2003 年 21 巻 2 号 p. 204-212
Welding of Al-Mg and Al-Mg-Si alloys was performed using twin spot beams formed with two Nd: YAG lasers for the purpose of reducing porosities and humping caused due to unstable phenomena of weld bead during welding of aluminum alloys. The relationship between the configuration of the twin spot beam and the quality of the weld beads was investigated using X-ray and high-speed camera observations of the keyhole shapes and weld beads. X-ray observation of the weld beads showed that beam distance had a strong influence on the amount of porosities. At a shorter beam distance, porosities were apt to occurred in the weld. The amount of porosities decreased with an increase of beam distance. Beam distance affects keyhole shapes. The amount of porosities was clearly related to the ratio of keyhole depth to keyhole opening. Larger keyhole opening and/or shallower keyhole depth, smaller amount of porosities caused by instability of the weld pool.