Atomistic Study of the Effect of Magnesium Dopants on the Strength of Nanocrystalline Aluminum

Atomistic simulations have been used to study the deformation mechanisms of nanocrystalline pure Al and Al-Mg binary alloys. Voronoi tessellation was used to fully create a three-dimensional polycrystalline model with a grain size of 10nm, while hybrid Monte Carlo and molecular dynamic simulations were used to achieve both mechanical and chemical equilibriums in nanocrystalline Al-5at.%Mg. The results of tensile tests show an improved strength, including the yield strength and ultimate strength, through doping 5at.%Mg into nanocrystalline aluminum. The results of atomic structures clearly reveal the multiple strengthening mechanisms related to doping in Al-Mg alloys. At the early deformation stage, up to an applied strain of 0.2, the strengthening mechanism of the dopants exhibits as dopant pinning grain boundary (GB) migration. However, at the late deformation stage, which is close to failure of nanocrystalline materials, dopants can prohibit the initiation of intergranular cracks and also impede propagation of existing cracks along the GBs, thus improving the flow stress of Al-Mg alloys.