Microstructure evolution and mechanical properties of high-strength Mg-Gd-Y-Zn-Mn alloy processed by asymmetric hot rolling

Asymmetric hot rolling was used to fabricate the high-strength Mg-9Gd-4Y–1Zn-0.8Mn (wt.%) alloys, which is strengthened by the lamellar long-period stacking ordered (LPSO) phases inside grains and the block-shaped LPSO phases surrounding grain boundaries. The reduction in total thickness shows a significant impact on the microstructure, texture, and mechanical properties of the alloy sheets. By keeping the velocity ratio between the top and lower rollers at 1.3, the shear strain is introduced all across the sheet thickness. The as-rolled sample exhibits a bimodal-grained structure made up of fine recrystallized (DRXed) grains with relatively random orientation and coarse elongated non-recrystallized (unDRXed) grains with intense basal texture and profuse substructure. As rolling strain increases, the volume fraction of the DRXed region and the basal texture intensity of the unDRXed region gradually increase. The dominating prismatic slip as well as the moderate basal slip and pyramidal slip are activated during rolling. The triggering of prismatic slip, among the activated multiple slip systems, results in the development of [101¯0]//RD texture component at high strains. The alloy sheet that underwent severer rolling strain (56.3%R sample) shows higher ultimate tensile strength (411 MPa) and tensile yield strength (348 MPa) but lower elongation to failure (3.5%). The dominant strengthening mechanisms for the preferable mechanical properties should be grain boundary strengthening of fine DRXed grains, texture strengthening of coarse elongated unDRXed grains, short-fiber strengthening of block-shaped LPSO phases, and dispersion strengthening of profuse lamellar LPSO phases and dense tiny Mg5(Gd, Y) particles.