MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF LASER-BEAM WELDINGOF A 8090-AL-LI THIN SHEET

In extension to a previous study on electron-beam welding (EBW) under vacuum on a 8090 thin sheet, the current paper reports the parallel re sults of laser-beam welding (LBW) of the same material. Autogenous ''b ead-on-plate'' laser-beam welding was performed by a 3 kW CO2 LBW mach ine. The power of the in put laser beam, the specimen moving speed, an d the focusing condition was varied from 700 to 1300 W, 1500 to 9000 m m min(-1), and 1 to 3 mm below the specimen top surface, respectively. The protection atmosphere and plasma jet were achieved by blowing eit her Ar or N-2 gas. The effects of using different gases were evaluated in terms of weld-line appearance, fusion-zone dimension, solute evapo ration, microhardness, post-weld tensile properties, as well as porosi ty distribution. In comparing with the EBW results, LBW on the 8090 al loy was characterized with a higher fusion-zone depth/width ratio, coo ling rate and porosity amount, and a lower solute loss and post-weld t ensile strain. The primary formation mechanism for porosity was though t to be related to the collapsed key-holes during LBW under Ar or N-2 and the hydride-induced gas pores during EBW under vacuum.