Microstructure Evolution of Al6061 Alloy Made by Additive Friction Stir Deposition

Abstract

In this paper, the phase structure, composition distribution, grain morphology, and hardness of Al6061 alloy samples made with additive friction stir deposition (AFS-D) were examined. A nearly symmetrical layer-by-layer structure was observed in the cross section (vertical with respect to the fabrication-tool traversing direction) of the as-deposited Al6061 alloy samples made with a back-and-forth AFS-D strategy. Equiaxed grains were observed in the region underneath the fabrication tool, while elongated grains were seen in the “flash region” along the mass flow direction. No clear grain size variance was discovered along the AFS-D build direction except for the last deposited layer. Grains were significantly refined from the feedstock (~163.5 µm) to as-deposited Al6061 alloy parts (~8.5 µm). The hardness of the as-fabricated Al6061 alloy was lower than those of the feedstock and their heat-treated counterparts, which was ascribed to the decreased precipitate content and enlarged precipitate size.

Effects of Printing Layer Orientation on the High-Frequency Bending-Fatigue Life and Tensile Strength of Additively Manufactured 17-4 PH Stainless Steel

“…These AM techniques can be classed according to several factors, such as the material used (i.e., metal, polymer), feedstock type (i.e., powder, rod, filament), the energy source used (i.e., laser, E-beam, arc, friction), size of the parts or deposition rate (small/large-scale), printing environment (i.e., open-air, gas shield, inert gas), etc. For metal AM, common methods include laser fusion techniques (i.e., laser power bed fusion, L-PBF, [ 3 , 4 , 5 , 6 ], selective laser sintering/melting, SLS/SLM, and direct metal laser sintering, DMLS), bound metal filament extrusion-based fabrications [ 7 ] (i.e., bound powder extrusion/deposition, BPE, or atomic diffusion additive manufacturing, ADAM), as well as fused deposition modeling (FDM) [ 8 , 9 , 10 ]), friction-based AM (i.e., additive friction stir deposition, AFSD [ 11 ]), powder adhesion AM (i.e., metal injection molding, MIM), etc.…”

Hardness Distribution of Al2050 Parts Fabricated Using Additive Friction Stir Deposition

“…Dynamic recrystallization results in a reduction in the average grain size, as well as an increase in the number of grains within the material. Zeng et al studied the microstructure of Al6061 parts processed by AFSD [ 18 ]. For the as-deposited parts, the examination revealed equiaxed grains with a significantly reduced grain size, in comparison to the grain size of the feedstock material.…”

“…Investigating the microstructure of the AFSD-manufactured Al6061 parts, Zeng et al concluded that the as-deposited AFSD parts have an equiaxed microstructure that can be further enhanced by heat treatment. The grain sizes in the as-deposited AFSD pieces are much smaller than those in the feedstock rod [ 18 ]. Williams et al [ 4 ] investigated how the AFSD processing parameters affect the microstructure and mechanical properties of the magnesium alloy WE43 component.…”

Neutron Imaging of Al6061 Prepared by Solid-State Friction Stir Additive Manufacturing

“…The AFS-D process has been used for fabricating parts with different types of materials. The focus is mostly on aluminum alloys [2][3][4][5][6][7][8][9] in the literature due to their low melting point. However, other materials including nickel alloys [10,11], titanium alloys [12], magnesium alloys [13], copper [14,15], and steel [16,17] have also been processed.…”

“…Given that the MELD process is quite a new additive manufacturing process, a limited number of papers are available in the literature. To date, researchers have been focusing on fabrication [18,19], microstructure characterization [4,6,15], static strength [6], fatigue strength [7,8,11], thermal analysis [20], and simulation [21]. Among characterization methods, MELD samples have mostly been investigated by Electron Backscatter Diffraction (EBSD) [6,11,22], Scanning Electron Microscope (SEM) [6,11,22], Transmission Electron Microscope (TEM) [22], Energy-Dispersive Spectroscopy (EDX) [6], and X-ray Computed Tomography (XCT) [2,23,24].…”