Influence of Mn solute content on grain size reduction and improved strength in mechanically alloyed Al–Mn alloys

Al–Mn alloys with a solid-solution Mn content ranging from 0 to 3.1 at% were successfully prepared by high energy mechanical alloying at room temperature of an Al–8 at% Mn sample. The solubility level obtained is up to five times the equilibrium solubility limit of Mn in Al (from 0.62 at% Mn). In general, the observed microstructures are consistent with being a nanocomposite composed of an Al–Mn solid solution matrix with dispersed Mn particles. For alloys with solid solutions up to 3.1 at%, increasing the Mn content correlated with a decrease in the matrix grain size down to a minimum of 12 nm. High hardness values of ~4 GPa were obtained. The main strengthening mechanism of the Al–Mn alloys is attributed to the grain size reduction. Further attempts to increase the dissolved solute content resulted in the precipitation of the Al6Mn equilibrium intermetallic phase.