A molecular dynamics study on the cyclic plastic deformation mechanism of Al–Mg alloys

The deformation mechanism and hardening law of single-crystal and polycrystalline Al–Mg alloy materials during the cyclic loading deformation process of different paths are studied herein according to the principle of molecular dynamics. An analysis of the single-crystal simulation results indicates that the Bauschinger effect decreases with the increase of strain. The cyclic loading leads to dislocation locking and other obstacles, which, in turn, lead to hardening of the material. After that, the force generated by the accumulated strain moves the dislocation obstacle and causes the material to soften. Based on the Voronoi polygon method, polycrystalline models with different grain sizes are established, and the plastic deformation mechanism of these models under cyclic loading is analyzed. The results show that the critical grain size of the direct and inverse Hall–Petch relationship exists in the Al–Mg alloy. When the grain size is below this value, grain rotation and grain boundary sliding become the main deformation mechanisms of the small polycrystalline grains. Dislocation blockage remains an important factor in the hardening of polycrystalline materials, while the aggregation of solute atoms at the grain boundaries is another contributing factor.