm/l of dextrin having a viscosity of 200 cP (measured in 50 percent solution at 20 C with the Brookfield rotary viscometer) in fully demineralized water at 100 C. Subsequently, the parts were rinsed briefly with fully demineralized water. The sections showed no sealing film. The thickness of the coating after the sealing was 29 u. The Testal value had dropped from over 300 to 400. The G rt'intest also indicated a perfect sealing ofthe Eloxal coating.
• EXAMPLE 4 Aluminum sections (Al Mg Si 0.5), alkaline degreased and pickled in the customary manner, which had been anodically oxidized by the direct current-sulfuric acid process (thickness of coating 20 to 22 ,u), were sealed for 10 minutes at 100 C in solutions containing 5 gm/l of the chemicals mentioned below, or they were treated in these solutions at 80 C for minutes and then, after an intermediate rinse, sealed in hot water at 100 C for 60 minutes. The thickness of the coating remained unchanged on the different sections after the sealing. The formation or prevention ofthe sealing film and the varying quality of the sealing, determined on the basis of the Testal value are summarized in the table. Only when the compounds in accordance with the invention were used, a sealing film did not form and any detrimental effect on the after-sealing was avoided.

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• Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (2)

• 0
  • BE BE755573D patent/BE755573A/fr unknown
• 1970
  • 1970-06-25 NL NL7009366.A patent/NL167481B/xx not_active IP Right Cessation
  • 1970-06-25 NO NO2484/70A patent/NO125687B/no unknown
  • 1970-06-25 SE SE08850/70A patent/SE367440B/xx unknown
  • 1970-07-08 US US53317A patent/US3657077A/en not_active Expired - Lifetime
  • 1970-07-24 GB GB3595770A patent/GB1302288A/en not_active Expired
  • 1970-09-01 ZA ZA705993A patent/ZA705993B/xx unknown
  • 1970-09-01 JP JP45076628A patent/JPS4927731B1/ja active Pending
  • 1970-09-01 CH CH1304370A patent/CH564611A5/xx not_active IP Right Cessation
  • 1970-09-01 AT AT792270A patent/AT298188B/de not_active IP Right Cessation
  • 1970-09-01 ES ES383287A patent/ES383287A1/es not_active Expired
  • 1970-09-02 FR FR707031900A patent/FR2060356B1/fr not_active Expired

Patent Citations (2)

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