Numerical Simulation Of Temperature Field And Fluid Flow Field During TIG Fusion-brazing Of Aluminum Alloy And Brass

Using the computational fluid dynamics (CFD) commercial software FLUENT, the mathematical model of Al/Cu lap joints was established, and the temperature flied and fluid flow flied were calculated. In addition, TIG fusion-brazing of Al/Cu was conducted, and the calculation result was validated by experimental result. The microstructure and tensile strength of joints with three different wires, Zn-15%Al solid-cored filler wire, Zn-15%Al flux-cored filler wire and Al-12%Si flux-cored filler wire, were investigated.When the welding current was50A, the calculated results of temperature field and fluid flow field in Al/Cu lap joint show that the maximum temperature in the molten pool was1242K. The temperature range in the heat affected zone (HAZ) on Al base metal side was900-933K, under this temperature the grain in HAZ could grow up and coarsen. Due to the influence of latent heat and fluid flowing, temperature gradient near the fusion line between aluminum plate and molten pool decreased. The maximum temperature was up to955K within the area of the interface layer between brass and molten pool, which could result in the formation of Al2Cu. In the longitudinal section (y=0) of the molten pool, the fluid flew from the center to the boundary at the surface and bottom of molten pool, and flowed from the boundary to the center at the middle tier of molten pool. In the cross section of molten pool, the flowing of fluid formed two vortices, and the distribution of which was asymmetric. On the xy plane (the top surface of aluminum plate and its extension in the molten pool), four vortices appeared in molten pool. Under the influence of vortices, some metals with low evaporation point escaped from the molten pool, forming pores. The maximum velocity in molten pool was0.48m/s.When welding current was40A, the calculation results of temperature field and fluid flow field of Al/Cu lap joint show that:The maximum temperature in molten pool was1213K, which slightly lower than that when the welding current was50A. The comparison of temperature field of molten pool with50A welding current and40A welding current shows that the decreasing of heat input reduced the width of weld. The maximum velocity in molten pool was0.57m/s. On the xy plane (the top surface of aluminum plate and its extension in the molten pool), compared with the fluid flow field using50A welding current, in addition to the four vortices, two new vortices formed in the molten pool. In the cross section of molten pool. the whole flow field formed the two vortices; different from the flow field of molten pool with50A welding current the distribution of vortices is symmetrical.The experimental results of TIG fusion-brazing of5A02aluminum alloy to H62brass show that when using Zn-15%Al solid-cored filler wire, the tensile strength of joint was164MPa in as-welded and160MPa after post-weld heat treatment (PWHT). The intermetallic compound layer was mainly composed of CuZn5phase, which grew to weld in the form of the columnar crystal. After PWHT part of columnar crystals detached into the weld from interface layer. When using Al-12%Si flux-cored filler wire, Cu diffused into the weld and combined with Al by forming Al2Cu phase, and the specimens fractured along the interfacial layer with tensile strength of122MPa. When using Zn-15%Al flux-cored filler wire, the interfacial layer mainly consisted of AlCu phases, and the specimens fractured through the weld with tensile strength of129MPa.