On the relationship between and conjugate twins and double extension twins in rolled pure Mg

The paper presents a new type of twin-like objects observed in rolled pure magnesium. They have and habit planes and their misorientations to the matrix are close to 56° and 63° about axis, respectively. The ad hoc performed theoretical analysis and atomic simulations allow to interpret the objects as double twins formed by the simultaneous action of two twinning shears with completely re-twinned volume of primary twin. The observed inclinations from the ideal misorientations for such double twins can be explained by the compliance of the strain invariant condition in the twin boundary. It seems plausible that, once the double twin is formed, its twin boundaries are hard to move by glide of twinning disconnections. If so, these twins represent obstacles for the motion of crystal dislocations increasing the hardness of the metal.