Effects of pH and chloride concentration on pitting corrosion of 6061 aluminium alloy

Effects of pH solution and chloride (Cl-) ion concentration on the corrosion behaviour of 6061 aluminium alloy immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy. The corrosion behaviour of the 6061Aluminum Alloy was found to be dependant on nature of the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion were occurred simultaneously since corrosion potentials (Ecor) coincided with pitting potentials (Epit). In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the 6061Aluminum Alloy was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 to 0.5%wt NaCl and an increase in the chloride concentration slightly shifted both the pitting Epit and corrosion Ecor potentials to more active values. Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6). © University of Manchester and the authors 2006.