Microstructure and microhardness of an Al-6061 metal matrix composite processed by high-pressure torsion

Disks of an Al-6061 metal matrix composite, reinforced with 10 vol.% Al2O3 particles, were processed by highpressure torsion (HPT) at room temperature for 1/4, 1/2, 1, 5 and 10 turns under an applied pressure of 6.0 GPa. The evolution of microstructure was investigated using optical microscopy and scanning electron microscopy. During HPT processing the average grain size within the aluminum matrix decreased from similar to 35 pm in the unprocessed condition to similar to 170 nm after processing through 10 turns but there was no significant effect on the size and distribution of the alumina particulate clusters. The values of the Vickers microhardness were recorded across the surface of each disk and then plotted as two-dimensional and three-dimensional color-coded contour maps. The results show the hardness increases from similar to 56 Hv in the initial condition to similar to 165 Hv after HPT for 10 turns. The results demonstrate that, as in many unreinforced metallic alloys, the evolution of hardness with strain exhibits strain hardening without any significant recovery. (C) 2016 Elsevier Inc. All rights reserved.