本文選題：Al-30%Si合金 + 初生硅形態(tài)　； 參考：《南京理工大學(xué)》2017年碩士論文

【摘要】：過共晶鋁硅合金是一種重要的鑄造合金,隨著硅含量的增加,過共晶鋁硅合金的耐磨性能顯著提高,熱膨脹系數(shù)大大降低,熱穩(wěn)定性提高,密度降低,耐高溫性能提高。未處理的鑄造過共晶鋁硅合金組織中存在大量粗大的板條狀、五瓣星狀初生硅組織,嚴(yán)重破壞了組織,大大降低了合金的性能。目前對于過共晶鋁硅合金中初生硅組織形貌控制的研究在變質(zhì)處理、快速凝固等方面取得了一定的成果,但是這些方法或是效果不顯著,或是技術(shù)復(fù)雜,成本高昂,不適合工業(yè)生產(chǎn)應(yīng)用。本文系統(tǒng)研究了機械攪拌工藝以及液固兩相區(qū)二次加熱工藝對Al-30%Si合金初生硅組織的影響,提出了合適的工藝參數(shù),制備出初生硅組織形貌較佳的Al-30%Si合金。實驗表明:穩(wěn)態(tài)下在一定溫度機械攪拌可以顯著改善初生硅組織形貌,細(xì)化初生硅組織,初生硅顆粒部分球化,棱角發(fā)生鈍化,但是攪拌時間過長會使組織顆粒粗化;連續(xù)冷卻的瞬態(tài)下機械攪拌,冷卻速度、攪拌時間對初生硅組織形貌影響顯著,在合適的工藝條件下,初生硅等效直徑降至25μm,形狀因子達到0.81,但若攪拌時間過長,會使熔體內(nèi)雜質(zhì)含量增加,組織顆粒偏聚、搭接;液固兩相區(qū)二次加熱可以有效的改善初生硅組織形貌,得到圓整球化的初生硅組織,初生硅等效直徑28μm左右,形狀因子升至0.87,分步二次加熱可以改善組織的均勻性,但是如果工藝參數(shù)設(shè)置不當(dāng)會使初生硅組織顆粒粗化長大;二次加熱組織在三維空間中初生硅組織以球形或橢球形存在,初生硅顆粒的各個方向都有鈍化。本文通過變質(zhì)、機械攪拌、二次加熱等手段,得到了細(xì)小、圓整、分布均勻的初生硅組織,初生硅組織形貌明顯改善,本實驗設(shè)備工藝簡單,操作簡便,效果較佳,并且成本較低,適合應(yīng)用于實際生產(chǎn),是一種較為有效的控制初生硅組織形貌的方法。
[Abstract]:Hypereutectic Al-Si alloy is an important casting alloy. With the increase of Si content, the wear resistance of hypereutectic Al-Si alloy is improved significantly, the thermal expansion coefficient is greatly reduced, the thermal stability is improved, the density is reduced and the high temperature resistance is improved. In the untreated cast hypereutectic Al-Si alloy there are a large number of thick plate strips and five starlike primary silicon structures which seriously destroy the microstructure and greatly reduce the properties of the alloy. At present, the research on morphology control of primary silicon in hypereutectic Al-Si alloy has made some achievements in modification treatment, rapid solidification and so on, but these methods are not effective, or the technology is complex, and the cost is high. Not suitable for industrial application. In this paper, the effects of mechanical stirring process and liquid-solid two-phase region secondary heating process on the primary silicon structure of Al-30%Si alloy were systematically studied, and the appropriate technological parameters were put forward to prepare the Al-30%Si alloy with better morphology of primary silicon structure. The experimental results show that mechanical stirring at a certain temperature can significantly improve the morphology of primary silicon, refine the primary silicon, partially spheroidize the primary silicon particles, and passivate the edges, but if the stirring time is too long, the microstructure particles will become coarse. Under the condition of continuous cooling, mechanical stirring, cooling rate and stirring time have a significant effect on the morphology of primary silicon. Under the appropriate technological conditions, the equivalent diameter of primary silicon decreases to 25 渭 m, and the shape factor reaches 0.81, but if the stirring time is too long, The secondary heating in the liquid-solid two-phase region can effectively improve the morphology of the primary silicon structure, and obtain the circular spheroidized primary silicon structure, the equivalent diameter of the primary silicon is about 28 渭 m. When the shape factor rises to 0.87, the secondary heating can improve the homogeneity of the microstructure, but if the technological parameters are not set properly, the primary silicon particles will grow and coarseness, and the secondary heating structure will exist in the shape of spherical or ellipsoid in the three-dimensional space. Primary silicon particles are passivated in all directions. In this paper, by means of modification, mechanical stirring and secondary heating, fine, round and evenly distributed primary silicon is obtained. The morphology of primary silicon is obviously improved. The experimental equipment is simple in technology, simple in operation and good in effect. Because of its low cost and suitable for practical production, it is an effective method to control the morphology of primary silicon.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG146.21

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