Comparison of aluminum alloy welding characteristics with 1 kW CO and CO2 lasers

Welding characteristics of various aluminum alloys (A1100, A2017, A5083, A6063, A7N01) are investigated with CW CO and CO2 lasers near 1 kW power level. The beam characteristics of both lasers at the welding point are similar, so that a comparison can be made of the effect of the wavelength difference. The welding characteristics are assessed by measuring the size of the weld bead. It is found that the threshold power between heat-conduction and deep-penetration type welds is lower for the CO laser. This effect is attributed to the higher Fresnel absorption on the material surface at shorter wavelength. Simple reflectivity experiments which measured the strength of the reflected laser beam from the material surface confirmed this. For both laser types, the threshold power also depends upon the thermal conductivity of the alloy. The operating power level is relatively low compared to most common welding conditions, so no difference between gas types is observed because of low-temperature plasma. The lower threshold power needed for deep-penetration welds with the CO laser may be exploited for high-speed welding of thin-sheet metals with high reflectivity and high thermal conductivity, such as aluminum or copper alloys.