【作者】 张先锋；

【导师】 余瑾；

【作者基本信息】 合肥工业大学 ， 材料加工工程， 2010， 硕士

【摘要】 近年来,关于熔体热历史对凝固影响方面的研究已取得一定成果,发现对熔体进行过热处理能显著改善合金的组织和性能,但熔体热历史对凝固行为影响的实质等一些深层次问题还有待进一步探讨。前期的研究工作表明:Pb26Sn42Bi32、Pb36.32Sn58.68Bi5和Pb3.82Sn6.18Bi90合金存在温度诱导的液-液结构转变现象,本文在前人研究的基础上,对这三种成分的合金进行不同的热处理,探究可逆和不可逆两类熔体结构转变对合金凝固行为、凝固组织和性能的影响。另外,本文还运用过热处理的方法对含铅焊料的绿色化做了一些探讨。主要内容和结论如下:(1)对于发生可逆结构转变的Pb26Sn42Bi32合金经过不同的热处理后,空冷条件下的凝固组织转变前后变化不明显;但由于在快冷条件下有效地抑制了Pb26Sn42Bi32熔体中可逆性原子团簇的回复,从而使得从高温直接快冷凝固的合金组织细化,硬度下降。对于发生不可逆结构转变的Pb36.32Sn58.68Bi5和Pb3.82Sn6.18Bi90合金经过不同的热处理后,由于不可逆性液-液结构转变发生使得熔体中原有的原子团簇彻底消失,液-液结构转变后的熔体结构更加均匀和无序,所以在空冷和快冷条件下,其结构转变都能使组织细化,成分均匀;特别在快速凝固组织中,前后差异尤为明显。(2)利用自制的定向凝固装置探究了液-液结构转变对三种成分的PbSnBi合金定向凝固组织的影响。研究结果表明:结构转变前后的定向凝固组织变化明显,经历结构转变后的试样定向凝固组织细小,方向性高度一致。(3)对含铅焊料Pb36.32Sn58.68Bi5经过过热处理使其发生不可逆结构转变,与结构转变前的相比较发现:结构转变后试样铅的挥发难度加大;在酸、碱、盐中的相对腐蚀率和腐蚀速度变小;在H2SO4溶液中,发生结构转变的试样钝化膜的形成相时间早于未发生结构转变的试样,在NaOH溶液中,经历结构转变的试样每个时间点的腐蚀电流都要小于未发生结构转变的试样,在NaCL溶液中,发生结构转变的试样一定会生成钝化膜,而未发生结构转变的试样则不生成钝化膜。通过研究液-液结构转变对凝固行为、凝固组织和性能的影响,不仅避免了传统熔体热处理工艺的盲目性,还为改进合金的制备工艺提供了行之有效的方法,为更深入地认识液态物质结构提供了科学依据。更多还原

【Abstract】 In recent years, the studies of effect of heat history on solidification have made some achievements, it has been found that the structures and properties of some alloys could be obviously improved by such superheat treatment,but some deep problems about the essence of effect of heat history on solidification behavior still needs further discussion.Prior investigation suggested that a temperature–induced liquid-liquid structure transition(TI-LLST) could occur in Pb26Sn42Bi32 ,Pb36.32Sn58.68Bi5 and Pb3.82Sn6.18Bi90 alloys. In this paper, on the basis of the previous studies, the three components alloys were experienced different heat treatment, the solidification behaviors,microstructures and property of melt with reversible TI-LLST and melt with irreversible TI-LLST were studied. At the same time, we do some research about the solder containing Pb PbSnBi Innoxiousness by use of heat-treatment.The major contents and conclusions are as follows:First,The Pb26Sn42Bi32 melt with reversible TI-LLST were experienced different heat treatment, the solidification microstructures of Pb26Sn42Bi32 alloy is invariant in the air,due to cooling speed is very big, inhibit the reversibility of atom clusters in Pb26Sn42Bi32 melt,So that the microstructures of melt became finer and the Vickers hardness of the sample is reduced after solidified from rapid solidification. The Pb36.32Sn58.68Bi5 and Pb3.82Sn6.18Bi90 melt with irreversible TI-LLST were experienced different heat treatment, due to irreversible TI-LLST, irreversibility of atom clusters in melt completely disappear,the melt structure becomes more homogeneous and disorder after structure transition,so the microstructures became finer, the components became homogeneous in the air cooling and rapidly cooling conditions, especially in rapid solidification microstructures,the differences is very significant.Second,the directional solidification experiments of three components PbSnBi alloys were carried out to investigate the effect of the TI-LLST on directional solidification microstructures by the using of self-made unidirectional solidification device.the results show that the directional solidification microstructures are changed obviously after TI-LLST, the directional solidification microstructures of sample became finer that experienced structure transition,and the directional is extraordinarily consistent.Third, the solder containing Pb Pb36.32Sn58.68Bi5 undergo irreversible TI-LLST after superheat treatment, compared with pre-structure transition,we found the evaporation of Pb in more difficult after structure transition; the relative corrosion rate and corrosion rate of the samples in acid, alkali, salt become smaller; the formation of passivation film of the sample experienced structure transition earlier than the sample unexperienced structure transition in H2SO4,the corrosion current of the sample experienced structure transition at each time should be less than the sample unexperienced structure transition in the NaOH, the passivation film of the sample experienced structure transition will be generated eventually in NaCL, while no passivation film is generated in the sample unexperienced structure transition.According to the studies that the influence of liquid-liquid structure transition on solidification behaviors, microstructure and property of alloys , not only to avoid the blindness of traditional melt heat treatment process, but also to provide effective method for improvement of the preparation technology of alloys,and provide scientific basises for more in-depth understanding of liquid material structure.更多还原