Additive manufacturing comprises layer-by-layer construction of 3D parts using computer controls. This present-day study reveals a list of novel concepts for additive manufacturing, where the addition of material is achieved in solid-state. Materials joined by solid-state techniques exhibits properties beyond those exhibited by material joined by conventional techniques. This has been investigated in both theoretical and experimental manner in length. However, with the development of additive manufacturing techniques, a wide range of possibilities for fabricating complex structures have been identified, which can never be accomplished by conventional techniques. Research on metal-based additive manufacturing has been comparatively less as these products deprive lateral and transverse strength and have issues of anisotropy, making them unfit for structural applications. Moreover, these techniques are not cost-effective. So to overcome these issues, methods incorporating friction into additive manufacturing have been developed. These solid-state techniques use the principle of layer-by-layer deposition. Most of these techniques utilize the principle of selective deposition of materials to form the desired material layer. In this literature review, different advances, approaches, features, and principles of friction-based material joining techniques alongside additive manufacturing are discussed in detail, which recommends new openings for researchers to work in interdisciplinary research to fabricate structures that can exhibit unique properties. This literature portrays an extensive account of the contemporary methods in the fabrication of structures using friction-based additive manufacturing techniques and highlights areas that are worth further research and necessitate a consistent effort on account of the aforementioned disciplines to advance the modernistic technique. Initially, a brief review of different solid-state additive manufacturing techniques is presented, followed by a comprehensive summary of friction stir-based additive manufacturing techniques such as friction assisted seam welding (FASW), additive friction stir (AFS) process, and friction stir additive manufacturing (FSAM) process.
This work analyzes a novel solid-state manufacturing approach of a friction stir additive manufacturing (FSAM) technique for fabricating multiple layers of alternating gradient composite structure using alternate layers of AA6061-T6 and AA7075-T6 aluminum alloys of 3 mm thickness. The evolution of the microstructure along the build direction and its impact on the tensile and microhardness properties were examined using optical microscopy, tensile tests, and Vickers microhardness tests. Nonuniform microstructures were detected along the build direction, and it was concluded that the most productive part of the construction was the nugget zone, which had fine equiaxed grains. It was identified that the grain sizes and precipitate sizes were affected by the varying thermal cycles created by the multiple passes of the tool. These events were identified as the primary reasons for the increase in strength and hardness of the FSAM build from the lower layer to the upper layer. In the final FSAM build the maximum hardness value was obtained as 182.3 HV and the ultimate tensile strength (UTS) was 420 MPa both of which were identified at the topmost layer. Moreover, the postmortem of the fractured samples revealed that the cause of failure was a combination of both ductile and brittle fractures. The findings of this study suggest that the FSAM approach may be used to fabricate large structures that are free of defects having expected mechanical characteristics and hence the newly fabricated composite can be used as a suitable substitute for the conventional AA6061 material applied in automobile components for its improved performance.
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