Study On Bead Formation And Defect Control Of NG-GMAW For 5083 Aluminum Alloy

5083 aluminum become one of the main welding structure alloys for liquefied natural gas tank storage tank,because of its moderate strength,good corrosion resistance,easy to shape,excellent low temperature toughness and other characteristics.NG-GMAW has the characteristics of small filling capacity,low energy consumption,high efficiency,small heat input and small deformation.It is one of the most promising welding technologies for welding 5083 aluminum alloy.Due to the combination of aluminum alloy welding and narrow gap welding technology,the defects of porosity and lack of fusion are the welding defects which affect the quality of welding most.In this paper,the influence of welding current,welding speed and welding voltage on weld formation was studied by using the Taguchi method.EDS analysis and theoretical analysis,which indicated that the mechanism of lack of fusion was mainly caused by insufficient heat input to the side wall and low molten pool temperature,resulting in a larger molten poor surface tension,poor wetting,and ultimately the formation of lack of fusion.The oxidation of the molten pool surface is also one of the reasons for the formation of lack of fusion.The arc swing process and the preheating process of the narrow gap welding were studied in order to solve the problem of lack of fusion defects.In this paper,the size,amount and distribution of pores in 5083 aluminum alloy welds in different groove types are observed.It is found that the stomatal phenomenon is serious in narrow gap groove welds,and there are large side wall pores.The effect of different welding parameters on the porosity in the weld of the narrow gap groove was studied.The possible mechanism of the stomatal formation was given after the SEM photograph and the theoretical analysis.The polarizing metallography and the EBSD photograph confirmed the reliable of the theory.On the basis of the above,a number of control measures are put forward to control the porosity defects in 5083 aluminum alloy narrow gap thick plate welding effectively.