| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 91 === The Electro Discharge Machining (EDM) features of the eutectic molding material with second phase were investigated in this study. Ferritic spheroidal graphite (SG) cast irons (2.1wt.%C~4.1wt.%C, 2.0wt.%Si~4.9wt.%Si) and Al-Si alloys (Al-1Si~29Si) were selected as testing materials. Effects of compositions, solidification rate, and EDM parameters were examined.
Experimental results indicated that the materials removal rate of the ferritic SG cast irons by EDM increased with a smaller graphite size and higher graphite nodule count. As for Al-Si alloys, the second phase, including primary and eutectic silicon particles, had remarkable effects on EDM characteristics. That is, higher primary silicon particles size and higher area fraction of silicon particles would accelerate the removal rate. The EDMed surfaces featured continuous ridges formed by overlapping discharge craters, and the ridge density also tended to increase with a finer graphite nodule size. Owing to the poor wettability between the cast iron melts and semi-molten graphite during solidification process, graphite particles were embedded in the cavities in-between the ridges. The Al-Si alloys EDMed surface feature was similar to that of SG cast irons, showing a wavy ridge pattern. The amount of silicon phase also affected the surface roughness. Notably, silicon particles were located in the ridge regions, not the troughs.
Finally, through this study that concerns the EDM characteristics of SG cast irons and Al-Si alloys, the effects of the heterogeneous second phase can be clearly clarified. This could serve as the practical reference for electro-discharge machining of mold materials with heterogeneous second phase and other engineering materials.
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