Li WANG
,
xiufang BIAN
材料科学技术（英文）
Several concepts of the grain refinement mechanism of B on hypoeutectic Al-Si alloys have been adopted: the refining effect of B on the alpha-Al and eutectic Si with the different additions of Al-B master alloys made at 850 degrees C was investigated, and the Al-B master alloys formed under different temperature conditions have been studied to explore the morphologies of AlB2 particles, slowly cooled sample with addition of Al-B was made to explore the refinement mechanism. Al-B master alloy can refine not only alpha-Al, but eutectic Si. Theoretical analysis indicates that, although AlB2 does not take part directly in the nucleation process in pure Al in the presence of Si, it provides a substrate for precipitation of a small content of Si from which alpha-Al will grow without any undercooling. When the temperature decreases to eutectic line, AlB2 subsequently nucleates eutectic Si, AlB2 particles appear in two different morphologies, namely, hexagonal platelet and tetradehedron morphology which depend on the processing temperature conditions.
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