垫板导热能力对钛合金薄板焊接残余应力的影响

针对钛合金TC4薄板钨极氩弧焊(GTAW)分别在试件背面衬以铜垫板与覆盖石棉的垫板两种情况下所焊的对接试件,采用切条应力释放法测量了其中纵向残余应力和纵向残余塑性应变的分布,比较研究了不同导热能力的垫板对钛合金薄板焊接残余应力及纵向残余塑性应变的影响。测量结果表明:钛合金GTAW焊接过程中垫板不仅提供了对焊缝背面的保护,也影响了焊接纵向残余应力与纵向残余塑性应变的分布与大小。不同导热能力的垫板控制应力与变形的效果不同。铜垫板控制应力与变形的效果好于覆盖石棉的垫板。

INFLUENCE OF HEAT CONDUCTION ABILITY OF BACKING BAR ON WELDING RESIDUAL STRESS IN TITANIUM ALLOY THIN PLATE

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.