Joining technology has played an important role in manufacturing since the industrial revolution. Welding methods are under constant development in response to real demands. Laser welding is considered an effective joining method that can provide high quality and cost effective results to bring economical benefits to industry. Nowadays, fibre lasers have the capability to fill some of the roles of the CO2 and Nd:YAG lasers in industrial welding applications because of their excellent characteristics such as higher energy density and superior beam quality. However, up to now, few quantitative evaluations of its performance against more traditional lasers have been conducted in laser material processing. This thesis presents an investigation into the fibre laser welding of dissimilar materials processes. The challenges in the welding of dissimilar materials are mainly related to the large differences in the physical and chemical properties of the welding materials. These differences readily cause residual stresses, intermetallic phases and chemical composition gradients. The aim of this work is to understand and explain mechanisms occurring in single mode fibre laser welding of dissimilar materials. The first part of this work addressed fibre laser butt welding of Ti-6Al-4V titanium alloy to Inconel 718 nickel alloy. Here, the weld quality was evaluated in terms of the weld geometry, microstructures, hardness distributions and the formation of intermetallic phases. Results showed that the offset position of the laser beam was an important factor affecting the weld quality. Furthermore, the thermal history of the weld was simulated using analytical modelling analysis and this was used to identify a parameter window for crack-free welding. The second part of this work focused on fibre laser lap welding of Zn-coated steel to Al alloy with different laser power delivery modes (pulsed wave and continuous wave). The relationship between the weld quality and process parameters, such as: pulse frequency, laser power, welding speed, the shielding gas type and number of welding passes, were investigated. The mechanical properties, metallurgical effects and corrosion performances of welds were analysed. Results showed that the shielding gas type and the number of welding passes were key factors in controlling the weld quality in the fibre laser welding of Zn-coated steel to Al alloy process. Finally, the common features, characteristics and the potential of fibre laser welding of dissimilar materials are presented.
|Date of Award||1 Aug 2010|
- The University of Manchester
|Supervisor||Lin Li (Supervisor)|