Microstructure evolutions and mechanical properties of tubular aluminum produced by friction stir back extrusion

Aluminum tubes were successfully fabricated using a novel process of friction stir back extrusion (FSBE) known as one of the severe plastic deformation (SPD) routes. It was found that this process is capable to form a tube with a significant fine grained structure resulting from dynamic recrystallization phenomenon in the stirred area. Several regions were identified in the formed tube in which various microstructural evolutions occur, i.e. dynamic recrystallized (RX), static RX, and partially static RX zones along with extruded base metal. There was also no considerable change in the hardness and strength values of the formed tube with respect to those of the extruded base metal. However, elongation of the tube formed by FSBE process was higher than that of produced by other SPD methods. The results achieved from mechanical assessments were consistent with those obtained from microstructure examinations. (C) 2014 Elsevier Ltd. All rights reserved.