Alcan International Limited

Nigel J Holroyd

Geoffrey M Scamans

Warren Hepples

Welded structures composed of aluminium alloy components are protected from white zone and exfoliation corrosion by means of a surface layer applied over the weld bead and consisting of an aluminium alloy containing 0.02 to 0.4% by weight of indium. Other elements which may be present include zinc 0.1 to 1.5%; manganese, 0.02 to 0.5%; tin, 0.12 to 0.50%; gallium, 0 to 0.2%; and magnesium, 0.01 to 6%. The surface coating may be applied by arc or flame spraying or by welding.

Welding aluminium alloys

Problems are caused by stress corrosion cracking and exfoliation cracking in the heat-affected zones adjacent welds in structure of welded components formed of Al alloys, particularly of the 7000 series but also of the 5000 series. The invention seeks to overcome these by the use of Al-Mg welding wire containing 0.01-0.5% Ga and/or In and/or Sn, the composition being chosen such that the weld bead has a potential at least as electronegative as the components and preferably in the range -1200 to -1300 mV with reference to a standard calomel electrode. To prevent diffusion of Ga/In/Sn, the components may be pre-coated e.g. by using a double-pass welding technique.

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Brackley, United Kingdom

Nigel J Holroyd