The Boeing Company

Yukimori Moji

J Arthur Marceau

Ralph H Firminhac

Chun-Ming Wong

Joseph Arthur Marceau

Joseph Corey McMillan

Dennis J Donnelly

Richard Q Taylor

A controlled method of anodizing aluminum comprises formation of an aqueous solution of sulfuric and boric acids, immersion of a workpiece in the solution maintained at about room temperature and controlled application of voltage to achieve a current density not greater than about 10 Amperes per square foot. Aluminum oxide coatings in the weight range of from about 200 to 600 milligrams per square foot applied in this manner have properties as good as or superior to coatings applied in traditional hexavalent chromium anodizing solutions.

Method for anodizing aluminum

A method of fabricating a honeycomb core sandwich structure with an embedded fastener and the resulting structure are disclosed. The method comprises laying down a first nonmetallic synthetic layer (11), preferably a graphite epoxy layer, which may be cured or uncured. Bonded to the first nonmetallic synthetic layer is a honeycomb core layer (15) into which one or more flush head fasteners (25) have been inserted. The flush head fasteners are inserted into holes (13) in the honeycomb core that have an indentation (19) at one end that is configured to mate with the underside (21) of the head (23) of a flush head fastener (25). Bonding is accomplished by priming the walls of the honeycomb core layer adjacent the surfaces of the layer, and the fastener, with a suitable primer, preferably before the fastener is installed, and, coating one of the surfaces of the first nonmetallic synthetic layer (11) with a suitable adhesive before joining the first nonmetallic synthetic layer (11) to the surface of the honeycomb core layer (15) containing the head (23) of the flush head fastener (25). Thereafter, the cells of the honeycomb core that surround the fastener are filled with a potting material (35). Then, a second nonmetallic synthetic layer (37) is bonded to the surface of the honeycomb core remote from the surface to which the first nonmetallic synthetic layer (11) is bonded.

Honeycomb core structure with embedded fastener

The corrosion resistance and coating adhesion characteristics of an aluminum oxide film produced by anodization is improved by contacting the film with a dilute aqueous solution of an oxidizing composition, for example chromic acid, and a pH altering substance that maintains the pH of the solution between 3.0 and 5.0. Exemplary pH altering compositions are respectively chromic acid and sodium or magnesium chromate.

Method for sealing an aluminum oxide film

Environmentally stable bond joints of aluminum metal and aluminum alloys in adhesively joined structures are formed by utilizing a prebonding anodization of the aluminum surfaces in a phosphoric acid electrolyte using an electrolyte bath temperature of 60.degree. to 85.degree. F. The anodized surface is then removed from the electrolyte bath and washed free of electrolyte within from one half to two and one half minutes from cessation of anodizing current, dried and coated with adhesive resin. The anodized aluminum metal surfaces are then juxtaposed with an adhesive resin and bonded together under pressure and heat to cure the adhesive resin. The resulting structure is resistant to failure of the bond joints on exposure to moist atmospheric conditions. The surface preparation provides a porous hydration resistant aluminum oxide surface which minimizes adhesive failure to the oxide-adhesive interface under aqeuous exposure. Alloys containing copper and other constituents may be successfully anodized and bonded by this process.

Method for providing environmentally stable aluminum surfaces for

Environmentally stable bond joints of aluminum metal and aluminum alloys in adhesively joined structures are formed by utilizing a prebonding anodization of the aluminum surfaces in a phosphoric acid electrolyte containing from about 1.5 to about 50% H.sub.3 PO.sub.4 at 1 to 50 volts for a period of 5 to 60 minutes using a bath temperature of 50.degree. to 100.degree. F. The anodized surface is then washed free of electrolyte, dried and coated with an adhesive resin. The aluminum metal segments are then arranged in a composite arrangement and bonded together under pressure and heat to cure the adhesive resin. The resulting structure is resistant to failure of the bond joints on exposure to moist atmospheric conditions. The surface preparation provides a hydration resistant aluminum oxide surface which minimizes adhesive-aluminum separation under aqueous exposure. Alloys containing copper and other alloying constituents may be successfully anodized and bonded by this process.

A method of preparing a stainless steel surface for bonding by anodically treating the steel in an electrolytic bath, at a temperature of 60.degree. F to 180.degree. F, of an aqueous solution of sulfuric acid or an aqueous solution of sulfuric and chromic acids with an impressed voltage during anodizing of a range to remain within the passive region of the stainless steel.

Preparing an environmentally stable stainless surface for bonding

An environmentally durable, aluminum honeycomb structure is obtained by surface treatment and application of a polymeric film forming substance to the aluminum foil used in manufacture of honeycomb core prior to application of the adhesive and expanding the stacked and bonded core whereby the cells of the honeycomb core structure are formed. By application of a polymeric film forming substance before bonding, all surfaces of the honeycomb core are protected from corrosion and other environmental degradations. The presence of a polymeric film forming substance on honeycomb core surfaces aids in the formation of strong core-to-face sheet bonds by improving the fillet configuration and thereby the strength obtained in face sheet-to-core bonding.

Environmentally durable metal honeycomb structure

Porous, adhesion-promoting oxide coatings are formed on titanium by anodizing in an aqueous solution containing fluoride ion and one or more oxidizing electrolytes at current densities of from 0.25 to 5 amp./ft..sup.2.

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Seattle, WA, United States of America

Yukimori Moji