Effects of high temperature surface reactions of aluminium-lithium alloy on the porosity of welded areas

The purpose of this investigation was to explain and prevent the formation of pores when welding commercial grade aluminium-lithium alloys by tungsten inert gas and electron beam processes. A correlation was shown between the formation of pores and hydrogen contamination of surface layers during solutionizing heat treatment of the alloy. The porosity could be a result of trapping of hydrogen bubbles as the welding bead solidified. Hydrogen contamination is related to the action of water vapour as oxidation occurs during heat treatment in air. Penetration of hydrogen into the material is still disputed. It could result from a mechanism entailing the formation of aluminium oxyhydroxides progressively covered by an oxide film. Hydrogen would be predent in the alloy mainly as lithium hydride.