CORROSION OF CADMIUM PLATED STEEL COUPLED TO DIFFERENT TYPES OF ALUMINIUM ALLOYS

In many applications of the aircraft industry, aluminium alloys
and steel components may come into electrical contact. In order to reduce the resulting danger of galvanic corrision of aluminium alloys, steel components are often coated with a metal or an alloy which is more active than the steel. Cadmium electroplatings are currently used to perform this function in the Egyptian aircraft industry. Some of the special characteristics that recommend the use of cadmium platings are the good lubricity, solderability and corrosion resistance. However, it is claimed that the service life of cadmium as a protective plating is relatively short. In this paper the main function of cadmium plating of providing cathodic protection for the coupled aluminium alloys is tested. Cadmium plated steel substrates of different plating thicknesses have been connected to 7075-T6, 2024-T3 and 5056 aluminium alloys in 3.5% Na cl salt solutions. Galvanic corrosion current measurements have shown that cadmium platings accelerate the corrosion of the 7075-T6 aluminium alloy and cathodically protect the 2024-T3 and 5056 alloys for short periods.