Product Code: ICAL08_1402

Study of Laser Lap Joining of Zinc Coated Sheet Steel Without a Preset Gap
Authors:
I. M. Richardson, Delft University of Technology; Delft Netherlands
Y. Pan, Materials Innovation Institute; Delft Netherlands
Presented at ICALEO 2008

Laser beam welding has been used for joining zinc coated steel in automotive industry. However, it is still a great challenge to weld coated steel in overlap configuration because of the low boiling temperature of the zinc compared with the melting temperature of the steel. To date welding is normally undertaken when a gap is present between the plates, introduced prior to welding, or when welding with a modified laser beam, such as using elongated or dual focal spots. These techniques have the disadvantage that an extra process step is introduced in the case of the preset gap or decrease the welding speed in the case of modified beam configuration. The study presented in this paper reveals the possibility to produce good quality welds without the use of predefined gap or any other special processing conditions. The results are potentially very useful for application of laser welding in the automotive industry. This paper focuses on the understanding of the process mechanisms through the study of zinc behaviour and material property, which account for the defects produced during laser welding of zinc coated steel. It is shown that during the welding process, there is a transient gap between two sheets caused by either thermal distortion or vaporization of zinc. This transient gap could provide the space for a liquid zinc transport prior to the onset of gross vaporisation. It is also shown the zinc coating thickness, base steel composition plays important roles in the stability of the welding process.