Solid State Processing of Aluminum Matrix Composites Reinforced with Nanoparticulate Materials

A simple powder metallurgy route is investigated at Empa for producing aluminum matrix nanocomposites. High energy ball milling has proven to be an efficient method for dispersing the nanoparticles into the matrix even up to high amount. The compaction of these blends at moderate temperature leads to dense nanocomposite materials with high strength whatever the nature of the reinforcement. Hot pressing, spark plasma sintering, and hot isostatic pressing induce the same tensile properties at rupture but higher yield strength can be observed for the simple hot pressing process. High strength can be only combined with high ductility for nanoparticle content below 1 vol%. These outstanding properties are achieved thanks to a homogenous nanoparticle dispersion as well as a bimodal grain size distribution with fine (<300 nm) and coarser grains (a few microns). The materials do not require subsequent heat or work hardening treatment and exhibit better or similar properties as the conventional high strength aluminum alloys. Finally, it is demonstrated that friction stir welding is a valuable process for joining these nanocomposites.