Characterization and mechanical properties of stir-rheo-squeeze cast AA5083/MWCNTs/GNs hybrid nanocomposites developed using a novel preform-billet method

Abstract

This study explores the development and characterization of Aluminum alloy (AA) 5083 based nanocomposites, reinforced with equal proportion of graphene nanosheets (GNs) and multi-walled carbon nanotubes (MWCNTs) using stir-rheo-squeeze casting. To control the problem of segregation of the nano dispersoids, the study successfully employs a novel approach of making nano-preform billets of the reinforcements by green compacting and then introducing their sections to the alloy melt having compositions 0.5, 1, 1.5, 2, and 2.5% by weight, while stirring. MWCNTs and GNs in 1:1 ratio mixed and milled with ten times the high purity Aluminum (Al) powder volume. HRTEM images and XRD patterns conformed to the size and purity of MWCNT and GNs. SEM images confirmed their sound mixture. The structure was refined by about 60% in 3 wt.% composite, but agglomeration and cracks appeared at this composition. BHN increased consistently as the reinforcement was increased. Tensile and compressive strength increased initially but declined in the composite with 3 wt.% nanofillers due to agglomerations and weak interface bonding. Elongation first decreased and then increased due to counter slip systems introduced by the presence of MWCNTs and GNs. Prominent crack growth was observed in the fractography in 3 wt.% composite. An optimum reinforcement concentration of 1.5–2 wt.% has emerged superior on a combined evaluation of dispersion, refinement of structure, and mechanical properties.

Keywords

• Powder metallurgy
• Ball milling
• Stir casting
• Rheocasting
• Squeeze casting
• Metal matrix composites