Influence of CNTs decomposition during reactive friction‐stir processing of an Al–Mg alloy on the correlation between microstructural characteristics and microtextural components

Abstract

Multipass friction-stir processing was employed to uniformly disperse multiwalled carbon nanotubes (MW-CNTs) within an Al-Mg alloy metal matrix. Decomposition of MW-CNTs occurs in situ as a result of solid-state chemical reactions, forming fullerene (C60) and aluminium carbide (Al C ) phases during reactive high temperature severe plastic processing. The effects of this decomposition on the microstructural features, dynamic restoration mechanisms and crystallographic microtextural developments are studied for the first time by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis. The formation of an equiaxed grain structure with an average size of ∼1.5 μm occurs within the stirred zone (SZ) under the influence of inclusions which hinder grain boundary migration via Zener-Smith pinning mechanisms during the discontinuous dynamic recrystallisation (DDRX). Formation of two strong Cubic and Brass microtextural components in the heat affected zone (HAZ) and thermomechanical affected zone (TMAZ) was noted as compared to the completely random and Cube components found in the base and SZ regions, respectively. The microstructural modification led to hardening and tensile strength improvement for the processed nanocomposite by ∼55% and 110%, respectively with respect to the annealed Al-Mg base alloy.

A Review on the Fabrication of <i>In Situ</i> Metal Matrix Composite during Friction Stir Welding

“…The extensive utilization of the MMC's are restricted by one of its major disadvantage of deprived weld ability by conventional fusion welding strategies. With the fusion welding processes, MMC's undergoes porosities [12], inclusions [13], matrix and reinforcements reaction [14], presence of residual stresses because of the significant dissimilarity in the thermal expansion coefficient (CTE) of the reinforcement and matrix [15][16][17]. However, recently developed friction stir welding (FSW) can avoid all these defects during the welding of MMC's and accepted as an effective substitute to join MMC's [18].…”