High strain rate superplasticity in a nano-structured Al–Mg/SiCP composite severely deformed by equal channel angular extrusion

Abstract

High strain rate superplastic deformation potential of an Al–4.5%Mg matrix composite reinforced with 10% SiC particles of 3μm nominal size was investigated. The material was manufactured using powder metallurgical route and mechanical alloying which was then processed by equal channel angular extrusion (ECAE). The composite showed a high resistance to static recrystallization. The manufacturing operations atomized SiC particles to nanoscale particles and the severe plastic deformation process resulted in a dynamically recrystallized microstructure with oxide dispersoids distributed homogeneously throughout the matrix. These particles stabilized the ultra-fine grained microstructure during superplastic (SP) deformation. Testing under optimum conditions at constant strain rates led to tensile elongations >360%, but it could be further increased by control of the strain rate path. Transmission electron microscope (TEM) studies showed that the low angle boundary sub-grain structure obtained on heating to the SP deformation temperature developed on straining into a microstructure containing high angle boundaries capable of sustaining grain boundary sliding.