Development of a double-layered AA6061 build using additive friction stir processing

Abstract

In this study, a double-layered AA6061 build was developed using solid-state additive friction stir processing (AFSP) at different linear and tool rotational speeds. The cross-section of the build was examined using optical macroscopy, and microhardness was measured using the Vickers hardness tester. Microstructural evolution was examined using advanced characterization techniques such as electron back scattered diffraction and transmission electron microscopy, while bulk texture evolution was investigated using the X-ray neutron diffraction method. Defect-free builds were attained at rotational speeds of 1100 and 1300 rpm. Compared to the starting alloy, hardness values were significantly lower along the builds, demonstrating loss in the material's strength due to precipitate dissolution. A maximum average hardness of 63.73 HV was observed on the build developed at 1100 rpm, 60 mm/min. AFSP caused grain refinement and reduced grain size to 4.95 μm in the build zone, but dissoluted strengthening β Mg2Si and AlFeMnSi phases due to the intense heat. The microstructure of base material exhibited a texture index of 1.4432, while the microstructure of the build zone showed a reduced texture index of 1.1742. Intense deformation caused randomized grain orientation with reduced texture but retained the shear type S {123}<634>, copper {112}<111> and brass {011}<211> components in the build zone.