A New Modified Cyclic Extrusion Channel Angular Pressing (CECAP) Process for Producing Ultrafine-Grained Mg Alloy

In this study, a new modified cyclic extrusion channel angular pressing (CECAP) process with multi-pass capability is presented for producing ultrafine-grained (UFG) Mg alloy. In this method, an additional extrusion stage with a low extrusion ratio is added at the end of the CECAP process to enhance hydrostatic stresses, equivalent strain, and facilitation of the process implementation. The experimental results showed a remarkable grain refinement with a relatively uniform distribution of microstructure and β-phase in the new CECAP processed sample. The average grain size decreased from ~75 µm in annealed condition to 4.5 µm and 3.5 µm in CECAP and new CECAP processes, respectively. Also, more dispersion of the β-phase with smaller sizes was observed in the processed microstructure. The hardness and its uniform distribution were increased significantly. The compressive yield stress (CYS) was enhanced to about 153.3 MPa from the initial value of ~85 MPa. Also, both the strength and ductility of the new CECAP processed sample were higher than those of CECAP processed one. These excellent properties might attribute to higher hydrostatic compressive stresses resulting from the last low ratio extrusion stage which was almost 50% higher in the new CECAP process.