( 1. 西安理工大學 材料科學與工程學院, 西安 710048；
2. 西北工業(yè)大學 應用物理系， 西安 710072)
摘 要: 采用單輥實驗技術(shù)研究了AZ91D鎂合金的急冷快速凝固特征。 合金條帶的凝固組織沿厚度方向分為3個晶區(qū)： 近輥面細晶區(qū)、 內(nèi)部柱狀晶區(qū)和自由面等軸晶區(qū)。 XRD分析表明， 在快速凝固條件下, L→α-Mg＋β-Mg17Al12的共晶反應受到抑制，條帶凝固組織由過飽和的單相α-Mg 固溶體組成。 TEM分析發(fā)現(xiàn)， α-Mg晶內(nèi)和晶界上離散分布著的少量Mg17Al12質(zhì)點， 系α-Mg 固溶體在連續(xù)冷卻過程中脫溶析出的產(chǎn)物； α-Mg中存在著大量的位錯線和位錯胞。 隨著輥速增大， 晶粒更加細化，柱狀晶區(qū)減小， 位錯密度增大， 條帶強度增加， 塑性降低， 電阻率增大。
關(guān)鍵字: 鎂合金; 快速凝固; 晶體生長；組織與性能
（ 1. School of Materials Science and Engineering,
Xi′an University of Technology,
Xi′an 710048, China;
2. Department of Applied Physics, Northwestern Polytechnical University, Xi′an 710072, China）
Abstract: The ribbons of melt-spun AZ91D magnesium alloy with thickness of 40-70μm and length of 80-100mm were obtained by a single roller apparatus. According to the grain morphology, the rapid solidification microstructure of melt-spun magnesium alloy is roughly subdivided into three crystal zones through the thickness section: the fine equiaxed zone near the roller surface, the inner columnar zone and the outer equiaxed zone near the free surface. The X-ray analysis results indicate that the microstructure of the alloy is composed of the single phase α-Mg supersaturated solid solution and the eutectic reaction of L→α-Mg+β-Mg17Al12 is suppressed due to rapid solidification. TEM analysis reveals that a little amount of β-Mg17Al12 compound, which disperses inside the α-Mg grains and locates at the grain boundaries, is the product of precipitation from supersaturated α-Mg solid solution during cooling processes. Lots of dislocations and dislocation cells exist in α-Mg grains. With the increasing of roller velocity, the α-Mg grains become gradually finer and the inner columnar zone tends to elimination, and the density of dislocation inside the grains increases, and hence the strength and electrical resistivity of the alloy increase remarkably, while the elongation of the alloy decreases.
Key words: magnesium alloy; rapid solidification; crystal growth; microstructures and properties
