Numerical Simulation on Nugget Formation and Evolution in Spot Welding of Aluminum Alloy

With the squeeze of electrode tips, the oxide film on aluminum (Al) alloy surface is broken and numbers of micro-gaps are formed randomly. The micro-gaps act as conducting spots at the beginning of welding, so the contact resistance is extremely high and unstable in spot welding of Al alloy. In this paper, a new contact resistance model is adopted to simulate the nugget forming process. This model describes the random distribution characteristic of conducting spots. The simulation results indicate that, within the first 5 ms of welding current (AC, 50 Hz), the temperature distribution at the workpieces interface is seriously irregular. In addition, the nugget does not nucleate from the weld center and grow continuously, however, it nucleates randomly from several points almost instantaneously and then merges into an entity quickly. Experimental results agreed with the numerical simulation.     

Analysis of Acoustic Emission Signal by Fractal Theory in Aluminum Alloy Spot Welding

Spot welding was widely applied inindustries such asaviation, automobile , and other production departments .Aluminumstructures gradually take a prominent positionowingto lightweight and high intensity. But in quality in-spectionof aluminumalloys ,a single electrical parameter orthermal parameters[1]cannot effectivelyforecast the diame-ter of the weld nugget ,the intensity of spot weld, andsplashing duetotheinstabilityof weldzone caused byalloycompositions and fragile surface oxidation. Theref…     

目前国内民族教育研究热点问题的回顾与展望——基于民族教育德育视角

当前我国民族教育德育研究主要围绕民族团结教育、传统文化与德育、家庭道德教育、德育资源开发、留守儿童教育、民族宗教对德育影响、民族教育德育理论、学生思想品德、心理健康、未成年人犯罪、民族认同等前沿与热点问题展开研究。反思研究现状,展望未来研究的关注点,对推动我国民族教育德育研究,进一步深化民族教育改革,不断提高教育教学质量,为少数民族地区社会发展和经济建设培养合格的有用之才有积极意义。     

6061-T5铝合金搅拌摩擦焊接头组织和力学性能

采用搅拌摩擦焊技术对6061-T5铝合金进行焊接,分析了焊接速度对接头成形、微观结构及力学性能的影响.结果表明:随着焊接速度的增加,沉淀相固溶度下降,晶粒细化;焊接速度过大时,热输入不足,呈现原始态组织.当转速为800 r/min,焊接速度为60 mm/min时,接头成形良好,抗拉强度达到最大值.采用合适的搅拌摩擦焊工艺参数,6061-T5铝合金能实现可靠的连接.     

Evolution of Surface Oxide Film of Typical Aluminum Alloy During Medium-Temperature Brazing Process简

The evolution of the surface oxide film along the depth direction of typical aluminum alloy under medium-temperature brazing was investigated by means of X-ray photoelectron spectroscopy （XPS）. For the alloy with Mg content below 2.0wt%, whether under cold rolling condition or during medium-temperature brazing process, the en-richment of Mg element on the surface was not detected and the oxide film was pure Al2O3. However, the oxide film grew obviously during medium-temperature brazing process, and the thickness was about 80 nm. For the alloy with Mg content above 2.0wt%, under cold rolling condition, the original surface oxide film was pure Al2O3. However, the Mg element was significantly enriched on the outermost surface during medium-temperature brazing process, and MgO-based oxide film mixed with small amount of MgAl2O4 was formed with a thickness of about 130 nm. The alloy-ing elements of Mn and Si were not enriched on the surface neither under cold rolling condition nor during medium-temperature brazing process for all the selected aluminum alloy, and the surface oxide film was similar to that of pure aluminum, which was almost entire Al2O3.     

Al-Mg-Si基合金车身板材的研究现状与发展趋势

在制作车身板材的铝合金中,6000系铝合金由于具有强度高,塑性好,优良的耐蚀性等优点而广泛应用于汽车工业。本文主要介绍国内外6000系车身板材的研究现状及发展趋势。分析了汽车铝合金板材主要存在的问题,展望了开发高性能Al-Mg-Si基铝合金板材的研究方向。     

消除测量深孔尺寸误差和形状误差的方法

在精度要求较高而且较深的内孔尺寸测量中,往往存在尺寸上的误差,通过采用百分表轴向方向尺寸测量和径向方向尺寸测量重合法,可有效消除测量时的深孔尺寸误差和形状误差,保证工件加工质量。     

Pinless Friction Stir Welding of AA2024-T3 Joint and Its Failure Modes

The joining of aluminum alloy sheets with thickness less than 2.0 mm is difficult via conventional frictionstir welding owing to the defects in the joint, such as root flaw, keyhole and lazy S. In the present research, a newlydesigned pinless tool with involute grooves on its shoulder surface was applied to weld 1.5 mm thick AA2024-T3. Theeffects of the rotating speed and welding speed on the microstructure and mechanical properties of the joints were analyzed.The experimental results showed that the root flaw and keyhole were successfully eliminated. The lazy S wasalso eliminated under the optimized welding parameters. The maximum tensile strength of the joints was 326 MPa,which is about 74.1% that of the base material. Moreover, all the tensile samples fractured from the retreating side.Two fracture modes were observed during the tensile tests, which are related with the lazy S.     

7075铝合金弧状TIG焊缝温度场数值模拟

对7075铝合金模型采用ANSYS有限元软件划分单元,利用函数功能实现热源移动的计算;并对该合金TIG焊接的热过程进行了计算机数值模拟的可行性研究。结果表明,焊接时温度场的分布呈现出一定的温度梯度,且以焊缝为中心对称。     

车身用6061-T6铝合金薄板电阻点焊工艺参数研究

采用MULTISPOT MI-100电阻焊机,对车身用6061-T6铝合金薄板实施电阻点焊,研究并得到电阻点焊最佳工艺参数。然后,运用正交试验方案和极差分析方法对电阻焊工艺参数进行试验和进一步优化设计。在对2mm厚度的6061-T6铝合金薄板进行搭接电阻点焊后,分析焊接外观并完成拉伸测试,测试结果表明:当焊接电流60KA、焊接压力0.63MPa、板材厚度2.00mm时,试样所获得的点焊接头无明显缺陷,成型较好,具有良好的焊接质量和外观,其抗拉剪力值最大为5.583KN。     

Sensors Array Technique for Monitoring Aluminum Alloy Spot Welding

In this paper,the sensors array technique is applied to the quality detection of aluminum alloy spot welding.The sensors array has three forms,i.e.,linear magnetic sensors array,annular magnetic sensors array and cross magnetic sensors array.An algorithm based on principal component analysis is proposed to extract the signal eigenvalues.The three types of magnetic sensors array are used in the experiment of monitoring the signal.After the eigenvalues are extracted,they are used to build a relationship with ...     

空调风机内部复杂旋涡流动现象研究

为了解不同空调风机的内流机制,采用数值分析和PIV实验研究相结合的方法对空调用贯流风机和轴流风机内部复杂的旋涡流动现象进行了研究。结果表明:空调壁挂机用贯流风机内部偏心涡沿轴向具有明显的三维分布特性,偏心涡径向位置沿轴向几乎没有变化,其周向位置沿轴向不断改变。贯流风机偏心涡卷吸区域随负载提高而增强。高负载时,偏心涡更加靠近叶轮中心和蜗壳方向。空调室外机用开式斜流风轮的叶尖涡产生于距叶片前缘1/4区域,靠近吸力面。叶尖涡随风轮转速的提高而增强,并沿着与风轮旋向相反的方向朝下游发展。     

铝合金焊接方法的研究现状

概述了铝合金几种先进的焊接方法:钨极氩弧焊、电子束焊、激光焊及搅拌摩擦焊。重点介绍了铝合金最有前途的固相连接方法——搅拌摩擦焊,并展望了铝合金搅拌摩擦焊的应用前景。指出搅拌摩擦焊是铝合金最好的连接工艺,应深入研究。     

超薄铝合金光纤激光焊接研究

针对超薄铝合金箔片（0.18mm）进行了光纤激光高速焊接试验研究,分析了影响光纤激光焊接效果的主要因素.通过对铝合金光纤激光焊接特性的分析,得出焊接头的准直镜与聚焦镜的焦距等对焊接接头形貌有着重要的影响的结论.在适宜的焊接工艺参数下,光纤激光焊接接头上、下表面焊缝形貌平整连续,焊缝一致性良好,拉力足够.     

Al-Li-Er合金的激光焊接工艺与组织性能研究

采用激光填丝焊对Al-Li-Er铝合金进行焊接处理,研究激光功率、焊接速度和送丝速度对焊接接头显微组织与力学性能的影响.结果表明,当送丝速度为3 m/min和4 m/min时,Al-Li-Er合金焊接接头的焊缝面积都会随着激光功率和焊接速度的增大而逐渐减小;在相同激光功率和焊接速度时,送丝速度的增加会增大焊缝面积,且随...     

半解析法求解含轴向浅槽复合材料圆柱壳的非线性动力响应及屈曲问题

The effect of axial shallow groove on the nonlinear dynamic response and buckling of laminated cylindrical shells subjected to radial compression loading was investigated. Based on the first-order shear deformation theory （FSDT）, the nonlinear dynamic equations involving the transverse shear deformation and initial geometric imperfections were derived with the Hamilton philosophy. The axial shallow groove of the laminated composite cylindrical shell was treated as the initial geometric imperfections in the dynamic equations. A semi-analytical method of expanding displacements and loads along the circumferential direction and employing the finite difference method along the axial direction and in the time domain is used to solve the governing equations and obtain the dynamic response of the laminated shell. The B-R criterion was employed to determine the critical loads of dynamic buckling of the shell. The effects of the parameters of the shallow groove on the dynamic response and buckling were discussed in this paper and the results show that the axial shallow grooves greatly affect the dynamic response and buckling.     

对A6061铝合金的镗孔表面粗糙度研究

铝合金材质具有质量轻、耐候性好、结构强度大、耐腐蚀等诸多优点,市场前景和潜力良好,已在航空、高铁、精密设备、通信设备等领域得到广泛应用。文章就铝合金材料的准高速切削进行试验,从镗削表面质量方面对铝合金工件的加工进行研究,力求能对铝合金工件的制造提供较为系统的制造工艺参数。     

Experimental and Finite Element Study of Steady State Micro-cutting Characteristics of Aluminum Alloy （2A12）

This paper studies the micro-cutting characteristics of aluminum alloy (2A12) based on a series of orthogonal experiments and finite element method (FEM) simulations. An energy-based ductile failure law was proposed in the FEM simulation. The simulated cutting forces and chip morphology were compared with experimental results. The simulation result indicates that there is a close relationship between the cutting force and cutting heat. The micro-cutting force decreases as the heat flux vector increases. Both the cutting heat and the micro-cutting force need a finite time to achieve a steady state. It is observed that with the cutting speed of 169.95 m/min and uncut chip thickness of 6 μm, the heat flux vector in the workpiece increases to a stable value after 0.06 ms; meanwhile, the principal cutting force decreases to a steady state correspondingly, i.e., the micro-cutting process achieves the steady state. It is concluded that the steady state micro-cutting simulation can reflect the cutting process accurately.     

永磁轴承动力学性能分析

本文中给出了由一对磁环轴向充磁组成的轴向永磁轴承,并采用等效电流法计算两磁环之间的轴向力,阐明了永磁轴承在某一方向不稳定的原因。根据特定的永磁轴承实体模型,给出了其动力学方程,并对轴向的非线性运动方程用迦辽金法求出了方程的解析解。通过利用matlab软件进行仿真,证明了特定的永磁轴承在小气隙内磁环可以获得小振幅的稳定模态。     

内压简体周向开设矩形排孔的三维有限元分析

利用有限元分析软件ANSYS Workbench对某内压筒体沿周向开设矩形排孔的结构进行有限元分析,得到该结构的应力分布状况和最高应力水平,并据标准对此结构进行了强度评定。分析结果表明,沿筒体轴向因开孔致应力集中的影响范围较小,而周向各接管开孔应力集中的影响互相叠加,其范围遍布筒体的整个周向,最大应力分布在各接管拐角和各接管与筒体的角焊缝处,故矩形接管的焊缝应全焊透且需进行表面渗透检测,以满足JB4730I级合格标准,并避免安排在拐角处。