Study On Process Of TIG Welding-brazing Of Aluminum Alloy To Galvanized Steel

In this paper, 5052 aluminum alloy and galvanized steel were investigated as the research objects, ER4043 Al-Si wire was as the filler metal, TIG welding-brazing was as the welding method, penning pre-treatment of the surface of aluminum alloy and ultrasonic vibration field were as the assistant processes in the meantime, dissimilar metal welding experiments of manufacturability between aluminum alloy and galvanized steel were conducted, and the microstructure and properties of aluminum-steel joints were tested and researched correlatively together with the analysis of comparison.Through a series of experiments, optimal welding parameters were worked out: welding rate of 200mm/min, welding current of 70 A, wire feed rate of 800mm/min, welding voltage of 13 V.Under the optimal welding parameter, the largest tensile strength of joints was 108 MPa. The joint was composed of the base metal area, the heat affected zone, the fusion zone and the interface region. The microstructure of fusion zone was mainly composed of the α-Al solid solution and the Al-Si eutectic phase. The width of the interface region was about 3.5~8um with the composition of brittle intermetallic compounds of aluminum and iron, the micro-hardness tests indicated that the micro-hardness in this region reached up to 210 HV. And the compounds which grow in the certain direction of aluminum side were FeAl3, those which grow in the certain direction of steel side were Fe2Al5. The width of the interface layer increased with the improvement of heat input. The fracture position primarily focused on the fusion zone with the main fracture way of toughness.Based on the optimal welding parameter, penning pre-treatment of the surface of aluminum alloy was added before welding and the largest tensile strength of joints was 113 MPa. The microstructure and properties didn’t change too much. The width of the interface layer increased more or less, though not obviously. All the joints fractured in the fusion zone which indicated that the strength of HAZ zone got promoted after penning treatment. Penning pre-treatment of the surface of aluminum alloy had broken or partly eliminated the dense oxide film layer that existed on the surface of aluminum alloy effectively, improved the efficiency of heat input and the protectiveness to the weld poor, reduced the defects such as slag after welding, and increased the wettability and spreadability of the molten metal on the galvanized steel meanwhile. On the other side, the grain refinements of local position and the addition of grain boundaries had supplied more channels for heat transmission. Overall, penning pre-treatment of the surface of aluminum alloy had optimized the properties of the aluminum-steel joints welded by TIG welding-brazing to a certain extent.Based on the optimal welding parameter, ultrasonic vibration field was added during welding process, and the largest tensile strength of joints was 117 MPa. The phase composition of every region in the joints didn’t get variation yet, but the amount of the columnar grains decreased distinctly in fusion zone and the size of the grains got refined. Correspondingly, the micro-hardness of fusion zone improved. The phase composition and the width of the interface layer stay the same. The existence of ultrasonic vibration field decreased the amount of detects of the joints after being welded, such as slag, pore and so on. Vibration had kept the grains refined to some extent and homogenized the overall microstructure. By means of breaking or partly eliminating the dense oxide film layer, ultrasonic vibration had made the distribution of heat input more uniform and supplied more channels for heat transmission. As a whole, the addition of ultrasonic vibration field had also optimized the microstructure and properties of the aluminum-steel joints welded by TIG welding-brazing to a certain extent.In the last part of this article, the varieties of the intermetallic compounds which were formed in the interface layer were analyzed and judged in the utilization of thermodynamics model. Through calculation, conclusion had been summarized that the main compounds consisted of FeAl3 and Fe2Al5, which was coincided with the results of welding processes primely.