The effects of trace Sr on the as-cast microstructure and mechanical properties of AZ91D magnesium alloy have been investigated by means of SEM（scanning electron microscope）

Hi-scope compact micro-vision system

multi-functional materials experimental machine

Brinell hardness tester and impact testing machine.The results indicate that trace Sr addition can change the β phase in AZ91D magnesium alloy from net-like structure into spheroid or short rod ones.Compared with that of AZ91D magnesium alloy without Sr addition

the tensile strength and elongation of the alloy with 0.05% Sr addition can reach 185.4 MPa and 6.7%

respectively

increased by 11.3% and by 139.3%

respectively

which is related to the change of Sr on morphology of β phase.In addition

the impact toughness of the magnesium alloy is 40.2 J/cm2 and 29 J/cm2 in graphite mold and in sand mold

respectively

improved by 26.4% and by 12.5%

respectively

compared with that of the alloy without Sr.Meanwhile

the hardness of alloy is increased with increasing in Sr addition.