A comparison between hot-rolling process and twin-screw rheo-extrusion process for fabrication of aluminum matrix nanocomposite

Abstract

Solid-state modification of SiC nanoparticles in a ball-mill is a known method for deagglomeration of as-received nanoparticles in a bed of metallic carriers that will also aid their better injection and releasing into the melt. The melt temperature and condition of the melt is very important for a better interaction of composite powders including ceramic nanoparticles and metallic carrier with the melt. In this study, aluminum A356 matrix nanocomposites were produced by liquid-state stir casting at 715 °C followed by twin-screw rheo-extrusion (TSRE) in the semi-solid state to enhance the produced composite properties. For this purpose, SiC nanocomposite superstructures were prepared using ball-milling of SiC nanopowders with micron-sized titanium and nickel (separately) as carrier agents. Also, hot-rolling (HR) process was applied on liquid-state stir cast nanocomposites to compare the mechanical properties of rolled sheets with TSRE-processed bars. The experimental results indicated that stir-cast samples before TSRE and HR consisted various types of defects with poor dispersion of nanoparticles in some areas. However, more improved dispersions for the nanoparticles were obtained after TSRE and HR and rolled sheets had considerable improved mechanical properties compared with TSRE bars. This latter improvement was determined to be mainly due to extensive fragmentation and dispersion of eutectic silicon, Ti-rich, and Ni-rich intermetallic phases.