PARTICLE COARSENING AND SUBGRAIN GROWTH IN A TWIN ROLL CAST AA8006 ALLOY

摘要

A low-eutectic twin roll cast and cold rolled AA8006 aluminium alloy (A11.8%Fe0.8%Mn0.2%Si) has been examined in TEM in order to follow the softening process during back-annealing. The alloy is characterised by a high volume fraction of finely dispersed intermetallics, mainly situated on the subgrain boundaries. Cold rolling to a strain ε=2 results in a nearly equiaxed, highly developed subgrain structure with a mean sub-boundary misorientation of about 5°. The behaviour during annealing has been followed with respect to the variations in subgrain size and particle size. The sub-boundary structure is stabilised by the intermetallic particles. As a consequence recrystallisation is delayed, leading to an almost complete softening only due to recovery. Studies of particle coarsening in recrystallised material have shown that volume diffusion contributes very little to the coarsening. It can therefore be concluded that in these type of alloys particle coarsening is mainly controlled by other diffusion mechanisms such as HAGB- or LAGB-diffusion.