Comparison of Post-Weld Microstructures and Mechanical Properties of Electron- and Laser-Beam Welded 8090 Al–Li Alloy Plates

Abstract

The current paper is to compare the welding characteristics as well as the post-weld impact and bending properties of electron-beam welded (EBW) and laser-beam-welded (LBW) 5 mm thick AA 8090 Al–Li alloy plates. In comparison under the same weld depth of 5 mm, the as-welded or T6 EBW specimens exhibited higher strength and fracture toughness than the LBW counterparts by ∼7% or ∼24%, respectively. The grain size and δ′ precipitate size in the EBW specimens were smaller than those in the LBW ones due to mainly the lower heat input absorbed. The uniformly dispersed pores in the EBW specimens originating from volatile element evaporation were spherical in shape, <0.2 mm in size, and ∼1.3% in volume fraction, compared with the spherical or elongated pores in the LBW ones of 0.05–1 mm in size and ∼7.2% in volume fraction originating primarily from the bubbles ejected into the molten pool due to intense evaporation at the bottom part of a keyhole with the entrapment of shielding gas during rapid solidification. The joint efficiency in terms of strength was typically around 80%, which might be considered to be acceptable. But if the welded specimens were loaded under high-rate impact with a V-notch and hence multiaxial stresses, both the EBW and LBW specimens would be subject to unacceptably low joint efficiency in terms of fracture absorbed energy E_t (below 20%). The E_t joint efficiency decreased with increasing loading rate.