Effect of temperature on microstructural evolution and subsequent enhancement of mechanical properties in a backward extruded magnesium alloy

摘要

The capability of backward extrusion (BE) method was assessed to achieve modified structures in AZ80 magnesium alloy. At first, 3D-Deform was employed to simulate the deformation flow through the deformed cup which gives an evidence from the flow behavior of the material. The material was processed via BE method at various temperatures of 250, 350, and 450 A degrees C. Metallographic investigations were conducted in three different regions of the BE-processed cup (wall, bottom, and flow channel). The main feature observed at the wall of the BE cup was the presence of mechanical twins, the frequency of which was reduced by raising the process temperature. The flow localization in the form of shear banding occurred within the flow channel at all deformation temperatures. The bottom of the BE-processed cup at 250 A degrees C exhibited coarse initial grains along with a continuous network of the eutectic phase at grain boundaries. However, increasing the process temperature to 350 and 450 A degrees C led to the fragmentation of the gamma-Mg17Al12 network to fine particles, where a considerable grain refinement was also traced, particularly at 450 A degrees C. Furthermore, a special testing technique, called the shear punch testing method, was utilized to examine the room temperature mechanical properties of the BE specimens. Results indicated that BE-processed materials would benefit from a higher strength in comparison to the initial material; conversely, the ductility follows a different trend depending on the deformation temperature.