Role of Different Fractions of Nano-size SiC and Milling Time on the Microstructure and Mechanical Properties of Al-SiC Nanocomposites

High energy ball milling was implemented to produce Al-matrix composites reinforced with 2.5, 5, 10, 15 and 20 wt% silicon carbide (SiC) nano-particles. In this regard, Scanning electron microscopy, X-ray diffraction and microhardness tests were applied to clarify the role of milling time and the percentage of nanometric SiC on structural evolutions and mechanical properties of the composites. An increase in the SiC proportion resulted in accelerating the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Thus, the crystallite size of Al in Al-20wt.%SiC composite reached a low of 20 nm after milling for 25 h and the microstrain trend experienced higher increasing rate in composites with higher amounts of SiC. Similarly, as a result of the rise in SiC percentage, there was a growth in the microhardness of composites. This phenomenon was mainly attributed to grain refinement, explained by Hall-Petch equation. On the other hand, inverse Hall-Petch behavior was observed for a ultra fine-grain sample, Al-20wt.%SiC milled for 25 h.