Abstract
Ultrasonic additive manufacturing (UAM) is a solid-state metal additive manufacturing process, with the combination of layer by layer ultrasonic seam welding and CNC machining. Due to the friction and deformation at the bonding interface, the ultrasonic softening effect and temperature generated, the microstructure of the substrate materials is evolving constantly. In this paper, in order to better understand the bonding mechanisms, the good practice and the capability of UAM, and the influence of different key process parameters on bonding quality, the microstructure evolution during UAM is reviewed in detail. Defects can be generated at the UAM bonding interface, but by choosing the right material combination and the right process parameters, defects can be reduced to minimum. Plastic deformation is very important for the bonding between layers during UAM, and plastic flow is important for redistribution of oxide layer, forming of mechanical interlocks, filling micro-valleys on the mating surface, and filling the gaps when embedding elements. UAM process can cause recrystallization and grain refinement at the welding interface and the intimate bulk materials around, and it will also gradually change the texture from rolling texture to shear texture. In the meantime, when further layers of materials are deposited on the top of the existing part, the microstructure will have some accumulative change. In order to reduce the defects number and increase the strength, sometimes, heat treatment needs to be carried out to the as-deposited parts, which will change the microstructure as well. Finally, the relevant research is summarised and the perspectives of further research are recommended.
Highlights
Ultrasonic additive manufacturing (UAM), previously ultrasonic consolidation (UC), is a solid-state metal additive manufacturing process, in which ultrasonic seam welding process is used to build thin layer of metal foils layer by layer, and by combining with computer numerical control (CNC) machining and additional elements embedding, a complex, hollow and smart structure can be built
Obielodan [26] studied the feasibility of joining multi-materials, including Al, Ni, Ti, Ta, stainless steel, MetPreg, Ag, Mo and Cu, by UC, and the results showed that all FCC materials and some other material combinations could be bonded well by UC with a good linear weld density (LWD)
There are different factors that affect the void level at the interface, the microstructure and texture evolution, plastic flow and mechanical strength
Summary
Ultrasonic additive manufacturing (UAM), previously ultrasonic consolidation (UC), is a solid-state metal additive manufacturing process, in which ultrasonic seam welding process is used to build thin layer of metal foils layer by layer, and by combining with computer numerical control (CNC) machining and additional elements embedding, a complex, hollow and smart structure can be built. During UAM process, due to the friction and highfrequency shear deformation at the mating interface, the high strain caused by plastic deformation, the ultrasonic softening effect, temperature generated and subsequent heat treatment, the microstructure of the materials, especially at the welding interfaces, is evolving at different stages. It is believed that a review on the microstructure evolution will help to understand the bonding mechanisms, the good practice, the capability and the influence of different process parameters on build quality of UAM. In this paper, it will be reviewed from the following four aspects: defects at the bonding interface, plastic flow during UAM, microstructure and texture evolution during UAM and influence of post-weld heat treatment on microstructure
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