Developing a low-alloyed fine-grained Mg alloy with high strength-ductility based on dislocation evolution and grain boundary segregation

A new low-alloyed Mg-2Sm-0.8Mn-0.6Ca-0.5Zn (wt.%) alloy is prepared by low-temperature and low-speed extrusion. The as-extruded alloy has ultra-high yield strength (YS, 453 MPa) but poor elongation (3.2%) mainly due to the formation of a fine-grained structure containing high-density residual dislocations and Mn nanoparticles. More importantly, after subsequent simple annealing, the alloy exhibits an excellent combination of high-strength and high-ductility, with the YS of 403 MPa and elongation of 15.5%. The effective inhibition of grain growth by grain boundary (GB) co-segregation of Sm/Zn/Ca is crucial for the annealed alloy to maintain high strength. Appropriately decreased dislocation density, especially the evolution of immovable long S-< c+a > dislocations towards new GBs, is a key factor for the remarkable increase of ductility for the annealed alloy. Thus, we put forward a new strategy for developing low-alloyed Mg alloy with high strength-ductility mainly based on dislocation evolution and GB segregation. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

A new low-alloyed Mg-2Sm-0.8Mn-0.6Ca-0.5Zn alloy is prepared by low-temperature and low-speed extrusion, which exhibits high strength but low ductility. After annealing, the alloy shows both high strength and high ductility due to the effective inhibition of grain growth by grain boundary co-segregation and decreased dislocation density. The evolution of immovable long dislocations towards new grain boundaries is a key factor for the remarkable increase of ductility in the annealed alloy.