中文摘要：

针对X70钢管道全位置激光一熔化极活性气体保护（MAG）电弧复合根焊焊接过程中，管道焊接3-6点位焊缝背面易出现内凹，开展了管道全位置激光一MAG电弧复合根焊焊缝成形试验研究。试验结果表明，激光一电弧复合焊接能量输入、焊枪角度对焊缝背面内凹影响较大；焊缝背面内凹可能是由于熔池液态金属重力作用导致焊缝熔融金属下淌所致。通过变参数能量输入方法，从3点位到6点位逐渐降低激光一电弧复合焊接功率；并向上倾斜焊枪角度使激光和焊缝切线方向成80。时，可利用保护气吹力和电弧力“托住”熔池，有效抑制内凹缺陷，改善焊缝成形。此外，发现焊缝背面有无内凹对静载拉伸性能基本无影响，有内凹管道的抗拉强度可达到596MPa以上，但焊缝背面内凹大幅降低了管道疲劳性能。

英文摘要：

This research is conducted to investigate the internal concave defects which are most likely to occur at 3-6 o＇ clock position （for all-position root welding） during the laser metal active gas （MAG） arc welding process of X70 steel. The results indicate that both heat input and torch angle have a significant impact on the internal concave defects. Owing to gravity, the liquid metal will drop into the weld pool, and thus lead to internal concave defects in the back weld. By decreasing heat input from 3 to 6 o＇ clock and with the upward inclined torch angle to 80~, the weld pool can be held by the shielding gas force and the arc force. In the way mentioned above, the internal concave defects are effectively controlled and better weld appearance can be achieved. In addition, it is found that the internal concave has little influence on the tensile properties of static load. While the internal concave enhances the strength of extension to more than 596 MPa, it significantly make the fatigue properties decrease.