Sm及CNTs在铝硅合金中的应用及性能研究

发布时间：2018-05-03 00:46

本文选题：Al-Si合金 + 稀土Sm　；参考：《南昌大学》2015年硕士论文

【摘要】：Al-Si系铸造合金是一种传统的工业用铝合金材料,因其原料成本低廉且具有良好的铸造、焊接及耐磨性能而广泛应用。ZL101和ZL102合金为两种典型的Al-Si系铸造合金。然而,其铸态显微组织特性为多边形块状的初晶硅和粗大针状的共晶硅,α-Al枝晶粗大,导致合金的力学性能恶化。本文主要对稀土钐(Sm)及碳纳米管(CNTs)在铝硅合金中的应用及性能进行研究。研究结果表明:稀土Sm能降低Al-Si合金的共晶温度。加入量越多,则降低幅度越大。当加入0.6wt.%Sm时,共晶温度最低。共晶温度低是具有良好变质组织合金的一个共同的特征。对显微组织而言:ZL101的α-Al二次枝晶臂间距随着Sm含量增加而减少,当Sm的含量达0.6wt.%时,二次枝晶臂间距值最低,由原来的40μm变为27μm;而此时ZL102合金的α-Al呈双重枝晶-晶胞结构和松树结构分布,枝晶数量增多。Sm对Al-Si合金的共晶硅相变质能力较强。可将Al-Si系合金中细长针状变质为细小圆整的颗粒状。对于ZL102合金,添加适量稀土Sm能同时变质初晶硅和共晶硅。此外,稀土Sm能提高Al-Si系合金的力学性能。当0.6wt.%Sm加入时,合金具有良好的综合力学性能。CNTs的韧性和结构稳定性良好,作为增强相加入合金后,复合材料的性能将带来一次飞跃。然而CNTs密度低,尺寸小,比表面积大,难以分散,与铝合金基体润湿性差。因此,为了解决上述问题,本课题首先制备了CNTs含量高的Al-CNTs中间纳米复合材料作为CNTs的载体,然后加入铝硅合金熔体稀释辅以施加机械搅拌或超声制备CNTs/ZL101复合材料。在Al-CNTs中间纳米复合材料中,CNTs含量越多,熔化时间越长,CNTs的最佳含量为5~8wt.%。Al-CNTs中间纳米复合材料经热挤压后可缩短其熔化时间。采用机械搅拌法制备的CNTs/ZL101复合材料,随着CNTs的加入,显微组织得到细化。但是由于机械搅拌法对CNTs的分散能力有限,当CNTs含量超过0.4wt.%时,复合材料的内部缺陷多,存在大量的CNTs团聚物,导致复合材料力学性能下降。当CNTs含量为0.2wt.%时,复合材料的显微硬度及力学性能最佳,与基体相比,硬度和极限抗拉强度分别提高了36.8%、18.8%。采用超声法制备的CNTs/ZL101复合材料与机械搅拌法相比,CNTs的团聚物在超声的空化效应作用下在复合材料内均匀分布,共晶硅及α-Al也得到细化。超声功率越大,复合材料的显微组织越好,最佳的超声功率为2.1kw。在功率2.1kw超声作用下,0.8wt.%CNTs/ZL101复合材料的硬度、极限抗拉强度和延伸率最高,最低功率(0.7kw)相比,分别提高了22.8%、17.8%和47.2%。另外,随着CNTs含量的增加,复合材料的硬度和抗拉强度不断上升,当CNTs加入量达1.2wt.%时最高,分别为HV106.3、267MPa,与基体相比,提高了36.1%、19.7%。
[Abstract]:Al-Si series casting alloy is a kind of traditional industrial aluminum alloy. Because of its low raw material cost and good casting, welding and wear resistance, it is widely used. ZL101 and ZL102 alloy are two typical Al-Si casting alloys. However, the as-cast microstructures are polygonal bulk primary silicon and coarse acicular eutectic silicon, and 伪 -Al dendrite is coarse, which results in the deterioration of mechanical properties of the alloy. In this paper, the application and properties of rare earth samarium and carbon nanotube (CNTs) in Al-Si alloy were studied. The results show that rare earth Sm can reduce the eutectic temperature of Al-Si alloy. The greater the addition, the greater the reduction. The eutectic temperature is the lowest when 0.6wt.%Sm is added. Low eutectic temperature is a common feature of good modified alloys. For microstructures, 伪 -Al secondary dendritic arm spacing decreases with the increase of Sm content. When Sm content reaches 0.6 wt.%, the secondary dendritic arm spacing is the lowest. At the same time, 伪 -Al of ZL102 alloy was distributed as double dendritic cell structure and pine tree structure, and the ability of eutectic silicon phase modification of Al-Si alloy was stronger when the number of dendrite increased. The fine needle shape of Al-Si alloy can be modified into fine round granular. For ZL102 alloy, the addition of appropriate amount of rare earth Sm can modify both primary silicon and eutectic silicon at the same time. In addition, rare earth Sm can improve the mechanical properties of Al-Si alloys. When 0.6wt.%Sm was added, the alloy had good comprehensive mechanical properties. The toughness and structural stability of the alloy were good, and the properties of the composites would take a leap forward when the alloy was added as a reinforcing phase. However, CNTs has low density, small size, large specific surface area, difficult to disperse, and poor wettability with aluminum alloy matrix. Therefore, in order to solve the above problems, the Al-CNTs intermediate nanocomposites with high CNTs content were prepared as the carrier of CNTs, and then the CNTs/ZL101 composites were prepared by adding melt dilution of Al-Si alloy and adding mechanical stirring or ultrasonic. The more the content of Al-CNTs is, the longer the melting time is, and the best content is that the melting time of 5~8wt.%.Al-CNTs intermediate nanocomposites can be shortened after hot extrusion. The microstructure of CNTs/ZL101 composites prepared by mechanical stirring method was refined with the addition of CNTs. However, due to the limited dispersion of CNTs by mechanical stirring method, when the content of CNTs exceeds 0.4 wt.%, the internal defects of the composites are more and a large number of CNTs aggregates exist, which leads to the decline of mechanical properties of the composites. When the content of CNTs is 0.2 wt.%, the microhardness and mechanical properties of the composites are the best. Compared with the matrix, the hardness and ultimate tensile strength of the composites are increased by 36.8% and 18.8%, respectively. Compared with the mechanical stirring method, the aggregates of CNTs/ZL101 prepared by ultrasonic method are uniformly distributed in the composites under the effect of ultrasonic cavitation, and the eutectic silicon and 伪 -Al are also refined. The higher the ultrasonic power, the better the microstructure of the composite, and the optimum ultrasonic power is 2.1 kw. The hardness, ultimate tensile strength and elongation of CNTs / ZL101 composites were increased by 22.8wt% and 47.2%, respectively. In addition, the hardness and tensile strength of the composites increased with the increase of CNTs content. When the content of CNTs reached 1.2wt.%, the highest content was HV106.3267MPa. compared with the matrix, the hardness and tensile strength of the composites were increased by 36.1% and 19.79.7MPa.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.21

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