It was studied the corrosion behaviour of two joints, obtained by Friction Stir Welding (FSW), of aluminium alloy metal matrix composites (MMCs), reinforced with alumina particles. W6A20A and W7A10A composite joints were examined. Corrosion tests were performed in EXCO or 3.5% NaCl solutions. The corrosion rates of MMCs and joints were compared. Corrosion tests were performed on both the nugget and the thermally affected zones of the joints. Pitting potentials were measured on electrodes prepared by isolating the different zones. Short-circuit currents were measured between the nugget, the thermally affected zone and the base. The results indicated the different behaviour of the two joints: the corrosive attack on the W7A10 joint was concentrated on the nugget and in its adjacent zones both in EXCO and 3.5% sodium chloride solution; in the case of W6A20A, the nugget remained protected while the adjacent zones and the base material were corroded. Electrochemical measurements confirmed these results. However, FSW, which produces welds without the formation of a fused zone, causes structural modifications in zones near the nugget, due to the higher temperature produced by the presence of the reinforcement. This negatively affects the corrosion resistance of the composite, also in relation to the base alloy composition.
Corrosion behaviour of aluminium alloy Metal Matrix Composite joints obtained by FSW
ZUCCHI, Fabrizio;GRASSI, Vincenzo;MONTICELLI, Cecilia;FRIGNANI, Alessandro
2005
Abstract
It was studied the corrosion behaviour of two joints, obtained by Friction Stir Welding (FSW), of aluminium alloy metal matrix composites (MMCs), reinforced with alumina particles. W6A20A and W7A10A composite joints were examined. Corrosion tests were performed in EXCO or 3.5% NaCl solutions. The corrosion rates of MMCs and joints were compared. Corrosion tests were performed on both the nugget and the thermally affected zones of the joints. Pitting potentials were measured on electrodes prepared by isolating the different zones. Short-circuit currents were measured between the nugget, the thermally affected zone and the base. The results indicated the different behaviour of the two joints: the corrosive attack on the W7A10 joint was concentrated on the nugget and in its adjacent zones both in EXCO and 3.5% sodium chloride solution; in the case of W6A20A, the nugget remained protected while the adjacent zones and the base material were corroded. Electrochemical measurements confirmed these results. However, FSW, which produces welds without the formation of a fused zone, causes structural modifications in zones near the nugget, due to the higher temperature produced by the presence of the reinforcement. This negatively affects the corrosion resistance of the composite, also in relation to the base alloy composition.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
