摘要
为适应我国经济发展,电气化列车不断向高速化发展。这必然要求增大接触线的悬挂张力,提高其载流能力及稳定性,来改善机车受流质量。在要求接触线材料有良好导电性的同时,还要有高的强度和抗软化温度。目前,普遍采用的CuAg合金接触线可以满足中低速列车运行需求,但是要满足350km/h及更高的列车运行速度,就必须开发新型的接触线。基于此背景,本文对CuSn合金的成形工艺进行了系统研究。研究的主体框架着重围绕合金化设计、电解抛光、组织性能、电子背散射衍射分析(EBSD)展开。
为给后续的工厂批量生产提供合理的成分依据,通过氩气保护气氛下的铜坩埚真空非自耗电弧炉对材料的合金化进行研究。对不同含Sn量的CuSn合金试样进行力学性能及显微组织形貌的对比分析,最终确定CuSn合金接触线的较佳的含Sn量为0.3%。考虑到在实际上引连铸过程中的元素损耗,配比时成分范围控制在0.3%～0.55%之间。
机械抛光制备金相试样,其表面易产生变形层。故本文以电解抛光原理为依据,以阳极极化曲线为参考,对高速电气化铁路用CuSn合金接触线的电解抛光工艺参数进行了研究。同时,通过对以往电解抛光装置的改进最终确定了CuSn合金接触线电解抛光的最佳工艺参数。研究结果表明:在室温条件下,采用1.5～1.9V的抛光电压,10～15分钟的抛光时间,可以获得CuSn合金接触线的优良金相照片。
本文对高速电气化铁道用CuSn合金接触线的成形工艺进行了系统研究。采用不同工艺对上引连铸法生产的CuSn合金接触线坯杆进行了冷、热成形加工试验,并比较、分析了成品线的性能差异。研究结果表明:CuSn合金接触线的最佳成形工艺为上引连铸→连续挤压→连续轧制→连续拉拔;其抗拉强度为538MPa,延伸率为12%,电阻率为0.02360Ω.mm~2/m,反复弯曲次数为9次,扭转圈数为11圈。综合性能均已达到或超过TB/T 2809—2005标准的要求,满足高速电气化铁道的使用要求。
通过对合金进行电子背散射衍射(EBSD)分析,结果表明:变形过程中晶粒取向、织构转变及晶界分布存在以下规律:
挤压态CuSn合金经30%拉拔冷变形后只出现了<100>丝织构,而当变形量增加至60%时,晶粒取向逐渐偏聚于[111]方向,继续增加变形量至75%后,则出现了稳定的<100>和<111>丝织构。由于剪切应力的作用织构组分由<100>向<111>转变,并且出现了较弱的<112>织构。而随退火温度升高最终也是形成稳定的<100>和<111>丝织构。
随着拉拔变形量的增加,取向差小于8°的小角度晶界数量逐渐上升,其峰值为2.95°,变形量增加至75%后,由于微观组织的演化机制而使59°～61°的大角度晶界数量却明显下降。其间,CSL晶界主要集中在Σ3、Σ9、Σ27、Σ29这四个位置。且Σ3的百分含量由79.56%提高至81%并最终上升至83%。随着退火温度的升高小角度晶界数量也不断上升,且取向分布中出现了较强的孪晶关系Σ3及二次孪晶Σ9和三次孪晶Σ27关系,其三者的总和最终高达90.35%。低ΣCSL晶界含量的增加,使晶界结合力强、晶界能降低,可以减少和避免微裂纹源的产生,且对微裂纹的扩展起到阻碍作用。
In order to meet China's economic development, high-speed electric trains are growing. In order to improve the quality of locomotives by the stream, we must improve the hanging tension carrying current capacity and stability of contact wire. This requires contact wire material not only has good conductivity, but also has a high strength and high resistance to softening temperature. At present, CuAg alloy contact wire is widely used to meet the needs of low-speed train operation. However, to meet the 350km / h and higher train speed, we must develop a new type of contact wire. Based on this background, the forming process of CuSn alloy was studied in detail in this paper. The main study framework will mainly focus on alloy design, electrolytic polishing, organizational performance, and EBSD.
Alloying of materials was studied in the article, in order to meet the needs of mass production in factories. The best amount of CuSn alloys containing Sn has been determined to be 0.3%, by analyzing mechanical properties and microstructure morphology of alloys with different Sn-containing. Because of the actual loss of elements in the smelting process, so control the composition range of 0.3% ~ 0.55%.
Mechanical polishing tends to easily cause deformation of the surface layer of the specimen.The electro-polishing parameters of high-speed electric railroad CuSn alloy contact wire were studied in this paper. This paper is based on the principle of electro-polishing and anodic polarization curves as a reference. The optimum electro-polishing parameters of CuSn alloy contact wire were finally defined by improving of electro-polishing apparatus. The results show that: at room temperature conditions, we can get an excellent CuSn alloy contact wire metallographic by 1.5 ~ 1.9V polishing voltage and 10 ~ 15 minutes polishing time.
The forming technology of high-speed electrified railway CuSn alloy contact wire was studied in this paper. The hot and cold forming test of CuSn alloy contact wire rod blanks were studied by different forming technology. And the performance differences of product lines were compared in this paper. The results show that: The optimum forming technology is upward continuous casting→continuous extrusion→continuous rolling→continuous drawing. The tensile strength reaches to 538MPa, elongation is 12%, electrical resistivity is 0.02360Ω.mm~2/m, alternating bending is 9,torsion test is 11 circle. Combination property have reached or exceeded the TB / T 2809-2005 standard. And it can meet the application requirements of high-speed electrified railway.
The electron backscatter diffraction (EBSD) analysis of alloys was studied in this paper. The results showed that: the law of deformation grain orientation, texture changes and the distribution of grain boundary are as follows.
The extruding CuSn alloy only has <100> silk texture with 30% cold drawing deformation. When the deformation increased to 60%, the grain orientation gradually segregated in [111] direction. Continued to increase to 75% in deformation, the stability of <100> and <111> silk structures can be found. Because of shearing stress the texture component changed from <100> to <111>.And a little <112> texture can be found. The stability of <100> and <111> silk structures also can be found in alloy with different annealing temperature.
There were more and more LAGBs(<8°), with the increase in the amount of drawing deformation.The peak is 2.95°. When the deformation increased to 75%, because of the microstructure evolution mechanismthe, the number of HAGBs(59°～61°) was decreased significantly. CSL grain boundarys mainly focus onΣ3,Σ9,Σ27,Σ29 these four locations. The content ofΣ3 from 79.56% up to 81% and eventually rose to 83%. As the annealing temperature lifting, the number of small-angle grain boundaries increase rapidly. Orientation distribution appeared very strongΣ3(compound twin),Σ9(Secondary compound twin) andΣ27(cubic compound twin). The sum of them was up to 90.35% at last. LowΣCSL grain boundary had strong binding force and low interface energy. They can reduce and avoid the source of micro-cracks generation and impede the expansion of micro-cracks.
引文
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