Fragmentation of 18R LPSO phases through multi-pass equal channel angular pressing and its impact on rollability of Mg97Y2Zn1 (at%) alloy

Abstract

In this study, the fragmentation process of 18R long period stacking ordered (LPSO) phase was investigated by comparing the microstructure of as-cast Mg97Y2Zn1 (at%) alloy and 32-pass equal channel angular pressing (ECAP) processed alloy. Results show that two fragmentation modes occurred either singly or in combination during ECAP, i.e., delamination of 18R phase parallel to its basal plane and rupture of 18R perpendicular to its basal plane. Due to these two modes of fragmentation, fine LPSO laths and particles, as well as tiny dynamic recrystallization (DRX) grains were generated in the ECAP alloy, which contributed to its moderate strength and good ductility. In addition, both as-cast and ECAP alloys were subjected to hot rolling to explore the differences of LPSO morphology on rollability of the alloys. The rollability of as-cast alloy was very poor because the coarse microstructure was easy to entangle dislocations and generate microcracks during rolling. However, the rollability of ECAP alloy was significantly improved owing to the additional fragmentation action of band-shaped and kinked LPSO phases, as well as dislocations pinned by LPSO particles or coordinated by more boundaries from fine LPSO particles and DRX grains. Compared with ECAP alloy, the ECAP-rolled alloy exhibited increased strength and moderate ductility with ultimate tensile strength of 384 MPa and fracture elongation of 8.1%.