Molecular Dynamics Study of Solute Pinning Effects on Grain Boundary Migration in the Aluminum Magnesium Alloy System

Molecular dynamics simulation, combined with the artificial driving force technique, has been used to study solute interactions with migrating grain boundaries, especially low angle boundaries, in the Al-Mg alloy system. The motion of [112] symmetric tilt boundaries was investigated employing two different approaches at 300 K (27 A degrees C). In the first approach, where solute atoms are segregated and surround the intrinsic dislocations at the grain boundary, a strong solute pinning effect was observed at all misorientations and at different Mg concentrations. A minimum driving force is found to be required for overcoming the barrier produced by the segregated solute at the boundary and a high magnitude of threshold force was observed in all alloys examined. In the alternative approach, where solutes are distributed in a confined region away from the grain boundary, we find that the velocity-driving force behavior in the high driving pressure regime depends on solute concentration, consistent with a recent solute pinning model by Hersent et al. The distributed solute approach provided less pining effect on low angle grain boundary migration compared to that of segregated solutes. The relationship between the restraining force and the solute concentration was computed and, when fit to the Hersent et al. analysis, the solute pinning constant was found to be alpha = 35 +/- A 7 MPa for a 7.785 deg boundary in the Al-Mg binary system.