Hot deformation of nickel particles reinforced aluminium based composites: Flow behaviour, microstructural evolution and processing map analyses

The hot deformation behavior and workability of stir cast Al 6063 alloy reinforced with 6 wt.%Nickel particles was investigated using flow stress-strain plots, microstructural analysis and processing maps. The composites were hot compression tested at temperatures of 200 °C, 250 °C, 300 °C, 350 °Cand 400 °C, and strain rates of 0.01, 0.1, 1, and 10 s-1, while scanning electron microscopy was utilized for characterization of the ensuing microstructures. The results show that the flow stress generally decreased with increase in deformation temperature, while anomalous flow stress oscillations, linked to the pattern of particle distribution in the matrix, characterized the flow stress - strain rate relations at 0.01 s-1 strain rate. The Murty's and Gegel's criteria utilized to establish domains of instability at the global strain of 0.5 were found to vary considerably and the combination of both left a very narrow safe processing window for the Al6063/Nip composite. Safe regions with peak power dissipation efficiencies occurred at temperature range of∼390 °C-400 °Cand 0.01 s-1 in the lower domain and 260 °C-350 °Cand 10 s-1 in the upper domain. The dominant flow softening mechanisms were established to be dynamic recrystallisation and dynamic recovery at the lower domain and upper domains, respectively.