J. F. dos Santos

Effects of inhibitors on corrosion behaviour of dissimilar aluminium alloy friction stir weldment

Abstract Dissimilar weldments comprising age hardenable AA7075 and AA6056 aluminium alloys were produced by friction stir welding. Corrosion behaviour of the weld nugget/thermomechanically affected zone and parent materials was characterised in chloride solutions. Chromate, molybdate and cerium nitrate were added to the chloride solution and their effect on the corrosion behaviour of the weldment was assessed. Electrochemical studies on different regions of the dissimilar friction stir weldment, performed in inhibited 3·5%NaCl solutions, suggest that chromates are better in terms of inhibition efficiency and inhibit all regions of the weld area to a similar extent. From the viewpoint of environmental issues, both molybdate and cerate may also be thought of as effective inhibitors; however, their efficiencies are definitely below that of chromates in neutral chloride environments.

Stress cracking behaviour of dissimilar friction stir weldment in chloride solution: dissolution assisted or hydrogen induced?

Abstract The environment assisted cracking behaviour of a dissimilar weldment composed of two age hardenable aluminium alloys (AA 7075 and AA 6056) and produced by the friction stir welding (FSW) process, was assessed using slow strain rate tensile (SSRT) tests in chloride solutions. It was observed that the region comprising the thermo-mechanically affected zone (TMAZ)/heat affected zone (HAZ) of the AA 7075 aluminium alloy in the weldment is susceptible to stress assisted environmental cracking. During tests in which chromate had been added as an inhibitor to the chloride solution, the same region of this dissimilar metal weldment was found to fail in a premature fashion, despite the inhibitor effect. The same weldment, however, tested in chloride solution under cathodically polarised conditions (potentiostatic at −1100 mV versus Ag/AgCl) exhibited a behaviour similar to that observed in the SSRT tests in air. Analysis of the results suggests that cracking of this weldment in chloride solutions is governed by dissolution rather than hydrogen embrittlement.