Fundamental characteristics of high power CO2 laser welding of 87%Al2O3 ceramics were investigated with an intention to develop a joining technique for thick ceramics. It was found that a penetration depth of 20 mm is possible at a welding speed of 6.5 mm/sec and a laser power of 10 kW. The porosity ratio was lower at lower input powers, and there was a tendency that the porosity ratio decreases with decreasing the welding speed at the same input power. The bending strength decreased as the porosity ratio increased. Porosities, in particular large porosities at bead center, were found to greatly influence the bending strength of welded joints of alumina ceramics. The root bending strength of butt weld of 4 mm thick plate had the same value as the base material.
