Enhancement in dispersoid precipitation and dispersion strengthening by prior deformation in an Al–Mg–Mn alloy

Abstract

Dispersion strengthening effect of Mn-containing dispersoids in the non-age hardenable Al–Mg–Mn alloys is generally limited since it is difficult to achieve the high-density and fine sized dispersoids through conventional homogenization treatment. In this work, inspired by the heterogeneous precipitation along dislocation for Mn-containing dispersoids, strain induced dislocations was introduced by prior deformation to increase the nucleation sites in the matrix. Based on the classical nucleation theory, the nucleation rate in the pre-strained specimen is improved by an order of magnitude compared with that of the as-cast specimen. Detailed electrical conductivity tests and transmission electron microscopy observations showed that prior deformation can promote the decomposition of supersaturated solid solution and successfully increase the number density of Mn-containing dispersoids, but decrease their sizes from 323 ± 83 nm to 118 ± 43 nm in long axis dimension after homogenization treatment. An improvement of 36.5 MPa in yield strength can be achieved through the enhanced dispersion strengthening mechanism. Simultaneously, the diffusion distance of Mn solute atoms dramatically increases from 0.85 μm to 27 μm due to the enhancement in diffusivity, which can be mostly attributed to the increase in diffusion paths caused by the higher density of strain-induced dislocations. Thus, the volume fraction of dispersoid free zones was decreased by 51% in the pre-strained specimen, indicating that a more uniform distribution of dispersoids in the Al matrix can be obtained by prior deformation. This work provides some insight into the enhanced dispersion strengthening effect of Mn-containing dispersoids by prior deformation, which is a promising approach to further improve mechanical properties of non-age hardenable Al alloy.