The microstructural evolution and preparation as well as control of non-dendrite in the microstructure of the semi-solid Mg-20Al-0.8Zn magnesium alloy which was refined by Al-Ti-B master alloy were investigated during isothermal treatment process.The results indicate that grain size in as-cast microstructure of Mg-20Al-0.8Zn magnesium alloy can be greatly refined with Al-Ti-B addition.The more uniform and finer spheroidal particle phase in the Al-Ti-B refined semi-solid magnesium alloy can be observed after isothermal treatment

in which the spheroidized particle exhibits slowly coarsening tendency.The grain size with average diameters of 55～65 μm can be observed in the microstructure of the prepared magnesium.The semi-solid magnesium slurry more suitable for thixo-forming process can be obtained

and more uniformly distributed fine particles phase can be prepared with isothermal treatment at 450℃ for 90～120 min or at 465℃ for 90 min or 485℃ for 60～90 min.