Late stages of high rate tension of aluminum melt: Molecular dynamic simulation

With the help of molecular dynamic simulation, we investigate late stages of aluminum melt tension up to the deformation degree of about 10, including a stage of bubble liquid, a foamed melt, and a fragmentation with formation of droplets. Complete fracture of melt is a complex process, which includes nucleation of pores, growth and coalescence of neighboring pores, thinning and breaking of walls between them with the formation of a system of jets, and, finally, breaking of jets into droplets. The transition from the foamed melt to the system of jets and the subsequent fragmentation into droplets occur at the volume fraction of condensed matter considerably smaller than 0.1. The number of pores at the volume fraction of condensed matter about 0.5 and the number of droplets at the final stage of fragmentation are not directly connected with each other. At the same time, both numbers are increased together with the increase in the strain rate and have the same order of magnitude. At the stage of melt with pores, the growth and coalescence of pores are controlled by surface tension, which allows us to construct an analytical estimation for time dependence of the pore average radius. Also, we propose analytical estimations for the mean pressure of melt with pores, which remain negative, and for the work of tension. A few times larger work is spent on the tension of melt with pores if compared with the initial stage of tension near the dynamic strength threshold. The last fact is favorable for the production of the foamed aluminum by means of the high-rate tension of its melt. Published by AIP Publishing.