高频脉冲变极性焊接工艺性能研究

分析了高频脉冲电流对变极性焊接电弧特性、焊接工艺及焊缝性能的影响,试验结果表明,高频电流脉冲能够较大程度地压缩电弧等离子体、提高电弧轴向压力及电弧挺度,在相同焊接电流有效值的情况下,频率在5kHz以上的电流脉冲能将电弧力提高到普通变极性焊接的260%左右.同时高频脉冲电流能够提高变极性焊接的焊缝熔深,减小焊缝正面余高以及改善焊接效率.对于2219-T6时效强化铝合金而言,采用叠加10 kHz高频脉冲变极性焊接工艺,焊缝抗拉强度在未经任何焊后热处理的情况下能够达到300 MPa左右,相当于母材强度的67%.     

HPVP-GTAW电弧力及焊接质量分析

分别以3种不同材质铝合金平板材料为试验对象,研究分析了复合超高频脉冲方波变极性钨极氩弧焊接(HPVP-GTAW)过程中电弧力的变化及其对焊缝成形特征和接头力学性能的影响.结果表明,与常规变极性氩弧焊工艺相比,脉冲方波电流的加入使得HPVP-GTAW电弧力显著增加,同时焊缝熔透率大幅提高,接头力学性能得到明显改善和提高;保持脉冲电流幅值和占空比基本不变,在10～80 kHz范围内,脉冲电流频率对焊接过程产生了重要影响,频率为40 kHz时,HPVP-GTAW电弧力和焊缝熔透率均达到最大,分别约为常规变极性焊接电弧的1.9倍和1.7倍.     

不同脉冲频率条件下2219-T87高强铝合金焊缝成形行为

采用复合超高频脉冲方波变极性钨极氩弧焊接技术完成了2219-T87高强铝合金平板堆焊试验,分析了脉冲电流频率对焊缝成形特征的影响及其规律.结果表明,脉冲电流频率对电弧特性及熔池流动行为有较大影响,造成焊缝熔宽、熔深及熔透率出现显著变化.脉冲频率f_H<60 kHz时,焊缝熔宽、熔深随脉冲频率的增加而增大,熔透率在f_H<35 kHz时基本保持不变,在f_H>35 kHz时出现显著提升,较常规变极性氩弧焊(VP-GTAW)至少提高了34%;当脉冲频率达到60 kHz时,焊缝熔透率达到最大,较VP-GTAW提高了约60%;脉冲频率f_H>65 kHz时,熔宽、熔深及熔透率呈现回落趋势.     

直流磁场作用下铜蒸气对电弧特性的影响

为研究直流纵向磁场作用下金属蒸气对熔化极气体保护焊(gas metal arc welding,GMAW)电弧特性的影响,将钨铜复合材料制成特殊钨极代替熔化极产生铜蒸气,利用高速摄像法、光谱测温法以及小孔探测法对其进行了测试研究.结果表明,铜蒸气进入电弧等离子体后,电弧出现分层,随铜蒸气含量的增加,弧芯外围区域半径随之增加,弧芯区的尺寸减小.当铜含量为0%时,外加直流磁场后,电弧在阴极区收缩阳极区扩张,其轴向最高温度明显上升;电弧压力峰值偏离轴线,在外加磁场强度为0.015 T时呈现双峰分布,电流密度与电弧压力分布趋势相似;随着铜蒸气的介入,弧芯区电弧表现为阴极区收缩,阳极区扩张,弧芯周围的铜蒸气则明显收缩,电弧轴向最高温度上升的幅度明显降低.随着铜含量的增加,电弧的导电面积增加,环向电磁力作用减弱,电弧中心压力下降幅度显著降低,阳极电流密度的分布趋势逐渐趋于扁平化.     

不锈钢超高频直流脉冲GTAW焊缝成形行为

基于超高频直流脉冲钨极氲弧焊技术（UHF—GTAW,ultrahigh frequency pulsegas tungsten arc welding）,完成了0Cr18Ni9Ti奥氏体不锈钢焊缝熔透特性试验,研究分析了超高频脉冲方波电流对焊缝成形及熔池金属流动的影响规律．结果表明,在高频脉冲电流作用下,熔透率随频率增加而增大,在同等平均电流条件下,当脉冲频率达到80kHz时,熔宽减小,熔深最大增加了88．7％,熔透率显著提升,至少增大了24．6％以上．结合试验数据对熔池流动行为进行了理论分析,讨论了熔池内部电磁力对焊缝成形的作用及对流体的驱动效果．     

脉冲电流参数对奥氏体不锈钢电弧行为的影响

基于0Crl8Ni9Ti奥氏体不锈钢超高频脉冲钨极氩弧焊（UHF—GTAW,ultrahigh frequency pulse gastungsten arc welding）试验,分析了脉冲电流参数对奥氏体不锈钢电弧行为的影响及其作用规律．结果表明,以脉冲电流频率、占空比为代表的脉冲电流参数对不锈钢UHF-GTAW电弧的电学特性、工作形态、电弧力及熔透特性具有较大影响,随着超高频脉冲方波电流频率的增加,电弧收缩效应增强,电弧覆盖面积在一定范围内减小,电弧力显著增长,以等离子流力及电磁力为主的轴向力作用于熔池表面液态金属,造成熔池表面凹陷、热源下移、焊缝熔深增大、熔透率显著提升．     

Pulsed ion extraction from a hybrid plasma using a shunting arc discharge

A hybrid plasma is generated by combining a burst methane rf (195 kHz) plasma with a carbon shunting arc discharge. The shunting arc discharge triggers the rf methane plasma. As a result, the rf plasma is initiated over a wide range of ambient gas pressure from 0.045 Pa as a base pressure to a methane pressure of 1.26 Pa, at which the rf plasma is not self-ignited. When a target is immersed in the rf- and shunting arc-hybrid plasma, and a negative pulse voltage is applied to the target, carbon ions are extracted from the hybrid plasma. When the carbon shunting arc ionizes the methane gas, an rf plasma is initiated and the ionization of methane is significantly enhanced in the rf plasma. The plasma density in the hybrid plasma increases by a factor of approximately 5-9 compared to that of the shunting arc discharge.     

Spectroscopic temperature measurements in direct current arc plasma jets used in thermal spray processing of materials

An experimental study was conducted to determine the plasma temperature field and its parametric variation with respect to plasma operating conditions using emission spectroscopy. The focus of our study was the direct current (DC) arc plasma systems used in thermal spray processing of ceramic materials. A commercial plasma system (Metco 9M series) was operated with mixtures of argon and hydrogen in the power input range from 12 to 36 kW. Temperature measurements were based on the detection of emission line intensities from Ar-I neutral species. Spatially resolved measurements were obtained of the plasma temperatures in axisymmetric plasma jets using Abel deconvolution. The variation of plasma axial and radial temperature distributions was measured as a function of the plasma input power, the total gas flow rate, and the binary gas composition of argon and hydrogen. Time-averaged plasma gas temperatures were found to increase with increasing plasma input power, increasing hydrogen content of the plasma gas, and decreasing total gas flow rate. Plasma temperatures decrease progressively with increasing distance from the nozzle exit. The peak temperatures near the nozzle exit are in the range of 12,500 to 14,000 K. The radial temperature profiles show an approximately self-similar decay in the near field of these plasma jets. It was also determined from time resolved intensity measurements that there are significant fluctuations in the argon emission intensity with increasing hydrogen fraction in the mixture. These fluctuations with a typical frequency of 5.2 kHz are attributed to the arc root instabilities observed before. Finally, the measured plasma temperature field is empirically correlated in terms of radial and axial coordinates, plasma electrical input power, plasma efficiency, and gas composition. These temperature data can be used to validate numerical simulations as well as in choosing locations where different materials can be introduced into the plasma jets. This is particularly important for “nanostructured” materials, which loose their structure upon melting as a result of being exposed to high plasma temperatures.     

Effect of pulse frequency on hardness characteristics of Al-Cu alloy HPVP-GTAW joints

AA 2219-O Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardness characteristics which mainly depicted by microhardness and its gradient were investigated systematically. The results show that pulse frequency has a great effect on the hardness characteristics. The weld zone microhardness and its gradient with different pulse frequency present an evident fluctuant trend. The fluctuation of gradient is slight, illustrating that the microstructure is uniform with pulse frequency varied from 35 kHz to 60 kHz. The fusion zone microhardness and its gradient follow the similar trends but fluctuate greatly. Maximum value of gradient appears around the fusion boundary due to the coarse and non-uniform microstructure. The maximum gradient at 60 kHz is only 25.5% of that at 45 kHz. According to the study, the best hardness characteristics are achieved at 60 kHz frequency.