Synergic enhancement of ductility and toughness in friction stir additively fabricated AA6061-T6 build

Abstract

This study comprehensively investigates the ductility and impact toughness aspects of friction stir additively fabricated (FSAF) components, particularly crucial for applications in aerospace components like stringers and stiffeners. FSAF technology is used to create a fifteen-layered AA6061-T6 build out of 3 mm thick aluminium sheets. A taper threaded tool with a pin length of 4.5 mm (corresponding to a plunge depth of 50% into the lower layer thickness) was used for the experiment. Dynamic recrystallisation resulted in the creation of a stir zone with fine grains, as demonstrated by optical microscopy. Differences in the size of grains, as well as alterations in the distribution, and size of precipitates were observed in the direction of fabrication. The hardness and tensile strength exhibited variations across layers, with the uppermost layer displaying the highest values (82.48 HV and 252.60 MPa, respectively). An impressive milestone was reached with the attainment of 66% ductility, primarily attributed to the process of fragmentation and partial reduction in grain boundary phases. The results of impact toughness have showcased a significant accomplishment as well. Impact tests yielded 112 J and 86 J for the crack-arrester and crack-divider orientations, with enhanced ductility playing a significant role. Delaminations in crack-arrester samples led to higher energy absorption.