Experimental and computational studies of competitive precipitation behavior observed in microstructures with high dislocation density and ultra-fine grains

The competitive precipitation behavior observed in microstructures with high dislocation density and ultra-fine grains has been studied experimentally and computationally for cold-rolled and severe plastic deformed Al-Mg-Si alloy. The age-hardenability at 443K was reduced by the two deformation processes due to the accelerated formation of larger precipitates on dislocations and grain boundaries, in place of the transgranular precipitation of refined β" in the matrix. The developed numerical model based on the classical heterogeneous nucleation theory clarified the dislocation density and grain size dependences of the volume fraction of precipitates nucleated at different sites, in good agreement with experimental results. It could be therefore possible that three strengthening mechanisms of strain hardening, hardening by grain refinement and precipitation hardening are optimally exploited according to the computationally estimated dependences.