Research On Laser Welding Joint Microstructure And Properties Of Stainless Steel 301L And Industrial Pure Titanium TA2

Stainless steel,titanium and titanium alloys are important engineering materials,and they play an important role in aerospace,construction machinery,chemical production and medical equipment.The performance demand of workpiece products has been improved as the development of science and technology.The single use of materials cannot meet the need of production and life,so the use of composite structures is the key to solve this problem.It is renowned that the acquisition of the effective connection between stainless steel and titanium is difficult owing to their differences of physical and chemical properties.Hence,the study investigates the microstructure and properties of 301L/TA2 laser welded joints from three aspects of offsets,intermediate layer and the combination of them,which is of great significance and value for further research and practical application.The 301L stainless steel and TA2 industrial pure titanium are welded by means of pulsed laser welding technology.The effects of process parameters(pulse frequency,pulse current,welding speed and pulse width),laser offsets(-0.3 mm,0mm,+0.3 mm),and the combination between the laser offsets and Cu intermediate layer on weld morphology,microstructure and properties are studied.Firstly,the microstructure and chemical composition of the joints were studied by an optical microscope,scanning electron microscope with energy spectrum analyzer.Then,the mechanical properties of the joint were tested by the micro-hardness tester and electro-hydraulic servo universal test,and the corrosion resistance of the joint was studied by an electrochemical tester.Finally,the parameter optimization of the laser welding process was realized by Response Surface Analysis(RSA).The main conclusions of experiment are as follows:(1)The penetration depth and width increased and a small amount of spatter appeared on the weld surface,as the increase in pulse current,pulse width and pulse frequency.However,melting depth and width decreased with the acceleration of welding speed.And the distance between adjacent welding spot gradually shorten with the increase in pulse frequency.Compared with the pulse frequency and welding speed,the change of pulse width and pulse current matter more significantly in the penetration depth and width of the welded joint.(2)When the pulse laser welding without intermediate layer was carried out,the microstructure analysis showed that a large amount of inter-metallic compounds(Fe₂Ti,Fe Ti)were produced in the weld zone,and brittle compounds improved the hardness of weld zone.When the offset is+0.3 mm,the joint is connected by two ways of base metal melting and element diffusion,which greatly improved the strength of the joint through the reduction of brittle phases.The hardness of the weld is higher than that of the matrix according to the results of the HV-hardness measurment.The tensile tests show that when the offset is+0.3 mm,the tensile strength of the joint is better,the fracture surface is relatively smooth and presents a river pattern,and it is a typical brittle fracture.The electrochemical tests show that the joint has good corrosion resistance when the offset is-0.3 mm.(3)The addition of Cu as the intermediate layer in the weld resulted in fluctuation of the hardness and improvment in the strength of the weld metal,which is attributed to the formation of copper-iron solid solutions and copper-titanium compounds according to the micstructure analysis conducted by XRD experiment.The mechanical property experiments showed that the tensile strength of the joint in the presence of intermediate layer is much better than that in the absence of intermediate layer ones.Furthermore,the tensile strength of the joints without offsets is higher than the ones applied with various offsets.The fracture morphology of the tensile specimens with Cu intermediate layer appears relatively rough and a small proportion of dimple like area was recognized.The electrochemical corrosion tests showed that the joint applied with 0 and+0.3 mm offsets exhibited excellent corrosion resistance.In addition,the joints with intermediate layer were more corrosion resistant than those without Cu intermediate layer.The RSA showed that the multiparameters of 6.00 Hz pulse frequency,110.16 A pulse current,197.70 mm/min welding speed and 9.00 ms pulse width are the optimal optimization scheme for laser welding of 301 L/Cu/TA2 joints.