Microstructures of rapidly solidified hypereutectic Al-Si alloy with low-titanium content

摘要

In the present work, rapidly solidified alloys strips with Al-0.24Ti and Al-21Si-0.24Ti(in wt.%) were prepared by single roller melt-spinning method. The microstructures, phase and morphology characteristics of the resultant strips were characterized by means of scanning electron microscopy (SEM),transmission electric microscopy (TEM) and XRD technique. The results show that the grains have been refined after rapid solidification processing, and the micro-nanocrystalline grain are formed. The morphology characteristics can be changed. The microstructures of Al-0.24Ti alloys strip are micro-nanostructure α-Al solid solutions which are similar with granular or nodular, the corresponding SAD pattern is rings, it presents characteristic of polycrystal; Compared with equilibrium solidification, the microstructures of hypereutectic Al-Si alloy are changed obviously. They are composed of primary micro-nanostructure α-Al supersaturated solid solution and nanocrystal granular (α+Si) eutectic which set in the supersaturated solid solution. The nucleation and growth of primary silicon are suppressed and primary silicon can not precipitate, meanwhile, α-Al phase is nucleated which prior to eutectic, therefore the microstructures become into the metastable state. The mechanism of the formation for microstructures of melt-spinning alloys has also been discussed.