超音频脉冲方波电流参数对2219铝合金焊缝组织和力学性能的影响

INFLUENCES OF ULTRASONIC PULSE SQUARE-WAVE CURRENT PARAMETERS ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF 2219 ALUMINUM ALLOY WELD JOINTS

采用新型超快速变换HPVP-TIG电弧焊接工艺进行2219-T87高强铝合金焊接,研究脉冲电流特征参数对焊接接头组织和力学性能的影响.结果表明,加入超音频脉冲方波电流(UPSWC)作用后,铝合金焊缝区显微组织由粗大柱状晶转变为细小等轴晶,在焊缝区内除了等轴树枝晶外,还存在一种呈带状分布的极细小等轴非枝晶组织,同时焊缝熔合区宽度明显减小,焊接接头抗拉强度和断后伸长率显著提高.在一定范围内增加脉冲电流幅值,提高脉冲频率,减小占空比,可增强组织细化作用,提高接头力学性能.与未加入UPSWC作用相比,脉冲电流幅值100A,脉冲频率40kHz,占空比20%时,接头抗拉强度和断后伸长率分别提高约22%和111%.

In order to overcome some problems in variable polarity gas tungsten arc welding （VP- GTAW） employed for welding aluminum alloy components, poor strength and ductility of weld metal, solidification cracking and weld porosity, a novel ultrafast convert high frequency pulsed current VP- GTAW technique is developed. The current converting speed in the novel technique is enhanced from less than 10 A/μs to more than 50-100 A/μs and high frequency pulsed current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration. It is expected that the novel pulsed VP-GTAW technique can improve the weld quality of aluminum alloy significantly. Thus, it is imperative to understand the effect of pulsed current parameters on the weld characteristics in the pulsed VP-GTAW process. The measured results of 2219-T87 high strength aluminum alloy weld joints show that the application of ultrasonic pulse current makes the coarse grains in weld zone change to the fine equiaxed grains, and a band-like zone with finer equiaxed non-dentrites appears. The width of weld fusion zone is obviously decreased and the mechanical properties of weld joints are predominantly improved. The improvements of the structure and weld properties can be significantly enhanced with the increases of the ultrasonic pulse current amplitude and pulse frequency, and decrease of the pulse duty cycle in certain ranges. Compared with the conventional VP-GTAW, tensile strength and elongation of weld joints are increased by about 22% and 111%, respectively, under the conditions of pulse current amplitude of 100 A, pulse frequency of 40 kHz and pulse duty cycle of 20%.