Abstract: The distributions of longitudinal residual stress and longitudinal residual plastic strain are determined experimentally using “slot-sectioning stress relaxation” method for titanium alloy Ti-6Al-4V thin plate welded by GTAW welding with copper backing bar and asbestos backing bar respectively. The influence of heat conduction ability of the backing bar on welding residual stress and longitudinal residual plastic strain of titanium alloy Ti-6Al-4V thin plate is studied comparatively. The experimental results showed that the backing bar not only provides Argon to prevent the weld from oxidation, but also influences the distributions and magnitudes of welding residual stress and longitudinal residual plastic strain. The residual stresses and distortions in specimen are different when using backing bars with different heat conduction abilities. The backing with good heat conduction ability is benefit to improve the distributions of longitudinal residual stress and longitudinal residual plastic strain of specimen. The high temperature isotherm is narrower in the specimen welded with the backing bar having good heat conduction ability, which makes the zones narrower in which residual tensile stress and residual plastic strain exist; the lower maximum temperature of the zone near the weld in welding process results in the lower tensile stress and longitudinal residual plastic strain. The effect of copper backing bar in controlling stress and distortion is better than that of asbestos backing bar.

Key words: Backing bar, Heat conduction ability, Residual plastic strain, Residual stress, Stress relaxation method, Titanium alloy