【作者】 邓延波；

【导师】 耿浩然；

【作者基本信息】 济南大学 ， 材料物理与化学， 2010， 硕士

【摘要】 本文利用高温DSC差热分析、热速处理、快速凝固等方法对Al-12wt.%Sn、Al-12wt.%Sn-4wt.%Si合金熔体进行了细致研究,并分析了合金熔体结构变化与凝固组织的关系。另外利用自行研制的电阻率测量仪采用直流四电极法测量了Ga-Sb合金熔体在不同成分和温度下的电阻率。对Al-12wt.%Sn合金进行了DSC测试,发现在DSC曲线温度点735-750℃和845-858℃左右存在着吸热峰,由此确定合金热速处理的过热温度为900℃和780℃。热速处理的结果显示经过热速处理的合金组织明显细化。组织中的Sn相也趋于均匀细小。同时,通过研究保温时间对合金熔体热速处理的影响发现,经900℃快速激冷到700℃时,由于驰豫现象的存在,保温时间短的熔体大部份保留了900℃的熔体结构,试样的组织比较细小。利用高温熔体黏度仪对Al-12wt.%Sn-4wt.%Si合金熔体进行了黏度测试。结果证明随着温度的降低,合金熔体黏度在998K-968K和1138K-1103K处出现不连续的变化。而利用DSC对Al-12wt.%Sn-4wt.%Si进行测试时发现合金熔化以后,在1013K和1083K处,曲线上仍然出现了吸热峰,说明合金熔体出现了不连续结构转变。分析认为,共价结合的Si-Si、Sn-Sn原子团簇的形成和Al、Si和Sn原子结合成原子团簇并迅速长大,分别是引起这两个温度区间内熔体结构不连续转变的原因。由黏度突变所反映出的熔体结构不连续转变温度和由DSC分析所得的熔体结构不连续转变温度虽然相近,但是还是存在一定的温度差。这是由于试验过程中,两种测量方法的升温制度以及它们所反映的物理性质不同引起的。找到异常温度点之后利用快速凝固的方法观察Al-12wt.%Sn-4wt.%Si合金在963K、1100K和1200K温度下快速凝固的铸态组织发现,熔体过热温度越高,快速凝固后组织越细小,尤其是含量较高的白色Sn相,在1200K下快速凝固后呈现接近弥散分布的颗粒状。这是由于温度越高,合金熔体中原子团簇的尺寸越小,在较高的温度下原子团簇可能分解,熔体趋于均匀,快速凝固可以将熔体的这些特征保留到铸态。因此,在试验温度范围内,过热度越高,熔体快速凝固后组织越均匀细小。使用自行研制的电阻率测量仪采用直流四电极法测量了液态III-V族体系的Ga-Sb合金熔体不同成分电阻率-温度曲线。研究发现,随着Sb含量的增加,Ga-Sb合金熔体的电阻率升高。Ga₅₀Sb₅₀合金熔体的电阻率在715-735℃温度区间内出现了异常变化,其余几个成分点的电阻率-温度曲线在熔点以上50-100℃的范围内由于有大量原子团簇的产生不成线性关系。由于Ga₅₀Sb₅₀是一种比较特殊的化合物,晶体属于半导体化合物,熔化后该合金的电阻率及其温度系数呈现典型的金属特征,原子之间的作用力为金属键。当温度降至735℃时,金属键开始大量向共价键转变,此时原子分布处于混乱状态,电子运动受到阻碍,随着共价键量的增加,熔体中原本处于自由态的电子逐渐被束缚,使电子输运性能下降,所以电阻率在735℃时升高,当熔体温度达到723℃时共价键基本形成,原子分布处于有序状态,电子运动的阻力减小,继而随温度的降低电阻率随之降低,直到降至熔点。更多还原

【Abstract】 The melts of Al-12wt.%Sn, Al-12wt.%4wt.%Si alloy have been researched using the methods such as high temperature DSC, differential thermal analysis, thermal rate treatment processing and rapid solidification.The relationship of the structure and the solidification of the melts has also been analysised. the resistivity of Ga-Sb alloy in different ingredients and in different temperature was studied by the method of DC Four electrodes using the resistivity measuring instrument .The Al-12wt.%Sn alloy was tested by the DSC, there exist heat-sink valleys in temperature of 735-750℃and 845-858℃in the DSC curve, from which the overheating temperature of thermal rate treatment of alloy was determined that is 900℃and 780℃. The results of the thermal rate treatment showed that the structure of the alloy is refined obviously.The Sn phase also tend to be evenly tiny. At the same time, through studies influence of the time of preservation to the hot speed processing of alloy, the most melt that the holding time is short retained the structure of melt at 900℃, and the structure of sample melts is small in the process of quickly quenching to 700℃, due to the existence of relaxation phenomenon.The viscosity of Al-12wt.%Sn-4wt%Si melt was tested by viscosity measurement.The results proved that the viscosity of the melt appear discontinuous changes in 998K-968K and 1138K- 1103K with the drop of the temperature. The Al-12wt.%Sn-4wt.%Si alloy also was tested using DSC, the results proved that the curve still appeared absorptionn in 1013K and 1083K after the alloy was melted , these proved that there exists discontinuous structural transformations in the melt. The formation of Si-Si and Sn-Sn clusters with covalent binding,and Al, Si and Sn atoms combine into clusters and grow rapidly respectively caused discontinuous structural transformations in the melt in the two range of temperature. The temperature of mutations structural transition reflected by the viscosity and the temperature of discontinuous structural transformations attained by DSC are similar, but there are still some difference. This because that the heating system of the two kinds of measurement and the physical properties reflected by them are different during the test process. The solidification of Al-12wt.%Sn-4wt.%Si alloy at 963K, 1100K and 1200K was observed using the method of rapid Solidification after finding abnormal temperature,the results displayed that the higher of the overheating temperature,the tinier of the rapid solidification, especially the high content of white Sn phase, which present diffuse distribution of granular in 1200K after rapid solidification. This is due to the higher of the temperature, the smaller of the size of clusters of atoms in alloy melt, the clusters of atoms can decompose at higher temperatures,the melt tends to be uniform, rapid solidification can retain these characteristics of the melt to as-cast. Therefore, the higher of overheat, the more uniform and fine of the solidification in the range of test temperature .The resistivity- temperature curve of Ga-Sb melts in different ingredientsin was measured by d.c four-probe methord. The instrument was developed by ourselves. It was found that the resistivity of Ga-Sb melts increased with the increase of content of sb.The resitivity-temperature curves of Ga-Sb alloys keep linearity relation, besides that of Ga₅₀Sb₅₀ melt shows an anomalous change in 989-1008 K, The resitivity-temperature curves of the rest of the components are inlinear in the range above the melting temperature 50-100℃due to the produce of clusters of atoms. Ga₅₀Sb₅₀ is a kind of special compound, of which, crystal belongs to semiconductor compound, and acting force among atoms is of covalent bond with covalent tetrahedron coordination structure, but after melting, the electric resistance and temperature coefficient of this alloy displays typical metal characteristics, with acting force among atoms is of metallic bond. When the temperature drops to 1008K, the metallic bonds start to transform to covalent bonds at large quantity, at this moment, atom distribution is in confusional state, and the electronic movement is hindered. With increase of amount of covalent bonds, the electrons in melt that are originally in freedom state are gradually restricted, making motion ability of electrons decrease;therefore, the electric resistance will rise at 1008 K. The covalent bond is basically formed when the melt temperature reaches 998 K, by now, the atom distribution is in ordered state, and the resistance of electronic movement is reduced. Afterwards, the electric resistance will decrease with the reduction of the temperature till the melting point.更多还原