| Recently,with the rapid development of the shipbuilding industry,more stringent requirements have been imposed on the design of structural parts and the research of new materials.The composite structure of titanium-steel/aluminum-steel could realize the design requirements of overall ship weight reduction and local load enhancement,and it's application range will be more extensive in the future.It will be necessary to seek suitable technological means to overcome the physical properties,chemical properties and surface conditions resulted from dissimilar metal welding.The achievement of good connection of titanium-steel/aluminum-steel dissimilar metal composite structures will continue to promote application and development of titanium-steel/aluminum-steel dissimilar metal composite structures in the shipbuilding industry.The new BC-Plasma MIG Process has been adopted to solve the problems of low welding efficiency and poor quality stability of titanium/steel and aluminum/steel dissimilar metal structural parts.The titanium-steel/aluminum-steel welding test has been conducted.Meanwhile,macro and micro organization and composition analysis and test of mechanical properties of welded joints have also been performed.In addition,the electrical signal and visual signal acquisition system for BC-Plasma MIG Process have been established to obtain the relationship between droplet transition form and process parameters during composite arc welding.The arc shape characteristics,the droplet transition form and the welding heat input mechanism in the BC-Plasma MIG Process were studied to further explain the advantages of the process in the titanium-steel/aluminum-steel dissimilar metal welding process,which provides experimental theoretical basis for the popularization and application of the process.The welding process test of titanium-steel/aluminum-steel welding test proved that BC-Plasma MIG Process could achieve good welding of titanium-steel/aluminum-steel dissimilar metals.The optimal process parameters were obtained in the test.The comparison manifested that the mechanical properties of the welded joint were better than the joint under ordinary welding process.The average tensile strength of titanium-steel joints reached 349.29MPa,and the highest tensile strength reached 375.48 MPa.The fracture mode was brittle fracture,which was related to the large amount of Ti-Cu intermetallic compounds such as CuTi,Cu4Ti3,etc.on the Ti/Cu side of the titanium-steel joint.The damage location of the aluminum-steel joint was at the weld toe,and damage level was one.Fe-Al intermetallic compounds such as FeAl3 and Fe2Al5 were generated in the Fe/Al side interface layer.It was been deduced that BC-Plasma MIG Process could ensure that the welding wire had the same melting speed while reducing the heat input to the base metal.The sinking force of the molten pool was reduced,which improved the stability of the molten pool.The arc pressure of the coupled arc had uniform on the workpiece surface and the molten pool,which was good for weld formation.Controlling the transition of the droplet transition from a short-circuit transition to a shot-drop transition during the test could stabilize the welding process,reduce welding spatter,and improve weld formation.The stability of the welding process is closely related to the size of the bypass current.Suitable process parameters could obtain high-quality titanium-steel/aluminum-steel dissimilar metal welded joints. |
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