HRTEM study of the effect of deformation on the early precipitation behaviour in an AA6060 Al-Mg-Si alloy

摘要

The effect of 10% pre-ageing deformation on the early precipitation behaviour in an AA6060 Al-Mg-Si alloy aged 10 min at 190°C was investigated by high-resolution transmission electron microscopy (HRTEM) in 100Al projections. The precipitate nucleation was heterogeneous since all precipitates were found to grow on dislocation lines. The pre-ageing deformation suppresses growth of Gunier-Preston zones and β″ phase. The resulting precipitates are still largely coherent with the aluminium matrix. They appear with two main morphologies; one consists of independent, small cross-sections arising from needles with disordered β′ and B′ structures. The other morphology is a much more continuous decoration where precipitates have elongated and conjoined cross-sections and where a particular precipitate phase could not be determined. All precipitates in this work were found to contain a common near-hexagonal sub-cell (SC) with projected bases a = b ≈ 0.4 nm. This strongly indicates that they are built over the same Si network, which recently has been demonstrated to exist in all precipitates in the Al-Mg-Si(-Cu) system. For the discrete morphology type the network has one hexagonal base vector parallel to or very near a 510Al direction. For the continuous type, one base vector falls along a 100Al direction. This orientation of the network is different from previous studies of ternary Al-Mg-Si alloys and must be a direct consequence of the deformation.