Twin-twin interactions and contraction twin formation in an extruded magnesium alloy subjected to an alteration of compressive direction

Abstract

Twinning and detwinning represent major deformation mechanisms in hexagonal close-packed (hcp) metals. The aim of this study was to identify twin-twin interactions and contraction twin formation in an AZ31 magnesium alloy when the compressive direction was changed from the extrusion direction (ED) to the normal direction (ND) via electron backscatter diffraction (EBSD) and Schmid factor analysis. {101¯2} extension twins of multiple variants were observed after compressive deformation of 4.3% along ED. The detwinning of {101¯2} extension twins occurred along with the formation of {101¯1} and {101¯3} contraction twins, when the compressive direction was changed to ND. The extension twins in some grains almost fully vanished, making the grains back to a twin-free state. A new twin-twin interaction mechanism being different from double twinning (defined as twins within a twin) was identified, due to the impingement of {101¯1} contraction twins nucleated in the matrix grain on a pre-existing {101¯2} extension twin.