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 hydroxy carboxylic acid selected from the group consisting of (A) citric acid, tartaric acid, gallic acid and saccharic acid, (B) a water soluble salt of said acids of (A), and (C) the mixtures thereof at a temperature ranging from 90 C. to the solution boiling point temperature and at a pH of from to 6, to the anodic oxidized surface.
• anodically produced oxide layers are frequently applied to aluminum surfaces. These oxide layers protect the aluminum surfaces from the effects of the weather and other corroding media. Further, the anodic oxide layers are also applied in order to obtain a harder surface and therewith to give the aluminum an increased resistance to wear. In particular, decorative effects can be attained by the self coloring of the OXide layers or can be attained in part by their easy colorability.
• a number of processes are known for the application of anodic oxide layers to aluminum.
• the production of the oxide layers takes place using direct current in solutions of sulfuric acid (the direct current-sulfuric acid process).
• solutions of organic acids such as in particular sulfophthalic acid or sulfanilic acid or mixtures of these organic acids with sulfuric acid, are also frequently used.
• the last named processes are particularly known as the autocolor processes.
• This velvety film is the socalled sealing coating and consists of amorphous aluminum hydroxide which is not resistant to handling, so that the decorative effect of the layer is thereby impaired. Furthermore, it reduces the adhesive strength during the bonding of such aluminum parts and, due to the increased effective surface, this sealing film promotes later soiling and corrosion. For these reasons it has previously been necessary to remove the coating by hand, mechanically or chemically.
• OBJECTS OF THE INVENTION is an object of the present invention to provide a development in the process for treating the surface of aluminum or an aluminum alloy which comprises subjecting said surface to an anodic oxidation and subsequently sealing with hot water or steam, the improvement which consists essentially of sealing said surface by applying an aqueous solution containing from 0.0005 to 0.05 gm. per liter of a hydroxy carboxylic acid selected from the group consisting of (A) citric acid, tartaric acid, gallic acid and saccharic acid, (B) a water soluble salt of said acids of (A), and (C) the mixtures thereof at a temperature ranging from C. to the solution boiling point temperature and at a pH of from 5 to 6, to the anodic oxidized surface.
• a hydroxy carboxylic acid selected from the group consisting of (A) citric acid, tartaric acid, gallic acid and saccharic acid, (B) a water soluble salt of said acids of (A), and (C) the mixtures thereof at
• the present invention is directed to a development in the process for treating the surface of aluminum or an aluminum alloy which comprises subjecting said surface to an anodic oxidation and subsequently sealing with hot water or steam, the improvement which consists essentially of sealing said surface by applying an aqueous solution containing from 0.0005 to 0.05 gm. per liter of a hydroxy carboxylic acid selected from the group consisting of (A) citric acid, tartaric acid, gallic acid and saccharic acid, (B) a water soluble salt of said acids of (A), and (C) the mixtures thereof at a temperature ranging from 90 C; to the solution boiling point temperature and at a pH of from 5 to 6, to the anodic oxidized surface.
• a hydroxy carboxylic acid selected from the group consisting of (A) citric acid, tartaric acid, gallic acid and saccharic acid, (B) a water soluble salt of said acids of (A), and (C) the mixtures thereof at a temperature ranging from 90 C; to the solution boiling
• the present invention provides a process for the treatment of a surface of aluminum or an aluminum alloy comprising subjecting said surfaces to anodic excitation and consolidating same at a temperature of from 90 C. and solution boiling temperature and at a pH value of from 5 to 6 with a solution which contains from 0.005 to 0.05 gm. per liter of a hydroxy carboxylic acid selected from the group; citric acid, tartaric acid, gallic acid and saccharic acid or a water soluble salt thereof.
• Suitable sealing solutions are those aqueous solutions containing 0.0005 to 0.05 gm. per liter of an aliphatic or an aromatic hydroxy carboxylic acid, for example, citric acid, tartaric acid, gallic acid and saccharic acid.
• the process may be carried out using the commercial acids or their water-soluble salts, for example, the corresponding alkali metal salts such as sodium or potassium salts, ammonium salts, and alkaline earth metal salts such as magnesium, calcium or barium salts.
• the corresponding alkali metal salts such as sodium or potassium salts, ammonium salts, and alkaline earth metal salts such as magnesium, calcium or barium salts.
• the said substances are used in amounts of 0.0005 to 0.05 gm. per liter, calculated as free acids.
• the use of greater concentrations has been found disadvantageous, since the quality of the sealing is reduced.
• a preferred form of the process comprises carrying out the sealing with a solution which contains from 0.0005 to 0.005 gm. per liter of citric acid.
• a solution which contains from 0.0005 to 0.005 gm. per liter of citric acid.
• citric acid instead of the citric acid, its water soluble salts may also be used in equivalent amounts.
• the solutions of the acids or salts according to the invention are adjusted to a pH value of 5 to 6. This adjustment may be effected using ammonia or acetic acid.
• ammonia or acetic acid For the preparation of the solutions it is advantageous to use completely desalted, distilled or condensed water.
• the sealing treatment with the solutions according to the invention is carried out at temperatures between 90 C. and the boiling point temperature. Preferably, a temperature of from 90 C. to 100 C. is utilized.
• the treatment time is maintained within the usual operating time schedule and preferably amounts to about 1.5 to 3.5 minutes per ,1. layer thickness of the anodic oxide layer.
• additives known for this purpose such as nickel or cobalt acetate may also be added in small amounts to the sealing solutions.
• the advantages of the process of the present invention include preventing the formation of sealing films without the anodic oxide layer being impaired or the quality of the sealing being reduced.
• a rinsing after the sealing step or a spraying, in order to remove any residues from the surface, is not necessary.
• the appearance of the surface is not affected by the process of the invention; the appearance remains the same as that obtained by the pretreatment and the anodization.
• the process is economical since the amounts of additives required are extremely small.
• the notation of the aluminum alloys is based upon nomenclature according to DIN 1,725.
• the quality of the oxide layers was determined by the socalled Testal value according to DIN 50,949 and by the loss factor d (Anotest apparatus) according to DIN 50,- 920 (design). Further, the products of the after-sealing were tested by means of the Green test according to DIN 50,146.
• DIN is the abbreviation for Deutsche Industrie- Norm representing a series of standard German published test procedures.
• EXAMPLE 1 Aluminum sections (AlMgSi 0.5) degreased with an aqueous alkali metal hydroxide solution and pickled in the usual way, which were anodically oxidized in the direct current-sulfuric acid process (layer thickness 21 1,) were sealed at 100 C. for 60 minutes with a solution of 0.0005 gm. per liter of citric acid in completely de-salted water, which was adjusted with ammonia to pH 5.7 prior
• EXAMPLE 3 Aluminum sections (AlMg3) degreased with an aqueous alkali metal hydroxide solution and pickled in the usual way, which were anodically oxidized by an autocolor process (layer thickness 30 were sealed at 100 C. for 80 minutes in a solution of 0.01 gm. per liter of the monopotassium salt of d-saccharic acid in completely desalted water, which was adjusted with ammonia to a pH value of 6.0 prior to sealing. The sections showed no sealing film. The Testal value had fallen from over 300 to 4.5 and the loss factor a amounted to 0.51.
• EXAMPLE 4 Aluminum sections (AlMgSi0.5) degreased with an aqueous alkali metal hydroxide solution and pickled in the usual way, which were anodically oxidized in the direct current sulfuric acid process (layer thickness 20- 2241..) were sealed at 100 C. for minutes at a pH value of 5.6 (adjusted with ammonia prior to scaling) in solutions which contained the chemicals mentioned below in the amounts given therein.
• the formation or prevention of the sealing film and the varying quality of the sealing measured by means of the Testal value, the loss factor 0. and the Green test (in percent of the reflection value), are summarized in Table I. Only when compounds according to the invention were used in suitable concentration did no sealing film result and no harmful effect on the subsequent sealing occur.

Landscapes

• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Preventing Unauthorised Actuation Of Valves (AREA)
• Chemical Treatment Of Metals (AREA)
• Paper (AREA)
• Sealing Material Composition (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=5828298

Family Applications (1)

Country Status (15)

Cited By (12)

Families Citing this family (4)

Family Cites Families (3)

• 0
  • BE BE792852D patent/BE792852A/xx not_active IP Right Cessation
• 1971
  • 1971-12-17 DE DE2162674A patent/DE2162674C3/de not_active Expired
• 1972
  • 1972-11-16 NL NLAANVRAGE7215524,A patent/NL171913C/xx not_active IP Right Cessation
  • 1972-11-20 SE SE7215079A patent/SE401531B/xx unknown
  • 1972-11-21 NO NO4239/72A patent/NO131207C/no unknown
  • 1972-12-05 US US00312341A patent/US3838023A/en not_active Expired - Lifetime
  • 1972-12-06 IT IT32547/72A patent/IT971590B/it active
  • 1972-12-13 BR BR8779/72A patent/BR7208779D0/pt unknown
  • 1972-12-14 FR FR7244480A patent/FR2163603B1/fr not_active Expired
  • 1972-12-14 ZA ZA728846A patent/ZA728846B/xx unknown
  • 1972-12-15 GB GB5791372A patent/GB1398589A/en not_active Expired
  • 1972-12-15 AT AT1072872A patent/AT316251B/de not_active IP Right Cessation
  • 1972-12-15 CH CH1831572A patent/CH584767A5/xx not_active IP Right Cessation
  • 1972-12-16 ES ES409718A patent/ES409718A1/es not_active Expired
  • 1972-12-18 JP JP12705672A patent/JPS559071B2/ja not_active Expired

Also Published As

Similar Documents