Using copper-mould spray casting and isothermal heat treatment

sub-rapid solidification and precipitation behavior of AZ91 alloy with 2% nano SiC were investigated to reveal the influences of SiC particle on grain refinement and precipitation.The experimental results show that both the quenching by copper mould and the addition of SiC can promote refinement and reduce solute segregation

which suppress the formation of divorce eutecticβphase in grain boundary.After aging treatment at 200 ℃for 2 h

the SiC particles can increase the dislocation density and lattice distortion energy.Consequently

granular discontinuous precipitates can be formed along the grain boundary

and the solute content of supersaturated solid solution is decreased.With increasing aging time to 16 h

sufficient atomic diffusion can take the coexistence of discontinuous precipitation and continuous precipitation modes

which forms aperpendicular distribution of strip precipitates to the grain boundary and non directional precipitates with granular or short rod inside grain.Moreover

the hardness of primary grain can be increased significantly.