Formation And Microstructure Analysis Of Copper Transition Layer By Laser Coaxial Cladding During Titanium/Steel Joining

Titanium/steel composite plates combine the excellent corrosion resistance of titanium with the high strength of steel,making them suitable for use in fields such as petrochemicals,power equipment,salt-making equipment,and marine engineering.Due to the large differences in physical properties between titanium and steel,micro-cracks,pores,and other defects can occur during the explosion welding process of titanium-steel composite plates,requiring manual TIG welding or electrode arc welding for stack welding repairs.To further improve repair quality and automation,the existing manual electrode arc welding repair process has been upgraded to a laser coaxial cladding technology system.However,when titanium and steel are connected directly,brittle intermetallic compounds with high hardness will form,leading to a significant decrease in joint quality.Therefore,the method of laser pre-positioning the copper cladding layer on the steel substrate surface and then TIG welding the titanium layer on the copper layer surface is proposed for the experimental cladding preparation of composite plates.Therefore,first,the influence and role of laser process parameters on cladding layer formation features and structure were analyzed.Then,the dynamic process of copper powder melting was synchronously captured by high-speed photography,and a dynamic model of powder melting was established.The energy distribution mechanism of laser heat in the process of powder melting and pool formation,and its relationship to cladding thickness formation of the copper layer was analyzed.Finally,the process and structural features of TIG welding and cladding on the surface of the copper layer were studied.The specific details are as follows.(1)The process experiments of laser coaxial powder feeding cladding copper transition layer were studied and analyzed.The influence of different laser process parameters(laser power,powder feeding rate,scanning speed)on the macroscopic forming characteristics of the cladding layer was analyzed.From the process characteristics of laser cladding,the microscopic structure characteristics of the bottom and top of the cladding layer were analyzed.Furthermore,the effect of different process conditions on the diffusion degree of iron element in the base material during laser cladding was examined,and a well-formed copper transition layer was prepared on the surface of the steel substrate.(2)The melting of powder during laser coaxial powder feeding cladding was detected and analyzed,and a melting model of a single powder particle was established.The different melting behaviors of powder in the interaction space of light and powder were collected and analyzed using high-speed photography.A thermal process model of a single powder particle was established based on the different stages of powder and laser interaction.Energy balance equations of different melting behaviors were used to calculate the duration of different melting behaviors.(3)The energy distribution relationship of powder-laser-molten pool interaction was analyzed.By combining powder movement and shielding,the interaction and influence of powder beam and laser were analyzed,and an opacity model of powder beam was established.The relationship between shielding rate and time of light-powder interaction was calculated,showing that the shielding rate increases with the increase of light-powder interaction time.Using the principle of energy conservation,the energy distribution relationship between laser and powder/melt pool was established and calculated.The relationship between process-energy distribution-shaping under different laser power and powder feeding conditions was fitted.Simultaneously,a Ti layer was TIG arc-clad on the surface of the copper layer.Through the detection and analysis of the microscopic structure of Ti-Cu and Ti-Cu-Fe joints,it was found that:(4)The copper transition layer effectively prevented the diffusion of iron elements to the titanium side,avoiding the formation of Ti-Fe brittle intermetallic compounds.Cu Ti2 intermetallic compounds were mainly formed in the joint.Shear tests showed an average shear strength of 194 MPa,meeting the interface shear strength requirements of Class 1 and Class 2 titanium/steel composite plates.The fracture mode was brittle fracture.The theoretical and experimental analyses above provide theoretical guidance and experimental basis for the laser coaxial cladding repair technology system of titanium/steel composite plates.