In this paper, 5Kw CO<sub>2</sub> laser and a special CNC table were used to weld automobile double-linked gears with
20CrMnTi material and Y gap. A lot of evaluations on microstructure, defects and mechanical properties for welding
seam were examined by OM, SEM and X-ray diffraction. It was shown that deep penetration welding in the double-linked
gear could be achieved at optimum parameters of 2.6~2.8KW and 2M/min. Laser welding had a small distortion
of 0.0408mm in gear diameter. Microstructure of fine martensite and austenite was observed in the welding seam.
Mechanical tests of hardness of HV400 and tordional strength of 1512Nm were measured. The welding seam had a
comprehensive intensity and toughness. The defects of blowhole and crack could be reduced or avoided by adjusting
parameter and preheating before welding. The allowable standard of laser welding of automobile double-linked gears