Grain refinement of Mg-6 Al-1 Y alloy was achieved by the collaboration of copper mold injection casting and cryogenics treatment. The influences of cryogenics treatment on non-equilibrium solidified structure and subsequent precipitation behavior were investigated. The results reveal that with the increase of undercooling and corresponding nucleation rate

the formation of fine equiaxed dendrite grains with partial micron-size granular grains can be observed

accompanied by the formations of high supersaturated structure and considerable dislocation defect under the non-equilibrium solidification condition. Stress accumulation induced by cryogenic treatment is beneficial to the fragmentation of fine dendrites in rapidly cooled alloy and spheroidization of segments occurs subsequently. The average grain size is decreased to 10 μm and the amount of dislocation density is increased significantly after cryogenics for 32 h. As for the rapid cooled and cryogenic treated alloy

discontinuous precipitation at grain boundary is accelerated during the isothermal annealing at 200 ℃ for 16 h. Moreover

both the morphology and quantity of continuous precipitation within grain are improved effectively. The resultant hardness is increased to 71.3 HV

which is 11.9% higher than that of the original rapidly cooled alloy.