Abstract
This work presents, for the first time, an in-depth investigation of the structure–property–fatigue relationships of an Al-Mg-Si alloy (AA6061) processed via additive friction stir-deposition (AFS-D). As industry focus continues to shift for more efficient and lightweight structures, quantitative studies on the cyclic performance of additively manufactured materials are needed. In this study, the AFS-D processed AA6061-T6 was machined into specimens in two orthogonal orientations and subjected to monotonic and strain-controlled fatigue testing. The microstructural features of as-deposited AA6061 exhibited evidence of dynamic recrystallization and grain refinement. In addition, significant reduction in the intermetallic particles was observed after AFS-D processing. The fatigue results demonstrate that the as-deposited material, particularly the longitudinal direction, exhibited similar fatigue performance to wrought AA6061-T6 in both low-cycle and high-cycle fatigue regimes, which is a promising result for additively manufactured material in the as-deposited condition. By contrast, the as-deposited build direction orientation possessed slightly lower fatigue resistance than the wrought feedstock material. The AFS-D material was observed to exhibit different damage mechanisms from porosity-based damage mechanisms observed in fusion-based additively manufactured materials. Lastly, a microstructure-sensitive fatigue model was employed to capture the fatigue effects of the AFS-D processing on the AA6061.
Highlights
The transportation industry has been researching potential techniques to improve the fuel efficiency, in both lightweight materials and additive manufacturing
In addition to DRX, Feng et al observed the dissolution of fine β” precipitates in the material when examined via transmission electron microscopy (TEM) [13]
The feedstock material used in this study was rolled AA6061-T651 that was machined using a water jet into dimensions of 9.5 mm × 9.5 mm × 304.8 mm in order to fit into the hollow opening of the additive friction stir-deposition (AFS-D) tool
Summary
The transportation industry has been researching potential techniques to improve the fuel efficiency, in both lightweight materials and additive manufacturing. Fusion-based additive techniques, e.g., selective laser melting and direct metal laser sintering, have been reported to experience difficulties in producing aluminum due to hot-cracking during solidification [1,2,3]. In addition to DRX, Feng et al observed the dissolution of fine β” precipitates in the material when examined via transmission electron microscopy (TEM) [13] This observation is suggested to be caused by the high temperatures experienced during FSW (T ≥ 250 ◦ C), and has a significant effect on AA6061, as β” is the primary strengthening phase of the alloy [18]. A microstructure-sensitive fatigue model is employed to elucidate the effect of AFS-D processing on the fatigue mechanisms As such, this present study provides, for the first time, a quantitative analysis of the mechanisms of cyclic deformation on an as-deposited Al-Mg-Si alloy processed via AFS-D
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