( 1. 西安理工大学 材料科学与工程学院, 西安 710048；
2. 西北工业大学 应用物理系， 西安 710072)
摘 要: 采用单辊实验技术研究了AZ91D镁合金的急冷快速凝固特征。 合金条带的凝固组织沿厚度方向分为3个晶区： 近辊面细晶区、 内部柱状晶区和自由面等轴晶区。 XRD分析表明， 在快速凝固条件下, L→α-Mg＋β-Mg17Al12的共晶反应受到抑制，条带凝固组织由过饱和的单相α-Mg 固溶体组成。 TEM分析发现， α-Mg晶内和晶界上离散分布着的少量Mg17Al12质点， 系α-Mg 固溶体在连续冷却过程中脱溶析出的产物； α-Mg中存在着大量的位错线和位错胞。 随着辊速增大， 晶粒更加细化，柱状晶区减小， 位错密度增大， 条带强度增加， 塑性降低， 电阻率增大。
关键字: 镁合金; 快速凝固; 晶体生长；组织与性能
（ 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
