Effects of Ni additions on the microstructure of Mg98-xGd2Nix（x=0

0.5

1.0

mole fraction）alloys were investigated using OM（optical microscope）

SEM（scanning electron microscope）

EDS（energy dispersed spectrometer）and XRD（X-ray diffraction）.The as-cast Mg98Gd2 alloy is composed of dendriteα-Mg matrix and Mg5 Gd phase.With the addition of 0.5% Ni

a new X phase instead of Mg5 Gd phase can be observed in the Mg97.5Gd2Ni0.5alloy with 27%in area fraction.With the increase of Ni addition from 0.5 % to 1.0%

the new phase structures in the Mg97Gd2Ni1 alloy can not be observed

while the area fraction of X phase is increased from 27% to 42%.During solid solution treatment at 500 ℃

with increasing in treating time

the Mg5 Gd phase in the Mg98Gd2 alloy is completely dissolved gradually.However

the Xphase in the Mg97.5Gd2Ni0.5or Mg97Gd2Ni1 alloy exhibits thermally stable with treating for 20 h.Meanwhile

the obvious growth of secondary dendrite arm spacing ofα-Mg matrix in the Mg97.5Gd2Ni0.5or Mg97Gd2Ni1 alloy is absent

which shows that the Xphase exhibits desirable thermal stability and inhibit effectively the growth of theα-Mg matrix.