Microstructure and Wear Resistance of Rapidly Solidified Hypereutectic Al-Si Alloys

Rapidly solidified hypereutectic Al-21Si and Al-30Si alloys were prepared by a single roller melt-spinning technique. The microstructure and phases of the alloys were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fine grains with a micro-nano composite microstructure were obtained by rapid solidification. The microstructures of the Al-21Si alloys were characterized by primary micro-nanostructured α-Al phase and feather-needle-like α-Al+β-Si eutectic. The nucleation and growth of primary silicon were effectively inhibited. α-Al phase had a higher priority to nuclate and grow than eutectic α+Si phase. The hypereutectic Al-21Si alloy showed the hypoeutectic microstructure. The primary Si phases in Al-30Si alloy were fine twins. And this microstructures were a typical hypereutectic microstructure. Microhardness and wear resistance (i.e. 5 times as high as that of traditional casting alloys) of alloys were greatly improved by rapidly solidification.