Hardening effects of sheared precipitates on { 1121 } twinning in magnesium alloys

The interactions between a plate-like precipitate and two twin boundaries (TBs) ( {101 over bar 2 }, {112 over bar 1 }) in magnesium alloys are studied using molecular dynamics (MD) simulations. The precipitate is not sheared by {101 over bar 2} TB, but sheared by {112 over bar 1} TB. Shearing on the (110) plane is the predominant deformation mode in the sheared precipitate. Then, the blocking effects of precipitates with different sizes are studied for { 112 over bar 1 } twinning. All the precipitates show a blocking effect on { 112 over bar 1 } twinning although they are sheared, while the blocking effects of precipitates with different sizes are different. The blocking effect increases significantly with the increasing precipitate length (in-plane size along TB) and thickness, whereas changes weakly as the precipitate width changes. Based on the revealed interaction mechanisms, a critical twin shear is calculated theoretically by the Eshelby solutions to determine which TB is able to shear the precipitate. In addition, an analytical hardening model of sheared precipitates is proposed by analyzing the force equilibrium during TB-precipitate interactions. This model indicates that the blocking effect depends solely on the area fraction of the precipitate cross-section, and shows good agreement with the current MD simulations. Finally, the blocking effects of plate-like precipitates on the {101 over bar 2} twinning (non-sheared precipitate), {112 over bar 1} twinning (sheared precipitate) and basal dislocations (non-sheared precipitate) are compared together. Results show that the blocking effect on { 112 over bar 1 } twinning is stronger than that on {101 over bar 2} twinning, while the effect on basal dislocations is weakest. The precipitate-TB interaction mechanisms and precipitation hardening models revealed in this work are of great significance for improving the mechanical property of magnesium alloys by designing microstructure.(c) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University