Effect of grain size on tensile deformation behavior of nano-polycrystalline Al and Al–Mg alloys with grain boundary segregation of Mg

Mg is easily segregated to the grain boundary of the Al–Mg alloy, which affects the mechanical properties of the alloy. In order to reveal the role of Mg element at grain boundaries in Al–Mg alloys, molecular dynamics simulation was used to study the tensile deformation behavior of nano-polycrystalline Al and Al–Mg alloys with different grain sizes. The results show that the elastic modulus and tensile strength of Al and Al–Mg alloys have a clear grain size dependence. The critical grain size at which the elastic modulus decreases as the grain size decreases is independent of Mg. As the Mg content increases to 3 at. %, the critical grain size for the transition from the Hall-Petch relationship to the inverse Hall-Petch relationship increases. The appropriate content of Mg segregation at the grain boundary can increase the elastic modulus, strength and plasticity of the alloy, and inhibit the grain boundary cracking. This result provides important theoretical support for the composition design and microstructure regulation of high-performance Al–Mg alloys.