Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrysta llization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in s ense where coarse second phase particles (> 1 mum) stimulate nucleation whi le fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra f ine grain size to the alloy. Addition of zirconium produces Al3Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al3Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconiu m. Transmission electron microscopy was employed to characterize the second ph ase particles, i.e. Al3Zr particles and found to be rod shaped and identifi ed to be cubic ordered L1(2) phase with a lattice parameter of 0.408 nm. Fu rther, it was observed that fine (100 nm) Al3Zr particles promote only cont inuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al3Zr particles inhibits both recr ystallization and grain growth in the commercial Al-Cu-Mg alloy.