Characterizing the Effect of Acoustoplasticity on the Microstructural Evolution and Hardness of Copper

Acoustoplasticity is the process of softening and plastically deforming metallic structures using high intensity acoustic waves. Acoustoplasticity has been used to join thin layers of metallic materials and therefore it is considered a welding technique. In this work, acoustoplasticity was performed on 6mm thick pure copper plate, with an average grain size of 20mm, to study the effects of power (varied from 4000-6000W) on the surface hardness and microstructural evolution. Although it is possible that some surface heating could occur during acoustoplastic processing, in general this is considered to be an ambient temperature process. Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and Vickers hardness characterization revealed three identifiable microstructural zones within the top 600mm from the acoustoplastically-deformed surface. The upper zone contained refined equiaxed grains ranging between 1mm-5mm. The intermediate zone exhibited a crystallographic reorientation zone containing wavy elongated grains. The third zone contained a separate crystallographic reorientation region. The hardness was greatest within the grain refined region and reduced gradually with increased distance from the surface until it plateaued to the values obtained for the as-received copper plate. The results suggest that acoustoplasticity may be used on bulk samples for grain refinement applications other than welding