Authors: Sedat ÖZBİLEN
Abstract: Alloys prepared with a chemical composition of Al-2.11%Cu-0.93%Mg (alloy-1) and Al-2.07%Cu-0.97%Mg-0.87%Li (alloy-2) were subjected to homogenisation, water-quenching, natural ageing for 3.15x107s & artificial ageing at 463K for 2.16x104s & 8.64x104s (double ageing). Selected samples were examined in detail under Transmission Electron Microscope (TEM). For this purpose, bright & dark field images together with electron diffraction patterns taken from , ,  & A1-matrix directions were used. It was observed that there was an effect of alloying elements, namely Li, Cu, Mg on the nature & density of lattice defects of dislocation loop type in Al-matrix during heat treatments. In alloy-2 Li & Cu atoms segragating on Frank & double-arc contrast, prismatic loops cause the formation of T1 (Al2CuLi) precipitates during double ageing; in alloys-1 & 2, Cu & Mg atoms segregating on unfaulted & orthorombic, prismatic dislocation loops cause the formation of heterogeneous S' (Al2CuMg) precipitates on these dislocation loops during the same heat treatment.
Keywords: Ageing, Crystallography, Al-Li Alloys, Precipitation