Study On The Process And Numerical Simulation Of TIG-GMAW Composite Arc Additive Manufacturing Of Aluminum Alloy

Aluminum alloy structural components are widely used in aerospace,automotive,and other fields due to their low density and high specific strength.It is moving towards high precision,large sizes and complex shapes.But the traditional processing technology has low manufacturing efficiency,dependence on mold,slow structural design response,and it is difficult to improve the mechanical properties of the formed aluminum alloy.Wire Arc Additive Manufacturing(WAAM)has the advantages of high deposition rate,fast forming speed,and adaptability to various forming environments,attracting more and more universities and scientific research institutions to invest in it.How to further develop the advantages of arc additive manufacturing is a current research hotspot.In this study,5356 aluminum alloy welds were formed using TIG-GMAW composite arc additive manufacturing system,and the influence mechanism of arc current and scanning speed on weld forming quality was analyzed.It is found that increasing arc current and decreasing scanning speed can increase weld pool depth,pool width and residual height by increasing heat input in welding process.Under the same process parameters,the cracks and porosity defects of the TIG-GMAW composite arc forming parts are less than those of the GMAW forming parts,and the parameters range of the composite arc forming parts is larger than the GMAW forming parts.That is the forming rate of TIG-GMAW composite arc process is not lower than that of GMAW process,and the quality of forming pass is better.Based on Fluent software,the transient numerical model of aluminum alloy TIG-GMAW threedimensional molten pool was established,and the integrated adaptive distribution of "current density-arc pressure-electromagnetic force-arc heat" on the surface of deformed molten pool was realized.The force and heating state of liquid metal in GMAW and TIG-GMAW processes were compared and analyzed,and the influence of temperature field,velocity field and molten pool shape on weld formation was studied.It is found that weld bead formation can be divided into three stages:arc heating,droplet impingement,and filling solidification.During the arc heating stage,the workpiece surface melts to form a thin layer of liquid metal and flows backward.During the droplet impact stage,the droplet heat plays a leading role,and the high-temperature liquid metal flows backward at high speed.During the filling and solidification stage,the inertial force plays a leading role,and the liquid metal accumulates and solidifies at the end of the molten pool to form a surplus height.After adding TIG arc,the average temperature of liquid metal in the molten pool is higher.The repulsive effect of TIG arc on GMAW arc increases the concentration of GMAW arc and intensifies the backward flow of liquid metal in the weld pool.After reaching a quasistable state,the length of the weld pool increases and the width decreases,resulting in a wider and deeper gouging region below the GMAW arc.Finally,the aluminum alloy thin-walled parts were formed by TIG-GMAW composite arc additive process.The effects of arc current and scanning speed on the macroscopic morphology,microstructure,main defects and mechanical properties of the parts were analyzed.The results show that changing the arc current and scanning speed can form aluminum alloy thin-walled parts with flat and smooth surfaces.The microstructure of a single pass multilayer formed part is divided into a deposition layer and a remelting zone,and the grains of the deposition layer are dendrites.Due to the heating of the next layer,the grains in the remelting zone are relatively fine equiaxed grains.The increase of arc current and the decrease of scanning speed lead to the increase of heat input in arc additive process,resulting in the decrease of temperature gradient of high temperature droplet and deposition,and the liquid metal can not solidify rapidly.The forming parts are heated uniformly in the horizontal direction,the temperature gradient is small,and the porosity defects are more uniform.The temperature gradient in the vertical direction is large and the microstructure distribution is uneven,so the tensile strength in the horizontal direction is obviously higher than that in the vertical direction,and the mechanical properties are anisotropic.