Severe plastic deformation of commercial purity aluminum by rotary swaging: Microstructure evolution and mechanical properties

The microstructure evolution and change in mechanical properties of commercially pure aluminum (Al 1050) were investigated during severe plastic deformation by rotary swaging (RS) at ambient temperature. Optical microscopy (OM) and scanning electron microscopy (SEM) using electron back scatter diffraction (EBSD) were utilized to document the evolution of the microstructure. Hardness and tensile tests were conducted to characterize mechanical properties. Rotary swaging was found to lead to a marked decrease in grain size. The microstructure consisted of cell structure of low angle grain boundaries (LAGBs) within bigger grains. After heavy swaging to true deformation degree of φ=3, the microstructure was quite uniform normal to flow direction in terms of cell size, average misorientation angle and content of low angle grain boundaries. Extremely fine dynamically recrystallized grains, heterogeneously nucleated at existing grain boundaries were evident on the section parallel to the flow direction. As compared to the as-received condition, the yield stress and ultimate tensile strength of the material was strongly increased by a factor of 8 and 2.3, respectively. Furthermore, the elongation to fracture was drastically reduced as was the uniform strain indicating a marked reduction in work hardening capability.