Microstructure evolutions and mechanical properties of nano-SiC-fortified AA7075 friction stir weldment: The role of second pass processing

In this study, two AA7075-O plates were friction stir Welded (FSWed) while SiC nano-particles were encapsulated along the joint line. Using a square pin tool, a single pass processed specimen was generated. To evaluate the effectiveness of second pass processing on microstructure and mechanical properties of the joint, friction stir welding (FSW) repeated under the same processing conditions. Cross-sectional investigation gave evidence to the soundness of both joints. Microstructural observations were conducted by optical microscopy. It was revealed that the 2-pass processed specimen had coarser microstructure than 1-pass processed one. Particles distribution within the stir zone (SZ) was studied through scanning electron microscopy (SEM) technique. An excellent bonding between reinforcements and the matrix was observed in each specimen. With respect to 2-pass processed specimen, however, 1-pass processed specimen exhibited less uniform particles distribution. All tensile specimens fractured outside the SZ during tensile testing. Interestingly, SEM analysis of fractured surfaces was in excellent agreement with ductility results. (C) 2015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.