Research On The Welding Process,Microstructure,and Mechanical Properties Of High-Speed Train Aluminum Alloys Weld By Hybrid Laser-MIG Welding

Recently,hybrid laser-arc welding technology has been applied to the manufacturing of high-speed train carbodies in foreign countries.However,research on the laser-arc hybrid welding has just been started in China,which has bad influence on the appciation of this technology on the manufacturing of high-speed train carbodies.In this paper,two kinds of aluminum alloys,A5083-H111,A6005,used in CRH3 high-speed train carbodies,has been investigated by hybrid laser-MIG welding.Welding process,Microstucture,and properties of the hybrid welding joint have been studied in order to understand the laser-MIG welding of aluminum alloys.The aim of this paper is to provide some theoretical foundation for hybrid welding aluminum alloys of high-speed train.The results are listed as follows:The welding process of the hybrid fibre laser-MIG welding was studied,with the criteria of surface forming,defects,and tensile strength.The results showed that the welding speed of hybrid laser-MIGwelding was 2-3 times higher than that of MIG welding,and the width of the hybrid laser-MIG welding joint was narrower that of MIG welding joint.The tensile strength of A5083-H111 hybrid welding joint wasnot higher than that of the MIG welding joints,while the tensile strength of A6005 hybrid welding joint was higher than that of MIG welding joint.The microstructure and precipitation of the hybrid welding joint has been investigsted by the means of optical microscope,SEM,and TEM.The reason for the strength loss of the hybrid welding joint has been studied from microstructure,precipitation,element loss,and the fracture.The fatigue of the hybrid welding joint has been investigated,the S-N curves and fatigue limits have been received.Comparing with the fatigue of MIG welding joints,the hybrid welding joints showed excellent fatigue resistance.With the analysis of fatigue fracture,the porosity in the hybrid welding joints was responsible for reducing the fatigue resisitance of the hybrid welding joints.The distribution of 3D porosity in A6005 hybrid welding joint was studied by SR-XRM.