  Mixing mechanisms bring the Li from the base of the convective zone to deeper
and warmer layers where it is destroyed. These mechanisms are investigated by
comparing observations of Li abundances in stellar atmospheres to models of
stellar evolution. Observations in open cluster are especially suitable for
this comparison, since their age and metallicity are homogeneous among their
members and better determined than in field stars. In this work, we compare the
evolution of Li abundances in three different clusters: the Hyades, NGC752, and
M67. Our models are calculated with microscopic diffusion and transport of
chemicals by meridional circulation, and calibrated on the Sun. These
comparisons allow us to follow the evolution of Li abundance as a function of
stellar mass in each cluster and as a function of the age by comparing this
evolution in each cluster. We evaluate the efficiency of the mixing mechanisms
used in the models, and we try to identify the lacking mechanisms to reproduce
the observed evolution of Li abundance.
