Research On The Key Technologies Of Superplastic Deformation Of Laser Welded Ti-6Al-4V Sheet With Homogenization

In this thesis,the uniformity problem of the superplastic deformation behavior and microstructure evolution of laser welded sheet of Ti-6Al-4V alloy with hydrogenation was investigated. Hot tensile tests were used to investigate the superplastic deformation of laser welded Ti-6Al-4V sheet with hydrogenation. the effects of parameters on the uniformity problem of deformation behavior were discussed Metallographic microscope and scanning electron microscope were used to observe the microstructure of weld joints before and after superplastic deformation.The main findings are as follows:The method can improve the uniformity of TC4 titanium alloy superplastic deformation of laser welded joints by hydrogenation. laser welded sheet can withstand high temperatures without damage during superplastic deformation. laser welded sheet can be provided with good superplastic deformation behavior. In the amount of hydrogen 0.291%-1.299%,in this high-temperature tensile test, the the peak flow stress of sample is below 80 MPA, minimum up 20 MPA. the the peak flow stress of sample can be 20.7 MPA and the elongation of the Weld plate can be 312% when the hydrogenational content is 0.291%,the temperature of deformation is 920℃,the strain rate is 10-4S-1.At the same deformation temperature and strain rate, with the increasing of hydrogen content of the material,the stress-strain curve shift;The peak flow stress of sample was increasing with the increasing of hydrogen content, decreasing with the increasing of temperature, increasing with the increasing of strain rate;The elongation of sample was decreasing with the increasing of hydrogen content, increasing with the increasing of temperature, decreasing with the increasing of strain rate.Superplastic of titanium laser welding can reduce with the increase of hydrogen contant when the hydrogen content was over 0.29%,, The peak flow stress was increasing and the Sectional shrinkage was decreasing with the increasing of hydrogen content,Base metal section shrinkage declined more than the decline of weld shrinkage section with the increasing of hydrogen content.Non-uniform deformation coefficient K can characterize property of non-uniform deformation on the the Laser Welding and superplastic deformation of titanium alloy with hydrogenation between the base and welded joint, K values was increasing withthe increasing of hydrogen content anddeformation temperature,with the decreasing of strain rate. The K value can reach 0.84 Maximally when the hydrogenational content is1.299%,the temperature of deformation is 920 ℃,the strain rate is 10-4S-1. Tissue homogenization coefficient can characterize the degree of uniformity after superplastic deformation of welded sheet,with the increasing of hydrogen content,the tissue homogenization coefficient was becoming larger and larger, the degree of uniformity was becoming higher; at the same position of hydrogen content, the increasing of the deformation temperature or the decreasing of initial strain would make the degree of uniformity rise, The tissue homogenization coefficient can reach 0.95 Maximally when the hydrogenational content is 1.299%,the temperature of deformation is 920 ℃,the strain rate is 10-4S-1.In addition, this paper also carried out numerical simulation of superplastic deformation laser-welded joints,taking advantage of ANSYS software,we can effectively simulate high-temperature tensile stress contours and the stress-strain curve with a constant strain rate.