I thought a great way to start off the discussion in the Mg forum is to talk about formability of Mg sheet, and specifically how to achieve the ultimate goal of room temperature formability. One intriguing question, is how can one take advantage of twinning in Mg to enhance plasticity. A lot of great work has been done in characterizing compression vs tensile twins and understand their role in plasticity. What should the approach be in enhancing plasticity via twinning, or is trying to take advantage of twinning futile, and should the approach be to explore other mechanisms i.e. grain refinment, texture optimization, etc. I look forward to the discussion!

I think a first step along these lines is to clarify the terminology. Contraction twins can be formed by applying a tensile stress (along the basal planes) and extension twins by similarly applying a compressive stress. Accordingly, I would like to propose that the terms compression and tensile twins be replaced by, respectively, contraction and extension twins.

I happen to be a huge fan of the importance of controlling twinning for improving the formability of wrought Mg. However, the question rapidly arises as how to achieve such control. Answers to this include things like: grain refinement, alloying addition and texture control.

Given the additional role of anisotropy in formability, probably the most potent method is texture control. Many would agree that the most desirable texture in sheet Mg is a random one. Indeed, if the sheet texture could be randomized one might expect considerable improvement in room temperature formability.

Along with other effects, random textures will tend to reduce contraction twinning (which I think is harmful to ductility) and increase in extension twinning (which I think is beneficial to ductility).