응고시 Al-Si 합금의 미세조직에 미치는 기계적 진동의 영향

Abstract

This study presents the effect of mechanical vibration during casting processes on the microstructure and mechanical properties of a binary Al-Si alloy, using a step-wise mold. Al-Si alloy system is the most common system among the casting aluminum alloys. And simplification of the alloy system makes it easy to focus on the pure dendritic growth without complication with third alloy elements or phases. We investigated the effect of Si mechanical vibration on the Secondary dendrite arm spacing(SDAS) of binary Al-Si alloys in the range of 4 to 10wt% Si with various cooling rates and the effect of mechanical vibration on the microstructure and mechanical properties of the Al-Si alloys. The mechanical vibration accelerated the solidification rate during the casting process. The α dendrites were fragmented due to mechanical vibration, showing a possible mechanism for transition of columnar microstructure to equiaxed one. Primary Si were also fragmented. The change of the as-cast microstructure explains that mechanical vibration increased micro-Vickers hardness of the alloy. Despite of the faster solidification rate than that of the cast without vibration, secondary dendrite arm spacing was greater than the conventionally cast alloy. Investigating on the cooling curves during the casting process, the mechanical vibration seems to lower the eutectic temperature of the alloy. The sensitivity of the cooling rate to SDAS decreased with Si contents from 4 to 8wt.%, and increased up to 10wt.% Si when no mechanical vibration was involved.. The alloy with 8wt.% Si had the highest microstructure stability in the Si content range. When the mechanical vibration is applied: Solidification rates increased, The α dendrites were fragmented due to mechanical vibration, SDAS of the α phase increased. The vibration lowered the eutectic temperature of the alloys.