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

摘要

High strain rate superplastic deformation potential of an Al-4.5%Mg matrix composite reinforced with 10% SiC particles of 3 μm 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.