Enhancement of pitting corrosion resistance of drawn aluminium tube

摘要

Lifetime of aluminium automotive A/C condensers, especially resistance to corrosion damage and perforation failure can be extended by application of diffused zinc coatings and correct electrochemical design in choice of materials used in the construction of the condenser. The corrosion of heat exchanger fittings such as connector tubes now appears to be the lifetime limiting factor.A process developed to apply thin, sub-micron zinc coating layers on extruded aluminium multi-port tubes has been applied to drawn aluminium round tubing. Modifications to the production process route ensures that sufficient diffusion of zinc into the aluminium is achieved to provide optimised resistance to pitting corrosion damage, irrespective of the future thermal process experienced by the tube.Zinc coating weights, draw reductions and thermal diffusion treatments have been investigated to derive the most effective process route commensurate with optimised resistance to pitting corrosion damage. A zinc diffusion depth of at least 100μm was considered to be necessary for long corrosion lifetime. The optimised tube has demonstrated the ability to exceed 50 days in a SWAAT environment without detrimental pitting damage.