Niyanth Sridharan

Characterisation of Al–Ti dissimilar material joints fabricated using ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid state manufacturing process for joining thin metal tapes using principles of ultrasonic metal welding. The process operates at low temperatures, enabling dissimilar material welds without generating harmful intermetallic compounds. In this study, a 9 kW UAM system was used to create joints of Al 1100 and commercially pure titanium. Viable process parameters were identified through pilot weld studies via controlled variation of weld force, amplitude and weld speed. Push-pin delamination tests and shear tests were performed, comparing as-built, heat treated and spark plasma sintering treated samples. Heat treated and spark plasma sintering treated samples yielded mechanical strengths over twice that of as-built samples. Electron backscatter diffraction measurements show that deformation and grain refinement only take place in the aluminium layers. Heat treated samples exhibit a thin intermetallic layer, which is hypothesised as constraining the interface, leading to the improved strength.

Microstructure and mechanical property characterisation of aluminium–steel joints fabricated using ultrasonic additive manufacturing

ABSTRACT Driven by the interest to weld steel and aluminium in the solid state to prevent intermetallic formation, 9 kW ultrasonic additive manufacturing (UAM) has been used to fabricate Al 6061-4130 steel dissimilar metal builds. In addition, Al 6061-Al-6061 builds were fabricated using similar techniques to provide a baseline for mechanical property measurement. Mechanical testing performed using pushpin testing shows that steel–aluminium dissimilar metal welds fail across multiple layers while Al–Al welds delaminate from the substrate. Multi-scale characterisation indicates that the change in failure morphology is due to the formation of metallurgical bonds in the Al–steel builds. Texture analysis shows identical textures at the interface of Al–steel, Al–Al and Al–Ti joints; showing that the bond formation in all cases relies extensively on plastic deformation across multiple materials. In addition, no changes to the bonding mechanism occurred when the materials used as foils and substrate were swapped.

Rationalization of solidification mechanism of Nd–Fe–B magnets during laser directed-energy deposition

Near-net fabrication techniques are highly beneficial to minimize rare earth metal usage to fabricate dense fully functional magnets. In this study, feasibility of using the directed-energy deposition technique for fabrication of magnets is evaluated. The results show that despite the ability to fabricate highly reactive materials in the laser deposition process, the magnetic coercivity and remanence of the hard magnets is significantly reduced. X-ray powder diffraction in conjunction with electron microscopy showed that the material experienced a primary Nd2Fe17Bx solidification. Consequently, the absence of the hard magnetic phase resulted in deterioration of the build properties.