臺灣博碩士論文加值系統

　　本研究的目的在於探討分別利用噴覆成型技術與重力鑄造技術製作低矽鋁合金。各製程中參數分別影響微結構生成與單軸熱壓機械性質、成形性質。比較重力鑄造方式，利用噴覆成型技術是因此一技術可輕易獲得組織相當微細化的鑄錠且沒有巨觀的偏析現象。
　　研究結果顯示，噴覆成型之低矽鋁合金晶粒尺寸40~50μm，鑄錠中心與中間(沿徑方向)，緃向與徑向上具有等軸晶的凝固組織特徵。降低氣液流量比(GMR, Gas Metal Flow Ratio, dimension = Kg/m3)由3.7級數至1.7級數能明顯降低鑄錠中的孔隙率。鑄造的鋁矽合金則呈樹枝狀晶結構。熱壓試片的金相觀察顯示兩材料都有不變形區(dead zone)與剪應變區(shearing zone)。噴覆成型者於不變形區金相呈等軸晶粒，重力鑄造者於不變形區金相呈樹枝狀晶。於剪應變區噴覆成型材晶粒明顯拉長而鑄造者因剪應變方向與二次樹枝狀晶交角不同而有呈拉長與樹狀晶曲折的結果。
　　單軸熱壓實驗顯示，降伏強度於溫度提高時降低，是因具有面心立方體的結構，溫度升高造成控制降伏機構中熱活化機構為控制因素造成降伏強度隨溫度提高而降低。夾頭速率提高時兩材料的降伏強度都提高，由初始應變速率提高造成材料中對於差排產生速率反應塑性的時間較短，使得差排密度較高而觀察到降伏強度較高。降伏強度以鑄造者為高，因噴覆成型者具有等軸晶而重力鑄造者具有樹枝狀晶，兩者微結構不同。
　　兩材料都具有一平坦的變形區域，但以噴覆成型者可達的上限值較大亦即噴覆成型的母材可進行的加工量較鑄造者為大，其原因是微結構上的不同所造成。在高應變量時重力鑄造者流應力都是提高，表示鑄造都有較嚴重的不均勻變形。兩材料流應力曲線分析得知，於壓縮變形過程中發生動態回復、動態應變時效與固溶的矽顆粒是不可切割的。這些反應造成流應力曲線在巨觀上有一平坦區，局部呈鋸齒狀。表面粗度分析所得頻譜顯示噴覆成型母材於壓縮時響應的波長較鑄造者為短使得在熱壓後的試片鑄造者有明顯的突起。

　　The study aims at, on one hand, the effect of process parameters on micro-structural evolution of low content silicon aluminum alloy when taking advantage of Sprayforming techniques which is compared with casting. And, on the other hand, the characteristics of mechanical behavior and bulk workability of as-sprayformed AlSi billet need estimated. Compared with conventional casting processes, as-sprayformed billet shows refined microstructure and macro-segregation elimination.
　　The experimental results show that the grain size of as-sprayformed billet is about 40~50 μm. At center and middle position of the billet, it shows equaxed structure. The porosity of as-sprayformed billet can be reduced by lowering the gas-to-metal-flow ratio from 3.7 level down to 1.7 level. The micro-structure of AlSi of the same composition by casting is dendrite. After being hot pressed, both of the as-sprayformed and as-cast samples show two typical common characteristics: undeformed zone and shearing zone. Undeformed zone in as-sprayformed samples show equaxed microstructure and that in the as-cast one shows dendrite. The shearing zone in the as-sprayformed samples show elongated grain. Since difference orientation exists between the shearing direction and the second dendrite arm, the dendrite shows either elongated or bended in as-cast samples.
　　The uniaxial compressing tests are carried out for as-sprayformed and as-cast samples. The experimental results indicate that yield strength decreases when the temperature is increased. Both samples are aluminum matrix and the crystal structure in FCC. In FCC structures, there two controllable mechanisms when yielding. One is based on material characteristic and the other is thermal activated. On increasing temperature, the thermal activated mechanism becomes more important, resulting in decrease of yield strength for both. When increasing cross head speed, the yield strength increases. Higher initial strain rate results in shorter response time for the production of dislocation. In the same time interval, higher initial strain rate produces higher density of dislocation. Difference yield strength is owing to the different micro-structure.
　　There exists a plateau deformation zone for both. The plateau deformation zone for as-sprayformed is more extended, indicating that the as-sprayformed sample is capable of being deformed more. There is serration in flow stress owing to the dynamic strain ageing (DSA) Dynamic strain ageing cause the flow stress curve zigzag-like when the cross head speed is 3 mm/sec and the temperature is ranging from 325℃ to 425℃。When deformed to high strain, the flow stress of as-cast samples increase. The experimental results indicate as-cast sample is deformed more inhomogeneous.
　　Finite Fourier Transformation of roughness indicates that the response wavelength of the as-sprayformed billet is even smaller than that of the as-cast ones. Different response wavelength produces different morphology for the as-sprayformed and as-cast samples after uniaxial compressing.

總目錄1
表目錄2
圖目錄2
誌謝5
中文摘要6
英文摘要8
第1章　序論與文獻回顧10
　　1.1 簡介10
　　1.2 文獻回顧11
　　　　1.2.1 鋁合金晶粒細化11
　　　　1.2.2 噴覆成型13
　　　　1.2.3 單軸熱壓機械性質15
第2章　實驗方法22
　　2.1 研究目的與構想22
　　2.2 實驗步驟23
　　2.3 實驗材料24
　　2.4 實驗與分析儀器25
　　2.5 試片準備與數據分析26
第3章　結果與討論39
　　3.1 熱分析39
　　3.2 鑄錠外觀與微結構分析40
　　　　3.2.1 霧化粉末(Overspray powder)影響40
　　　　3.2.2 氣液流量比(GMR)的影響41
　　　　3.2.3 微結構特徵42
　　3.3 熱壓塑性變形微結構分析43
　　3.4 熱壓機械性質與成型性質45
　　　　3.4.1 降伏區(Yielding zone)46
　　　　3.4.2 平坦變形區(plateau deformation zone)49
　　　　3.4.3 不同材料不同的響應波長52
第4章　結論54
參考文獻57

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