Corrosion behaviour of AA6061 and AA7005 reinforced with Al2O3 particles in aerated 3.5% chloride solutions: potentiodynamic measurements and microstructure evaluation

The influence of the heat treatments on the corrosion behaviour of three al uminium matrix composites (AA6061/Al2O3/10p20p and AA7005/Al2O3/10p) has be en analysed in an aerated 3.5% sodium chloride solution. Corrosion potentials were determinated in a 3.5% sodium chloride solution ( NaCl) using the ASTM standard G69-81 [1]. The galvanic series and the pitti ng potentials were calculated in this medium for all composites. The follow ing heat treatments were applied on the base composites: (a) as-received st ate (T4), (b) T6 treatment, (c) an annealing, consisting of a solution stag e at 560 degrees C for 3 h for the AA6061 MMC and (d) an annealing at 482 d egrees C for 2 h for the AA7005/Al2O3/10p, followed by a cooling in the atm osphere furnace. The localised corrosion susceptibility of each material an d for each heat treatment were analysed by measurement of the cyclic potent iodynamic polarization. Optical microscopy and SEM metallographic studies w ere carried out on the samples, before and after corrosion tests, to determ ine the influence of the microstructural changes during heat treatments on the corrosion behaviour. (C) 1999 Elsevier Science Ltd. All rights reserved .