Distribution of intermetallics in an AA 2099-T8 aluminium alloy extrusion

Microstructural characterisation of an AA 2099-T8 alloy extrusion has shown elongated grains with high angle grain boundaries and approximately equiaxed subgrains with low angle grain boundaries. The constituent particles in the alloy contain Al, Fe, Mn, and Cu, and fall into two groups of high and reduced contents of copper. The high-copper-containing and low-copper-containing phases are present individually or together in the form of multiphase particles. For the multiphase particles, the high-copper-containing phase is at the centre of the particle, surrounded by the low-copper-containing phase. The alloy also contains rod-like Al–Cu–Mn–Li and spherical β′ (Al3Zr) dispersoids, and fine age hardening precipitates of T1 (Al2CuLi), δ′ (Al3Li) and θ′ (Al2Cu).