| Due to the light weight,heat resistance,good performance in low temperature,2A14 alloy is widely used in aerospace,shipbuilding and other fields.Laser-TIG arc hybrid welding of aluminum alloy is a hot topic.The traditional welding methods are easy to produce defects as bucking,deformation and joint softening.Through the interaction of laser and arc,laser-TIG arc hybrid welding could avoid the welding defects of single heat source,greatly improve the bridging ability,and reduce the demand of preparation and assembling precision.Now,more studies are focused on laser-MIG hybrid welding of aluminum,while the study of laser-TIG hybrid welding of aluminum is less,especially,few efforts have been carried out to study the effect of hybrid mode on weld bead formation and joint mechanical properties in laser-TIG arc hybrid welding of aluminum alloy.LWS-1000 Nd:YAG laser and WSM-400(PNE61-400P)digital welding machine are used in laser-TIG arc hybrid welding.The experiment is carried out on aluminum alloy 2A14 with a thickness of 3 mm.The effect of covering surface with carbon ink or metal powder before welding on weld bead appearance,microstructure and hardness distribution are compared and studied.The processes of covering alloy plates with TiC and Al powder before welding are also investigated,which is aimed at improving tensile strength of the weld joints.Besides,the influence of two hybrid modes of laser-TIG arc hybrid welding on weld bead appearance and microstructure are analyzed in this paper and the hybrid mechanisms are studied.Finally,the influence of heat treatment processes on tensile strength of joints is explored.The experimental results show that the treatment covering the plate with carbon ink or TiC powder can improve the absorption of laser energy and increase the weld penetration.However,the laser absorption rate of specimen being blackened is better than that of being painted with TiC.The change of the width of the black area has little effect on the weld formation.By using the optimum parameters,in contrast with direct joining of 2A14 alloy without filler,the addition of TiC powder plays a key role in the transformation of bonding mode of the joint.The experimental results show that the process of painting with TiC and Al powder before welding could improve the tensile strength obviously.The tensile strength of base material after heat treatment is 279.14 MPa.The tensile strength of the joints without powder is 184.33 MPa,which is about 66% of the 2A14 base metal,while the joints with 10% TiC powder attains the value of 252.90 MPa,which is about 90.6% of base material.With the same welding parameters,the forming quality of weld surface in laser-leading mode is better than that of arc-leading mode,and the weld penetration is obviously deeper than that of arc-leading mode.Additionally,the weld surface in laser-leading mode is bright and with a little depression,while it appears dark with a slight upheaval in arc-leading mode.The conclusion is drawn that the prime difference of the synergistic interaction between the laser and arc in hybrid welding is that laser breaks the oxidation layer firstly in laser-leading mode which leads to different utilization of the energy.As a result,the weld depth and weld width obtained by two hybrid modes are different.The existence and sequence of the heat treatment process have great influence on the tensile strength of the joints.The tensile strength of joints after heat treatment is better than that without heat treatment.The joints obtained by the process of welding the annealing plate and heat treatment could have a maximum tensile strength. |
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