Welding Process Optimization And Research On Microstrueture And Properties Fnr Laser Weld Joints Of TC4Titanium Alloy

Ti-6Al-4V is Titanium-based alloy which is widely used in aerospace industry, power industry, navigation, marine engineering, chemical engineering, automobile manufacturing and other fields, because of its superior performance. But thepoor weld ability of titanium alloy, welding defect serious, coarse grain and joint embrittlement phenomenon, which result in welded joint mechanical propertiesdecrease. Laser welding is widely used in practical production, because of its many advantages compared with the traditional welding method, such as small heat affected zone, small deformation, small grain size, high energy density and fast speed. Study on the influence factors on mechanical properties of the weld inlaser welding, so as to change the welding process and improve the quality ofthe weld.3mm thick TC4titanium alloy was welded with the Laser Coordinating protector and fixture self-designed in different power and welding speed. With tensile, bending and measurement experiment and comprehensive tensile fracture characteristics, test and analyze mechanical properties after welding joints; throughmetallographic and quantitative metallographic determination test, TC4titaniumalloy microstructure of the welded joints, welding process, the organizational changes in the law, and further joint fracture at the grain size and Markov thesize of the body needle-quantitative determination of phase content, they studied the mechanical properties of the joint. And then we draw the following conclusions:After welding, mechanical properties of the weldment can reach1/3of thebase metal, and effective connection can be made success. Mechanical properties of the weld are related with welding speed and keyhole morphology. When thepower under the2300W, the less the speed, the larger width, the more serioussubsidence, the worse comprehensive mechanical properties. The smaller the keyhole and the more near the front, the more uniform weld holes, the better tensile strength of TC4titanium alloy laser welding joints. Welding fracture is formatio n with metallic luster, River like stripes can be found in the fracture surface observing in the electron microscope, and it is a typical brittle transgranular fracture. There are small columnar grains perpendicular to the surface appears at the junction of weld and base metal through metallographic pictures, the microstructureof weld center is small grain and surrounding coarse equiaxed grains. The weldcenter is acicular alpha+beta and spread the complete original beta grain boundaries clearly, which is the typical of Widmanstatten structure. In the process ofTC4laser welding, Al evaporation significantly, and the weld alloy elements betastable phase V relative content increased. In the cooling process, the amount of transformation from the beta phase to acicular α’ phase in weld is decrease, whichcause the increasing of the brittleness and decreasing of the plastic, so the mechanical properties decrease.