Strengthening and toughening mechanisms of an ultrafine grained Mg-Gd-Y-Zr alloy processed by cyclic extrusion and compression

Cyclic extrusion and compression (CEC) was implemented to process the Mg-Gd-Y-Zr alloy. Microstructure characters, including the matrix grain, precipitates and texture evolution, were tried to correlate with the mechanical performance of the post-processed alloy. Results show that after 14 passes of CEC, the average grain size of GW102K is greatly refined to ~100-200 nm. Secondary-phase particles are broken due to the occurrence of tension tearing and shearing fracture. Quantitative texture analysis elucidates that CEC weakens the initial fiber texture of the extruded GW102K. Unlike most of the severe plastic deformed Mg alloys, the CEC processed GW102K alloy follows the normal Hall-Petch equation, which is closely associated with the disintegrated texture as well as the nanoscale second-phase particles. A considerable increase in elongation is witnessed and the introducing of rare-earth elements (RE) is found to change the deformation mechanisms of the Mg alloy by facilitating non-basal slip systems, twinning and shear bands.