Study on the microstructure evolution and mechanical properties of an Al-Mg-Li alloy aged by electropulsing assisted ageing processing

The electropulsing assisted ageing (EAA) processing was proposed as a novel energy-saving heat treatment processing for ageing, and how it influenced the microstructure evolution and mechanical properties of an Al-Mg-Li alloy was investigated in this paper. The mechanical properties and deformation behavior of the alloy were closely correlated with the precipitation and coarsening of the delta' precipitates. Compared with the conventional ageing (CA), the EAA could accelerate the coarsening of the delta' precipitates owing to the combination of the electro-migration offering another delta' precipitate growth coefficient and the enhancement of diffusion due to the interaction between the vacancies and drift electrons, which lowered the ageing temperature for reaching peak-strength under the same ageing time. Besides the strength increased as the coarsening of the delta' precipitates, the elongation and fracture mode were associated with the volume fraction of the delta' phase. The easier occurrence of planer slip in the case of the higher volume fraction of the delta' phase resulted in the low elongation and brittle intergranular fracture of the under-aged and peak-aged alloys, but the slight increase in elongation and reduction of intergranular cracks when the over-ageing occurred. The associated mechanism were discussed in detail.