Synthesis of A356-MWCNT nanocomposites through a novel two stage casting process

In this study, A356-0.5 wt% MWCNT nanocomposites were successfully fabricated using a novel two stage composite casting process. First, Al-MWCNT composite stripes were produced by the accumulative roll bonding (ARB) method. The composite stripes were then diluted in a molten matrix of appropriate composition followed by squeeze casting. The purpose of ARB treatment was to improve wettability of MWCNTs with the matrix and reduce their agglomeration tendency. The results showed that addition of 0.5 wt% MWCNT and application of pressure during solidification of the composite led to microstructural refinement and improvement in mechanical properties of the cast composites. Secondary dendrite arm spacing of the nanocomposites was decreased by 52% and the hardness, shear strength and shear elongation were improved by 38%, 20% and 46.6%, respectively, at the highest squeeze casting pressure employed. Evidence of low agglomeration of MWCNTs in the matrix was detected on the sheared surfaces of the castings. The results are discussed in terms of the effects of the processing parameters on reinforcement wettability, distribution and engulfment in the matrix.