Microscale channels produced by micro friction stir channeling (μFSC)

Abstract

The current literature lacks comprehensive research on the processing limits of the Friction Stir Channeling process (FSC) for creating the smallest continuous and integral channels, using tools with threaded probes 2 mm in diameter or smaller. This study pioneers the exploration of the extreme limits of the microscale FSC process, with potential applications in the development of ultra-compact heat exchangers, seeking to enhance the efficiency and sustainability of these systems. Customized tools were designed and manufactured, with predefined dimensions and geometries to establish a set of parameters that consistently produce continuous microchannels, maximizing the hydraulic diameter within the constraints of each tool's specifications and geometry. Comprehensive evaluations—including continuity, watertightness, micro-computed tomography, neutron computed tomography, microhardness testing, and thermal measurements—were conducted to ensure the channels' structural integrity and suitability for super-compact heating and cooling applications. Internal channels were successfully created using tools with threaded probes measuring 2.0, 1.0, and 0.5 mm in diameter, and corresponding shoulder diameters of 5, 4, and 3.5 mm, within 5 mm thick AW1050-H111 aluminum alloy plates. The smallest channel achieved a hydraulic diameter of 191 μm, using a 0.5 mm diameter threaded probe, thus qualifying it as a microchannel. The thermal performance of a compact heat exchanger model was also tested, demonstrating that despite the high cost associated with tool production, particularly due to the specialized manufacturing processes required, the FSC process remains viable, reliable, and repeatable for the production of mini- and micro-channels.