Comparison of the microstructure and mechanical performance of 2A97 Al-Li alloy joints between autogenous and non-autogenous laser welding

Abstract

2A97 Al-Li joints were achieved by using a fibre laser welding with filler wire (non-autogenous) and without filler wire (autogenous), of which the microstructures, mechanical properties and underlying relationships were examined. The results of microhardness tests showed that the fusion zones (FZ) in both types of joints were relatively soft. The width of the softened zone and the degree of softening with autogenous laser welding (ALW) was approximately 1/3 and 3/4 those with non-autogenous laser welding (NLW), respectively. The main reason for the softening was that the alloying elements were more concentrated in the grain boundary but non-uniformly distributed. Both types of welded joints fractured in the FZ during tensile processes, and the tensile strengths of the NLW joint decreased about 17% that of the ALW joint, while the elongation increased about 30%. By using high-speed imaging in low-cycle fatigue tests, it was found that cracks originated near the pores and slowly propagated in the NLW joint, whereas cracks first appeared in the FZ, and then rapidly propagated to the EQZ in the ALW joint. Satisfactory strength and plasticity in NLW joints can be expected by careful selection of the welding parameters and the alloy elements in the filler wire.