Carbon nanotubes（CNTs）reinforced AZ91Dmagnesium matrix nanocomposites were fabricated by mechanical stirring combined with ultrasonic vibration dispersion.Microstructure and mechanical properties of CNTs/AZ91Dcomposites were investigated by optical metallographic microscope（OM）

scanning electronic microscope（SEM）and tensile test

and fracture morphology of the tensile samples was also observed by SEM and energy spectrum analysis（EDS）.The results show that carbon nanotubes can be added smoothly and distributed dispersedly in the AZ91D magnesium matrix alloy by the semi-solid mechanical stirring and high-energy ultrasonic treatment.When CNTs addition is in range of0

1

.0 %

with the increase of CNTs content

tensile strength and elongation of the composites prepared are improved obviously.Tensile strength

yield strength and elongation of 1.0% CNTs/AZ91D magnesium matrix composites reach 200MPa

114MPa and 5.4%

respectively

compared with those of matrix alloy

increased by 51.5%

42.5%and by 170%

respectively

showing excellent comprehensive mechanical properties.Carbon nanotubes mainly play the role in refining grains of the nanocomposites and bearing deformation loading.