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.