| Abstract Scope |
Continuous cast AA 2037 Al alloy hotband was annealed at temperatures ranging from 25 to 500ºC for 3h. Vacancy-solute interactions and precipitates in the samples during annealing were investigated using positron annihilation techniques (coincidence Doppler broadening (CDB) and lifetime, respectively) and TEM. It was found that there were vacancy-Cu and vacancy-Cu-Mg complexes at room temperature. Positron mean lifetime peaked at 200ºC because of the formation of semicoherent precipitates. The measured CDB ratio curve, characteristic to Mn in shape, indicated the formation of vacancy-Mg-Mn complexes or Mn clusters in these precipitates. Above 250ºC, coarsening and dissolution of semicoherent precipitates resulted in decrease in mean lifetime and disappearance of Mn signal, but Cu signal increased clearly with annealing temperature. Over 350ºC, Cu signal started to saturate, indicating that Cu dissolved might agglomerate and cluster with vacancies, while new increase in mean lifetime might be attributed to the formation of incoherent phase. |