Al-Zn-Mg合金多种角焊缝接头焊接性与力学性能研究

发布时间：2018-04-30 10:15

本文选题：7N01铝合金 + 角焊缝　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：我国的高速列车研发及生产正处于快速发展的阶段,Al-Zn-Mg系合金中的7N01铝合金在满足轻量化制造要求的同时由于其优秀的力学性能广泛应用在高速列车车体底架的枕梁、抗蛇形运动减震器等关键部位。由于轻量化及抗形变等性能的要求,在进行焊接时通常只能采取含角焊缝的焊接接头实现连接,复杂的多维应力载荷和接头结构使得接头成为车体底架联系的关键和薄弱部位。本研究中通过对7N01铝合金搭接、T型、十字(联系焊缝)、十字(工作焊缝)接头及其厚板性能的综合性能探究,为高速列车的高质量制造提供了科学性依据。为了探究含角焊缝的焊接接头在多向承载的服役过程中的性能,对四种接头进行对比性多角度的静力学性能及组织分析,得到了接头间抗拉强度、弯曲性能、接头内各局部区域显微性能的对比性结果。从微观组织角度分析了宏观性能方面的差异,对角焊缝接头静载性能进行了综合性总结。针对高速列车中焊接结构的主要破坏形式即疲劳失效行为,为了探究不同类型角焊缝接头之间疲劳性能的差异,对四种接头进行了不同最高应力等级的疲劳性能实验,计算得到了各接头的疲劳性能并进行对比,对产生疲劳断裂的试件进行宏观及扫描电镜微观形貌观察分析,分析了疲劳由源区到扩展区直至发生瞬断的破坏过程。结合疲劳性能实验中四种接头出现的对比性疲劳强度结果以及疲劳试件均断裂于焊趾而非焊根这一规律性现象。基于缺口应力法,利用有限元模拟软件Abaqus/CAE对四种接头具体模型进行拟合,模拟缺口局部位置的应力分布状态,计算出对应区域的缺口应力强度因子,通过相关理论转化为平均能应变能密度并进行对比,得到各接头局部平均应变能密度即应力分布与其疲劳极限值成反比,基于缺口应力法建立平均应变能密度与疲劳寿命之间的关系。作为焊接母材的厚板铝合金为轧制过程而来,由于焊接热过程的应力及低熔物质聚集的影响,在焊接加工过程中可能会产生液化裂纹等危险破坏。为了探究这一失效形式的倾向性,进行了Z向窗口试验,放大了角焊缝对厚板铝合金的拘束作用,通过扫描电镜线扫描对层间液化位置的低熔点物质元素含量分布进行分析,结合高温延性理论得出垂直于铝合金轧制方向为其高温承载危险取向。
[Abstract]:The development and production of high speed train in China is in the stage of rapid development. The 7N01 aluminum alloy in Al-Zn-Mg series alloy can meet the requirements of lightweight manufacturing, and its excellent mechanical properties are widely used in the sleeper beam of the frame of high-speed train body because of its excellent mechanical properties. Anti-snake motion shock absorber and other key parts. Due to the requirement of lightweight and anti-deformation, welding joints with fillet welds can only be welded. The complex multi-dimensional stress load and joint structure make the joint become the key and weak part of the frame connection. In this study, the comprehensive properties of 7N01 aluminum alloy lap T type, cross (joint weld), cross (working weld) joints and their thick plates were investigated, which provided scientific basis for high quality manufacture of high speed trains. In order to investigate the performance of welded joints with fillet welds in the service process of multi-direction bearing, the static properties and microstructure of four kinds of joints were analyzed at different angles, and the tensile strength and bending properties of the joints were obtained. Comparative results of the microscopic properties of the local areas in the joints. The differences in macroscopic properties were analyzed from the point of view of microstructure, and the static load properties of fillet weld joints were summarized. In view of the fatigue failure behavior of welded structure in high-speed train, in order to explore the difference of fatigue performance among different types of fillet weld joints, four kinds of joints with different highest stress levels were tested. The fatigue properties of the joints were calculated and compared. The microscopic morphology of the specimens with fatigue fracture was observed and analyzed, and the failure process from the source region to the spreading region to the transient fracture was analyzed. In combination with the comparative fatigue strength results of the four joints in the fatigue performance test and the regularity that the fatigue specimens are broken at the weld toe instead of the weld root. Based on the notch stress method, four specific models of joints are fitted by finite element simulation software Abaqus/CAE, and the stress distribution of the local position of the notch is simulated, and the notch stress intensity factor in the corresponding region is calculated. The local average strain energy density of the joints is inversely proportional to the fatigue limit value of the joints, which is transformed into the average strain energy density by the relevant theory and compared with the local average strain energy density of the joints. The relationship between average strain energy density and fatigue life is established based on notch stress method. The thick plate aluminum alloy, which is the base metal of welding, comes from rolling process. Because of the stress of welding heat process and the effect of low melting material accumulation, liquefaction crack and other dangerous damage may occur in welding process. In order to explore the tendency of this failure form, the Z-direction window test was carried out to amplify the restraint effect of the fillet weld on the thick plate aluminum alloy, and the distribution of the low melting point material elements in the liquefaction position between the layers was analyzed by scanning electron microscope (SEM) line scanning. Combined with the theory of high temperature ductility, it is concluded that the direction perpendicular to the rolling direction of aluminum alloy is the dangerous orientation of high temperature bearing capacity.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407

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