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In this paper, continuous SiC fibers were embedded in an Al 6061 O matrix through ultrasonic consolidation at room temperature. The optimum embedding parameters were determined through peel tests and metallographic analysis. The influence of the embedded fiber volume fraction and base metal thickness on the interface bond strength was studied, and the fiber/matrix bond strength was tested through fiber pullout test. The results showed that embedding ≥0.8% volume fraction of SiC fiber in a 6061 O matrix could significantly increase and even its interfacial strength, but there is a threshold for embedded fiber volume fraction at specific parameters, over which the plastic flow and friction may be insufficient to have a strong bond at foil/foil interfaces between fibers. The study also showed that base metal thickness did not have significant influence on the interfacial strength with an exception of samples with a base metal thickness of 500 μm. Based on the results, it was proposed that microfriction at consolidation interfaces plays an important role for joint formation, and localized plastic flow around fibers is important to have fibers fully and safely embedded.

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.