Effect of aluminium on electrochemical corrosion behaviour of Fe-0.5C and Fe-1C alloys in 0.25M H2SO4

Abstract

Electroslag remelted iron – aluminium alloys, with carbon contents of 0.5 and 1 wt-%, were used to investigate the effect of Al on the electrochemical corrosion behaviour in 0.25M sulphuric acid solution. The alloy compositions were (wt-%): (1) Fe – 16Al – 0.5C, (2) Fe – 10Al – 0.5C, (3) Fe – 8Al – 0.5C, (4) Fe – 16Al – 1C, (5) Fe – 10Al – 1C, and (6) Fe – 8Al – 1C. Lowering the Al content of the alloys resulted in a deterioration of the passivation behaviour during potentiodynamic polarisation testing. This deterioration was attributed to the reduced Al content of the matrix phase on lowering the Al content of the alloy. Examination of the polarised surfaces via SEM revealed that in high Al content alloys carbides are preferentially attacked, while in low Al content alloys the attack is more general. Alloys with a carbon content of 1 wt-% displayed somewhat inferior passivation tendencies compared with those of alloys containing 0.5 wt-% carbon.