Mechanical and Civil Engineering Seminar

Magnesium alloys are the lightest structural metals, but their structural application is hampered by the complexity of their crystallite-scale deformation that operates with multiple slip and twin mechanisms. They are hence prime candidates to benefit from advanced polycrystalline models and an extensive literature formed to address their anisotropic and load-path-dependent behavior. While these attempts typically seek validity in an aggregate-average sense, there is also a recent physics-based drive towards higher-fidelity modeling that can represent strain fields at some microstructural length scale.

In this talk, we present data that can counterpart such models, detailing the intergranular strain localization signature of wrought Magnesium AZ31 polycrystals. The method is area-scanning digital image correlation with optical microscopy and the focus will be on the sharp rolling texture. In one sense of the load, the material exhibits profuse twin propagation, and we detail the multi-scale nature of the tensile-twin-driven band formation. In the reverse load where twin activity is subdued, the material presents another interesting network of strain localization, rooted in dynamic recrystallization events in the previous rolling process. With the two dominant localization superstructures identified in each sense of the load, we finally present how they interact over a fully-reversed strain cycle. The major result can be put it in simple terms: Stretching and compressing this material back to zero macroscopic strain produces a much higher remnant strain heterogeneity than the reverse operation of compressing and stretching it.