Baoqiang Cong

Influence of Cold Metal Transfer Process and Its Heat Input on Weld Bead Geometry and Porosity of Aluminum-Copper Alloy Welds

Abstract The weld bead geometry and the porosity of AA2219-T851 high strength aluminum alloy welds with ER2319 wire produced by different cold metal transfer (CMT) processes and heat inputs were investigated. The results show that a narrow finger-shaped geometry is observed using the conventional CMT process and a large number of gas pores exist in the lower and upper parts of welds. Compared to results of above mentioned CMT process, the weld melting area is increased using CMT-pulse (CMT-P) process, and it is beneficial to reduce the porosity effectively with an appropriate heat input. The finger-shaped geometry with lower melting depth using CMT-advanced (CMT-ADV) process and the spherical-shaped bead geometry with lower dilution using CMT-pulse advanced (CMT-PADV) process are achieved. The gas pore is reduced predominantly and even eliminated due to the lower heat input and the effective oxide cleanliness of wire ends for the two processes.

Study on Electromagnetic Force in Arc Plasma With UHFP-GTAW of Ti-6Al-4V

Ti-6Al-4V titanium alloy is processed by ultrahigh-frequency pulsed gas tungsten arc welding (UHFP-GTAW), and the correlation between electromagnetic force and pulsed welding efficacy is studied. A mathematical model is formulated to analyze the macroscopic and internal electromagnetic forces. The axial and radial electromagnetic forces inside the arc plasma are evaluated with arc constriction. Meanwhile, the arc profile is also experimentally observed by a camera system to be the experimental evidence for the pinch effect. Owing to arc constriction during the UHFP-GTAW process, the axial component of the macroscopic electromagnetic force decreases, and the arc area diminishes, reducing the root radius. Therefore, larger axial pressure is found. The radial electromagnetic force inside the arc plasma is the most important factor for arc constriction. In addition, the reduced root radius makes the radial electromagnetic force to get reduced with increased pulsed frequency. The attenuation coefficient of magnetic force could be a key parameter for evaluating strength of the arc constriction. With decreased root radius with the UHFP-GTAW, the axial electromagnetic force inside the arc plasma can be maintained at a high level, which affects surface and mobility of the molten pool. The electromagnetic force is observed to have a close correlation with the root radius of the arc, which depends on the pulsed frequency.

ANALYSIS AND COMPARISON OF ALUMINUM ALLOY WELDED JOINTS BETWEEN METAL INERT GAS WELDING AND TUNGSTEN INERT GAS WELDING

Surface contamination usually occurs during welding processing and it affects the welds quality largely. However, the formation of such contaminants has seldom been studied. Effort was made to study the contaminants caused by metal inert gas (MIG) welding and tungsten inert gas (TIG) welding processes of aluminum alloy, respectively. SEM, FTIR and XPS analysis was carried out to investigate the microstructure as well as surface chemistry. These contaminants were found to be mainly consisting of Al2O3, MgO, carbide and chromium complexes. The difference of contaminants between MIG and TIG welds was further examined. In addition, method to minimize these contaminants was proposed.