真空激光焊接具有更大的熔深和更小的气孔敏感性，为了利用真空激光焊接的优点，同时消除真空室尺寸对工件大小的限制，设计了局部负压激光焊接方法。此方法将负压腔与激光焊接头固定，通过真空泵对负压腔快速抽气从而在焊接熔池上方形成负压环境，在此环境下进行了一系列的激光点焊试验和连续焊试验，并与相同焊接参数下的常压和常压带侧吹条件的焊缝进行对比。通过高速摄影分析了负压环境下的金属蒸汽羽烟特点和熔池行为。结果表明，点焊时负压环境下金属蒸汽羽烟抑制效果明显，焊缝熔深增加，除去凹坑深度的焊缝熔深相比常压侧吹最大可增加4.5 mm。连续焊时熔池后方匙孔闭合，金属液向后堆叠，获得的焊缝成型良好，负压下焊缝熔深比常压侧吹条件下平均增加2 mm。

Deeper penetration depth and less pore sensitivity are the advantages of laser welding in vacuum. In order to make use of these advantages and eliminate the size limit of workpiece by the vacuum chamber as well, a new vacuum chamber is designed which can maintain a subatmospheric pressure above the welding molten pool. The chamber is fixed on the laser nozzle and the relatively lower pressure is generated with a vacuum pump. A series of spot welding and continuous welding experiments are taken under subatmospheric pressures. The results are compared with the weld bead under normal atmosphere with and without side-blowing shielding gas. The behaviors of plasma plume and molten pool are observed by the high-speed camera. The results show that the plasma plume is suppressed obviously and the penetration depth increases under subatmospheric pressure in spot laser welding. The penetration depth of spot weld bead is 4.5 mm deeper at most than the weld bead with side-blowing shielding gas. During continuous laser welding under subatmospheric pressure, the keyhole closed at the rear of the molten pool, the molten metal stacks backwards and sound weld can be achieved. The penetration depth of weld bead under subatmospheric pressure is averagely 2 mm deeper than the weld bead in normal atmosphere with side-blowing shielding gas.