  Mg grain boundary (GB) segregation and GB diffusion can impact the processing
and properties of Al-Mg alloys. Yet, Mg GB diffusion in Al has not been
measured experimentally or predicted by simulations. We apply atomistic
computer simulations to predict the amount and the free energy of Mg GB
segregation, and the impact of segregation on GB diffusion of both alloy
components. At low temperatures, Mg atoms segregated to a tilt GB form clusters
with highly anisotropic shapes. Mg diffuses in Al GBs slower than Al itself,
and both components diffuse slowly in comparison with Al GB self-diffusion.
Thus, Mg segregation significantly reduces the rate of mass transport along GBs
in Al-Mg alloys. The reduced atomic mobility can be responsible for the
improved stability of the microstructure at elevated temperatures.
