| With the economic development and social urbanization caused by the growing energy crisis and environmental pollution problem,urban rail vehicle must be developed toward the direction of lightweight,energy saving and environmental protection.Aluminum alloy has the advantage of light mass,high intensity,good processing performance and excellent corrosion resistance,thus improving the usage of Al alloy in the urban rail vehicle is one the most direct and effective way to realize rail vehicle lightweight.Recently,manual arc welding and semiautomatic welding are widely used to weld Al alloy in the production of urban rail vehicle,these methods have the drawbacks such as backward technique,poor product stability,low qualified rate,long production cycle,low production efficiency,and high labor intensity.Hence,we develop a medium thickness plate aluminum alloy double-sided arc MIG welding method,and also investigate the key technology in this paper.This method could reduce the complexity of the process,avoid the root process,save the material,and enhance the welding efficiency significantly,thus show great theoretical significance and practical value for the large scale use of Al alloy in urban rail vehicle.In this paper,we firstly study the microstructure features and mechanical performances of 6082-T6 Al alloy double-sided arc MIG welding butt joint and T joint.The results show that the macro morphology of Al alloy double-sided arc MIG welding butt joint and T joint can be divided to the weld zone,fusion zone and heat affected zone.When the preheating temperature is 100? and the welding arc spacing is 0 mm,the weld thickness of butt joint backing weld reaches the largest.And when the preheating temperature is 100? and the T joint root gap is 3 mm,the weld thickness of T joint backing weld is the largest.The microstructure of butt joint and T joint of Al alloy double-sided arc MIG welding specimens are isometric crystal,equiaxial dendrites and columnar crystal from the weld area to the fusion zone,respectively.The particle sizes increase with the increasing heating input,and the grain size of columnar crystal in the weld side is larger than that of parent mental side.When the T joint root gap is too small and preheating temperature is too low,pore,crack and incomplete fusion are easily to appear at the joint.The weld area of Al alloy double-sided arc MIG welding joint have Mg2 Si precipitation.Researches show that,the microhardness of Al alloy double-sided arc MIG welding butt joint and T joint is lower that that of weld area.The width of butt joint heat affected zone increases with the increasing preheating temperature and welding arc distance.The width of T joint heat affected zone increases with the increasing preheating temperature,and first increase then decrease with the increasing root gap,and reaches the highest when the gap is 3 mm.The tensile strength and yield strength of Al alloy double-sided arc MIG welding decreases with the increasing of temperature and welding arc distance,and tensile fracture exhibits a typical ductile structure,regarding as ductile fracture.When the preheating temperature is 100? and the welding arc spacing is 0 mm,the qualification rate of Al alloy double-sided arc MIG welding butt joint bend samples reach highest,and show the best bending property.Based on analysis of the temperature field and stress field of the double-sided arc welding butt joint and T joint,it has been founded that under the suitable technological conditions,the heat input of butt joint and T joint is basic symmetric on both sides,and can form a common molten pool.The calculated results show that the double-sided arc technology can not only adjust the residual stress distribution of the specimen,but can decrease residual stress at some extent,which can benefit to the manufacturability and usability of the workpiece. |
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