Abstract:

The thin-strip (TS) casting process developed by Hazelett-CASTechnology™ enables the continuous production of 2-5 mm aluminum strips, achieving solidification cooling rates as high as ~10³ K/s, which are significantly higher than those of conventional casting methods (~10¹-10² K/s). Such a rapid solidification promotes the formation of a distinctive microstructure, characterized by finer grains in the as-cast state, a markedly reduced fraction of intermetallic phases, and consequently, higher solute supersaturation within the matrix. In addition, the TS process streamlines sheet manufacturing by eliminating intermediate steps (e.g., homogenization and scalping), thereby lowering production costs and enhancing sustainability through a reduced environmental footprint.

For industrial applications, particularly in the transportation sector, TS strips require thermomechanical processing to achieve the desired gauge. In this study, TS AA5182 Al-Mg cast strips of 3 mm thickness were subjected to successive hot-rolling and cold-rolling steps, reducing the thickness to 1 mm, followed by annealing at 350°C for 3h. The resulting recrystallized structure was then deformed under uniaxial tensile loading at quasi-static strain rates of 10-3 and 10-1 s-1. The microstructure evolution and texture development were examined in tensile samples with prior histories of hot-rolling and cold-rolling, and compared with their pre-deformed states. Detailed characterization using electron backscatter diffraction (EBSD) revealed how variations in the pre-deformation processing influenced grain size distribution, kernel average misorientation (KAM) profiles, fractions of grain boundary misorientations, and texture evolution in the deformed microstructure. It was demonstrated that the higher degree of freedom in grain rotation—arising from the reduced intermetallic particle fraction in TS samples—significantly affected microstructure and texture evolution. This effect was linked to the grains favorably oriented relative to the loading direction. Analysis of KAM maps further suggested possible strain accommodation mechanisms: (i) grain rotation and dislocation annihilation (indicative of enhanced freedom in grain rotation), and (ii) dislocation pile-ups and boundary-mediated processes (reflecting constrained deformation). Texture maps also enabled identification of grain rotation trajectories and comparison of distinct texture evolution pathways in cold-rolled versus hot-rolled samples.

The sensitivity of independent texture components and fibers to tensile deformation at different strain rates was also analyzed, with particular attention given to the influence of processing route. The mechanical behavior of the fabricated samples was further investigated, focusing on rate-dependent instability patterns and the onset of heterogeneity. Analysis of serrated flow revealed distinct instability signatures, characterized by the formation of various types of Portevin-Le Chatelier (PLC) bands. Strain localization patterns were captured using digital image correlation (DIC), and these were correlated with microstructure and texture development. The results demonstrate how strain-rate effects, combined with prior thermomechanical history, govern both instability mechanisms and texture. Overall, the findings provide new insights into the role of rapid solidification in Al-Mg alloys, highlighting its potential for industrial applications.

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Mr. Andrew Howells