Influence of Some Additional Elements on the Aging Kinetics in Al–Cu and Al–Cu–Mg Alloys

Abstract

Aging kinetics in Al-1.9 at%Cu and Al-1.9 at%Cu-1.7 at%Mg alloys containing small amounts of Zr, Cr, Mn, Ag and Cd have been investigated by the measurements of electrical resistivity and hardness and also by electron microscope observations.The addition of Zr, Cr or Mn retards the clustering of solute atoms in Al–Cu and Al–Cu–Mg alloys and then reduces the age-hardening when these elements are finely distributed as the insoluble compounds. This effect can be reasonably explained by a similar mechanism to that of Al–Zn and Al–Zn–Mg alloys, that is, in terms of the increase in vacancy sinks rather than the decrease in supersaturated solute atoms or the existence of binding energy between a solute atom and a vacancy.The aging kinetics in Al–Cu alloys are little affected by the addition of Ag, despite the well-known fact that Cd reduces remarkably the rate of G. P. zone formation and stimulate the nucleation of intermediate precipitates. This is probably due to the reason that the clustering of Cu atoms takes place on the {100} matrix plane, whereas Ag atoms cluster on the {111} plane and do not participate in the G. P. zones of Cu atoms. The additions of these elements to Al–Cu–Mg alloys decrease the rate of clustering but increase the age-hardening at high temperature. This may be due to the participation of Ag or Cd atoms in G. P. zones of Cu and Mg atoms.