  Observations show that radial metallicity gradients in disk galaxies are
relatively shallow, if not flat, especially at large galactocentric distances
and for galaxies in the high-redshift universe. Given that star formation and
metal production are centrally concentrated, this requires a mechanism to
redistribute metals. However, the nature of this mechanism is poorly
understood, let alone quantified. To address this problem, we conduct
magnetohydrodynamical simulations of a local shearing sheet of a thin,
thermally unstable, gaseous disk driven by a background stellar spiral
potential, including metals modeled as passive scalar fields. Contrary to what
a simple \alpha\ prescription for the gas disk would suggest, we find that
turbulence driven by thermal instability is very efficient at mixing metals,
regardless of the presence or absence of stellar spiral potentials or magnetic
fields. The timescale for homogenizing randomly distributed metals is
comparable to or less than the local orbital time in the disk. This implies
that turbulent mixing of metals is a significant process in the history of
chemical evolution of disk galaxies.
