Influence of tool pin profile on microstructure and corrosion behaviour of AA2219 Al-Cu alloy friction stir weld nuggets

To overcome the problems of fusion welding of aluminium alloys, the friction stir welding(FSW) is recognized as an alternative joining method to improve the mechanical and corrosion properties. Tool profile is one of the important variables which affect the performance of the FS weld. In the present work, the effect of tool profile on the weld nugget microstructure and pitting corrosion of AA2219 aluminium-copper alloy was studied. FSW of AA2219 alloy was carried out using five profiles, namely conical, square, triangle, pentagon and hexagon. The temperature measurements were made in the region adjacent to the rotating pin. It was observed that the peak temperature is more in hexagonal tool pin compared to the welds produced with other tool pin profiles. It is observed that the extensive deformation experienced at the nugget zone and the evolved microstructure strongly influences the hardness and corrosion properties of the joint during FSW. It was found that the microstructure changes like grain size, misorientation and precipitate dissolution during FSW influence the hardness and corrosion behaviour. Pitting corrosion resistance of friction stir welds of AA2219 was found to be better for hexagon profile tool compared to other profiles, which was attributed to material flow and strengthening precipitate morphology in nugget zone. Higher amount of heat generation in FS welds made with hexagonal profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone.

A New Characterization Approach of Weld Nugget Growth by Real-Time Input Electrical Impedance

The in-process changes of weld nugget growth during the Resistance Spot Welding were investigated based on the resistance of input electrical impedance. To compute the time varying resistance of input electrical impedance, the welding voltage and current signals are measured simultaneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying resistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nugget growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions.

Effects of nugget alloying on microstructures and properties of resistance spot welded joints of aluminum and steel

The resistance spot welding of 6063-T6 aluminum alloy and 16Mn steel was studied by nugget alloying. The results indicated that the Al-steel joint had characteristics of welding-brazing. The nugget zone consisted mainly of α-Al solid solution with dislocations and fine Mg2Si particles. The interface zone had a double-layer structure： Fe2Al5 layer at steel side and Fe4Al13 layer at Al nugget side. The nugget alloying has a significant effect on the joint properties by changing phase composition and refinement of grains. When alloy elements Cu, Zn, Ti and Ni were added, the tensile shear load of Al-steel joints reached 2 780 N, 2 910 N, 2 915 N and 2 929 N respectively, which increased by 24. 1%, 29.9%, 30. 1% and 30. 7% respectively compared with that （2 241 N） of joint without nugget alloying. Therefore, it is an effective way for improving mechanical properties of resistance spot welded Al-steel joints.

FEATURE ANALYSIS AND EXTRACTION OF INNER DEFECTS FOR SPOT WELD NUGGET OF ALUMINUM ALLOY

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Effect of retained austenite and nonmetallic inclusions on the thermal/electrical properties and resistance spot welding nuggets of Si-containing TRIP steels

Five advanced high-strength transformation-induced plasticity(TRIP) steels with different chemical compositions were studied to correlate the retained austenite and nonmetallic inclusion content with their physical properties and the characteristics of the resistance spot welding nuggets. Electrical and thermal properties and equilibrium phases of TRIP steels were predicted using the JMatPro? software. Retained austenite and nonmetallic inclusions were quantified by X-ray diffraction and saturation magnetization techniques. The nonmetallic inclusions were characterized by scanning electron microscopy. The results show that the contents of Si, C, Al, and Mn in TRIP steels increase both the retained austenite and the nonmetallic inclusion contents. We found that nonmetallic inclusions affect the thermal and electrical properties of the TRIP steels and that the differences between these properties tend to result in different cooling rates during the welding process. The results are discussed in terms of the electrical and thermal properties determined from the chemical composition and their impact on the resistance spot welding nuggets.

Numerical and Experimental Study on Nugget Formation Process in Resistance Spot Welding of Aluminum Alloy

The weld nugget formation in the resistance spot welding(RSW) of aluminum alloy was investigated in the present study. The nugget formation process was directly observed by using a digital high-speed camera. Numerical simulation was also employed to investigate the nugget formation process. The results showed that for the RSW of two aluminum alloy sheets, a nugget was first formed in the workpiece/workpiece(W/W) interface and grew along the radial direction and axial direction of the sheets, and then it became a large elliptical nugget. For the RSW of three aluminum alloy sheets, two small nuggets were firstly formed in two W/W interfaces and grew along the axial direction and radial direction; finally they fused into one nugget. Besides, there existed a critical welding time, after which the nugget size remained nearly unchanged. This indicates that a long welding time is unnecessary for the RSW of aluminum alloy. In addition, the calculated nugget radius was compared with the experimental results, which showed that the simulation results agreed well with the experimental results.

An Artificial Neural Network for Estimating Sizes of Spot Welding Nuggets

Sizes of nuggets are often used to evaluate spot weld quality in production. This paper presents a neural estimator used to carry out non-destructive on-line analysis of spot weld quality in which trained ANN functions to map dynamic resistance characteristics into sizes of spot weld nuggets and results confirm the validity of neural network for this type of application.

6061铝合金FSW接头组织与耐蚀性能的研究

对4 mm厚的6061-T6铝合金板进行了搅拌摩擦焊接,通过浸泡腐蚀试验和电化学腐蚀试验研究焊缝腐蚀性能,采用金相显微镜、透射电镜等观察接头的微观组织。结果表明:6061铝合金FSW焊核区晶粒显著细化,晶界第二相较少;焊核区的耐剥落腐蚀和晶间腐蚀性能优于热影响区的;焊核区比热影响区的腐蚀电位较高,腐蚀电流密度较小,焊核区表现出更好的耐腐蚀性能。

Friction stir welding of aluminum to copper—An overview

Components made by joining different materials are required in various engineering applications.Fabrication of suchcomponents is a challenging task due to the vast difference in mechanical,thermal and electrical properties of the materials beingused.Friction stir welding(FSW)is capable of joining dissimilar materials such as aluminum(Al)and copper(Cu)and thereforeresearchers have used this novel process for dissimilar joining.Consequently,several works pertaining to dissimilar joining,specifically Al?Cu,are available in the literature but they are scattered in different sources,which makes the task of gatheringinformation about dissimilar FSW of Al?Cu cumbersome.This work has been written with an aim to provide all pertinentinformation related to dissimilar FSW of Al?Cu at one place to ease the problems of researchers.It comprehensively covers andsummarizes the topics such as the effect of tool design and geometry,FSW process parameters,FSW strategies on mechanicalproperties,microstructure and formation of defects during dissimilar FSW of Al?Cu.In addition,it also presents and discussesseveral variants of dissimilar FSW of Al?Cu.Finally,this work not only puts forth major findings of the previous researchers but alsosuggests future recommendations for dissimilar FSW of Al?Cu.

基于相关性分析和SSA-BP神经网络的铝合金电阻点焊质量预测

基于电阻点焊过程中工艺信号特征,在不同间距、不同间隙和不同间距与间隙3种条件下,引入相关性分析方法分析工艺信号与熔核直径之间的相关性,并建立基于麻雀搜索算法-BP神经网络(sparrow search algorithmback propagation neural network,SSA-BP)的电阻点焊质量预测模型,将功率、焊接电流、焊接电压和动态电阻作为预测模型输入特征.结果表明,经麻雀搜索算法优化后的BP神经网络在测试集上的决定系数R2、均方误差(meansquare error,MSE)、均方根误差(root mean square error,RMSE)和平均绝对误差(mean absolute error,MAE)分别为0.95,1.55,1.24和0.90,均优于BP模型.获得了功率、焊接电流、焊接电压和动态电阻与熔核直径的映射关系,可为焊接的工艺参数设计提供依据.

MICROSTRUCTURAL STUDIES OF FRICTION STIR WELDED AZ31 MAGNESIUM ALLOY

Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.

Comparison of 2A12 aluminium alloy joint by ultrasonic assisted friction stir welding and friction stir welding

Ultrasonic assisted friction stir welding （UAFSW） is a recent modification of conventional friction stir welding, which adds ultrasonic energy directly into the friction stir welding area by the pin. In this study, 2A12 aluminum alloy was welded by this process and conventional, respectively. The tensile tests, microstructure and fracture surface of FSW joint and UAFSW joint were analyzed. The research results show that the surface forming texture of ultrasonic assisted friction stir welding joint, compared with conventional, is finer and more uniform, showing metallic matte color. The grains are much finer in weld nugget zone, thermo-mechanically affected zone and heat-affected zone; S-phase particles size is much smaller and distribution is more homogeneous in the matrix. The tensile strength of UAFSW joint is 94. 13% of base metal, and the elongation is 11.77%. The tensile strength of FSW joint is 83.15% of base metal, and the elongation is 8.81%. The tests results reveal that ultrasonic vibration can improve the tensile strength and the elongation of welded joints.

机器人点焊板材厚度检测的数值模拟与变量程序应用研究

针对轿车车门内板点焊过程中,机器人伺服焊枪经过多个焊点操作后工件间隙扩大,以及钣金厚度变化造成的焊接质量下降问题。基于ANSYS有限元技术对高强度双相钢机器人点焊过程进行热传导数值模拟分析,研究板材厚度变化对焊接热传导效率及熔核直径大小的影响。试验结果表明,当板材厚度为1.9~2.0 mm时,熔核直径达到最大值,随着板材厚度的增加,熔核直径减小,焊接质量下降。为解决这一问题,运用KUKA机器人伺服焊枪的板材厚度动态检测功能和变量程序跳转指令,在板材厚度超出公差值(1.8~2.5 mm)时中断机器人焊接程序并及时报警,减少了板材间隙增大带来的飞溅、虚焊等缺陷,提高形核质量和焊接精度,保证车门内板高强度双相钢点焊的前后焊点质量稳定。

Cracking Phenomenon in Spot Welded Joints of Austenitic Stainless Steel

The spot welds nugget cracking of austenitic stainless steel at temperatures between 700°C - 1010°C was investigated. Traditionally, the cracks have been observed around the spot nugget in welded temperature. Actually, these cracks are developed due to incomplete melting and inappropriate electrode pressure, which causes an expulsion of molten metal. These cracks start to grow and cause either the interface or plug fracture according to the loading type. In this work, the micro-cracks in the weld nugget were indicated for this type of steel at elevated temperature. Cracks appear in a certain range of temperature;about 700°C - 750°C. The cracks like defect and cavitations were presented. According to the fracture mechanics point of view, these cracks reduce the mechanical strength. Therefore, these cracks have to be taken into account with a certain precaution. Moreover, considering the working temperature and reducing the element may develop ferrite particles.

Energy-storage welding connection characteristics of rapidly solidified Cu-Co alloy foils

The connection characteristics of rapidly solidified Cu-40%Co alloy foils were studied using a self-developed micro-type energy-storage welding machine. The results show that the microstructure of the alloy foils is characterized by uni form and fine equiaxed grains,whose maximum grain size is 1.8 μm. Under the o ptimum energy,the regular flat nugget is formed,low voltage and high capacitan ce are favorable for obtaining the perfect connection joints,whereas high volta ge and low capacitance are likely to result in the surface burn of the alloy foi ls. With the increase of welding energy,the spot welding joint will be transfor med from regular flat nugget to nugget-free one,and the microstructure tends t o coarsen. The welding parameters recommended are: welding voltage 80100 V,(electric) capacitance 1 8002 500 μF,and welding force 48 N.

A cooperative control strategy of resistance spot welding process by combining the constant current control with the DRC method

The modeling control method based on the dynamic resistance characteristics of good nuggets, that is the DRC method, is an improvement on the dynamic resistance threshold method for the quality control of resistance spot welding. But there is still a control blind area in the initial four cycles. For this reason, the quality of every weld nugget could not be fully ensured. Thus a new fuzzy cooperative control method is put forward. It uses a multi-information time-control mechanism by combining the constant current control technology with the DRC method in a relay way. This whole-process control strategy has led to a good control effect and produced the dual-identical results in the weld nugget quality and the welding time.

Ultrasonic C-scan Detection for Stainless Steel Spot Welding Based on Wavelet Package Analysis

An ultrasonic test of spot welding for stainless steel is conducted. Based on wavelet packet decomposition, the ultrasonic echo signal has been analyzed deeply in time - frequency domain, which can easily distinguish the nugget from the corona bond. The 2D C-scan images produced by ultrasonic C scan which contribute to quantitatively calculate the nugget diameter for the computer are further analyzed. The spot welding nugget diameter can be automatically obtained by image enhancement, edge detection and equivalent diameter algorithm procedure. The ultrasonic detection values in this paper show good agreement with the metallographic measured values. The mean value of normal distribution curve is 0.006 67, and the standard deviation is 0.087 11. Ultrasonic C-scan test based on wavelet packet signal analysis is of high accuracy and stability.

An Electrothermal Model Based Adaptive Control of Resistance Spot Welding Process

Resistance Spot Welding (RSW) is a process commonly used for joining a stack of two or three metal sheets at desired spots. The weld is accomplished by holding the metallic workpieces together by applying pressure through the tips of a pair of electrodes and then passing a strong electric current for a short duration. Inconsistent weld and insufficient nugget size are some of the common problems associated with RSW. To overcome these problems, a new adaptive control scheme is proposed in this paper. It is based on an electrothermal dynamical model of the RSW process, and utilizes the principle of adaptive one-step-ahead control. It is basically a tracking controller that adjusts the weld current continuously to make sure that the temperature of the workpieces or the weld nugget tracks a desired reference temperature profile. The proposed control scheme is expected to reduce energy consumption by 5% or more per weld, which can result in significant energy savings for any application requiring a high volume of spot welds. The design steps are discussed in details. Also, results of some simulation studies are presented.

Rapid ultrasonic C-scan on image test for spot welding based interpolation

In this paper, ultrasonic C-scan test of spot welds for stainless steel has been studied. It is concluded that large scanning step length contributes to high testing efficiency, however, the low-resolution C-scan image generated cannot be used to assess spot welding quality reliably. Based on bicubic image interpolation, the C-scan image in low resolution with the large step length 1 000 ~xm is subdivided and reconstructed. By this means, the C-scan image resolution is greatly enhanced and testing results obtained are satisfactory, realizing rapid assessment of spot welds. The results of rapid ultrasonic C-scan test fit the actual metallographic measured value well. Mean value of normal distribution of error statistics is O. 006 67, and the standard deviation is O. 087 11. Rapid ultrasonic C-scan test based on image interpolation is of high accuracy and excellent stability.