US2941930A - Decorative aluminum surface - Google Patents

Description

June 21, 1960 N. MOSTOVYCH ETAL DECORATIVE ALUMINUM SURFACE Filed May 28. 1957 INVENTORS Mam/1s MOSTOVICH n/v BY WALTER nm/mm, J/a

DECORATIVE ALUMINUM SURFACE Nicholas Mostovych, Louisville, and Walter A. Mitchell,

Jr., Anchorage, Ky., assignors to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed May 28, 1957, Ser. No. 662,141

12 Claims. (Cl. 204-29) This invention relates to ornamental aluminum and aluminum alloy products and to a method for producing the same.

An object of our invention is the production of aluminum and aluminum alloy products having highly valuable decorative and ornamental characteristics, and in which products the decorative finish achieved not only affords protection against corrosion of the underlying metal but itself is durable under many and varied conditions of exposure.

Another object is the provision of products of the character indicated in which the ornamental surface finish introduces to the eye a variety of different shades or tones of any particular color of the finish.

A further object of our invention is the provision of finish is in an integral filmformed of the metal itself.

Another object is that of providing a direct and thoroughly practical method for producing aluminum and aluminum alloy metal products, having ornamental and decorative properties.

A still further object of our invention is the provision of a method for coloring aluminum and aluminum alloys which with regard to a particular decorative color application simultaneously produces varied shades and tones of the color from a given uniform source of the color.

Other objects of the invention in part will be obvious and in part will be pointed out more fully hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts, and in the several steps and the relation of each of the same to one or more of the others as described herein and the scope of the application of which is indicated in the following claims.

In the drawing which forms a part of this specification,

Figure 1 represents an enlarged corner section of lightly etched metal treated in accordance with the principles of the present invention.

Figure 2 is similar to Figure 1 except the etching action has continued until a pronounced surface relief results.

Figure 3 is a representative cross-section of Figure 2.

Figure 4 shows a metal sheet whose large crystals have become elongated during roll bonding to a base sheet.

Figure 5 represents a ribbed sheet whose ribs have been considerably reduced in thickness by cold working.

Figure 6 represents a ribbed sheet whose ribs have been moderately reduced in thickness by cold work.

Figure 7 represents a ribbed sheet whose ribs are only slightly reduced in thickness by cold work.

As conducive to a clearer understanding of certain features of our invention it may be noted at this point that aluminum, by which we mean to call the high purity metal itself or aluminum-base alloys, are relatively lightweight metals Which fulfill a wide variety of well known needs and for example in so doing take the form of sheet, strip, bars, rods, tubes, structural members, household articles and utensils, hardware, trim, blocks and a host of other shapes, articles and products. There is a great possible outlet for ornamental and decorative products of the metal in the form of any of the products just named and there are many other possible outlets, illustratively United States Patent 0 products of the character indicated in which the decorative ice ornamental Wall panels for inside or outside use in buildings, store or restaurant furnishings, objects of art, ornamental edgings, frames and especially extruded, rolled, or spun articles of manufacture but in order to supply this demand a solution enabling the commercially feasible production of widely useful ornamental and decorative finishes which are pleasant, beautiful and durable become necessary.

An outstanding object of our invention accordingly is the commercially practical production of decorative and ornamental aluminum and aluminum alloy manufactures having durable surface beauty and which production in general lends itself to the provision of any of a great variety of products having the desired surface finish.

Referring now more particularly to the manner of producing a decorative or ornamental product, we find that aluminum, by which we mean the high purity aluminum metal itself or any of a variety of aluminum-base alloys including heat treatable alloys responds to anodizing treatment and dye coloring with most striking after .effect if at least the metal grains in certain areas of the metal surface first are adjusted to coarse sizes which are visible to the naked eye and the metal is etched before treatment in the anodizing bath. When the faces of the macroscopic crystals undergo the anodizing treatment, these faces take on by alteration a thin oxide film in the bath and thus the underlying metal is shielded and has its resistance to corrosion appreciably enhanced, but of further importance the oxide when introduced to dye, very distinctively takes on different tones and hues of the dye color over the macroscopic crystal faces depending upon which of the anodized grain faces in the great maze of crystals the dye encounters. To the eye of an observer, the depths of the color tones actually seem to alter when the viewing angle is changed. A most beautiful, varied and interesting anodized aluminum surface thus becomes a reality. The dye coloring is carried in the electrochemically derived oxide film which itself is integral with the underlying metal.

Very. pleasing ornamental effects on aluminum thus are had from our anodizing and dyeing treatments where the metal subjected to those operations has crystals developed :by heat, treatment to predominately macroscopic sizes at least in localized surface areas or over the entire product surface. The majority of the macroscopic crystals preferably have sizes anywhere in the approximate range of a fraction of a millimeter to three centimeters or more when measured in plan across the crystal boundaries on the metal surface. For bringing the crystals to sizes falling within this approximate range we usually impose strain in the metal such as by cold rolling, bending, pressing, drawing, or stretching from a substantially dead-annealed or stress-free condition of the aluminum body to which the strain is to be applied, and then follow with recrystallization heat treatment. Grain size is primarily a function of strain, annealing temperature and heat-up rate. With little or no strain, no crystal growth is induced. With a critical amount of strain, a large grain size results. As the strain is increased above the critical amount, the grain size diminishes in size, rapidly at first and then more slowly. Small strain and high annealing temperatures produce the largest crystals. A strain which is equivalent to about 1% to 15% reduction in thickness of the metal followed by annealing at approximately' 600 F. to 1150 F. for re-crystallization are preferred. The period of time which the metal is held at the rte-crystallization temperature to grow crystals of desired size may vary considerably depending upon such factors as whether the aluminum is in the form of high purity aluminum or is some specific aluminum base alloy, the particular amount of strain imparted, the actual temperature of re-crystallizationheat treatment, and heat-up 3 rate. For strains and temperatures within the preferred ranges of strain and re-crystallization temperatures hereinbefore noted, a period of about ten minutes to three hours time is usually satisfactory for developing a continuous crystal lattice in the metal which has been so strained.

The coarse grained aluminum product is subjected to an etching or crystal revealing treatment and for this purpose We use one or more acids such as hydrochloric acid in combination with nitric acid, sometimes with additions of hydrofluoric acid, in an aqueous bath. A caustic solution may also be used. The metal conveniently is immersed in the crystal revealing bath for a period of time which produces a clean, etched aluminum surface having the crystal faces exposed so that the faces and their boundaries are clearly visible to the naked eye. For a mild etch and to give only a slightly high-low crystal pattern on the metal surface we restrict the etching period to just a few minutes time and then remove the metal, at which point some of the crystal faces on the surface are slightly outward from others of the crystal faces making up the surface. In this condition of slight relief, (see Figure 1), the metal may be finished by anodizing and dying to produce the colored product. In other instances the etching treatment is prolonged to give pronounced depth dimensions (see Figure 2) which are derived by the selective action of the etching solution on the various crystal faces. Some of the faces are selectively eaten away and finally the relief of some of the macroscopic crystal faces with respect to others is so pronounced as to introduce substantial physical depths.

A durable and highly effective etching bath which we prefer for the purpose is one heated to approximately 120 F. and which contains in approximate amounts, by volume, to 40% nitric acid, 20% to 40% hydrochloric acid, and the remainder substantially all water. To this may be added 1% to 3% hydrofluoric acid if etching at room temperature is desired. The acids identified above usually are commercial grades of the acids. By treating the coarse grained aluminum in the bath for about one minute to ten minutes time a mild etch results and by prolonging the treatment for a time ranging up to an hour or more a relatively severe .action takes place to produce a surface having certain grain faces a great deal deeper than the faces of adjacent grains. After the etching action has progressed the desired amount, the metal is removed from the bath and .is rinsed clean in water.

After etching the ahuninum and exposing the crystal faces and their boundaries, We make the metal the anode of an anodizing bath and accordingly electrolytically oxidize the exposed areas of the product such as the faces of the various macroscopic crystals. Usually we anodize the entire metal surface and thus add the protection of the oxide layer. We prefer to use an electrolytic bath which produces relatively transparent oxide film on the metal surface for, with a film of that sort, especially desirable optical properties are gained for the final product. In Figure 3 can be seen the difference in surface roughness between the more resistant and only slightly etched crystals and those crystals which are less resistant which have been deeply etched. The rough surface of the'less resistant crystals has a greater thickness of oxide film thereon which will absorb more dye than the more resistant crystals. Also, the surface roughness of the less resistant crystals causes a diflusion of the light in contrast to the high reflectivity of the mirror-like surface of the more resistant crystal faces. Thus, after anodizing the coarse grained metal, some of the crystal faces have relatively high specular reflectivity and other faces have a more difiuse reflectance, and this is all the more prevalent when the anodized fil'm is itself transparent. On anodizing, it appears that the resulting oxide film thickness depends upon orientation of each particular crystal and, in fact, thickness may vary as much as or 4 more with crystallographic direction. Those crystal faces which have been most etched during the etching and crystal revealing treatment will have the heaviest oxide film and most diifuse surface after anodizing and accordingly absorb more dyestufl than a face which has been relatively resistant to etching. On being colored, certain crystals-on the metal surface are revealed in lighter color than are others with the result that many and different color shades and hues attract the eye, and by making the oxide film transparent, as preferred, 'the reflectance of the aluminum under the oxide film contributes a metallic aspect through the color. A sulfuricacid anodizing bath is preferred for it gives a very good transparent oxide film on the aluminum and the film has excellent dyeing properties. A typical sulfuric acid anodizing bath which we employ for the purpose is given as follows along with certain operating conditions which have been found to be practical with use:

15% sulphuric acid (by weight) 70 F. electrolyte temperature 12 amperes square foot current density (direct current) '15 to'3O minutes anodizing time In coloring the oxide film we usually immerse the aluminum .product in a dye bath having the desired color. Among the types of dyes utilized are well known commercial dyes such as ferric ammonium oxalate for gold and Alizarin 'Saphiral B for blue. The colors applied to the oxide may, of course, be any of a wide variety including red, pink, :yellow, orange, green, blue, black, 'bufi, brown, 'or gold, depending on the dye selected. After coloring, the film is sealed to advantage such as by treatment in boiling water, steam, or other sealing media.

Sometimes, especially when high purity aluminum is used, the surface is too bright for the intended purposes. This brightness may be reduced by a low temperature, high current density anodizing treatment, preferably using A.C. current although DC. current is also satisfactory. AC. anodizing for a few minutes at 40 to 60 F. and a current density of to 300 amperes per square foot gives very satisfactory results. Another way of reducing brightness is by dislocating and straining the crystals after the recrystallization treatment but before the crystal revealing etch.

Our process also readily lends itself to the frequently useful aspect of masking out with a suitable masking composition any desired areas of the oxide film which are not to be colored in the dye bath, thus to contribute to ornamentation. .Also, the high spots may be dyed one color and the low spots a different color by means of well known masking and bleaching techniques. After dyecoloring the exposed areas of the film, the masking composition is -removed and the entire film then is sealed. This selective masking may also be employed to present the action of the grain revealing etch in selected areas if such be desired.

In making wrought aluminum products such as sheet or strip, starting from ingot the metal conveniently is reduced by a series of hot and cold rolling passes to a gauge which is somewhat thicker than the desired final product. The cold reductions are accompanied by annealing steps which destroy the effects of cold working. The reductions and annealing temperatures introduced at this point usually are conducive to the formation of grains of microscopic sizes and as a further result the metal is soft, stress relieved, and ready for further cold work. Then after the last of these cold reduction passes and annealing treatments, as described, the metal is ready to receive a critical amount of cold work which is needed for growing crystals of macroscopic sizes. Thus, by cold-deforming the dead-annealed aluminum sheet or strip, such as by forming, bending, stretching or rolling .to introduce amounts of strain which are commensurate with strains developed by a cold reduction in thickness ranging from 1% to 15%, or somewhat more, we prepare the metal for crystal growth. Then, on heating the metal up to 600 F. to 1150" 'F. in an annealing furnace, crystals of macroscopic sizes grow while the heating is continued. To a degree, the heat-up rate controls the ultimate sizes of the grains for the same amount of strain. A high heat-up rate gives smaller crystals than where the rate is lower and in this connection relatively slow rates up to 1000 F. per hour are preferred for attaining annealing temperature. Heating the metal for about ten minutes to thirty minutes, especially at the lower end of the preferred range of re-crystallization temperatures given, usually produces uniform aquiaxed crystals which in size are approximately equal to the thickness of the metal sheet or strip. A longer annealing time, especially at a higher temperature in the preferred heating range usually favors continuous crystal growth and continuous migration of the crystal boundaries resulting in larger grains as viewed in the plane of the surface of the sheet or strip. By prolonging the annealing period and using annealing temperatures which are close to the melting point of the metal, very large crystals as viewed in the plane of the sheet or strip develop which are some one or more centimeters in size across their opposite boundaries. This type of crystal pattern comes most readily from aluminum alloys having a crystal inhibiting phase such as insoluble impurities.

Since the aluminum has been re-crystallized, it is in the soft fully annealed condition. In order to impart to the aluminum hardness and strength, which is sometimes desirable, it is necessary to cold work the aluminum after recrystallization or else use a heat treatable alloy which is given a solution heat treatment to improve same after the recrystallization treatment. The heat treatable alloys and the solution heat treatment necessary for making them strong are well known to those skilled in the art. Both in the specification and claims, re-crystallized aluminum which is either cold worked or made from a heat treatable aluminum alloy which has been solution heat treated is referred to as strong aluminum. Further, it is to be understood that solution heat treated aluminum means a heat treatable aluminum alloy which has been solution heat treated to improve its physical properties.

Our process lends itself to such modifications as rolling or otherwise attenuating the coarse grains in the aluminum product and this, for example, is done immediately after growing the crystals by the recrystallization heat treatment already described. The coarse grains are soft and elongate in the direction of working such as to give a striated crystal pattern on the metal surface, illustratively a surface having the crystal pattern represented in Figure 4 of the drawing. After elongating the crystals by working, .the metal is etched to expose the crystal faces, is anodized and colored in the manner hereinbefore set forth. Rolling to attenuate the coarse grains often is practiced by us in order to increase the properties of the metal by the cold working while simultaneously achieving the attractive elongated grains. Cold working of the metal after recrystallization to make strong aluminum can be accomplished in numerous ways. For example, the aluminum may be flexed back and forth by passing through a series of rollers arranged similar to those used to straighten wire. Also, the rolling may be used for the further purpose of roll cladding a sheet or strip of the coarse grained aluminum to a stronger backing (see also Figure 4) which for example may be a sheet of other metal such as an alloy of aluminum hardened by heat treatment. Such rolling and bending has to be done below the recrystallization temperature in order to preserve the large grains. Quite often the aluminum which we treat in accordance with our process is the highly pure metal itself since it is particularly easy to control from the standpoint of growing grains of desired size and is quite amenable to the growth of grains of uniform size and to secure high brightness after anodizing, yet

e the metal is deficient in physical strength for certain needs. By roll cladding this metal onto a strong backing, strength or other requirements are conveniently met and a highly ornamental product is readily had by finishing in accordance with our process.

When critically straining the metal preparatory to growing grains of macroscopic size we often vary the amount of strain from area to area of the metal and thereafter by heat treatment grow crystals in one or more of the areas which are larger than the crystals in areas elsewhere orfthe surface. The crystals illustratively may be of macroscopic sizes in all of the areas or of macroscopic size in certain of the areas depending upon the stress pattern imposed and the subsequent heating. 'Ihus, sometimes strain is developed to a sufiiciently high degree in some of the areas to preclude large grain growth entirely and thus the grains remain invisible to the naked eye after heat treatment which grows macroscopic size grains in other areas which were less strained. Selective straining of the metal may be achieved in many possible ways. As a first example we have pressed a design into an annealed aluminum sheet or strip. Thus, subsequent heat treatment for growing crystals will give large crystals in the area of the design.

Certain ribbed sheet aluminum products which we frequently provide are made to have raised ridges which define valleys between the ridges, these ridges for example being spaced parallel ribs running the length of the metal body. Then starting with the ribbed product in a dead-annealed condition we imposed varying strainon the ridges and valleys or exclusively strain either the ridges or the valleys as by rolling, peening, pressing, or the like. The strain differential between ridges and valleys on' re-crystallization heat treatment accordingly is made great enough to induce marked differences in the sizes of grains on the high and low areas whether the grains in several areas become macroscopic with heat treatment or whether the grains are macroscopic exclusively on the ridges or the valleys. In other instances we roll the ridges completely into the plane of the valleys and in so doing impose a relatively light strain on the valleys and high on the ribs, and then grow grains which produce a pattern commensurate with the stress. Examples of the above are illustrated in Figures 5, 6 and 7. In Figure 5 the ribs were reduced 22% to give microscopic grains on the ribs and macroscopic grains in the slightly worked valleys. The ribs of Figure 6 were reduced 8% to give small grains on the ribs and larger grains in the valleys. The ribs of Figure 7 were only reduced 1% to give large grains on the ribs with no visible grains in the-unworked valleys.

We frequently resort to localized flexing of deadennealed aluminum sheet, strip, or the like to vary the strain pattern before crystal growth heat treatment. Stamping or pressing an emblem or the like against the metal surface to introduce localized strains in accordance with particular areas of the emblem is a further alternative, thus to produce a strain impression which in accordance with macroscopic crystals develop in at least enough of the areas to delineate the emblem or other pattern on heat treatment. The emblem or pattern strain impression .of course lends itself to being repeated at intervals 'on the metal surface, either alone or with other emblems on patterns to pluralize the ornamental effect.

In those instances Where certain areas on the product surface are characterized by a microscopic grain structure while other areas on the same surface have developed grains of macroscopic size after heat treatment, etchcing of course brings out the coarse grains, but fails to reveal the microscopic grains to the naked eye. The entire product surface advantageously is anodized to gain the benefit of the protective oxide film even over those areas which have the minute grains, and on applying dye color to the film surface the coarse grained areas take on a variated color shade aspect, as previously exgold and diffuse yellow.

, 7 plainedfwhile those portions of the'film overlying the areas having the minute grains retain a more even tone.

EXAMPLE A 0.020 inch gauge sheet of high purity aluminum is provided containing approximately 99.87% aluminum and the remainder small and incidental amounts of impurities of which iron and silicon are present each in amounts up to 0.06% maximum. The sheet is annealed at about 700 F. for approximately one hour in a suitable annealing furnace and then is air cooled to room temperature giving full stress-relief and microscopic size of the metal grains. Then, the dead annealed all); minum sheet is rolled so as to elongate it about 8%, and accordingly introduce a substantially constant amount of strain throughout the sheet. Thereafter, the sheet is annealed at about 1100 F. for two hours using a slow heat-up rate of less than about 1000 F. per hour to attain annealing temperature. After air cooling the heated treated product to room temperature, it is etched for about three minutes at 120 F. in an acid bathcontaining by volume, 35% commercial nitric acid, 40% commercial hydrochloric acid, and the remainder sub? stantially all water. The mildly etched product is rinsed in clean water and then the entire sheet is anodized in an aqueous acid bath containing by weight 15% sulphuric acid and the remainder substantially all water. Thebath is maintained at about 70 F. during this treatment and the anodizing period endures for approximately fifteen minutes using direct current and a current density of 12 amperes per square foot of the aluminum metal surface being anodized. Thus, a transparent oxide film forms on the exposed grain faces of the metal. The anodized product is rinsed free of electrolyte in clean water and thereafter is immersed in a dye bath of ferric ammonium oxalate which imparts a gold color to the oxide film. The colored film is sealed by immersion for about fifteen minutes in water heated to 200 F. and the colored product is removed and dried. The grain faces on the surface of the sheet, though differently oriented and different in outline at their boundaries, each measure about 0.10 inch in diameter. The entire aluminum sheet metal surface treated is characterized by the presence of bright gold with other shades of gold and diffuse yellow and has great beauty such as for ornamental wall panel use or the sheet may serve any of a wide variety of other possible uses. On occasions we cut the sheet into blocks such as those which serve as substitutes for wall block tile, or make strips which for example are used for trim, edgings, striping, or the like, or the sheet is otherwise cut or fabricated to desired ornamental shape.

A 0.020 inch gauge alloy aluminum panel containing about 0.20% to 0.40% manganese, 0.90% to 1.2% magnesium, copper 0.05% maximum, iron 0.15% maximum, silicon 0.1% maximum and the remainder substantially all aluminum treated in accordance with Example I except for being subjected to a grain growing annealing heat of about 1000" F. for two hours, has a beautiful gold finish including bright gold with other shades of The grain faces on the surface of the panel each measure about 0.30 inch in diameter.

EXAMPLE III A homogenized cast aluminum alloy billet containing seventy to ninety seconds to an extrusion temperature s 0 F. t and. 3 0 While-s9 h a e iving intermediate products. The extruded lengths are cooled in still air and subsequently are stretched cold at room temperature to achieve an elongation of about 8%. Following this, the products are subjected .to a crystal growing heat treatment and solution heat treatment a 925 F. to 1025" F. for about two hours in. an annealing furnace and thereafter are dip quenched in water to room temperature. An aging heat treatment then is given the metal products, this being a heat at 350 F. for three hours to improve the ultimate strength of the products. From this point on, the extruded prodnets are etched, anodized, dyed and sealed consistent with the same steps and working conditions set forth in Example I. The coloring achieved on the metal is in general somewhat less bright than on the products .in Examples 1 and II but nevertheless is very attractive in the subdued color sense. The grain size is quite uniform and on the order of 0.10 inch diameter across each crystal face exposed.

EXAMPLE IV A ribbed material as shown in Figures 6, 7 and 8 of aluminum alloy 5,357 comprising approximately 0.3% manganese, 1.0% magnesium, a maximum of 0.1%

silicon, a maximum of 0.15% iron, a maximum of 0.05%

copper and the remainder aluminum was soft annealed at 750? F. for thirty minutes. They were then cold rolled to produce strain. The amount of reduction on the ribs varied from 1.-22%. After rolling, the metal was annealed at 1080" F. for a period of two hours to re-crystallize. The metal was etched, anodized and dyed as in Example I. Results were as follows:

When the ribs received about 1% reduction, crystals were formed on the ribs with no noticeable crystals in the valleys. The ribs were bright and the valleys were etched in appearance.

When the ribs received about 8% reduction, small crystals appeared on the ribs with large crystals in the valleys.

When the ribs received 22% reduction, the valleys were reduced a few percent, the ribs had no noticeable crystals and .was of an etched appearance whereas bright large crystals appeared in the valleys. i

All three samples presented a very attractive appearance.

EXAMPLE V Ashtrays were produced by a two-step drawing with aluminum alloy 1187 comprising at least 99.87% a111 minum with the remainder being impurities with a maxiof 0.06% silicon, 0.06% iron and 0.005% titanium.

In thefirst step, the metal was formed up to After soft annealing between 700800 F., final forming was done upon the remaining amount up to. 15% to induce critical strain. After annealing at 1050" F. for one hour, the sample was etched, anodized dyed above, presenting a very decorative finish. In order to get uniform crystals, proper dies should be used to assure uniform critical strain during the final operation. H 6' EXAMPLE v1 Dinner plates of regular household size and shape were formed by shallow drawing with the alloy of Example .IV. Group A was annealed for two hours at 1050 .F. Group B at 800 for three to five minutes. Group .C at 800 F. for seven to ten minutes. After annealing, the plates were etched, anodized and dyed as above. The following results were obtained:

Group A. ,These plates showed complete coverage of small and large crystals depending on strain.

Group B.These plates showed one ring of smal crystals at the place of greatest strain. V Group C.T hese plates showed two rings of small crystals at the two places of greatest strain.

All plates had an appealing effect.

In practicing the process herein described, a sheet of aluminum can be critically strained and then annealed to provide the grain growth desired. Subsequently, an ar-, ticle can be formed from this sheet such as a lamp shade made by spinning. This formed article is then etched to reveal the grain structure which simultaneously removes the tool marks. After anodizing the articles and dying them, they take on a very attractive appearance.

Thus it will be seen that in this invention there is provided a method and products in which the various objects hereinbefore noted, together with many thoroughly practical advantages, are successfully achieved. It will be seen that the products may take any of a wide variety of forms among which are sheet, strip, bars, rods, tubes, structural and ornamental members for inside and outside use such as for automobiles, buildings, stores, restaurants, or the like, ornamental edgings, wall panels, blocks, frames, furnishings, grills, objects of art and especially formed, extruded, rolled, or spun articles of manufacture, and that in view of the highly attractive durable finishes achieved, the products are most desirable and appealing. Further, machining marks are removed and the products are made relatively scratch-proof and corrosion resistant by the process. Also it will be noted that our method is highly commercially feasible and practiced and advances the general art to the end of yielding articles and products having extremely worthwhile ornamental and decorative values and widespread utility.

As many possible embodiments may be made of our invention and as many changes or alterations may be made in the embodiment hereinbefore set forth, it is to be distinctly understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

We claim:

1. In a method of ornamenting and decorating aluminum base metal from the class consisting of aluminum and aluminum base alloys, the improvement comprising providing said metal in a dead-annealed condition with its grains minute in size, cold-deforming said metal equivalent to a reduction of approximately 1% to in thickness thereof, heating the cold-deformed metal for recrystallization to a temperature of about 600 F. to 1150 F. for approximately ten minutes to three hours to develop large crystals in the metal body, said crystals having faces of macroscopic size which are visible on the metal surface after etching, etching the surface of said metal in an etching solution to clearly expose said crystal faces and their boundaries at said metal surface, making the metal the anode of an electrolytic anodizing bath and forming a corrosion-resistant transparent film of aluminum oxide integral with the metal on said crystal faces and sealing said film to render it non-porous, whereby upon viewing said crystal faces through said film, different shadings are seen which differ from crystal face to crystal face.

2. In a method of ornamenting and decorating aluminum base metal from the class consisting of aluminum and aluminum base alloys, the improvement comprising providing said metal in a dead-annealed condition with its grains minute in size, cold-deforming said metal equivalent to a reduction of approximately 1% to 15% in thickness thereof, heating the cold-deformed metal for recrystallization to a temperature of about 600 F. to 1150" F. for approximately ten minutes to three hours to develop large crystals in the metal body, said crystals having faces of macroscopic size which are visible on the metal surface after etching, etching the surface of said metal in an etching solution to clearly expose said crystal faces and their boundaries at said metal surface, making the metal the anode of an electrolytic anodizing bath and forming a corrosion-resistant film of aluminum oxide integral with the metal on said crystal faces, dyeing said oxide film overlying said crystal faces to impart a visual characteristic to said crystal faces viewed through said oxide film, and sealing said film to render it nonporous, whereby upon viewing said crystal faces through said film, ornamental and decorative shades and hues of color differing from crystal face to crystal face are observed.

3. A method as claimed in claim 1 wherein said metal is cold-worked by rolling after said recrystallization step and before said anodizing step, whereby said crystals are appreciably elongated in the direction of said rolling as viewed in plan on said visible surface and having generally the same direction of attenuation.

4. A method as claimed in claim 1 wherein said aluminum metal is clad to a backing sheet of metal which is stronger than said aluminum metal.

5. A method as claimed in claim 1 wherein said metal is an alloy of aluminum which is solution heat-treated after said recrystallization step and before said anodizing step to increase the hardness without changing the size of said large crystals.

6. A method as claimed in claim 1 wherein said metal is work-hardened after said recrystallization step and before said anodizing step to increase the hardness of said large crystals.

7. A method as claimed in claim 1 wherein said coldworked metal is heated to a temperature of about 600 F. to about 1150 F. at a heat-up rate of not more than 1000 F. per hour.

8. A method as claimed in claim 1 wherein said metal is formed into a finished article of manufacture after said recrystallization step and before etching.

9. An ornamental decorative aluminum metal product having a corrosion-resistant non-porous transparent surface of aluminum oxide, comprising crystals in the body of said metal disposed in physical relief and having etched crystal faces of macroscopic sizes on the visible surface of the metal made by the process of claim 1.

10. An ornamental decorative aluminum metal product having a corrosion-resistant non-porous transparent surface of aluminum oxide, comprising crystals in the body of said metals disposed in physical relief and having etched crystal faces of macroscopic sizes on the visible surface of the metal made by the process of claim 2.

11. An ornamental decorative aluminum metal product having a corrosion-resistant non-porous transparent surface of aluminum oxide, comprising crystals in the body of said metal disposed in physical relief and having etched crystal faces of macroscopic sizes on the visible surface of the metal made by the process of claim 3.

12. An ornamental decorative aluminum metal product having a corrosion-resistant non-porous transparent surface of aluminum oxide, comprising crystals in the body of said metal disposed in physical relief and having etched crystal faces of macroscopic sizes on the visible surface of the metal made by the process of claim 4.

References Cited in the file of this patent UNITED STATES PATENTS 2,050,069 Smith Aug. 4, 1936 2,165,027 Bitter July 4, 1939 2,186,721 Guild Jan. 9, 1940 2,262,696 Nook et al. Nov. 11, 1941 2,363,339 Kraft et al. NOV. 21, 1944 2,538,317 Mason et al Jan. 16, 1951 2,647,865 Freud Aug. 4, 1953 2,683,113 Prance et al. July 6, 1954 2,703,781 Hesch Mar. 8, 1955 2,769,265 Page Nov. 6, 1956 2,780,591 Frey Feb. 5, 1957 FOREIGN PATENTS 763,336 Great Britain Dec. 12, 1956 OTHER REFERENCES The Nature of Metals, Bruce A. Rogers (1951), American Society for Metals, Cleveland, Ohio, and The Iowa State College Press, Ames, Iowa, pages -185.

Claims (1)

1. IN A METHOD OF ORNAMENTING AND DECORATING ALUMINUM BASE METAL FROM THE CLASS CONSISTING OF ALUMINUM AND ALUMINUM BASE ALLOYS, THE IMPROVEMENT COMPRISING PROVIDING SAID METAL IN A DEAD-ANNEALED CONDITION WITH ITS GRAINS MINUTE IN SIZE, COLD-DEFORMING SAID METAL EQUIVALENT TO A REDUCTION OF APPROXIMATELY 1% TO 15% IN THICKNESS THEREOF, HEATING THE COLD-DEFORMED METAL FOR RECRYSTALLIZATION TO A TEMPERATURE OF ABOUT 600*F. TO 1150*F. FOR APPROXIMATELY TEN MINUTES TO THREE HOURS TO DEVELOP LARGE CRYSTALS IN THE METAL BODY, SAID CRYSTALS HAVING FACES OF MACROSCOPIC SIZE WHICH ARE VISIBLE ON THE METAL SURFACE AFTER ETCHING, ETCHING THE SURFACE OF SAID METAL IN AN ETCHING SOLUTION TO CLEARLY EXPOSE SAID CRYSTAL FACES AND THEIR BOUNDARIES AT SAID METAL SURFACE, MAKING THE METAL THE ANODE OF AN ELECTROLYTIC ANODIZING BATH AND FORMING A CORROSION-RESISTANT TRANSPARENT FILM OF ALUMINUM OXIDE INTEGRAL WITH THE METAL ON SAID CRYSTAL FACES AND SEALING SAID FILM TO RENDER IT NON-POROUS, WHEREBY UPON VIEWING SAID CRYSTAL FACES THROUGH SAID FILM, DIFFERENT SHADINGS ARE SEEM WHICH DIFFER FROM CRYSTAL FACE TO CRYSTAL FACE.

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