Abstract: For 100 mm and 31 mm thick TC4 Ti-alloy magnetically controlled narrow gap TIG weldments, residual stresses distribution of the surface is measured by indentation strain-gage method and triaxial stresses distribution in the thickness direction is measured by sectioning relaxation strain-gage method. Results show that welding residual stresses values of the two weldments are different. Longitudinal and transverse stresses peak values of the 100 mm thick weldment reached as high as 600-700 MPa, close to 70%-80% of the material yield strength. Longitudinal and transverse stresses peak values of the 31 mm thick weldment are low, only 40%-50% of the material yield strength. The reason for large difference of residual stresses between the two thicknesses weldments was mainly due to the cumulative effect of lateral shrinkage in large thickness weldment. After 650℃ vacuum heat treatment, longitudinal and transverse stresses of the two thickness weldments are significantly reduced, maximum stress reduction is more than 50%, remaining residual stresses peak values do not exceed 200 MPa, and stresses along the thickness direction of the weld is close to zero, stresses at surface are also redistributed.

Key words: mathematical induction method, process mechanism, reciprocating bending, springback, thin-walled pipe, three-roller setting round, magnetically controlled narrow TIG welding, PWHT, residual stress, TC4 Ti-alloy