Correlation of surface finish and cover gas with weld defects in autogenous AL 5083 laser beam welds

Aluminum laser weld quality is influenced by gas porosity and surface reflectivity. The experimental study was performed on A1 5083 in three parts: the first, to correlate surface finish and cover gas with porosity formation, the second, to establish the effects of the laser sustained plasma on porosity formation, and the third, to ascertain the effect of surface finish on reflectivity of 10.6 μm radiation at room temperature. The first part consisted of a series of CO₂ laser welds varying cover gas and surface finish. The subsequent metallographic examination revealed no correlation between surface finish and porosity, but that the cover gas selection strongly influenced the type and quantity of pores formed. In the second part, laser welds were made varying only the cover gas while monitoring the spectral emission of the laser sustained plasma. The subsequent gravimetric measurement of porosity and the emitted spectrum from the plasma indicated a linear relationship between hydrogen content of the plasma and the quantity of porosity. Calorimetric measurements of the absorptivity were made on the surface treatments of the first part. The reflectivities inferred from these measurements were 97%, 94%, 26.6%, and 78.3% for the polished, brushed, blackened, and sandblasted surfaces, respectively.