Study of advanced nanostructured al-based matrix compositesThursday (07.11.2019) 11:25 - 11:45 Part of:
The worldwide requirements for reducing the energy consumption and pollution have increased the demand of new high performance lightweight materials to be used in vehicles. Aluminium based matrix composites (AMCs) have become an important class of engineering materials because of the unique properties and higher performance that they offer over traditional alloys. AMCs have been utilised for a wide range of engineering applications, particularly in aerospace, defence and automotive industry among others. In this work, examples of several nanostructured AMCs are presented produced by powder metallurgy, hot extrusion and cold rolling techniques. A high strength nanoquasicrystalline Al-Fe-Cr based alloy was used as matrix. The manufacturing process of the nanocomposites containing a nanoquasicrystalline matrix and nanoreinforcements present two main challenges. The plastic deformation processes must be controlled in order not to induce the quasicrystal transformation and secondly avoiding the nanoparticles clustering to allow obtaining a homogeneous distribution of the nanoreinforcements. Results are compared to AMCs using a conventional Aluminium alloy as matrix.
AMCs produced using ceramic nanoparticles as reinforcement were manufactured with different volume fractions using ball milling and followed by extrusion. Transmission electron microscopy, scanning transmission electron microscopy and focused ion beam were used to study the effect of mechanical milling on the microstructure and alumina distribution on the quasicrystalline matrix of the nanocomposite powders. Hot extrusion was used to produce bulk materials and the microstructure and microhardness of the extruded materials were investigated. It is a challenge to retain a metastable phase during mechanical milling therefore the quasicrystalline phase transformation due to the ball milling effect was analysed and parameters that allowed retaining the quasicrystalline phase were established. The milling regime behaviour was identified, and showed to have a significant effect on the rate of change of uniformity of the reinforcement distribution. Strain increased and the crystallite size of the aluminium phase decreased with milling time, with the aluminium crystallite size reaching a steady state. The microhardness of the nanocomposites produced was significantly harder than both the unreinforced quasicrystalline alloy and crystalline aluminium nanocomposites.