Quantitative Evaluation of Bulk and Interface Microstructures in Al-3003 Alloy Builds Made by Very High Power Ultrasonic
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INTRODUCTION
ULTRASONIC additive manufacturing (UAM) is a promising technique to generate functional components directly from thin metallic tapes/foils.*[1] This process is *In this document, tapes and foils are used interchangeably to allow for better readability.
also known as ultrasonic consolidation (UC). The tapes are joined to each other by systematically using the ultrasonic seam welding technique.[2] Since ultrasonic seam welding is a solid-state joining process, the bulk heating of the builds is minimal. Ultrasonic oscillations, typically 20 kHz, are locally applied to the metal foils through a sonotrode under a static normal force. The process is interspersed with metal removing (drilling or machining) to achieve a desired geometry. Therefore, this process is expected to be a powerful tool for many applications such as composite parts, dies, embedded sensors, and so on, which have complicated structures. Recent publications[1–14] showed that the bonding process between tapes progresses through many metallurgical phenomena including plastic deformation,
HIROMICHI T. FUJII, Assistant Professor, Department of Material Science and Engineering, The Ohio State University, Columbus, OH 43221, is on leave from the Department of Materials Processing, Graduate School of Engineering, Tohoku University, Sendai 908-8579, Japan. Contact e-mail: [email protected] M.R. SRIRAMAN, Postdoctoral Fellow, and S.S. BABU, Associate Professor, are with the Department of Materials Science and Engineering, The Ohio State University. Manuscript submitted February 8, 2011. Article published online September 2, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
frictional heating, deformation heating, recrystallization, diffusion, and contact between nascent surfaces. However, all the preceding works have focused on representative interfaces extracted from these builds. It is envisioned that, due to the inherent nature of the additive process, the interface and bulk regions are expected to receive a wide range of accumulative thermomechanical cycles. As a result, one may expect a wide range of property scatter through the thickness of the builds.[1] Interestingly, this aspect of the process has not been investigated yet. The current research focuses on characterizing these accumulative effects on microstructure evolution. In order to provide context, a brief summary of the published information with reference to UAM is presented subsequently. The role of welding parameters (speed, normal force, and oscillation amplitude) on bonding were investigated by many researchers using microscopy[3–13] and mechanical property testing. These investigations focused on minimization of void fraction[3,7–10,12] at interfaces due to inefficient solid-state joining. In general, the quality of the joining is related to the linear weld density (LWD), which is defined by the ratio of the bonded interface length to the total interface length. Using these measurements, as well as lap-shear and peel tests, Kong et al. identified the processing windows for
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