Electrochemical behaviour of retrogressed and reaged (RRA) 8090 and 1441 Al–Li–Cu–Mg–Zr alloys

Abstract

8090 and 1441 Al–Li–Cu–Mg–Zr alloys of peak aged T8 tempers were subjected to retrogression treatment followed by reageing to peak aged (RRA) T77 tempers. Electrochemical polarization studies were carried out on the alloys of T8, T77 and over aged T7 tempers, in 3.5% NaCl, 3.5% NaCl + 0.1M LiCl + 0.3% H2O2 and 3.5% NaCl + 0.1M LiCl + 0.7% H2O2 solutions. The shape of the polarization curves is similar for all the tempers of both alloys in all environments. The corrosion rates are more or less the same irrespective of the tempers. However, the open circuit potentials (OCP) shift towards more negative potential with the RRA treatment and ageing time. The OCP values of the T7 tempers were found to be the most negative; for the T77 tempers it lies between that of the T7 and T8. Further, the OCP values for all tempers of both alloys shifted anodically with addition of LiCl and H2O2 in 3.5% NaCl solution. TEM, XRD and DSC studies of microstructural features of the alloys in the T8, RRA and T7 tempers have been used to explain the observed electrochemical behaviour.