Controlling texture in magnesium alloy sheet by shear-based deformation processing

Abstract

Constrained chip (sheet) formation by large strain extrusion machining is used to impose effective strains of ∼1 in Mg alloy AZ31B sheet in a single step of deformation. High-speed image analysis shows the deformation underlying sheet formation to be simple shear that is confined to a narrow zone. This confinement of the deformation limits the need for pre-heating of the workpiece to realize continuous sheet forms. Tilted-basal textures, wherein the basal poles are inclined from the sheet surface normal, are achieved by this processing. These textures are quite different from those prevalent in rolled sheet. By controlling the strain path, the basal pole inclination could be varied in the range 32–53°. The primary texture component is the B-fiber, indicating basal slip to be the main deformation mode over the temperature range 165–400°C. An additional C2-fiber component appears above 250°C due to the activation of pyramidal 〈c+a〉 slip. In conjunction with these textures, microstructures ranging from ultrafine-grained (∼200nm) to fine-grained (∼2μm) could be obtained by controlling the deformation temperature. Implications of the results for production of Mg sheet are discussed.