Modification of the Anisotropy and Strength Differential Effect of extruded AZ31 by Extrusion-Shear

The extrusion of magnesium alloys results in a pronounced fiber texture in which the basal planes arc mostly oriented parallel and the c-axes are oriented perpendicular to the extrusion direction. Due to this texture the Strength Differential Effect (SDE), which describes the strength difference between tensile and compression yield strength, and the elastic anisotropy in the sheet plane are obtained during extrusion. The objective of the investigation was to decrease the SDE and anisotropy through specifically influencing the microstructure and texture. To accomplish this objective, the forming processes extrusion (EX) and equal channel angular pressing (ECAP) were combined and integrated into one extrusion die. This combination is called extrusion-shear (ES). With an ES-die, billets of the magnesium alloy AZ31B were formed into a sheet with the thickness of 4 mm and the width of 70 mm. The angles of the used ECAP-applications in the ES-dies were set to 90 degrees and 135 degrees. The results show that the extrusion-shear process is able to decrease the anisotropy and SDE through transformation of the texture compared to conventional extrusion process. Also grain refinement could be observed. However, the outcomes seem to be very sensitive to the process parameters. Only by using the ES-die with an angle of 135 degrees the desired effect could be accomplished.