A study of copper distribution in lamellar Al–CuAl2eutectics using an energy analysing electron microscope

Plasmon energy loss measurements are used to investigate the copper distribution in the lamellar Al–CuAl2 eutectic. The results for aged, decanted and splat-quenched crystals show that there is considerably less copper present in the Al-rich lamellar phase than predicted by eutectic growth theories. This discrepancy is explained in terms of a post-solidification precipitation of the copper epitaxially on to the CuAl2, lamellae. The aged crystals show a higher copper solute concentration in bands ∼ 1000 Å wide parallel with the interphase boundaries. These copper concentration gradients are tentatively interpreted as being due to the non-stoichiometry of the equilibrium CuAl2, phase. Observations of surface plasmon losses at the interface between the lamellar phases are also reported.