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

• the present invention relates generally to improvements in metal treating and it relates particularly to an improved method for the production of integrally colored anodic oxidation coatings on articles of aluminum and alloys thereof and an improved electrolyte composition therefor.
• the conventional process for forming a colored anodic oxidized coating on articles of aluminum or aluminum alloys includes the step of immersing the aluminum article, which defines an anode, and a cathode defining electrode into an electrolyte, generally sulfuric acid, and applying a voltage between the article and cathode to effect the formation of an oxide coating on the article.
• the resulting coating is greatly deficient because of its high porosity a consequence of which is a low corrosion resistance.
• an additional separate dye treating step is required.
• the conventional aluminum anodizing procedure accordingly leaves much to be desired.
• Another object of the present invention is to provide an improved method and composition for the production of anodic oxidation coatings on surfaces of aluminum and alloys thereof.
• Still another object of the present invention is to provide an improved method and composition for producing on aluminum containing articles a hard highly corrosion resistant, colored, anodic oxidation coating.
• a further object of the present invention is to provide an improved single step method of the above nature characterized by a relatively low voltage requirement and power consumption, great versatility and adaptability, a wide range of colors and depths of color, and a superior resulting coating.
• the present invention is based on the discovery that the use, in the formation of an anodic oxidation coating on an aluminum containing surface, of an electrolyte comprising an aqueous solution containing, in addition to acetamide and oxalic acid, a small amount of sulfuric acid or a water soluble sulfate compound which provides sulfate ions in the aqueous solution, produces a hard, nonporous, highly corrosion resistant, deeply colored coating on the aluminum surface, and the voltage requirements between the aluminum surface and the cathode are greatly reduced with a corresponding reduction in power consumption.
• the present invention accordingly contemplates an electrolyte for the anodic oxidation of aluminum and alloys thereof comprising an aqueous solution of acetamide, oxalic acid, and sulfuric acid or a water soluble sulfate or a combination thereof, as well as the method of treating an aluminum containing work piece comprising immersing the work piece and another electrode in the improved electrolyte and applying a voltage between said work piece and said electrode of a value sufficient to form an oxidation coating on said work piece.
• the concentration of the sulfate ion in the aqueous electrolyte solution should be sufiicient to reduce the anodic oxidation coating voltage, advantageously to an initial voltage of less than 70 volts and a final voltage of less than volts, and advantageously constitutes by weight of the electrolyte of 0.01% and 0.5% sulfuric acid or its molar equivalent of a water soluble sulphate compound or a combination thereof with sulfuric acid, that is between about 0.01% and 0.5 of the sulfate ion.
• the electrolyte contains between 0.1 and 2.0 grams sulfuric acid per liter of electrolyte or the molar equivalent thereof of the sulfate compound or of said compound in combination with sulfuric acid.
• the electrolyte advantageously contains, by weight, 1% to 50% acetamide, preferably 30 to 200 grams acetamide per liter of electrolyte, and 0.1% to 10% oxalic acid, preferably 3 to 30 grams oxalic acid per liter of electrolyte.
• the temperature of the electrolyte in the anodizing procedure, the current density and the anodizing time may be greatly varied depending on the desired coating, and the optimum parameters are easily and readily determined by one skilled in the art. Thus an electrolyte temperature between 15 C. and 25 C. and a current density of the order of 2 a./dm. has been found to be highly satisfactory.
• the color of the anodic oxidation coating is dependent on the composition of the aluminum alloy of the article being treated.
• the present invention is characterized by an increased efficiency consequent to a reduction in the required anodizing voltage and in the power consumption and results in a significant reduction in equipment and costs.
• the improved process is capable of producing a very wide range and depth of colors without the need of separate dyeing steps.
• the color of the resulting coating is highly resistant to light and weathering and exhibits very little discoloration even when exposed for long periods to out-of-door infiuences and environments.
• articles coated by the present process posses such high wear and corrosion resistance properties that they are highly suitable for outdoor uses and applications.
• the coating obtained table, the voltage between the anode and cathode being with the use of the improved electrolyte is tough and regulated in known manner to maintaina constant current 1 high in wear resistance and is substantially free of any density: pores.
• Porhole test results in no deposition of copper Current Voltage range Temperature Time of density of solution anodizin N0. Material (aJdmfl) Starting Final 0 (min.
• an electrolyte similar to that ing in accordance with the present invention can 'be formed described above but without addition of sulfuric acid and in a wider range of colors which covers deeper colors as having the following composition was prepared: compared with the coating produced by anodic oxidation Grams/liter which utilizes an aqueous solution consisting of acetamide Acetamide 80 and oxalic acid. The higher the ratio of the amount of oxalic acid 10 acetamide to that of oxalic acid, the darker color of the Water 1 B a1 ance oxidized article is attained.
• the improved electrolyte set forth above may be 11 liter in total amounitmodified as earlier described by varying the concentra- Employing the above electrolyte Without sulfuric acid, tions of the acetamide, oxalic acid, and sulfuric acid or three aluminum plate work pieces were treated in the 40 sulfate ion in the manner earlier described.
• acid may be substituted in whole or in part by a water and parameters: soluble sulfate salt or compound which provides sulfate
• soluble sulfate salt or compound which provides sulfate The properties of the anodic oxidation coatings of the ions in aqueous solution whereby the sulfuric acid conlast treated samples are as follows: centration is as specified, preferably in the range of 0.1
• An electrolyte for the anodic oxidation of alumdensltles i c9nslderablii.less.wlth the Improved .electro inum and alloys thereof comprising an aqueous solution lyte resulting in a reduction in power consumption and containi b of S 1 t 01 t t 507 f equipment and installation costs.
• the electrolyte of claim 1 wherein said electrolyte performed but is preferably accomplished automatically Contains 30 to 200 grams P liter of Said acetamide, 3 by known electrical regulator networks so that the current to 30 grams per er of Said OXalic acid, and f0 2 density does not vary during the full treatment period grams per liter of said sulfuric acid or the molal equivalent thereof of a water soluble sulfate or a combiuation thereof with sulfuric acid.

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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)
• Chemical Treatment Of Metals (AREA)
• Electrochemical Coating By Surface Reaction (AREA)

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• 1969
  • 1969-01-17 JP JP44003522A patent/JPS4924329B1/ja active Pending
  • 1969-07-15 US US842030A patent/US3597338A/en not_active Expired - Lifetime

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