半固態鎂合金流動行為之研究分析; The Research of the Flow Behavior of the Semi-Solid State Magnesium Alloy

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题名:	半固態鎂合金流動行為之研究分析;The Research of the Flow Behavior of the Semi-Solid State Magnesium Alloy
作者:	陳學億;Hsueh-I Chen
贡献者:	機械工程研究所
关键词:	鎂合金;半固態;流動行為;Magnesium Alloy;Semi-Solid State;Flow Behavior
日期:	2009-01-08
上传时间:	2009-09-21 11:42:50 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	研究的目的在於探討鎂合金AZ91D在半固態時的流動行為。實驗中，利用可在高溫下量測黏度的同心圓柱黏度計，觀測半固態鎂合金黏漿的視黏度與剪應變和溫度之間的關係。由實驗結果發現，黏漿的視黏度隨著溫度的上升而降低，隨著剪應變率的增加而減少，具有剪變薄流體的特性。並根據本實驗數據，知道數學冪次式中的n值為接近於0.84。鎂合金AZ91D半固態黏漿觸變程度會隨著恆定剪應變率作用時間的增加而變大，但是，剪應力減少比例的曲線會越趨平緩，因為晶粒被球化至一定程度之後，更長的恆定剪應變率作用時間對剪應力將不會有顯著的影響。長時間的攪拌效應會讓視黏度先減少後逐漸增加，由於內部結構從樹枝狀結構破壞成顆粒較小的非樹枝狀結構，晶粒尺寸也會跟著減少，隨著攪拌時間的持續增加，晶粒會因為粗化效應逐漸長大，尺寸也會逐漸增大。不同的固相分率、預先攪拌時間與停留時間對流動性質也會產生影響，當預先攪拌時間固定時，較高固相分率的視黏度會隨著停留時間的增加而增加，這是由於顆粒聚合主導粗化機制並讓包覆液體維持在晶粒裡面；較低固相分率的視黏度會隨著停留時間的增加而減少，因為晶粒內部的包覆液體會藉由奧斯特瓦爾德成長主導的粗化作用被釋放，這將會導致流動性變佳。當固相分率固定時，較短預先攪拌時間的視黏度會隨著停留時間的增加而增加，較長預先攪拌時間的視黏度會隨著停留時間的增加而減少，這都是因為顆粒聚合與奧斯特瓦爾德成長等粗化機制對包覆液體產生不同影響所導致流動性的變化。 In this study, the flow behavior of the semi-solid AZ91D magnesium alloy is investigated by a high-temperature coaxial-cylinder viscometer. The relations between the steady-state apparent viscosity, shear rate and temperature of the magnesium alloy are observed. According to the results, the apparent viscosity decrease as the isothermal temperature and shear rate increase. The semi-solid AZ91D magnesium alloy shows the shear-thinning behavior. Basing on the experimental data, the power-law constant n is around 0.84. As the shearing time of maintained shear rate increase, the thixotropic behavior of magnesium slurry is more obvious. But the curve of reducing ratio is gradual, and the longer shearing time of maintained shear rate would not affect the shear stress. As the stirring time increases, the apparent viscosity initially decreases, and then it follows increasing curve. It is because that the dendritic structure is destroyed into the smaller non-dendritic one. As the stirring time continuously increases, the coarsening effect causes the particle size to increase. The solid fraction, pre-stirring time and resting time have influence on the flow behavior. When the pre-stirring time is fixed, the apparent viscosity increases as the resting time increases at high solid fraction. At the low solid fraction, the apparent viscosity decreases as the resting time increases. When the solid fraction is fixed, the apparent viscosity increases for shorter pre-stirring time as the resting time increases, and the apparent viscosity decreases for longer pre-stirring time as the resting time increases.
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