The chopped carbon fibers reinforced magnesium composites（Csf/AZ91Dcomposite）were prepared by vacuum assisted pressure infiltration method.The hot deformation behavior of Csf/AZ91 Dcomposites prepared was investigated at 400

4

90 ℃ and strain rate of 0.001

0

.1s-1 as well as maximum deformation strain of 50%.The microstructure of the composites before and after deformation was observed by optical microscope

and the hot plastic deformation mechanism of the composites prepared was approached by comparing with the magnesium alloy.The results indicate that the strain softening of the composites prepared is the more significant than that of the corresponding magnesium alloy due to the rotation and breakage of whiskers during hot compression process.The matrix microstructure is refined by the chopped carbon fibers during fabrication

and the quantity of interface including grain boundary and phase interface is increased accordingly.As a result

the composites prepared exhibit a high strain rate sensitivity.In addition

the strengthening effect of short carbon fiber and grain boundary is weaken

and the stress level of the composites is decreased significantly with the increase of the deformation temperature.The apparent deformation activity energy of the composites is the higher than that of the corresponding magnesium alloy.