Surface related features of laser welding of aluminium alloys

Abstract

A program of research was carried out to investigate the dependence of laser welds in aluminium alloys upon process parameters. Four different laser systems were used: carbon dioxide (CO2), carbon monoxide (CO), pulsed neodymium yttrium aluminium garnet (Nd:YAG) and high powered continuous Nd:YAG lasers. This paper describes phenomenon that occur at the surface of the weld pool and keyhole. The energy transfer from the laser beam to the workpiece, termed the coupling is a crucial factor in determining the heat input to the weld which is one of the major process variables. The physical mechanisms involved in this multi-part transfer are complex, hence an experimental route was taken to determine the coupling and its dependence upon laser and material properties. Coupling was measured for the combinations of five aluminium alloys and four laser systems. The high surface temperatures found in laser welding result in preferential evaporation of certain alloying elements. By studying welds made with a range of laser systems, the dependence of this effect upon process parameters could be observed. The high evaporation rates were also found to be linked to another problem that arises in laser welding - that of undercutting in autogenous welds. Porosity was observed and is discussed here in terms of its mechanism of formation. © 2000 ISIJ.