Effects of welding parameters on electrode element diffusion during micro-resistance spot welding

Copper electrodes are commonly employed in micro-resistance spot welding (MRSW), a dominant process used to join ultra-thin metallic sheets. During welding, some copper from the electrodes inevitably diffuses into the spot welds, changing the chemical compositions and properties of the resulting welded joints. In this study, 0.05-mm-thick Ti alloy metallic sheets were welded via MRSW under various combinations of welding parameters (ramping time, welding time, holding time, welding current, and electrode force). The effects of these welding parameters on electrode elemental diffusion were investigated via elemental analysis. Elemental composition of welded joints was measured via energy-dispersive spectrometry after tensile-shear tests. No copper was detected in the heat-affected zone or base material, but the amount of copper in the welding nuggets varied significantly with the welding parameters. Moreover, comparing copper element and hardness maps in weld nugget, the welding nugget hardness increased when more copper diffused into it.     

Statistical analysis to predict grain size and hardness of the weld nugget of friction-stir-welded AA6061-T6 aluminium alloy joints

AA6061 aluminum alloy has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to-weight ratio and good corrosion resistance. Friction-stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The FSW process and tool parameters play a major role in deciding the joint strength. Joint strength is influenced by grain size and hardness of the weld nugget region. Hence, in this investigation an attempt was made to develop empirical relationships to predict grain size and hardness of weld nugget of friction-stir-welded AA6061 aluminium alloy joints. The empirical relationships are developed by response surface methodology incorporating FSW tool and process parameters. A linear regression relationship was also established between grain size and hardness of the weld nugget of FSW joints.     

搅拌摩擦焊工艺参数对2198铝锂合金焊缝成形及接头力学性能的影响

对2198铝锂合金薄板进行了搅拌摩擦焊试验,分析了搅拌头旋转速度和焊接速度对焊缝成形及接头力学性能的影响。结果表明:旋转速度(n)与焊接速度(v)的比值大于15.7时,能形成表面成形良好,且内部致密无缺陷的焊缝;接头焊核区形成了细小的等轴晶,前进侧热力影响区大部分为等轴状晶粒,后退侧热力影响区的板条状组织发生了变形,其周围出现了细晶粒;焊接速度为30mm·min-1时,接头的抗拉强度随旋转速度的增大而变小,其最大值为432.17MPa,焊缝的硬度低于母材的,热力影响区的硬度最低,焊核区的硬度略高于热力影响区的。随着n/v的增大,热影响区的软化区间变宽。     

铍青铜弹簧触指焊接及热处理关键技术研究

采用熔焊技术,通过硬度、抗拉强度检测及金相分析,对铍青铜（QBe2）弹簧触指成形过程中的焊接及热处理关键技术进行了研究。试验证明,热处理前的弹簧触指焊接接头硬度偏低（平均值为133.6HV）,抗拉强度平均值为534MPa。在真空条件下,Y态＋时效处理条件下的母材与焊接接头的硬度比固溶＋时效状态下的稍高些;时效时间延长至90min时,焊接接头与母材的硬度均达到400HV以上,焊接接头抗拉强度平均值为820MPa,接近QBe2原材料Y态的抗拉强度（872MPa）,从而满足了弹簧触指的使用要求。     

包铝层对7B04-O铝合金薄板搅拌摩擦搭接性能影响

对2 mm厚的带有包铝层的退火态(O态)7B04铝合金薄板进行搅拌摩擦搭接焊接(Friction stir lap welding, FSLW)。分析包铝层、焊接参数、热处理对FSLW接头质量、微观组织及力学性能的影响。结果表明,焊核中的原始包铝层无法被完全打碎分散,其中前进侧的分散比较明显,而后退侧的包铝层则基本保持了原来状态。通过增加转速或轴肩尺寸,可以有效消除焊核中心的孔隙缺陷,但仍无法使界面处的包铝层充分破碎分散。随着转速增加或焊接工具轴肩尺寸增大,FSLW接头强度提高。包铝层对焊态FSLW接头强度影响不明显,接头强度约为母材强度的94%;淬火后,包铝层对接头强度的影响显著,接头强度仅为淬火态母材的64%。     

机械振动对激光焊接接头组织的影响

振动焊接工艺能有效细化接头组织晶粒,降低残余应力,提高焊接质量。为了研究振动焊接工艺在激光焊接方面的应用,选用316不锈钢作为试验材料,利用机械振动辅助激光焊接的工艺方法,通过改变机械振动参数和焊接速度,利用光学显微镜和扫描电镜观察焊后接头组织,对比分析不同振动频率和焊接速度下接头的微观组织形貌。结果表明,机械振动可以细化焊后组织中形成的柱状晶,使柱状枝晶破碎且向不同方向生长,晶轴间与焊缝中心处的等轴晶增加。提高焊接速度后,振动的加入能够细化焊缝区出现的粗大柱状晶。同时,振动可以减少焊后在奥氏体基体晶界处形成的网状高温铁素体和点状碳化物,使其趋于弥散。试验还对焊接接头进行显微硬度测试,发现振动焊接下得到的焊缝区接头组织硬度较高,且较高共振频率下硬度增加明显。     

Effect of weld parameters on mechanical properties and tensile behavior of tungsten inert gas welded AW6082-T6 aluminium alloy

The effect of different welding parameters on the mechanical properties and tensile behavior of tungsten inert gas (TIG) welded joints was analyzed. Four different groove angles were chosen, 60°, 70°, 80° and 90°, to ascertain the tendency of microstructure formation and quality of the weld. Mechanical properties were assessed in the terms of Vickers HV1 hardness. Microanalysis of test samples produced using different current 165 A, 180 A, 200 A with same groove angle of 90° was done in fusion, partially melted, and heat affected zone; all the images showed good penetration and clear transition from one to following zone. The transverse tensile tests were accomplished on the welded joints to evaluate influence of welding parameters and groove geometry to the joint tensile strength and its behavior during exploitation. It was verified that the tensile strength of the welds is closely related to the welding parameters. The chosen 180 A welding current ensured highest tensile strength of test samples; the same as proper selection of groove angle (90°) provides good fusion and high quality of major welds. The results revealed that the weld penetration depends on welding current.

     

Characterization of nugget nucleation quality based on the structure-borne acoustic emission signals detected during resistance spot welding process

Acoustic emission signals detected during the resistance spot welding of aluminum alloy were studied in order to assess the characterizations of welding process, the characterizations of the effect of welding parameters to nugget nucleation and the characterizations of the nugget quality by the analysis to acoustic emission signals. The results showed that the physical phases of nugget nucleation can be characterized by the acoustic emission signals detected during the resistance spot welding process. The effects of welding current and current duration to nugget nucleation can be characterized by the characteristic parameters of acoustic emission signals. The characteristic parameters of acoustic emission signals had a better relevance to nugget dimensions and weld strength, which made it possible to measure or predict the weld strength by the characteristic parameters of acoustic emission signals detected during the resistance spot welding process.     

The effect of welding parameters on fracture toughness of resistance spot-welded galvanized DP600 automotive steel sheets

The aim of this study was to evaluate the fracture toughness of resistance spot welded (RSW) lap joints of galvanized DP600 steels. RSW lap joints galvanized DP600 steel sheets were performed on spot welded in a pneumatic, phase-shift-controlled, and 0–9?kA effective weld current capable AC spot welding machine. Defect-free RSW lap joints were produced on galvanized DP600 steel sheets. Fracture toughness of RSW lap joints were calculated from the results of shearing tensile tests: the dependence of fracture toughness to welding current, welding time, and hardness of welding zone for galvanized DP600 steel sheets. According to the experimental data, the fracture toughness increases as welding current and welding time increase up to a certain value, then the fracture toughness starts to decrease. Also, it was seen that the fracture toughness varies with the hardness of the welding zone. This variation is related to welding current.     

Grey relational and neural network approach for multi-objective optimization in small scale resistance spot welding of titanium alloy

The prediction and optimization of weld quality characteristics in small scale resistance spot welding of TC2 titanium alloy were investigated. Grey relational analysis, neural network and genetic algorithm were applied separately. Quality characteristics were selected as nugget diameter, failure load, failure displacement and failure energy. Welding parameters to be optimized were set as electrode force, welding current and welding time. Grey relational analysis was conducted for a rough estimation of the optimum welding parameters. Results showed that welding current played a key role in weld quality improvement. Different back propagation neural network architectures were then arranged to predict multiple quality characteristics. Interaction effects of welding parameters were analyzed with the proposed neural network. Failure load was found more sensitive to the change of welding parameters than nugget diameter. Optimum welding parameters were determined by genetic algorithm. The predicted responses showed good agreement with confirmation experiments.

     

Study on the thermo-effect of nugget growing in single-phase AC resistance spot welding based on the calculation of dynamic resistance

According to the welding current and electrode voltage detected in resistance spot welding, the dynamic resistance was calculated and the nugget growing thermo-effect in process of nugget forming was studied. The results showed that the process of nugget growth in resistance spot welding can be divided into three stages, which were initial stage, growing stage and stable stage. The welding current provided energy for nugget growth, which showed a high linear relationship with mean dynamic resistance and more prominent polynomial relationship with dynamic resistance heat. The dynamic resistance heat was an important evaluating indicator to the nugget growing thermo-effect, which was closely related to the characteristics of nugget forming. As the dynamic resistance heat was increased, the nugget diameter and tensile shear strength of spot weld were raised and showed a more prominent polynomial relationship. According to the calculation of dynamic resistance heat, these relationships provided a method for the nondestructive test of nugget quality features.     

Design of tool system for the external nonrotational shoulder assisted friction stir welding and its experimental validations on 2219-T6 aluminum alloy

The nonrotational shoulder assisted friction stir welding (NRSA-FSW) is still in the feasibility study stage. To reveal details in the tool system designing and highlight advantages of this novel technology, the tool system for the NRSA-FSW was designed and utilized to weld high-strength aluminum alloy 2219-T6 for validations. Compared with the joints welded by the friction stir welding (FSW) without assistance of the nonrotational shoulder (NRS), the effect of the NRS on the weld formation and mechanical properties was illustrated. At a constant welding speed 100 mm/min, defect-free joints can only be obtained at the tool rotation speed 800 rpm by the FSW without assistance of the NRS, but the NRSA-FSW can produce defect-free joints in a wider range of tool rotation speeds 600–900 rpm. The NRS prevented all plasticized materials from escaping from the stirring zone, thus the weld nugget zone transformed from the basin-type formation to the spherical formation with increasing of the stirring effect when the tool rotation speed increased gradually. For joints welded by these two FSW processes, both the tensile strength and the elongation showed nearly the same trend with the tool rotation speed, but the NRSA-FSW can produce joints with the maximum tensile strength in a wider range. Compared with the maximum joint efficiency 71.2 % of the FSW without assistance of the NRS, the maximum tensile strength obtained by the NRSA-FSW also reached 69.0 % of the base material. All tensile specimens machined from defect-free joints fractured at the weakest region with minimum Vicker’s hardness; while for those joints with cavity defects, the fracture occurred at the defect location.     

正交实验方法在激光焊接中的应用

为获得优先的激光焊接工艺参数,采用四因素、三水平的正交实验方法设计激光焊接实验,以抗拉强度为标准,获得焊接优化水平参数为电流180A,脉宽3ms,频率30Hz,速度10mm/s.采用金相显微镜、显微硬度计、激光扫描显微镜、万能实验机等设备对焊接接头做金相分析、硬度测试以及拉伸试样断口分析,焊接接头硬度、基材硬度范围为H...     

含孔洞缺陷焊接接头电磁热强化及组织与性能分析

通过自制的ZL-2型超强脉冲放电装置对含孔洞缺陷的A356铝合金焊接接头进行了电磁热强化实验,采用金相显微镜对强化前后焊接接头各区域微观组织和孔洞附近组织进行了对比分析,利用微机控制万能实验机对强化前后试件的拉伸性能进行了测试,并用SEM扫描电镜对拉伸断口进行了分析,采用型号为FM-700的显微硬度计对强化前后试件进行了硬度测试。结果表明:合适的脉冲电流有较好的晶粒细化效果,强化后的焊接接头各区域组织得到细化,焊接接头的力学性能得到改善,经脉冲放电后的抗拉强度平均提高了11%,延伸率平均提高了14.2%,且强化后接头的硬度明显较强化前高。     

Quality monitoring based on dynamic resistance and principal component analysis in small scale resistance spot welding process

The present study aims at solving weld quality monitoring problem in small scale resistance spot welding of titanium alloy. Typical dynamic resistance curves were divided into several stages based on the weld nugget formation process. A smaller electrode force or lower welding current was found to promote the initial resistance peak. The bulk material heating stage could not be detected under very high welding current condition. Electrode force effect on dynamic resistance and failure load was much smaller than that of welding current. Principal component analysis was made on discrete dynamic resistance values. The first principal component was selected as independent variable in regression analysis for quality estimation. A back propagation neural network model was then proposed to simultaneously predict the nugget size and failure load. The electrode force, welding current, welding time, and first five principal components were designed as network inputs. Effectiveness of the developed model was validated through data training, testing, and validation. The realtime and online quality monitoring purpose could be realized.     

Influences of rotation speed on microstructures and mechanical properties of 6061-T6 aluminum alloy joints fabricated by self-reacting friction stir welding tool

A 6061-T6 aluminum alloy was self-reacting friction stir welded by using the specially designed tool with unequal shoulder diameters at a constant welding speed of 150 mm/min to investigate the effect of rotation speed on microstructure and mechanical properties of the joints. Excessive flash on the bottom surface of the joint and groove defects on both surfaces of the joint were formed when the lower shoulder diameter was much smaller. The suitable shoulder sizes were determined as 16 and 18 mm in lower shoulder diameter and upper shoulder diameter, respectively. The grain size and the dislocation density in the weld nugget zone (WNZ) increased with increasing rotation speed. The tensile strength of joints first increased with increasing rotating speed and then decreased remarkably as a result of the formation of void defect. The joints welded at lower rotation speeds were fractured in the thermal mechanically affected zone (TMAZ). However, the fracture locations of the defect-free joints were changed to the heat affected zone (HAZ) at higher rotation speeds.     

2219铝合金双轴肩搅拌摩擦焊工艺及接头组织性能研究

通过对8mm厚2219铝合金进行双轴肩搅拌摩擦焊试验,研究了不同焊接速度对接头成形、组织演变及其对力学性能的影响规律。工艺试验结果表明:在固定转速(200r/min)下,不同焊接速度下的接头均成形良好,未出现微裂纹、隧道以及疏松等焊缝表面缺陷。随着焊接速度的增加,接头区域晶粒尺寸减小;接头显微硬度受到晶粒尺寸与沉淀相分布的制约,硬度分布曲线呈“W”形,热影响区硬度最低。并且随着焊接速度的增加,接头最低硬度和抗拉强度逐渐提高,断裂位置发生在热影响区与热影响区交界处。在焊接速度为350mm/min时,接头抗拉强度达到最大值335MPa,约为母材的72.8%。     

Magnetic Thermal Method for Controlling Geometric Characteristics of Fusion Joints by Contact and Arc Welding

A new approach to estimating the quality of joints made by contact spot welding and arc welding is proposed on the basis of studies on the interaction of thermal and electromagnetic fields during welding of St3 steel. Parts welded by contact spot welding are magnetized by a solenoid immediately after the welding current is switched off. The diameter of the cast nugget is estimated from the change in the normal component of residual induction in the center of the contact spot of an electrode. The parts to be arc-welded are magnetized before welding. The fusion depth is estimated from the size of the demagnetization band adjacent to the weld.     

预热及保温对严寒环境X80钢管道全自动外焊焊缝组织与性能的影响

研究了-30 ℃严寒环境下采用不同预热及保温措施进行电弧焊接的X80钢,观察了不同焊接条件下接头各区域的显微组织特点,通过硬度测试、拉伸试验、低温冲击试验对接头的力学性能进行了表征。研究结果表明：严寒环境下焊接得到的X80钢焊缝以柱状晶为主,填充区主要由针状铁素体、先共析铁素体及少量魏氏组织组成,随着预热及保温温度升高,魏氏组织的尺寸和数量都有所减小;接头硬度的极大值与极小值分别出现在热影响区的粗晶区与不完全重结晶区,随着预热及保温温度的升高,接头的整体硬度降低,焊缝区域的低温冲击韧性增强,而抗拉强度先提高后降低;预热及保温是接头在严寒环境下获得具有良好综合性能的有效措施,预热及保温温度为100 ℃时接头性能最优。     

Effects of welding speed on microstructures and mechanical properties of AA2219-T6 welded by the reverse dual-rotation friction stir welding

Reverse dual-rotation friction stir welding (RDR-FSW) is a novel FSW technology in which the tool pin and the assisted shoulder rotates reversely, thus it has the capability to obtain appropriate welding conditions through adjusting the rotating tool pin and surrounding assisted shoulder independently. In the present study, a RDR-FSW tool system was designed and successfully applied to weld high strength aluminum alloy 2219-T6, and the effects of welding speed on microstructures and mechanical properties were investigated in detail. At a constant rotation speed of 800 rpm for both the rotating tool pin and the reversely rotating assisted shoulder, defect-free joints were obtained at welding speeds ranging from 50 to 150 mm/min, while a cavity defect appeared at the three-phase confluction on the advancing side when the welding speed increased to 200 mm/min. With increasing of the welding speed, the width of the softened region decreased, but the minimum microhardness value increased gradually. When compared with the joints welded by the conventional FSW, there is only a minor variation of the Vickers hardness across the stirring zone in the joint welded by the RDR-FSW. The maximum tensile strength 328 MPa (73.7 % of the base material) was obtained at the welding speed of 150 mm/min, while the elongation reached its maximum 7.0 % (60.9 % of the base material) at the welding speed of 100 mm/min. All defect-free joints were fractured at the weakest region with the minimum Vickers hardness, while for the joint with cavity defects the fracture occurred at the defect location. The tensile fracture was in the ductile fracture mode.