7N01空心铝型材挤压横向焊缝演变规律研究

发布时间：2018-03-27 21:58

本文选题：7N01铝合金　切入点：空心型材　出处：《山东大学》2017年硕士论文

【摘要】：随着全球大气污染问题不断突出,节能减排的重要性日益凸显。在高速列车领域,车体轻量化是实现节能减排的重要途径之一。铝合金具有质量轻、比强度高、可焊性好、导电导热性好、耐腐蚀、回收再生性高等优点,是目前高速列车实现车体轻量化的最理想材料之一。目前高速列车的承载结构主要采用7×××系铝合金挤压型材。在铝型材连续挤压生产过程中,两根相邻挤压坯料间的界面会在型材内部形成横向焊缝,而横向焊缝将导致型材性能下降,需要对包含横向焊缝区域的型材进行切除,显著降低了产品的成品率。由于7×××系铝合金硬度较高,材料流动性能较差,所以型材中横向焊缝的延伸长度会大大增加,特别是空心型材中横向焊缝延伸长度增加更为明显,严重影响了产品成品率。因此,开展对7×××系空心铝型材挤压横向焊缝的相关研究具有非常重要的工程意义。本文以高速列车用7N01空心铝型材为研究对象,采用实验研究和数值模拟相结合的方法开展对横向焊缝演变规律和微观组织的系统研究。本文所做的主要工作和所获得主要结论如下:(1)进行了 7N01空心铝型材挤压实验,研究获得了空心型材中横向焊缝的宏观形貌和演变规律。同时利用SEM和EBSD测试技术对横向焊缝区域的微观组织、织构组成及含量和拉伸断口形貌等进行了观察和分析,研究结果表明,横向焊缝区域新坯料和旧坯料的晶粒尺寸、织构含量和拉伸断口形貌等均存在明显差异。(2)实验测试了 7N01铝合金铸锭的力学性能参数及热物理性能参数。通过热压缩实验获得了不同应变速率和不同变形温度下7N01铝合金的应力-应变数据,并且对实验数据进行了摩擦和温度的双重修正,基于修正后的数据建立了7N01铝合金应变补偿型Arrhenius本构模型和热加工图。(3)根据所获得的力学-热物性参数及本构模型参数,利用HyperXtrude软件建立了 7N01空心铝型材横向焊缝演变过程模拟模型。通过与挤压实验中所获得的料头形状、挤压压力曲线、横向焊缝形貌及横向焊缝延伸长度等结果进行对比,验证了本文所采用的力学-热物性参数、本构模型及横向焊缝数值模型的准确性。(4)利用所建立的横向焊缝模拟模型,研究了挤压工艺参数和模具结构参数对横向焊缝延伸长度的影响规律。研究发现,除挤压温度外,适当调整挤压速度、挤压比以及阻流块高度、焊合室圆角半径和分流桥下沉深度等均可有效减小横向焊缝的延伸长度。
[Abstract]:The importance of energy saving and emission reduction is becoming more and more prominent along with the global air pollution problem. In the field of high-speed trains, the lightweight of the car body is one of the important ways to achieve energy saving and emission reduction. Aluminum alloy has light quality, high specific strength, good weldability. Good thermal conductivity, corrosion resistance, high recovery and regeneration, etc. At present, it is one of the most ideal materials for the high-speed train to realize the lightweight of the car body. At present, the bearing structure of the high-speed train mainly adopts the 7 脳脳脳 series aluminum alloy extruded section. In the process of continuous extrusion of aluminum profile, The interface between the two adjacent extruded billets will form a transverse weld inside the profile, and the transverse weld will lead to the deterioration of the profile properties. Because the hardness of 7 脳脳脳 series aluminum alloy is higher and the material flow property is poor, the extension length of transverse weld in the profile will increase greatly, especially in the hollow section. Therefore, it is very important to study the extrusion transverse weld of 7 脳脳脳 series hollow aluminum profile. In this paper, the 7N01 hollow aluminum profile used in high-speed train is taken as the research object. A systematic study on the evolution and microstructure of transverse weld was carried out by means of experimental study and numerical simulation. The main work and main conclusions obtained in this paper are as follows: (1) the extrusion experiment of 7N01 hollow aluminum profile is carried out. The macroscopic morphology and evolution of transverse weld in hollow profile were studied. The microstructure, texture composition, content and tensile fracture morphology of transverse weld were observed and analyzed by SEM and EBSD. The results show that the grain size of the new and old billets in the transverse weld zone, The mechanical properties and thermophysical properties of 7N01 aluminum alloy ingot were tested by experiments. Different strain rates and different deformation temperatures were obtained by thermal compression test. Stress-strain data of 7N01 aluminum alloy under degree, Based on the modified data, the strain compensated Arrhenius constitutive model and hot working diagram of 7N01 aluminum alloy are established. A simulation model of transverse weld evolution of 7N01 hollow aluminum profile was established by using HyperXtrude software. The results were compared with the results obtained from extrusion experiments, such as head shape, extrusion pressure curve, transverse weld appearance and transverse weld extension length, etc. The accuracy of the mechanical and thermal physical parameters, constitutive model and numerical model of transverse weld are verified by using the established transverse weld simulation model. The influence of extrusion process parameters and die structure parameters on the extension length of transverse weld is studied. It is found that, besides extrusion temperature, extrusion speed, extrusion ratio and block height should be adjusted properly. The angle radius of welding chamber and the sinking depth of shunt bridge can effectively reduce the extension length of transverse weld.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG379

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