Oral Presentation

¹Farshad Akhlaghi ; ²Mohammad Moazami-Goudarzi

¹School of Metallurgy and Materials Eng., Faculty of Eng., University of Tehran

²Department of Materials Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

One of the main challenges in processing of metal matrix nanocomposites through the powder metallurgy method is achieving a dense compact with minimum internal porosity. Pores act as stress risers and deteriorate the mechanical properties of nano-materials. In the present investigation, powder mixtures of commercially pure Al (CPAl) and 5252 Al alloy reinforced with nanometric (SiCn) particles (0-7 wt.%) were produced by in situ powder metallurgy (IPM) method. These powders were consolidated through cold compaction, sintering and hot extrusion processes and subjected to density measurements, microstructural studies and thermal analysis. Microstructural studies showed that in the compacts prepared by the CPAl powders, SiCn particles aggregate and form a reinforcing network, hindering effective densification in the cold compaction process. This network was shown to prevent metal to metal contact during sintering, especially at higher SiCn contents. Therefore, a remarkable decrease in the sintered relative density was observed with increasing SiCn contents in the CPAl/SiCn compacts. However, in the 5252 Al/SiCn composite powders, the SiC nanoparticles embedded within the alloy matrix during the IPM process. As a result, a more homogeneous SiCn particle distribution was attained. This led to enhanced cold densification and improved sinterability compared with those of CPAl/SiCn powder mixture. Besides, the presence of Mg in the 5252 alloy matrix was effective in reducing the oxide film covering the Al particles. The differential scanning calorimetry (DSC) revealed the formation of liquid phase during the sintering of 5252 Al/SiCn powder compacts. As a result, mass transfer promoted through the liquid phase sintering enhancing densification. However, improved densification was obtained after hot extrusion of the nano-SiC reinforced composites. Results showed that the pressure required for extrusion increased with increasing SiCn content. This was attributed to the enhanced redundant work induced by SiCn particles.

Al/SiC nanocomposite; Cold densification; Liquid phase sintering; Hot extrusion