  The mechanisms of dislocation/precipitate interaction as well as the critical
resolved shear stress were determined as a function of temperature in a Mg-4
wt. % Zn alloy by means of micropillar compression tests. It was found that the
mechanical properties were independent of the micropillar size when the
cross-section was $>$ 3 x 3 $\mu$m$^2$. Transmission electron microscopy showed
that deformation involved a mixture of dislocation bowing around the
precipitates and precipitate shearing. The initial yield strength was
compatible with the predictions of the Orowan model for dislocation bowing
around the precipitates. Nevertheless, precipitate shearing was dominant
afterwards, leading to the formation of slip bands in which the rod
precipitates were transformed into globular particles, limiting the strain
hardening. The importance of precipitate shearing increased with temperature
and was responsible for the reduction in the mechanical properties of the alloy
from 23C to 100C.
