Influence of copper inclusions on the strength of aluminum matrix at high-rate tension

In this work, we perform the molecular dynamics (MD) investigations of Al-Cu nanocomposite strength in the conditions of a high-rate uniaxial tension. The investigated material is an Al matrix with spherical nanoinclusions of Cu. The obtained results show that the formation of voids leading to fracture begins inside the aluminum matrix near the interface between Al and Cu. From a viewpoint of the nanocomposite strength, the main effect of Cu inclusions is connected with the stress concentration that leads to an action of increased stresses inside the matrix near the interface with inclusions; these increased stresses are 1.2-1.3 times higher than the volume-average value of stress (for the temperature of 300 K). With the increase of temperature, the plastic relaxation becomes more active due to increased rate of dislocations generation that reduces the role of stress concentrators; the effect finally disappears at temperatures >700 K. A few atomic layers of aluminum remain on the copper inclusions after the fracture, which indicates good adhesion properties of the Al-Cu interface. We propose a continuum model of the nanocomposite fracture that is based on the equations of nucleation and growth of voids inside the aluminum matrix; the model takes into account the stress concentration around inclusions. A comparison with the MD results shows that the continuum model allows us to describe the rate and temperature dependences of the nanocomposite strength at least for strain rates ≥108s−1. At moderate strain rates, the strength values that are calculated with the continuum model correspond to the experimental data for the aluminum alloy 2024 with the second phase precipitates.