Research Of Wetting Spreading And Interface Behavior Of Aluminum And Galvanized Steel By The Method Of MIG Brazing

In this paper, AlSi₅ and AlSi₁₂ were used as the filler metal, the CMT welding was employed to achieve lap joint between aluminum and galvanized steel, and the weldability was studied. It mainly studied the influence of welding process parameters and different content of Si element to the quality of welded joints. At the same time, based on the method of response surface methodology, a mathematical model is established between CMT brazing process parameters and the feature size of bead height H, bead width W and wetting angle θ, and it is validated, the weld morphology is predicted and process parameters are optimized.The results showed that: the galvanized zinc evaporated seriously when the wire feed speed is too large, which affected the stability of the arc, and it is easy to form an adverse effect on the weld, such as: weld irregular, undercut, porosity and welding tumors and other defects. Except that, position of torch and angle of work has a significant impact on the weld, when the forward angle of torch is 20°, and angle of work is also 20°, which can get a good weld. With the increase content of Si alloying elements, the viscosity of the liquid solder increased, which caused liquid solder can not be fully spreading on the surface of the base material.The joints showed obvious lap joint morphology on the condition of ultra depth microscope. At the same time, combined with scanning electron microscopy and XRD analysis results, the melting zone is mainly composed of Al-Si eutectic composition. Interfacial reaction layer near the galvanized steel side is mainly consisted of a dense Fe₂Al₅ composition, close to the side of the aluminum base material is mainly composed of needle FeAl₃, and it can be found intermetallic compounds Al₈Fe₂ Si ternary alloy around FeAl₃ edge; there was non-brittle intermetallic compound Al₅Fe₂Zn_0.4 generated beyween the transition interface region and zinc-rich zone, which can reduce its brittleness tendency to some extent, Thereby improving the quality of the joints. As the role of the plasma stream force, electromagnetic force and arc force, zinc-rich zone is mainly consisted of zinc/aluminum dendritic and aluminum/zinc intergranular eutectic.At the same time, based on the response surface analysis basis, it is verified by experimental predictions data and actual measurement data, between the predicted value and the actual weld profile measurements analysis of variance model, the test showed that the mathematical model was highly significant, which proves that the model can be used to predict weld profile, and to optimize the process parameters on this basis.Tensile tests showed that most of the specimens break in the heat affected zone of the base metal aluminum alloy. When the filler metal is AlSi₅, the maximum tensile strength is 175.2MPa; on the other hand, when the filler metal is AlSi₁₂, the maximum tensile strength is 112.8MPa. With the increase content of Si element, interfacial intermetallic compound layer increase, and the brittleness tendency to increase, Thereby causing the lower tensile-shear strength joint. The microscopic fracture morphology exists both cleavage steps and dimple features, which is a brittle-ductile fracture.