Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
  • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent
• • 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

• ABSTRACT OF THE DISCLOSURE An alloy specially adapted to color anodizing by close control of composition and method of preparation.
• the alloy contains from 0.090.l5% silicon, from OAS-0.65% iron, from 0.03-0.07% copper, from 0.70.9% magnesium, from 0.050.1% chromium and a maximum of 0.04% manganese and 0.25% zinc.
• the alloy is prepared by solution heating between 1100ll50 R, cooling to below 950 F. at a maximum rate of 30 F. per hour, cooling to below 250 F. at any rate, and reheated to a temperature below 950 F. for rolling.
• This invention relates to an aluminum alloy and a method for treating it which particularly adapts the alloy to accept an inherently colored anodic oxide coating.
• the process for producing inherently colored anodic oxide coatings on aluminum and aluminum alloys is now familiar.
• the coatings are produced by immersing the aluminum article to be anodized as the anode in an electric circuit which includes the anode, an inert cathode, and an electrolyte containing sulfuric acid and any of certain substituted aromatic sulfonic acids.
• aromatic sulfonic acids having particular utility are sulfosalicylic acid and sulfophthalic acid although others have been found to be operative.
• the anodizing process may be carried out with heavy metal sulfates dissolved in the electrolyte instead of or in addition to sulfuric acid, the most common of which is ferric sulfate.
• the anodic oxide coatings obtained by this process range in color from gold to black and may be made with almost any intermediate shade of bronze or brown. Such color anodizing processes have gained wide acceptance for producing aluminum for architectural and other decorative uses.
• one element that is beyond the anodizers control is the color response an alloy has to a color-anodizing treatment that results from metallurgical considerations.
• two specimens of a given aluminum alloy may have slightly differently colored anodic oxide coatings produced on them by identical anodizing processes if,
• alloys designated by the Aluminum Association classification system as 5005 have demonstrated desirable properties with respect to their ability to produce colored anodic oxides, and their ability to be formed into smooth sheets with physical properties adequate for architectural uses.
• the Aluminum Association composition designations for 5005 alloy are:
• This invention includes the discovery of composition limits for aluminum alloys used for producing inherently colored anodic oxide coatings, and thermal treatments for those alloys which create a sheet material that is not sensitive either to reasonable variations in composition or in thermal history. Therefore, this invention provides aluminum which is easy to anodize with reproducible and predictable appearance and aluminum which has these anodizing response properties locked in by mill practice so that anodizers, who are usually poorly equipped to carry out metallurgical processes, can simply anodize the material in the as-received thermally-treated condition and rely on the appearance-response that wiil be produced from the anodizing process.
• the invention includes constituting an aluminum alloy which consists essentially of aluminum, from about 0.06- 0.15% silicon, from about OAS-0.65% iron, from about 0.03-0.10% copper, up to about 0.07% manganese, from 07-09% magnesium, from about 0.05 to about 0.10% chromium, up to about 0.25% zinc and up to about 0.15% miscellaneous impurities. All compositions stated in the specification and appended claims are on a weight basis.
• the alloy thus constituted is cast as an ingot and heated to homogenizing temperature, preferably between 1100 and 1150 P. where it is maintained until most of the soluble elements enter solid solution, preferably for a period of at least 7 hours.
• the objective of this treatment is to produce a metallurgical structure in which the primary alloying ingredients and impurities are uniformly dispersed or dissolved in the aluminum.
• the alloy is then cooled slowly to a temperature lower than 950 F. the cooling being at an average rate of 30 F. per hour or slower.
• the ingot can be cooled to room temperature at substantially any rate and it may then be scalped or otherwise prepared for rolling.
• the ingot is reheated to a temperature below 950 F. preferably from 850-950 F. and maintained at that temperature for about 1 hour. Rolling may then be performed in the usual manner to produce sheet or plate of any desired thickness.
• milkiness or cloudiness in anodic oxide coatings is caused by particles of precipitated alloying elements or combinations of alloying elements.
• the cooling rate from homogenizing temperature is so rapid that the alloy quickly reaches a temperature at which diffusion of atoms or molecules within the alloy is very slow.
• precipitation is in the form of many small particles, and these many small particles will appear in a later produced anodic oxide coating where they will scatter light to give the effect of a cloudy or milky coating.
• the iron-containing particles which are usually combinations of iron with aluminum, manganese, chromium and other ingredients of the alloy.
• the time spent between homogenizing temperature where all of the soluble ingredients are either in solid solution or dissolving, and 950 R, where the diffusion rate for iron-bearing particles becomes too slow to permit significant growth of particles of precipitate, is prolonged enough to permit the iron-containing precipitate particles to form as relatively large particles.
• Example 1 Over an extended period, about 500 lots of 5005 alloy were cast and rolled. Metal compositions of these lots were within the following limits, expressed in percent:
• anodizing cell voltage reached 50 volts, anodizing was continued at that voltage until 10.5 ampere-hours per square foot of electricity had passed through the sheet.
• the anodized sheets were then immersed for 20 minutes at 195-205 F. in an aqueous bath containing 1.0 g./l. of sodium lignosulfonate and 0.5 g./l. of nickel acetate at pH 50:50.2.
• the color of each anodized sheet was measured according to the CIE system of color measurement. Green reflectance, an indication of the lightness or darkness of the surface, was measured by the percentage of incident green light reflected by the surface.
• Yellowness factor as defined by the term Amber Reflectance-Blue Reflectance Green Reflectance X Si 0.06-0.15 Fe 0.47-0.61 Ou 0.05-0.08 Mn 0.01-0.07 Mg 0.75-0.87 Cr 0.05-0.08 Zn (max.) I 0.25 Others (each, max.) 0.05 Others (total, max.) 0.15
• Example 1 All ingots were homogenized by holding for not less than nine hours at 1100-1150 F. and cooled at an average rate of 30 F. per hour, or slower, to 950 F. The ingots were then air-cooled to room temperature and scalped. For hot-rolling the ingots were reheated to 850-950 F., held for at least one hour, and then rolled. Cold rolling and annealing practice were as in Example 1. All sheet samples from this example were then etched, anodized and sealed as in Example 1 and the color factors measured. The green reflectances ranged from 19 to 27 inclusive and the yellowness factors from 22 to 29 inclusive. This represents a substantially smaller color range than in Example 1 and would be the preferred material for architectural use.
• the alloy constituted, thermally treated and rolled as set forth above has the following properties. It is a 5005 alloy with desirable properties of strength, fabricability,
• the alloy is not unduly sensitive to variations in thermal history. That is, two ingots having any thermal histories within the ranges characteristic of this invention will have substantially the same response to a color anodizing treatment.
• the material constituted as above is not sensitive to variations in composition, within the stated limits. That is, two ingots having any composition characteristic of this invention will have substantially the same response to a color anodizing treatment.
• the compositions and thermal treatments specified above lockin the color anodizing response of the sheet so that anodizers can rely on the color response of the alloy they receive and nee-d only concentrate on the details of the electrolytic anodizing function that they perform to insure reproducible colors in their product.
• the method of preparing aluminum sheet for color anodizing which comprises:
• '(A) constituting an alloy consisting essentially of from about 0.06-0.15% silicon, from about OAS-0.65% iron, from about 0.03-0.10% copper, not more than 0.07% manganese, from about 0.7-0.9% magnesium, from about ODS-0.1% chromium, not more than 0.25% zinc, not more than 0.15% other ingredients and the balance aluminum,

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Metal Rolling (AREA)
• Heat Treatment Of Steel (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (2)

• 1965
  • 1965-09-20 US US488715A patent/US3379580A/en not_active Expired - Lifetime
• 1966
  • 1966-03-31 GB GB14380/66A patent/GB1084988A/en not_active Expired
  • 1966-04-14 DE DE19661533306 patent/DE1533306B1/de active Pending
  • 1966-04-29 CH CH620566A patent/CH479713A/de not_active IP Right Cessation

Patent Citations (2)

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