Effect of Processing Parameters on the Microstructure of Mechanically Alloyed Nanostructured Al-Mn Alloys

High-energy mechanical alloying was utilized to study the alloy formation between Al and Mn. A modified SPEX mill was designed to investigate the role of milling energy and milling power on enhancing the solubility of Mn in Al. Despite having a large influence on alloying kinetics (an increased rate of 3.25×) no further grain refinement or degree of alloying was observed with increasing milling energy. It is hypothesized that alloying in this particular binary system takes place and is controlled by the increasing interfacial surface area created between the Mn particles and the Al matrix. However, extensive comminution eventually likely leads to an autocatalytic exothermic reaction between the Mn particles and Al matrix, leading to the formation of the equilibrium phase Al₆Mn. This reaction reduces the degree of and, in turn, frustrates further alloying, highlighting the practical limits of creating solid solutions in this system through mechanical alloying.