Strengthening mechanism based on dislocation-twin interaction under room temperature multi-directional forging of AZ80 Mg alloy

Twin and dislocation have critical influence on the mechanical properties of the widely used AZ80 magnesium alloy. In the present work, we designed room temperature multi-direction forging (MDF) at different strain amplitudes (3% and 6%) with a same strain, introduced twin and dislocation structures and improved the mechanical properties of the alloy. The results showed that the material reached the limit of deformation with a cumulative strain of 0.72. With the increase of strain, the grain size decreased and the dislocation density increased gradually. At low strain amplitude, the transformation of dislocations at twin boundaries (TBs) caused twinning expansion and detwinning. While at high strain amplitude, interactive twin structure hindered the over-expansion of twins. In addition, high-density dislocations accumulate at the twin boundaries, which stimulates the nucleation of twin variants and further refines the grains. In the process of plastic deformation, dislocation strengthening contributed the main yield strength, and fine twins provided a certain level of hardening ability. Through the interaction between the dislocations and twins, the strength and plasticity of the material were synergistically improved, and excellent mechanical properties with ultimate tensile strength of 486 MPa, yield strength of 385 MPa, and elongation of 8.1% were finally obtained.