Enhancing the plasticity of magnesium alloys

The limited plasticity of magnesium alloys is one reason why it has not seen application in products requiring complex shapes or in applications subjected to large crush strains. This paper describes our current research using in-situ indentation of carefully oriented nanopillars inside a transmission electron microscope that captures the nucleation and propagation of dislocations and twins. Magnesium readily twins under room temperature deformation. We have found an intrinsic, previously unobserved nanotwinned structure where the lath spacing is on the order of 1-2 nm. By measuring the stress of the deformation twinning event and the evolution of the microstructure, we are able to experimentally probe the fundamental mechanisms for the formation of different types of deformation twins and compare our results with theoretical studies. The absence of external constraints, such as grain boundaries in our single crystal samples, suggests that the nanotwinned structure is formed homogeneously or in an autocatalytic response. This remarkable structure points to the possibility of achieving high strength and high ductility in Mg alloys through the formation of the nanotwinned structure and open new approaches for controlling chemistry and microstructure to reduce deformation anisotropy to enhance plasticity. Copyright © 2013 MS&T'13®.