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Exploratory research of friction stir extrusion additive manufacturing using AA6060 T6

Ariës, R.C.G. (2021) Exploratory research of friction stir extrusion additive manufacturing using AA6060 T6.

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Embargo date:30 April 2024
Abstract:Additive Manufacturing (AM) is an upcoming advanced production process, also known as 3D printing. Most of the currently employed AM techniques for metals are based on melting of the added material. However, processing materials in the solid state brings a number of advantages. Solidification related metallurgical problems such as crack formation and porosity, can be avoided. Also, evaporation of alloying elements is prevented and often a fine-grained microstructure is obtained. The recently developed solid-state printing technique Friction Screw Extrusion Additive Manufacturing (FSEAM) has been investigated. The FSEAM process is based on a solid rotating tool that transports and heats the supplied metal through friction and intense plastic deformation. The heated metal is pressed on top of the substrate which moves relative to the deposition tool to create a product layer by layer. The MSc thesis concentrated on the effect of the feed ratio. If the ratio is larger than 1 more material is supplied than required (“overfeeding”). If it is less than 1 the tool does not deliver enough material (“starvation”). During the experiments, the feed ratio was varied by changing the velocity of the table. Tensile test specimens were extracted in the build direction. Best values of the tensile strength (> 100 MPa) and the elongation at fracture (> 15 %) were obtained for a feed ratio of 1.14 – 1.26. Dimple formation was seen at the fracture surfaces of these tensile test specimens confirming strong plastic deformation behavior and excellent layer-to-layer bonding in the build direction. At lower feed ratios the mechanical properties were strongly reduced due to the formation of porosity and poor bonding showing the importance of a proper feed ratio selection. In general, relatively small equiaxed grains were formed, which may contribute to the strength development. However, the strength of the printed material was actually reduced by 50 % as compared to that of the feed material. The reduction can be explained by growth/dissolution of the strengthening precipitates. Additionally, an isothermal, mechanical 3D flow model was developed describing the high-temperature behavior of an AA6063 (comparable to AA6060 T6) alloy employing a power-law description with shear thinning characteristics. The model is capable of reproducing the experimentally observed trends in the extrusion forces, but additional work is required to obtain more quantitative agreement. Most likely more advanced boundary conditions are required.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Link to this item:http://purl.utwente.nl/essays/86118
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