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研究生:高森田
研究生(外文):Kao, Sen-Tien
論文名稱:鋁合金凝固微縮孔預測模式研究
論文名稱(外文):Modeling of Porosity Prediction in Aluminum Alloys
指導教授:---
學位類別:博士
校院名稱:國立成功大學
系所名稱:材料科學(工程)學系
學門:工程學門
學類:材料工程學類
論文種類:學術論文
論文出版年:1996
畢業學年度:84
語文別:中文
論文頁數:127
中文關鍵詞:微縮孔凝固參數壓力指標氫含量流體流動鋁合金鑄造
外文關鍵詞:PorositySolidification ParameterPressure IndexHydrogen ContentFluid FlowAluminum Casting
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本論文以實驗及理論推導方法研究A206 (Al-4.5Cu-0.3Mg-0.4Mn) 和
A356 (Al-7Si-0.3Mg) 鋁合金的微縮孔形成預測模式。實驗上有系統地變
化鑄件的幾何形狀及冒口尺寸、模具材料、模具溫度和鋁液氫含量,另外
也設計低壓鑄件並變化外加的壓力,以驗証理論並提出鑄件微縮孔含量(
Porosity volume percent)預測模式。
微縮孔形成量為冒口及幾何形狀的函數考量下,一個以微縮孔含量為縱軸
,凝固比(FR)為橫軸而體積比(VR)為第三變數的圖形被建立。根據此圖,
鑄件內最大微縮孔含量隨凝固比的減少和體積比的增加而趨向於減少。冒
口直徑的增加有效地提高體積比,平板鑄件推拔的使用有效地降低凝固比
。兩者都可有效地使鑄件的最大微縮孔含量減少。
實驗結果也顯示;微縮孔含量不僅受合金物理常數的影嚮,同時也是熱參
數及氫含量的函數;鑄件因溫度梯度(G)的升高、固相線速度(Vs)的變慢
及凝固時間(tf)的減短都使微縮孔含量減少;降低冒口尺寸及模具溫度,
使固相線速度提高因此也引起凝固補充效率(Feeding efficiency)的負面
效果。
有關凝固補充效率的參數指標中,A206合金設定為G0.4/Vs1.6而A356合金
設定為G0.38/Vs1.62,用以計算凝固過程中樹狀晶間液體之壓力降(
Pressure drop),並藉以預測鑄件微縮孔之形成。當A206合金G0.4/Vs1.6
小於7 K0.4s1.6/mm2 而A356合金G0.38/Vs1.62 小於0.6 K0.38s1.62/mm2
時,則孔洞含量隨此指標增加而趨向於減少。但當A206合金之指標值大
於7 K0.4s1.6/mm2 時,A356 指標值大於0.6 K0.38s1.62/mm2 時,則孔
洞含量被發現與熱參數指標無關。然而不管此指標之值為何,微縮孔含量
都受鋁液氫含量影嚮;亦即提高鋁液氫含量將使鑄件微縮孔含量增加。
壓力指標(P*)結合大氣壓力、液體壓力頭、由Darcy*s法產生的壓力降及
樹狀晶間液體表面張力效應的壓力(Ps),也被提出以解釋A206 和A356合
金微縮孔形成的問題。P* 可以由凝固參數(G、Vs及tf)和合金之物理常數
表示,而微縮孔含量和P*成反比關係。實驗及理論推導顯示鑄件微縮孔體
積百分率Vp%可被簡單以Vp%=K(H)/P*表示,其中K(H)為氫含量的涵數,隨
氫含量之增加而提高。在低壓鑄造的實驗中,發現雖然外加壓力(Pa)有抑
制微縮孔形成的正面效果,但同時卻使鑄件凝固的方向性程度變差有增加
微縮孔形成量的負面效果,而P*在低壓鑄造的應用上可表示為P*= Pa+ P+
Ps
Porosity formation in A206 alloy (Al-4.5Cu-0.3Mg-0.4Mn) and A356
alloy (Al-7Si-0.3Mg) was studied experimentally and
theoretically. Castings with the variation of geometry, riser
size , mold temperature, mold material and initial hydrogen
content, and low pressure castings with varied gauge pressure
(Pa) were tested in order to allow the measured porosity content
to be verified by the theoretical model of porosity formation.
A monogram with a plot of porosity content as the ordinate,
freezing ratio (FR) as the abscissa and volume ratio (VR) as the
third variable was established in order to determine the
porosity formation as a function of riser size and casting
geometry. Accordingly, the amount of porosity tends to decrease
with decreasing freezing ratio and with increasing volume ratio.
Increasing riser size and placement of taper decrease the amount
of porosity through increasing the volume ratio and decreasing
freezing ratio
The experimental results also indicate that the amount of
porosity depends not only on alloy physical constants but also
thermal parameters and initial hydrogen content; the porosity
content decreases with increasing thermal gradient (G), and with
decreasing solidus velocity (Vs), solidification time (tf) and
initial hydrogen content ([H]); both decreasing riser size and
lowering mold temperature increase the solidus velocity and
cause to degrade the feeding efficiency during the
solidification process. The solidifification feeding
efficiency of a thermal index, denoted as G0.4/Vs1.6 for A206
alloy and G0.38/Vs1.62 for A356 alloy, is employed to estimate
the value of local pressure drop within interdendritic liquid
during the solidification process and to predict the formation
of porosity in castings. The porosity content tends to decrease
with increasing the solidification feeding efficiency of thermal
index when the index is less than 7 K0.4s1.6/mm2 for A206 alloy
or 0.6 K0.38s1.62/mm2 for A356 alloy. B as the value of the
index is increased over approximately 7 K0.4s1.6/mm2 for A206
alloy or 0.6 K0.38s1.62/mm2 for A356 alloy, the porosity
content is found to be independent of this thermal index. Based
on the effect of the thermal index on the local pressure drop or
porosity formation, the feeding efficency during solidification
process in A356 alloy is about 13 times higher as compared with
A206 alloy castings. However, whatever the value of thermal
index is, an increase of
Furthermore, a pressure index (P*), determined from the
atmospheric and hydrostatic pressure and from the effect of
local pressure drop based on Darcy*s law and the pressure of
surface tension effect (Ps), is introduced. The P* index could
be expressed in terms of the thermal parameters G, Vs, Tf and
the alloy physical constants, and was proposed to evaluate the
formation of porosity in alloys; the porosity content is
inversely proportional to P*. Based on the experimental and
theoretical results, the porosy content (Vp%) can be simply
represented as Vp(vol%) = K(H)/P*, where K(H) is a contant
depending on the hydrogen content. An increase of hydrogen
content increases the value of K(H). For low pressure casting,
although the gauge pressure exerts an effect of reducing
porosity content meanwhile it also causes the negative effect of
reducing the degree of directional solidification. In the
application of low pressure casting, P* can be represented by
P*= Pa+ P+ Ps.
封面
第一章 緒論
1.1前言
1.2文獻回顧
1.3研究目的
第二章 微縮孔含量形成理論分析
2.1樹狀晶間流體流動的壓力降
2.2表面張力的壓力效應
2.3微縮孔的形成
第三章 實驗方法
3.1鑄件型態
3.2鑄造流程
3.3熱參數量測
3.4試片拉伸強度及黴孔含量之量測
第四章 結果與討論
4.1A206合金的推拔與平板鑄件體積比、凝固比與微縮孔關係
4.2A206合金的推拔與平板鑄件體積比、凝固比與鑄件健全性
4.3A206合金的推拔與平板鑄件微縮孔含量分佈、抗拉強度與凝固時間(gf)關係
4.4固相線移動速度(Vs)、溫度梯度(G)對微縮孔含量之影響
4.5熱參數指標G0.4/Vs1.6或G0.38/Vs1.62預測微縮孔含量
4.6A206和A356合金之補充行為比較
4.7模溫變化下微縮孔含量與補充參數之關係
4.8A206合金鑄件微縮孔含量與凝固時間(tf)及G0.4/Vs1.6關係
4.9微縮孔含量與壓力指標P*關係
4.10氫含量對鑄件健全性之影響
4.11氫含量與G0.38/Vs1.62對微縮孔形成之影響
4.12氫含量P*對微縮孔形成之影響
4.13低壓鑄造之外加壓力對熱參數及微縮孔含量之影響
第五章結論
參考文獻
誌謝與自述
其他
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