Mg-9Gd-4Y-0.65Mn and Mg-9Gd-4Y-0.6Zr alloys were prepared by the fluxing procedures method and then extruded into rods.The microstructures and tensile properties of the alloys both at as-cast state and at deformation state were investigated by using optical microscopy,X-ray diffractometry,scanning electron microscopy,and transmitting electron microscopy.The results show that the grains of the alloy containing Mn at as-cast state are coarser and those of the alloy containing Zr are much finer,which obviously demonstrates grain refining effect of additional element Zr on Mg-RE alloys.Hot extrusion of the two alloys can enormously decrease the grain size and increase their strength.The grain refining effect of the magnesium alloy containing Mn through extrusion will be more remarkable than that of alloy containing Zr.The two extruded magnesium alloys at room temperature and at 300℃ have rather high strength,furthermore,the elongation of the alloy containing Mn is higher.It is suggested that the extruded magnesium alloy containing Zr is introduced to precipitation heat treatment to T5 temper for high mechanical properties,while the extruded magnesium alloy containing Mn to T6 temper.