Multi-scale study of microstructure evolution in hot extruded nano-sized TiB2 particle reinforced aluminum composites

The microstructural evolution of in-situ TiB2 nano-particle reinforced AlZnMgCu composites during hot extrusion was investigated from micro to macro scales by a combination of various techniques, including neutron and synchrotron X-ray diffraction, optical microscopy, scanning and transmission electron microscopy and electron backscatter diffraction (EBSD). The development of microstructure has shown a bimodal grain structure with distinctive spatial distributions of TiB2 particles: the elongated coarse grain structure with smaller dispersed particles and the fine grains mixed with clusters of relatively larger particles. The particle stimulated nucleation occurs at large particle clusters, resulting in recystallized (sub)micron sized fine grains. The dispersed smaller particles are observed to promote dislocation generation and to prohibit recovery. They are shown to reduce the misorientation of low angle grain boundaries due to the pinning effects on independent dislocations, which also lead to the suppression of dynamic recovery and increase of driving force for dynamic recrystallization. Quantitative texture analysis combined with neutron diffraction and EBSD has exhibited the development of a strong (111) and (001) dual fiber texture, and both texture volume fractions are changing with the particle content In addition, the synchrotron diffraction experiments have shown that dislocation density increases with the particle content in both texture components. The microstructure evolution is the result from a complex process of particles/matrix interaction during the deformation and dynamic recrystallization. In comparison with its particle-free alloy counterpart, the thermomechanical response of the composites at high temperature is discussed in terms of aluminum deformation and recrystallization mechanisms combined with nanosized particle effects. (C) 2016 Elsevier Ltd. All rights reserved.