GAS CONTAMINATION DURING PLASMA WELDING IN AL-LI ALLOY-2195

Keyhole and cover pass variable polarity plasma arc welds were made on aluminium alloy 2195 with measured contamination levels of nitrogen, oxygen, and hydrogen. Contamination levels ranged from less than 10 to 500 ppm in both the argon plasma gas and the helium shield gas. It wa s found that nitrogen leads to more severe porosity than either hydrog en or oxygen, and that rear shielding is required for keyhole welding of Al-Li 2195 alloy to protect the weld from nitrogen in the atmospher e. Both nitrogen and oxygen contamination produced a dark surface on t he weld bead, which comprised metallic aluminium particles, nucleated in the melt, that had aggregated at the surface of the weld pool. (C) 1997 The Institute of Materials.