(46h) Extracting Anisotropy Strength and Interfacial Free Energy of Al-Mg Alloy Under Rapidcooling Conditions Using Molecular Dynamics Simulations

Many pure metals and alloys produced in industry suffer from manufacturing defects, such as the formation of microstructural branching defects called dendrites. The microstructure is strongly affected by solid liquid interfacial properties during solidification process. The anisotropy of the interfacial free energy (γ) has an especially strong impact on both the tip radius and growth direction of dendrite defects. It has been previously shown that the composition and undercooling temperature of both pure metal and binary alloys can strongly affect the anisotropy and cause the dendrites to change growth directions. Due to their wide use in industry, understanding these effects in aluminum-based alloys are of great interest. Specifically, the Al-Mg binary alloy was studied at various undercooling temperatures to determine if a possible temperature dependence of the anisotropy of γ exists. Molecular Dynamics (MD) simulations were performed in the Large-Scale-Atomic/Molecular Massively Parallel Simulator (LAMMPS) using a Modified Embedded Atom Method (MEAM) interatomic potential from the NIST IPR database. The solid-liquid interface was identified using an order parameter, which classifies atoms with nearest neighbors in both the solid and liquid states. The Fast Fourier Transform (FFT) and wavenumber (k) were used to quantify the rough behavior of this interface and extract the interfacial stiffness. This was done for the (100) and (110) orientations at undercooling temperatures of 910, 850, and 750K and the anisotropic parameters ε₁ and ε₂ were determined. Our results show that the interfacial free energy typically followed a relationship of γ₁₀₀ > γ₁₁₀ > γ₁₁₁. Except for 910K which followed a γ₁₁₀ > γ₁₀₀ > γ₁₁₁ relationship. Our results further predict that the dendrite growth in the (100) direction at 910K followed by a switch to a hyperbranched direction at 850K, followed by a return to the (100) direction at 750K.

Acknowledgements: The work is supported by ARL Grant No. W911NF-2020032 and used the Extreme Science and Engineering Discovery Environment (XSEDE) TACC at the stampede2 through allocation [TGDMR140131]. This work utilized resources from the University of Colorado Boulder Research Computing Group, which is supported by the National Science Foundation (awards ACI-1532235 and ACI-1532236), the University of Colorado Boulder, and Colorado.