Novel insights into porosity formation mechanisms in laser beam welding of aluminium

Porosity formation of laser beam seams in aluminium alloys is problematic for the properties of the welded pieces. For more than a decade extensive research had been conducted to determine the causes for porosity formation and the design of according welding techniques to suppress porosity. In this paper a novel empirical insight into porosity formation in aluminium alloys is presented. A bifocal hybrid laser system consisting of a combination of an Nd:YAG laser with a high power diode laser, both of 3 kW maximum output power, will be used to obviate this pore formation mechanism additionally explaining some antimonies in experimental measurements of a presumed eigenfrequency of oscillatory keyhole modes. The application of non-invasive process gas shielding by virtue of a novel process gas supply nozzle gives rise to the deduction of another cause of porosity formation. Based on these observations a holistic empirical process model is formulated accounting for well established observations in the past as well as those recent findings. Experimental results prove the success of this approach to suppress process porosity in aluminium.