CO₂ laser welding of A1 6061 using A1 4043 filler and spectral monitoring of the weld plasma plume to predict cracking

Spectral sampling of emissions from the weld plasma plume is investigated as a technique for monitoring conditions which affect cracking in laser welded Al 6061. The approach is to study the effect of Al 4043 wire filler additions on the degree of weld cracking and to correlate the degree of cracking with the ratio of intensities from the 383.8 nm magnesium line and the 396.2 nm aluminum line emitted from the weld plasma.

A 3 kW CO₂ laser and a wire feeder were used to produce bead on plate welds for the experiment while a 0.25 m spectrometer with an optical multi-channel analyzer (OMA) was used for the spectral sampling. The feed rate of 0.76 mm diameter filler wire was varied over a range of (0-11500 mm/min while other welding parameters were held constant. Welds were characterized by examining overviews for surface cracks and inconsistencies in the weld bead, and by determining an average ratio of the total crack length (l) to the length of the fusion zone perimeter (p) for five transverse cross sections. Also, from seven spectral samples taken during each weld, the average ratio of intensities for the 383.8 nm magnesium line to the 396.2 nm aluminum line was found. The line intensity ratio was correlated with lip.

For wire feed rates in the range of 6000-11500 mm/min, the line intensity ratio was found to vary linearly with the degree of cracking (l/p) when curve fits were applied to the data. Outside of this range, cracking was too inconsistent to be used for correlation.