Twinning and the ductility of magnesium alloys: Part II. “Contraction” twins

TLDR: In this paper, a series of tensile and compression tests results are reported for common wrought alloys: AZ31, ZK60 and ZM20, and these data are combined with EBSD analysis and simple flow stress models to argue the following: (i) contraction double twinning (which enables contraction along the c axis) can decrease the uniform elongation, and (ii) compression double twinening can also account for shear failure at low strains.

Abstract: Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work presents part II of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile and compression tests results are reported for common wrought alloys: AZ31, ZK60 and ZM20. These data are combined with EBSD analysis and simple flow stress models to argue the following: (i) that “contraction” double twinning (which enables contraction along the c axis) can decrease the uniform elongation, and (ii) that compression double twinning can also account for shear failure at low strains. The last of these is described as a combined consequence of strain softening of the continuum and the local generation of twin sized voids.