本文關(guān)鍵詞： Sn-58Bi合金 上引連續(xù)鑄造 拉拔 延伸率 塑性加工　出處：《江西理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：Sn-58Bi合金熔點(diǎn)低且無毒,具有較高的抗拉強(qiáng)度、剪切強(qiáng)度、抗蠕變性能及疲勞壽命,其性能在很多方面與Sn-Pb焊料相當(dāng),是較有應(yīng)用前景的低溫?zé)o鉛焊料。由于傳統(tǒng)鑄造法制備的Sn-58Bi合金中含有大量脆性初晶Bi相,難以實(shí)現(xiàn)Sn-Bi桿/絲的高效加工,如何提高Sn-58Bi合金的道次加工率,縮短制備加工流程,實(shí)現(xiàn)細(xì)徑Sn-Bi合金材料的低成本、高效率的制備始終是該領(lǐng)域的關(guān)鍵技術(shù)問題。本文采用上引連續(xù)鑄造的方法制備直徑8 mm的Sn-58Bi合金桿材,與傳統(tǒng)直接澆鑄的同成分合金材料進(jìn)行了組織和力學(xué)性能對比,發(fā)現(xiàn)上引連續(xù)鑄造的方法有效改善了材料的微觀組織,大幅度提高材料的塑性,在此基礎(chǔ)上,通過自行設(shè)計的在線加熱拉拔減徑裝置實(shí)現(xiàn)了上引連鑄Sn-58Bi桿材的大變形量多道次拉拔,跟蹤研究材料組織性能在拉拔變形過程中的變化規(guī)律,并研究評價熱處理工藝參數(shù)對材料拉伸性能的影響規(guī)律。主要結(jié)論如下:(1)通過上引連續(xù)鑄造制備Sn-58Bi合金桿材,并研究熱處理對上引桿材組織性能的影響。與直接澆鑄的Sn-58Bi合金相比,上引桿材的組織得到了顯著的細(xì)化,形成Sn相相互連接的組織特征,消除了圓形的初晶富Sn相,在縱向方向上形成平行排列的長條狀富Bi相一次枝晶,組織特征的顯著變化影響了材料的斷裂機(jī)制,由此引起上引桿材延伸率的大幅度提高,達(dá)到42.5%,與之相比,直接澆鑄合金的延伸率僅為5%。熱處理對上引桿材組織性能影響顯著,保溫?zé)崽幚泶龠M(jìn)富Sn相中過飽和固溶Bi元素的析出,出現(xiàn)粗大富Sn相,高溫保溫和低溫長時保溫均導(dǎo)致延伸率的降低,僅在低溫短時保溫時,上引桿材的塑性得以提高。(2)通過拉拔工藝優(yōu)化實(shí)現(xiàn)上引Sn-58Bi合金桿材多道次(37)8 mm→(37)7 mm→(37)6.5 mm→(37)6 mm→(37)5.5 mm加熱拉拔。研究拉拔溫度、拉拔速度對(37)8 mm→(37)7 mm單道次拉拔的影響規(guī)律,得到了較優(yōu)的拉拔溫度范圍為45℃—55℃之間,拉拔速度范圍為250mm/min—500 mm/min之間,在此基礎(chǔ)上,進(jìn)一步研究拉拔參數(shù)對(37)7 mm→(37)6.5 mm→(37)6mm→(37)5.5 mm多道次拉拔力和拉拔態(tài)合金性能的影響規(guī)律,優(yōu)化工藝參數(shù),成功實(shí)現(xiàn)上引桿材(37)8 mm→(37)5.5 mm的穩(wěn)定拉拔。(3)研究退火熱處理對拉拔態(tài)Sn-58Bi合金性能的影響規(guī)律。在40—60℃溫度范圍內(nèi),隨著保溫時間的延長,經(jīng)熱處理后的拉拔態(tài)Sn-58Bi合金抗拉強(qiáng)度均不斷提高,延伸率先升高后降低,通過對直徑5.5 mm拉拔態(tài)合金進(jìn)行50℃/0.5 h的保溫處理,實(shí)現(xiàn)了(37)5.5 mm→(37)5 mm單道次拉拔。(4)通過減小道次變形量和增加加工道次,順利實(shí)現(xiàn)(37)5.5→(37)3.8 mm的多道次拉拔,研究對比了直徑為5.5 mm拉拔態(tài)桿材是否進(jìn)行熱處理對合金后續(xù)各道次拉拔力的影響。
[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，

本文編號：1456260