This paper analyses the evolution process of rheological microstructures in spray deposition. Presents that the fine equiaxe grain in spray casting alloys is the results of rapid cooling of the melt during droplet flight and evolution of rheological microstructures in mushy layer on the top of deposition billet. The microstructure evolution in deposition billet can be viewed as a micron scale rheocasting. A mass of droplet which have different size

different state

different temperature and speed impact the surface layer of billet and consolidate on it. The stress and strain velocity is high enough to break - up of fine dendrites in rapidly cooled droplets. The mushy layer on top of billet possess rheological characteristic. The fine dendrites in rapid solidification droplets during droplet flight coarsen in the mushy rheological layer. Finally the fine equiaxe grain formed