An experimental analysis of solid state pulsed laser melting of aluminium
Novel aspects of solid state laser spot melting of aluminium using a pulsed solid state laser were investigated. After a thorough characterisation of the performance of the solid state laser, an initial series of ranging trials were performed to identify parameters which produced cosmetically satisfactory consistent melt spots on the surface of a commercially available aluminium alloy. These melt spots demonstrated a number of features of interest, including symmetrical concentric ring structures on the surface of the spots. A review of published literature on the use of laser beams as an intense radiation source for pulsed laser surface melting was carried out which confirmed that these phenomena have not been researched or reported in any depth. Experimental work identified the conditions under which they could be reliably reproduced, and these conditions are very close to laser parameters used commercially for pulsed laser welding. Further investigations to understand their origin involved using modified aluminium surfaces and temporally shaped laser pulses. Experimental details are included which will allow reliable reproduction of this effect in the future. Specific thresholds were identified for these phenomena and this has led to an improved understanding of solid state laser spot melting on aluminium. It appears that these rings are part of a continuum of irradiance which leads to melt expulsion due to reactive vapour pressure.