Sn-58Bi合金上引—拉拔连续制备及其组织性能研究

发布时间：2018-01-23 01:11

  本文关键词： Sn-58Bi合金 上引连续铸造 拉拔 延伸率 塑性加工　出处：《江西理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：Sn-58Bi合金熔点低且无毒,具有较高的抗拉强度、剪切强度、抗蠕变性能及疲劳寿命,其性能在很多方面与Sn-Pb焊料相当,是较有应用前景的低温无铅焊料。由于传统铸造法制备的Sn-58Bi合金中含有大量脆性初晶Bi相,难以实现Sn-Bi杆/丝的高效加工,如何提高Sn-58Bi合金的道次加工率,缩短制备加工流程,实现细径Sn-Bi合金材料的低成本、高效率的制备始终是该领域的关键技术问题。本文采用上引连续铸造的方法制备直径8 mm的Sn-58Bi合金杆材,与传统直接浇铸的同成分合金材料进行了组织和力学性能对比,发现上引连续铸造的方法有效改善了材料的微观组织,大幅度提高材料的塑性,在此基础上,通过自行设计的在线加热拉拔减径装置实现了上引连铸Sn-58Bi杆材的大变形量多道次拉拔,跟踪研究材料组织性能在拉拔变形过程中的变化规律,并研究评价热处理工艺参数对材料拉伸性能的影响规律。主要结论如下:(1)通过上引连续铸造制备Sn-58Bi合金杆材,并研究热处理对上引杆材组织性能的影响。与直接浇铸的Sn-58Bi合金相比,上引杆材的组织得到了显著的细化,形成Sn相相互连接的组织特征,消除了圆形的初晶富Sn相,在纵向方向上形成平行排列的长条状富Bi相一次枝晶,组织特征的显著变化影响了材料的断裂机制,由此引起上引杆材延伸率的大幅度提高,达到42.5%,与之相比,直接浇铸合金的延伸率仅为5%。热处理对上引杆材组织性能影响显著,保温热处理促进富Sn相中过饱和固溶Bi元素的析出,出现粗大富Sn相,高温保温和低温长时保温均导致延伸率的降低,仅在低温短时保温时,上引杆材的塑性得以提高。(2)通过拉拔工艺优化实现上引Sn-58Bi合金杆材多道次(37)8 mm→(37)7 mm→(37)6.5 mm→(37)6 mm→(37)5.5 mm加热拉拔。研究拉拔温度、拉拔速度对(37)8 mm→(37)7 mm单道次拉拔的影响规律,得到了较优的拉拔温度范围为45℃—55℃之间,拉拔速度范围为250mm/min—500 mm/min之间,在此基础上,进一步研究拉拔参数对(37)7 mm→(37)6.5 mm→(37)6mm→(37)5.5 mm多道次拉拔力和拉拔态合金性能的影响规律,优化工艺参数,成功实现上引杆材(37)8 mm→(37)5.5 mm的稳定拉拔。(3)研究退火热处理对拉拔态Sn-58Bi合金性能的影响规律。在40—60℃温度范围内,随着保温时间的延长,经热处理后的拉拔态Sn-58Bi合金抗拉强度均不断提高,延伸率先升高后降低,通过对直径5.5 mm拉拔态合金进行50℃/0.5 h的保温处理,实现了(37)5.5 mm→(37)5 mm单道次拉拔。(4)通过减小道次变形量和增加加工道次,顺利实现(37)5.5→(37)3.8 mm的多道次拉拔,研究对比了直径为5.5 mm拉拔态杆材是否进行热处理对合金后续各道次拉拔力的影响。
[Abstract]:Sn-58Bi alloy has high tensile strength, shear strength, creep resistance and fatigue life due to its low melting point and non-toxic properties. The properties of Sn-58Bi alloy are similar to those of Sn-Pb solder in many aspects. Sn-58Bi alloy prepared by traditional casting method contains a lot of brittle primary crystal Bi phase, so it is difficult to realize the efficient processing of Sn-Bi rod / wire. How to improve the pass rate of Sn-58Bi alloy, shorten the manufacturing process and realize the low cost of fine diameter Sn-Bi alloy material. The preparation of high efficiency is always the key technical problem in this field. In this paper, Sn-58Bi alloy rod with diameter of 8 mm is prepared by continuous casting. The microstructure and mechanical properties of the alloy were compared with that of the conventional direct casting alloy. It was found that the continuous casting method improved the microstructure of the material and greatly improved the plasticity of the material. Through the self-designed on-line heating drawing reducing device, the large deformation amount multi-pass drawing of Sn-58Bi rod is realized, and the variation of microstructure and properties of the material during drawing deformation is studied. The influence of heat treatment process parameters on the tensile properties of the material was studied. The main conclusions are as follows: 1) the Sn-58Bi alloy rod was prepared by continuous casting. The effect of heat treatment on the microstructure and properties of the upper rod was studied. Compared with the directly cast Sn-58Bi alloy, the microstructure of the upper rod was significantly refined and the Sn phase was connected with each other. The circular primary Sn-rich phase was eliminated, and the primary dendrite was formed in the longitudinal direction of the long stripe Bi-rich phase. The obvious change of the microstructure affected the fracture mechanism of the material. As a result, the elongation of the upper rod is greatly increased, reaching 42.5, compared with that of the casting alloy, the elongation is only 5. The heat treatment has a significant effect on the microstructure and properties of the upper rod. Heat treatment can promote the precipitation of solid solution Bi elements in Sn-rich phase, and the appearance of coarse Sn-rich phase, high temperature insulation and low temperature long time heat preservation all lead to the decrease of elongation, only at low temperature and short time heat preservation. The plasticity of upper drawing rod can be improved. (2) by optimizing drawing process, the Sn-58Bi alloy rod can reach 378mm by multi-pass. 鈫，

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