過共晶鋁矽合金之初晶矽細化參數最適化研究

Optimization of Key Factors Controlling the Refinement of Primary Silicon in a Hyper-eutectic Al-Si Alloy

鄭裕達(Yu-Ta Cheng)

指導教授 ： 楊智富

大同大學/工程學院/材料工程學系所/碩士(2012年)

摘要

本研究探討如何有效的對過共晶鋁矽合金之初晶矽進行細化，以及避免細化效果之衰退。首先採用單純之二元Al-P合金系統，討論如何於熔湯冷卻凝固時以「均質成核」方式晶出細密的AlP顆粒，來作為過共晶鋁矽合金初晶矽之成核點；接著對含P之Al-17% Si合金進行細化研究，分析熔湯溫度及P含量兩項重要參數對初晶矽細化之影響。主要實驗參數包括：細化劑之添加量、熔湯溫度、熔湯持溫時間及取樣方式等。實驗結果顯示，二元Al-P合金熔湯經持溫靜置後，其固相AlP顆粒因密度較液相大而下沉至鋁湯底部，澆鑄時若採用「不擾動鋁湯方式取樣」，則不會撈取到沉底之固相AlP顆粒，試片冷凝時液相內之P可藉由「均質成核」產生大量細密的AlP，可作為過共晶鋁矽合金初晶矽的成核劑以獲致良好的細化效果；但若採用「上下翻攪鋁湯後取樣」者，試片冷凝時液相內之P以「異質成核」方式於既存在的固相AlP顆粒上進行成核與成長，如此所生成之AlP顆粒數量大幅減少，造成過共晶鋁矽合金初晶矽無法有效細化。此外，於過共晶鋁矽合金之細化參數最適化研究發現，在所探討的60 ~120 ppm P含量範圍及720 ℃~780 ℃溫度範圍內，較低P含量與較高熔湯溫度者皆可呈現良好細化效果，因其能避免在鋁湯中生成固相AlP顆粒，故其會有較佳之細化效果。本研究亦發現，過共晶鋁矽合金之初晶矽粒度與初晶矽空白率成正比關係，當細化處理控制得當，初晶矽粒度將可小於30 μm，此時初晶矽顆粒分佈將會十分均勻，其矽空白率會低於12%。

關鍵字

過共晶鋁矽合金 ； 初晶矽 ； 細化 ； 鋁化磷

並列摘要

In this research the refinement of primary silicon in hyper-eutectic Al-Si alloys were studied. The reason of refinement fading and the way to avoid it were also studied. A variety of key variables which have profound influences on the refinement of primary silicon were examined, which include P content, melt holding temperature and time, and the method to take melt samples. The results show that only by homogeneous nucleation can fine precipitates of AlP be produced from the alloy melt. And these fine AlP precipitates act as nucleus of primary silicon for proper refinement. When there are coarse pre-existed AlP particles present in alloy melt, heterogeneous nucleation takes place and results in very limited amount of AlP particles. Consequently, this results in a poor refinement of primary silicon. It was found from the optimization of refinement control that, in the range of P content from 60 to 120 ppm and melt temperatures from 720 to 780 oC, alloy melts with less P content and higher melt temperature exhibit better refining effect. It was also found that by proper refinement treatment the particle size of primary silicon can be reduced to 30 um or less. In which case, the distribution of primary silicon would be very uniform and the Si-depletion ratio was found to be less 12%.

並列關鍵字

Hyper-eutectic Al-Si Alloy ； Primary Silicon ； Refinement ； AlP

參考文獻

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