Alcan International Limited

Nigel C Davies

Jonathan Ball

Peter G Sheasby

Mark W Puddle

William F Marwick

Peter Karl Limbach

Armin Kumpart

Eric Barlow

Peter M Bullivant-Clark

Rodney Charles Jones

An aluminum workpiece, e.g. sheet for containerstock, having an anodic oxide film whose thickness varies from location to location on the surface, whereby interference contrast effects are visible on the surface. Aluminum foil having on a surface thereof an unsealed anodic oxide film 5-1000 nm thick which provides a clean surface with fretting resistance. A method of anodizing thin aluminum foil is also described.

Aluminium workpiece

Cleaning aluminum workpieces

Electrodes used for spot welding of aluminium workpieces are improved by a combination of steps:

Resistance welding of aluminium

The invention concerns a method of forming a joint between aluminium workpieces. These carry an artifically applied e.g. chromate or anodic oxide coating on their surface. A curable adhesive containing up to 40% by weight of particulate filler having a maximum particle size of 300 microns is provided between the workpieces to be joined. Resistance welding is performed using a welding electrode whose tip has a surface with an average roughness depth of at least 10 microns. This increases electrode life and makes it possible to use lower welding currents than previously recommended.

Method of forming a joint between aluminum workpieces with curable

An anodic oxide film is formed on aluminium strip by continuously passing the strip through a phosphoric acid electrolyte at from 25.degree. C. to 80.degree. C., the contact time between the strip and the electrolyte being not more than 15 seconds during which time the strip is anodized at a current density of at least 250 A/m.sup.2. In the resulting film, the pores are enlarged so that the effected surface area is increased. The film forms an excellent substrate for lacquer, paint, or adhesive.

Anodic aluminium oxide film and method of forming it

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Banbury, United Kingdom

Nigel C Davies