Product Code: ICA10_P167

Laser Keyhole Welding of Galvanized High-Strength Steel in a Gap-Free Lap Joint Configuration
Authors:
Shanglu Yang, General Motors China Science Lab; Shanghai Peoples Republic of China
Blair Carlson, GM R&D center; Warren MI USA
Radovan Kovacevic, Research Center for Advanced Manufacturing, Southern Methodist University; - TX USA
Presented at ICALEO 2010

The use of high-strength galvanized steels has significantly increased in different industries. However, welding of the galvanized steels in a gap-free lap joint configuration presents a difficulty in dealing with the highly-pressurized zinc vapor due to the lower boiling point of zinc than the melting point of steel. When failing to vent out the highly-pressurized zinc vapor, a large amount of spatters and blowholes are produced in the welds during the welding process, which leads to the significant degradation of the mechanical properties of weld. In order to vent out the zinc vapor, it is a common way for the industries to costly set up a small gap at the faying surface of two metal sheets prior to the welding process. Industries are always seeking for a method with a single laser welding technique without the pre- or post weld processing.
In this study, a novel laser welding is proposed to lap join the galvanized steels in a gap-free configuration. A side shielding gas is introduced to suppress the instable laser-induced plasma, thus improving the coupling of laser beam energy into the welded materials. At the same time, the drag force generated by the highly-pressurized zinc vapor, which results in the turbulent molten pool, is balanced by the external force from the side shielding gas. Under these welding conditions, the stable keyhole is maintained during the laser welding process, which provides a channel for the highly-pressurized zinc vapor to escape from the faying surface of two metal sheets. The completely defect-free lap joints are obtained by this laser welding process. In addition, a high-speed CCD camera is used to real time monitor the dynamic behavior of the molten pool under different welding conditions. Furthermore, influences of thermocapillary force, recoil pressure and buoyancy force on the dynamic behavior of the molten pool are studied.