Research On Mechanical Property Of Laser Spot Welding/Double Beam Welding Joint In Titanium Alloy

TC4 titanium alloy is an indispensable structure material in modern aircraft structure which is widely used in and abroad.In recent years,a large number of laser welding techniques have been used in connectors of aircraft fuselage panels.In order to realize the lightweight of the aircraft and improve the mechanical properties of the connection between the skin and the ribs,this topic is based on the development of the T-shaped structure of the laser double beam technology applied in the aircraft fuselage wall,two kinds of T-joints for bearing welds were welded to TC4 titanium alloy by laser spot welding technology and laser double beam welding technology,The microstructure,tensile properties,fatigue properties and fracture mechanism of welded joints were systematically analyzed and studied,which provided a basis for the fatigue strength design of aircraft fuselage panels and aircraft safety performance evaluation.Firstly,the microstructure analysis of two different laser welded joints was carried out to observe the two-phase microstructure and volume fraction of different areas of the welded joint.The results show that the fused zone is a basket-like structure composed of acicular ?' martensite,compared with the laser double beam welding microstructure,the volume fraction of the laser spot welding ?' net basket structure increases,needle-shaped ?' martensite increases in size and phase spacing decreases.Secondly,The T-weld joints of two kinds of load-bearing welds under the action of laser spot welding and laser double beam welding were compared and the median fatigue life and tensile properties of the two alloys were compared.The results show that the laser double beam welded T-joint has better median fatigue life and tensile properties under both load conditions,while the median fatigue life distribution of laser spot welding is more concentrated.Finally,the fracture morphology of the fatigue samples was observed by scanning electron microscopy,it shows that the crack source of the two welded joints of titanium alloy was mainly generated from the surface of the sample.In the later stage of the crack propagation zone,compared with the previous period the fatigue zone spacing of the two welded specimens increased significantly,this indicated that the crack growth rate increased.The difference is that the fatigue fringe spacing of the laser spot welding specimen is larger than that of the laser double beam specimen,indicating that the crack growth rate is faster.