| Aluminum alloy has a series of excellent properties such as low density,light weight,strong plasticity,good machining performance,corrosion resistance and so on.It is widely used in aerospace,shipping,rail transportation,mechanical equipment and other fields.The laser-arc hybrid welding technology,which combines high penetration,high efficiency of laser,and good bridging performance,composition adjustability of arc,is the first choice for high efficiency and high quality aluminum alloy joint.However,laserarc hybrid welding is only used maturely in thin plate structure of aluminum alloys,and there are still many pain points and problems in industrial application of medium thick plate structure,such as high cost of improving the penetration depth,high porosity and crack tendency,and uneven microstructure and properties.In this paper,a new idea of introducing active welding technology into laser-MIG hybrid welding is proposed,and a new active laser-MIG hybrid welding technology is formed by developing a kind of active agent suitable for laser-MIG hybrid welding of aluminum alloys.This paper focuses on the influence of process parameters of reactive laser-MIG hybrid welding on weld appearance,porosity,microstructure and properties.The main results are as follows:By adopting single component and multi-component mixing test design method,a multi-component optimized active agent ratio with arc stabilizer and nucleating agent with high penetration depth and good weld surface morphology was obtained.The specific mass fraction was 13.485% Si O2,13.485% Cr2O3,53.78% Ni O,12.35%potassium carbonate,1.9% sodium carbonate,2.5% titanium aluminum alloy and 2.5%zirconium aluminum alloy.The results of the research that the influence of welding parameters on weld forming characteristics of reactive hybrid welding showed that,compared with conventional hybrid welding,reactive hybrid welding showed excellent and efficient welding characteristics.The current required by reactive hybrid welding was reduced by 50.6%,the welding speed was increased by 50%,and the laser power was decreased by 14%.The mechanism of improving welding efficiency is as follows:(1)The active agent significantly improved the laser absorption rate,increased the effective heat input of laser,and then enhanced the weld depth;(2)The active agent changed the gradient tension on the surface of the weld pool,and formed a tension flow from the periphery to the inside of the pool.The welding current threshold of the weld without porosity defect was reduced from250 A to 220 A of conventional hybrid welding.The mechanism of suppressing porosity in active hybrid welding is as follows:(1)Arc stabilizer in active agent increased arc concentration and arc force.The increased arc force increased the sag of the weld pool surface and reduced the escape distance of the porosity from the bottom to the surface of the weld.(2)The active agent can improve the laser absorption rate,enhance the stability of keyhole,and reduce the formation probability of process pores;(3)The active agent changed the convection direction in the molten pool,formed a tension flow from the periphery of the molten pool to the interior of the molten pool,and increased the escape velocity of the pore.The experimental results of microstructure and mechanical properties of active laserMIG hybrid butt welding showed that compared with conventional welding,the center grain size of active hybrid butt welding was reduced from 41μm to 19.8μm,which was reduced by 51.7%.The average hardness of arc zone and laser zone of reactive hybrid welding was about 10% higher than that of conventional hybrid welding.The tensile strength of the active hybrid weld was 284.4MPa,which was 6.3% higher than that of the conventional hybrid weld.The active agent contains titanium/zirconium nucleation elements,which can refine the grains of the weld and reduce the tendency of crack formation,which is the main reason for the performance improvement. |
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