| Metal sandwich plate is a new lightweight structural material made of two panels and intermediate core plates by welding.Compared with the traditional steel plate structure,it is widely used in shipbuilding,aerospace and other fields For its good specific strength,specific stiffness and impact resistance.For the closed type Ⅰ sandwich plate unit(T-joint),it is difficult to obtain a wellformed weld between the panel and the core plate by traditional welding.In view of this welding problem,this paper proposes a new welding process method for Flux Bands Constricting Arc Welding(FBCA)to weld T-joints of high-strength steel sandwich plates,and realizes the effect of single-sided welding and three-sided forming of welded sandwich plates.However,how to control the position of the arc and the flow effectively form of the molten pool is an urgent problem to be solved in FBCA welding of high-strength steel sandwich plates to obtain good weld formation and excellent joint performance.The aim of this study is using the unique regulation mechanism of Flux bands in ultra-narrow gap weld.In this study,we establishes the regulation relationship between Al alloy elements and FBCA welding dynamic process by adding different contents of Al alloy elements to the Flux bands.This study will provide a new method for regulating the welding process by using the composition of flux alloy elements,and provide a theoretical basis for improving the quality of FBCA welding and flux development.In this paper,Flux bands with different Al element contents were successfully prepared,and the FBCA joint samples of Flux bands with different Al elements were analyzed by inductively coupled plasma atomic emission spectrometer(ICP-AES),ON-nitrogen and oxygen-830.The analysis showed that the addition of Al element changed the alloying composition of the weld.The original addition amount of Al alloy elements in the Flux bands was almost all transferred to the weld.With the increase of Al content in the Flux bands,the alloy elements added by Mn,Ni,Cu and other welding wires were transferred to the weld.The content increased until the Al content reached 0.39%.The increase of alloy elements such as Mn,Ni and Cu in the welding wire slows down.At 0%-0.39%,Al element can promote the transition of high strength steel weld metal alloy.At the same time,the Al/O ratio also increased from 0.08%to 8.33%,while the O content in the weld decreased significantly.By building a high-speed camera matching electrical signal acquisition system,the droplet transfer behavior and electrical signal fluctuation of FBCA welding under different Al content of Flux bands were deeply explored.The results show that with the increase of Al content in Flux bands,the droplet transition form changes from slag wall transition and arc bridge transition to large droplet transition or short circuit transition.When the flux is added more than,the electrical signal fluctuates violently,the welding arc will swing left and right,and there will be multiple arc breaks,and the welding instability will increase.Furthermore,through the side high temperature resistant glass observation system,the side arc morphology and molten pool fluctuation of FBCA welding under different Al content of Flux bands were collected,and the relevant characteristic information of arc morphology was extracted and calculated by MATLAB.The results show that the addition of Al element to Flux bands significantly shrinks the arc morphology.With the increase of Al element,the welding arc changes from divergent spherical shape to contracted ellipsoidal shape,the combustion position is compressed to the middle and lower part of the weld bead,and the maximum compression depth reaches 2 mm below the core plate.Meanwhile,the addition of Al element significantly enhances the flow of molten pool.With the increase of Al element content,the fluctuation mode of molten pool surface changes from shallow concave to deep V-shaped.The addition of Al alters the molten pool Marangoni convection pattern and significantly affects the weld seam formation.When the Al content reaches 0.80%,the weld depth-to-width ratio reaches a maximum of 1.32.As Al2O3 gathered on the surface of the molten pool,the molten pool dr/dt changed from negative to positive,and the molten pool Marangoni convection mode changed from the centre to the surrounding flow mode to surrounding to the centre,and the weld seam forming quality improved.The microstructure and mechanical properties of FBCA welded T-joints with different Al contents were studied.It was found that:on the one hand,the addition of Al element to the Flux bands can obviously refine the microstructure of the joint.With the increase of Al element content,the microstructure of the weld and heat affected zone is refined.The weld zone is mainly caused by the addition of Al element.The poor manganese zone appears,and the acicular ferrite is easily formed on the surface of Al2O3,resulting in grain refinement.And the addition of Al element hinders the recrystallization transformation of the structure,resulting in grain refinement of the weld and heat affected zone.The microstructure refinement of the heat-affected zone is mostly due to the redistribution of heat in the molten pool caused by the arc contraction at the bottom of the molten pool,resulting in no time for the microstructure to coarsen.On the other hand,with the increase of Al content,the hardness of weld and heat affected zone increased by 35%respectively.Due to the fine grain strengthening effect,the strength of the welded joint is significantly enhanced.When the Al content in the weld is 0.18%and 0.92%,the tensile strength is increased to 955.7 MPa and 1044 MPa,respectively,and the strength is increased by up to 23.5%.At the same time,The elongation decreased from 11.4%to 5.2%,and the decrease was as high as 54%.The impact toughness in the heataffected zone decreased from 94.13 J to 65.77 J due to the aggregation of smallangle grain boundaries,resulting in higher dislocation density and increased storage distortion energy,and the impact toughness in the weld zone was not significantly affected by the Al element. |
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