Multi-layer solid-state ultrasonic additive manufacturing of aluminum/copper: local properties and texture

Ultrasonic additive manufacturing (UAM) is an advanced joining technique that utilizes ultrasonic vibrations to bond layers of metal foil together. UAM offers several benefits over traditional manufacturing methods, including enhanced design flexibility and reduced material waste, and its potential applications in various industries such as aerospace, automotive, and biomedical engineering are being actively explored. The study employs a nanoindentation apparatus to investigate the effect of the UAM process on the local mechanical properties of the bonded interface, along with changes in microstructure, which were investigated using scanning electron microscopy and electron back-scattered diffraction. The results revealed a significant correlation between material hardness and local plasticity. EBSD has revealed that the grain size distribution of Al far from the interface contains 57% of the grains less than 3 µm in size, while at the interface this number rises to approximately 78%, indicating that the average grain size decreases as it approaches the interface. This result is consistent with nanoindentation results that demonstrated a gradual change in the hardness of Al foil far from the interface to close to the interface (the maximum penetration depth near the interface was 500 nm less than far from the interface). Both EBSD and nanoindentation disclose the effect of work hardening close to the interface, which is related to dislocation accumulation with a density of \(8.6\times {10}^{-10} {{\text{cm}}}^{-2}\) $8.6\times {10}^{-10}{\text{cm}}^{-2}$ beneath the interface. The consistency of hardness and Young’s modulus with the pole figures and microscopic images demonstrated that plasticity flow and fine grain distribution would only occur in the vicinity of the interface in the softer metal region. Although the harder metal did not exhibit plasticity or recrystallization, the hardness, and Young’s modulus map indicated the formation of a layer of small grains close to the interface on the aluminum side owing to strain hardening and dynamic recrystallization.