The synthesis of materials by high energy ball milling of powders was first developed for the production of complex oxide dispersion-strengthened nickel alloys for structural, high temperature applications but has been attracting attention in the field of fabrication processes like the production of intermetallic compounds, supersaturated solid solutions, amorphous materials and metal matrix composites. However, due to the high level of deformation imposed, the aluminum mechanically alloyed undergo extensive grain growth during the extrusion process, resulting in serious damage in the extruded materials. This work investigates the effects of mechanical alloying on the extrusion of AA6061 aluminum alloy and the same alloy reinforced with silicon nitride. In both cases, the energy of deformed particles produced extruded bars with coarse grains in the core, while in the periphery the higher rate of deformation in the extrusion process has prevented this coarsening, resulting in a material with heterogeneous microstructure and with poor mechanical properties. This grain growth can be prevented by a higher percentage of reinforcement in the composite materials or by annealing before extrusion.
Metal matrix composite; mechanical alloying; powder metallurgy
