  We present numerical simulations of three-dimensional compressible
magnetoconvection in a rotating rectangular box that represents a section of
the solar convection zone. The box contains a convectively unstable layer,
surrounded by stably stratified layers with overshooting convection. The
magnetic Reynolds number, Rm, is chosen subcritical, thus excluding spontaneous
growth of the magnetic field through dynamo action, and the magnetic energy is
maintained by introducing a constant magnetic field into the box, once
convection has attained a statistically stationary state. Under the influence
of the Coriolis force, the advection of the magnetic field results in a
non-vanishing contribution to the mean electric field, given by uxb. From this
electric field, we calculate the alpha-effect, separately for the stably and
the unstably stratified layers, by averaging over time and over suitably
defined volumes. From the variation of alpha we derive an error estimate, and
the dependence of alpha on rotation and magnetic field strength is studied.
Evidence is found for rotational quenching of the vertical alpha-effect, and
for a monotonic increase of the horizontal alpha-effect with increasing
rotation. For Rm~30, our results for both vertical and horizontal alpha-effect
are consistent with magnetic quenching by a factor 1/[1+Rm(B_0/B_eq)^2]. The
signs of the small-scale current helicity and of the vertical component of
alpha are found to be opposite to those for isotropic turbulence.
