過共晶鋁矽合金之初晶矽細化效果研究

Modification of Primary Silicon in a hyper-eutectic Al-Si alloys

陳亮宇(Liang-yu Chen)

指導教授 ： 楊智富

大同大學/工程學院/材料工程學系所/碩士(2011年)

摘要

本研究採用較單純之二元Al-P細化劑，分析其對Al-17%Si合金之細化效果，來模擬一般商用細化劑對A390(Al-17Si-4.5Cu-0.5Mg-0.5Fe)之細化效益，藉由簡化之合金系統來作學理上之驗證。本研究之主要研究項目是，細化劑之添加量、攪拌動作、熔湯持溫時間、細化衰退之熔湯重熔處理、熔湯高溫過熱處理、回爐料重熔處理、回爐料稀釋等。為了解過共晶鋁矽合金熔湯長期持溫所發生之細化效果衰退之原因，本研究對可能造成細化效果衰退之因素加以檢驗，找出原因及提出解決對策。
結果顯示，Al-0.1%P進行0至61小時持溫靜置後，由金相可發現持溫0小時之金相存在許多3 μm以下之AlP顆粒，而在持溫61小時者則相對少了許多3 μm以下之細粒徑AlP顆粒，且AlP顆粒數量變少，平均粒徑變粗大，由此可知造成過共晶含P之Al-Si合金細化效果衰退之主因乃是細小AlP(初晶矽成核點)變少，造成初晶矽之粗大化。
另外，參考本實驗室學長所模擬製作之低P含量之二元Al-P相圖，所獲致之較佳細化條件範圍為將P含量控制在某一略高於飽和溶解度之P含量範圍內，即可避免初晶矽細化衰退現象(80~150 ppm之間) ；由結果可知，當Al-17%Si鋁湯中P含量不超過150 ppm，於765℃持溫 8小時內不會有細化衰退之問題。於765℃以120 ppm P細化Al-17%Si合金時，在長達22小時之持溫時間內其初晶矽粒度均保持約為25 μm，有在標準範圍30 μm之內，呈現良好的細化效果。對細化衰退後之回爐料進行「稀釋」或「重熔」活化處理，皆能略為改善細化效果。
至於A390-100 ppm P及A390-120 ppm P合金，於765℃經長時間持溫下(26小時)，有以下特性；(1)P含量較高者(120 ppm)在持溫初期細化效果較佳，(2)P含量較高者(120 ppm)較易發生(或在較短持溫時間內發生)「細化效果衰退」現象，(3)降低合金之P含量(使其靠近P之飽和溶解度)可減少、延緩，甚至避免「細化效果衰退」現象。

關鍵字

細化劑 ； 初晶矽 ； 過共晶鋁矽合金

並列摘要

In this study the effects of P on a hyper-eutectic Al-17 Si alloy were thoroughly studied by using a binary Al-P alloy modifier, instead of other commercially available chemical modifiers such as Cu3P, P-bearing flux and Al-Cu-P alloys. A variety of melt treatments which have profound influences on the refinement of primary silicon in the Al-Si alloy were examined. These include: adding different amount of P, mechanical stirring to speed up the P treatment, melt holding treatment, re-melting, melt over-heating treatment and P dilution treatment.
The results of a prolonged melt holding (61 h) test of an Al-0.1% P alloy showed that coarsening of AlP particles takes place during the melt holding treatment. This practically sweep off the majority of fine AlP particles (particles size below 3μm) and causes an increase in the average AlP particles size. Observations of the change in the AlP particles size indicate that the reason for the fading of P refinement in hyper-eutectic Al-Si alloys is most likely due to the coarsening of fine AlP particles in the course of melt holding.
According to the above theory, one can avoid the P fading by limiting the occurrence of coarsening of AlP particles. This can be achieved simply by restricting the P content of the melt to its P solubility. The results of P fading tests performed in Al-17 Si alloy melts containing 80, 120, 150, 200 and 400 ppm P showed that there is no fading observed in the Al-Si alloy melts which contains 80-150 ppm P. But when adding 200-400 ppm P to the alloy melt, fading occurs in about 8 hours. In a prolonged fading test of Al-17 Si alloy containing 120 ppm P, it was shown that the average primary Si particles remained nearly unchanged at about 25μm. Re-melting treatment of the prolonged fading tested Al-17 Si-120 ppm P alloy was found having little effects on the particle size of the primary Si.
In the studies of P fading tests in A390-100 ppm P and A390-120 ppm P alloys, it was found that the A390 alloy with higher P content (120ppm) exhibits a better modification effect in the early stage of melt holding period (0 – 3 hours) and a more distinct fading behavior in a long period od holding (after 8 hours). Reducing the P content to 100 ppm can effectively minimize and defer the occurrence of P fading in the A390 alloy.

並列關鍵字

modification ； primary silicon ； Al-P

參考文獻

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