ELECTRON-BEAM WELD MICROSTRUCTURES AND PROPERTIES OF ALUMINUM-LITHIUMALLOY-8090

Lithium-containing aluminium alloys are of considerable current intere st in the aerospace and aircraft industries because lithium additions to aluminium improve the modulus and decrease the density compared to conventional aluminium alloys. Few commercial aluminium-lithium alloys have emerged for use in the aerospace industry. One such candidate is 8090, a precipitation-hardenable Al-Li-Cu-Mg alloy. The influence of electron-beam welding on the microstructure and mechanical properties of alloy 8090 material has been evaluated through microscopical observ ations and mechanical tests. Microscopic observations of the electron- beam welds revealed an absence of microporosity and hot cracking, but revealed presence of microporosity in the transverse section of the we ld. Mechanical tests revealed the electron-beam weld to have lower str ength, elongation and joint efficiency. A change in microscopic fractu re mode was observed for the welded material when compared to the unwe lded counterpart. An attempt is made to rationalize the behaviour in t erms of competing mechanistic effects involving the grain structure of the material, the role of matrix deformation characteristics, grain-b oundary chemistry and grain-boundary failure.