A390鋁合金之初晶矽細化

Refinement of Primary Silicon in an A390 Al alloy

龔啟良(Chi-Liang Gong)

指導教授 ： 楊智富

大同大學/工程學院/材料工程學系所/碩士(2010年)

摘要

本研究首先比較Cu3P 化合物、Al-Cu-P 母合金和Al-Si-Cu-P 母合金等三種不同細化劑對A390 鋁矽合金之細化效果，並探討在熔湯處理及鑄造過程中，有關細化處理所需注意之製程參數，並分析這些參數之細化效應。接著對細化退化進行研究，並分析數種可能改善細
化之活化處理，檢驗其是否具改善或活化之效果。結果顯示，Al-Si-Cu-P 母合金細化劑為工業應用上細化A390 鋁合金之最佳選擇。本研究所模擬製作低P 含量之二元Al-P 相圖，可用來說明與釐清AlP 對初晶矽之細化特性。本研究所獲較佳細化條件範圍(P 含量
為0.016~0.032%、溫度為720~800℃)，對Al-P 而言皆為L + AlP 之兩相區。以添加量為0.020% P、溫度為765℃之鋁湯而言，液相鋁湯將含有87 ppm 之P，另外113 ppm 之P 原子則以固態AlP 顆粒存在(沉澱或懸浮)於熔湯中。其中溶在鋁湯中之P 原子與懸浮在鋁湯中之固態AlP 顆粒可提供初晶矽異質成核點。於765℃以0.02% P 細化A390鋁合金時，在細化後之初始0~60 分鐘持溫期間，初晶矽由35 μm 降至最低點的25 μm，顯示在這段期間內細化效果逐漸發揮出來；持溫時間在60~210 分鐘期間，初晶矽平均尺寸大致皆維持在27 μm 上下(保持相當好的細化效果)；當持溫時間超過240 分鐘，開始出現細化退化現象，在240~480 分鐘之細化退化期間，初晶矽尺寸由31μm 逐漸增加至43μm。對細化退化後之鋁湯進行「補P」或「重熔」之活化處理，皆能略為改善細化效果。本研究使用含P 細化劑所獲得A390鋁合金之「初晶矽尺寸」與其「矽空白率」呈正相關，當初晶矽尺寸愈細小則矽空白率愈小，表示細化越好者，不僅初晶矽較細小，其分佈也愈均勻。

關鍵字

過共晶鋁矽合金 ； 初晶矽 ； 細化 ； 鋁磷

並列摘要

In this study, the effect of refinement on primary silicon in an A390 alloy by P-bearing chemical modifiers including Cu3P compound, Al-Cu-P and Al-Si-Cu-P master alloys was examined. Key variables governing the modification of primary silicon in A390 alloy, such as the amount of P added and the holding temperature and time of the alloy melt were analyzed. The results show that among three chemical modifiers the Al-Si-Cu-P master alloy produces the most satisfactory modification results, which were obtained under conditions of applying 0.016%~0.032% P and melt treating at 720℃~800℃ for a time span no
more than 210 minutes. Most of the primary silicon modification behavior can be explained fairly well by the heterogeneous nucleation of primary silicon at AlP particles, with the help of using an Al-P phase diagram constructed in this
study. In the case of applying 0.020% P and under 765℃ melt holding condition, the average particle size of primary silicon, d, was found to be
time-dependent. In the first hour (t = 0~60 minutes) d decreases from 35
μm to a minimum value of 25 μm. In the next two and half hours (t = 60~210 minutes) d remain in a well modified value of about 27 μm. When holding over 240 minutes a modification fading phenomenon (coarsening of primary silicon) was observed in the A390 alloy castings, in which d increases gradually from 31 μm to 43 μm when the holding time extended from 240 min to 480 min. The P-modification effect can be refreshed by either refilling modifier or a casting and re-melting process of the A390 alloy. The results also showed that the percentage of primary silicon-free zone is linearly proportional to the particle size of primary silicon.

並列關鍵字

Hypereutectic Al-Si alloy ； Primary Silicon ； Refinement ； AlP

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