Effect of Fe and Si impurities on the precipitation kinetics of the GPB zones in the Al-3wt%Cu-1wt%Mg alloy

The formation of the Guinier-Preston-Bagaryatsky zones in Al-Cu-Mg, controlled by the solute atoms diffusion, occurs through a nucleation, growth and coarsening phenomenon. Both growth and coarsening regime are well described, respectively, by the JMAK model of growth and the LSW theory. In the commercial Al-Cu-Mg alloy, the presence of Fe and Si atoms leads to the formation of soluble particles such Al2Cu and Mg2Si, and insoluble particles such Al12Fe3Si, Al7Cu2Fe and Al6(Fe, Cu) during heat treatment. Then, some of the Cu and Mg atoms are removed from the solid solution and the effective solute atom concentration in the matrix during the heat treatment is reduced leading a reduction in the driving force of the GPB nucleation and growth and a slowing down the nucleation growth reaction .The diffusion coefficient of the solute atom in the alloy, in both pure Al-Cu-Mg and commercial Al-Cu-Mg alloys, are determined during the GPB zones coarsening. No significative difference exists between the diffusion coefficient of the solute atoms in the pure and in the commercial Al-Cu-Mg alloys during the GPB zones coarsening because some of the excess vacancies are eliminated at the sinks and the driving force of the coarsening reaction is due only to the interfacial energy.