Fundamentals and Applications of Electrically-assisted MicrorollingPublic Deposited
In this presented study, rolling in micro scale level, termed as microrolling, has been advanced and extended its application to surface texturing and roll bonding. Meanwhile, continuous direct current (DC) is introduced to the processes to establish two new microrolling processes: the Electrically-assisted Roll Bonding (EARB) and the Electrically-assisted Microrolling-based Texturing (EAμRT). The continuous DC serves as a heating mean with a rapid effect over the conventional furnace heating method for material softening. The Joule heating effect, which is induced by electric current passage, softens the material resulting in flow stress reduction to ease material deformation. The effect of electric current on easing deformation is shown in both the EARB and EAμRT processes. The EARB process is applied to the production of laminated metal composite (LMC) sheets, Al/Al and Al/Cu in this study. Beyond easing the deformation of the metal sheets for bonding, improvement is found in the bond strength. The local heating effect at the interface contributes to the overall bond strength enhancement of the bonded LMC. In order to further prove the existence of local heating at bonding interface and its influences on joining effect as well as to understand the behavior of Joule heating effect at the interface with the consideration of bonding surface topography, an analytical has been developed for local and macro interface temperatures prediction. Modeling results show that the local temperature can be so high to reach the recrystallization temperature and even the melting point of aluminum. Because the hot spots, i.e. local regions have higher temperatures than surroundings, is in a small area compared to the interface, their temperature is not necessarily to be captured by the macro interface temperature; a hot spot with a few hundred degree Celsius can be found in an interface with a temperature below 100°C. Besides roll bonding process enhancement, electric current is also utilized for surface microtexturing. EAμRT applied with 100A continuous DC is used for the texturing of micro grooves on aluminum (AA3003) and titanium (Ti-6Al-4V). By the result comparison between two materials, the significance of local heating in the process can be observed. Depending on the material, the significance of softening effect varies. Materials with higher electrical resistivities usually result in a more significant heating effect. With the application of electric current, deeper micro grooves are produced on both Al and Ti. To predict the micro groove depth in EAμRT, an analytical model with the consideration of roll wear has been developed. Additionally, investigation on the effect of surface texture on the surface hydrophobicity improvement is conducted as a case study of surface texture application.
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