  The interaction between Mg edge basal dislocations and rod-shaped
$\beta_1'$-MgZn$_2$ precipitates was studied by atomistic simulations using a
new interatomic potential. The atomistic model was carefully built taking into
account the experimental information about the orientation relationship between
the matrix and the precipitate to ensure minimum energy interfaces. It was
found that the dislocations initially overcame the precipitate by the formation
of an Orowan loop that penetrated in the precipitate. The precipitate was
finally sheared after several Orowan loops were piled-up. The number of loops
necessary to shear the precipitate decreased as precipitate cross-section
decreased and the temperature increased but was independent of the precipitate
spacing. Precipitate shearing did not take place along well-defined
crystallographic planes but it was triggered by the accumulation of the elastic
energy in the precipitate which finally led to formation of an amorphous layer
below and above the slip plane of the basal dislocations. The kink induced in
the precipitate by this mechanism was in good agreement with transmission
electron microscopy observations.
